JP2025092851A - Detection method and processing device - Google Patents

Abstract

To detect local thickness abnormality in a wafer.SOLUTION: A method for detecting a thickness abnormality in a wafer includes a measuring step for measuring the thickness of the wafer at a plurality of locations in the wafer by relatively moving a sensor head of a thickness measuring device for measuring the thickness of the wafer without contacting the wafer and a first holding table for holding the wafer on a first holding surface within a predetermined plane, and a detection step for detecting the thickness abnormality in the wafer using a measurement result from the measuring step.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for detecting thickness anomalies in a wafer, and a processing device that includes a holding table and a processing unit that has a spindle and is capable of processing a wafer held on the holding surface of the holding table with a processing tool attached to the lower end of the spindle.

When thinning a wafer held on a chuck table by grinding the back surface with a grinding wheel, the front surface may be protected by applying protective tape to prevent damage to the devices formed on the front surface opposite the back surface (see, for example, Patent Document 1).

Even if a protective tape is applied to the surface of a wafer, the outer surface of the protective tape does not necessarily become flat, and the unevenness of the device may be reflected on the outer surface of the protective tape. In this case, the protective tape may be cut and flattened with a surface planer (also called a cutting tool) before grinding the wafer so that the unevenness on the outer surface of the protective tape is not reflected on the wafer after grinding (see, for example, Patent Document 2).

The surface planer has a chuck table and a spindle, and a cutting tool is attached to the lower end of the spindle. When cutting the protective tape with the cutting tool, the wafer is first held by suction on the chuck table in such a manner that the protective tape is exposed upward and the holding surface of the chuck table is in contact with the wafer.

At this time, for example, the protective tape may locally bulge due to the presence of particles such as (i) cutting chips or (ii) burrs generated during self-grinding to correct the shape of the holding surface on the holding surface. If the outer surface of the protective tape is flattened by cutting in this state, the protective tape will locally become thinner at the bulged areas after cutting.

Similarly, if there is a localized depression on the holding surface, the wafer and protective tape are held by suction so that they conform to the shape of the holding surface, and after cutting, the protective tape becomes locally thicker in the area where the holding surface was depressed.

In this way, if localized thickness abnormalities in the protective tape occur even though the outer surface of the protective tape has been flattened by cutting, in the subsequent grinding process, the wafer is ground while the outer surface of the protective tape is held by suction so that the back surface of the wafer is exposed, and localized thickness abnormalities are also formed in the wafer at the locations of the localized thickness abnormalities in the protective tape.

Even if there are no local thickness anomalies in the protective tape, if localized irregularities are formed on the holding surface of the chuck table of the grinding device, localized thickness anomalies will be formed in the wafer that has been thinned by grinding.

Furthermore, when the wafer is held by suction on the chuck table of the grinding device in a manner that the wafer is in direct contact with the holding surface without attaching a protective tape to the wafer, if localized irregularities are formed on the holding surface of the chuck table of the grinding device, localized thickness anomalies will also be formed on the wafer that has been thinned by grinding.

Local thickness anomalies in a wafer can adversely affect the device chips formed when the wafer is diced into individual devices, and can also lead to processing defects in the manufacturing process after the grinding process.

JP 2023-000307 A JP 2022-151350 A

The present invention was made in consideration of these problems, and aims to detect local thickness anomalies on a wafer.

According to one aspect of the present invention, there is provided a method for detecting thickness anomalies in a wafer, the method comprising: a measurement step for measuring the thickness of the wafer at multiple locations on the wafer by relatively moving a sensor head of a thickness gauge that measures the thickness of the wafer without contacting the wafer and a first holding table that holds the wafer on a first holding surface within a predetermined plane; and a detection step for detecting thickness anomalies in the wafer using the measurement results from the measurement step.

Preferably, the measurement step includes measuring the thickness of the wafer on a first circumference having a first diameter while rotating the first holding table that holds the wafer with the position of the sensor head fixed within the predetermined plane.

Moreover, preferably, the measurement step includes measuring the thickness of the wafer on a second circumference having a second diameter smaller than the first diameter and on a third circumference having a third diameter larger than the first diameter while rotating the first holding table that holds the wafer with the position of the sensor head fixed within the predetermined plane.

In addition, preferably, in the detection process, an abnormality in the thickness of the wafer is detected by comparing the difference between the maximum thickness of the wafer measured in the measurement process and the minimum thickness of the wafer with a predetermined threshold value.

More preferably, the detection method further includes a grinding step in which the first surface of the wafer is held by the first holding table, and the second surface of the wafer, which is located on the opposite side to the first surface in the thickness direction of the wafer, is ground by a grinding wheel, and the grinding step is started before the measurement step.

In addition, preferably, in the detection process, the difference between the maximum thickness of the wafer measured in the measurement process and the minimum thickness of the wafer is compared with a predetermined threshold value that is greater than the waviness of the thickness of the wafer after the grinding process, thereby detecting an abnormality in the thickness of the wafer.

In addition, preferably, in the grinding step, the second surface of the wafer is ground to form a circular recess having a depth from the second surface in the thickness direction of the wafer that does not reach the first surface, and a ring-shaped reinforcing portion surrounding the outer periphery of the circular recess.

Preferably, the detection method further includes, before the grinding step, an adhering step of adhering a protective tape to the first surface of the wafer so as to cover the first surface, and a cutting step of cutting the protective tape with the cutting tool by rotating a cutting tool having a cutting blade around a spindle and linearly moving a second holding table holding the wafer on a second holding surface along a predetermined direction relative to the spindle so that the protective tape is exposed, while the cutting blade is fixed at a predetermined height.

According to another aspect of the present invention, there is provided a holding table having a holding surface for holding a wafer, a rotary drive mechanism including a first motor for rotating a rotation axis of the holding table arranged at the center of the holding surface, a first moving mechanism having a second motor for moving the holding table along a first direction, a processing unit having a spindle and capable of processing the wafer held on the holding surface with a processing tool attached to the lower end of the spindle, a thickness gauge having a sensor head for measuring the thickness of the wafer without contacting the wafer, a second moving mechanism having a third motor for moving the sensor head relative to the holding table along a second direction intersecting the first direction, and a fourth motor for moving the fourth motor. A processing device is provided that includes one or both of a third movement mechanism that rotates the sensor head relative to the holding table within a predetermined plane defined by the first direction and the second direction, and a controller having a processor and memory and controlling the rotation drive mechanism, the processing unit, the thickness measuring device, the first movement mechanism, the second movement mechanism, and the third movement mechanism, the controller including a discrimination unit that discriminates an abnormality in the thickness of the wafer by executing a program stored in the memory with the processor, and the discrimination unit discriminates an abnormality in the thickness of the wafer based on the measurement results obtained by measuring the thickness of the wafer at multiple points on a predetermined circumference around the center of rotation of the rotation axis.

According to yet another aspect of the present invention, a processing device includes a holding table having a holding surface for holding a wafer, a rotation drive mechanism including a first motor for rotating a rotation axis of the holding table arranged at the center of the holding surface, a first moving mechanism having a second motor for moving the holding table along a first direction, a processing unit having a spindle and capable of processing the wafer held at the holding surface with a processing tool attached to the lower end of the spindle, a thickness gauge having a sensor head arranged directly above the moving path of the center of the holding surface and for measuring the thickness of the wafer without contacting the wafer, and a controller having a processor and a memory and controlling the rotation drive mechanism, the processing unit, the thickness gauge, and the first moving mechanism, the controller including a discrimination unit for discriminating an abnormality in the thickness of the wafer by executing a program stored in the memory with the processor, and the discrimination unit discriminates an abnormality in the thickness of the wafer based on the measurement results obtained by measuring the thickness of the wafer at multiple points on a predetermined circumference around the center of rotation of the rotation axis.

Preferably, the processing device further includes a display whose operation is controlled by the controller, and when the discrimination unit determines that there is an abnormality in the thickness of the wafer, the controller causes the display to display either or both of the thickness value of the wafer that has been determined to be abnormal and a message indicating that there is an abnormality in the thickness.

In a detection method according to one aspect of the present invention, the thickness of the wafer is measured at multiple locations on the wafer by moving a sensor head of a thickness gauge, which measures the thickness of the wafer without contacting the wafer, and a first holding table, which holds the wafer on a first holding surface, relatively in a predetermined plane. Then, an abnormality in the wafer thickness can be detected based on the measurement results in the measurement process.

In another aspect of the processing device of the present invention, a discrimination unit in the controller of the processing device can discriminate anomalies in the thickness of the wafer based on the measurement results obtained by measuring the thickness of the wafer at multiple points on a predetermined circumference around the center of rotation of the rotation axis of the holding table.

FIG. 1 is a flow diagram of a detection method. FIG. FIG. FIG. 4A is a cross-sectional view of the wafer unit etc. after the cutting process, and FIG. 4B is a cross-sectional view of the wafer unit etc. removed from the chuck table. FIG. 1A to 1C are diagrams showing an inclination adjustment mechanism, a rotation drive mechanism, etc. FIG. 7A is a partially sectional side view of the second moving mechanism, and FIG. 7B is a top view of the thickness measuring device. FIG. 8A is a diagram showing a grinding step, and FIG. 8B is a cross-sectional view of a wafer unit thinned in the grinding step. FIG. 9A is a diagram showing a measurement process on a first circumference, and FIG. 9B is a diagram showing measurement of the thickness of a wafer on a plurality of circumferences concentric with the first circumference. FIG. 2 is a more detailed flow diagram of the measurement and detection steps. FIG. 11A is a side view of a third moving mechanism that pivots and moves the sensor head, and FIG. 11B is a top view of the pivoting sensor head. FIG. 12A is a top view showing the wafer and the sensor head, and FIG. 12B is a diagram showing measurement steps on the first, second and third circumferences. FIG. 13 is a side view showing a combination of the second moving mechanism and the third moving mechanism. FIG. 14A is a diagram showing a sensor head disposed directly above the center of the holding surface, and FIG. 14B is a diagram showing measurement steps on the first, second, and third circumferences.

(First embodiment) An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Figure 1 is a flow diagram of a detection method for detecting thickness anomalies in a wafer 11 (see Figure 8 (B)) in the first embodiment.

In this embodiment, the steps are performed in the following order: bonding step S10, cutting step S20, grinding step S30, measuring step S40, and detection step S50. More specifically, after completion of bonding step S10, cutting step S20 is started, and after completion of cutting step S20, grinding step S30 is started.

However, as described in detail below, in the present embodiment, the grinding process S30, the measuring process S40, and the detecting process S50 are started after the grinding process S30 is started but before it is completed, and the detecting process S50 is started after the measuring process S40 is started but before it is completed.

In other words, there is a time when the grinding process S30, the measurement process S40, and the detection process S50 are performed simultaneously in parallel. Of course, this is not limited to this embodiment, and thickness anomalies in the wafer 11 can be detected even if the measurement process S40 is started after the grinding process S30 is completed, and the detection process S50 is started after the measurement process S40 is completed.

First, referring to FIG. 2, the wafer 11 and protective tape 19 to be processed will be described. In this embodiment, the wafer 11 is disk-shaped and is mainly composed of a silicon (Si) single crystal substrate. However, the wafer 11 has a metal layer, an insulating layer, etc. formed thereon, and the inside of the wafer 11 is doped with impurities.

The diameter of the wafer 11 is, for example, 4 inches (approximately 100 mm) or more and 12 inches (approximately 300 mm) or less. The thickness of the wafer 11 before the grinding process S30 varies depending on the diameter of the wafer 11, but is, for example, in the range of approximately 500 μm to approximately 800 μm.

The wafer 11 has a circular front surface (first surface) 11a and a circular back surface (second surface) 11b. The back surface 11b and the front surface 11a are located on opposite sides in the thickness direction 11c of the wafer 11, and the distance from the back surface 11b to the front surface 11a is the thickness of the wafer 11.

There are no limitations on the material, shape, structure, size, etc. of the wafer 11. The material of the single crystal substrate constituting the wafer 11 may be a semiconductor material other than silicon, such as gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), etc.

The surface 11a of the wafer 11 is partitioned by a number of planned division lines (i.e., streets) 13 arranged in a grid pattern, and devices 15 such as ICs (Integrated Circuits) and LEDs (Light Emitting Diodes) are formed in each of these partitioned areas. There are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15.

On the front surface 11a side, the wafer 11 has a circular device region 17a in which multiple devices 15 are arranged, and an annular peripheral surplus region 17b surrounding the device region 17a. Note that in FIG. 2, for ease of explanation, the boundary between the device region 17a and the peripheral surplus region 17b is indicated by a dashed line, but no clear boundary line is shown on the actual wafer 11.

As described below, in the grinding process S30, the back surface 11b side of the circular area corresponding to the device area 17a is ground, but the back surface 11b side corresponding to the peripheral surplus area 17b is not ground. Therefore, the thickness of the peripheral surplus area 17b does not change before and after the grinding process S30.

The peripheral excess region 17b after the grinding process S30 functions as a ring-shaped reinforcement portion 11e (see FIG. 8B) for reducing the deflection of the device region 17a thinned in the grinding process S30. The ring-shaped reinforcement portion 11e prevents a significant decrease in the rigidity of the wafer 11, making it easier to transport, process, etc. the wafer 11 compared to when the ring-shaped reinforcement portion 11e is not present.

In this embodiment, before grinding the wafer 11, a circular protective tape 19 is attached to the surface 11a of the wafer 11 to prevent damage to the device 15 during grinding. The protective tape 19 has a base layer that is approximately the same diameter as the wafer 11.

The substrate layer has a thickness of, for example, 5 μm or more and 200 μm or less, and is formed from a resin such as polyolefin (PO), polyethylene terephthalate (PET), polyvinyl chloride (PVC), or polystyrene (PS).

An adhesive layer (i.e., glue layer) is provided on substantially the entire surface of the base layer. The adhesive layer is, for example, a layer of resin adhesive that hardens and loses adhesive strength when exposed to heat or ultraviolet light, and is made of a silicone-based material, an acrylic-based material, an epoxy-based material, or the like.

The base layer is exposed on the outer surface 19a of the protective tape 19, and the adhesive layer is exposed on the inner surface 19b of the protective tape 19. Figure 2 shows the attachment step S10. In the attachment step S10, the inner surface 19b of the protective tape 19 is attached to the wafer 11 so that the protective tape 19 covers substantially the entire surface 11a, thereby forming the wafer unit 21.

In the wafer unit 21, the outer surface 19a (i.e., the base layer) is exposed, and the inner surface 19b (i.e., the adhesive layer) is in contact with the surface 11a. However, this is not limited to the example, and the protective tape 19 may have only the base layer without the adhesive layer.

If the protective tape 19 does not have an adhesive layer, the protective tape 19 is attached to the wafer 11 by thermocompression bonding the protective tape 19 to the surface 11a. In this case, there is an advantage that even if the protective tape 19 is peeled off from the wafer 11, no adhesive layer residue remains on the surface 11a.

In the application step S10, when the protective tape 19 is applied to the surface 11a, the unevenness of the device 15 is reflected on the outer surface 19a. Therefore, in order to reduce the unevenness of the outer surface 19a, the protective tape 19 is cut using a surface planer 2 (see FIG. 3) to flatten the outer surface 19a of the protective tape 19 (cutting step S20).

As shown in FIG. 3, the surface planer 2 has a disk-shaped chuck table (second holding table) 4. Note that the X-axis direction (machining feed direction), Y-axis direction, and Z-axis direction (height direction) shown in FIG. 3 are mutually perpendicular.

The chuck table 4 has a disk-shaped frame made of a metal such as stainless steel. A disk-shaped recess with a diameter smaller than the outer diameter of the outer periphery of the frame is formed on the top surface of the frame. This recess has multiple support pins arranged at approximately equal intervals.

The longitudinal direction of each support pin is approximately parallel to the thickness direction of the chuck table 4. Note that in FIG. 3, for ease of viewing, only the pins located at the front are shown, but there are many pins in the depth direction of the page as well. Each support pin is also made of a metal such as stainless steel.

A flow path is formed in the frame body at the center of the frame body in the radial direction so as to penetrate the frame body. A suction source such as a vacuum pump (not shown) is connected to this flow path. The negative pressure generated by the suction source is transmitted to the gaps between each support pin.

A plating layer made of a metal such as nickel is formed on the top surface of the frame body and the top surface of each support pin. The top surface of the frame body and the top surface of each support pin are substantially flush with each other, forming a substantially flat holding surface (second holding surface) 4a along the XY plane.

Foreign matter 4b, such as the above-mentioned particles and burrs, may adhere to the holding surface 4a. In FIG. 3, the foreign matter 4b is shown in an exaggerated manner. The size of the foreign matter 4b is several μm. For example, if the holding surface 4a is set as the reference position (zero μm) in the Z-axis direction, the position of the upper end of the foreign matter 4b in the Z-axis direction is 2 μm to 3 μm.

The chuck table 4 is supported by an X-axis direction moving plate (not shown) via a support portion 6. The X-axis direction moving plate is slidably mounted on a pair of guide rails arranged along the X-axis direction.

A nut portion (not shown) is fixed to the underside of the X-axis direction moving plate. A screw shaft (not shown) arranged along the X-axis direction is rotatably attached to the nut portion via multiple balls (not shown).

A stepping motor (not shown) is attached to one end of the screw shaft. When the stepping motor is operated, the X-axis moving plate moves along the X-axis direction together with the chuck table 4.

A cylindrical spindle housing (not shown) is provided above the holding surface 4a. The spindle housing is arranged with its longitudinal direction aligned with the Z-axis direction. A Z-axis direction movement mechanism (not shown) having a ball screw is fixed to the spindle housing.

The height position of the spindle housing is adjusted by a Z-axis movement mechanism. A part of the cylindrical spindle 8 is rotatably accommodated in the spindle housing using an air bearing or the like.

A motor (not shown) is provided near the upper end of the spindle 8. The rotor of this motor corresponds to the spindle 8. A metallic, disk-shaped wheel mount 10 is fixed to the lower end of the spindle 8.

A circular bite wheel (biting tool) 12 is attached to the underside of the wheel mount 10. The bite wheel 12 has a circular base 12a. The upper end of a rectangular shank 12b is attached to a part of the base 12a.

The longitudinal direction of the shank 12b is aligned along the Z-axis direction. A cutting blade 12c made of diamond or the like is fixed to the lower end of the shank 12b. When the spindle 8 is rotated, the bite wheel 12 rotates around the spindle 8.

Figure 3 shows the cutting step S20 in which the outer surface 19a of the protective tape 19 is flattened using a surface planer 2. In the cutting step S20, first, the back surface 11b is in contact with the holding surface 4a, and negative pressure is transmitted to the holding surface 4a to suction-hold the wafer 11 on the holding surface 4a so that the protective tape 19 is exposed.

Next, rotate the spindle 8 and the bite wheel 12, and adjust and fix the position of the spindle housing in the Z-axis direction so that the height of the lower end of the cutting blade 12c is slightly lower than the height of the outer surface 19a.

When adjusting the height of the cutting blade 12c, it is usually unclear whether there is an abnormally protruding or recessed area on the outer surface 19a. Furthermore, the abnormally protruding or recessed area is generally only a small part of the outer surface 19a. Therefore, in this embodiment, such areas are not taken into consideration when adjusting the height of the cutting blade 12c.

The distance Δ in the Z-axis direction from the outer surface 19a to the lower end of the cutting blade 12c corresponds to the thickness of the protective tape 19 that is removed by cutting. Therefore, the distance Δ is appropriately adjusted according to the finished thickness of the protective tape 19.

Next, with the height of the cutting blade 12c fixed, the bite wheel 12 is rotated and cutting water (not shown) such as pure water is supplied from a nozzle (not shown) to the outer surface 19a while the chuck table 4 is moved along the X-axis direction.

In other words, the chuck table 4 is moved linearly along the X-axis direction (predetermined direction) perpendicular to the Z-axis direction relative to the spindle 8 arranged along the Z-axis direction. This cuts and flattens the outer surface 19a of the protective tape 19.

In the cutting step S20, it is the base layer of the protective tape 19 that is cut, and the adhesive layer is not cut. In addition, in the cutting step S20, the base layer is not entirely removed, but a certain thickness is left. Figure 4 (A) is a cross-sectional view of the wafer unit 21 etc. after the cutting step S20.

As shown in FIG. 4A, the height of the outer surface 19a after the cutting step S20 is the same as the height of the lower end of the cutting blade 12c, so it is approximately flat. However, the protective tape 19 has a thinned area 19c with an amorphous shape like an amoeba that is locally thinned due to the presence of the foreign matter 4b.

Figure 4 (B) is a cross-sectional view of the wafer unit 21 and other parts removed from the chuck table 4. When the suction holding on the holding surface 4a is released, the deformation of the wafer 11 is also eliminated. As shown in Figure 4 (B), in the cutting process S20, the protective tape 19 is locally thinned.

In other words, in the cutting process S20, a thinned area 19c is formed in which the protective tape 19 is locally thinned at a protruding portion of the protective tape 19 corresponding to the foreign object 4b on the holding surface 4a.

In one example, the thickness of the protective tape 19 before the cutting step S20 is 255 μm, and the thickness of the protective tape 19 excluding the thinned region 19c after the cutting step S20 is 235 μm. After the cutting step S20, the back surface 11b side of the wafer 11 is ground using a grinding device 20.

First, the grinding device 20 will be described with reference to Figs. 5 to 7. Fig. 5 is a perspective view of the grinding device (processing device) 20. The X-axis direction (first direction), Y-axis direction, and Z-axis direction (height direction) shown in Fig. 5 are mutually orthogonal.

The grinding device 20 in this embodiment is a manual type in which the wafer unit 21 is loaded and unloaded by an operator, but it may be a fully automatic type in which loading, grinding, cleaning, and unloading are performed automatically.

The grinding device 20 has a base 22 that supports or houses components. A rectangular opening 22a having a longitudinal portion in the X-axis direction is formed on the upper surface of the base 22. In a plan view of the grinding device 20, a disk-shaped chuck table (holding table, first holding table) 24 is provided in the opening 22a.

The chuck table 24 has a disk-shaped frame made of non-porous dense ceramics. A disk-shaped recess with a diameter smaller than the outer diameter of the outer periphery of the frame is formed on the top surface of the frame. A disk-shaped porous plate with approximately the same diameter as the recess is fixed in this recess.

The porous plate is made of porous ceramics. A suction source such as a vacuum pump (not shown) is connected to the porous plate via a flow path formed in the frame. The negative pressure generated by the suction source is transmitted to the top surface of the porous plate.

The porous plate has a generally flat bottom surface and a top surface with an annular recessed area around the center. In other words, when the porous plate is viewed in a cross section passing through the center of the bottom surface and perpendicular to the bottom surface, the top surface has a biconcave shape in which the center of the top surface and the outer peripheral edge of the top surface protrude compared to other areas.

For example, the annular recessed area on the top surface of the porous plate is recessed by a predetermined distance of 10 μm to 30 μm in the thickness direction of the chuck table 24 compared to the center and outer peripheral edge of the top surface. However, since the amount of recession is so small, the top surface of the porous plate is shown as approximately flat in Figures 8(A) and 8(B) described below.

The top surface of the frame and the top surface of the porous plate are substantially flush with each other and function as a holding surface (first holding surface) 24a that suction-holds the wafer unit 21 (i.e., the wafer 11).

A first cover 26 having a generally square outer shape is disposed on the outer periphery of the chuck table 24. A bellows-shaped second cover 28 that can expand and contract along the X-axis direction is provided on both sides of the first cover 26 in the X-axis direction.

As shown in FIG. 6, the chuck table 24 is rotatably supported by an annular table base 30 having bearings. The rotation shaft 24b of the chuck table 24 is inserted into a through hole (not shown) in the center of the table base 30. The rotation shaft 24b is disposed in the radial center of the chuck table 24. The table base 30 is supported by a tilt adjustment mechanism 32.

6 is a diagram showing the tilt adjustment mechanism 32, the rotation drive mechanism 42, etc. of the chuck table 24. The tilt adjustment mechanism 32 adjusts the tilt of the table base 30 so that the center _24a1 , the recessed region, and the arc-shaped region connecting the outer circumferential end in a cross-sectional view of the holding surface 24a mesh with the outer circumferential side surfaces (see FIG. 8A) of multiple grinding stones 80b of a grinding wheel 80 described later.

However, the tilt angle of the table base 30 with respect to the XY plane is extremely small. The tilt adjustment mechanism 32 has a fixed shaft 32a that supports a part of the table base 30, and multiple movable shafts 32b that each support another part of the table base 30. The fixed shaft 32a and the two movable shafts 32b are arranged at approximately equal intervals along the circumferential direction of the table base 30.

In FIG. 6, the fixed shaft 32a and the two movable shafts 32b are shown in a simplified manner. The length of the fixed shaft 32a in the Z-axis direction is fixed, and the length of the movable shaft 32b in the Z-axis direction is adjustable. For example, the height position of the upper end of the movable shaft 32b is adjusted by the amount of screwing of the screw shaft that constitutes the movable shaft 32b into the screw hole.

The fixed shaft 32a and the two movable shafts 32b are supported by a moving plate 44. A servo motor (first motor) 34 that rotates the rotating shaft 24b of the chuck table 24 is fixed to the moving plate 44. A drive pulley 36 is fixed to the output shaft of the servo motor 34.

A driven pulley 38 is fixed to the lower end of the rotating shaft 24b of the chuck table 24, and an endless belt 40 is looped between the driving pulley 36 and the driven pulley 38. When the servo motor 34 is operated, power is transmitted to the rotating shaft 24b.

This causes the chuck table 24 to rotate around the rotating shaft 24b. The servo motor 34, the drive pulley 36, the driven pulley 38, the endless belt 40, etc., constitute a rotation drive mechanism 42 for rotating the rotating shaft 24b.

Returning to FIG. 5, the movable plate 44 is slidably mounted on a pair of guide rails 46 that are arranged along the X-axis direction. A nut portion 48 is fixed to the underside of the movable plate 44. A screw shaft 50 that is arranged along the X-axis direction is rotatably attached to the nut portion 48 via a number of balls (not shown).

A stepping motor (second motor) 52 is attached to one end of the screw shaft 50. The nut portion 48, screw shaft 50, stepping motor 52, etc. constitute a first ball screw 54. The pair of guide rails 46, the nut portion 48, screw shaft 50, multiple balls, stepping motor 52, etc. constitute a first movement mechanism 56.

When the stepping motor 52 is operated, the moving plate 44, the tilt adjustment mechanism 32, and the chuck table 24 move integrally along the X-axis direction. Note that the first moving mechanism 56 may use a belt (not shown) to move the moving plate 44, which is slidably attached on a pair of guide rails 46, instead of the first ball screw 54.

In this case, the first moving mechanism 56 has a stepping motor (second motor), a toothed pulley fixed to the output shaft of the stepping motor, and a toothed belt with ribs on its inner surface that mesh with the toothed pulley (all not shown), and the power of the stepping motor is transmitted to the moving plate 44 via the toothed belt.

A square column 58 is provided on the rear side of the base 22. A grinding feed mechanism 60 is provided on the front side of the column 58. The grinding feed mechanism 60 has a pair of guide rails 62 fixed to the front side of the column 58. A moving plate 64 is attached to the pair of guide rails 62 so as to be able to slide along the Z-axis direction.

A nut portion (not shown) is provided on the rear side of the moving plate 64. A screw shaft 66 is rotatably attached to the nut portion via a number of balls (not shown). A pulse motor 68 is connected to the upper end of the screw shaft 66.

When the screw shaft 66 is rotated by the pulse motor 68, the moving plate 64 moves in the Z-axis direction along the guide rail 62. A grinding unit (machining unit) 70 is fixed to the front side of the moving plate 64. The grinding unit 70 has a cylindrical holding member 72 with a bottom.

A cylindrical spindle housing 74 is disposed inside the holding member 72. A part of a cylindrical spindle 76 (see FIG. 8(A)) disposed substantially parallel to the Z-axis direction is rotatably held inside the spindle housing 74. The longitudinal direction of the spindle 76 is disposed substantially parallel to the Z-axis direction.

A rotation drive source (not shown), such as a servo motor, is provided near the upper end of the spindle 76 inside the spindle housing 74. The lower end 76a of the spindle 76 (see FIG. 8(A)) protrudes downward beyond the lower end of the spindle housing 74.

As shown in FIG. 8(A), a disk-shaped wheel mount 78 is fixed to the lower end 76a of the spindle 76. A grinding wheel (machining tool) 80 capable of grinding (machining) the wafer 11 is attached to the underside of the wheel mount 78 using a fixing member (not shown) such as a bolt.

The grinding wheel 80 has an annular base 80a made of a metal material such as an aluminum alloy. On the underside of the base 80a, multiple grinding stones 80b are arranged at approximately equal intervals along the circumferential direction of the base 80a. The outer side surfaces of the multiple grinding stones 80b form a circle with a predetermined diameter that corresponds to approximately half the diameter of the wafer 11.

Each grinding wheel 80b is formed by kneading abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as metal, ceramics, or thermosetting resin, and then molding and firing the mixture. Note that the grinding wheels 80 are consumables and are replaced with new ones as necessary depending on the degree of wear.

Therefore, in the grinding device 20, the grinding wheel 80 is not always attached to the lower end 76a of the spindle 76. For example, when the grinding device 20 is manufactured or transferred, the grinding wheel 80 may not be attached to the spindle 76.

Directly below the spindle 76, a nozzle (not shown) is provided for supplying grinding water such as pure water to the contact area between the wafer 11 and the grinding wheel 80b when grinding (i.e., processing) the wafer 11.

Returning to FIG. 5, a contact-type thickness gauge 82 is provided near the opening 22a. The thickness gauge 82 has a first height gauge 82a and a second height gauge 82b. Each of the first height gauge 82a and the second height gauge 82b has an arm.

The base end of each arm is connected to a cylindrical base, and a head is fixed to the tip of each arm. The head has a hemispherical contact part made of diamond or the like at its lower end.

The Z-axis position of the contact part relative to a predetermined reference position is measured, for example, to the order of 0.1 μm, using a pulse counting method that optically or magnetically reads a scale, or a linear variable differential transformer (LVDT).

The base can be moved by a lifting mechanism (not shown). The lifting mechanism lowers the base when measuring the thickness of the object to be measured. When the base is lowered, the contact portion of the first height gauge 82a comes into contact with the object to be measured, and the contact portion of the second height gauge 82b comes into contact with a part of the holding surface 24a (i.e., the top surface of the frame).

When the thickness of an object is measured using the thickness gauge 82, the thickness of the object is calculated from the difference between the height of the contact part of the first height gauge 82a relative to the above-mentioned reference position and the height of the contact part of the second height gauge 82b relative to the same reference position.

On the other hand, when the thickness is not being measured, the base is raised. When the base is raised, the contact portion of the first height gauge 82a moves away from the object to be measured, and the contact portion of the second height gauge 82b also moves away from the holding surface 24a.

A non-contact thickness gauge 84 is provided near the contact thickness gauge 82. The thickness gauge 84 is a spectroscopic interference type gauge that uses infrared light, and is positioned so as not to interfere with the first height gauge 82a and the second height gauge 82b.

The thickness gauge 84 has an arm 84a. A cylindrical base 84b is fixed to the base end of the arm 84a. In this embodiment, the arm 84a is disposed approximately parallel to the XY plane and is tilted at a predetermined angle of 30 degrees to 60 degrees (e.g., 45 degrees) with respect to the X-axis direction.

In this embodiment, the direction inclined at a predetermined angle with respect to the X-axis direction on the XY plane is referred to as the second direction 84d. As is clear from the definition of this second direction 84d, the X-axis direction and the second direction 84d form a predetermined plane parallel to the XY plane.

A cylindrical sensor head 84c is fixed to the tip of the arm 84a. A laser beam having a wavelength in the infrared band is emitted from the sensor head 84c. For example, the distance from the bottom end of the sensor head 84c to the back surface 11b of the wafer 11 is set to about 80 mm, and the spot diameter of the laser beam is set to approximately 25 μm.

The laser beam emitted from the sensor head 84c is reflected by the wafer 11 and the protective tape 19 and enters the sensor head 84c. The light entering the sensor head 84c includes a first reflected light from the back surface 11b of the wafer 11 and a second reflected light from the front surface 11a of the wafer 11 (i.e., the interface between the wafer 11 and the protective tape 19).

The interference light of the first reflected light and the second reflected light is received by a light receiving element such as a photodetector or a photodiode via a spectroscope (not shown) such as a diffraction grating. The intensity of the interference light increases at a wavelength corresponding to the thickness of the wafer 11.

The signal from the light receiving element is analyzed by (i) a computer having a predetermined program and a general-purpose processor that executes the program (both not shown), and (ii) a dedicated circuit such as an ASIC (Application Specific Integrated Circuit), and the thickness of the wafer 11 according to the wavelength of the interference light is calculated.

The thickness gauge 84, the spectrometer, the light receiving element, the computer, etc. constitute a non-contact thickness measurement system that measures the thickness of the wafer 11 (i.e., the distance from the front surface 11a to the back surface 11b at the laser beam irradiation position) without contacting the wafer 11.

As shown in Figures 7(A) and 7(B), the sensor head 84c of this embodiment is configured to be linearly movable along the second direction 84d by the second moving mechanism 86. Figure 7(A) is a partially sectional side view of the second moving mechanism 86 that moves the sensor head 84c, and Figure 7(B) is a top view of the thickness gauge 84.

The second moving mechanism 86 has a moving plate 88 that supports the base 84b. The moving plate 88 is slidably attached to a pair of guide rails 90 that are arranged along the second direction 84d. For convenience, only one of the guide rails 90 is shown in FIG. 7(A).

A nut portion 92 is fixed to the underside of the movable plate 88. A screw shaft 94 is rotatably attached to the nut portion 92 via a number of balls (not shown) arranged along the second direction 84d.

A stepping motor (third motor) 96 is attached to one end of the screw shaft 94. The nut portion 92, screw shaft 94, stepping motor 96, etc., constitute a second ball screw 98. When the stepping motor 96 is operated, the moving plate 88 and the sensor head 84c move along the second direction 84d relative to the chuck table 24.

In addition, the second moving mechanism 86 may use a belt to move the moving plate 88 slidably mounted on a pair of guide rails 90, instead of the second ball screw 98. In this case, the second moving mechanism 86 has a stepping motor (third motor), a toothed pulley fixed to the output shaft of the stepping motor, and a toothed belt with ribs on the inner surface that mesh with the toothed pulley (all not shown), and the power of the stepping motor is transmitted to the moving plate 88 via the toothed belt.

Returning now to FIG. 5, an exterior panel is provided above the base 22, and the upper and sides of the chuck table 24, column 58, etc. are covered with the exterior panel. A touch panel display (display) 100 is provided on one surface of the exterior panel.

The touch panel display 100 functions as an input device for the operator to input instructions, and also functions as a display device that displays a GUI (Graphical User Interface), processing conditions, the thickness of the wafer 11 measured by the thickness gauges 82, 84, etc., a warning message indicating that the thickness of the wafer 11 is abnormal, etc.

In addition, instead of the touch panel display 100, a display device (display) that does not have the function of an input device may be provided. In this case, however, an input device (keyboard, mouse, trackball, touchpad, digitizer, etc.) for the worker to input instructions is provided separately.

A thin, cylindrical indicator light 102 is provided on the top surface of the exterior panel. The indicator light 102 has a base with a built-in speaker (not shown). The speaker may be provided in the grinding device 20 separately from the indicator light 102.

A light-emitting unit capable of emitting light in different colors is provided on the base. The light-emitting unit has multiple light-emitting regions arranged to overlap in the Z-axis direction. Each of the multiple light-emitting regions includes an LED and a light-diffusing lens arranged to surround the LED, and can light up or flash in different predetermined colors such as red, yellow, blue, and green.

The grinding device 20 has a controller 104 that controls the above-mentioned rotation drive mechanism 42, grinding unit 70, nozzle, thickness gauge 84, first moving mechanism 56, second moving mechanism 86, touch panel display 100, indicator light 102, etc.

Note that in FIG. 5, for convenience, the controller 104 is shown outside the exterior panel, but in reality, the controller 104 is provided inside the exterior panel or inside the base 22.

The controller 104 is configured by a computer including a processor 104a, such as a CPU (Central Processing Unit), and a memory 104b. The memory 104b includes a main storage device such as a DRAM (Dynamic Random Access Memory), and an auxiliary storage device such as a flash memory, a hard disk drive, or a solid state drive.

The auxiliary storage device stores software including a specific program. The functions of the controller 104 are realized by operating the processing device and the like in accordance with this software. Note that a program for analyzing the received light signal measured using the thickness measuring device 84 may be executed by this processor 104a.

The controller 104 includes a discrimination unit 104c (see FIG. 9(A) etc.) that discriminates anomalies in the thickness of the wafer 11 by executing a program stored in the memory 104b with the processor 104a.

The non-contact thickness gauge 84 is electrically connected to the controller 104. The discrimination unit 104c discriminates anomalies in the thickness of the wafer 11 by comparing the thickness of the wafer 11 measured by the thickness gauge 84 with a predetermined threshold value.

In this embodiment, the discrimination unit 104c discriminates that the thickness of the wafer 11 is abnormal when the thickness of the wafer 11 is equal to or greater than a predetermined threshold. However, the discrimination unit 104c may also discriminate that the thickness of the wafer 11 is abnormal when the thickness of the wafer 11 is equal to or less than a predetermined threshold.

When the wafer 11 is thinned to 200 μm or less by grinding, the thickness of the wafer 11 has a waviness of, for example, about 0.3 μm to 0.5 μm. However, in this embodiment, the predetermined threshold value used by the discrimination unit 104c when discriminating that the thickness of the wafer 11 is abnormal is larger than the waviness value of the wafer 11 after the grinding process S30.

That is, the predetermined threshold in this embodiment is greater than the waviness value of the wafer 11 after the thickness of the device region 17a reaches the finished thickness. The predetermined threshold is, for example, 2.0 μm or more and 5.0 μm or less, and in one example, 3.0 μm. The same threshold may be used when a locally thin thickness abnormality occurs in the wafer 11.

The discrimination unit 104c discriminates anomalies in the thickness of the wafer 11 based on the measurement results obtained by measuring the thickness of the wafer 11 at multiple points on a predetermined circumference around the center of rotation of the rotation axis 24b of the chuck table 24.

Since the area that can be measured on one circumference is only a portion of the device area 17a, it is preferable to measure the thickness of the wafer 11 over the entire back surface 11b that corresponds to the device area 17a while changing the position of the sensor head 84c relative to the holding surface 24a using the second moving mechanism 86.

The discrimination unit 104c, for example, compares the difference between the maximum and minimum thickness values of the wafer 11 with the above-mentioned predetermined threshold value. If the discrimination unit 104c determines that there is an abnormality in the thickness of the wafer 11, the controller 104 displays on the touch panel display 100 either the thickness value of the wafer 11 that has been determined to be abnormal or a message indicating that there is an abnormality in the thickness, or both.

The method of determining whether or not there is an abnormality in the thickness is not limited to the above-mentioned method. For example, the determination unit 104c may determine whether or not there is an abnormality in the thickness of the wafer 11 based on whether or not the difference between the average thickness measurement value on the circumference and each measurement value is greater than or equal to a predetermined threshold value (or less than or equal to the predetermined threshold value). In this case, the predetermined threshold value may be greater than or equal to 1.0 μm and less than or equal to 2.5 μm (for example, 1.5 μm).

In addition, the discrimination unit 104c may discriminate an abnormality in the thickness of the wafer 11 by calculating the rate of change of the measured thickness value on the circumference. In this way, the discrimination unit 104c can discriminate an abnormality in the thickness of the wafer 11 based on the measurement results of the thickness of the wafer 11.

Next, the grinding process S30, the measurement process S40, and the detection process S50 will be described with reference to Figures 8 to 11. Note that the above-mentioned attachment process S10 and cutting process S20 are completed before the grinding process S30.

Figure 8 (A) shows the grinding process S30. In the grinding process S30, first, the front surface 11a of the wafer 11 is suction-held by the holding surface 24a of the chuck table 24 via the thinned protective tape 19. This causes the back surface 11b to be exposed upward.

Next, the back surface 11b of the wafer 11 is ground with a grinding wheel 80. In the grinding process S30 of this embodiment, as described above, a circular area corresponding to the device region 17a is ground on the back surface 11b.

As a result, as shown in FIG. 8(B), a circular recess 11d is formed that has a depth that does not reach the front surface 11a in the thickness direction 11c of the wafer 11 from the back surface 11b, and a ring-shaped reinforcing portion 11e that surrounds the outer periphery of the circular recess 11d.

Figure 8 (B) is a cross-sectional view of the wafer unit 21 thinned in the grinding process S30. In the grinding process S30, a local thickened region 11f is formed on the wafer 11 due to the local thinned region 19c of the protective tape 19 described above.

The diameter of the thickened region 11f depends on the diameter of the wafer 11, the size of the foreign object 4b, etc., but for example, in a wafer 11 having a diameter of 12 inches, the diameter of the thickened region 11f is 50 mm.

In the grinding process S30, grinding of the wafer 11 is continued while measuring the thickness of the wafer 11 in the device region 17a with a contact-type thickness gauge 82 (see FIG. 5) until the thickness of the wafer 11 reaches a predetermined thickness. The predetermined thickness is, for example, a value between 150 μm and 250 μm.

In the grinding process S30, for example, the rotation speed of the spindle 76 is set to a predetermined value of 1000 rpm or more and 7000 rpm or less. In addition, the grinding feed rate downward along the Z-axis direction is set to 0.5 μm/s or more and 1.0 μm/s or less, and the flow rate of the grinding water is set to 1.5 L/min or more and 4.0 L/min or less.

The rotation speed of the chuck table 24 is set to a predetermined value of 200 rpm or more and 400 rpm or less until the thickness of the wafer 11 reaches a predetermined thickness, and when the thickness of the wafer 11 falls below the predetermined thickness, it is set to a predetermined value of 60 rpm or more and 150 rpm or less.

During grinding, the sensor head 84c of the non-contact thickness gauge 84 is also positioned above the device region 17a, but due to the performance of the thickness gauge 84, it is not possible to measure the thickness of the wafer 11 until the thickness of the wafer 11 reaches a predetermined thickness.

In contrast, for example, when the thickness of the wafer 11 becomes equal to or smaller than a predetermined thickness, measurement with the thickness gauge 84 becomes possible, and grinding of the wafer 11 is continued while measuring the thickness of the wafer 11 with the thickness gauge 84. At this time, in order to suppress damage to the back surface 11b, the contact portion of the first height gauge 82a in the thickness gauge 82 is moved away from the wafer 11.

In this manner, in this embodiment, the grinding process S30 is performed until the thickness of the wafer 11 in the device region 17a reaches a thickness that can be measured by the thickness gauge 84 (i.e., the above-mentioned predetermined thickness), and then the measurement process S40 is started.

More specifically, the measurement process S40 is started after the thickness of the wafer 11 in the device region 17a becomes a thickness that can be measured by the thickness gauge 84, but before it reaches the desired finished thickness. In other words, in the method for detecting thickness anomalies in the wafer 11, the grinding process S30 is started before the measurement process S40.

9A is a diagram showing a measurement step S40 on a first circumference. As shown in FIG. 9A, in the measurement step S40, the thickness of the wafer 11 is measured on the first circumference 23a having a first diameter _23a1 while rotating the chuck table 24 that holds the wafer 11 by suction, with the position of the sensor head 84c fixed in the XY plane (a predetermined plane).

For example, the rotation speed of the chuck table 24 is set to 60 rpm or more and 150 rpm or less, and the sampling frequency of the non-contact thickness measurement system including the thickness gauge 84 is set to 4 kHz. However, in order to avoid measuring the same location multiple times, it is preferable to determine at least one of the frequency and the rotation speed so that the value (f/R) obtained by dividing the frequency (f) by the rotation speed (R) is not an integer.

For example, if the rotation speed is set to a predetermined value between 60 rpm and 150 rpm, and the sampling frequency is 4 kHz, the value obtained by dividing the frequency by the rotation speed is an integer, so it is preferable to avoid rotation speeds of 125 rpm, 100 rpm, or 50 rpm.

By avoiding cases where the value obtained by dividing the frequency during measurement by the number of rotations of the chuck table 24 is an integer, the number of points where the thickness is measured on the same circumference can be increased compared to cases where the value obtained by dividing the frequency by the number of rotations is an integer, so that the thickened region 11f can be detected more reliably.

In the measurement process S40, the thickness of the wafer 11 is measured at multiple locations on the wafer 11 by moving the sensor head 84c and the chuck table 24, which holds the wafer 11 on the holding surface 24a, relatively within the XY plane (a specified plane).

In this embodiment, the position of the sensor head 84c relative to the wafer 11 is adjusted using the second moving mechanism 86. Figure 9(B) is a diagram showing the measurement of the thickness of the wafer 11 on multiple circumferences concentric with the first circumference 23a.

The measurement process S40 includes measuring the thickness of the wafer 11 on the second circumference 23b having a second diameter 23b1 smaller than the first diameter _23a1 while rotating the chuck table 24 that holds the wafer ₁₁ by suction with the position of the sensor head 84c fixed in the XY plane.

The measurement process S40 also includes measuring the thickness of the wafer 11 on a third circumference 23c having a third diameter _23c1 larger than the first diameter _23a1 while rotating the chuck table 24 with the position of the sensor head 84c fixed.

Figure 10 is a more detailed flow diagram of the measurement step S40 and the detection step S50. While the wafer 11 is being ground, or after the wafer 11 has been thinned to its finishing thickness by grinding, the thickness of the wafer 11 is measured on one circumference in an area corresponding to the device region 17a.

This allows the maximum and minimum thickness values on the circumference to be obtained (measurement step S40). If the difference between the maximum and minimum values is equal to or greater than the threshold value (YES in S52), either or both of an abnormal thickness value and a message indicating that there is an abnormality in the thickness are displayed on the touch panel display 100 (S56).

On the other hand, if the difference between the maximum and minimum values is less than the threshold value (NO in S52), the position of the sensor head 84c relative to the chuck table 24 is moved in the radial direction of the chuck table 24 (S54). Then, the process returns to S40.

The rotation axis 24b of the chuck table 24 is not completely parallel to the Z-axis direction, but is slightly tilted relative to the Z-axis direction. However, because the angle of inclination of the rotation axis 24b relative to the Z-axis direction is extremely small, even if the sensor head 84c is moved along the second direction 84d, it can be considered that the sensor head 84c is moved in the radial direction of the chuck table 24.

S52, S54, and S56 correspond to the detection process S50, which uses the measurement results from the measurement process S40 to detect an abnormality in the thickness of the wafer 11. In this way, the detection process S50 can detect an abnormality in the thickness of the wafer 11.

If an abnormality in thickness is detected, the shape of the holding surface 4a may be corrected by performing self-grinding on the holding surface 4a of the chuck table 4 of the surface planer 2 (i.e., cutting the holding surface 4a with the cutting blade 12c).

(First modified example) The sensor head 84c does not necessarily move linearly, but may move in a pivoting manner. FIG. 11(A) is a side view of the third moving mechanism 118 that pivots the sensor head 84c, and FIG. 11(B) is a top view of the pivoting sensor head 84c.

As shown in FIG. 11(A), a driven pulley 110 is fixed to the lower end of the base 84b of the thickness gauge 84. A stepping motor (fourth motor) 112 is fixed to the base 22 of the grinding device 20. The output shaft of the stepping motor 112 can rotate both clockwise and counterclockwise.

A drive pulley 114 is fixed to the output shaft of the stepping motor 112, and an endless belt 116 is looped between the drive pulley 114 and the driven pulley 110. When the stepping motor 112 is operated, the sensor head 84c rotates around the base 84b as the rotation axis.

The driven pulley 110, the stepping motor 112, the drive pulley 114, and the endless belt 116 constitute a third movement mechanism 118 that rotates the sensor head 84c relative to the chuck table 24 within the XY plane (a specified plane). The third movement mechanism 118 is also controlled by the controller 104 described above.

Figure 12(A) is a top view showing the wafer 11 and sensor head 84c held by the holding surface 24a, and Figure 12(B) is a diagram showing the measurement process S40 on the first circumference 23a, the second circumference 23b, and the third circumference 23c. As indicated by the double arrow, the sensor head 84c can be rotated within a predetermined angle range.

(Second modified example) It should be noted that the second moving mechanism 86 and the third moving mechanism 118 may be used in combination rather than using only one of them. Figure 13 is a side view showing the combination of the second moving mechanism 86 and the third moving mechanism 118.

The second moving mechanism 86 has already been explained in FIG. 7, and the third moving mechanism 118 has already been explained in FIG. 11(A), so explanations will be omitted. A cylindrical support part 120 having a bearing that rotatably supports the driven pulley 110 is fixed onto the moving plate 88.

In this example, the sensor head 84c can move linearly in the XY plane by the second moving mechanism 86 and pivot in the XY plane by the third moving mechanism 118.

(Second embodiment) However, the second moving mechanism 86 and the third moving mechanism 118 may be omitted, and the sensor head 84c may be moved relative to the chuck table 24 in the XY plane using only the first moving mechanism 56 that moves the chuck table 24 along the X-axis direction.

14A is a diagram showing a sensor head 84c disposed directly above the center _24a1 of the holding surface 24a. In the second embodiment, the sensor head 84c is disposed directly above a movement path _24a2 of the center _24a1 of the holding surface 24a by the first movement mechanism 56.

Since the chuck table 24 is rotatable around the rotation axis 24b, by disposing the sensor head 84c directly above the movement path _24a2 of the center _24a1 by the first moving mechanism 56, it is possible to scan substantially the entire wafer 11 with the laser beam from the sensor head 84c even without the second moving mechanism 86 and the third moving mechanism 118.

Figure 14 (B) is a diagram showing a measurement process S40 on the first circumference 23a, the second circumference 23b, and the third circumference 23c according to the second embodiment. In addition, the structures, methods, etc. according to the above-mentioned embodiments can be modified as appropriate without departing from the scope of the purpose of the present invention.

For example, the protective tape 19 is not essential, and the above-mentioned detection method for detecting thickness anomalies can be performed when grinding a wafer 11 to which the protective tape 19 is not attached. Also, the grinding process S30 is not limited to so-called TAIKO grinding, which grinds the area corresponding to the device area 17a, and the entire back surface 11b may be ground uniformly.

In the above embodiment, the case where the thickness of the thickened region 11f is equal to or greater than a threshold value has been described. However, even if the wafer 11 is locally thinned by a thinned region (not shown) instead of the thickened region 11f, the thickness abnormality can be detected in the detection process S50, for example, by checking whether the difference between the maximum value and the minimum value is equal to or greater than a threshold value.

2: Surface planer 4: Chuck table (second holding table), 4a: Holding surface (second holding surface), 4b: Foreign object 6: Support portion, 8: Spindle, 10: Wheel mount 11: Wafer, 11a: Front surface (first surface), 11b: Back surface (second surface), 11c: Thickness direction 11d: Circular recess, 11e: Ring-shaped reinforcing portion, 11f: Thickened region 12: Bit wheel (bit tool)
12a: base, 12b: shank, 12c: cutting blade 13: planned division line, 15: device, 17a: device region, 17b: outer peripheral excess region 19: protective tape, 19a: outer surface, 19b: inner surface, 19c: thinned region 20: grinding device (processing device), 22: base, 22a: opening 21: wafer unit 23a: first circumference, 23a ₁ : first diameter 23b: second circumference, 23b ₁ : second diameter 23c: third circumference, 23c ₁ : third diameter 24: chuck table (holding table, first holding table)
24a: holding surface (first holding surface), 24a ₁ : center, 24a ₂ : movement path, 24b: rotation axis, 26: first cover, 28: second cover, 30: table base, 32: inclination adjustment mechanism, 32a: fixed axis, 32b: movable axis, 34: servo motor (first motor), 36: driving pulley, 38: driven pulley, 40: endless belt, 42: rotation drive mechanism, 44: moving plate, 46: guide rail, 48: nut portion, 50: screw shaft, 52: stepping motor (second motor), 54: first ball screw, 56: first movement mechanism, 58: column, 60: grinding feed mechanism, 62: guide rail, 64: moving plate, 66: screw shaft, 68: pulse motor, 70: grinding unit (machining unit), 72: holding member, 74: spindle housing, 76: spindle, 76a: lower End 78: Wheel mount 80: Grinding wheel (machining tool), 80a: Base, 80b: Grinding wheel 82: Thickness gauge, 82a: First height gauge, 82b: Second height gauge 84: Thickness gauge, 84a: Arm, 84b: Base, 84c: Sensor head 84d: Second direction 86: Second moving mechanism, 88: Moving plate, 90: Guide rail, 92: Nut part 94: Screw shaft, 96: Stepping motor (third motor), 98: Second ball screw 100: Touch panel display (display), 102: Indicator light 104: Controller, 104a: Processor, 104b: Memory, 104c: Discrimination part 110: Driven pulley, 112: Stepping motor (fourth motor)
114: driving pulley, 116: endless belt, 118: third moving mechanism, 120: support part, S10: bonding process, S20: cutting process, S30: grinding process, S40: measuring process, S50: detection process, Δ: distance

Claims (11)

A method for detecting thickness anomalies in a wafer, comprising:
a measuring step of measuring the thickness of the wafer at a plurality of points on the wafer by relatively moving a sensor head of a thickness measuring device that measures the thickness of the wafer without contacting the wafer and a first holding table that holds the wafer on a first holding surface within a predetermined plane;
a detection step of detecting an anomaly in the thickness of the wafer using a measurement result from the measurement step;
A detection method comprising: The detection method according to claim 1, characterized in that the measurement step includes measuring the thickness of the wafer on a first circumference having a first diameter while rotating the first holding table that holds the wafer with the position of the sensor head fixed within the predetermined plane. The detection method according to claim 2, characterized in that the measurement step includes measuring the thickness of the wafer on a second circumference having a second diameter smaller than the first diameter and on a third circumference having a third diameter larger than the first diameter while rotating the first holding table that holds the wafer with the position of the sensor head fixed within the predetermined plane. The detection method according to claim 1, characterized in that in the detection step, an abnormality in the thickness of the wafer is detected by comparing the difference between the maximum thickness of the wafer measured in the measurement step and the minimum thickness of the wafer with a predetermined threshold value. The detection method according to any one of claims 1 to 4, further comprising a grinding step in which the first surface of the wafer is held by the first holding table, and the second surface of the wafer, which is located on the opposite side to the first surface in the thickness direction of the wafer, is ground by a grinding wheel, and the grinding step is started before the measurement step. The detection method according to claim 5, characterized in that in the detection step, the difference between the maximum thickness of the wafer measured in the measurement step and the minimum thickness of the wafer is compared with a predetermined threshold value that is greater than the waviness of the thickness of the wafer after the grinding step, thereby detecting an abnormality in the thickness of the wafer. The detection method according to claim 5, characterized in that in the grinding step, the second surface of the wafer is ground to form a circular recess having a depth from the second surface in the thickness direction of the wafer that does not reach the first surface, and a ring-shaped reinforcing portion surrounding the outer periphery of the circular recess. Prior to the grinding step,
a step of applying a protective tape to the first surface of the wafer so as to cover the first surface;
a cutting process in which a cutting tool having a cutting blade is rotated around a spindle while the cutting blade is fixed at a predetermined height, and a second holding table holding the wafer on a second holding surface is linearly moved along a predetermined direction relative to the spindle so that the protective tape is exposed, thereby cutting the protective tape with the cutting tool to flatten the protective tape;
The method of claim 5 further comprising: a holding table having a holding surface for holding a wafer;
a rotation drive mechanism including a first motor that rotates a rotation shaft of the holding table disposed at the center of the holding surface;
a first moving mechanism having a second motor and configured to move the holding table along a first direction;
a processing unit having a spindle and capable of processing the wafer held by the holding surface with a processing tool attached to a lower end of the spindle;
a thickness gauge having a sensor head for measuring the thickness of the wafer without contacting the wafer;
one or both of a second moving mechanism having a third motor and moving the sensor head relative to the holding table along a second direction intersecting the first direction, and a third moving mechanism having a fourth motor and rotating the sensor head relative to the holding table within a predetermined plane defined by the first direction and the second direction;
a controller having a processor and a memory, and controlling the rotation drive mechanism, the processing unit, the thickness gauge, the first movement mechanism, the second movement mechanism, and the third movement mechanism;
Equipped with
the controller includes a determination unit that determines an abnormality in the thickness of the wafer by executing a program stored in the memory with the processor;
The processing apparatus is characterized in that the discrimination unit discriminates an abnormality in the thickness of the wafer based on measurement results obtained by measuring the thickness of the wafer at multiple points on a predetermined circumference around the center of rotation of the rotation axis. a holding table having a holding surface for holding a wafer;
a rotation drive mechanism including a first motor that rotates a rotation shaft of the holding table disposed at the center of the holding surface;
a first moving mechanism having a second motor and configured to move the holding table along a first direction;
a processing unit having a spindle and capable of processing the wafer held by the holding surface with a processing tool attached to a lower end of the spindle;
a thickness gauge having a sensor head disposed directly above a moving path of the center of the holding surface for measuring a thickness of the wafer without contacting the wafer;
a controller having a processor and a memory, and controlling the rotation drive mechanism, the processing unit, the thickness gauge, and the first moving mechanism;
Equipped with
the controller includes a determination unit that determines an abnormality in the thickness of the wafer by executing a program stored in the memory with the processor;
The processing apparatus is characterized in that the discrimination unit discriminates an abnormality in the thickness of the wafer based on measurement results obtained by measuring the thickness of the wafer at multiple points on a predetermined circumference around the center of rotation of the rotation axis. a display whose operation is controlled by the controller;
The processing apparatus according to claim 9 or 10, characterized in that when the discrimination unit determines that there is an abnormality in the thickness of the wafer, the controller causes the display to display one or both of the thickness value of the wafer determined to be abnormal and a message indicating that there is an abnormality in the thickness.

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