JP7271468B2 - Grinding method of sapphire substrate - Google Patents

Description

The present invention relates to a grinding method for a single-crystal sapphire substrate having an r-plane as its main surface.

Surface acoustic wave (SAW) devices, such as lithium tantalate and lithium niobate, are used as frequency adjustment and selection parts for mobile phones. used.

In recent years, communication standards have narrowed the interval between transmission and reception frequency bands and widened the bandwidth. Under such communication standards, unless the change in characteristics due to temperature changes in the surface acoustic wave device materials is sufficiently small, the frequency selection range will deviate, which will interfere with the device's filter and duplexer functions. A problem arises.

As a countermeasure against these problems, bonding a heterogeneous substrate such as silicon, sapphire, or quartz to a piezoelectric substrate can be mentioned. This makes it possible to reduce characteristic fluctuations with respect to temperature as compared with the use of a single piezoelectric substrate. Such a substrate is called TC-SAW, and is currently popular in the SAW device market.

A sapphire substrate is one of the heterogeneous substrates. TC-SAW uses a sapphire substrate having an r(01-12) plane as a principal surface (Non-Patent Document 1).

However, the r-plane of such a sapphire substrate is said to have "pits" deeper than the working marks on the machined surface compared to the a(11-20) and c(0001) planes. It is easy for dents to occur. If such pits are generated, the polishing allowance is increased more than necessary when mirror-finishing the substrate by polishing or the like, which deteriorates the flatness of the substrate and increases the cost of polishing. Therefore, a grinding method capable of suppressing the generation of pits is desired.

According to Patent Document 1, when the c-plane of a sapphire substrate having the r-plane as the main surface is regarded as the wood grain, grinding from the regular grain direction of the c-plane reduces the surface fracture layer and causes only mild warping.

Japanese Patent Publication No. 63-2735

"SAW Device with Improved Temperature Characteristics Using LiTaO3/Sapphire Bonded Substrate", Michio Miura, Shogo Inoue, Jun Tsutsumi, Takashi Matsuda, Masanori Ueda, Yoshio Sato, Osamu Igata, Yasuo Ebata, IEEJ Trans. EIS, Vol.127, No.8, 2007 p1161-1165

An r-plane sapphire substrate was ground from the processing direction G by generally used infeed grinding in accordance with the method described in Patent Document 1 (FIGS. 16 and 17 and FIGS. 19 and 20). In-feed grinding is a method in which a rotating grindstone is lowered to grind a rotating workpiece to a specified thickness. As a result, in the pit-prone region shown in FIG. 18 and the pit-prone region shown in FIGS.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a grinding method for a sapphire substrate that does not generate pits on the surface even when sapphire having an r-plane as a principal surface is ground.

As a result of intensive studies, the present inventors have found that the actual cause of pit formation is not slippage or peeling along the c-plane direction, but the processing direction forming an acute angle with respect to the m-plane. Furthermore, as a result of extensive studies, the present inventors have found that by holding a sapphire substrate on a chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is in a predetermined direction, the processing direction is the m-plane. On the other hand, the present inventors have found that an acute angle can be suppressed, thereby suppressing the formation of pits on the surface of the sapphire substrate, and have completed the following invention.
[1] holding a sapphire substrate having an r-plane as a main surface on a chuck table; and grinding the main surface of the sapphire substrate held on the chuck table with a grinding wheel, In the step of holding on the table, the main surface of the sapphire substrate forms an obtuse angle with the m-plane of the sapphire substrate, and the direction in which the angle formed with the m-plane is maximum is 0°, and the clockwise direction is plus. In this case, the method of grinding a sapphire substrate holds the sapphire substrate on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is -90° or more and +90° or less.
[2] In the step of holding the sapphire substrate on the chuck table, the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is -45° or more and +45° or less. The method for grinding a sapphire substrate according to the above [1], wherein the sapphire substrate is held at

According to the present invention, even when a sapphire substrate having an r-plane as a principal surface is ground, it is possible to suppress the formation of pits on the surface. As a result, the polishing allowance is reduced, the flatness of the sapphire substrate is good even when mirror-finished, and the manufacturing cost of the sapphire substrate can be suppressed.

It is a figure which shows the crystal structure of a sapphire substrate. It is a figure which shows an example of a sapphire substrate, Fig.2 (a) is a top view, FIG.2(b) is sectional drawing. It is a figure which shows the relationship between a sapphire substrate and a unit cell of a sapphire crystal, Fig.3 (a) is a top view, FIG.3(b) is sectional drawing. It is a figure which shows the relationship between the substrate direction A used as the reference|standard of the processing direction in a sapphire substrate, and the m plane of a sapphire substrate. It is a figure which shows the relationship between the substrate direction A used as the reference|standard of the processing direction in a sapphire substrate, and the m plane of a sapphire substrate. It is a figure which shows the positional relationship of a grinding wheel, a sapphire substrate, and a chuck table, Fig.6 (a) is a perspective view, FIG.6(b) is a top view. It is a figure which shows an example of the cross section of a grinding wheel. FIG. 10 is a diagram showing an example of the grinding marks and the processing direction when the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is 0°; FIG. 10 is a diagram showing an example of the grinding marks and the processing direction when the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is −90°; FIG. 10 is a diagram showing an example of the grinding marks and the processing direction when the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is +90°; 11(a) is a perspective view and FIG. 11(b) is a plan view showing the positional relationship of a grinding wheel, a sapphire substrate, and a chuck table when a plurality of sapphire substrates are held on the chuck table. FIG. be. It is a figure which shows the grinding method of the sapphire substrate of another embodiment of this invention, Fig.12 (a) is a perspective view, FIG.12(b) is a top view. In the method of grinding a sapphire substrate according to another embodiment of the present invention, the grinding marks and the processing when the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is 0° It is a figure which shows an example of a direction. In the method for grinding a sapphire substrate according to another embodiment of the present invention, the grinding marks and the It is a figure which shows an example of a processing direction. In the method of grinding a sapphire substrate according to another embodiment of the present invention, the grinding marks and processing when the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is +90° It is a figure which shows an example of a direction. It is a figure which shows an example of a grinding mark when grinding a sapphire substrate by the conventional infeed grinding. It is a figure which shows the processing direction of the sapphire substrate by the conventional infeed grinding. FIG. 4 is a diagram showing a pit-prone region; It is a figure which shows an example of a grinding mark when grinding a sapphire substrate by the conventional infeed grinding. It is a figure which shows the processing direction of the sapphire substrate by the conventional infeed grinding. FIG. 4 is a diagram showing a pit-prone region; It is a figure which shows an example of the pit which generate|occur|produced in the surface of a sapphire substrate.

A method for grinding a sapphire substrate according to one embodiment of the present invention will be described in detail below, but the method for grinding a sapphire substrate according to the present invention is not limited to this. TECHNICAL FIELD The present invention relates to a grinding method for surface grinding a sapphire substrate having an r-plane as a principal surface.

A method for grinding a sapphire substrate according to one embodiment of the present invention includes a step (A) of holding a sapphire substrate having an r-plane as a main surface on a chuck table, and a grinding wheel to grind the main surface of the sapphire substrate held on the chuck table. A step (B) of grinding is included.

The sapphire substrate having the r-plane as the main surface used in the sapphire substrate grinding method of one embodiment of the present invention is obtained by slicing an ingot pulled by the CZ (Czochralski) method or by the EFG (Edge Defined Film Growth) method. It is preferable that the substrate is obtained by cutting out the substrate pulled up by . For ingot slicing, for example, a diamond wire saw in which diamond is fixed to a piano wire is used.

The sapphire substrate thus obtained is subjected to chamfering, lapping, etching, and the like to adjust the diameter, thickness, and surface condition to a predetermined value.

A large work-affected layer is formed on the surface of the sapphire substrate by the lapping. Since the sapphire substrate is a hard material, it takes a very long time to remove this large work-affected layer only by polishing. For this reason, the sapphire substrate is then ground using fine-grained diamond. FIG. 1 shows the crystal structure of a sapphire substrate. The crystal structure of the sapphire substrate has c-axis, a1 _- axis, _a2 and _a3- axis. In FIG. 1, the vertical axis is the c-axis and the horizontal axis is the _a2- axis. Reference numeral 1 denotes a unit cell of sapphire crystal, reference numeral 2 denotes an r-plane, and reference numeral 3 denotes an m-plane. As described above, the main surface of the sapphire substrate used in the sapphire substrate grinding method of the embodiment of the present invention is the r-plane.

FIG. 2 shows an example of a sapphire substrate. A sapphire substrate 101 has a substantially circular shape, and an orientation flat (orientation flat) 102 or a notch is formed in a direction of 45° with respect to _{the a3-} axis and c-axis directions. However, the orientation flats and notches are not limited to these orientations, and the orientations of the orientation flats and notches can be selected as appropriate. The c-axis of the sapphire substrate 101 forms an angle of approximately 32.4° with respect to the main surface (r-plane) of the sapphire substrate.

FIG. 3 shows the relationship between the sapphire substrate used in the sapphire substrate grinding method of the embodiment of the present invention and the sapphire crystal unit cell. It can be seen that the m-plane 3 of the sapphire crystal unit cell is tilted with respect to the main surface of the sapphire substrate.

FIG. 4 shows the relationship between the substrate direction A, which serves as a reference for the processing direction of the sapphire substrate, and the m-plane 3 of the sapphire substrate. The substrate direction A forms an obtuse angle with the m-plane 3 of the sapphire substrate in the main surface of the sapphire substrate, and is the direction in which the angle 4 (α) formed with the m-plane 3 is maximum. This substrate direction A is assumed to be 0°. Also, the clockwise direction is positive. The substrate direction B is a direction obtained by rotating the substrate direction A by 180°. The substrate direction B forms an acute angle with the m-plane 3 and is the direction in which the angle 4 (β) formed with the m-plane 3 is the smallest.

With reference to FIG. 5, the relationship between the substrate direction A, which serves as a reference for the processing direction of the sapphire substrate, and the m-plane 3 of the sapphire substrate will be described more specifically. The substrate direction A forms an obtuse angle with a straight line 6 in the thickness direction of the sapphire substrate along the m-plane 3 and is the direction in which the angle θ formed with the m-plane 3 is the maximum. The substrate direction B is a direction obtained by rotating the substrate direction A by 180°, but it can also be said that the direction of the arrow 7, which is perpendicular to the m-plane 3 and extends toward the main surface, is projected onto the main surface. .

In FIGS. 3 and 5, of the two intersections of the straight line in the substrate direction A passing through the center of the circle circumscribing the main surface of the sapphire substrate 101 and the outer periphery of the sapphire substrate 101, with respect to the center of the circle, Point A is the intersection on the substrate direction B side, and point B is the intersection on the substrate direction A side. Therefore, the direction from A to B is the same direction as the substrate direction A. That is, the direction from A to B is the reference direction of the processing direction, and is the direction of 0°. The center of the main surface of the sapphire substrate is the center of the circle circumscribing the main surface of the sapphire substrate. In addition, when the shape of the sapphire substrate is not circular, the position of the center of the main surface of the sapphire substrate is the position corresponding to the center of gravity of the plate having the same outer shape as the sapphire substrate and having a constant thickness and density. be.

FIG. 6 shows the positional relationship among the grinding wheel, sapphire substrate and chuck table. A sapphire substrate 101 is held on a chuck table 302, and the chuck table 302 and grinding wheel 301 rotate in directions D and E, respectively. Note that the chuck table 302 can be rotated in the direction opposite to the direction D without any problem. Moreover, in order that the processing direction of the grinding wheel 301 at the center of the main surface of the sapphire substrate 101 is within a predetermined range, it is preferable that the sapphire substrate 101 only revolves on the chuck table and does not rotate. .

For the grinding wheel 301, for example, a superabrasive wheel as shown in FIG. 7 can be used. The superabrasive wheel 301 comprises, for example, a base metal 304 and a superabrasive layer 305 . The superabrasive layer 305 contains abrasive grains and bonds that fix the abrasive grains. Since sapphire is a very hard material, diamond, for example, is used as an abrasive grain. As a bond for fixing abrasive grains, for example, resinoid, metal, vitrified or the like is used. A superabrasive wheel consisting entirely of a superabrasive layer can also be used. As shown in FIG. 7 , the grinding wheel 301 grinds the sapphire substrate 101 mainly at the outer peripheral portion 303 .

Although the method of fixing the sapphire substrate to the chuck table 302 is not particularly limited, it is preferable to fix the sapphire substrate with a vacuum chuck in order to grind with good flatness.

Grinding wheel 301 descends from the top of sapphire substrate 101 at a predetermined speed, and contacts sapphire substrate 101 only in a working range (peripheral portion) 303 of grinding wheel 301, as shown in FIG. The grinding wheel 301 grinds the sapphire substrate 101 only in the processing range 303 of the grinding wheel 301 .

The processing direction of the sapphire substrate 101 is the relative movement direction of the grinding wheel 301 with respect to the sapphire substrate 101 . Grinding wheel 301 is rotating in direction E, which is counterclockwise. Further, as described above, the grinding wheel 301 processes the sapphire substrate 101 only within the processing range 303 of the grinding wheel 301 . Therefore, the processing direction of the sapphire substrate 101 is the rotation direction E in the processing range 303 of the grinding wheel 301 , that is, the rotation direction E in the outer periphery of the grinding wheel 301 . Although the chuck table 302 also rotates, the rotation of the chuck table 302 is much slower than the rotation of the grinding wheel 301, so the influence of the rotation of the chuck table 302 in the processing direction of the sapphire substrate 101 can be ignored. can be done.

The sapphire substrate 101 is held on the chuck table 302 so that the point A is on the center side of the chuck table 302 and the point B is on the outer peripheral side of the chuck table 302 . As a result, the sapphire substrate 101 is held on the chuck table 302 so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate 101 is 0°.

Alternatively, the grinding wheel 301 may be rotated clockwise. In this case, the sapphire substrate 101 is held on the chuck table 302 so that the point A is on the outer peripheral side of the chuck table 302 and the point B is on the center side of the chuck table 302 . Also in this case, the sapphire substrate 101 is held on the chuck table 302 so that the processing direction of the grinding wheel 301 at the center of the main surface of the sapphire substrate 101 is 0°.

FIG. 8 shows an example of the grinding marks 201 and the processing direction when the sapphire substrate 101 is held on the chuck table 302 so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate 101 is 0°. Since the machining direction can be prevented from forming an acute angle with respect to the m-plane of the sapphire substrate, the generation of pits in the sapphire substrate can be suppressed. In addition, the arrow shown in FIG. 8 indicates the processing direction.

It is not limited to the case where the sapphire substrate is held on the chuck table so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate is 0°, and the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is -. The sapphire substrate may be held on the chuck table so that the angle is 90° or more and +90° or less. In this case as well, it is possible to prevent the processing direction from forming an acute angle with respect to the m-plane of the sapphire substrate, thereby suppressing the formation of pits in the sapphire substrate. For example, as shown in FIG. 9, the sapphire substrate may be held on the chuck table so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate is -90°. Note that the curve shown in FIG. 9 is the grinding trace, and the arrow is the processing direction. Further, as shown in FIG. 10, the sapphire substrate may be held on the chuck table so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate is +90°. Note that the curve shown in FIG. 10 is the grinding mark, and the arrow indicates the processing direction. From the viewpoint of suppressing the generation of pits in the sapphire substrate, the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is preferably −45° or more and +45° or less, more preferably −30° or more and +30° or less. The sapphire substrate is held on the chuck table such that the angle is -15° or more and +15° or less, more preferably -5° or more and +5° or less. Thereby, in the sapphire substrate, it is possible to further suppress the processing direction from forming an acute angle with respect to the m-plane of the sapphire substrate.

As shown in FIG. 11, a plurality of sapphire substrates 101 may be held on the chuck table. This increases throughput and leads to cost reduction.

FIG. 12 shows a sapphire substrate grinding method according to another embodiment of the present invention. In FIG. 6, the chuck table 302 was rotating. However, as shown in FIG. 11, the chuck table 302 may reciprocate in the vertical direction (F direction) with respect to the tangential line at the center of the processing range 303 of the grinding wheel 301 . Also in this case, the sapphire substrate 101 is held on the chuck table 302 so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate 101 is 0°. In this case, the chuck table 302 can be made smaller than the chuck table 302 shown in FIG. FIG. 13 shows the grinding marks 201 and the processing direction of the sapphire substrate. The arrow shown in FIG. 13 is the processing direction. The processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate 101 is 0°. By grinding in this way, it is possible to prevent the processing direction from forming an acute angle with respect to the m-plane of the sapphire substrate, thereby suppressing the generation of pits in the sapphire substrate.

In this case also, the sapphire substrate is not limited to being held on the chuck table so that the grinding direction of the grinding wheel at the center M of the main surface of the sapphire substrate is 0°, and the grinding wheel at the center of the main surface of the sapphire substrate is used. The sapphire substrate may be held on the chuck table so that the processing direction is -90° or more and +90° or less. As a result, it is possible to prevent the processing direction from forming an acute angle with respect to the m-plane of the sapphire substrate, thereby suppressing the generation of pits in the sapphire substrate. For example, as shown in FIG. 14, the sapphire substrate may be held on the chuck table so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate is −90°. Note that the curve shown in FIG. 14 is the grinding mark, and the arrow is the machining direction. Further, as shown in FIG. 15, the sapphire substrate may be held on the chuck table so that the processing direction of the grinding wheel at the center M of the main surface of the sapphire substrate is +90°. Note that the curve shown in FIG. 15 is the grinding mark, and the arrow is the machining direction. From the viewpoint of suppressing the generation of pits in the sapphire substrate, in this case also, the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is preferably −45° or more and +45° or less, more preferably −30° or more. The sapphire substrate is held on the chuck table so that the angle is +30° or less, more preferably −15° or more and +15° or less, and still more preferably −5° or more and +5° or less.

The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

Examples will be described below, but the present invention is not limited to these.

<Example 1>
First, a 4-inch diameter sapphire single crystal ingot pulled by the CZ method is adjusted to the r-plane orientation, sliced, chamfered, lapped, and etched, and the r-plane with a thickness of 400 μm is the main surface. A sapphire substrate was produced. Orientation flats were also made with respect to the crystallographic axis, as shown in FIG.

Next, the sapphire substrate was placed on a chuck table of 230 mmφ (FIG. 6) so that the processing direction at the center of the main surface of the sapphire substrate was from A to B (FIG. 8), and #1000 diamond was applied. Using a 200 mmφ grinding wheel equipped with abrasive grains, both sides were ground to 20 μm on one side while rotating the chuck table to prepare a total of 10 sapphire substrates. The rotation speed of the grinding wheel was 2000 rpm, and the rotation speed of the chuck table was 150 rpm.

When the surface after grinding was observed with a laser microscope, no pits were confirmed on the entire surface of all 10 sheets.

When these ground substrates were polished on both sides, the average polishing allowance was 8 μm, and the average TTV (Total Thickness Variation) after polishing was 1.4 μm.

<Example 2>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a chuck table of 230 mmφ so that the processing direction at the center of the sapphire substrate was −90° with respect to the direction from A to B (FIG. 9), and #1000 diamond abrasive grains were used. A grinding wheel of 200 mm in diameter was used to grind 20 μm on one side while rotating the chuck table, and a total of 10 sapphire substrates were produced. The number of revolutions of the grinding wheel and the number of revolutions of the chuck table were the same as in the first embodiment.

When the surface after grinding was observed with a laser microscope, pits were not confirmed on the entire surface of 7 out of 10 sheets, but pits were partially confirmed on 3 sheets.

When the substrate without pits after grinding was polished on both sides, the average value of polishing stock was 11 μm, and the average TTV value after polishing was 1.8 μm.

<Example 3>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a chuck table of 230 mmφ so that the processing direction at the center of the sapphire substrate was +90° with respect to the direction from A to B (Fig. 10), and #1000 diamond abrasive grains were applied. A grinding wheel of 200 mm in diameter was used to grind 20 μm on one side while rotating the chuck table, and a total of 10 sapphire substrates were produced. The number of revolutions of the grinding wheel and the number of revolutions of the chuck table were the same as in the first embodiment.

When the surface after grinding was observed with a laser microscope, pits were not confirmed on the entire surface of 8 out of 10 sheets, but pits were partially confirmed on 2 sheets.

When the substrate without pits after grinding was polished on both sides, the average value of polishing stock was 10 μm, and the average TTV value after polishing was 1.6 μm.

<Example 4>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate is placed on a chuck table of 120 mmφ (FIG. 12) so that the processing direction at the center of the sapphire substrate is from A to B (FIG. 13), and #1000 diamond abrasive grains are applied. A total of 10 sapphire substrates were produced by grinding both sides to 20 μm on one side while reciprocating the chuck table using the provided 200 mmφ grinding wheel. The number of revolutions of the grinding wheel was the same as in Example 1.

When the surface after grinding was observed with a laser microscope, no pits were confirmed on the entire surface of all 10 sheets.

When these ground substrates were polished on both sides, the average polishing removal was 7 μm, and the average TTV after polishing was 1.2 μm.

<Example 5>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a chuck table of 120 mmφ so that the processing direction at the center of the sapphire substrate was −90° with respect to the direction from A to B (FIG. 14), and a #1000 diamond grind was applied. Using a 200 mmφ grinding wheel with granules, both sides were ground to 20 μm on one side while reciprocating the chuck table to prepare a total of 10 sapphire substrates. The number of revolutions of the grinding wheel was the same as in Example 1.

When the surface after grinding was observed with a laser microscope, no pits were observed in 9 out of 10 sheets, but pits were partially confirmed in 1 sheet.

When the substrate without pits after grinding was polished on both sides, the average value of the polishing removal was 9 μm, and the average TTV value after polishing was 1.4 μm.

<Example 6>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a chuck table of 120 mmφ so that the processing direction at the center of the sapphire substrate was +90° with respect to the direction from A to B (FIG. 15), and #1000 diamond abrasive grains were applied. A total of 10 sapphire substrates were manufactured by grinding 20 μm on one side on both sides while reciprocating the chuck table using a 200 mmφ grinding wheel equipped with a . The number of revolutions of the grinding wheel was the same as in Example 1.

When the surface after grinding was observed with a laser microscope, no pits were observed in 8 out of 10 sheets, but pits were partially confirmed in 2 sheets.

When the substrate which had no pits after grinding was polished on both sides, the average polishing allowance was 10 μm, and the average TTV after polishing was 1.5 μm.

<Comparative Example 1>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a 230 mmφ chuck table so that the processing direction at the center of the sapphire substrate was +135° with respect to the direction from A to B, and a 200 mmφ chuck table was provided with #1000 diamond abrasive grains. A total of 10 sapphire substrates were prepared by grinding each side to 20 μm on both sides while rotating the chuck table. The number of revolutions of the grinding wheel and the number of revolutions of the chuck table were the same as in the first embodiment.

When the surface after grinding was observed with a laser microscope, partial pits were confirmed in all of the 10 sheets.

When these ground substrates were polished on both sides, an average polishing allowance of 25 μm was required until the entire surface including the pit portion was mirror-finished, and the average TTV after polishing was 3.5 μm.

<Comparative Example 2>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a 230 mmφ chuck table so that the processing direction at the center of the sapphire substrate was +180° with respect to the direction from A to B, and a 200 mmφ chuck table with #1000 diamond abrasive grains was placed on the sapphire substrate. A total of 10 sapphire substrates were prepared by grinding each side to 20 μm on both sides while rotating the chuck table. The number of revolutions of the grinding wheel and the number of revolutions of the chuck table were the same as in the first embodiment.

When the surface after grinding was observed with a laser microscope, pits were confirmed on the entire surface of all 10 sheets.

When the substrates obtained by grinding these substrates were polished on both sides, an average polishing removal value of 33 μm was required until a mirror finish was obtained, and the average TTV value after polishing was 4.2 μm.

<Comparative Example 3>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, this sapphire substrate was placed on a chuck table of 120 mmφ so that the processing direction at the center of the sapphire substrate was +135° with respect to the direction from A to B, and #1000 diamond abrasive grains were provided. A total of 10 sapphire substrates were produced by grinding each side to 20 μm on both sides while reciprocating the chuck table using a grinding wheel of 200 mmφ. The number of revolutions of the grinding wheel was the same as in Example 1.

When the surface after grinding was observed with a laser microscope, partial pits were confirmed in 9 out of 10 sheets.

When these ground substrates were polished on both sides, an average polishing allowance of 23 μm was required until the entire surface including the pit portion was mirror-finished, and the average TTV after polishing was 2.9 μm.

<Comparative Example 4>
A sapphire substrate having an r-plane as a main surface was produced in the same manner as in Example 1.

Next, the sapphire substrate was placed on a 120 mmφ chuck table so that the processing direction at the center of the sapphire substrate was +180° with respect to the direction from A to B, and a 200 mmφ chuck table with #1000 diamond abrasive grains was placed on the sapphire substrate. A total of 10 sapphire substrates were produced by grinding each side to 20 μm on both sides while reciprocating the chuck table using a grinding wheel of No. The number of revolutions of the grinding wheel was the same as in Example 1.

When the surface after grinding was observed with a laser microscope, pits were confirmed on the entire surface of all 10 sheets.

When the substrates obtained by grinding these substrates were polished on both sides, an average polishing removal value of 29 μm was required until a mirror finish was obtained, and the average TTV value after polishing was 3.6 μm.

Table 1 shows the results of Examples 1-6 and Comparative Examples 1-4.

1 sapphire crystal unit cell 2 r-plane 3 m-plane 4 angle between m-plane and substrate direction 5 c-plane 101 sapphire substrate 102 orientation flat or notch 201 grinding mark 301 grinding wheel (superabrasive wheel)
302 Chuck table 303 Processing range of grinding wheel (peripheral portion of grinding wheel)
D Direction of rotation of chuck table E Direction of rotation of grinding wheel F Direction of reciprocating motion of chuck table G Processing direction

Claims (2)

holding a sapphire substrate having an r-plane as a main surface on a chuck table; and grinding the main surface of the sapphire substrate held on the chuck table with a grinding wheel,
In the step of holding the sapphire substrate on the chuck table, the main surface of the sapphire substrate forms an obtuse angle with the m-plane of the sapphire substrate, and the direction in which the angle formed with the m-plane is maximum is set to 0°. Grinding of the sapphire substrate held on the chuck table so that the processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is −90° or more and +90° or less when the direction of rotation is positive. Method. The step of holding the sapphire substrate on the chuck table includes holding the sapphire substrate on the chuck table such that a processing direction of the grinding wheel at the center of the main surface of the sapphire substrate is −45° or more and +45° or less. The method of grinding a sapphire substrate according to claim 1.

Images