JP5233241B2 - Method for manufacturing silicon carbide wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon carbide wafer capable of improving the accuracy of the thickness of a silicon carbide wafer (hereinafter referred to as a SiC wafer).

  Conventionally, methods for polishing an SiC wafer have been proposed in, for example, Patent Documents 1 to 3. FIG. 6 is a diagram showing a conventional polishing method. As shown in this figure, a polishing cloth 51 is affixed to the polishing surface plate 50, and a wafer holding table 52 is disposed above the polishing cloth 51. Further, the SiC wafer 53 obtained by slicing and cutting from the SiC ingot in the wafer manufacturing process is pressed against the polishing cloth 51 while being held on the wafer holding table 52 after grinding or lapping, and the polishing cloth 51 And the wafer holding table 52.

In such a state, CMP processing is performed. That is, a liquid injector 54 is disposed on the polishing pad 51, and the chemical solution 55 is dropped from the liquid injector 54 onto the polishing pad 51. Then, the surface to be polished of the SiC wafer 53 is pressed against the polishing cloth 51 by the wafer holding table 52, and the wafer holding table 52 and the polishing surface plate 50 are rotated while dropping the chemical solution 55 on the polishing cloth 51. Thereby, the SiC wafer 53 is polished.
JP 2006-121111 A Japanese Patent Laid-Open No. 8-66850 JP-A-9-248758

  However, in the above conventional technique, the SiC wafer 53 is extremely hard and is chemically stable and difficult to polish, and it is difficult to maintain the accuracy of the thickness of the SiC wafer 53. This will be described with reference to FIGS. 7 and 8. FIG.

  As shown in FIG. 7A, the surface 53a of the SiC wafer 53 polished by the CMP process shown in FIG. 6 is inclined at a certain angle with respect to the back surface 53b opposite to the surface 53a. There is a case. On the other hand, as shown in FIG. 7B, the sagging of the surface 53a of the SiC wafer 53, that is, the outer peripheral portion of the surface 53a of the SiC wafer 53 is rapidly polished, and the vicinity of the center axis is near the back surface 53b. It may become a convex shape.

  Further, as shown in FIG. 8A, when the epitaxial growth film 56 is formed on the surface 53a of the SiC wafer 53, for example, the thickness of the epitaxial growth film 56 may vary. On the other hand, as shown in FIG. 8B, the epitaxial growth film 56 formed on the front surface 53 a of the SiC wafer 53 may be formed around the back surface 53 b of the SiC wafer 53.

  As shown in FIG. 7 and FIG. 8 described above, the accuracy of polishing of the SiC wafer 53 affects the difference between the maximum thickness and the minimum thickness of the SiC wafer 53. As described above, when the variation of the thickness of the SiC wafer 53 becomes large, it affects the yield of the subsequent device process and the like.

  In view of the above points, an object of the present invention is to improve the accuracy of the thickness of a SiC wafer by reducing the difference between the maximum thickness and the minimum thickness of the SiC wafer.

In order to achieve the above object, the present invention provides a step of preparing a plate-like workpiece (40) in which an ingot formed of silicon carbide is sliced, a surface of the workpiece (40) as a surface (41), and a workpiece ( 40) When the other surface is the back surface (42), the surface (41) of the work (40) is ground and polished, so that the surface (41) of the work (40) is smooth to the atomic level and has no damage. And smoothing the surface (41) of the workpiece (40), and then applying the protective tape (23) to the smoothed surface (41), and further attaching the outer edge of the protective tape (23) to the resin sheet ( 24) The surface of the work (40) is fixed without pressing the step of forming an oxide film on the front surface (41) and the back surface (42) of the work (40) by pressing the work (40). (41) As a quasi, characterized in that it contains the step of grinding the back surface (42) of the workpiece (40).

  According to this, since the surface (41) of the workpiece (40) is first ground and polished to smooth the workpiece (40), even if the thickness variation of the workpiece (40) is deteriorated by polishing, the workpiece (40) ) To smooth the back surface (42) with reference to the surface (41) of the work (40) after smoothing the surface (41), the difference between the maximum thickness and the minimum thickness of the work (40) ( A work (40) having a small total thickness variation can be obtained. As described above, the accuracy of the thickness of the silicon carbide wafer can be improved.

  In the step of grinding the back surface (42) of the workpiece (40), the back surface (42) may be polished after the back surface (42) is ground.

  Thereby, since the back surface (42) of a workpiece | work (40) can be mirror-finished, a silicon carbide wafer without a curvature can be obtained.

  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. Below, the method to manufacture a silicon carbide wafer is demonstrated. 3 and 4 are views showing a wafer manufacturing process and showing a cross section of the workpiece 40. FIG. FIG. 1 is a schematic view of a grinding apparatus 1 used in the wafer manufacturing process according to the first embodiment of the present invention. FIG. 2A shows a perspective view of the fixed base 20, and FIG. 2B is an exploded perspective view of the fixed base 20.

  A method for manufacturing a silicon carbide wafer will be described with reference to the drawings. First, the manufacturing process of a SiC ingot is performed. Specifically, an SiC seed crystal is placed at the top of the crucible in a graphite crucible, and the SiC powder raw material placed at the bottom of the crucible is heated to 2300 ° C., for example. Thereby, the SiC powder raw material is sublimated, and the sublimated gas is crystallized on a seed crystal set to a temperature lower than the raw material temperature. Thus, an SiC ingot is formed on the seed crystal.

  Next, a wafer manufacturing process is performed. First, in the step shown in FIG. 3A, a work 40 is prepared. That is, the workpiece 40 is prepared by processing the SiC ingot manufactured as described above into a cylindrical shape having a constant diameter, and slicing and cutting with a wire saw at a constant interval. Thereby, the workpiece 40 having a constant thickness is formed. As described above, the workpiece 40 is formed by slicing a SiC ingot, and has a plate shape having one surface and the other surface. Hereinafter, one surface of the workpiece 40 is referred to as a front surface, and the other surface of the workpiece 40 is referred to as a back surface. Both surfaces of the workpiece 40 obtained by slicing the SiC ingot are rough and the surfaces are wavy.

  In this embodiment, the diameter of the workpiece 40 is φ2 inches. Further, as described above, both surfaces 41 and 42 of the workpiece 40 obtained by this wafer manufacturing process are rough and wavy.

  Subsequently, in the step shown in FIG. 3B, the undulation of the slice generated on both surfaces 41 and 42 of the workpiece 40 is removed by rough grinding or lapping. In order to remove this undulation, in this step, both surfaces of the workpiece 40 are roughly ground. This is a method of processing using a grindstone provided with diamond abrasive grains, for example, # 300 or more. Thereby, the wave | undulation of the surface 41 and the back surface 42 of the workpiece | work 40 is made small. In addition, the arrow shown by FIG.3 (b) means processing the surface 41 and the back surface 42 of the workpiece | work 40 in this process.

  Then, in the step shown in FIG. 3C, both surfaces 41 and 42 or the surface 41 of the workpiece 40 are finished. In this step, the surface 41 of the workpiece 40 is ground using, for example, a # 4000 or more grindstone provided with fine diamond abrasive grains. In this case, the surface 41 of the workpiece 40 is finished with the small abrasive grains from the large abrasive grains.

  Next, in the step shown in FIG. 3D, the surface 41 of the workpiece 40 is mirror-finished. Even if the finishing shown in FIG. 3C is performed, a work-affected layer and a work strain remain on the surface 41 of the workpiece 40. For this reason, the CMP (Chemical Mechanical Polishing) process completely removes the work-affected layer and the processing strain on the surface 41 of the workpiece 40, and polishes the surface 41 to a mirror surface that is smooth at the atomic level and has no damage. . Thereby, the surface 41 of the workpiece 40 becomes a mirror surface and is finished to a surface on which a semiconductor device can be formed.

  As described above, grinding or lapping to remove the undulation generated by slicing the workpiece 40 is performed on both surfaces 41 and 42, and polishing to reduce the surface roughness is performed on the surface 41. Not. For this reason, as shown in FIG. 3E and FIG. 4A, the back surface 42 of the workpiece 40 is not parallel to the front surface 41, and the difference between the maximum thickness and the minimum thickness of the workpiece 40. (TTV) is increasing. In other words, although the surface 41 of the workpiece 40 can be formed smooth at the atomic level and has no damage by this step, it is the final processing even if high precision processing with good flatness is performed by grinding or lapping processing. Since the thickness variation of the workpiece 40 is deteriorated by CMP processing, the accuracy of the thickness of the workpiece 40 is deteriorated.

  Therefore, in the step shown in FIG. 3E, the back surface 42 is flattened with the front surface 41 of the flattened workpiece 40 as a reference. The flattening of the back surface 42 of the workpiece 40 will be described with reference to FIGS. 1, 2, and 4.

  Note that the workpiece 40 shown in FIG. 3 (e) has a roughened back surface 42, and the back surface 42 of the workpiece 40 shown in FIGS. 4 (a) and 4 (b) is the front surface. Although the thing inclined with respect to 41 is drawn, all show only that the precision of the thickness of the workpiece | work 40 is bad as a figure, and it is the same workpiece | work 40, respectively.

  First, the workpiece 40 is set on the fixed base 20 shown in FIG. That is, after placing the table 22 on the pedestal 21 and pasting the protective tape 23 on the table 22, the surface 41 of the workpiece 40 faces the protective tape 23 as shown in FIG. The work 40 is affixed to the protective tape 23. Thereby, it protects so that the surface 41 of the workpiece | work 40 may not be damaged.

  In addition to using a back grind tape as the protective tape 23, the surface 41 of the workpiece 40 is not damaged by forming an oxide film or a resist on the surface 41 of the workpiece 40 or by applying wax to the surface 41. Can also be protected. The variation in the thickness of the back grind tape, oxide film, resist, and wax is desirably 1 μm or less in terms of the difference between the maximum thickness and the minimum thickness.

  Then, as shown in FIG. 2A, a resin sheet 24 is placed on the table 22. Thereby, as shown in FIG. 2D, the outer edge portion of the protective tape 23 is sandwiched between the resin sheet 24 and the table 22, and the back surface 42 of the workpiece 40 protrudes from the through hole 24 a of the resin sheet 24. Become. The fixed base 20, pedestal 21, table 22, protective tape 23, and resin sheet 24 will be described in detail later.

  Here, the grinding apparatus 1 in which the fixed base 20 shown in FIG. 2 is installed will be described. As shown in FIG. 1, the grinding apparatus 1 is a reciprocating type grinding machine that includes a straight grindstone 10, a fixed base 20, and an electromagnetic chuck 30.

  The straight grindstone 10 has a cylindrical shape, and diamond abrasive grains are sintered on a side surface of the straight grindstone 10 with a binder, and the side surface serves as a surface for grinding a workpiece 40 that is a workpiece. The straight grindstone 10 can be rotated around the central axis of the straight grindstone 10 by a rotation mechanism (not shown).

  The fixing base 20 fixes the workpiece 40. A specific configuration of the fixed base 20 will be described with reference to FIG. As shown in FIG. 2, the fixed base 20 includes a pedestal 21, a table 22, a protective tape 23, and a resin sheet 24.

  The pedestal 21 is formed in a cylindrical shape. One of the two end faces of the pedestal 21 faces the electromagnetic chuck 30 shown in FIG. 1, and the table 22 is disposed on the other face. The pedestal 21 is provided with a hole (not shown) that connects an end surface on which the table 22 is arranged and a side surface. The hole provided in the side surface of the base 21 is connected to a vacuum pump (not shown).

  The pedestal 21 is attracted to the electromagnetic chuck 30 by the electromagnetic force generated by the electromagnetic chuck 30. For this reason, a metal and a magnetic material are employ | adopted as a material of the base 21. FIG. Note that the pedestal 21 is not limited to a cylindrical shape, and may be other pillar shapes or electromagnetic chuck shapes.

  The table 22 is formed in a disc shape, and is provided with a plurality of holes 22a penetrating both end faces. The table 22 is placed on the pedestal 21, and when the pedestal 21 is evacuated by a vacuum pump, the table 22 is attracted to the end face of the pedestal 21, and air is supplied to the pedestal 21 through the holes 22 a of the table 22. It comes to be sucked.

  The protective tape 23 is an adhesive tape that fixes the work 40 on the table 22. As such a protective tape 23, for example, a back grind tape is employed.

  The resin sheet 24 is thinner than the workpiece 40 and has a disk shape disposed on the table 22. The resin sheet 24 is provided with a through hole 24 a into which the workpiece 40 is inserted at a location facing the workpiece 40. The through hole 24 a is smaller than the protective tape 23 and larger than the workpiece 40.

  When evacuation is performed from a vacuum pump (not shown) in such a fixed base 20, air is sucked into the pedestal 21 through the holes 22 a of the table 22 in the adsorption region of the table 22 shown in FIG. For this reason, the protective tape 23 and the resin sheet 24 are sucked and fixed to the table 22.

  FIG. 2D is an enlarged cross-sectional view of part A in FIG. As shown in this figure, when air is drawn into the pedestal 21 and air is drawn into the pedestal 21 from the holes 22 a of the table 22, the protective tape 23 and the resin sheet 24 are adsorbed to the table 22. In this case, the outer edge portion of the protective tape 23 is pressed by the resin sheet 24, so that the protective tape 23 and the resin sheet 24 are in close contact with each other without any gap, and the protective tape 23 is firmly adsorbed to the table 22.

  And the end surface of the workpiece 40 protrudes from the surface of the resin sheet 24. As will be described later, the protective tape 23 is affixed to the front surface 41 of the work 40, and the back surface 42 of the work 40 protrudes from the resin sheet 24. That is, the back surface 42 of the workpiece 40 is ground and polished. The fixing table 20 is disposed and fixed on the electromagnetic chuck 30 when the workpiece 40 is ground and polished.

  The electromagnetic chuck 30 shown in FIG. 1 is an electromagnet including a coil that generates a magnetic force when a direct current flows. That is, the electromagnetic chuck 30 is configured to adsorb and fix the fixing base 20 with a magnetic force. The electromagnetic chuck 30 is provided with a moving mechanism (not shown) that is movable in the horizontal direction, and moves the position of the fixed base 20 in accordance with grinding by the straight grindstone 10. The above is the overall configuration of the grinding apparatus 1.

  Then, as shown in FIG. 1, the fixing base 20 is disposed on the electromagnetic chuck 30. Subsequently, the straight grindstone 10 is rotated, and the side surface of the rotating straight grindstone 10 is ground against the back surface 42 of the workpiece 40 to grind the back surface 42 of the workpiece 40 with reference to the surface of the electromagnetic chuck 30. If the grinding machine can grind with high precision parallel to the surface of the electromagnetic chuck 30, the flatness of the workpiece adsorbed on the electromagnetic chuck 30 and the difference between the maximum thickness and the minimum thickness (TTV) are 1 μm or less. Can be ground. Therefore, since the surface 41 of the workpiece 40 and the surface of the electromagnetic chuck 30 are parallel to each other by the above-described method of holding the workpiece 40, the surface 42 of the workpiece 40 can be flattened based on the surface 41 of the workpiece 40. In this case, the entire back surface 42 of the workpiece 40 is directly ground by fixing the position of the straight grindstone 10 and moving the electromagnetic chuck 30 by a moving mechanism (not shown). In this grinding process, the warp of the workpiece 40 can also be controlled by changing the grindstone count of the straight grindstone 10.

  As a result, as shown in FIG. 4C, the difference (TTV) between the maximum thickness and the minimum thickness of the workpiece 40 is reduced, and a SiC wafer having a constant thickness is formed. According to this method, the difference (TTV) between the maximum thickness and the minimum thickness of the workpiece 40 can be set to 1 μm or less. In this way, a SiC wafer having a highly accurate thickness with reduced thickness variation is completed.

  As described above, in the present embodiment, the surface 41 of the work 40 obtained by slicing and cutting the ingot is smoothed by grinding and polishing, and then the back surface 42 of the work 40 is used with the surface 41 of the work 40 as a reference. It is characterized by obtaining a SiC wafer with high precision thickness by grinding and polishing.

  According to this, since the back surface 42 is flattened on the basis of the front surface 41 in a state where the front surface 41 of the work 40 has been smoothed first, the thickness accuracy of the work 40 is smoothed by smoothing the front surface 41 of the work 40. However, the accuracy of flattening the back surface 42 with respect to the front surface 41 of the workpiece 40, that is, the difference (TTV) between the maximum thickness and the minimum thickness of the SiC wafer can be reduced. Therefore, the accuracy of the thickness of the SiC wafer can be improved.

  By forming the device on the surface side of the SiC wafer by forming the device on the SiC wafer in which the difference between the maximum thickness and the minimum thickness (TTV) is reduced, the thickness of the SiC wafer is caused The yield of device formation on the SiC wafer can be improved.

(Second Embodiment)
In the present embodiment, only different parts from the first embodiment will be described. In FIG. 2, the fixed base 20 has a form in which one work 40 is installed. However, the present embodiment is characterized in that a plurality of works 40 can be installed.

  FIG. 5 is a view showing a fixing base according to the present embodiment. As shown in FIG. 5A, four protective tapes 23 are placed on the table 22, and the workpiece 40 is disposed on each protective tape 23. The resin sheet 24 is provided with four through holes 24a.

  Then, by evacuating with a vacuum pump (not shown), as shown in FIG. 5B, the resin sheet 24 is adsorbed to the adsorbing area where air is sucked from each hole 22a of the table 22. As a result, the four workpieces 40 are fixed to the fixed base 20, and the back surface 42 of the workpiece 40 is ground and polished by the polishing apparatus 1 shown in FIG.

  As described above, a plurality of workpieces 40 can be installed on the fixed base 20, and the problem of mass production can be avoided. Thus, in the case where a plurality of workpieces 40 are fixed to the fixed base 20, the size of the fixed base 20 also increases, so that the adsorption area of the resin sheet 24 with respect to the table 22 also increases, and the effect of improving the attractive force can be obtained. Can do.

(Other embodiments)
In each of the above embodiments, the back surface 42 of the workpiece 40 is ground to improve the flatness. However, if warpage of the SiC wafer or the like becomes a problem, the back surface 42 is polished after the back surface 42 of the workpiece 40 is ground. You may do it.

  In each of the above embodiments, the SiC wafer manufacturing method has been described as an example. However, the method of the present invention can also be employed when manufacturing a material whose flatness deteriorates due to polishing, for example, a wafer such as sapphire or diamond. it can.

It is the schematic of the grinding device used for the wafer manufacturing process which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the fixed base shown by FIG. It is the figure which showed the wafer manufacturing process. It is the figure which showed the process shown in FIG.3 (e). It is the figure which showed the fixed base which concerns on 2nd Embodiment. It is the figure which showed the method of the conventional grinding | polishing process. It is sectional drawing of the SiC wafer which showed the inclination of the grinding | polishing surface which arises in a SiC wafer by grinding process. It is sectional drawing of what formed the epitaxial growth film, for example in the SiC wafer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Fixed base, 21 ... Base, 22 ... Table, 22a ... Hole, 23 ... Protection tape, 24 ... Resin sheet, 24a ... Through-hole, 40 ... Workpiece, 41 ... Surface of workpiece, 42 ... Back surface of workpiece.

Claims (2)

Preparing a plate-like workpiece (40) in which an ingot formed of silicon carbide is sliced;
When one surface of the workpiece (40) is the front surface (41) and the other surface of the workpiece (40) is the back surface (42), the surface (41) of the workpiece (40) is ground and polished, Smoothing the surface (41) of the workpiece (40) to a mirror surface;
After smoothing the surface (41) of the workpiece (40) , a protective tape (23) is applied to the smoothed surface (41), and the outer edge of the protective tape (23) is attached to the resin sheet (24). The surface of the workpiece (40) can be fixed without fixing the workpiece (40) by performing an oxide film formation on the front surface (41) and the back surface (42) of the workpiece (40). And a step of grinding the back surface (42) of the work (40) with reference to (41) to improve the flatness. 2. The silicon carbide wafer according to claim 1, wherein in the step of grinding the back surface (42) of the workpiece (40), the back surface (42) is polished after the back surface (42) is ground. Method.

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