Gallium oxide substrate and method for manufacturing the same

Abstract

The present invention provides a gallium oxide substrate having a first main surface and a second main surface facing opposite to the first main surface. If z(r, θ) in the formula (1) in the specification is used to fit the measured data z of the height difference of the first main surface with the least square plane of the first main surface as the reference plane, 0 (r, θ), then when the second main surface is placed opposite to a horizontal flat surface, j is all a of 4, 9, 16, 25, 36, 49, 64, and 81. nm z nm The value (PV1 / D) obtained by dividing the first maximum height difference (PV1) of the component obtained by adding (r, θ) by the diameter (D) of the first main surface is 0.39×10 －4 Hereinafter, when the second main surface is opposed to the flat chuck surface and the entire surface is adsorbed, all a values ​​where j is 4 or more and 81 or less are nm z nm The value (PV2 / D) obtained by dividing the second maximum height difference (PV2) of the component obtained by adding (r, θ) by the diameter (D) of the first main surface is 0.59×10 －4 the following.

Description

Technical Field

[0001] The present disclosure relates to a gallium oxide substrate and a method for manufacturing the gallium oxide substrate. Background Art

[0002] In recent years, a solution to use a compound semiconductor substrate to replace a silicon semiconductor substrate has been proposed. Examples of compound semiconductors include silicon carbide, gallium nitride, and gallium oxide. Compound semiconductors have an advantage over silicon semiconductors in that they have a large band gap. The compound semiconductor substrate is ground, and an epitaxial film is formed on the ground surface.

[0003] Patent Document 1 describes a method for manufacturing a gallium oxide substrate. The method includes polishing only one surface of the gallium oxide substrate using a slurry containing colloidal silica. The subject of Patent Document 1 is to improve the shape of a gallium oxide substrate whose crystal system is a monoclinic system with poor symmetry and has very strong cleavage.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2016-13932

[0005] The single-sided polishing device generally has a lower platform, an upper platform and a nozzle. The lower platform is configured horizontally, and a polishing pad is attached to the upper surface of the lower platform. The upper platform is configured horizontally, and a gallium oxide substrate is fixed to the lower surface of the upper platform. The gallium oxide substrate has a first main surface and a second main surface facing opposite to the first main surface. The upper platform holds the gallium oxide substrate horizontally and presses the first main surface of the gallium oxide substrate onto the polishing pad. The lower platform rotates around its vertical rotation center line. The upper platform rotates passively with the rotation of the lower platform. The nozzle supplies polishing slurry to the polishing pad from above. The polishing slurry is supplied between the gallium oxide substrate and the polishing pad to grind the first main surface of the gallium oxide substrate flatly. Since the second main surface of the gallium oxide substrate is fixed to the lower surface of the upper platform, the concavo-convexity of the lower surface of the upper platform is transferred to the second main surface.

[0006] Since the single-side polishing device polishes only the first main surface, a residual stress difference is generated between the first main surface and the second main surface after polishing. As a result, warping occurs due to the Twyman Effect. In addition, if the second main surface of the gallium oxide substrate is removed from the upper platform and fully adsorbed against the flat chuck surface, the first main surface is deformed into the same shape as the lower surface of the upper platform, and the concavity and convexity of the lower surface of the upper platform appear on the first main surface.

[0007] Conventionally, the flatness of the gallium oxide substrate was poor, and the transfer accuracy of the exposure pattern to the gallium oxide substrate was poor. Summary of the invention

[0008] One aspect of the present disclosure provides a technology capable of improving the flatness of a gallium oxide substrate and transferring an exposure pattern to the gallium oxide substrate with high precision.

[0009] A gallium oxide substrate according to one embodiment of the present disclosure includes a first main surface and a second main surface facing opposite to the first main surface.

[0010] If the measured data z0(r, θ) of the height difference of the first main surface with the least square plane of the first main surface as the reference plane is fitted by the following formula (1),

[0011] When the second main surface is placed opposite to a horizontal flat surface, j is all a of 4, 9, 16, 25, 36, 49, 64, and 81. nm z nm The value (PV1 / D) obtained by dividing the first maximum height difference (PV1) of the component obtained by adding (r, θ) by the diameter (D) of the first main surface is 0.39×10 －4 the following,

[0012] When the second main surface is facing the flat chuck surface and the entire surface is adsorbed, all a values ​​where j is greater than or equal to 4 and less than or equal to 81 are nm z nm The value (PV2 / D) obtained by dividing the second maximum height difference (PV2) of the component obtained by adding (r, θ) by the diameter (D) of the first main surface is 0.59×10 －4 the following.

[0013] [Formula 1]

[0014]

[0015] [Formula 2]

[0016]

[0017] [Formula 3]

[0018]

[0019] [Formula 4]

[0020]

[0021] [Formula 5]

[0022]

[0023] In the above equations (1) to (5), (r, θ) is the polar coordinate on the reference plane, n is a natural number greater than 0 and less than k, k is 16, when n is an even number, m is only an even number in the range of -n to +n, when n is an odd number, m is only an odd number in the range of -n to +n, j is an index representing a combination of n and k, and a nm is the coefficient.

[0024] According to one aspect of the present disclosure, the flatness of the gallium oxide substrate can be improved, and an exposure pattern can be transferred to the gallium oxide substrate with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flowchart showing a method for manufacturing a gallium oxide substrate according to one embodiment.

[0026] Figure 2 It means implementation Figure 1 A perspective view of an example of a single-side polishing device performing single-side polishing.

[0027] Figure 3 It means implementation Figure 1 A cross-sectional view of an example of a single-side polishing device performing single-side polishing.

[0028] Figure 4 It means implementation Figure 1 A perspective view of an example of a double-side polishing apparatus for double-side polishing.

[0029] Figure 5 It means implementation Figure 1 A cross-sectional view of an example of a double-side polishing apparatus for double-side polishing.

[0030] Figure 6 This is a cross-sectional view showing an example of the state of the gallium oxide substrate when measuring the first maximum height difference (PV1).

[0031] Figure 7 is the z representing j=1 (n=0, m=0), j=2 (n=1, m=1), j=4 (n=2, m=0), j=9 (n=4, m=0) nm Graph of (r, θ).

[0032] Figure 8 This is a cross-sectional view showing an example of the state of the gallium oxide substrate when measuring the second maximum height difference (PV2). DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments of the present disclosure will be described with reference to the accompanying drawings. In addition, in the crystallographic description of this specification, [] is used to represent individual orientations, <> is used to represent collective orientations, () is used to represent individual faces, and {} is used to represent collective faces. The negative crystallographic index is usually represented by marking a horizontal bar above the number, but in this specification, a negative crystallographic index is represented by marking a minus sign before the number.

[0034] Figure 1 FIG. 1 is a flow chart showing a method for manufacturing a gallium oxide substrate according to an embodiment of the present invention. Figure 1 As shown, the method for manufacturing a gallium oxide substrate includes single-sided grinding of the gallium oxide substrate (S1). As the gallium oxide substrate, for example, a β-Ga2O3 single crystal is cut into a plate shape by a wire saw or the like, and then ground into a predetermined thickness by a grinding device or the like. The gallium oxide substrate may contain a dopant or may not contain a dopant. As the dopant, for example, Si, Sn, Al, or In is used.

[0035] Figure 2 It means implementation Figure 1 A perspective view of an example of a single-side polishing device performing single-side polishing. Figure 3 It means implementation Figure 1 A cross-sectional view of an example of a single-side grinding device for single-side grinding. Figure 3 In the figure, the concavo-convex of the lower surface 121 of the upper platform 120 is exaggeratedly shown. Figure 1 The single-side grinding device of the secondary single-side grinding (S2) is Figure 2 and Figure 3 The single-side polishing device 100 shown is the same and therefore is not shown in the drawings.

[0036] The single-side polishing device 100 includes a lower platform 110, an upper platform 120, and a nozzle 130. The lower platform 110 is arranged horizontally, and a lower polishing pad 112 is attached to an upper surface 111 of the lower platform 110. The upper platform 120 is arranged horizontally, and a gallium oxide substrate 10 is fixed to a lower surface 121 of the upper platform 120. The upper platform 120 holds the gallium oxide substrate 10 horizontally and presses the gallium oxide substrate 10 onto the lower polishing pad 112. In addition, the lower polishing pad 112 may not be provided, in which case the upper platform 120 presses the gallium oxide substrate 10 onto the lower platform 110. The diameter of the upper platform 120 is smaller than the radius of the lower platform 110, and the upper platform 120 is arranged radially outward of the rotation center line C1 of the lower platform 110. The rotation center line C2 of the upper platform 120 is arranged to be parallel to and offset from the rotation center line C1 of the lower platform 110. The lower platform 110 rotates about its vertical rotation center line C1. The upper platform 120 passively rotates along with the rotation of the lower platform 110. In addition, the upper platform 120 and the lower platform 110 may rotate independently or by respective rotation motors.

[0037] The gallium oxide substrate 10 has a circular first main surface 11 and a circular second main surface 12 facing opposite to the first main surface 11. A notch (not shown) indicating the crystal orientation of gallium oxide is formed on the periphery of the gallium oxide substrate 10. Instead of the notch, an orientation flat may be formed. The first main surface 11 is, for example, a {001} plane. The {001} plane is a crystal plane perpendicular to the <001> direction, and may be either a (001) plane or a (00-1) plane.

[0038] In addition, the first main surface 11 may be a crystal plane other than the {001} plane. In addition, the first main surface 11 may have a so-called off angle relative to a predetermined crystal plane. The off angle improves the crystallinity of the epitaxial film formed on the first main surface 11 after grinding.

[0039] The nozzle 130 supplies the polishing slurry 140 to the lower polishing pad 112. The polishing slurry 140 includes, for example, particles and water. The particles are dispersed substances, and the water is a dispersion medium. In addition, the dispersion medium may also be an organic solvent. The polishing slurry 140 is supplied between the gallium oxide substrate 10 and the lower polishing pad 112 to polish the lower surface of the gallium oxide substrate 10 evenly.

[0040] In a single-sided grinding (S1), diamond particles are used as particles, for example. The Mohs hardness of the diamond particles is 10. The D50 of the diamond particles is not particularly limited, and is, for example, 50 μm. “D50” refers to the 50% particle size of the cumulative percentage of the volume basis in the particle size distribution measured by the dynamic light scattering method. The dynamic light scattering method is a method of measuring the particle size distribution by irradiating the polishing slurry 140 with a laser and observing the scattered light using a photodetector.

[0041] In the single-side polishing (S1), the first main surface 11 of the gallium oxide substrate 10 is pressed against the lower polishing pad 112 and polished flat by the lower polishing pad 112 and the polishing slurry 140. On the other hand, the second main surface 12 of the gallium oxide substrate 10 is fixed to the lower surface 121 of the upper platform 120, so that the concavity and convexity of the lower surface 121 are transferred to the second main surface 12.

[0042] In addition, although the upper surface 111 of the lower platform 110 has the same unevenness as the lower surface 121 of the upper platform 120, the unevenness is hardly transferred to the first main surface 11 of the gallium oxide substrate 10. This is because the lower platform 110 is relatively displaced with respect to the gallium oxide substrate 10, unlike the upper platform 120.

[0043] like Figure 1 As shown, the manufacturing method of the gallium oxide substrate includes performing secondary single-side grinding (S2) on the gallium oxide substrate. In the secondary single-side grinding (S2), similar to the primary single-side grinding (S1), the first main surface 11 of the gallium oxide substrate 10 is pressed against the lower grinding pad 112 and is ground flat by the lower grinding pad 112 and the grinding slurry 140.

[0044] In the secondary single-side grinding (S2), particles with a smaller D50 and a smaller Mohs hardness (i.e., softer) than those in the primary single-side grinding (S1) can be used. As particles, for example, silica gel is used. On the other hand, since the second main surface 12 of the gallium oxide substrate 10 is fixed to the lower surface 121 of the upper platform 120, the concavoconvexity of the lower surface 121 is transferred to the second main surface 12.

[0045] In addition, as described above, although the upper surface 111 of the lower platform 110 has the same unevenness as the lower surface 121 of the upper platform 120, the unevenness is hardly transferred to the first main surface 11 of the gallium oxide substrate 10. This is because the lower platform 110 is relatively displaced with respect to the gallium oxide substrate 10, unlike the upper platform 120.

[0046] However, since only the first main surface 11 is ground in the first single-side grinding (S1) and the second single-side grinding (S2), residual stress difference is generated between the first main surface 11 and the second main surface 12 after grinding. As a result, warping occurs due to the Tyman effect. In addition, if the second main surface 12 of the gallium oxide substrate 10 is removed from the upper platform 120 and is fully adsorbed relative to the flat chuck surface, the first main surface 11 is deformed into the same shape as the lower surface 121 of the upper platform 120, and the concavity and convexity of the lower surface 121 appear on the first main surface 11.

[0047] Therefore, if Figure 1 As shown, the method for manufacturing a gallium oxide substrate includes double-sided grinding (S3) of the gallium oxide substrate. The double-sided grinding (S3) is different from the single-sided grinding (S1) and the double-sided grinding (S2), and includes grinding the first main surface 11 and the second main surface 12 at the same time.

[0048] Figure 4 It means implementation Figure 1 A perspective view of an example of a double-side polishing apparatus for double-side polishing. Figure 5 It means implementation Figure 1 A cross-sectional view of an example of a double-sided polishing device for double-sided polishing. The double-sided polishing device 200 includes a lower platform 210, an upper platform 220, a planetary carrier 230, a sun gear 240, and an internal gear 250. The lower platform 210 is configured horizontally, and a lower polishing pad 212 is attached to an upper surface 211 of the lower platform 210. The upper platform 220 is configured horizontally, and an upper polishing pad 222 is attached to a lower surface 221 of the upper platform 220. The planetary carrier 230 holds the gallium oxide substrate 10 horizontally between the lower platform 210 and the upper platform 220. The planetary carrier 230 is configured on the radially outer side of the sun gear 240 and on the radially inner side of the internal gear 250. The sun gear 240 and the internal gear 250 are configured concentrically and mesh with the outer peripheral gear 231 of the planetary carrier 230.

[0049] The double-side polishing device 200 is, for example, a 4-way type, and the lower platform 210, the upper platform 220, the sun gear 240, and the internal gear 250 rotate around the same vertical rotation center line. While the lower platform 210 and the upper platform 220 rotate in opposite directions, the lower polishing pad 212 is pressed against the lower surface of the gallium oxide substrate 10, and the upper polishing pad 222 is pressed against the upper surface of the gallium oxide substrate 10. In addition, at least one of the lower platform 210 and the upper platform 220 supplies polishing slurry to the gallium oxide substrate 10. The polishing slurry is supplied between the gallium oxide substrate 10 and the lower polishing pad 212 to polish the lower surface of the gallium oxide substrate 10. In addition, the polishing slurry is supplied between the gallium oxide substrate 10 and the upper polishing pad 222 to polish the upper surface of the gallium oxide substrate 10.

[0050] For example, the lower platform 210, the sun gear 240, and the internal gear 250 rotate in the same direction when viewed from above. Their rotation direction is opposite to the rotation direction of the upper platform 220. The planetary carrier 230 rotates while revolving. The revolving direction of the planetary carrier 230 is the same direction as the rotation directions of the sun gear 240 and the internal gear 250. On the other hand, the rotation direction of the planetary carrier 230 is determined by the product of the rotation speed of the sun gear 240 and the pitch circle diameter, and the product of the rotation speed of the internal gear 250 and the pitch circle diameter. If the product of the rotation speed of the internal gear 250 and the pitch circle diameter is greater than the product of the rotation speed of the sun gear 240 and the pitch circle diameter, the rotation direction of the planetary carrier 230 and the revolving direction of the planetary carrier 230 become the same direction. On the other hand, if the product of the rotation speed and the pitch circle diameter of internal gear 250 is smaller than the product of the rotation speed and the pitch circle diameter of sun gear 240 , the rotation direction of planetary carrier 230 and the revolution direction of planetary carrier 230 become opposite directions.

[0051] In addition, the double-side polishing device 200 may be a 3-way method or a 2-way method. The 3-way method may be, for example, any of the following methods: (1) the internal gear 250 is fixed, and the lower platform 210, the upper platform 220, and the sun gear 240 rotate; (2) the upper platform 220 is fixed, and the lower platform 210, the sun gear 240, and the internal gear 250 rotate. In addition, the 2-way method may be, for example, a method in which the lower platform 210 and the upper platform 220 are fixed, and the sun gear 240 and the internal gear 250 rotate.

[0052] The planetary carrier 230, for example, keeps the gallium oxide substrate 10 horizontal by making the first main surface 11 of the gallium oxide substrate 10 face downward. Alternatively, the planetary carrier 230 can keep the gallium oxide substrate 10 horizontal by making the first main surface 11 of the gallium oxide substrate 10 face upward. In either case, the first main surface 11 and the second main surface 12 of the gallium oxide substrate 10 are polished at the same time.

[0053] In the double-side grinding (S3), unlike the primary single-side grinding (S1) and the secondary single-side grinding (S2), the first main surface 11 and the second main surface 12 are ground at the same time, so that the residual stress difference between the first main surface 11 and the second main surface 12 after grinding can be reduced. As a result, the warpage caused by the Tyman effect can be reduced.

[0054] The warpage caused by the Twyman effect is evaluated by a first maximum height difference (PV1) described later. Figure 6 1 is a side view showing the state of the gallium oxide substrate when measuring the first maximum height difference (PV1). Figure 6 As shown in FIG. 1 , the first maximum height difference (PV1) is measured in a state where the second main surface 12 is placed opposite to the horizontal flat surface 20 so that the gallium oxide substrate 10 is not deformed. Figure 6 In the example, the xy plane including the mutually orthogonal x-axis and y-axis is the least square plane of the first main surface 11. The least square plane of the first main surface 11 refers to a plane obtained by fitting the first main surface 11 by the least square method. Figure 6 , a z-axis perpendicular to the x-axis and the y-axis is set to pass through the center of the first major surface 11 .

[0055] The measured data z0 (r, θ) of the height difference of the first main surface 11 with the least square plane of the first main surface 11 as the reference plane 13 is fitted by z (r, θ) of the following equation (1).

[0056] [Formula 1]

[0057]

[0058] [Formula 2]

[0059]

[0060] [Formula 3]

[0061]

[0062] [Formula 4]

[0063]

[0064] [Formula 5]

[0065]

[0066] In the above equations (1) to (5), (r, θ) is the polar coordinate on the reference plane 13, n is a natural number greater than or equal to 0 and less than or equal to k, k is 16, when n is an even number, m is only an even number in the range of -n to +n, when n is an odd number, m is only an odd number in the range of -n to +n, j is an index representing a combination of n and k, and a nm It is a coefficient. As can be seen from the above formula (4), as a method of expressing the combination of two indices n and m with one index j, a notation based on a band (Fringe) is used. The above formula (2) is a Zernike polynomial. Zernike polynomials are orthogonal polynomials, so the coefficient a nm It can be obtained by the above formula (5).

[0067] Figure 7 is the z representing j=1 (n=0, m=0), j=2 (n=1, m=1), j=4 (n=2, m=0), j=9 (n=4, m=0) nm Graph of (r, θ).

[0068] like Figure 7 The solid line shows that z with j = 1 nm (r, θ) is an offset plane parallel to the xy plane. nm (r, θ) depends neither on r nor on θ.

[0069] like Figure 7 The dashed line shows that z with j = 2 nm (r, θ) is an inclined plane obtained by rotating the xy plane around the y axis. nm (r, θ) is an inclined plane obtained by rotating the xy plane around the x-axis.

[0070] like Figure 7 The dotted line shows that z with j = 4 nm (r, θ) is a curved surface obtained by rotating a quadratic curve symmetrical about the z axis on the xz plane by 180° around the z axis. nm (r, θ) depends only on r and not on θ.

[0071] like Figure 7 As shown by the double-dotted line, z with j=9 nm (r, θ) is a curved surface obtained by rotating a quartic curve symmetrical about the z axis on the xz plane by 180° around the z axis. nm (r, θ) depends only on r and not on θ.

[0072] j is the square of a natural number (e.g. 4, 9, 16, 25, 36, 49, 64, 81, etc.) nm (r, θ) depends only on r and not on θ. In addition, z with j = 1 (n = 0, m = 0) nm As described above, (r, θ) depends on neither r nor θ.

[0073] The warpage caused by the Tyman effect is caused by the residual stress difference between the first main surface 11 and the second main surface 12. The residual stress difference depends only on r and does not depend on θ.

[0074] Therefore, the warping caused by the Thyman effect is reduced by changing j to 4, 9, 16, 25, 36, 49, 64, 81. nm z nm The first maximum height difference (PV1) of the component obtained by adding (r, θ) is evaluated. The first maximum height difference (PV1) refers to the height difference between the highest point relative to the reference plane 13 and the lowest point relative to the reference plane 13. The smaller the warpage caused by the Tyman effect, the smaller the first maximum height difference (PV1).

[0075] In addition, j is greater than 81 a nm znm (r, θ) has almost no influence on the unevenness of first major surface 11 and is therefore ignored for the sake of calculation simplification.

[0076] In the double-sided grinding (S3), unlike the first single-sided grinding (S1) and the second single-sided grinding (S2), the first main surface 11 and the second main surface 12 are ground simultaneously, so that the warpage caused by the Thyman effect can be reduced as described above. As a result, the value (PV1 / D) obtained by dividing the first maximum height difference (PV1) by the diameter (D) of the first main surface 11 can be reduced to 0.39×10 －4 In addition, the first maximum height difference (PV1) can be reduced to less than 2 μm. In addition, PV1 / D is a dimensionless quantity, and the value of PV1 / D is “10 －4 ” is equivalent to “μm / cm”.

[0077] As mentioned above, PV1 / D is, for example, 0.39×10 －4 Below. If PV1 / D is 0.39×10 －4 The following figure shows that the warpage caused by the Tyman effect can be reduced, so the flatness of the gallium oxide substrate 10 can be improved, and further, the exposure pattern can be transferred to the gallium oxide substrate 10 with high accuracy. PV1 / D is preferably 0.2×10 －4 Below, more preferably 0.1×10 －4 From the viewpoint of productivity, PV1 / D is preferably 0.02×10 －4 above.

[0078] As described above, PV1 is, for example, 2 μm or less. If PV1 is 2 μm or less, the warpage caused by the Tyman effect can be reduced, thereby improving the flatness of the gallium oxide substrate 10, and further, the exposure pattern can be transferred to the gallium oxide substrate 10 with high precision. PV1 is preferably 1 μm or less, and more preferably 0.5 μm or less. In addition, from the perspective of productivity, PV1 is preferably 0.1 μm or more.

[0079] D is not particularly limited, and is, for example, 5 cm to 31 cm inclusive. D is preferably 10 cm to 21 cm inclusive, and more preferably 12 cm to 15 cm inclusive.

[0080] However, in the double-side polishing (S3), unlike the first single-side polishing (S1) and the second single-side polishing (S2), not only the lower surface plate 210 but also the upper surface plate 220 is relatively displaced with respect to the gallium oxide substrate 10. As a result, it is possible to suppress the transfer of the concavities and convexities of the lower surface 221 of the upper surface plate 220 to the upper surface of the gallium oxide substrate 10, and it is possible to grind the upper surface of the gallium oxide substrate 10 in parallel with the lower surface of the gallium oxide substrate 10. Therefore, when the second main surface 12 of the gallium oxide substrate 10 is completely adsorbed relative to the flat chuck surface 30, it is possible to suppress the concavities and convexities of the lower surface 221 of the upper surface plate 220 from appearing on the first main surface 11.

[0081] The shape transfer of the upper surface plate 220 to the gallium oxide substrate 10 is evaluated by the second maximum height difference (PV2) described later. Figure 8 1 is a side view showing the state of the gallium oxide substrate when measuring the second maximum height difference (PV2). Figure 8 As shown in FIG. 1 , the second maximum height difference (PV2) is measured in a state where the second main surface 12 and the flat chuck surface 30 are facing each other and the whole surface is adsorbed. The adsorption is, for example, vacuum adsorption, and the chuck surface 30 is formed of a porous body. Figure 8 In the example, the xy plane including the mutually orthogonal x-axis and y-axis is the least square plane of the first major surface 11. Figure 8 , a z-axis perpendicular to the x-axis and the y-axis is set to pass through the center of the first major surface 11 .

[0082] The measured data z0(r, θ) of the height difference of the first main surface 11 with the least square plane of the first main surface 11 as the reference plane 13 is fitted by z(r, θ) in (1) above. nm As described above, (r, θ) are both flat surfaces and therefore are insignificant components when measuring the second maximum height difference (PV2).

[0083] Therefore, the upper platform 220 transfers the shape of the gallium oxide substrate 10 by transferring all a values ​​where j is greater than or equal to 4 and less than or equal to 81. nm z nm The second maximum height difference (PV2) of the component obtained by adding (r, θ) is evaluated. The second maximum height difference (PV2) refers to the height difference between the highest point relative to the reference plane 13 and the lowest point relative to the reference plane 13. The smaller the shape transfer of the upper platform 220 relative to the gallium oxide substrate 10, the smaller the second maximum height difference (PV2).

[0084] In addition, j is greater than 81 a nm z nm (r, θ) has almost no influence on the unevenness of first major surface 11 and is therefore ignored for the sake of calculation simplification.

[0085] In the double-side polishing (S3), unlike the first single-side polishing (S1) and the second single-side polishing (S2), the first main surface 11 and the second main surface 12 are polished at the same time, so as described above, the shape transfer of the upper platform 220 to the gallium oxide substrate 10 can be suppressed. As a result, the value (PV2 / D) obtained by dividing the second maximum height difference (PV2) by the diameter (D) of the first main surface 11 can be reduced to 0.59×10 －4 In addition, the second maximum height difference (PV2) can be reduced to less than 3 μm. In addition, PV2 / D is a dimensionless quantity, and the value of PV2 / D is “10 －4 ” is equivalent to “μm / cm”.

[0086] As mentioned above, PV2 / D is, for example, 0.59×10 －4 Below. If PV2 / D is 0.59×10 －4 The shape transfer of the upper platform 220 to the gallium oxide substrate 10 can be suppressed, thereby improving the flatness of the gallium oxide substrate 10 and further accurately transferring the exposure pattern to the gallium oxide substrate 10. PV2 / D is preferably 0.2×10 －4 Below, more preferably 0.1×10 －4 From the viewpoint of productivity, PV2 / D is preferably 0.02×10 －4 above.

[0087] As described above, PV2 is, for example, 3 μm or less. If PV2 is 3 μm or less, the shape transfer of the upper platform 220 relative to the gallium oxide substrate 10 can be suppressed, so that the flatness of the gallium oxide substrate 10 can be improved, and further, the exposure pattern can be transferred to the gallium oxide substrate 10 with high precision. PV2 is preferably 1 μm or less, and more preferably 0.5 μm or less. In addition, from the viewpoint of productivity, PV2 is preferably 0.1 μm or more.

[0088] The double-side polishing (S3) includes polishing the first main surface 11 and the second main surface 12 of the gallium oxide substrate 10 facing opposite directions simultaneously using a polishing slurry containing particles having a Mohs hardness of 7 or less. When the Mohs hardness is 7 or less, the particles are soft, so the occurrence of damage to the gallium oxide substrate 10 can be suppressed, and the cracking of the gallium oxide substrate 10 can be suppressed. The Mohs hardness is preferably 6 or less, and more preferably 5 or less. From the viewpoint of polishing speed, the Mohs hardness is preferably 2 or more.

[0089] As particles with a Mohs hardness of 7 or less, for example, silica gel is used. The Mohs hardness of silica gel is 7. In addition, the material of particles with a Mohs hardness of 7 or less is not limited to SiO2, and may also be TiO2, ZrO2, Fe2O3, ZnO or MnO2. The Mohs hardness of TiO2 is 6, the Mohs hardness of ZrO2 is 6.5, the Mohs hardness of Fe2O3 is 6, the Mohs hardness of ZnO is 4.5, and the Mohs hardness of MnO2 is 3. The polishing slurry used in double-sided polishing (S3) does not contain particles with a Mohs hardness exceeding 7, and may contain two or more particles with a Mohs hardness of 7 or less.

[0090] In the double-sided polishing (S3), the D50 of the particles contained in the polishing slurry is, for example, 1 μm or less. If the D50 is 1 μm or less, the particles are small, so it is possible to suppress the situation where excessive stress acts locally on the gallium oxide substrate 10, thereby suppressing the cracking of the gallium oxide substrate 10. The D50 is preferably 0.7 μm or less, and more preferably 0.5 μm or less. From the viewpoint of polishing speed, the D50 is preferably 0.01 μm or more.

[0091] During more than 50% of the first half of the double-sided grinding (S3), the grinding pressure is, for example, 9.8 kPa or less. In the first half of the double-sided grinding (S3), since the first main surface 11 and the second main surface 12 are not sufficiently flattened, the unevenness is large and stress concentration is easily generated. If the grinding pressure is 9.8 kPa or less during more than 50% of the first half of the double-sided grinding (S3), it is possible to suppress the situation where excessive stress acts locally on the gallium oxide substrate 10, thereby suppressing the cracking of the gallium oxide substrate 10. During more than 50% of the first half of the double-sided grinding (S3), the grinding pressure is preferably 8.8 kPa or less, and more preferably 7.8 kPa or less. In addition, from the viewpoint of grinding speed, during more than 50% of the first half of the double-sided grinding (S3), the grinding pressure is preferably 3 kPa or more.

[0092] In addition, during the whole period of double-sided grinding (S3), grinding pressure can also be constant. In addition, in double-sided grinding (S3), due to the passage of time, the first main surface 11 and the second main surface 12 are gradually flattened, and the concavoconvexity decreases, so in order to improve the grinding speed, the grinding pressure can also be made to become larger in stages.

[0093] In addition, the method for manufacturing the gallium oxide substrate is not limited to Figure 1 The method shown in the figure may include double-sided grinding (S3). In addition, the method for manufacturing the gallium oxide substrate may also include Figure 1Treatments other than the treatments shown may include, for example, cleaning for washing away deposits (e.g., particles) on the gallium oxide substrate 10. Cleaning is performed, for example, between the first single-side polishing (S1) and the second single-side polishing (S2), and between the second single-side polishing (S2) and the double-side polishing (S3).

[0094] Example

[0095] Examples and comparative examples are described below. Among Examples 1 to 7 described below, Examples 1 to 3 are examples, and Examples 4 to 7 are comparative examples.

[0096] [Example 1 ~ Example 3]

[0097] In Examples 1 to 3, a β-Ga2O3 single crystal substrate with a diameter of 50.8 mm and a thickness of 0.7 mm was Figure 1 As shown, the first single-side polishing ( S1 ), the second single-side polishing ( S2 ), and the double-side polishing ( S3 ) are performed under the same conditions.

[0098] In a single-side grinding (S1), Figure 2 The single-side polishing device 100 shown polishes the (001) surface of a β-Ga2O3 single crystal substrate. The polishing is performed using a lower platform 110 made of tin and diamond particles with a particle size of 0.5 μm. In a single-side polishing (S1), the substrate is pressed against the lower platform 110 for polishing without using the lower polishing pad 112.

[0099] In the secondary single-side grinding (S2), Figure 2 The single-side polishing device 100 shown polishes the (001) surface of a β-Ga2O3 single crystal substrate. In the secondary single-side polishing (S2), unlike the primary single-side polishing (S1), a lower polishing pad 112 is used. In the secondary single-side polishing (S2), a lower polishing pad 112 made of polyurethane and colloidal silica particles with a particle size of 0.05 μm are used for polishing.

[0100] In double-sided grinding (S3), Figure 4The double-sided polishing device 200 shown polishes the (001) surface and (00-1) surface of the β-Ga2O3 single crystal substrate at the same time. The double-sided polishing device 200 is a product name DSM9B manufactured by SPEEDFAM, and the lower polishing pad 212 and the upper polishing pad 222 are a product name N7512 manufactured by FILWEL. The polishing slurry is a slurry containing 20% ​​by mass of colloidal silica and 80% by mass of water, and the D50 of the colloidal silica is 0.05 μm. During the entire period of double-sided polishing (S3), the polishing pressure is 9.8 kPa, the rotation speed of the lower platform 210 is 40 rpm, the rotation speed of the upper platform 220 is 14 rpm, the rotation speed of the sun gear 240 is 9 rpm, and the rotation speed of the internal gear 250 is 15 rpm. The pitch circle diameter of the sun gear 240 is 207.4 mm, and the pitch circle diameter of the internal gear 250 is 664.6 mm.

[0101] [Example 4~Example 6]

[0102] In Examples 4 to 6, a β-Ga2O3 single crystal substrate having a diameter of 50.8 mm and a thickness of 0.7 mm was subjected to only one single-side polishing (S1) and two single-side polishings (S2) under the same conditions as in Examples 1 to 3. In Examples 4 to 6, double-side polishing (S3) was not performed.

[0103] [Example 7]

[0104] In Example 7, except that diamond particles with a particle size of 0.5 μm were used as particles for double-side polishing (S3), and a polishing pad made of epoxy resin was used as a polishing pad for diamond particles, the first single-side polishing (S1), the second single-side polishing (S2), and the double-side polishing (S3) were performed under the same conditions as in Examples 1 to 3. As a result, the gallium oxide substrate 10 was cracked during the double-side polishing (S3).

[0105] [Grinding results]

[0106] For the first maximum height difference (PV1) of the (001) plane as the first main surface 11, as Figure 6 As shown, the measurement was performed in a state where the (00-1) plane as the second main surface 12 was placed opposite to the horizontal flat surface 20 so that the gallium oxide substrate 10 would not be deformed. As a measuring device, a product name PF-60 manufactured by Mitaka Koki was used.

[0107] For the second maximum height difference (PV2) of the (001) plane as the first main surface 11, as Figure 8 As shown, the measurement was performed in a state where the (00-1) plane as the second main surface 12 was facing the flat chuck surface 30 and the entire surface was sucked. As a measuring device, a product name PF-60 manufactured by Mitaka Koki was used.

[0108] Table 1 shows the polishing results of Examples 1 to 6. In Example 7, as described above, the gallium oxide substrate 10 was cracked during the double-side polishing (S3).

[0109] [Table 1]

[0110]

[0111] As can be seen from Table 1, Examples 1 to 3 are different from Examples 4 to 6 in that double-side polishing (S3) is performed, so PV1 / D is 0.39×10 －4 PV1 is 2 μm or less. It is found that the warpage caused by the Tyanman effect can be reduced by double-side polishing ( S3 ).

[0112] In addition, it can be seen from Table 1 that Examples 1 to 3 are different from Examples 4 to 6 in that double-side polishing (S3) is performed, so PV2 / D is 0.59×10 －4 Hereinafter, PV2 is 3 μm or less. It is found that the double-side polishing ( S3 ) can suppress the transfer of the shape of the upper surface plate 220 to the gallium oxide substrate 10 .

[0113] In Examples 1 to 3, the Mohs hardness of the particles used in the double-side polishing (S3) was 7 or less, the D50 of the particles was 1 μm or less, and the polishing pressure was 9.8 kPa or less during more than 50% of the first half, so the gallium oxide substrate 10 was not broken during the double-side polishing. On the other hand, in Example 7, since the Mohs hardness of the particles used in the double-side polishing (S3) exceeded 7, the gallium oxide substrate 10 was broken during the double-side polishing.

[0114] In addition, in the single-side grinding (S1), the gallium oxide substrate 10 was not broken even though grinding was performed using diamond particles with a Mohs hardness of 10. The gallium oxide substrate 10 is less likely to be broken in single-side grinding than in double-side grinding, and this is presumably the reason why Patent Document 1 adopts single-side grinding.

[0115] The above describes the embodiments of the gallium oxide substrate and the method for manufacturing the gallium oxide substrate involved in the present disclosure, but the present disclosure is not limited to the above embodiments, etc. Various changes, corrections, substitutions, additions, deletions and combinations can be made within the scope of the claims. These also fall within the technical scope of the present disclosure.

[0116] This application claims priority based on Japanese Patent Application No. 2019-073548 filed with the Japan Patent Office on April 8, 2019, and all the contents of Japanese Patent Application No. 2019-073548 are incorporated herein by reference.

[0117] Description of Reference Numerals

[0118] 10 ... gallium oxide substrate; 11 ... first main surface; 12 ... second main surface.

Claims

1. A method for manufacturing a gallium oxide substrate, comprising: providing a first main surface and a second main surface facing opposite to the first main surface, wherein the first main surface is a {001} plane or has a desired off-angle relative to the {001} plane; The method for manufacturing the gallium oxide substrate comprises: The first main surface is ground once and then ground twice, and then the first main surface and the second main surface are ground simultaneously, In the simultaneous polishing, the first main surface and the second main surface of the gallium oxide substrate facing opposite directions are polished in parallel using a polishing slurry containing particles having a Mohs hardness of 7 or less.

2. The method for manufacturing a gallium oxide substrate according to claim 1, wherein: The particles contained in the polishing slurry have a 50% particle size of 1 μm or less in terms of cumulative percentage on a volume basis in a particle size distribution measured by a dynamic light scattering method.

3. The method for manufacturing a gallium oxide substrate according to claim 1 or 2, wherein: During 50% or more of the first half of the period in which the first main surface and the second main surface are polished simultaneously, the polishing pressure is 9.8 kPa or less.

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