Semiconductor device and manufacturing method thereof

Abstract

To suppress a gallium nitride substrate from warping in processing a semiconductor device using the gallium nitride substrate and the gallium nitride substrate.SOLUTION: A semiconductor device comprises a gallium nitride substrate and a pattern film provided on a surface of the gallium nitride substrate. The gallium nitride substrate has a larger Young's modulus in a first direction along the surface than that in a second direction along the surface and orthogonal to the first direction. Here, R1<R2 holds for a first ratio R1 obtained by dividing the dimension of the gallium nitride substrate in the first direction by the dimension of the gallium nitride substrate in the second direction and a second ratio R2 obtained by dividing the dimension of the pattern film in the first direction by the dimension of the pattern film in the second direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a semiconductor device and a method for manufacturing the same.

[0002] Patent Document 1 discloses a technology for thinning a substrate made of gallium nitride by irradiating the substrate with a laser to form a modified layer inside the substrate and then dividing the substrate along the modified layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-126844 Summary of the Invention [Problem to be solved by the invention]

[0004] Gallium nitride has multiple crystal planes, and the Young's modulus varies depending on the direction along each crystal plane. A plane direction with a small Young's modulus experiences a larger amount of strain in response to stress than a plane direction with a large Young's modulus, making the gallium nitride substrate prone to warping in a specific direction. When the gallium nitride substrate is warped, it is difficult to irradiate a laser beam parallel to the desired plane, making it difficult to accurately separate the gallium nitride substrate along the desired plane. Furthermore, because the gallium nitride substrate may warp in a specific direction, semiconductor devices manufactured using the gallium nitride substrate, for example, have the problem of unstable characteristics. This specification proposes a technique for suppressing warping of a gallium nitride substrate in semiconductor devices using the gallium nitride substrate and in processing the gallium nitride substrate. [Means for solving the problem]

[0005] The semiconductor devices (10, 100) disclosed in this specification include a gallium nitride substrate (12, 52) and a patterned film (40, 140) provided on the surface (12a, 52a) of the gallium nitride substrate. The gallium nitride substrate has a Young's modulus in a first direction along the surface that is greater than the Young's modulus in a second direction along the surface and orthogonal to the first direction. A first ratio R1 obtained by dividing the dimension of the gallium nitride substrate in the first direction by the dimension of the gallium nitride substrate in the second direction and a second ratio R2 obtained by dividing the dimension of the patterned film in the first direction by the dimension of the patterned film in the second direction satisfy R1 < R2.

[0006] The amount of strain in the gallium nitride substrate in a specific direction is proportional to the stress applied in the specific direction of the gallium nitride substrate and inversely proportional to the Young's modulus in the specific direction of the gallium nitride substrate. Also, the stress applied in a specific direction of the gallium nitride substrate is proportional to the dimension of the gallium nitride substrate in the specific direction. On the other hand, the patterned film provided on the surface of the gallium nitride substrate expands and contracts due to temperature changes during formation and after formation, and the heat generation cycle during the operation of the semiconductor device. Therefore, tensile stress and compressive stress caused by the expansion and contraction of the patterned film provided on its surface are applied to the gallium nitride substrate. The stress applied from the patterned film to the gallium nitride substrate in a specific direction is proportional to the dimension of the patterned film in the specific direction. In this semiconductor device, the ratio R1 is smaller than the ratio R2. That is, the patterned film has a smaller dimension in the second direction with respect to the first direction than the gallium nitride substrate. For this reason, the amount of strain caused by the difference between the Young's modulus in the first direction and the Young's modulus in the second direction of the gallium nitride substrate is relaxed by the stress applied from the patterned film to the gallium nitride substrate, and the difference in the amount of strain between the first direction and the second direction is reduced. Therefore, in the above semiconductor device, the gallium nitride substrate is less likely to warp, and the characteristics of the semiconductor device can be stabilized.

[0007] The present specification discloses a method for manufacturing a semiconductor device, comprising the steps of: forming grooves (114, 214) in a surface (112a, 212a) of a gallium nitride substrate (112, 212) to partition the surface of the gallium nitride substrate into a plurality of regions (120, 220); irradiating the gallium nitride substrate with a laser (132) to form a modified layer (116) extending along the surface within the gallium nitride substrate and within a depth range of the grooves; and dividing the gallium nitride substrate along the modified layer. The gallium nitride substrate has a larger Young's modulus in a first direction along the surface than in a second direction along the surface and perpendicular to the first direction. In the step of forming the grooves, the grooves are formed along the first direction and the second direction, thereby partitioning the surface into the plurality of regions such that the dimension of each region in the first direction is larger than the dimension of each region in the second direction.

[0008] The amount of strain of a gallium nitride substrate in a specific direction is proportional to the stress applied to the gallium nitride substrate in that specific direction and inversely proportional to the Young's modulus of the gallium nitride substrate in that specific direction. Furthermore, the stress applied to the gallium nitride substrate in that specific direction is proportional to the dimension of the gallium nitride substrate in that specific direction. In the above manufacturing method, the grooves are formed so that the dimension in a first direction, in which the Young's modulus is large, is larger than the dimension in a second direction, in which the Young's modulus is small. That is, in each region partitioned by the grooves, the dimension in the first direction is larger than the dimension in the second direction. In each region, the dimension in the first direction, in which the Young's modulus is large (i.e., less susceptible to strain), is larger than the dimension in the second direction, in which the Young's modulus is small (i.e., more susceptible to strain). Therefore, within the depth range where the grooves are formed, the difference in the amount of strain between the first and second directions is reduced, and warpage is suppressed in each region. Since a modified layer is formed by irradiating a laser onto a gallium nitride substrate with suppressed warpage, the modified layer can be formed along the surface (i.e., along the desired plane). [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a main part of a semiconductor device according to a first embodiment. [Figure 2] FIG. 1 is a plan view of a semiconductor device according to a first embodiment. [Figure 3] FIG. 1 is a diagram showing the relationship between the surface direction of gallium nitride and Young's modulus. [Figure 4] FIG. 10 is a cross-sectional view of a main part of a semiconductor device according to a second embodiment. [Figure 5] FIG. 10 is a plan view of a semiconductor device according to a second embodiment. [Figure 6] FIG. 1 is a diagram showing the relationship between the surface direction and Young's modulus of gallium nitride grown on a sapphire substrate. [Figure 7] FIG. 10 is a plan view of a gallium nitride substrate in a manufacturing method according to a third embodiment. [Figure 8] 10A to 10C are diagrams illustrating a groove forming step in the third embodiment. [Figure 9] 10A to 10C are diagrams illustrating a groove forming step in the third embodiment. [Figure 10] 10A to 10C are diagrams illustrating a groove forming step in the third embodiment. [Figure 11] 10A to 10C are diagrams illustrating a modified layer forming step in Example 3. [Figure 12] 10A to 10C are diagrams illustrating a substrate dividing step according to the third embodiment. [Figure 13] FIG. 10 is a plan view of a sapphire substrate in a manufacturing method according to a fourth embodiment. [Figure 14] FIG. 10 is a diagram illustrating the gallium nitride growth process of Example 4. [Figure 15] 10A to 10C are diagrams illustrating a groove forming step in Example 4. [Figure 16] 10A to 10C are diagrams illustrating a groove forming step in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] In one example semiconductor device disclosed in this specification, the first ratio R1 may be greater than 1, and the second ratio R2 may be greater than 1. The Young's modulus of the gallium nitride substrate in the first direction may be greater than the Young's modulus in the second direction. In this configuration, the dimension of the gallium nitride substrate in the first direction is greater than the dimension in the second direction, so that warpage caused by the difference in Young's modulus between the directions can be reduced.

[0011] In one example of a semiconductor device disclosed in this specification, the surface may be an m-plane, the first direction may be a (0001) direction, and the second direction may be a (11-20) direction. In such a configuration, by making the first direction and the second direction perpendicular to a crystal plane of gallium nitride, the variation in Young's modulus in each direction is reduced, and warpage of the gallium nitride substrate can be stably reduced.

[0012] In one example of a semiconductor device disclosed in this specification, 1.01R1≦R2≦1.25 R1 In this configuration, the amount of strain in the first direction and the second direction of the gallium nitride substrate can be made uniform.

[0013] In one example of a semiconductor device disclosed in this specification, 1.01R1≦R2≦1.05 R1 In this configuration, the amount of strain in the first direction and the second direction of the gallium nitride substrate can be made more uniform.

[0014] In one example of a manufacturing method disclosed herein, the surface may be an m-plane, the first direction may be a (0001) direction, and the second direction may be a (11-20) direction. In such a configuration, a modified layer is formed along the m-plane. Because the m-plane is a plane that is easily cleaved, it can be easily split along the modified layer. In addition, the m-plane has good processability, making it easy to form a semiconductor structure inside the gallium nitride substrate in a subsequent process.

[0015] In one example manufacturing method disclosed herein, a ratio S obtained by dividing the dimension of each region in the first direction by the dimension of each region in the second direction may satisfy 1.01≦S≦1.25. With this configuration, the amount of strain in the first direction and the second direction of the gallium nitride substrate after division can be made uniform.

[0016] In one example manufacturing method disclosed herein, a ratio S obtained by dividing the dimension of each region in the first direction by the dimension of each region in the second direction may satisfy 1.01≦S≦1.05. With this configuration, the amount of strain in the first and second directions of the gallium nitride substrate after division can be made more uniform.

[0017] Example 1 A semiconductor device 10 according to a first embodiment will be described with reference to the drawings. As shown in Fig. 1, the semiconductor device 10 is a lateral MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The semiconductor device 10 includes a gallium nitride substrate 12, a drain electrode 32, a source electrode 34, a gate electrode 36, and an insulating film 40.

[0018] The gallium nitride substrate 12 is made of a single crystal of gallium nitride. As shown in Fig. 2, in this embodiment, the gallium nitride substrate 12 has a substantially square shape when viewed from above, defined by two parallel end faces 12b and two parallel end faces 12c perpendicular to the end faces 12b. The gallium nitride substrate 12 has a hexagonal crystal structure. The surface 12a is the m-plane, the end face 12b is the a-plane, and the end face 12c is the c-plane. The direction perpendicular to the m-plane is the (10-10) direction, the direction perpendicular to the a-plane is the (11-20) direction, and the direction perpendicular to the c-plane is the (0001) direction.

[0019] As shown in FIG. 1, a plurality of drain regions 22, a plurality of source regions 24, and a body region 26 are provided inside the gallium nitride substrate 12.

[0020] The drain region 22 is an n-type region. The drain region 22 is provided at a position exposed on the surface 12a of the gallium nitride substrate 12. The source region 24 is an n-type region. The source region 24 is spaced apart from the drain region 22 and provided at a position exposed on the surface 12a of the gallium nitride substrate 12. The body region 26 is a p-type region. The body region 26 is exposed on the surface 12a of the gallium nitride substrate 12 in a range between the drain region 22 and the source region 24. The body region 26 extends from a range between the drain region 22 and the source region 24 to below the drain region 22 and below the source region 24. The body region 26 separates the drain region 22 and the source region 24 from each other.

[0021] The insulating film 40 covers the surface 12a of the gallium nitride substrate 12 in a range spanning from one drain region 22 to one source region 24. The insulating film 40 has a through-hole 40a above the drain region 22. The insulating film 40 also has a through-hole 40b above the source region 24.

[0022] The drain electrode 32 is in ohmic contact with the drain region 22 via a through-hole 40a in the insulating film 40. The source electrode 34 is in ohmic contact with the source region 24 via a through-hole 40b in the insulating film 40. The gate electrode 36 is provided on the upper surface of the insulating film 40. The gate electrode 36 is provided in an area facing the body region 26 located between the drain region 22 and the source region 24. The gate electrode 36 is insulated from the gallium nitride substrate 12 by the insulating film 40.

[0023] As shown in FIG. 2, in this embodiment, nine insulating films 40 are provided on the surface 12a of the gallium nitride substrate 12. Note that the drain electrode 32, the source electrode 34, and the gate electrode 36 are not shown in FIG. 2. Each insulating film 40 has a rectangular shape when viewed from above. Each insulating film 40 is arranged so that its sides are parallel to the end faces 12b and 12c. As shown in FIG. 2, when the dimension of the gallium nitride substrate 12 in the (11-20) direction is L1, the dimension of the gallium nitride substrate 12 in the (0001) direction is L2, and the dimension of each insulating film 40 in the (11-20) direction is l1 and the dimension of the insulating film 40 in the (0001) direction is l2, the ratio of L1 to L2, L1 / L2=R1, and the ratio of l1 to l2, l1 / l2=R2, satisfy the relationship 1.01R1≦R2≦1.05R1.

[0024] When the semiconductor device 10 is in use, an on-voltage is applied to the gate electrode 36. This causes an inversion layer to form in the body region 26 in the area facing the insulating film 40 (i.e., the area between the drain region 22 and the source region 24). As a result, the drain region 22 connected to the drain electrode 32 and the source region 24 connected to the source electrode 34 are connected via the inversion layer, and the drain electrode 32 and the source electrode 34 are brought into conduction. This turns on the semiconductor device 10. When the voltage of the gate electrode 36 is reduced to the off-voltage, the inversion layer formed in the body region 26 disappears, and the semiconductor device 10 turns off.

[0025] The semiconductor device 10 generates heat during use. Temperature changes in the semiconductor device 10 apply stress to the gallium nitride substrate 12. The amount of strain in a specific direction of the gallium nitride substrate 12 is proportional to the stress applied to the gallium nitride substrate 12 in that specific direction and inversely proportional to the Young's modulus of the gallium nitride substrate 12 in that specific direction. Figure 3 shows literature values ​​for the Young's modulus in each plane direction of single-crystal gallium nitride (Huang et al., Nanoscale Research Letters, 7(150), 2012; Cheng et al., Basis Solid State Physics, 255(5), 2018) and the ratio of the (0001) direction to the (11-20) direction for each literature value. As shown in Figure 3, single-crystal gallium nitride has different Young's moduli in the (10-10) direction, the (11-20) direction, and the (0001) direction. Specifically, in single-crystal gallium nitride, the Young's modulus in the (0001) direction is 1.01 to 1.05 times that in the (11-20) direction. That is, the Young's modulus of the gallium nitride substrate 12 in the (11-20) direction is smaller than that in the (0001) direction. Furthermore, the stress generated in the gallium nitride substrate 12 in a specific direction increases as the dimension in the specific direction increases. In this embodiment, the gallium nitride substrate 12 has a substantially square shape when viewed from above, and the dimension L1 in the (11-20) direction is equal to the dimension L2 in the (0001) direction. Since the dimension L1 in the (11-20) direction is equal to the dimension L2 in the (0001) direction and the Young's modulus in the (11-20) direction is smaller than that in the (0001) direction, the gallium nitride substrate 12 is more susceptible to distortion in the (11-20) direction than in the (0001) direction. However, in this embodiment, an insulating film 40 is provided on the surface 12a of the gallium nitride substrate 12. The insulating film 40 expands and contracts due to temperature changes during and after its formation and due to heat cycles during operation of the semiconductor device 10. Therefore, tensile stress and compressive stress resulting from the expansion and contraction of the insulating film 40 provided on the surface 12a are applied to the gallium nitride substrate 12. The stress applied from the insulating film 40 in a specific direction of the gallium nitride substrate 12 is proportional to the dimension of the insulating film 40 in that specific direction.In this embodiment, as described above, the ratios R1 and R2 satisfy 1.01R1≦R2≦1.05R1. Because the ratio R1 is greater than the ratio R2, the insulating film 40 has a shape in which the ratio of the length in the (11-20) direction is greater than that of the gallium nitride substrate 12. Therefore, the stress applied to the gallium nitride substrate 12 from the insulating film 40 is greater in the (11-20) direction than in the (0001) direction. Therefore, the difference in strain between the (11-20) direction and the (0001) direction is reduced. In particular, R2 is 1.01 to 1.05 times R1, which is set to a value approximately equal to the ratio of the Young's modulus in the (11-20) direction to the Young's modulus in the (0001) direction of the gallium nitride substrate 12 shown in FIG. 3 . Therefore, the stress applied from the insulating film 40 equalizes the strain in the (11-20) direction and the (0001) direction of the gallium nitride substrate 12. Therefore, the gallium nitride substrate 12 is less likely to warp, and the semiconductor device 10 has stable characteristics.

[0026] (Correspondence) The insulating film 40 is an example of a “patterned film.” The (11-20) direction and the (0001) direction are examples of a “first direction” and a “second direction,” respectively.

[0027] Example 2 In the semiconductor device 100 of Example 2, as shown in FIG. 4, a gallium nitride substrate 52 is provided on the surface of a sapphire substrate 50. The gallium nitride substrate 52 is a layer formed by epitaxial growth on the surface of the sapphire substrate 50. As shown in FIG. 5, when viewed from above, the gallium nitride substrate 52 has a substantially square shape defined by two parallel end faces 52b and two parallel end faces 52c perpendicular to the end faces 52b. In this example, the surface 52a of the gallium nitride substrate 52 is the a-plane, the end face 52b is the m-plane, and the end face 52c is the c-plane. The internal structure of the gallium nitride substrate 52 (drain region 22, source region 24, body region 26) is the same as that of Example 1.

[0028] 5, nine insulating films 140 are provided on the surface 52a of the gallium nitride substrate 52. Each insulating film 140 has a rectangular shape when viewed from above. Each insulating film 140 is arranged so that each side is parallel to the end face 52b and the end face 52c. As shown in Figure 5, when the dimension of the gallium nitride substrate 52 in the (10-10) direction is L1, the dimension in the (0001) direction is L2, the dimension of each insulating film 140 in the (10-10) direction is l3, and the dimension in the (0001) direction is l4, the ratio of L1 to L2, L1 / L2 = R1, and the ratio of l3 to l4, l3 / l4 = R3, satisfy the relationship 1.01R1≦R3≦1.25R1.

[0029] In Example 2, a gallium nitride substrate 52 is formed on the surface of a sapphire substrate 50 by epitaxial growth. The gallium nitride substrate 52 grows on the sapphire substrate 50 while undergoing strain due to the difference in lattice constants between sapphire and gallium nitride. FIG. 6 shows the literature values ​​(Roder et al., Journal of Applied Physics, 100(103511), 2006) for the Young's modulus of gallium nitride in each plane direction when grown on a sapphire substrate, and the ratio of the Young's modulus in the (0001) direction to the (11-20) direction in the literature values. As shown in FIG. 6, compared with single crystal gallium nitride, the Young's modulus of the gallium nitride substrate 52 in the (0001) direction may be larger than that in the (10-10) direction. Therefore, the gallium nitride substrate 52 formed on the sapphire substrate 50 is more likely to strain in the (10-10) direction than in the (0001) direction. However, in this embodiment, the ratios R1 and R3 satisfy the relationship 1.01R1≦R3≦1.25R1. Therefore, the stress applied from the insulating film 140 to the gallium nitride substrate 52 is greater in the (10-10) direction than in the (0001) direction. By sizing the insulating film 140 in this way, the amount of strain between the (10-10) direction and the (0001) direction of the gallium nitride substrate 52 is reduced. In particular, R3 is 1.01 to 1.25 times R1, which is set to a value approximately equal to the ratio of the Young's modulus in the (10-10) direction to the Young's modulus in the (0001) direction of the gallium nitride substrate 52 shown in FIG. 6. Therefore, the amount of strain in the gallium nitride substrate 52 is uniform due to the stress applied from the insulating film 140.

[0030] (Correspondence) The insulating film 140 is an example of a “patterned film.” The (10-10) direction and the (0001) direction are examples of a “first direction” and a “second direction,” respectively.

[0031] Example 3 Next, a manufacturing method of Example 3 will be described with reference to the drawings. In the manufacturing method of Example 3, a semiconductor device is manufactured from a gallium nitride substrate 112. FIG. 7 shows the gallium nitride substrate 112 to be processed. The gallium nitride substrate 112 is made of single crystal gallium nitride. An orientation flat 112f is provided on part of the outer periphery of the gallium nitride substrate 112. The surface 112a of the gallium nitride substrate 112 is the m-plane, the plane parallel to the orientation flat 112f of the gallium nitride substrate 112 is the c-plane, and the plane perpendicular to the m-plane and c-plane is the a-plane. Hereinafter, the direction perpendicular to the m-plane will be referred to as the (10-10) direction, the direction perpendicular to the c-plane will be referred to as the (0001) direction, and the direction perpendicular to the a-plane will be referred to as the (11-20) direction.

[0032] (Groove formation process) When manufacturing a semiconductor device from a gallium nitride substrate 112, a groove forming process is first performed. As shown in FIG. 8, in the groove forming process, grooves 114 are formed in the front surface 112a of the gallium nitride substrate 112. Here, as shown in FIG. 8, a laser 130 is irradiated from the rear surface 112b of the gallium nitride substrate 112. The laser 130 is irradiated so as to form a focal point F1 within the gallium nitride substrate 112. The grooves 114 are formed at the positions irradiated with the laser 130. By moving the irradiation position of the laser 130, the front surface 112a of the gallium nitride substrate 112 is partitioned into a plurality of regions 120 as shown in FIG. 9. Here, grooves 115a extending along the (11-20) direction and grooves 115b extending along the (0001) direction are formed. As a result, the front surface 112a of the gallium nitride substrate 112 is partitioned into a plurality of rectangular regions 120 defined by the grooves 115a and 115b.

[0033] 10 , the grooves 114 are formed so that the dimension S2 in the (0001) direction of each region 120 is larger than the dimension S1 in the (11-20) direction. Specifically, in this embodiment, the grooves 114 are formed in the surface 112a of the gallium nitride substrate 112 so that S1 / S2 is 1.01 or more and 1.05 or less in each region 120. Note that in the groove forming step, the grooves 114 may be formed in the surface 112a of the gallium nitride substrate 112 by irradiating the gallium nitride substrate 112 with a laser 130 from the surface 112a side of the gallium nitride substrate 112. The grooves 115a and 115b may be formed so as to extend to the end face (outer peripheral edge) of the gallium nitride substrate 112.

[0034] (Modified layer forming process) Next, a modified layer forming process is performed to form a modified layer 116 inside the gallium nitride substrate 112. In the modified layer forming process, as shown in FIG. 11 , a laser 132 is irradiated onto the gallium nitride substrate 112 from the back surface 112b side. The laser 132 is irradiated so as to form a focal point F2 inside the gallium nitride substrate 112. At the position of the focal point F2, gallium nitride (GaN) is heated and decomposed. As a result, a modified layer 116 composed of a gallium precipitate layer or the like is formed at the position of the focal point F2. The strength of the modified layer 116 is lower than that of the original gallium nitride single crystal. Here, the irradiation position of the laser 132 is moved in a direction parallel to the front surface 112a and back surface 112b of the gallium nitride substrate 112 to form the modified layer 116 extending along the front surface 112a and back surface 112b. Here, the modified layer 116 is formed so that the modified layer 116 and the groove portion 114 overlap in depth. In other words, the modified layer 116 is formed so that the range 116a of the modified layer 116 in the thickness direction of the gallium nitride substrate 112 overlaps with the range 114a of the groove portion 114 in the thickness direction of the gallium nitride substrate 112. Herein, the modified layer 116 is formed over the entire direction parallel to the front surface 112a and back surface 112b of the gallium nitride substrate 112. Hereinafter, the portion of the gallium nitride substrate 112 closer to the front surface 112a than the modified layer 116 will be referred to as a first portion 160, and the portion closer to the back surface 112b than the modified layer 116 will be referred to as a second portion 161.

[0035] (Substrate division process) Next, a substrate dividing step is performed. In the substrate dividing step, as shown in FIG. 12, a support member 180 is attached to the surface 112a of the gallium nitride substrate 112. The support member 180 may be a hard plate or a flexible sheet-like member. Then, a force is applied to the second portion 161 in a direction away from the first portion 160, thereby dividing the gallium nitride substrate 112 along the modified layer 116. That is, the second portion 161 is separated from the first portion 160. As described above, the strength of the modified layer 116 is lower than that of the gallium nitride single crystal, so the gallium nitride substrate 112 can be divided along the modified layer 116. Note that, because the first portion 160 has grooves formed therein that extend from the surface 112a to the modified layer 116, the first portion 160 is divided into a plurality of chips 170. The divided chips 170 are then used to manufacture semiconductor devices by a conventionally known method.

[0036] The amount of strain of the gallium nitride substrate 112 in a specific direction is inversely proportional to the Young's modulus of the gallium nitride substrate 112 in that specific direction. Specifically, as shown in FIG. 3, the Young's modulus in the (11-20) direction is smaller than the Young's modulus in the (0001) direction, so the gallium nitride substrate 112 is more likely to strain in the (11-20) direction. Furthermore, the amount of strain of the gallium nitride substrate 112 in that specific direction is proportional to the stress applied to the gallium nitride substrate 112 in that specific direction, i.e., the dimension of the gallium nitride substrate 112 in that specific direction. In the manufacturing method of this embodiment, when forming the grooves 114 in the surface 112a of the gallium nitride substrate 112, the grooves 114 are formed so that the dimensional ratio S1 / S2 of each region 120 partitioned by the grooves 114 between the (0001) direction and the (11-20) direction is 1.01 or more and 1.05 or less. Because dimension S1 is greater than dimension S2, in each region 120, the stress applied in the (0001) direction is greater than the stress applied in the (11-20) direction. Therefore, the difference in strain between the (0001) and (11-20) directions is reduced. In particular, S1 / S2 is set to 1.01 to 1.05, which is approximately equal to the ratio of the Young's modulus in the (11-20) direction to the Young's modulus in the (0001) direction of the single-crystal gallium nitride shown in FIG. 3 . Therefore, in the depth range where the grooves 114 are formed, the strain between the (0001) and (11-20) directions is uniform, and warpage is suppressed in each region 120. Because warpage is suppressed in each region 120, the laser 132 can be irradiated parallel to the surface 112a (i.e., the m-plane). Therefore, the modified layer 116 can be formed along the m-plane. Furthermore, the chips 170 separated along the modified layer 116 have dimensional ratios that make warping less likely to occur, so that semiconductor devices manufactured using the chips 170 have stable characteristics.

[0037] The gallium nitride substrate 112 is not partitioned in a portion closer to the back surface 112b than the grooves 114 (portion 161 in FIG. 11). Therefore, warping may occur in the gallium nitride substrate 112 in portion 161. However, the modified layer 116 is formed at a position that overlaps the depth range of the grooves 114. Warping is suppressed in the depth range where the grooves 114 are formed. Since the laser 132 is moved in the range where warping is suppressed, the laser 132 can be moved approximately parallel to the m-plane.

[0038] In this embodiment, the modified layer 116 is formed along the m-plane. Since the m-plane is easier to cleave than other planes, it can be easily split along the modified layer 116. Furthermore, the m-plane is easier to process than other planes. Therefore, by using the m-plane as the splitting plane, it is possible to easily form a semiconductor structure in a subsequent process.

[0039] (Correspondence) The (11-20) direction and the (0001) direction are examples of the "first direction" and the "second direction", respectively.

[0040] Example 4 In Example 4, a semiconductor device is manufactured using a sapphire substrate 200 shown in Fig. 13. First, as shown in Fig. 14, a gallium nitride layer 212 is formed by epitaxial growth on the surface of the sapphire substrate 200. Here, gallium nitride is grown as a crystal on the surface of the sapphire substrate 200 so that a surface 212a of the gallium nitride layer 212 is the a-plane.

[0041] Next, a groove forming step is performed. As shown in FIG. 15, grooves 214 are formed in the surface 212a of the gallium nitride layer 212. Here, similar to FIG. 8 of Example 3, the grooves 214 are formed by irradiating the gallium nitride layer 212 with a laser. By moving the laser irradiation position, the surface 212a of the gallium nitride layer 212 is partitioned into a plurality of regions 220, as shown in FIG. 16. Here, grooves 215a extending along the (10-10) direction perpendicular to the m-plane and grooves 215b extending along the (0001) direction perpendicular to the c-plane are formed, thereby partitioning the surface 212a of the gallium nitride layer 212 into a plurality of rectangular regions 220 defined by the grooves 215a and 215b.

[0042] 16, unlike Example 3, grooves 214 are formed in surface 212a of gallium nitride layer 212 so that the ratio S3 / S4 of dimension S4 in the (0001) direction to dimension S3 in the (10-10) direction is 1.01 or more and 1.25 or less in each region 220. Thereafter, similar to Example 3, modified layers are formed in the interior of gallium nitride layer 212 in areas overlapping with grooves 214, and gallium nitride layer 212 is divided along the formed modified layers.

[0043] In this example, a gallium nitride layer 212 is formed on the surface of a sapphire substrate 200 by epitaxial growth. The gallium nitride layer 212 grows on the sapphire substrate 200 while generating strain due to the difference in lattice constant between sapphire and gallium nitride. Therefore, as described in Example 2, the Young's modulus of the gallium nitride layer 212 in the (0001) direction may be larger than that in the (10-10) direction, as compared with that of single-crystal gallium nitride (see FIG. 6). In this example, S3 / S4 is in the range of 1.01 to 1.25. Therefore, in each region 220, the stress applied in the (0001) direction is larger than the stress applied in the (10-10) direction. In particular, S3 / S4 is set to 1.01 to 1.25, which is approximately equal to the ratio of the Young's modulus in the (10-10) direction to the Young's modulus in the (0001) direction of gallium nitride shown in FIG. 6. Therefore, in the depth range where the grooves 214 are formed, the amount of strain between the (0001) direction and the (10-10) direction is uniformed, and warpage in each region 220 is suppressed.

[0044] (Correspondence) The (10-10) direction and the (0001) direction are examples of the "first direction" and the "second direction", respectively.

[0045] In the above-described Examples 1 and 3, examples were described in which the (11-20) direction and the (0001) direction were the "first direction" and the "second direction," respectively. In Examples 2 and 4, examples were described in which the (10-10) direction and the (0001) direction were the "first direction" and the "second direction," respectively. However, the first and second directions are not limited to the above. The dimensions of the gallium nitride substrate and the pattern film, and the dimensions of the grooves formed in the gallium nitride substrate, may be adjusted depending on the difference in Young's modulus between the directions. Therefore, for example, the first direction may be the (0001) direction and the second direction may be the (11-20) direction, or the first direction may be the (0001) direction and the second direction may be the (10-10) direction. Furthermore, for example, the first direction may be the (10-10) direction and the second direction may be the (11-20) direction, or the first direction may be the (11-20) direction and the second direction may be the (10-10) direction. In other words, the surface of the gallium nitride substrate may be the c-plane, the a-plane, or the m-plane.

[0046] In addition, in the above-described first and second embodiments, the insulating films 40 and 140 have a rectangular shape when viewed from above, but this is not limiting. For example, they may have a hexagonal or other polygonal shape, or may be circular. For example, in the first embodiment, R2 may be the ratio obtained by dividing the maximum dimension of the insulating film 40 in the (11-20) direction by the maximum dimension in the (0001) direction, and in the second embodiment, R2 may be the ratio obtained by dividing the maximum dimension of the insulating film 140 in the (10-10) direction by the maximum dimension in the (0001) direction.

[0047] Furthermore, in the above-described first and second embodiments, the gallium nitride substrates 12 and 52 are described as being substantially square when viewed from above, but the ratio of L1 to L2 is not particularly limited.

[0048] Furthermore, in the above-mentioned Examples 1 and 2, an insulating film was used as an example of the pattern film provided on the surfaces 12a, 52a of the gallium nitride substrates 12, 52, but the type of pattern film provided on the surfaces 12a, 52a is not particularly limited, and may be, for example, a metal film or the like.

[0049] Furthermore, in the first and second embodiments, the semiconductor devices 10 and 100 are described as lateral MOSEFTs, but they may also be vertical semiconductor devices.

[0050] It has been reported in a paper (Bahat Treidel et al., Journal of the Electron Devices Society, 9, 215-228, 2021) that when the inner surface of a trench formed on the surface of a gallium nitride substrate is treated with tetramethylammonium hydroxide (TMAH), the a-plane has higher channel mobility than the m-plane. Therefore, when performing treatment with TMAH in the manufacturing process of a semiconductor device, for example, by performing the treatment so that the channel is formed along the a-plane direction, a semiconductor device with high channel mobility (i.e., low on-resistance) can be obtained.

[0051] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0052] 12: Gallium nitride substrate 40: insulating film 114: Groove 116: Modified layer

Claims

1. A semiconductor device (10, 100), a gallium nitride substrate (12, 52); a pattern film (40, 140) provided on the surface (12a, 52a) of the gallium nitride substrate; Equipped with the gallium nitride substrate has a Young's modulus in a first direction along the surface that is greater than a Young's modulus in a second direction along the surface and perpendicular to the first direction; a first ratio R1 obtained by dividing the dimension of the gallium nitride substrate in the first direction by the dimension of the gallium nitride substrate in the second direction, and a second ratio R2 obtained by dividing the dimension of the pattern film in the first direction by the dimension of the pattern film in the second direction satisfy R1<R2; Semiconductor device.

2. the first ratio R1 is greater than 1, the second ratio R2 is greater than 1; The semiconductor device according to claim 1 .

3. 3. The semiconductor device according to claim 1, wherein the surface is an m-plane, the first direction is a (0001) direction, and the second direction is a (11-20) direction.

4. 4. The semiconductor device according to claim 3, wherein 1.01R1≦R2≦1.25R1 is satisfied.

5. 4. The semiconductor device according to claim 3, wherein 1.01R1≦R2≦1.05R1 is satisfied.

6. A method for manufacturing a semiconductor device, comprising: A step of dividing the surface of a gallium nitride substrate (112, 212) into a plurality of regions (120, 220) by forming grooves (114, 214) in the surface (112a, 212a) of the gallium nitride substrate; forming a modified layer (116) extending along the surface of the gallium nitride substrate within the depth range of the grooves within the gallium nitride substrate by irradiating the gallium nitride substrate with a laser (132); dividing the gallium nitride substrate along the modified layer; Equipped with the gallium nitride substrate has a Young's modulus in a first direction along the surface that is greater than a Young's modulus in a second direction along the surface and perpendicular to the first direction; In the step of forming the groove portion, the groove portion is formed along the first direction and the second direction, thereby dividing the surface into the plurality of regions such that a dimension of each of the regions in the first direction is larger than a dimension of each of the regions in the second direction. Manufacturing method.

7. 7. The manufacturing method according to claim 6, wherein the surface is an m-plane, the first direction is a (0001) direction, and the second direction is a (11-20) direction.

8. The manufacturing method according to claim 7 , wherein a ratio S obtained by dividing the dimension of each of the regions in the first direction by the dimension of each of the regions in the second direction satisfies 1.01≦S≦1.

25.

9. The manufacturing method according to claim 7 , wherein a ratio S obtained by dividing the dimension of each of the regions in the first direction by the dimension of each of the regions in the second direction satisfies 1.01≦S≦1.05.

Images