JP2018058084A - Laser processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing apparatus capable of imagining gently changing unevenness on the entire surface of a wafer and accurately locating a focal position of a condenser when performing laser processing. SOLUTION: A control means operates a processing feed means to position a plurality of predetermined positions of the waier held by the holding means on the height measuring means, measures the height of the predetermined position, and measures the height of the predetermined position. A coordinate storage unit that stores the height of a predetermined position as the X coordinate and the Z coordinate corresponding to the Y coordinate, and the three-dimensional coordinate axes of the X coordinate axis, the Y coordinate axis, and the Z coordinate axis are displayed on the display means 47 and are displayed on the coordinate storage unit. A laser processing device that creates a three-dimensional graph by expressing the stored X-coordinates, Y-coordinates, and Z-coordinates of the plurality of predetermined positions on the three-dimensional coordinate axes. [Selection diagram] Fig. 5

Description

  The present invention relates to a laser processing apparatus capable of visually confirming unevenness that gradually changes on the entire surface of a wafer.

  A wafer formed by dividing a plurality of devices such as IC and LSI on the surface by dividing lines, the condensing point of the laser beam having a wavelength having transparency to the wafer is positioned inside the dividing line, A modified layer serving as a starting point of the division is formed along the inside, and is divided into individual devices by applying an external force and used for electric devices such as mobile phones and personal computers (see, for example, Patent Document 1). .

  The laser processing apparatus for forming the modified layer includes: a holding unit that holds the wafer; a laser beam irradiation unit that includes a condenser that irradiates a laser beam having a wavelength that is transparent to the wafer held by the holding unit; Measuring means for measuring the height of the wafer held on the chuck table, and processing and feeding the holding means relative to the laser beam irradiation means and the height measuring means in the X-axis direction and the Y-axis direction. The processing feed means and the control means including the display means are configured, and the condensing point of the laser beam can be appropriately positioned inside the division planned line (see, for example, Patent Document 2).

Japanese Patent No. 3408805 JP 2007-152355 A

  The height measuring means in the laser processing apparatus described in Patent Document 2 described above corresponds to the X-coordinate position and Y-coordinate position of each scheduled division line in order to accurately position the focal point of the condenser inside the wafer. It measures the height, but does not grasp the so-called undulations that slowly change over the entire surface of the wafer, but determines the focal position according to only locally measured height measurements. However, since the operator does not consider the waviness of the entire wafer surface, there is a risk of making mistakes when setting the machining conditions, or even if machining errors occur due to setting mistakes, Discovery may be delayed. In addition, even if it is found that the surface of the wafer is excessively uneven due to processing defects and the wafer is not suitable for processing based on the height measurement value, what kind of waviness is observed when viewed from the whole wafer. There is a problem in that it cannot be visually visualized whether it is formed or it takes time to investigate the cause.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that it is possible to image unevenness that changes gently over the entire surface of the wafer, and the focal position of the condenser when performing laser processing. It is an object of the present invention to provide a laser processing apparatus capable of accurately positioning a laser beam.

  In order to solve the above main technical problems, according to the present invention, a holding means for holding a wafer, a laser beam irradiation means for irradiating a wafer held by the holding means with a laser beam, and the wafer held by the holding means. A height measuring means for measuring the height of the workpiece, a processing feeding means for processing and feeding the holding means relative to the laser beam means and the height measuring means in the X-axis direction and the Y-axis direction, and a display means. A laser processing apparatus comprising at least a control means, wherein the control means operates the processing feed means to position a plurality of predetermined positions of the wafer held by the holding means on the height measuring means. A coordinate storage unit that measures the height of the predetermined position and stores the height of the predetermined position as a Z coordinate corresponding to the X coordinate and the Y coordinate, and a three-dimensional coordinate of the X coordinate axis, the Y coordinate axis, and the Z coordinate axis Is provided on the display means, and a laser processing apparatus is provided that creates a three-dimensional graph by representing the X, Y, and Z coordinates of the plurality of predetermined positions stored in the coordinate storage unit on the three-dimensional coordinate axis. Is done.

  A laser processing apparatus constructed according to the present invention comprises a holding means for holding a wafer, a laser beam irradiation means for irradiating a laser beam to the wafer held by the holding means, and a height of the wafer held by the holding means. Control means including: a height measuring means for measuring, a processing feeding means for processing the holding means relative to the laser beam means and the height measuring means in the X-axis direction and the Y-axis direction, and a display means The control means operates the processing feed means to position a plurality of predetermined positions of the wafer held by the holding means on the height measuring means, and sets the height of the predetermined position. A coordinate storage unit for measuring and storing the height of the predetermined position as a Z coordinate corresponding to the X coordinate and the Y coordinate, and displaying the three-dimensional coordinate axes of the X coordinate axis, the Y coordinate axis, and the Z coordinate axis on the display means Since the three-dimensional graph is generated by representing the X coordinate, Y coordinate, and Z coordinate of the plurality of predetermined positions stored in the mark storage unit on the three-dimensional coordinate axis, the worker can Gradually changing irregularities on the entire surface can be visually grasped, and if a wafer unsuitable for processing is found, the cause of the entire surface of the wafer can be investigated at an early stage. Occurrence can be reduced overall.

It is a whole perspective view of the laser processing apparatus comprised based on this invention. It is a block diagram for demonstrating the laser beam irradiation means applied to the laser processing apparatus shown by FIG. 1, and a height measurement means. It is drawing which shows an example of the control map applied to a height measurement means to this invention. It is a figure which shows an example of the value of Z coordinate corresponding to the X coordinate and Y coordinate memorize | stored in the coordinate memory | storage part of the control means. It is a figure which shows an example of the three-dimensional graph created based on this invention displayed on the display means of the laser processing apparatus shown in FIG.

  Hereinafter, a laser processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a perspective view of a laser processing apparatus 40 for carrying out a laser processing method configured according to the present invention, and a wafer 10 as a workpiece. The wafer 10 as a workpiece is made of, for example, a silicon (Si) substrate, and a plurality of division lines 12 are formed in a lattice shape on the surface of the wafer 10 having a substantially disk shape. 12, the surface of the wafer 10 is partitioned into a plurality of regions. A device 14 is formed in each of the plurality of regions, and the wafer 10 is held by being attached to the adhesive tape T whose outer periphery is attached to the annular frame F with the back surface side attached.

  A laser processing apparatus 40 shown in FIG. 1 includes a base 41, a holding mechanism 42 that holds the workpiece, a processing feed means 43 that moves the holding mechanism 42, and a workpiece that is held by the holding mechanism 42. A laser beam irradiating means 44 for irradiating a laser beam, an image pickup means 45, a frame 46 containing the laser beam irradiating means 44 extending upward from the upper surface of the base 41 and then extending substantially horizontally, and a computer described later. Control means, and display means 47 placed on the frame 46 and connected to the control means to display various information, and each means is controlled by the control means. .

  The holding mechanism 42 has a rectangular X-axis movable plate 51 mounted on the base 41 so as to be movable in the X-axis direction and a rectangular shape mounted on the X-axis movable plate 51 so as to be movable in the Y-axis direction. A Y-axis movable plate 53, a cylindrical column 50 fixed to the upper surface of the Y-axis movable plate 53, and a rectangular cover plate 52 fixed to the upper end of the column 50 are included. The cover plate 52 is formed with a long hole 52a extending in the Y-axis direction. On the upper surface of the chuck table 54 as a holding means for directly holding a circular workpiece extending upward through the elongated hole 52a, a circular adsorption formed from a porous material and extending substantially horizontally. A chuck 56 is disposed. The suction chuck 56 is connected to suction means (not shown) by a flow path passing through the support column 50. A plurality of clamps 58 are arranged on the periphery of the chuck table 54 at intervals in the circumferential direction. The X-axis direction is a direction indicated by an arrow X in FIG. 1, and the Y-axis direction is a direction indicated by an arrow Y in FIG. 1 and is a direction orthogonal to the X-axis direction. A plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

  The machining feed means 43 includes an X-axis direction moving means 60, a Y-axis direction moving means 65, and a rotating means (not shown). The X-axis direction moving means 60 has a ball screw 60b extending in the X-axis direction on the base 41 and a motor 60a connected to one end of the ball screw 60b. A nut portion (not shown) of the ball screw 60 b is fixed to the lower surface of the X-axis direction movable plate 51. Then, the X-axis direction moving means 60 converts the rotational motion of the motor 60a into a linear motion by the ball screw 60b and transmits it to the X-axis direction movable plate 51, and is movable along the guide rail 43a on the base 41 in the X-axis direction. The plate 51 is advanced and retracted in the X-axis direction. The Y-axis direction moving means 65 has a ball screw 65b extending in the Y-axis direction on the X-axis direction movable plate 51, and a motor 65a connected to one end of the ball screw 65b. A nut portion (not shown) of the ball screw 65 b is fixed to the lower surface of the Y-axis direction movable plate 53. Then, the Y-axis direction moving means 65 converts the rotational motion of the motor 65 a into a linear motion by the ball screw 65 b and transmits it to the Y-axis direction movable plate 53, along the guide rail 51 a on the X-axis direction movable plate 51. The Y-axis direction movable plate 53 is advanced and retracted in the Y-axis direction. The rotating means is built in the column 50 and rotates the suction chuck 56 with respect to the column 50.

  The laser beam irradiation means 44 is built in a frame 46 that extends upward from the upper surface of the base 41 and then extends substantially horizontally. The laser beam irradiating means 44 irradiates the upper surface of the division line 12 of the wafer 10 that is a workpiece, and a laser beam having a wavelength that is transmissive to the wafer 10 held on the chuck table 54. This is for carrying out a plasma layer forming step in which a condensing point is irradiated at a predetermined depth position from the surface of the wafer 10 and a modified layer is formed along the planned division line 12 to be a division starting point. .

  Based on FIG. 2, the laser beam irradiation means 44 will be described in more detail. The illustrated laser beam application means 44 is built in the frame 46. In this frame 46, as shown in FIG. 2, a processing pulse laser beam oscillator 44c, a dichroic mirror 44b that transmits the processing pulse laser beam oscillated by the processing pulse laser beam oscillator 44c toward the chuck table 54, and And a condenser 44a for condensing the processing pulse laser beam transmitted through the dichroic mirror 44b onto the workpiece. The concentrator 44a condenses the pulsed laser beam transmitted through the dichroic mirror 44b toward the wafer 10 and the reflecting mirror 44a2 for converting the direction of the pulsed laser beam to the wafer 10 to form a condensing point inside the wafer 10 Objective condenser lens 44a1. For example, the processing pulse laser beam oscillator 44c oscillates a pulse laser beam having a wavelength that is transmissive to the workpiece. If the workpiece is a wafer made of a silicon substrate, the wavelength is 1064 nm. A YVO 4 pulse laser oscillator or a YAG pulse laser oscillator that oscillates a pulse laser beam can be used. The wavelength of the laser beam oscillated in the processing pulse laser beam oscillator 44c is appropriately selected according to the member forming the substrate, but may be a substrate including a silicon carbide substrate, a lithium tantalate substrate, a glass substrate, or a quartz substrate. For example, a pulse laser having a wavelength of 1064 nm can be used. Although illustration is omitted, the laser beam irradiation means 44 is also provided with a focusing point position adjusting means for adjusting the vertical position of the focusing point P when the wafer 10 is irradiated with the laser beam. Yes.

  Continuing the description with reference to FIG. 2, the laser processing apparatus 40 in the illustrated embodiment, together with the laser beam irradiation means 44, measures the height of the upper surface of the wafer 10 held on the chuck table 54. Measuring means 70 is provided. The height measuring means 70 includes a measurement laser beam oscillator 71 that oscillates a measurement laser beam as a light source that emits light having a predetermined wavelength, and the measurement laser beam oscillated from the measurement laser beam oscillator 71. The reflected light reflected and irradiated to the upper surface of the wafer 10 held by the chuck table 54 through the objective condenser lens 44a1 is guided to the first path 70a on the side where the optical axis 44b is disposed, and the objective condenser lens 44a1, There is provided a first beam splitter 72 that leads to a second path 70b on the side of light receiving elements 76a and 76b, which will be described later, via a dichroic mirror 44b.

  The measurement laser beam oscillator 71 is different from the wavelength of the processing pulse laser beam oscillated from the processing pulse laser beam oscillator 44c, and is a measurement laser beam of 632 nm, for example, having a reflectivity with respect to the wafer 10 made of a silicon substrate. A He—Ne laser oscillator that oscillates can be used.

  In the second path 70b, a band-pass filter 74 for removing outside light having a wavelength other than 632 nm of the reflected light is disposed. The reflected light that has passed through the bandpass filter 74 is evenly branched by the second beam splitter 73 into the third path 70c and the fourth path 70d at a ratio of 1: 1. At the terminal portion of the third path 70c, a first condenser lens 75a that condenses the reflected light branched by the second beam splitter 73, and a reflection condensed by the first condenser lens 75a. A first light receiving element 76a that receives 100% of light is disposed, and the first light receiving element 76a sends a voltage signal corresponding to the received light quantity to the control means 20. Further, at the end of the fourth path 70d, the second condensing lens 75b that condenses the reflected light branched by the second beam splitter 73 and the second condensing lens 75b collect the reflected light. A mask 77 having a slit 77a for blocking the outside of the reflected light and allowing the central portion of the reflected light to pass in a band shape, and a second light receiving element 76b for receiving the reflected light that has passed through the slit 77a, The second light receiving element 76b sends a voltage signal corresponding to the received light quantity to the control means 20 described later. In the present embodiment, the measurement laser beam irradiated to the wafer 10 by the height measuring means 70 is used in the form of sharing the objective condensing lens 44a1 used for irradiation of the processing pulse laser beam, and the measurement laser beam is irradiated. However, the present invention is not necessarily limited to this, and a dedicated objective condenser lens for irradiating the measurement laser beam may be prepared separately. In that case, the objective collector for irradiating the processing pulse laser beam may be prepared. The optical lens 44a1 may be disposed adjacent to the X axis direction.

  The control means 20 is constituted by a computer and temporarily stores a central processing unit (CPU) that performs arithmetic processing according to a control program, a read-only memory (ROM) that stores a control program and the like, detected detection values, arithmetic results, and the like. A random access memory (RAM) that can be read and written, an input interface, and an output interface (details are not shown).

The measurement principle of the height measuring means 70 described above will be described below.
The condensing point when the measurement laser beam is irradiated from the objective condensing lens 44a1 is a predetermined reference position from the surface of the suction chuck 56, and is positioned slightly inside from the surface of the wafer 10 for measurement. The reference condensing point P0 where the position does not change is set. Here, the reflected light of the measuring laser beam received by the first light receiving element 76a is condensed by the first condenser lens 75a and is always received by 100%, so the amount of received light is constant, The voltage value (D1) output from the light receiving element 76a is also constant (for example, 10V). On the other hand, the reflected light of the measurement laser beam received by the second light receiving element 76b is condensed by the second condenser lens 75b, and then the reflected light that can pass through the slit 77a of the mask 77 is regulated. Only the reflected light that has passed through the slit 77a is received by the second light receiving element 76b.

  When the surface of the wafer 10 is partially increased due to processing variation or the like, and the distance from the reference focusing point P0 to the surface of the wafer 10 is increased, the diameter of the spot formed on the surface of the wafer 10 is increased. Reflected light having a large cross-sectional area is formed. This reflected light is separated by the second beam splitter 73 via the dichroic mirror 44b and the first beam splitter 72, but the cross-sectional area of the reflected light is increased by the height of the surface of the wafer 10. Even if it changes so as to increase, the first light receiving element 76a receives 100% light, so that the output voltage value does not change. However, since the second light receiving element 76b receives only the reflected light that has passed through the slit 77a, the output voltage value changes. Note that the width of the slit 77a is 100% when the height position of the surface of the wafer 10 is at the same height position as the reference condensing point P0, and passes when the height position is higher than that. The reflected light that can be generated is set to be limited according to the height.

  More specifically, the higher the height position of the surface of the wafer 10, the larger the spot diameter on the wafer 10, and the larger the cross-sectional area of the reflected light separated into the fourth path 70d. The ratio of shielding by the slit 77a increases, and the ratio of reflected light that can pass through the slit 77a decreases. As a result, the proportion of light actually received by the second light receiving element 76b decreases, and the output voltage value (D2) also decreases accordingly. That is, as the position of the surface of the wafer 10 with respect to the position of the reference condensing point P0 becomes higher, the voltage value (D2) output by the second light receiving element with respect to the voltage value (D1) output by the first light receiving element becomes smaller. It decreases and changes so that the value of D1 / D2 increases.

  Here, the value of D1 / D2 and the distance from the reference condensing point P0 to the surface of the wafer 10, that is, the height of the surface of the wafer 10 with reference to the height of the reference condensing point P0 (= 0). Is previously verified by experiments, a control map as shown in FIG. 3 is created, and stored in a read only memory (ROM) of the control means 20. Then, by obtaining D1 / D2 and referring to the control map, it is possible to grasp the height of the predetermined position being measured. Note that the position of the reference condensing point P0, which serves as a reference for the height position, is set to a position that does not become higher than the surface of the wafer 10 even if the height of the wafer 10 varies.

  An embodiment of laser processing that uses the laser processing apparatus 40 described above to measure the height along the scheduled division line 12 of the wafer 10 and forms a modified layer along the planned division line 12 inside the wafer 10. explain.

  In order to detect the height of the wafer 10, first, the back surface was held on the annular frame F via the adhesive tape T on the chuck chuck 56 of the chuck table 54 of the laser processing apparatus 40 shown in FIG. The wafer 10 is placed and sucked and held. The chuck table 54 that sucks and holds the wafer 10 is positioned directly below the imaging means 45 by the processing feed means 43.

  When the chuck table 54 is positioned directly below the image pickup means 45, the image pickup means 45 and the control means 20 execute an alignment operation for detecting a processing region to be laser processed on the wafer 10. That is, the imaging unit 45 and the control unit 20 execute image processing such as pattern matching for aligning the planned division line 12 formed in a predetermined direction of the wafer 10 with the objective condenser lens 44a1. Execute alignment. In addition, alignment is similarly performed on the division lines 12 formed in the direction orthogonal to the predetermined direction formed on the wafer 10.

  Then, when the division line 12 formed on the wafer 10 held on the chuck table 54 is detected and the height measurement position is aligned, the chuck table 54 is moved to the measurement start position. One end of the planned dividing line 12 is positioned directly below the objective condenser lens 44a1. Then, the position of the condensing point is positioned at the reference condensing point P0 which becomes a reference when measuring the height, the height measuring means 70 is operated, and the chuck table 54 is moved to the arrow X while irradiating the measuring laser beam. It moves in the direction indicated by (the direction perpendicular to the paper surface on which the drawing is written) and moves to the processing feed end position. As a result, a ratio of voltage values D1 / D2 output from the first light receiving element 76a and the second light receiving element 76b corresponding to each predetermined position on the division planned line 12 of the wafer 10 is obtained. When D1 / D2 is obtained, the control map as shown in FIG. 3 is referred to each time, and the height at each predetermined position (the distance from the reference condensing point P0 to the surface of the wafer 10) is calculated. Is done. The height calculated here is made to correspond to the X coordinate and Y coordinate of the predetermined position on the planned dividing line 12 in the coordinate storage unit formed in the storage area of the random access memory (RAM) of the control device 20. The stored Z coordinate value is stored (see FIG. 4). In this way, the height measurement step is performed along all the planned division lines 12 formed on the wafer 10, and the heights (Z coordinate values) at all predetermined positions in the respective division lines 12 are measured. The data is stored in a coordinate storage unit of a random access memory (RAM) of the control means 20.

  If the height measurement process is performed along all the planned division lines 12 formed on the wafer 10 as described above, a modified layer is formed inside the wafer 10 along the planned division line 12. The layer forming process is performed. When the modified layer forming process is performed, the control unit 20 stores the height data in the division line 12 of the wafer 10 stored in the coordinate storage unit of the random access memory (RAM). Based on the above, a three-dimensional graph as shown in FIG. Thereby, the operator can visually imagine the unevenness of the surface of the wafer 10. Note that the X-axis and Y-axis scales when the display of this three-dimensional graph is executed are adjusted in display units (inch) based on the diameter of the wafer 10 (for example, 8 inches), and the Z-axis scale is the wafer scale. The height change of 10 is adjusted and displayed in a unit (μm) so that the change in height can be more clearly grasped and visually recognized. Here, as a typical example of a three-dimensional graph, an example displayed by a so-called mesh graph is shown, but it is not necessarily limited to a mesh graph. Any other display format may be employed as long as the user can visually recognize the unevenness of the wafer 10.

  When the modified layer forming step is performed on the division line 12 of the wafer 10, the processing pulse laser beam is generally irradiated in the same procedure as the case of irradiating the measurement laser beam described above. When irradiating the processing pulse laser beam, based on the height data (see FIG. 4) of the surface of the wafer 10 acquired by the height measuring means 70 and stored in the coordinate storage unit. A condensing point position adjusting means (not shown) is controlled to correct the condensing point position when irradiating the processing pulse laser beam. More specifically, the objective condensing lens 44a1 is moved in the vertical direction corresponding to the height position of the wafer 10 on the street 12, so that the condensing point is always a certain predetermined depth from the surface of the wafer 10. The modified layer parallel to the surface of the wafer 10 is controlled to have a constant depth. At this time, not only the numerical value indicating the height of the surface of the wafer 10 at the irradiation position where the laser beam is currently irradiated but also the three-dimensional indicating the unevenness of the entire wafer 10 as shown in FIG. A graph may be displayed, and the division line 12 of the currently processed wafer 10 may be displayed with an emphasis line L as shown in the figure, and various applications are possible.

  In the present embodiment, the reference position when the height measuring unit 70 measures the height is the reference condensing point P0. However, the reference position for detecting the height is not limited to this, and the suction position The surface height of the chuck 56 may be used as a reference, and any position can be used as a reference position as long as the position is a constant value that does not change even if the surface height of the wafer 10 changes. it can. In that case, a control map corresponding to the reference position may be created.

  In the present embodiment, the height of the surface of the wafer 10 is measured by the height measuring means 70, and before the step of forming the modified layer by irradiating the processing pulse laser beam, the wafer on the display means 47 is displayed. Although the three-dimensional graph indicating the height of 10 is displayed, the timing for displaying the three-dimensional graph can be arbitrarily selected by the operator. For example, the display timing is not limited, for example, when a processing defect occurs.

  Furthermore, in this embodiment, the laser processing apparatus 40 to which the height measuring means 70 of the present invention is applied is an example of a laser processing apparatus that forms a modified layer inside the wafer 10, but the present invention is The present invention is not limited to this, and any laser processing apparatus can be applied as long as it is useful to measure the height position of the surface of the wafer 10.

10: Wafer 12: Scheduled division line 14: Device 20: Control device 40: Laser processing device 42: Holding means 43: Processing feed means 44: Laser beam irradiation means 47: Display means 54: Chuck table 56: Adsorption chuck 70: Height Measuring means 71: He-Ne laser oscillator 72: First beam splitter 73: Second beam splitter 74: Band pass filter 75a: First condenser lens 75b: Second condenser lens 76a: First light reception Element 76b: Second light receiving element 77: Mask 77a: Slit

Claims (1)

Holding means for holding the wafer, laser beam irradiation means for irradiating the wafer held by the holding means with a laser beam, height measuring means for measuring the height of the wafer held by the holding means, and the holding means In a laser processing apparatus comprising at least processing feed means for processing and feeding in the X-axis direction and Y-axis direction relative to the laser beam means and the height measuring means, and control means including display means,
The control means includes
A plurality of predetermined positions of the wafer held by the holding means are positioned on the height measuring means by operating the processing feeding means, and the height of the predetermined position is measured. , A coordinate storage unit that stores Z coordinates corresponding to Y coordinates,
The three-dimensional coordinate axes of the X coordinate axis, the Y coordinate axis, and the Z coordinate axis are displayed on the display means, and the X coordinate, Y coordinate, and Z coordinate stored in the coordinate storage unit are represented on the three-dimensional coordinate axis. Laser processing equipment that creates 3D graphs.