JP2009099788A - Method of manufacturing wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately grind a wafer as a first purpose, and to grind one-side surface of the wafer without damaging the one-side surface of the wafer as a second purpose, in grinding the wafer by using an ELID grinding method. <P>SOLUTION: A grinding surface of a grinder is pressed against one-side surface of a wafer to grind the one-side surface in a T2 period. In the T2 period, a main shaft current according to the value of a processing load applied to the wafer by the grinder is measured by a device-side shaft current measurement part. When the main shaft current exceeds an upper-limit current value, the position of the grinder is fixed, and the grinding surface of the grinder is subjected to electrolytic dressing by an ELID method in a T3 period. When the main shaft current exceeding the upper-limit current value in the T2 period falls below a lower-limit current value smaller than the upper-limit current value, the wafer is ground by the grinder again. The process from the T2 period to a T4 period is repeated multiple times, and thus the one-side surface of the wafer is ground. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a wafer including a step of grinding by an electrolytic in-process dressing (ELID) grinding method.

  Conventionally, a method of grinding one surface of a wafer using an ELID grinding method is known (see, for example, Patent Documents 1 and 2). In the ELID grinding method, an electrode facing the grinding surface of the grindstone is provided, the grindstone is the anode, the electrode is the cathode, and a DC pulse voltage, for example, is applied between the grindstone and the electrode while grinding the workpiece with the grindstone. This is a grinding process performed while electrolytically dressing the grindstone by removing only the bond portion of the grindstone.

  When such an ELID grinding method is performed using a rotary grinder, processing thickness control using a sizing device is generally performed. This will be described with reference to FIG. In FIG. 5, an apparatus related to the ELID grinding method is omitted.

  First, as shown in FIG. 5A, a porous chuck 81 as a wafer suction table using a porous structure and negative pressure is arranged on the suction table 80, and on the porous chuck 81. A plate-like wafer 82 is disposed as an object to be ground. Further, an L-shaped sizing gauge 84 provided in a sizing device (not shown) is disposed above one surface 83 of the wafer 82.

  Then, as shown in FIG. 5B, the sizing gauge 84 is brought into contact with the one surface 83 of the wafer 82, and the grindstone 85 and the suction table 80 disposed on the suction table 80 are rotated in opposite directions, The surface 83 of the wafer 82 is ground by pressing the grindstone 85 against the wafer 82 while flowing a grinding liquid (not shown) on the surface 83 of the wafer 82. In this case, the wafer 82 is ground by a desired thickness by monitoring the position of the sizing gauge 84 that changes when the one surface 83 of the wafer 82 is ground by the sizing device.

Patent Document 2 proposes a method of controlling the current value of the electrolytic dress based on the motor current, and the grinding process is interrupted and only the electrolytic dress is performed.
JP-A-8-197422 JP-A-6-304866

  However, in the above conventional technique, the sizing gauge 84 is brought into contact with the rotating wafer 82, so that a current caused by friction between the wafer 82 and the sizing gauge 84 flows to the sizing gauge 84. As a result, current flows into the sizing device via the sizing gauge 84, and there is a possibility that an accurate change in the position of the sizing gauge 84 cannot be detected. In particular, when a high count grindstone 85 is used, since the amount of processing removal on the wafer 82 is small, control for grinding the wafer 82 becomes difficult.

  In addition, when the wafer 82 rotates, the sizing gauge 84 in contact with the wafer 82 rubs the one surface 83 of the wafer 82, so that the one surface 83 of the wafer 82 is damaged.

  In view of the above points, the present invention has a first object of grinding a wafer with high precision when grinding a wafer using an ELID grinding method, and grinding a wafer without damaging it. The purpose of 2.

  In order to achieve the above object, the present invention provides a process for preparing a wafer (60), and moves the grindstone (30) disposed above the wafer (60) to the wafer (60) side, and also provides an ELID current. A constant dressing current is caused to flow between the grindstone (30) and the electrode (70) opposed to the grindstone (30) by the generator (50), and the surface (31) of the grindstone (30) is placed on one surface of the wafer (60). A first step of grinding the one surface (61) by pressing against the (61), and a grinding stone (30) according to the processing load applied by the grinding wheel (30) to the wafer (60) during the first step. An upper limit indicating that the spindle current is measured by the apparatus-side axial current measuring unit (40) and the spindle current measured by the apparatus-side axial current measuring unit (40) cannot grind the wafer (60) with the grindstone (30). If the current value is exceeded, the grinding wheel (30) The movement is stopped and the position of the grindstone (30) is fixed, and the grinding surface (31) of the grindstone (30) is electrolytically dressed by the ELID method, and the wafer (60) is utilized using the processing load applied to the wafer (60). 60) in the second step and the second step, the spindle current that has exceeded the upper limit current value is smaller than the upper limit current value, indicating that the electrolytic dressing of the grindstone (30) has been completed. When the value is lower than the lower limit current value, the process includes the third step of returning to the first step again. By repeating the steps from the first step to the third step a plurality of times, the one surface (61) of the wafer (60) is ground. It is characterized by that.

  According to this, in order to grind the wafer (60) to a desired thickness by the feed amount and the cutting amount of the grindstone (30) without using the sizing device and the sizing gauge, the sizing device is used by using the sizing gauge. Can be avoided. Since the wafer (60) can be ground while electrolytically dressing the grindstone by the ELID method, the wafer (60) can be ground with high accuracy.

  In this case, in the second step, one surface (61) of the wafer (60) can be ground by the grinding surface (31) of the grindstone (30) with the position of the grindstone (30) fixed.

  Further, since the sizing device and the sizing gauge are not used, the sizing gauge can prevent the one surface (61) of the wafer (60) from being damaged.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a rotary grinding apparatus used in a manufacturing method according to an embodiment of the present invention. As shown in this figure, the rotary grinding apparatus includes an adsorption table 10, a porous chuck 20, a grindstone 30, an apparatus-side axial current measuring unit 40, and an ELID current generating unit 50.

  The suction table 10 has a disk shape that serves as a base on which the porous chuck 20 is sucked and fixed. The porous chuck 20 is a wafer suction table using a porous structure and negative pressure. The porous chuck 20 is disposed on the suction table 10, and the wafer 60 is disposed on the porous chuck 20. The suction table 10 is provided with a rotation mechanism (not shown) so that it can be rotated around the central axis.

  The grindstone 30 grinds one surface 61 of the wafer 60 and has a grinding surface 31 in which diamond abrasive grains are hardened with a grindstone bond material or the like. In the present embodiment, a cup shape in which a grinding surface 31 is provided at the open end of the container is employed. The cup-shaped grindstone 30 includes a straight cup shape, a tapered cup shape, a dish shape, and the like. The grinding surface 31 has a ring shape, and the grinding surface 31 is provided at the opening end of the container at regular intervals. You can also use things. In the present embodiment, a cup-shaped grindstone 30 having a grinding surface 31 in a ring shape is used.

  The grindstone 30 is provided with a rotation mechanism (not shown) that rotates the grindstone 30 (for example, a motor or a spindle) and a movement mechanism (not shown) that moves in the axial direction of the central axis of the suction table 10.

  The apparatus-side axial current measuring unit 40 detects a processing load, that is, measures a current corresponding to the size of the processing load applied to the wafer 60 by the grindstone 30. That is, the apparatus side shaft current measuring unit 40 measures a current (corresponding to a main shaft current described later) flowing through the main shaft that rotates the grindstone 30. For example, the apparatus-side axial current measurement unit 40 acquires a larger current value as the processing load on the grindstone 30 is larger, and obtains a smaller current value as the processing load on the grindstone 30 is smaller.

  The ELID current generator 50 detects film deterioration on the grinding surface 31 of the grindstone 30 and electrolytically dresses the grinding surface 31 of the grindstone 30. For this reason, the ELID current generator 50 uses the grindstone 30 as an anode and the electrode 70 disposed at a location facing a portion of the grinding surface 31 of the grindstone 30 that is not in contact with the wafer 60 as a cathode. For example, a direct-current pulse voltage is applied between the electrode 70 and the electrode 70 so that the ground surface 31 is dressed by electrolysis. That is, the ELID current generator 50 allows a constant dress current to flow between the grindstone 30 and the electrode 70 during grinding of the wafer 60.

  The above is the configuration of the rotary grinding apparatus. In this rotary grinding apparatus, the position of the grindstone 30 relative to the wafer 60, the apparatus-side axial current measuring unit 40, the ELID current generating unit 50, and the like are controlled by a control device (not shown).

  Next, the characteristics of the ELID grinding process when grinding using the rotary grinding apparatus will be described. FIG. 2 is a diagram showing the characteristics of ELID grinding. In the graph shown in FIG. 2, the horizontal axis indicates the machining time, the vertical axis indicates the wheel drop amount (■ in the figure), the current flowing through the wheel axis (♦ in the figure), and the ELID current (● in the figure). Yes.

  As shown in FIG. 2, the ELID current is always constant during processing. That is, the ELID current generator 50 applies voltages to the grindstone 30 and the electrode 70 so that a constant current flows between the grindstone 30 and the electrode 70.

  Then, the grindstone 30 located above the wafer 60 is brought close to the wafer 60. As a result, the grindstone 30 contacts the wafer 60, and the wafer 60 is ground by the grindstone 30. If the abrasive grains on the grinding surface 31 of the grindstone 30 are worn by this grinding and the wafer 60 cannot be ground, the position of the grindstone 30 cannot be moved to the wafer 60 side, so that the load on which the grindstone 30 is pressed against the wafer 60 is large. Become. For this reason, the electric current which flows into a grindstone axis increases rapidly.

  In this case, for example, the position of the grindstone 30 is fixed for a certain time at a place where the amount of grindstone drop is 30 μm. For example, when it is determined that the value of the current flowing through the grindstone shaft exceeds a certain threshold value, or when it is determined that the differential value of the value of the current flowing through the grindstone shaft exceeds a certain value, the descent of the grindstone 30 is stopped. To fix the position.

  By fixing the position of the grindstone 30 in this way, grinding of the wafer 60 is temporarily stopped. Then, while the position of the grindstone 30 is fixed, the ELID current generator 50 causes a constant ELID current to flow between the grindstone 30 and the electrode 70 as described above, whereby the grindstone 30 is ground by the ELID method. Electrolytic dressing of surface 31 is performed.

  Thus, the grinding of the wafer 60 with the grindstone 30 becomes possible again. Therefore, by grinding the wafer 60 in a state where the position of the grindstone 30 is fixed, the load on which the grindstone 30 is pressed against the wafer 60 is reduced. Thereby, the electric current which flows into a grindstone axis also decreases.

  Thereafter, when the grindstone 30 is further moved to the wafer 60 side and the wafer 60 is ground, the load applied to the grindstone 30 increases again due to wear of the abrasive grains as described above. Therefore, for example, the grindstone 30 is fixed at a position where the grindstone descending amount of the grindstone 30 is 35 μm, and the grindstone 30 is electrolytically dressed at this position.

  Similarly, after the current flowing through the grindstone shaft decreases and the load on the grindstone 30 decreases, the grindstone 30 is moved to the wafer 60 side to grind the wafer 60. For example, the grindstone descending amount of the grindstone 30 is 40 μm. Electrolytic dressing of the grindstone 30 is performed at the position. Thus, the grinding of the wafer 60 is completed.

  Thus, in this embodiment, when a load is applied to the grindstone 30, electrolytic dressing of the grindstone 30 is performed by fixing the position of the grindstone 30 for a certain period of time. Then, the grinding of the wafer 60 and the electrolytic dressing of the grindstone 30 are repeated a plurality of times to grind the one surface 61 of the wafer 60. That is, grinding is performed in multiple stages. Since the thickness of the wafer 60 is determined by the feed amount of the grindstone 30, the grinding amount by the grindstone 30, and the like, a gauge for detecting the thickness is not necessary.

  A process of grinding the wafer 60 using a rotary grinding apparatus based on the above ELID characteristics will be described with reference to FIGS. FIG. 3 is a diagram showing a positional relationship between the wafer 60 and the grindstone 30 in grinding. FIG. 4 is a diagram showing the relationship between the machining time and the position of the grindstone 30 and the relationship between the machining time and the current value corresponding to the machining load.

  For example, a silicon carbide semiconductor wafer composed of a silicon carbide single crystal is ground as the wafer 60 to be a workpiece. That is, when grinding the wafer 60 obtained in the wafer manufacturing process, the wafer 60 is ground using the rotary grinding apparatus shown in FIG.

  First, voltages are applied to the grindstone 30 and the electrode 70 by the ELID current generator 50, respectively. In addition, a porous chuck 20 is disposed on the suction table 10, and a wafer 60 is disposed on the porous chuck 20.

  In the step shown in FIG. 3A, the grindstone 30 is lowered and positioned at a position of 10 μm or more from the one surface 61 of the wafer 60. Accordingly, the grindstone 30 is maintained at a constant height for the time T1 shown in FIG. Further, the current flowing through the grindstone shaft (main shaft current value) is an idling value. The main shaft current value is measured by the apparatus side shaft current measuring unit 40.

  Subsequently, in the step shown in FIG. 3B, grinding is started. This step is performed during the time T2 shown in FIG. According to this, the grindstone 30 is moved to the wafer 60 side at a constant speed. Then, a grinding liquid (not shown) is passed through the one surface 61 of the wafer 60 and the one surface 61 of the wafer 60 and the grindstone 30 are brought into contact with each other to grind the one surface 61 of the wafer 60. 3A and 3B corresponds to the first step of the present invention.

  Thus, when the wafer 60 is ground, the abrasive grains protruding on the grinding surface 31 of the grindstone 30 are worn. For this reason, even if the grindstone 30 is pressed against the wafer 60, grinding cannot be performed, so that the grindstone 30 is pressed against the wafer 60. Therefore, as shown in the lower diagram of FIG. 4, the spindle current value gradually increases in order to keep the rotational speed of the grindstone 30 constant. When the spindle current value exceeds an upper limit current value that is a preset threshold value, the descent of the grindstone 30 is stopped because the processing load on the grindstone 30 has increased. This upper limit current value is a current value indicating that the wafer 60 cannot be ground with the grindstone 30. When the maximum current value is 9 A, for example, the upper limit current value is 7 A, which is smaller than this value.

  Thereby, grinding is stopped for T3 time. In this case, in this embodiment, the grindstone 30 is fixed away from the wafer 60 by a certain distance. Then, as described above, electrolytic dressing by the ELID method using the ELID current generator 50 is performed. Thereby, since the load concerning the grindstone 30 falls, a spindle current value falls. At this time, the wafer 60 is ground using the processing load applied to the wafer 60 while electrolytically dressing the grinding surface 31 of the grindstone 30 by the ELID method. In addition, the process between T3 time is corresponded to the 2nd process of this invention.

  When the spindle current value decreases during the time T3 and the spindle current value becomes smaller than the lower limit current value, which is a preset threshold value, the processing load of the grindstone 30 is stabilized and the electrolytic dressing of the grinding surface 31 of the grindstone 30 is completed. . This lower limit current value is a current value indicating that the electrolytic dressing of the grindstone 30 has been completed. The lower limit current value is 4A, for example. In this way, the grinding surface 31 of the grindstone 30 is regenerated.

  The time T3 shown in FIG. 4 is a time during which grinding is stopped, but during this time T3, the delay after the movement of the grindstone 30, the spindle current drop waiting time, and the spindle current value falls below the lower limit current value. The time for the timer is included. Further, the process in which the main shaft current value becomes smaller than the lower limit current value, which is a threshold value, and the subsequent process proceeds to the process shown in FIG. 3C corresponds to the third process of the present invention.

  Thereafter, in the step shown in FIG. 3C, the wafer 60 is ground again. That is, similarly to the process shown in FIG. 3B, the grindstone 30 is lowered toward the wafer 60 at a constant speed for the time T4 shown in FIG.

  Thus, the grinding of the wafer 60 and the electrolytic dressing of the grindstone 30 are performed, the grindstone 30 is brought close to the wafer 60, and the grinding of the wafer 60 and the electrolytic dressing of the grindstone 30 are performed again. Therefore, by grinding the wafer 60 and electrolytic dressing of the grindstone 30 a plurality of times, the wafer 60 is ground by a target grinding amount. That is, it corresponds to repeating the first to third steps of the present invention.

  Here, since the thickness of the wafer 60 is obtained from the correlation between the descending amount of the grindstone 30 and the grinding amount of the wafer 60, the wafer 60 is ground while measuring the thickness of the wafer 60 by preparing a sizing gauge. There is no need to do it.

  When grinding is performed until the wafer 60 has a desired thickness, in the step illustrated in FIG. 3D, grinding by the grindstone 30 is finished and the grindstone 30 is moved away from the wafer 60. Thus, the grinding of the one surface 61 of the wafer 60 is completed.

  As described above, in this embodiment, the wafer 60 is ground, and when the grindstone 30 applies a large load to the wafer 60, the position of the grindstone 30 is fixed and the electrolytic dressing of the grindstone 30 is performed. It is characterized by grinding the wafer 60 by repeating grinding and electrolytic dressing a plurality of times.

  In this case, the wafer 60 is shaved to a desired thickness by the feed amount and the shaving amount of the grindstone 30. As described above, it is possible to avoid that the accurate thickness of the wafer 60 cannot be measured due to the current flowing through the sizing device by using the sizing gauge. When grinding of the wafer 60 becomes difficult, electrolytic grinding of the grinding wheel 30 is performed, so that clogging on the grinding surface 31 of the grinding wheel 30 can be eliminated and good grinding can be performed. Thereby, the wafer 60 can be ground with high accuracy.

  By not using the sizing gauge, the one surface 61 of the wafer 60 can be prevented from being damaged by the sizing gauge. Therefore, the wafer 60 can be ground with high quality.

(Other embodiments)
In the above embodiment, one wafer 60 is ground. However, a plurality of wafers 60 can be ground simultaneously by disposing a plurality of wafers 60 on the porous chuck 20.

  Although the silicon carbide semiconductor wafer has been described as an example of the wafer 60 in the above-described embodiment, the method of the present invention can be employed when grinding the wafer 60 formed of, for example, sapphire or diamond. When grinding such a hard thing, since the grindstone 30 is easy to wear, said ELID grinding method is effective.

  In each of the above embodiments, a straight cup type was used as the grindstone 30, but other types may also be used.

  In the ELID grinding method shown in the above embodiment, for example, as shown in FIGS. 2 and 4, when a load is applied to the grindstone 30, the feeding of the grindstone 30 is stopped and the grindstone 30 is separated from the wafer 60 by a certain distance. The grinding stone surface 31 was subjected to electrolytic dressing while the grinding wheel 30 was in a low load state. That is, grinding and electrolytic dressing were performed simultaneously. However, the grinding of the wafer 60 may be advanced by stopping the grindstone 30 at a position in the idling state completely separated from the wafer 60 and performing only the electrolytic dressing. That is, grinding and electrolytic dressing can be performed simultaneously, or grinding and electrolytic dressing can be performed separately.

It is a schematic block diagram of the rotary grinding apparatus used for the manufacturing method which concerns on one Embodiment of this invention. It is the figure which showed the characteristic of ELID grinding process. It is the figure which showed the positional relationship of the wafer and grindstone in grinding. It is the figure which showed the relationship between processing time and the position of a grindstone, and the relationship between processing time and the electric current value corresponding to processing load. It is the figure which showed the mode of the thickness control process using a sizing apparatus in the conventional rotary grinding apparatus which performs ELID grinding.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 30 ... Grinding wheel, 31 ... Grinding surface of grinding wheel, 40 ... Apparatus side axial current measuring part, 60 ... Wafer, 61 ... One surface of wafer.

Claims (5)

The grindstone (30) is rotationally driven by a motor or a spindle so that the grindstone surface is pressed against one surface (61) of the plate-like wafer (60), and the one surface of the wafer (60) is subjected to electrolytic dressing using ELID grinding ( 61) a wafer manufacturing method including a grinding step of rotary grinding,
The grinding step includes
Preparing the wafer (60);
The grindstone (30) disposed above the wafer (60) is moved to the wafer (60) side, and is disposed opposite to the grindstone (30) and the grindstone (30) by the ELID current generator (50). A constant dressing current is passed between the electrode (70) and the surface (31) of the grindstone (30) is pressed against one surface (61) of the wafer (60) to grind the one surface (61). Process,
During the first step, the spindle current of the grinding wheel (30) corresponding to the processing load applied by the grinding wheel (30) to the wafer (60) is measured by the apparatus-side axial current measuring unit (40). When the spindle current measured by the apparatus-side axial current measuring unit (40) exceeds the upper limit current value indicating that the wafer (60) cannot be ground by the grinding wheel (30), the grinding wheel (30) The movement is stopped and the position of the grindstone (30) is fixed, and the grinding surface (31) of the grindstone (30) is electrolytically dressed by ELID method, and the processing load applied to the wafer (60) is used. A second step of grinding the wafer (60);
In the second step, the spindle current that has exceeded the upper limit current value is smaller than the upper limit current value and is lower than the lower limit current value indicating that the electrolytic dressing of the grindstone (30) has been completed. A third step of returning to the first step again,
The method for manufacturing a wafer, wherein one surface (61) of the wafer (60) is ground by repeating the first step to the third step a plurality of times. In the second step, the position of the grindstone (30) after the spindle current exceeds the upper limit current value is fixed such that the surface of the grindstone (30) is in contact with one surface (61) of the wafer (60). The wafer manufacturing according to claim 1, characterized in that the grinding surface (31) is electrolytically dressed by fixing the grinding wheel (30) within a range at a position separated from the wafer (60) by a certain distance. Method. In the second step, the position of the grindstone (30) after the spindle current exceeds the upper limit current value is fixed when the surface of the grindstone (30) is separated from one surface (61) of the wafer (60). The method for manufacturing a wafer according to claim 1, wherein the grinding stone (30) is fixed to the wafer (60) at a position separated by a certain distance and the ground surface (31) is electrolytically dressed. The method for manufacturing a wafer according to any one of claims 1 to 3, wherein in the step of preparing the wafer (60), a plurality of the wafers (60) are prepared. 5. The method of manufacturing a wafer according to claim 1, wherein in the step of preparing the wafer (60), a wafer formed of silicon carbide is prepared as the wafer (60).

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