JP2007235092A - Method for grinding silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for grinding a silicon carbide single crystal capable of efficiently and easily cutting silicon carbide without damaging such as cracking. <P>SOLUTION: The method for grinding a silicon carbide single crystal includes a process that allows an opening of a hollow cylindrical grindstone 30 to contact a growth surface opposed to a seed crystal side of the silicon carbide single crystal 10 formed by sublimation process and a process that cuts the silicon carbide single crystal 10 by rotating the hollow cylindrical grindstone 30 and lowering the hollow cylindrical grindstone in the seed crystal direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for grinding a silicon carbide single crystal, and more particularly to a method for grinding a silicon carbide single crystal that does not generate cracks or chips during processing.

  Silicon carbide is attracting attention as a small and high-power electronic device material such as a semiconductor because it has a larger band gap and is superior in dielectric breakdown characteristics, heat resistance, radiation resistance, and the like. In addition, silicon carbide has been attracting attention as an optical device material because it has excellent bonding properties with other compound semiconductors having excellent optical characteristics.

  As one aspect of a method for producing a silicon carbide single crystal wafer, a raw material powder for sublimation is enclosed in a crucible, and a sublimation gas is supplied onto a seed crystal disposed on the opposite side, while a silicon carbide single crystal is formed on the seed crystal. There is a method of recrystallizing (sublimation method) and cutting a wafer from the obtained silicon carbide single crystal. As a method for cutting out such a wafer, there has been proposed a method of cutting a single crystal by rotating a disk-shaped grindstone and pressing the outer peripheral surface of the grindstone against a side surface of the single crystal as a grinding surface (see Patent Document 1).

However, crystal defects such as screw dislocations are liable to occur at the peripheral portion of the single crystal growth surface, particularly the outer peripheral portion of the contact surface with the crucible, and cracks are liable to occur when cylindrical grinding is performed. As a result, a sufficient processing method has not been proposed yet regarding the processing method, such as cracks reaching the surface of the single crystal and making it unusable.
JP 2001-261491 A

  There has been a demand for a grinding method of a silicon carbide single crystal that can efficiently cut out a silicon carbide single crystal without causing breakage such as cracks.

That is, the present invention relates to the following items:
(1) contacting the opening of the hollow cylindrical grindstone with the growth surface facing the seed crystal side of the silicon carbide single crystal formed by the sublimation method;
Rotating the hollow cylindrical grindstone and lowering the hollow cylindrical grindstone in the seed crystal direction to grind the silicon carbide single crystal;
A method for grinding a silicon carbide single crystal, comprising:

(2) The method for grinding a silicon carbide single crystal according to (1), wherein, in the grinding step, the shape of the opening of the hollow cylindrical grindstone is elliptical.

(3) The silicon carbide according to (2), wherein, in the grinding step, the shape of the opening of the hollow cylindrical grindstone is an elliptical shape having a difference between a major axis and a minor axis in a range of 0.01 mm to 2.0 mm. Single crystal grinding method.

(4) In the grinding step, the hollow cylindrical grindstone is lowered in the seed crystal direction in a state where the central axis in the growth direction of the silicon carbide single crystal coincides with the central axis of the hollow cylindrical grindstone. (1) The method for grinding a silicon carbide single crystal according to (1).

(5) The method for grinding a silicon carbide single crystal according to (4), wherein, in the grinding step, the silicon carbide single crystal and the hollow cylindrical grindstone are relatively moved and oscillated.

(6) The carbonization according to (5), wherein a rocking width defined by a deviation between a central axis in the growth direction of the silicon carbide single crystal and a central axis of the hollow cylindrical grindstone is 0.1 to 1.0 mm. A method for grinding a silicon single crystal.

(7) The method for grinding a silicon carbide single crystal according to any one of (4) to (6), wherein the rotational speed of the cylindrical grindstone is 300 to 3000 rpm.

(8) The grinding method of the silicon carbide single crystal according to any one of (4) to (7), wherein a feeding speed of the cylindrical grindstone is 0.1 to 1.0 mm / min.

(9) The method for grinding a silicon carbide single crystal according to any one of (4) to (8), wherein the cylindrical grindstone includes notches at a constant interval at a grindstone tip.

(10) The hollow cylindrical grindstone includes an ejection port for supplying a lubricant on a central axis, and grinds the silicon carbide single crystal while supplying the lubricant from the ejection port. (9) The grinding method of the silicon carbide single crystal according to any one of (9).

(11) The silicon carbide according to any one of (4) to (10), further including a step of grinding the vicinity of the growth surface and the vicinity of the seed crystal bonding surface of the cylindrical silicon carbide single crystal cut out in the grinding step. Single crystal grinding method.

  According to the present invention, a silicon carbide single crystal can be easily cut out efficiently and without breakage such as cracks.

  Hereinafter, the present invention will be described with reference to embodiments, but it goes without saying that the present invention is not limited to the following embodiments. In the figure, components having the same functional application are denoted by the same reference numerals and description thereof is omitted.

(Grinding wheel)
The grinding apparatus for mounting the grinding wheel used in the silicon carbide single crystal grinding method according to the embodiment of the present invention is not particularly limited as long as it has a rotation function and a vertical movement function. Specifically, as shown in FIGS. 4A, 4 </ b> B, or 4 </ b> C, the grinding stone 30 rotates about the central axis Z in the longitudinal direction and moves up and down along the central axis Z. (Z axis direction). The illustration of the drive unit is omitted in the figure. It is preferable that the internal diameter of the hollow cylindrical portion 32 has a sufficient internal diameter to surround the single crystal region 12. The grinding wheel 30 is preferably provided with notches at regular intervals in the opening of the hollow cylindrical portion 32. This is because the machining waste is easily cut out and the grinding resistance is reduced. Further, as shown in the partial cross-sectional view of FIG. 4A, the grinding wheel 30 includes an ejection port (center through) 31 for supplying a lubricant such as water onto the central axis Z of the grinding wheel main body 33. preferable. This is because the grinding resistance can be reduced by preventing the temperature rise at the machining point and discharging the machining waste by the water stream 34.

  The grinding wheel 30 shown in FIG. 4 (b) has a circular opening, whereas the grinding wheel 30 shown in FIG. 4 (c) has an elliptical opening. By making the grinding wheel 30 elliptical, the efficiency with which the machining waste is discharged from the notch is made higher than when it is circular. That is, since the opening of the grinding wheel 30 has an elliptical shape, a difference in grinding trajectory can be generated due to the difference between the major axis and the minor axis of the elliptical shape, and machining is performed from the gap generated by the difference in the grinding trajectory. Waste can be discharged. As a result, when the grinding wheel 30 is pulled out of the silicon carbide single crystal 10, the grinding wheel 30 is not clogged by the processing waste, and the cracks in the silicon carbide single crystal 10 are not widened by the blurring of the grinding wheel 30.

  The difference between the major axis “a” shown in the Y-axis direction and the minor axis “b” shown in the X-axis direction in FIG. 4C is preferably within the range of 0.01 mm to 2.0 mm, and more preferably 0.05 mm to It is more desirable to be within the range of 0.5 mm. When the difference between the major axis a and the minor axis b is small, the processing efficiency of discharging waste scraps is the same as that of the circular grinding wheel 30, and the cutting resistance increases as the difference between the major axis a and the minor axis b increases. The grindstone 30 is easily broken, and cracks are easily generated in the silicon carbide single crystal 10.

(First embodiment)
A method for grinding a silicon carbide single crystal will be described with reference to FIGS.
(A) First, the silicon carbide single crystal 10 grown on the crucible lid 20 shown in FIG. 1A is prepared, and the lid 20 surface is arranged on the fixing device 21 and fixed. As shown in the cross-sectional view of FIG. 1B, the silicon carbide single crystal 10 preferably has a single crystal region 12 whose diameter gradually increases in the growth direction of the silicon carbide single crystal.

(B) Next, a grinding wheel 30 having a hollow cylindrical portion (blade) 32 as shown in FIG. 2 is prepared.

(C) Then, as shown in FIG. 2, the central axis Z of the silicon carbide single crystal 10 and the central axis in the longitudinal direction of the grinding wheel 30 are aligned. In FIG. 2, the left-right direction on the paper is the X direction, and the front-back direction is the Y direction.

(D) Next, as shown in FIG. 3, the grinding wheel 30 is lowered at a predetermined speed toward the seed crystal direction 11 of the silicon carbide single crystal 10 while rotating about the central axis Z. Grind. The rotational speed of the cylindrical grindstone at this time is 300 to 3000 rpm, preferably 500 to 1000 rpm. This is because sufficient grinding efficiency cannot be obtained when the rotational speed is less than 300 rpm. Also, if the rotational speed exceeds 3000 rpm, grinding wheel slip occurs and machining becomes unstable. The downward feed speed of the grindstone is preferably 0.1 to 1.0 mm / min. This is because when the downward feed speed is less than 0.1 mm / min, not only the cost increases but also grinding of the grindstone occurs. This is because when the downward feed speed exceeds 1.0 mm / min, the grinding resistance increases too much, and the grinding stones run away and sway, resulting in poor processing accuracy and lead to cracking.

  As shown in FIG. 4A, it is preferable to perform grinding while spraying a water flow 34 (lubricant) from the ejection port 31 of the grinding wheel 30 together with the rotation and vertical movement. This is because it is possible to prevent the temperature rise at the processing point and reduce the grinding resistance.

(E) Next, a single wire 40 including winding portions 41a and 41b shown in FIGS. 5 and 6 and a wire 42 held by the winding portions 41a and 41b is prepared. For the grinding, a wire 42 coated with abrasive grains such as diamond may be used, or grinding may be performed while supplying diamond abrasive grains. Then, as shown in FIG. 5, the single wire 40 is brought into contact with the vicinity of the growth surface of the columnar silicon carbide single crystal, that is, the upper end of the cut portion. Then, the upper part (near the growth surface) of the cylindrical silicon carbide single crystal formed in the single crystal region 12 of the silicon carbide single crystal 10 is cut and removed. Further, as shown in FIG. 6, the upper end of the seed crystal 11 and the single wire 40 are brought into contact with each other. Then, the lower part (near the seed crystal bonding surface) of the cylindrical silicon carbide single crystal of the silicon carbide single crystal 10 is cut.

  The cylindrical single crystal region 10a can be cut out from the silicon carbide single crystal 10 as described above. Note that a silicon carbide single crystal wafer having a desired wafer thickness can be obtained by cutting the single crystal regions 10a at predetermined intervals using a multi-wire (not shown).

  As shown in FIG. 9, the conventional grinding method for silicon carbide single crystal 110 is such that a grinding wheel 130 having a grinding part 131 and a rotary shaft 132 is brought close to the side of the silicon carbide single crystal 110, and the rotary shaft 132 is used as an axis. The silicon carbide single crystal 110 was formed into a cylindrical shape by rotating the grinding part 131 to perform grinding. However, the polycrystal 113 exists on the side portion of the silicon carbide single crystal 110, and cracks are likely to occur due to the screw dislocations in the polycrystal 113, and it has been difficult to form into a cylindrical shape. However, according to the present embodiment, since the hollow cylindrical portion 32 of the grinding wheel 30 is pressed and ground against the single crystal region 12 of the silicon carbide single crystal, there is an effect that cracks hardly occur. Further, the cylindrical single crystal region 10a can be efficiently cut out from the silicon carbide single crystal 10.

  As Examples 1 and 2 of the first embodiment and a comparative example, a 6H-type silicon carbide single crystal (growth height: 10 mm, maximum diameter: 75 mm) as a grinding object was subjected to a grinding experiment under the following conditions, and cracks were observed. Visual observation was made about the occurrence. The number of cracks that occurred when grinding under the same conditions was examined as the crack generation rate (%).

Example 1
Grinding equipment: Gliding Center (Mitsui Seiki, trade name “VU65”),
Grinding wheel: inner diameter 51.0 mm, blade thickness 1.0 mm, diamond abrasive, particle size # 140,
Grinding conditions: 500 rpm, feed rate 0.3 mm / min, center through pressure 0.17 MPa,
Result: The crack occurrence rate was 20/100 times (20%).

(Example 2)
Grinding equipment: Gliding Center (Mitsui Seiki, trade name “VU65”),
Grinding wheel: inner diameter 51.8 mm (minor axis) to 52.2 mm (major axis), blade thickness 1.0 mm, diamond abrasive, particle size # 140,
Grinding conditions: rotation speed 1000 rpm, feed rate 0.3 mm / min, center through pressure 0.17 MPa,
Result: The crack occurrence rate was 1/10 times (10%).

(Comparative Example 1)
As a comparative example, using a cylindrical grinding machine (trade name “OGM340UEX” manufactured by Okamoto Machine Tool Co., Ltd.), one-side cutting (cutting amount: 17.5 mm, left and right feed: 98 mm / min), workpiece rotation speed 100 rpm, spark out 4 An experiment similar to that in Example 1 was performed, except that grinding was performed under reciprocating conditions. As a result, the crack occurrence rate was 50/100 times (50%).

(Second Embodiment)
(A) First, the same steps as shown in FIGS.

(B) Next, in place of the steps shown in FIGS. 3 and 4, as shown in FIGS. 7A to 7C, the grinding wheel 30 is rotated and swung while the grinding wheel 30 is made of silicon carbide. The silicon carbide single crystal 10 is ground by being lowered with respect to the crystal 10. By swinging in addition to rotation, for example, when water is ejected from the ejection port 31 of the grinding wheel 30, a gap is created between the grinding wheel 30 and the non-workpiece, and the cooling water is used as a processing point. Easy to supply. Moreover, as shown in FIG. 8, the processing waste 10b is easily discharged, and there is an effect that the processing load and blurring of the grinding wheel 30 can be suppressed. As shown in FIGS. 7B and 7C, the “oscillation” is performed so that the center axis Z of the grinding wheel 30 and the center axes ZL1 and ZL2 in the growth direction of the silicon carbide single crystal are shifted from each other. This can be done by relatively moving the fixing device 21. The rocking may be moved so that the central axis Z of the grinding wheel 30 draws an arc, or the fixing device 21 is moved so as to draw an arc on the X and Y planes while fixing the central axis Z of the grinding wheel 30. You may let them. Further, the rocking can be performed by using means for making the cross-sectional shape of the grinding wheel elliptical and decentering the central axis of the grinding wheel and the shank. The swing width l shown in FIG. 7 (b) is not particularly limited as long as the machining waste 10b can be discharged, but from a silicon carbide single crystal having a growth height of 10 mm and a maximum diameter of 75 mm to a cylindrical single crystal. The rocking width l when cutting out the region is preferably 0.1 to 3.0 mm. If the thickness is less than 0.1 mm, the effect of reducing the cutting resistance cannot be sufficiently obtained, and if it exceeds 3.0 mm, the diameter of the wafer is reduced and the cost is increased. In order to effectively eliminate grinding waste, other means such as chopping the grinding wheel in the Z direction can be used.

(C) Subsequently, a cylindrical single crystal region 10a is cut out from the silicon carbide single crystal 10 by performing the same steps as in FIGS.

  According to the second embodiment, there is an effect that the grinding resistance can be reduced as compared with the first embodiment by swinging.

As Examples 3, 4, 5 and Comparative Example 2 of the second embodiment, a grinding experiment was performed on a 6H-type silicon carbide single crystal (growth height: 10 mm, maximum diameter: 75 mm) as a grinding object under the following conditions. The occurrence of cracks was visually observed. And the frequency | count of the crack which arose when grinding 100 times on the same conditions was investigated as a crack generation rate (%). The results obtained are summarized in the table:
Grinding equipment: Gliding Center (Mitsui Seiki, trade name “VU65”),
Grinding wheel: inner diameter 51.0 mm, blade thickness 1.0 mm, diamond abrasive, particle size # 140,
Grinding conditions: rotational speed 500 rpm, feed rate 0.3 mm / min, center through pressure 0.17 MPa, grinding wheel central axis moving speed 30 mm / min, incision 20 mm
On the other hand, as a comparative example, grinding is performed with a cylindrical grinding machine (OGM340UEX, manufactured by Okamoto Machine Tool Co., Ltd.), one-sided cutting (cutting amount: 17.5 mm, left and right feed: 98 mm / min), workpiece rotation speed of 100 rpm, and sparkout 4 reciprocation. Processing was performed.

(Silicon carbide single crystal)
According to the method for grinding a silicon carbide single crystal according to an embodiment of the present invention, a high-quality silicon carbide single crystal can be efficiently cut out in a state where there is no breakage such as cracks. The silicon carbide single crystal to be ground is not particularly limited as long as it is produced by a sublimation method, but it is preferable to have a very high quality without polycrystals, polymorphs, or micropipe crystal defects. . This is because it can be particularly suitably used for electronic devices such as semiconductor wafers, optical devices such as light emitting diodes, and the like. Specifically, the number of crystal defects (pipe defects) evaluated by etching with molten alkali is preferably 50 / cm 2 or less, and more preferably 10 / cm 2 or less. The total content of metal impurity elements in the silicon carbide single crystal is preferably 10 ppm or less.

Fig.1 (a) shows the side view of a silicon carbide single crystal, FIG.1 (b) shows sectional drawing of a silicon carbide single crystal. FIG. 2 is a process diagram (part 1) of the grinding method for a silicon carbide single crystal according to the first embodiment of the present invention. FIG. 3: shows process drawing (the 2) of the grinding method of the silicon carbide single crystal concerning the 1st Embodiment of this invention. FIG. 4A is a cross-sectional view showing the steps of the silicon carbide single crystal grinding method according to the first embodiment of the present invention, FIG. 4B is a partial cross-sectional view of the grinding wheel, and FIG. (C) shows a partial cross-sectional view of another example of a grinding wheel. FIG. 5: shows process drawing (the 3) of the grinding method of the silicon carbide single crystal concerning the 1st Embodiment of this invention. FIG. 6 is a process diagram (part 4) of the method for grinding a silicon carbide single crystal according to the first embodiment of the present invention. FIG. 7 (a) is a cross-sectional view showing the steps of the silicon carbide single crystal grinding method according to the second embodiment of the present invention, FIG. 7 (b) is a partial cross-sectional view of the grinding wheel, and FIG. (C) shows a partial cross-sectional view of the grinding wheel. FIG. 8: shows the expanded sectional view which shows the process of the grinding method of the silicon carbide single crystal concerning the 2nd Embodiment of this invention. FIG. 9 is a cross-sectional view showing the steps of a conventional method for grinding a silicon carbide single crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Silicon carbide single crystal 10a ... Cylindrical silicon carbide single crystal 12 ... Seed crystal 20 ... Lid 21 ... Fixing device 30 ... Hollow cylindrical grindstone 40 ... Single wire

Claims (11)

Contacting the opening of the hollow cylindrical grindstone with the growth surface facing the seed crystal side of the silicon carbide single crystal formed by the sublimation method;
Rotating the hollow cylindrical grindstone and lowering the hollow cylindrical grindstone in the seed crystal direction to grind the silicon carbide single crystal;
A method for grinding a silicon carbide single crystal, comprising:   2. The method for grinding a silicon carbide single crystal according to claim 1, wherein the shape of the opening of the hollow cylindrical grindstone is an ellipse.   3. The silicon carbide single crystal grinding according to claim 2, wherein an opening shape of the hollow cylindrical grindstone is an elliptical shape having a difference between a major axis and a minor axis within a range of 0.01 mm to 2.0 mm. Method.   In the grinding step, the hollow cylindrical grindstone is lowered in the seed crystal direction in a state where the central axis in the growth direction of the silicon carbide single crystal coincides with the central axis of the hollow cylindrical grindstone. The method for grinding a silicon carbide single crystal according to claim 1.   2. The method for grinding a silicon carbide single crystal according to claim 1, wherein in the grinding step, the silicon carbide single crystal and the hollow cylindrical grindstone are relatively moved and oscillated.   The rocking width defined by the deviation between the central axis in the growth direction of the silicon carbide single crystal and the central axis of the hollow cylindrical grindstone is 0.1 to 1.0 mm. A method for grinding a silicon carbide single crystal.   The method for grinding a silicon carbide single crystal according to any one of claims 4 to 6, wherein a rotational speed of the cylindrical grindstone is 300 to 3000 rpm.   The method for grinding a silicon carbide single crystal according to any one of claims 4 to 7, wherein a feed rate of the cylindrical grindstone is 0.1 to 1.0 mm / min.   The method for grinding a silicon carbide single crystal according to any one of claims 4 to 8, wherein the cylindrical grindstone includes notches at a constant interval at a grindstone tip.   The said hollow cylindrical grindstone is provided with the ejection port which supplies a lubricant on a center axis | shaft, The said silicon carbide single crystal is ground, supplying a lubricant from the said ejection port. The grinding method of the silicon carbide single crystal in any one of -9.   The silicon carbide single crystal according to any one of claims 4 to 10, further comprising a step of grinding the vicinity of the growth surface and the vicinity of the seed crystal bonding surface of the cylindrical silicon carbide single crystal cut out in the grinding step. Crystal grinding method.

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