Semiconductor device and manufacturing method thereof

Abstract

To accurately control a shape of a division surface when dividing a semiconductor substrate after laser irradiation.SOLUTION: A method for manufacturing a semiconductor device includes a step of irradiating a semiconductor substrate (12) with a laser so that a focal point of the laser shifts inside the semiconductor substrate, and a step of dividing the semiconductor substrate. The semiconductor substrate includes a specific crystal surface being easier to cleave than a crystal surface parallel to a surface (12a) of the semiconductor substrate and inclined to the surface. In the laser irradiation step a specific modified layer forming is repeated for forming a specific modified layer (16) extending along the specific crystal surface by shifting the focal point along the specific crystal surface. In the laser irradiating step a plurality of specific modified layers are formed so as to be arranged along a direction parallel to the surface.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a method for dividing a semiconductor substrate. This method includes a laser irradiation step and a dividing step. In the laser irradiation step, a laser is irradiated onto the semiconductor substrate so that the focal point of the laser moves along the surface of the semiconductor substrate inside the semiconductor substrate. This forms a modified layer inside the semiconductor substrate. In the dividing step, the semiconductor substrate is divided along the modified layer. As a result, a thin semiconductor substrate is obtained. [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] In general, semiconductor substrates have the property that cleavage occurs more easily along specific crystal planes than other crystal planes. As in Patent Document 1, when a modified layer is formed inside a semiconductor substrate by laser irradiation, stress is generated inside the semiconductor substrate. As a result, when the modified layer is formed, cracks are generated from the modified layer along the specific crystal plane. For this reason, when dividing the semiconductor substrate, the semiconductor substrate may be divided along the cracks in some regions, resulting in large irregularities on the dividing surface. This specification proposes a technology that can accurately control the shape of the dividing surface when dividing a semiconductor substrate after laser irradiation. [Means for solving the problem]

[0005] A method for manufacturing a semiconductor device disclosed in this specification includes the steps of irradiating a semiconductor substrate with a laser so that the focal point of the laser moves within the semiconductor substrate, and dividing the semiconductor substrate. The semiconductor substrate has a specific crystal plane that is easier to cleave than a crystal plane parallel to the surface of the semiconductor substrate and is inclined relative to the surface. In the laser irradiation step, a specific modified layer formation process is repeated to form a specific modified layer extending along the specific crystal plane by moving the focal point along the specific crystal plane. The specific modified layer may include a modified layer formed at the laser focal point and a modified layer formed to connect the focal points. In the laser irradiation step, multiple specific modified layers are formed so that the multiple specific modified layers are arranged in a direction parallel to the surface. In the dividing step, the semiconductor substrate is divided along the multiple specific modified layers.

[0006] In this manufacturing method, in the laser irradiation step, a specific modified layer formation process is repeated, in which the laser focus is moved along a specific crystal plane inside the semiconductor substrate. By moving the laser focus along the specific crystal plane, cracks are less likely to occur along the specific crystal plane when the specific modified layer is formed. In the laser irradiation step, multiple specific modified layers are formed so that the multiple specific modified layers are arranged in a direction parallel to the surface of the semiconductor substrate. Therefore, in the subsequent dividing step, the semiconductor substrate can be divided along the surface of the semiconductor substrate. Because cracks are less likely to occur in the laser irradiation step, the occurrence of large irregularities on the dividing surface of the semiconductor substrate can be suppressed. In other words, this manufacturing method allows for accurate control of the shape of the dividing surface. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. [Figure 2] FIG. 2 is a cross-sectional view of the semiconductor substrate taken along line II-II in FIG. [Figure 3] FIG. 10 is a cross-sectional view of the semiconductor substrate after an element structure forming step. [Figure 4] 4A to 4C are cross-sectional views showing a laser irradiation step in the first embodiment. [Figure 5] FIG. 3 is a plan view showing the trajectory of the laser focus in the laser irradiation step of Example 1. [Figure 6] 4A to 4C are cross-sectional views showing a laser irradiation step in the first embodiment. [Figure 7] 4A to 4C are cross-sectional views showing a substrate dividing step in the first embodiment. [Figure 8] 4A to 4C are cross-sectional views showing a substrate dividing step in the first embodiment. [Figure 9] 10A and 10B are cross-sectional views showing a laser irradiation step of a comparative example. [Figure 10] 10A to 10C are cross-sectional views showing a substrate dividing step of a comparative example. [Figure 11] 4A to 4C are cross-sectional views showing a laser irradiation step in the first embodiment. [Figure 12] 10A to 10C are cross-sectional views showing a laser irradiation step in a modified example of the first embodiment. [Figure 13] FIG. 10 is a plan view showing the trajectory of the laser focus when it is moved back and forth. [Figure 14] 10A to 10C are cross-sectional views showing a laser irradiation step in Example 2. [Figure 15] 10A to 10C are cross-sectional views showing a laser irradiation step in Example 2. [Figure 16] 10A to 10C are cross-sectional views showing a laser irradiation step in Example 3. [Figure 17] 10A and 10B are cross-sectional views showing a laser irradiation step in Example 4. [Figure 18] 10 is a cross-sectional view showing the inclination angles of the specific modified layer and the connectivity modified layer on the m-plane in Example 4. FIG. [Figure 19] 10A to 10C are cross-sectional views showing a substrate dividing step according to the fourth embodiment. [Figure 20] 10 is a graph showing changes in laser energy in the laser irradiation step of Example 5. [Figure 21] 10 is a graph showing changes in laser energy in a laser irradiation step in a modified example of Example 5. [Figure 22] 10 is a graph showing changes in laser energy in a laser irradiation step in a modified example of Example 5. [Figure 23] 10 is a graph showing changes in laser energy in a laser irradiation step in a modified example of Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the above-described manufacturing method, in the step of irradiating the laser, a plurality of the specific modified layers may be formed so that, when viewed along the thickness direction of the semiconductor substrate, one of the specific modified layers partially overlaps with another adjacent specific modified layer.

[0009] With this configuration, if a crack occurs at the laser focus, the crack is likely to intersect with an already formed specific modified layer. When the crack intersects with the specific modified layer, the crack's propagation is likely to stop at the specific modified layer. Therefore, with this configuration, the occurrence of deep cracks can be suppressed.

[0010] In the above-mentioned manufacturing method, in the step of irradiating the laser, a process of forming a connection modification layer may be carried out between two of the specific modification layer formation processes by moving the focus from the end position of the focus in the previous specific modification layer formation process to the start position of the focus in the next specific modification layer formation process.

[0011] According to this configuration, the modified layer is formed continuously, which makes it easier to divide the semiconductor substrate in the dividing step.

[0012] In the above-described manufacturing method, the connection modification layer may be inclined toward an opposite side to the specific modification layer with respect to the surface of the semiconductor substrate.

[0013] Furthermore, when forming a connection improving layer, the above-described manufacturing method may have the following configurations. The specific crystal plane may be a first specific crystal plane. The semiconductor substrate may have a second specific crystal plane that is easier to cleave than the crystal plane parallel to the surface and is tilted relative to the surface. The connection improving layer may extend along the second specific crystal plane.

[0014] In this configuration, the connectivity improving layer is formed along the second specific crystal plane that is easy to cleave, so cracks are less likely to occur when the connectivity improving layer is formed.

[0015] Furthermore, when forming a connectivity improving layer, the angle between the connectivity improving layer and the surface may be equal to the angle between the specific improving layer and the surface. With this configuration, cracks are less likely to occur when the connectivity improving layer is formed.

[0016] In the above-described manufacturing method, the surface may be a first surface. The semiconductor substrate may have a second surface located opposite the first surface. In the step of irradiating with a laser, the laser may be irradiated onto the semiconductor substrate from the second surface side. In each of the specific modified layer formation processes, the focal point may be moved from the second surface toward the first surface along the specific crystal plane.

[0017] This configuration makes it possible to more effectively prevent the occurrence of cracks extending from the laser focus position toward the second surface.

[0018] In the manufacturing method in which the focal point is moved from the second surface toward the first surface along the specific crystal plane, in each of the specific modified layer formation processes, when the focal point is moved from the starting position of the focal point, the energy of the laser may be increased as the focal point is moved.

[0019] This configuration makes it possible to more effectively prevent the occurrence of cracks extending from the laser focus position toward the second surface.

[0020] In the above-described manufacturing method, the semiconductor substrate may be made of gallium nitride, the surface of the semiconductor substrate may be parallel to a c-plane, and the specific crystal plane may be a (11-28) plane.

[0021] In the above-described manufacturing method, the semiconductor substrate may be made of gallium nitride. The surface of the semiconductor substrate may be parallel to a c-plane. The specific crystal plane may be inclined at an angle of 21.8 degrees with respect to the c-plane in a cross section along an m-plane. [Example]

[0022] FIG. 1 shows a semiconductor substrate 12 to be processed. The semiconductor substrate 12 is made of a single crystal of gallium nitride and has a hexagonal crystal structure. The symbols a1, a2, a3, and c in each figure represent the a1 axis, a2 axis, a3 axis, and c axis of the hexagonal crystal structure. FIG. 2 shows a cross section taken along line II-II in FIG. 1. That is, the cross section shown in FIG. 2 represents the m-plane (i.e., the (1-100) plane). As shown in FIG. 2, the semiconductor substrate 12 has a first surface 12a and a second surface 12b as major surfaces. The first surface 12a is formed by the c-plane (i.e., the (0001) plane). The second surface 12b is located on the opposite side of the first surface 12a and is parallel to the first surface 12a. The dashed line in FIG. 2 represents the (11-28) plane, which is perpendicular to the [11-28] direction. 2 indicates the inclination angle of the (11-28) plane with respect to the first surface 12a. The angle θ1 is 21.8 degrees. The (11-28) plane is a crystal plane that is easier to cleave than the c-plane.

[0023] (Element structure formation process) In the manufacturing method of Example 1, first, an element structure forming step is performed. In the element structure forming step, as shown in Fig. 3, a semiconductor element structure is formed in a region on the first surface 12a side of the semiconductor substrate 12. For example, a dopant diffusion layer is formed in a semiconductor region near the first surface 12a. In addition, an electrode 13 is formed on the first surface 12a.

[0024] (Laser irradiation process) Next, a laser irradiation process is performed. As shown in FIG. 4, in the laser irradiation process, a laser beam L is irradiated onto the semiconductor substrate 12 from the second surface 12b side. The semiconductor substrate 12 is optically transparent. Here, the laser beam L is irradiated onto the semiconductor substrate 12 so that a focal point S is formed inside the semiconductor substrate 12. At the position of the focal point S, the semiconductor substrate 12 is heated and decomposed. As a result, a modified layer 14 with reduced crystallinity is formed at the position of the focal point S. For example, the modified layer 14 is composed of gallium precipitated by the decomposition of gallium nitride. Here, the modified layer 14 is formed extending along the first surface 12a by moving the focal point S in the a3 direction. Also, here, as shown by the arrow in FIG. 5, the process of moving the focal point S in the a3 direction is repeatedly performed at intervals in the [1-100] direction. As a result, the modified layer 14 is formed over substantially the entire semiconductor substrate 12 when the semiconductor substrate 12 is viewed along the c-axis.

[0025] FIG. 6 is a detailed explanatory diagram of the process of moving the focal point S in the a3 direction, showing an enlarged view of the modified layer 14. As indicated by the arrow in FIG. 6, in the process of moving the focal point S in the a3 direction, instead of moving the focal point S parallel to the a3 direction, the process of moving the focal point S along the (11-28) plane inclined relative to the a3 direction is repeated. By moving the focal point S along the (11-28) plane, a specific modified layer 16 extending along the (11-28) plane is formed. Hereinafter, each process of moving the focal point S along the (11-28) plane is referred to as a specific modified layer formation process. Hereinafter, the specific modified layer formation process is repeatedly performed while moving in the a3 direction. That is, after one specific modified layer formation process is completed, the specific modified layer formation process is performed again at a position shifted in the a3 direction. By repeating the specific modified layer formation process in this manner, multiple specific modified layers 16 extending along the (11-28) plane are formed. When a plurality of specifically modified layers 16 are formed in this manner, the plurality of specifically modified layers 16 are formed so as to be arranged along the a3 direction. The modified layer 14 described above is an aggregate of a plurality of specifically modified layers 16.

[0026] In each specific modified layer formation process, the focal point S is moved along the (11-28) plane from the second surface 12b toward the first surface 12a. That is, the end 16b of each specific modified layer 16 on the second surface 12b side is the starting position of the focal point S in the specific modified layer formation process, and the end 16a of each specific modified layer 16 on the first surface 12a side is the ending position of the focal point S in the specific modified layer formation process. In each specific modified layer formation process, the specific modified layer 16 is formed along the movement trajectory of the focal point S from the starting position of the focal point S to the ending position. After the focal point S has been moved to the ending position, the irradiation of the laser L is stopped, and the target point of the laser L is moved to the starting position of the next specific modified layer formation process, and the next specific modified layer formation process is started. Therefore, no modified layer is formed between two specific modified layers 16 (i.e., between the end 16a of one specific modified layer 16 and the end 16b of the adjacent specific modified layer 16). Furthermore, in each specific modified layer forming process, the energy of the laser L is maintained approximately constant.

[0027] (Substrate division process) Next, a substrate dividing step is performed. In the substrate dividing step, the semiconductor substrate 12 is divided along the modified layer 14 (i.e., the plurality of specific modified layers 16) as shown in FIGS. 7 and 8. That is, the element structure portion 12s (i.e., the portion of the semiconductor substrate 12 on the first surface 12a side (in other words, the portion on which the semiconductor element structure is formed)) is peeled off from the base portion 12t (i.e., the portion of the semiconductor substrate 12 on the second surface 12b side). For example, the first surface 12a is fixed to a first support plate, the second surface 12b is fixed to a second support plate, and the first support plate is separated from the second support plate, thereby allowing the element structure portion 12s to be peeled off from the base portion 12t. Hereinafter, the dividing surface on the element structure portion 12s side is referred to as dividing surface 12d-1, and the dividing surface on the base portion 12t side is referred to as dividing surface 12d-2.

[0028] Thereafter, the element structure portion 12s is divided into a plurality of chips to manufacture semiconductor devices. After the dividing surface 12d-2 of the base portion 12t is polished, the base portion 12t is used to manufacture other semiconductor devices.

[0029] The manufacturing method of Example 1 can prevent the occurrence of unintended irregularities on the dividing surfaces 12d-1 and 12d-2 of the semiconductor substrate 12. The manufacturing method of Example 1 will be described below in comparison with a manufacturing method of a comparative example.

[0030] FIG. 9 shows a laser irradiation step in the manufacturing method of the comparative example. In the laser irradiation step of the comparative example, the focal point S is moved parallel to a crystal plane (i.e., the c-plane) parallel to the first surface 12a of the semiconductor substrate 12. Therefore, the modified layer 14 is formed parallel to the c-plane. As described above, in Example 1, when the microscopic area is enlarged as shown in FIG. 6, the modified layer 14 (i.e., each specific modified layer 16) is formed parallel to the (11-28) plane. In contrast, in the comparative example, when the microscopic area is enlarged as shown in FIG. 9, the modified layer 14 is formed parallel to the c-plane. Thus, in Example 1 and the comparative example, the direction in which the modified layer 14 extends when the microscopic area is enlarged is different. In the laser irradiation step, the semiconductor substrate 12 is heated to a high temperature at the focal point S, so high stress is generated around the focal point S. Furthermore, as described above, the semiconductor substrate 12 is easily cleaved along the (11-28) plane. As shown in FIG. 9 , in the laser irradiation process of the comparative example, high stress is generated at the focal point S, which easily causes deep cracks 90 to form in the modified layer 14 along the (11-28) plane. Thus, in the comparative example, deep cracks 90 are easily generated from the modified layer 14 to its periphery. Therefore, as shown in FIG. 10 , in the substrate dividing process of the comparative example, when dividing the semiconductor substrate 12 along the modified layer 14, the semiconductor substrate 12 is easily cracked along the cracks 90. As a result, large irregularities are easily generated on the dividing surfaces 12d-1 and 12d-2. Furthermore, because the cracks 90 are generated unintentionally, it is difficult to control the irregular shape of the dividing surfaces 12d-1 and 12d-2. Furthermore, deep cracks 90 remain on the dividing surfaces 12d-1 and 12d-2. Therefore, after the dividing process, the dividing surfaces 12d-1 and 12d-2 must be heavily polished to remove the cracks 90.

[0031] In contrast, in the laser irradiation process of Example 1, the specific modified layers 16 are formed to extend along the (11-28) plane, as shown in FIG. 6 . Forming the specific modified layers 16 along the (11-28) plane, which is prone to cleavage, reduces the likelihood of cracks 90. Therefore, in the substrate dividing process, the semiconductor substrate 12 is likely to be divided accurately along the modified layers 14. Therefore, as shown in FIG. 7 , large irregularities are unlikely to occur on the dividing surfaces 12d-1 and 12d-2. As shown in FIG. 7 , in the manufacturing method of Example 1, irregularities are formed on the dividing surfaces 12d-1 and 12d-2 along the modified layers 14, but these irregularities are smaller than the irregularities caused by cracks. Therefore, the manufacturing method of Example 1 can prevent large irregularities from occurring on the dividing surfaces 12d-1 and 12d-2. Furthermore, in the manufacturing method of Example 1, the semiconductor substrate 12 is likely to be divided along the modified layers 14, making it easier to control the irregular shape of the dividing surfaces 12d-1 and 12d-2. Furthermore, in the manufacturing method of Example 1, cracks 90 are unlikely to exist on the dividing surfaces 12d-1 and 12d-2. Therefore, the amount of polishing required to remove the cracks 90 on the dividing surfaces 12d-1 and 12d-2 can be small. Furthermore, if the cracks 90 have little effect, polishing the dividing surfaces 12d-1 or 12d-2 may not be necessary.

[0032] If the dividing surface 12d-1 is not polished, the uneven dividing surface 12d-1 becomes the back surface of the semiconductor device. That is, a semiconductor device having a structure in which the back surface has multiple protrusions, each of which has an inclined surface extending along the (11-28) plane, is obtained. In this case, if an electrode is formed on the uneven dividing surface 12d-1, the adhesion between the electrode and the dividing surface 12d-1 can be improved.

[0033] When the laser beam L is irradiated from the second surface 12b side, the semiconductor region closer to the second surface 12b than the modified layer 14 (i.e., the base portion 12t) is likely to reach a higher temperature than the semiconductor region closer to the first surface 12a than the modified layer 14 (i.e., the element structure portion 12s). Therefore, as shown in FIG. 9, for example, deep cracks 90 may easily occur from the modified layer 14 toward the second surface 12b. In this case, as in Example 1 (i.e., FIG. 6), by moving the focal point S along the (11-20) plane from the second surface 12b toward the first surface 12a in each specific modified layer formation process, the occurrence of cracks 90 can be more effectively suppressed. For example, FIG. 11 shows a state during the specific modified layer formation process of Example 1. During the specific modified layer formation process, the specific modified layer 16 exists in the direction toward the second surface 12b along the (11-28) plane as viewed from the focal point S (the direction of the arrow 100 in FIG. 11). The specifically modified layer 16 is a region with reduced crystallinity, and therefore cracks are less likely to occur in the specifically modified layer 16. Therefore, cracks are prevented from occurring from the position of the focal point S along the (11-28) plane toward the second surface 12b.

[0034] In addition, in cases where the occurrence of cracks 90 on the second surface 12b side is not a significant problem, the direction in which the focal point S is moved may be opposite to that shown in Figure 6. That is, the focal point S may be moved from end 16a toward end 16b as shown by the arrow in Figure 12. Furthermore, the movement methods shown in Figures 6 and 12 may be combined to move the focal point S back and forth as shown in Figure 13. [Example]

[0035] The manufacturing method of Example 2 differs from the manufacturing method of Example 1 in the laser irradiation step. The other configurations of the manufacturing method of Example 2 are the same as those of the manufacturing method of Example 1.

[0036] In Example 2, as shown in Fig. 14, a plurality of specific modified layers 16 are formed so that adjacent specific modified layers 16 partially overlap each other when viewed along the thickness direction (i.e., direction c) of the semiconductor substrate 12. That is, in Fig. 14, when viewed along the thickness direction of the semiconductor substrate 12, a portion 16ax near the end 16a of each specific modified layer 16 overlaps a portion 16bx near the end 16b of the adjacent specific modified layer 16.

[0037] According to the manufacturing method of Example 2, as described below, the occurrence of cracks 90 near the end 16b of each specifically modified layer 16 can be more effectively suppressed. As described above, the end 16b is the starting position of the focal point S in each specifically modified layer formation process. The starting position of the focal point S is the position where crystal defects in the specifically modified layer 16 are first formed, and cracks 90 are likely to occur there. If the portion 16ax of each specifically modified layer 16 overlaps the portion 16bx of an adjacent specifically modified layer 16 as in Example 2, when a crack 90 occurs downward from near the starting position of the focal point S (i.e., near the end 16b) as shown in FIG. 15, the crack 90 will collide with another specifically modified layer 16. Then, because the crystallinity of the specifically modified layer 16 is low, the propagation of the crack 90 stops at the intersection of the specifically modified layer 16 and the crack 90. ​​This suppresses the occurrence of deep cracks 90. Therefore, according to the manufacturing method of Example 2, the occurrence of cracks 90 near the end 16b can be effectively suppressed. [Example]

[0038] The manufacturing method of Example 3 differs from the manufacturing method of Example 1 in the laser irradiation step. The other configurations of the manufacturing method of Example 3 are the same as those of the manufacturing method of Example 1.

[0039] In the laser irradiation step of Example 3, as shown in FIG. 16, a connection modified layer 18 is formed so as to connect the end 16b of one specific modified layer 16 to the end 16a of the adjacent specific modified layer 16. Specifically, after one specific modified layer formation process is completed, the focal point S is moved from the end position of the previous specific modified layer formation process to the start position of the next specific modified layer formation process while continuing to irradiate with the laser L. That is, for example, in FIG. 16, after the formation process of the specific modified layer 16-1 is completed, the focal point S is moved from the end position of the specific modified layer 16-1 (i.e., the end 16a) to the start position of the specific modified layer 16-2 (i.e., the end 16b) while continuing to irradiate with the laser L. In other words, the focal point S is moved in a zigzag pattern. By moving the focal point S in this manner, a connection modified layer 18 that connects the specific modified layers 16 is formed.

[0040] In the substrate dividing step of Example 3, the substrate is divided along the specific modified layer 16 and the connectivity modifying layer 18. That is, the semiconductor substrate 12 is divided in the region between adjacent specific modified layers 16 while being guided by the connectivity modifying layer 18. Therefore, the shapes of the dividing surfaces 12d-1 and 12d-2 can be controlled more accurately. [Example]

[0041] The manufacturing method of Example 4 differs from the manufacturing method of Example 1 in the laser irradiation step. The other configurations of the manufacturing method of Example 4 are the same as those of the manufacturing method of Example 1.

[0042] As shown in FIG. 17, in the laser irradiation step of Example 4, the interval between the specific modified layers 16 in the a3 direction is wider than in Example 1. That is, in Example 4, a wider interval C1 is provided between the end 16b of one specific modified layer 16 and the end 16a of the adjacent specific modified layer 16. Furthermore, in the laser irradiation step of Example 4, similar to Example 3, a connectivity modified layer 18 is formed so as to connect the end 16b of one specific modified layer 16 to the end 16a of the adjacent specific modified layer 16. In Example 4, the connectivity modified layer 18 is formed so as to be inclined toward the opposite side of the specific modified layer 16 with respect to the first surface 12a. FIG. 18 shows the inclination angles of the specific modified layer 16 and the connectivity modified layer 18. Note that the dashed line 101 in FIG. 18 indicates a plane parallel to the first surface 12a. 18, the specific modified layer 16 is inclined at an angle θ1 with respect to the first surface 12a, and the connectivity modified layer 18 is inclined at an angle θ2 with respect to the first surface 12a on the side opposite to the specific modified layer 16. As described above, the angle θ1 is 21.8 degrees. The angle θ2 is equal to the angle θ1 (i.e., 21.8 degrees). That is, the connectivity modified layer 18 extends along the (-1-128) plane.

[0043] The (-1-128) plane is a crystal plane that is symmetrical with respect to the (11-28) plane and is a crystal plane that is relatively prone to cleavage. Therefore, cleavage occurs more easily in the (-1-128) plane than in the c-plane. Therefore, when the connectivity improving layer 18 is formed along the (-1-128) plane, cracks are less likely to occur during the formation of the connectivity improving layer 18.

[0044] In the substrate dividing step of Example 4, as shown in Fig. 19, the substrate is divided along the specific modified layer 16 and the connectivity modifying layer 18. That is, the semiconductor substrate 12 is divided in the region between adjacent specific modified layers 16 while being guided by the connectivity modifying layer 18. Therefore, the shapes of the dividing surfaces 12d-1 and 12d-2 can be controlled more accurately. Furthermore, in Example 4, the corners of the irregularities formed on the dividing surfaces 12d-1 and 12d-2 are obtuse, so chipping is less likely to occur in the substrate dividing step.

[0045] In Example 4, the connectivity improving layer 18 was formed along the (-1-128) plane, but the connectivity improving layer 18 may be formed along another crystal plane that is more likely to cleave than the c-plane. [Example]

[0046] The manufacturing method of Example 5 differs from the manufacturing method of Example 1 in the laser irradiation step. The other configurations of the manufacturing method of Example 5 are the same as those of the manufacturing method of Example 1.

[0047] As described above, in Example 1, the energy of the laser L is maintained approximately constant during each specific modified layer formation process. In contrast, in Example 5, the energy of the laser L is increased during each specific modified layer formation process. Figure 20 shows the change in energy E of the laser L during the specific modified layer formation process of Example 5. The horizontal axis of Figure 20 indicates the position of the focal point S.

[0048] As described above, cracks 90 are likely to occur at the starting position of the focal point S. For this reason, in the specific modified layer formation process of Example 5, as shown in FIG. 20, the laser L is irradiated with low energy EL at the starting position of the focal point S (i.e., end 16b). Therefore, the occurrence of cracks at the starting position of the focal point S is suppressed. As shown in FIG. 20, the energy E of the laser L is increased as the focal point S moves during the specific modified layer formation process. At the end position of the laser L irradiation (i.e., end 16a), the energy E of the laser L increases to energy EH. In this way, by increasing the energy E of the laser L during the specific modified layer formation process, the specific modified layer 16 can be suitably formed while suppressing the occurrence of cracks at the starting position of the focal point S.

[0049] Since cracks are likely to occur at the starting position of the focal point S, the energy E may be increased near the starting position of the focal point S and kept constant in the latter half of the specific modified layer formation process, as shown in Fig. 21. Alternatively, the energy E may be increased near the starting position of the focal point S and decreased in the latter half of the specific modified layer formation process, as shown in Fig. 22. Alternatively, the energy E of the laser L may be changed in steps, as shown in Fig. 23.

[0050] Although the first to fifth embodiments have been described above, the first to fifth embodiments may be combined and implemented.

[0051] The (11-28) plane in the embodiment is an example of a specific crystal plane and a first specific crystal plane. The a3 direction in the embodiment is an example of a direction parallel to the surface of the semiconductor substrate. The end 16b in the embodiment is an example of a starting position of the focus in the specific modified layer formation process. The end 16a in the embodiment is an example of an ending position of the focus in the specific modified layer formation process. The (-1-128) plane in the embodiment is an example of a second specific crystal plane. The first surface 12a in the embodiment is an example of a front surface of the semiconductor substrate of the semiconductor device. The dividing surface 12d-1 in the embodiment is an example of a back surface of the semiconductor substrate of the semiconductor device.

[0052] 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]

[0053] 12: semiconductor substrate, 14: modified layer, 16: specific modified layer

Claims

1. A method for manufacturing a semiconductor device, comprising: irradiating the semiconductor substrate with a laser so that the focal point of the laser moves within the semiconductor substrate; dividing the semiconductor substrate; and the semiconductor substrate has a specific crystal plane that is more easily cleaved than a crystal plane parallel to a surface (12a) of the semiconductor substrate and is inclined with respect to the surface, In the step of irradiating the laser, a specific modified layer forming process is repeated to form a specific modified layer (16) extending along the specific crystal plane by moving the focus along the specific crystal plane; In the step of irradiating the laser, a plurality of the specific modified layers are formed so that the plurality of specific modified layers are arranged along a direction parallel to the surface, In the step of dividing the semiconductor substrate, the semiconductor substrate is divided along the plurality of specific modified layers. Manufacturing method.

2. The manufacturing method described in claim 1, wherein in the step of irradiating the laser, multiple specific modified layers are formed so that one specific modified layer partially overlaps with another adjacent specific modified layer when viewed along the thickness direction of the semiconductor substrate.

3. The manufacturing method described in claim 2, wherein in the step of irradiating the laser, a process of forming a connection modification layer (18) is carried out by moving the focus from the end position of the focus in the previous specific modification layer formation process to the start position of the focus in the next specific modification layer formation process between two specific modification layer formation processes.

4. the connection modification layer is inclined toward the opposite side to the specific modification layer with respect to the surface of the semiconductor substrate; The method of claim 3.

5. the specific crystal plane is a first specific crystal plane, the semiconductor substrate has a second specific crystal plane that is easier to cleave than the crystal plane parallel to the surface and is inclined with respect to the surface, the connectivity improvement layer extends along the second specific crystal plane; The method of claim 4.

6. The manufacturing method according to claim 4 , wherein the angle between the connection modification layer and the surface is equal to the angle between the specific modification layer and the surface.

7. the surface is a first surface (12a), the semiconductor substrate has a second surface (12b) located opposite the first surface; In the step of irradiating with a laser, the laser is irradiated onto the semiconductor substrate from the second surface side; In each of the specific modified layer forming processes, the focus is moved along the specific crystal plane from the second surface toward the first surface. The method according to any one of claims 1 to 6.

8. The manufacturing method according to claim 7 , wherein in each of the specific modified layer forming processes, when the focal point is moved from the starting position of the focal point, energy of the laser is increased in accordance with the movement of the focal point.

9. the semiconductor substrate is made of gallium nitride, the surface of the semiconductor substrate is parallel to the c-plane; The specific crystal plane is the (11-28) plane. The method according to any one of claims 1 to 7.

10. the semiconductor substrate is made of gallium nitride, the surface of the semiconductor substrate is parallel to the c-plane; the specific crystal plane is inclined at an angle of 21.8 degrees with respect to the c-plane in a cross section along the m-plane; The method according to any one of claims 1 to 7.

11. A semiconductor device, a semiconductor substrate having a front surface and a back surface opposite to the front surface; the semiconductor substrate has a specific crystal plane that is more easily cleaved than a crystal plane parallel to the surface and is inclined with respect to the surface, The back surface has an uneven shape including a plurality of protrusions, each of the protrusions has an inclined surface extending along the specific crystal plane, the semiconductor substrate is made of gallium nitride, the surface of the semiconductor substrate is parallel to the c-plane; The specific crystal plane is the (11-28) plane. Semiconductor device.

12. A semiconductor device, a semiconductor substrate having a front surface and a back surface opposite to the front surface; the semiconductor substrate has a specific crystal plane that is more easily cleaved than a crystal plane parallel to the surface and is inclined with respect to the surface, The back surface has an uneven shape including a plurality of protrusions, each of the protrusions has an inclined surface extending along the specific crystal plane, the semiconductor substrate is made of gallium nitride, the surface of the semiconductor substrate is parallel to the c-plane; the specific crystal plane is inclined at an angle of 21.8 degrees with respect to the c-plane in a cross section along the m-plane; Semiconductor device.

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