阅读说明：本技术 氧化镓基板以及氧化镓基板的制造方法 (Gallium oxide substrate and method for manufacturing gallium oxide substrate ) 是由 平林佑介 于 2020-03-18 设计创作，主要内容包括：本发明提供氧化镓基板,具有第一主表面、和与上述第一主表面相反朝向的第二主表面,若由说明书中的式(1)的z(r,θ)拟合以上述第一主表面的最小二乘平面为基准面的上述第一主表面的高低差的测定数据z-(0)(r,θ),则在将上述第二主表面与水平的平坦面相对地进行了载置时的、j为4、9、16、25、36、49、64、81的全部的a-(nm)z-(nm)(r,θ)相加而得的成分的第一最大高低差(PV1)除以上述第一主表面的直径(D)而得到的值(PV1/D)为0.39×10～(－4)以下,在将上述第二主表面与平坦的卡盘面相对地进行了全面吸附时的、j为4以上且81以下的全部的a-(nm)z-(nm)(r,θ)相加而得的成分的第二最大高低差(PV2)除以上述第一主表面的直径(D)而得到的值(PV2/D)为0.59×10～(－4)以下。(The invention provides a gallium oxide substrate, comprising a first main surface and a second main surface opposite to the first main surface, wherein measurement data z of height difference of the first main surface using a least square plane of the first main surface as a reference plane is fitted by z (r, theta) of formula (1) in the specification 0 (r, θ) when the second main surface is placed so as to face the 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, theta) by the diameter (D) of the first main surface is 0.39 x 10 －4 The second step is described belowA has j of 4 to 81 inclusive when the main surface is opposed to the flat chuck surface and the entire surface is sucked nm z nm The value (PV2/D) obtained by dividing the second maximum height difference (PV2) of the component obtained by adding (r, theta) by the diameter (D) of the first main surface is 0.59 x 10 －4 The following.)

1. A gallium oxide substrate, wherein,

having a first major surface and a second major surface oppositely facing the first major surface,

fitting measurement data z of a height difference of the first main surface with a least square plane of the first main surface as a reference plane by z (r, theta) of the following formula (1)₀(r，θ)，

When the second main surface is placed so as to face the horizontal flat surface, a is set to be all of j 4, 9, 16, 25, 36, 49, 64 and 81_nmz_nmA value (PV1/D) obtained by dividing a first maximum height difference (PV1) of a component obtained by adding (r, theta) by a diameter (D) of the first main surface is 0.39 x 10^－4In the following, the following description is given,

a is 4 to 81 inclusive, when the second main surface is adsorbed on the entire surface of the flat chuck surface in a manner to face the flat chuck surface_nmz_nmA value (PV2/D) obtained by dividing a second maximum height difference (PV2) of the component obtained by adding (r, theta) by a diameter (D) of the first main surface is 0.59 x 10^－4In the following, the following description is given,

[ formula 1]

[ formula 2]

[ formula 3]

[ formula 4]

[ formula 5]

In the above expressions (1) to (5), (r, θ) is a polar coordinate on the reference plane, n is a natural number of 0 or more and k or less, k is 16, m is only an even number ranging from-n to + n in the case where n is an even number, m is only an odd number ranging from-n to + n in the case where n is an odd number, j is an index representing a combination of n and k, a_nmIs a coefficient.

2. The gallium oxide substrate according to claim 1, wherein,

the first maximum height difference (PV1) is 2 [ mu ] m or less,

the second maximum height difference (PV2) is 3 [ mu ] m or less.

3. A method for manufacturing a gallium oxide substrate, comprising:

a first main surface and a second main surface of a gallium oxide substrate, which are opposite to each other, are simultaneously polished with a polishing slurry containing particles having a Moss hardness of 7 or less.

4. The method for producing a gallium oxide substrate according to claim 3, wherein,

the polishing slurry contains particles having a volume-based cumulative percentage of 50% particle diameter of 1 [ mu ] m or less in the particle diameter distribution measured by a dynamic light scattering method.

5. The method for producing a gallium oxide substrate according to claim 3 or 4,

a polishing pressure is 9.8kPa or less during 50% or more of a first half of a period of simultaneously polishing the first main surface and the second main surface.

Technical Field

The present disclosure relates to a gallium oxide substrate and a method of manufacturing the gallium oxide substrate.

Background

In recent years, a compound semiconductor substrate has been proposed as a substitute for a silicon semiconductor substrate. Examples of the compound semiconductor include silicon carbide, gallium nitride, and gallium oxide. The compound semiconductor has an advantage of having a large band gap compared with a silicon semiconductor. The compound semiconductor substrate is polished, and an epitaxial film is formed on the polished surface.

Patent document 1 describes a method for producing a gallium oxide substrate. The method includes polishing only one surface of the gallium oxide substrate with a slurry containing colloidal silica. The problem of patent document 1 is to improve the shape of a gallium oxide substrate whose crystal system is a monoclinic system having poor symmetry and whose cleavage property is very strong.

Patent document 1: japanese patent laid-open publication No. 2016-13932

A single-side polishing apparatus generally has a lower platen, an upper platen, and a nozzle. The lower platen is disposed horizontally, and a polishing pad is attached to an upper surface of the lower platen. The upper platform is configured to be horizontal, and a gallium oxide substrate is fixed on 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 platen holds the gallium oxide substrate horizontally, and presses the first main surface of the gallium oxide substrate against the polishing pad. The lower stage rotates around the vertical rotation center line. The upper platform passively rotates along 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, and the first main surface of the gallium oxide substrate is polished flat. Since the second main surface of the gallium oxide substrate is fixed to the lower surface of the upper stage, the irregularities of the lower surface of the upper stage are transferred to the second main surface.

Since the single-side polishing apparatus 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 tayman Effect (Twyman Effect). When the second main surface of the gallium oxide substrate is removed from the upper stage and is placed opposite to the flat chuck surface to be adsorbed on the entire surface, the first main surface is deformed into the same shape as the lower surface of the upper stage, and the irregularities of the lower surface of the upper stage appear on the first main surface.

Conventionally, the flatness of a gallium oxide substrate is poor, and the accuracy of transferring an exposure pattern to the gallium oxide substrate is poor.

Disclosure of Invention

An aspect of the present disclosure provides a technique capable of improving the flatness of a gallium oxide substrate and transferring an exposure pattern to the gallium oxide substrate with high accuracy.

A gallium oxide substrate according to one aspect of the present disclosure has a first main surface and a second main surface facing opposite to the first main surface,

fitting measurement data z of a height difference of the first main surface with a least square plane of the first main surface as a reference plane by z (r, theta) of the following formula (1)₀(r，θ)，

When the second main surface is placed so as to face the horizontal flat surface, a is set to be all of j 4, 9, 16, 25, 36, 49, 64 and 81_nmz_nmThe value (PV1/D) obtained by dividing the first maximum height difference (PV1) of the component obtained by adding (r, theta) by the diameter (D) of the first main surface is 0.39 x 10^－4In the following, the following description is given,

a is 4 to 81 inclusive, when the second main surface is adsorbed on the entire surface of the flat chuck surface in a manner to face the flat chuck surface_nmz_nmThe value (PV2/D) obtained by dividing the second maximum height difference (PV2) of the component obtained by adding (r, theta) by the diameter (D) of the first main surface is 0.59 x 10^－4The following.

[ formula 1]

[ formula 2]

[ formula 3]

[ formula 4]

[ formula 5]

In the above expressions (1) to (5), (r, θ) is a polar coordinate on the reference plane, n is a natural number of 0 or more and k or less, k is 16, m is an even number only ranging from-n to + n in the case where n is an even number, m is an odd number only ranging from-n to + n in the case where n is an odd number, j is an index representing a combination of n and k, a_nmIs a coefficient.

According to one embodiment 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.

Drawings

Fig. 1 is a flowchart illustrating a method for manufacturing a gallium oxide substrate according to an embodiment.

Fig. 2 is a perspective view showing an example of a single-side polishing apparatus for performing the single-side polishing in fig. 1.

Fig. 3 is a cross-sectional view showing an example of a single-side polishing apparatus for performing the single-side polishing of fig. 1.

Fig. 4 is a perspective view showing an example of a double-side polishing apparatus for performing double-side polishing in fig. 1.

Fig. 5 is a cross-sectional view showing an example of a double-side polishing apparatus for performing double-side polishing in fig. 1.

Fig. 6 is a cross-sectional view showing an example of the state of the gallium oxide substrate when the first maximum level difference (PV1) is measured.

Fig. 7 shows z in each case where j is 1(n is 0, m is 0), j is 2(n is 1, m is 1), j is 4(n is 2, m is 0), and j is 9(n is 4, m is 0)_nm(r, θ).

Fig. 8 is a cross-sectional view showing an example of the state of the gallium oxide substrate when the second maximum level difference (PV2) is measured.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the crystallographic descriptions in this specification, the individual orientation is represented by [ ], the collective orientation is represented by < > the individual plane, and the collective plane is represented by { }. The negative crystallographic index is usually expressed by a bar above the number, but in the present specification, the negative crystallographic index is expressed by a minus sign before the number.

Fig. 1 is a flowchart illustrating a method for manufacturing a gallium oxide substrate according to an embodiment. As shown in fig. 1, the method for manufacturing a gallium oxide substrate includes performing one-side polishing on the gallium oxide substrate (S1). As the gallium oxide substrate, for example, β -Ga is used in advance₂O₃The single crystal is cut into a plate shape by a wire saw or the like, and then ground into a substrate having a predetermined thickness by a grinding device or the like. The gallium oxide substrate may or may not contain a dopant. As the dopant, for example, Si, Sn, Al, In, or the like is used.

Fig. 2 is a perspective view showing an example of a single-side polishing apparatus for performing the single-side polishing in fig. 1. Fig. 3 is a cross-sectional view showing an example of a single-side polishing apparatus for performing the single-side polishing of fig. 1. In fig. 3, the unevenness of the lower surface 121 of the upper stage 120 is exaggeratedly shown. The single-side polishing apparatus for performing the secondary single-side polishing (S2) in fig. 1 is the same as the single-side polishing apparatus 100 shown in fig. 2 and 3, and therefore, illustration thereof is omitted.

The single-side polishing apparatus 100 includes a lower platen 110, an upper platen 120, and a nozzle 130. The lower platen 110 is disposed horizontally, and a lower polishing pad 112 is attached to an upper surface 111 of the lower platen 110. The upper stage 120 is disposed horizontally, and a gallium oxide substrate 10 is fixed to a lower surface 121 of the upper stage 120. The upper platen 120 holds the gallium oxide substrate 10 horizontally, and presses the gallium oxide substrate 10 against the lower polishing pad 112. In addition, the lower polishing pad 112 may not be provided, and in this case, the upper platen 120 presses the gallium oxide substrate 10 against the lower platen 110. The upper surface plate 120 has a smaller diameter than the lower surface plate 110, and the upper surface plate 120 is disposed radially outward of the rotation center line C1 of the lower surface plate 110. The rotation center line C2 of the upper stage 120 is arranged to be offset in parallel with the rotation center line C1 of the lower stage 110. The lower surface plate 110 rotates about a vertical rotation center line C1. The upper stage 120 passively rotates along with the rotation of the lower stage 110. The upper stage 120 and the lower stage 110 may be independently rotated or may be rotated by respective rotation motors.

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 or the like, not shown, indicating the crystal orientation of gallium oxide is formed on the outer periphery of the gallium oxide substrate 10. Instead of the notches, orientation flat may also 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 the (001) plane or the (00-1) plane.

The first main surface 11 may be a crystal plane other than the {001} plane. The first main surface 11 may have a so-called off angle (off angle) with respect to a predetermined crystal plane. The off-angle improves the crystallinity of the epitaxial film formed on the polished first main surface 11.

The nozzle 130 supplies the polishing slurry 140 to the lower polishing pad 112. The abrasive slurry 140 contains, for example, particles and water. The particles are the dispersoids and water is the dispersion medium. Further, the dispersion medium may be an organic solvent. The polishing slurry 140 is supplied between the gallium oxide substrate 10 and the lower polishing pad 112, and the lower surface of the gallium oxide substrate 10 is polished flat.

In the primary single-side polishing (S1), for example, diamond particles are used as the particles. The Moss hardness of the diamond particles was 10. The D50 of the diamond particles is not particularly limited, and is, for example, 50 μm. "D50" refers to the 50% particle size as the cumulative percentage on a volume basis in the particle size distribution as determined by dynamic light scattering. The dynamic light scattering method is a method of measuring the particle size distribution by irradiating the slurry 140 with laser light and observing the scattered light by a photodetector.

In the first single-side polishing (S1), the first main surface 11 of the gallium oxide substrate 10 is pressed against the lower polishing pad 112, and is 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 stage 120, and thus the irregularities of the lower surface 121 thereof are transferred onto the second main surface 12.

In addition, although the upper surface 111 of the lower stage 110 also has irregularities like the lower surface 121 of the upper stage 120, the irregularities are hardly transferred to the first main surface 11 of the gallium oxide substrate 10. This is because the lower stage 110 is relatively displaced with respect to the gallium oxide substrate 10 unlike the upper stage 120.

As shown in fig. 1, the method for manufacturing a gallium oxide substrate includes performing secondary single-side polishing on the gallium oxide substrate (S2). In the secondary single-side polishing (S2), the first main surface 11 of the gallium oxide substrate 10 is pressed against the lower polishing pad 112, and is polished flat by the lower polishing pad 112 and the polishing slurry 140, as in the primary single-side polishing (S1).

In the secondary single-side polishing (S2), particles having a smaller D50 and a smaller morse hardness (i.e., being soft) than in the primary single-side polishing (S1) can be used. As the 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 stage 120, the irregularities of the lower surface 121 thereof are transferred onto the second main surface 12.

As described above, the upper surface 111 of the lower stage 110 also has irregularities as in the lower surface 121 of the upper stage 120, but the irregularities are hardly transferred to the first main surface 11 of the gallium oxide substrate 10. This is because the lower stage 110 is relatively displaced with respect to the gallium oxide substrate 10 unlike the upper stage 120.

However, since only the first main surface 11 is abraded in the first single-side abrasion (S1) and the second single-side abrasion (S2), a residual stress difference is generated in the first main surface 11 and the second main surface 12 after the abrasion. As a result, warping occurs due to the taylon effect. When the second main surface 12 of the gallium oxide substrate 10 is removed from the upper stage 120 and is placed opposite to a flat chuck surface to be overall-adsorbed, the first main surface 11 is deformed into the same shape as the lower surface 121 of the upper stage 120, and the irregularities of the lower surface 121 appear on the first main surface 11.

Therefore, as shown in fig. 1, the method for manufacturing a gallium oxide substrate includes double-side polishing the gallium oxide substrate (S3). The double-side lapping (S3) includes lapping the first main surface 11 and the second main surface 12 simultaneously, unlike the primary single-side lapping (S1) and the secondary single-side lapping (S2).

Fig. 4 is a perspective view showing an example of a double-side polishing apparatus for performing double-side polishing in fig. 1. Fig. 5 is a cross-sectional view showing an example of a double-side polishing apparatus for performing double-side polishing in fig. 1. The double-side polishing apparatus 200 includes a lower platen 210, an upper platen 220, a planetary carrier 230, a sun gear 240, and an internal gear 250. The lower platen 210 is disposed horizontally, and a lower polishing pad 212 is attached to an upper surface 211 of the lower platen 210. The upper platen 220 is disposed horizontally, and an upper polishing pad 222 is attached to a lower surface 221 of the upper platen 220. The planetary carrier 230 holds the gallium oxide substrate 10 horizontally between the lower stage 210 and the upper stage 220. The carrier 230 is disposed radially outward of the sun gear 240 and radially inward of the internal gear 250. The sun gear 240 and the internal gear 250 are arranged concentrically and mesh with the outer peripheral gear 231 of the planetary carrier 230.

The double-side polishing apparatus 200 is, for example, a 4-Way (4Way) type, and the lower platen 210, the upper platen 220, the sun gear 240, and the internal gear 250 rotate around the same vertical rotation center line. While the lower platen 210 and the upper platen 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 platen 210 and the upper platen 220 supplies the gallium oxide substrate 10 with a polishing slurry. The polishing slurry is supplied between the gallium oxide substrate 10 and the lower polishing pad 212, and the lower surface of the gallium oxide substrate 10 is polished. Further, the polishing slurry is supplied between the gallium oxide substrate 10 and the upper polishing pad 222, and the upper surface of the gallium oxide substrate 10 is polished.

For example, the lower stage 210, the sun gear 240, and the inner gear 250 rotate in the same direction when viewed from above. Their rotation direction is opposite to that of the upper stage 220. Planetary carrier 230 rotates while revolving. The revolving direction of the planetary carrier 230 is the same direction as the rotating direction 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 magnitude of the product of the rotational speed of the sun gear 240 and the pitch circle diameter and the product of the rotational speed of the internal gear 250 and the pitch circle diameter. If the product of the rotational speed and the pitch circle diameter of internal gear 250 is larger than the product of the rotational speed and the pitch circle diameter of sun gear 240, the rotation direction of carrier 230 and the revolution direction of carrier 230 are the same direction. On the other hand, if the product of the rotational speed and the pitch circle diameter of internal gear 250 is smaller than the product of the rotational speed and the pitch circle diameter of sun gear 240, the rotation direction of carrier 230 and the revolution direction of carrier 230 are opposite.

The double-side polishing apparatus 200 may be of a 3-Way (3Way) type or a 2-Way (2Way) type. The 3-way method may be, for example, any of the following methods: (1) the inner gear 250 is fixed, and the lower stage 210, the upper stage 220, and the sun gear 240 rotate; (2) the upper stage 220 is fixed and the lower stage 210, the sun gear 240, and the inner gear 250 rotate. The 2-way system is a system in which, for example, the lower stage 210 and the upper stage 220 are fixed and the sun gear 240 and the internal gear 250 rotate.

The planetary carrier 230 holds the gallium oxide substrate 10 horizontally, for example, with the first main surface 11 of the gallium oxide substrate 10 directed downward. The planetary carrier 230 may hold the gallium oxide substrate 10 horizontally with the first main surface 11 of the gallium oxide substrate 10 facing upward. In either case, the first main surface 11 and the second main surface 12 of the gallium oxide substrate 10 are polished simultaneously.

In the double-side polishing (S3), the first main surface 11 and the second main surface 12 are simultaneously polished unlike the first single-side polishing (S1) and the second single-side polishing (S2), and therefore the residual stress difference between the first main surface 11 and the second main surface 12 after polishing can be reduced. As a result, the warp due to the taylon effect can be reduced.

The warpage due to the Taeman effect is evaluated by a first maximum height difference (PV1) described later. Fig. 6 is a side view showing a state of the gallium oxide substrate when the first maximum level difference (PV1) is measured. As shown in fig. 6, the first maximum level difference (PV1) was measured in a state where the second main surface 12 was placed so as to face the horizontal flat surface 20, so that the gallium oxide substrate 10 was not deformed. In fig. 6, an xy plane containing mutually orthogonal x and y axes is a least squares plane of the first main surface 11. The least square plane of the first main surface 11 is a plane obtained by fitting the first main surface 11 by the least square method. In addition, in fig. 6, a z-axis perpendicular to the x-axis and the y-axis is set to pass through the center of the first main surface 11.

Measurement data z of height difference of first main surface 11 with least square plane of first main surface 11 as reference plane 13₀(r, θ) is fitted by z (r, θ) of the following formula (1).

[ formula 1]

[ formula 2]

[ formula 3]

[ formula 4]

[ formula 5]

In the above expressions (1) to (5), (r, θ) is a polar coordinate on the reference plane 13, n is a natural number of 0 or more and k or less, k is 16, m is an even number only ranging from-n to + n in the case where n is an even number, m is an odd number only ranging from-n to + n in the case where n is an odd number, j is an index indicating a combination of n and k, a_nmIs a coefficient. As is clear from the above formula (4), as a method for expressing a combination of two indices n and m by using one index j, a notation based on a band (Fringe) is used. The above formula (2) is a Zernike polynomial (Zernike Polynomials) which is an orthogonal polynomial, and therefore the coefficient a_nmCan be obtained by the above formula (5).

Fig. 7 shows z in each case where j is 1(n is 0, m is 0), j is 2(n is 1, m is 1), j is 4(n is 2, m is 0), and j is 9(n is 4, m is 0)_nm(r, θ).

As shown by the solid line in fig. 7, z is 1 for j_nm(r, θ) is an offset plane parallel to the xy plane. Z where j is 1_nm(r, θ) depends on neither r nor θ.

As shown by the dotted line in fig. 7, z of 2 is j_nm(r, θ) is an inclined plane rotating the xy plane about the y axis. In addition, z of j-3 (n-1, m-1)_nm(r, θ) is an inclined plane rotating the xy plane about the x axis.

As shown by the chain line in fig. 7, z is 4 for j_nmThe term (r, θ) denotes a curved surface obtained by rotating a quadratic curve on the xz plane, which is symmetrical with respect to the z axis, by 180 ° around the z axis. Z with j equal to 4_nm(r, θ) depends only on r, not on θ.

As shown by the two-dot chain line in fig. 7, z is 9 for j_nmThe term (r, θ) denotes a curved surface obtained by rotating a quartic curve on the xz plane, which is symmetrical with respect to the z axis, by 180 ° around the z axis. j is 9 z_nm(r, θ) depends only on r, not on θ.

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

The warpage caused by the taylon effect is generated by a residual stress difference of the first main surface 11 and the second main surface 12. This residual stress difference depends only on r and not on θ.

Therefore, the warpage due to the Taeman effect is caused by setting j to be a of all of 4, 9, 16, 25, 36, 49, 64, and 81_nmz_nm(r, θ) was added to obtain a first maximum height difference (PV 1). The first maximum height difference (PV1) is a height difference between a point highest with respect to the reference plane 13 and a point lowest with respect to the reference plane 13. The smaller the warpage caused by the Taeman effect, the smaller the first maximum difference in elevation (PV 1).

In addition, a with j greater than 81_nmz_nmThe (r, θ) has little influence on the unevenness of the first main surface 11, and is therefore also omitted for the sake of simplifying the calculation.

In the double-side polishing (S3), the first main surface 11 and the second main surface 12 are simultaneously polished unlike the primary single-side polishing (S1) and the secondary single-side polishing (S2), and therefore, as described above, the warp caused by the tyeman effect can be reduced. 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^－4The following. In addition, the first maximum height difference (PV1) can be reduced to 2 μm or less. Furthermore, PV1/D is a dimensionless quantity, "10" in the value of PV1/D^－4"is equivalent to" μm/cm ".

As described above, PV1/D is, for example, 0.39X 10^－4The following. If the PV1/D is 0.39X 10^－4Hereinafter, since warpage due to the taylon effect can be reduced, the flatness of the gallium oxide substrate 10 can be improved, and the exposure pattern can be transferred to the gallium oxide substrate 10 with high accuracy. PV1/D is preferably 0.2X 10^－4Hereinafter, more preferably 0.1 × 10^－4The following. From the viewpoint of productivity, PV1/D is preferableIs 0.02X 10^－4The above.

As described above, PV1 is, for example, 2 μm or less. When PV1 is 2 μm or less, since warpage due to the tatman effect can be reduced, the flatness of gallium oxide substrate 10 can be improved, and the exposure pattern can be transferred to gallium oxide substrate 10 with high precision. PV1 is preferably 1 μm or less, more preferably 0.5 μm or less. From the viewpoint of productivity, PV1 is preferably 0.1 μm or more.

D is not particularly limited, and is, for example, 5cm or more and 31cm or less. D is preferably 10cm or more and 21cm or less, and more preferably 12cm or more and 15cm or less.

However, in the double-side polishing (S3), unlike the primary single-side polishing (S1) and the secondary single-side polishing (S2), not only the lower platen 210 but also the upper platen 220 is relatively displaced with respect to the gallium oxide substrate 10. As a result, the irregularities of the lower surface 221 of the upper stage 220 can be prevented from being transferred to the upper surface of the gallium oxide substrate 10, and the upper surface of the gallium oxide substrate 10 can be polished parallel to the lower surface of the gallium oxide substrate 10. Therefore, when the second main surface 12 of the gallium oxide substrate 10 is adsorbed on the entire surface of the flat chuck surface 30, the unevenness of the lower surface 221 of the upper stage 220 can be suppressed from appearing on the first main surface 11.

The shape transfer of the upper stage 220 to the gallium oxide substrate 10 was evaluated by a second maximum height difference (PV2) described later. Fig. 8 is a side view showing a state of the gallium oxide substrate when the second maximum level difference (PV2) is measured. As shown in fig. 8, the second maximum level difference (PV2) is measured in a state where the second main surface 12 is opposed to the flat chuck surface 30 and is fully adsorbed. The suction is, for example, vacuum suction, and the chuck surface 30 is formed of a porous body. In fig. 8, an xy plane containing mutually orthogonal x and y axes is a least squares plane of the first main surface 11. In addition, in fig. 8, a z-axis perpendicular to the x-axis and the y-axis is set to pass through the center of the first main surface 11.

Measurement data z of height difference of first main surface 11 with least square plane of first main surface 11 as reference plane 13₀(r, θ) fitted with z (r, θ) of the above (1). j is 1, 2, 3 z_nmSince (r, θ) are flat surfaces as described above, they are meaningless components when the second maximum height difference (PV2) is measured.

Therefore, the shape of the upper stage 220 is transferred to the gallium oxide substrate 10 by transferring a of all a's where j is 4 to 81 inclusive_nmz_nm(r, θ) was added to obtain a second maximum height difference (PV 2). The second maximum level difference (PV2) is a level difference between a point highest with respect to the reference plane 13 and a point lowest with respect to the reference plane 13. The smaller the shape transfer of the upper stage 220 with respect to the gallium oxide substrate 10, the smaller the second maximum height difference (PV 2).

In addition, a with j greater than 81_nmz_nmThe (r, θ) has little influence on the unevenness of the first main surface 11, and is therefore also omitted for the sake of simplifying the calculation.

In the double-side polishing (S3), the first main surface 11 and the second main surface 12 are simultaneously polished, unlike the primary single-side polishing (S1) and the secondary single-side polishing (S2), and therefore, as described above, the shape transfer of the upper stage 220 with respect 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^－4The following. In addition, the second maximum height difference (PV2) can be reduced to 3 μm or less. Furthermore, PV2/D is a dimensionless quantity, "10" in the value of PV2/D^－4"is equivalent to" μm/cm ".

As described above, PV2/D is, for example, 0.59X 10^－4The following. If the PV2/D is 0.59X 10^－4Hereinafter, since the shape transfer of the upper stage 220 to the gallium oxide substrate 10 can be suppressed, the flatness of the gallium oxide substrate 10 can be improved, and the exposure pattern can be transferred to the gallium oxide substrate 10 with high accuracy. PV2/D is preferably 0.2X 10^－4Hereinafter, more preferably 0.1 × 10^－4The following. From the viewpoint of productivity, PV2/D is preferably 0.02X 10^－4The above.

As described above, PV2 is, for example, 3 μm or less. If PV2 is 3 μm or less, the shape transfer of upper stage 220 to gallium oxide substrate 10 can be suppressed, so that the flatness of gallium oxide substrate 10 can be improved, and the exposure pattern can be transferred to gallium oxide substrate 10 with high accuracy. PV2 is preferably 1 μm or less, more preferably 0.5 μm or less. From the viewpoint of productivity, PV2 is preferably 0.1 μm or more.

The double-side polishing (S3) includes simultaneously polishing the first main surface 11 and the second main surface 12 of the gallium oxide substrate 10, which are oriented opposite to each other, with a polishing slurry containing particles having a morse hardness of 7 or less. When the morse hardness is 7 or less, the particles are soft, and therefore, generation of damage to the gallium oxide substrate 10 can be suppressed, and cracking of the gallium oxide substrate 10 can be suppressed. The Moss hardness is preferably 6 or less, more preferably 5 or less. From the viewpoint of polishing rate, the morse hardness is preferably 2 or more.

As the particles having a morse hardness of 7 or less, for example, silica gel is used. The Moss hardness of the silica gel was 7. The material of the particles having a Moss hardness of 7 or less is not limited to SiO₂Or may be TiO₂、ZrO₂、Fe₂O₃ZnO or MnO₂And the like. TiO 2₂Has a Moss hardness of 6, ZrO₂Has a Moss hardness of 6.5 and Fe₂O₃Moss hardness of 6, Moss hardness of ZnO of 4.5, MnO₂Has a Moss hardness of 3. The polishing slurry used in the double-side polishing (S3) may contain two or more types of particles having a morse hardness of 7 or less, as long as the particles do not contain particles having a morse hardness of more than 7.

In the double-side polishing (S3), the D50 of the particles contained in the polishing slurry is, for example, 1 μm or less. When D50 is 1 μm or less, the particles are small, so that excessive stress can be suppressed from locally acting on gallium oxide substrate 10, and cracking of gallium oxide substrate 10 can be suppressed. D50 is preferably 0.7 μm or less, more preferably 0.5 μm or less. From the viewpoint of polishing rate, D50 is preferably 0.01 μm or more.

During 50% or more of the first half of the double-side polishing (S3), the polishing pressure is, for example, 9.8kPa or less. In the first half of the double-side polishing (S3), the first main surface 11 and the second main surface 12 are not sufficiently flattened, and therefore, the irregularities are large, and stress concentration is likely to occur. If the polishing pressure is 9.8kPa or less during 50% or more of the first half of the double-side polishing (S3), it is possible to suppress local application of excessive stress to the gallium oxide substrate 10, and to suppress cracking of the gallium oxide substrate 10. The polishing pressure is preferably 8.8kPa or less, more preferably 7.8kPa or less, during 50% or more of the first half of the double-side polishing (S3). From the viewpoint of polishing rate, the polishing pressure is preferably 3kPa or more for 50% or more of the first half of the double-side polishing (S3).

Further, the polishing pressure may also be constant throughout the period of the double-side polishing (S3). In the double-side polishing (S3), since the first main surface 11 and the second main surface 12 are gradually flattened and the irregularities are reduced with the passage of time, the polishing pressure may be increased in stages in order to increase the polishing rate.

The method for producing the gallium oxide substrate is not limited to the method shown in fig. 1, and may be a method including double-side polishing (S3). The method of manufacturing the gallium oxide substrate may include a process other than the process shown in fig. 1, and may include, for example, cleaning for washing off deposits (e.g., particles) on the gallium oxide substrate 10. The 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).

Examples

Hereinafter, examples and comparative examples will be described. Of the following examples 1 to 7, examples 1 to 3 are examples, and examples 4 to 7 are comparative examples.

[ examples 1 to 3]

In examples 1 to 3, beta-Ga having a diameter of 50.8mm and a thickness of 0.7mm was used₂O₃As shown in fig. 1, the single crystal substrate was subjected to primary single-side polishing (S1), secondary single-side polishing (S2), and double-side polishing (S3) under the same conditions.

In the primary single-side polishing (S1), beta-Ga is polished by the single-side polishing apparatus 100 shown in FIG. 2₂O₃The (001) plane of the single crystal substrate. The polishing was performed using a lower surface plate 110 made of tin and diamond particles having a particle size of 0.5 μm. In the first single-side polishing (S1), the lower polishing pad 112 is not used, but the substrate is pressedGrinding is performed on the lower platen 110.

In the second single-side polishing (S2), beta-Ga is polished by the single-side polishing apparatus 100 shown in FIG. 2₂O₃The (001) plane of the single crystal substrate. In the secondary single-side polishing (S2), the lower polishing pad 112 is used, unlike the primary single-side polishing (S1). In the second single-side polishing (S2), the polishing was performed using a lower polishing pad 112 made of polyurethane and silica gel particles having a particle diameter of 0.05 μm.

In the double-side polishing (S3), beta-Ga is simultaneously polished by using the double-side polishing apparatus 200 shown in FIG. 4₂O₃The (001) plane and the (00-1) plane of the single crystal substrate. The double-side polishing apparatus 200 is a product name DSM9B manufactured by speedfa, and the lower polishing pad 212 and the upper polishing pad 222 are a product name N7512 manufactured by fil. The polishing slurry was a slurry containing 20 mass% of silica gel and 80 mass% of water, and the D50 of the silica gel was 0.05 μm. During the entire period of the double-side polishing (S3), the polishing pressure was 9.8kPa, the rotation speed of the lower platen 210 was 40rpm, the rotation speed of the upper platen 220 was 14rpm, the rotation speed of the sun gear 240 was 9rpm, and the rotation speed of the ring gear 250 was 15 rpm. The pitch circle diameter of the sun gear 240 is 207.4mm, and the pitch circle diameter of the inner gear 250 is 664.6 mm.

[ examples 4 to 6]

In examples 4 to 6, beta-Ga having a diameter of 50.8mm and a thickness of 0.7mm was used₂O₃The single crystal substrate was subjected to only one single-side polishing (S1) and two single-side polishing (S2) under the same conditions as in examples 1 to 3. In examples 4 to 6, double-side polishing was not performed (S3).

[ example 7]

In example 7, primary single-side polishing (S1), secondary single-side polishing (S2), and double-side polishing (S3) were carried out under the same conditions as in examples 1 to 3, except that diamond particles having a particle size of 0.5 μm were used as the particles for double-side polishing (S3), and an epoxy resin polishing pad was used as the polishing pad for diamond particles. As a result, the gallium oxide substrate 10 is cracked during the double-side polishing (S3).

[ results of polishing ]

As shown in fig. 6, the first maximum level difference (PV1) of the (001) plane as the first main surface 11 was measured in a state where the (00-1) plane as the second main surface 12 was placed so as to face the horizontal flat surface 20, so that the gallium oxide substrate 10 was not deformed. As the measuring apparatus, a trade name PF-60 manufactured by Sanying optical instrument was used.

As shown in fig. 8, the second maximum level difference (PV2) of the (001) plane as the first main surface 11 was measured in a state where the (00-1) plane as the second main surface 12 was adsorbed on the entire surface of the flat chuck surface 30. As the measuring apparatus, a trade name PF-60 manufactured by Sanying optical instrument was used.

Table 1 table shows the polishing results of examples 1 to 6. In example 7, as described above, the cracking of the gallium oxide substrate 10 was caused in the double-side polishing (S3).

[ Table 1]

As is clear from Table 1, examples 1 to 3 differ from examples 4 to 6 in that the double-side polishing (S3) was carried out, and thus PV1/D was 0.39X 10^－4Hereinafter, PV1 is 2 μm or less. It is found that the warp due to the Taeman effect can be reduced by double-side polishing (S3).

Table 1 shows that examples 1 to 3 are different from examples 4 to 6 in that the PV2/D is 0.59X 10 because double-side polishing (S3) is performed^－4Hereinafter, PV2 is 3 μm or less. It is found that the shape transfer of the upper surface plate 220 to the gallium oxide substrate 10 can be suppressed by the double-side polishing (S3).

In examples 1 to 3, the particles used in the double-side polishing (S3) had a morse hardness of 7 or less, a D50 of 1 μm or less, and a polishing pressure of 9.8kPa or less during 50% or more of the first half, and thus the gallium oxide substrate 10 was not cracked during the double-side polishing. On the other hand, in example 7, since the morse hardness of the particles used in the double-side polishing (S3) exceeded 7, cracking of the gallium oxide substrate 10 was caused in the double-side polishing.

In addition, in the primary single-side polishing (S1), although the polishing was performed using diamond particles having a morse hardness of 10, the gallium oxide substrate 10 was not cracked. In the single-side polishing, the gallium oxide substrate 10 is less likely to be broken than in the double-side polishing, and it is presumed that this is the reason why the single-side polishing is adopted in patent document 1.

While the embodiments of the gallium oxide substrate and the method for manufacturing the gallium oxide substrate according to the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and the like. Various changes, modifications, substitutions, additions, deletions, and combinations may be made within the scope of the claims. These are of course also within the technical scope of the present disclosure.

The entire contents of Japanese patent application No. 2019-073548 are incorporated into the present application, based on the priority claim of Japanese patent application No. 2019-073548, which was filed on the office in 8/4/2019.

Description of the reference numerals

10 … a gallium oxide substrate; 11 … first major surface; 12 … second major surface.