JP7849320B2 - Semiconductor device manufacturing method - Google Patents

Description

The technology disclosed herein relates to a method for manufacturing semiconductor devices.

Patent Document 1 discloses a technique for creating a thin substrate by dividing a semiconductor substrate vertically. In this technique, a modified layer extending laterally is formed within the semiconductor substrate by irradiating it with a laser. Next, the semiconductor substrate is divided along the modified layer. This allows for the creation of a thin substrate.

Japanese Patent Publication No. 2018-133487

When a laser is irradiated onto a semiconductor substrate, the crystal is decomposed at the laser irradiation site, forming a modified layer. Gas is generated during the formation of this modified layer. In conventional techniques, the pressure of the gas generated during the formation of the modified layer can cause cracks in the semiconductor substrate. This specification proposes a technique to suppress cracks when forming a modified layer for dividing a semiconductor substrate.

The method for manufacturing a semiconductor device disclosed in this specification comprises a semiconductor substrate preparation step, a decomposition region formation step, a first modified layer formation step, a second modified layer formation step, and a division step. In the semiconductor substrate preparation step, a semiconductor substrate is prepared in which a plurality of device regions are provided on the upper surface layer. Here, a semiconductor substrate is prepared in which the plurality of device regions are arranged in a matrix on the upper surface. In the decomposition region formation step, a decomposition region is formed on the upper surface, extending linearly along the boundaries of the plurality of device regions. In the first modified layer formation step, a first modified layer is formed inside the semiconductor substrate by irradiating the semiconductor substrate with a laser. Here, the first modified layer is formed such that, when viewed from above, the first modified layer extends along the decomposition region while overlapping it, the first modified layer exists in a part of the range in which the decomposition region exists in the thickness direction of the semiconductor substrate, and the first modified layer has a wider width than the decomposition region. In the second modification layer formation step, a laser is irradiated onto the element region in a scanning manner to form a second modification layer within the element region. Here, the area where the second modification layer exists and the area where the first modification layer exists overlap in the thickness direction of the semiconductor substrate, and the second modification layer is formed so that it connects to the first modification layer. In the splitting step, the semiconductor substrate is split along the first and second modification layers.

Furthermore, the "modified layer" refers to a layer composed of materials generated by the decomposition of the crystal structure of the original semiconductor substrate. The "decomposition region" refers to a region where the crystallinity of the original semiconductor substrate has been decomposed. The decomposition region may be a groove or a modified layer.

In the first modified layer formation process, gas is generated at the laser irradiation site (i.e., the site where the first modified layer is formed). Since the first modified layer is formed in an area that overlaps with the decomposition region, the gas generated at the site where the first modified layer is formed escapes to the outside of the semiconductor substrate through the decomposition region. Therefore, in the first modified layer formation process, the pressure rise inside the semiconductor substrate is suppressed, and the occurrence of cracks is suppressed. In the second modified layer formation process, the second modified layer is formed inside the device region by irradiating the device region with a laser in a scanning manner. Since the first modified layer has a wider width than the decomposition region, the distance from the site where the second modified layer is formed to the first modified layer is shorter than the distance from the site where the second modified layer is formed to the decomposition region. Therefore, the gas generated at the site where the second modified layer is formed can easily reach the first modified layer. For this reason, the gas generated at the site where the second modified layer is formed escapes to the outside of the semiconductor substrate through the first modified layer and the decomposition region. Therefore, even in the second modification layer formation step, the pressure rise inside the semiconductor substrate is suppressed, and the occurrence of cracks is suppressed. As explained above, this manufacturing method can suppress cracks when forming a modification layer to divide the semiconductor substrate.

Plan view of the semiconductor substrate 12. A plan view of the semiconductor substrate 12 after the groove 30 has been formed. Enlarged longitudinal cross-sectional view of the semiconductor substrate 12 after groove 30 has been formed. Enlarged longitudinal cross-sectional view of the semiconductor substrate 12 showing the first modification layer formation process. An enlarged plan view showing the movement path of focal point X in the first modified layer formation process. A plan view of the semiconductor substrate 12 after the formation of the first modified layer 61. Enlarged longitudinal cross-sectional view of the semiconductor substrate 12 showing the second modified layer formation process. A plan view of the semiconductor substrate 12 after the formation of the second modified layer 62. Enlarged longitudinal cross-sectional view of semiconductor substrate 12 showing the splitting process. An enlarged plan view showing the movement path of the focal point X during the second modified layer formation step in Example 2. An enlarged plan view showing the movement path of focal point X during the second modified layer formation step of the comparative example. An enlarged plan view showing the movement path of the focal point X during the second modified layer formation step in Example 3. A plan view of the semiconductor substrate 12 after the formation of the third modified layer 63. An enlarged longitudinal cross-sectional view of the semiconductor substrate 12 showing the first modified layer formation process of a modified example.

An example of a semiconductor device manufacturing method disclosed herein may include a step of forming a third modified layer inside the semiconductor substrate by irradiating the semiconductor substrate with a laser, after the first modified layer formation step and before the second modified layer formation step. In this step, the third modified layer may be formed such that, when viewed from above, the third modified layer intersects with the first modified layer, and the area where the third modified layer exists and the area where the first modified layer exists overlap in the thickness direction of the semiconductor substrate.

This configuration allows for more effective suppression of crack formation during the formation of the modified layer.

In one example of a semiconductor device manufacturing method disclosed herein, the device region may be rectangular. In the second modified layer formation step, the process of moving the laser focal point parallel to the short side of the rectangle may be repeatedly performed while shifting the position in a direction parallel to the long side of the rectangle.

With this configuration, the gas generated at the formation site of the second reformed layer can more easily escape to the outside of the semiconductor substrate.

In one example of a semiconductor device manufacturing method disclosed herein, the second modification layer formation step may involve moving the laser focal point in a spiral pattern from the outer periphery towards the center within the region demarcated by the first modification layer.

With this configuration, the gas generated at the formation site of the second reformed layer can more easily escape to the outside of the semiconductor substrate.

In one example of a semiconductor device manufacturing method disclosed herein, the decomposition region formation step may involve forming grooves on the upper surface using a dicing blade. These grooves may also constitute the decomposition region.

In the manufacturing method of Example 1, the semiconductor substrate preparation step, the decomposition region formation step, the first modified layer formation step, the second modified layer formation step, and the division step are carried out in order.

First, in the semiconductor substrate preparation process, the semiconductor substrate 12 shown in Figure 1 is prepared. In this embodiment, the semiconductor substrate 12 is made of GaN. However, the semiconductor substrate 12 may be made of other semiconductor materials such _{as Ga2O3} . Multiple element regions 20 are provided on the upper surface layer of the semiconductor substrate 12. Although not shown, each element region 20 is provided with a semiconductor element structure composed of a p-type semiconductor layer, an n-type semiconductor layer, electrodes, etc. Each element region 20 is arranged in a matrix shape vertically and horizontally on the upper surface of the semiconductor substrate 12.

Next, the decomposition region formation process is performed. In Example 1, grooves 30 are formed as decomposition regions. Here, as shown in Figures 2 and 3, grooves 30 are formed on the upper surface, extending linearly along the boundaries of each element region 20. That is, the grooves 30 extend in a grid pattern on the upper surface of the semiconductor substrate 12. The grooves 30 can be formed by cutting the semiconductor substrate 12 with a dicing blade or the like.

Next, the first modified layer formation process is carried out. Here, as shown in Figure 4, the semiconductor substrate 12 is irradiated with a laser L so that a focal point X is formed inside the semiconductor substrate 12. In this embodiment, the laser L is pulsed. However, in other embodiments, the laser may be irradiated continuously. When the semiconductor substrate 12 is irradiated with the laser L, GaN is decomposed at the focal point X and gallium is deposited. A modified layer is formed by the deposited gallium. Hereinafter, the modified layer formed in the first modified layer formation process will be referred to as the first modified layer 61. Here, as shown in Figure 4, the first modified layer 61 is formed at the bottom of the depth range in which the groove 30 exists in the thickness direction of the semiconductor substrate 12. Also, here, as shown in Figure 5, the focal point X is moved along the groove 30 while reciprocating so that it crosses the groove 30 when the semiconductor substrate 12 is viewed from above. As a result, as shown in Figure 4, the first modified layer 61 is formed so as to overlap with the groove 30. Specifically, as shown in Figure 6, the first modified layer 61 is formed so that, when viewed from above, it overlaps with the groove 30 and extends along the groove 30. Furthermore, the first modified layer 61 is formed to have a width wider than the groove 30. Nitrogen gas is generated when the modified layer is formed (i.e., when GaN decomposes). The nitrogen gas generated during the formation of the first modified layer 61 is discharged to the outside of the semiconductor substrate 12 through the groove 30. Because the first modified layer 61 is adjacent to the groove 30, the nitrogen gas generated in the first modified layer 61 is easily discharged to the outside through the groove 30. Therefore, the occurrence of cracks in the semiconductor substrate 12 is suppressed during the first modified layer formation process.

Furthermore, in the first modified layer formation step, the focal point X may be moved along a different path than that shown in Figure 5. For example, the process of moving the focal point X parallel to the groove 30 may be repeatedly performed in the area where the first modified layer 61 is to be formed. Alternatively, for example, the focal point X may be moved to scan the entire semiconductor substrate 12, and the laser output may be turned off in areas other than the vicinity of the groove 30.

Next, the second modified layer formation process is carried out. In the second modified layer formation process, as shown in Figure 7, a laser L is irradiated onto the semiconductor substrate 12 so that a focal point X is formed inside the semiconductor substrate 12. This forms a modified layer inside the semiconductor substrate 12. Here, the modified layer formed in the second modified layer formation process is called the second modified layer 62. Here, the second modified layer 62 is formed in a region that overlaps with the region where the first modified layer 61 exists in the thickness direction of the semiconductor substrate 12. More specifically, the second modified layer 62 is formed at the same depth as the first modified layer 61. Also, here, the focal point X is moved so that it scans the entire area of the semiconductor substrate 12 when viewed from above. As a result, as shown in Figure 8, the second modified layer 62 is formed over the entire area of each element region 20 when viewed from above. The second modified layer 62 is connected to the first modified layer 61. Therefore, the nitrogen gas generated during the formation of the second modified layer 62 is discharged to the outside of the semiconductor substrate 12 via the first modified layer 61 and the groove 30. As described above, in the first modified layer formation process, the first modified layer 61, which has a wider width than the groove 30, is formed around the groove 30. Therefore, when forming the second modified layer 62 within the device region 20, the distance from the second modified layer 62 to the first modified layer 61 is short. Consequently, the nitrogen gas generated in the second modified layer 62 is easily discharged to the outside via the first modified layer 61 and the groove 30. Therefore, gas accumulation (i.e., a space where nitrogen gas accumulates) is less likely to form within the device region 20 during the formation of the second modified layer 62. Consequently, the occurrence of cracks within the device region 20 can be suppressed.

Next, the splitting process is performed. In the splitting process, as shown in Figure 9, a support member 40 is attached to the upper surface of the semiconductor substrate 12, and force is applied in a direction that separates the upper part 12a of the semiconductor substrate 12 from the lower part 12b of the semiconductor substrate 12. Because the strength of the modified layers 61 and 62 is lower than the strength of the original semiconductor crystal, the upper part 12a of the semiconductor substrate 12 peels off from the lower part 12b of the semiconductor substrate 12, using the modified layers 61 and 62 as the boundary. This reduces the thickness of the semiconductor substrate 12 in each element region 20. Furthermore, this divides each element region 20 into multiple semiconductor chips (i.e., semiconductor elements). The lower part 12b of the semiconductor substrate 12 is reused in the manufacture of semiconductor elements. Afterward, electrodes are formed on the lower surface of each element region 20 to complete the semiconductor element.

As shown in Figure 10, in Example 2, the element region 20 is rectangular. In other respects, Example 2 is identical to Example 1.

In Example 2, during the second modified layer formation process, the focus X is moved to scan the entire area of the semiconductor substrate 12. The dashed arrows in Figure 10 indicate the movement path of the focus X during the second modified layer formation process in Example 2. In Example 2, the process of moving the focus X in a direction parallel to the shorter side of the rectangle is repeatedly performed, while shifting its position in a direction parallel to the longer side of the rectangle. Although the dashed arrows in Figure 10 indicate a back-and-forth movement of the focus X, the focus X may also be moved in one direction along the shorter side. Furthermore, the dashed arrows in Figure 11 indicate the movement path of the focus X during the second modified layer formation process in the comparative example. In the comparative example, the process of moving the focus X in a direction parallel to the longer side is repeatedly performed, while shifting its position in a direction parallel to the shorter side. In Figures 10 and 11, the area indicated by the dashed arrows (i.e., the area already traversed by the focus X) already has the second modified layer 62 formed.

In Figure 11, no reforming layer 62 is formed between the first reforming layer 61 located on the lower side of Figure 11 and the focus X. Therefore, the nitrogen gas generated at focus X flows mainly through the paths shown by arrows 100 to 102 to the first reforming layer 61 located on the upper, left, and right sides of Figure 11. In this case, the distance of path 100 is approximately equal to the length of the short side, and the distances of paths 101 and 102 are approximately equal to half the length of the long side. In contrast, in Figure 10, no reforming layer 62 is formed between the first reforming layer 61 located on the right side of Figure 10 and the focus X. Therefore, the nitrogen gas generated at focus X flows mainly through the paths shown by arrows 200 to 202 to the first reforming layer 61 located on the left, upper, and lower sides of Figure 10. In this case, the distances of paths 201 and 202 are approximately equal to half the length of the short side, and are short. Thus, according to the method of Example 2, the exhaust path for nitrogen gas generated at focus X is shorter compared to the method of the Comparative Example, and the nitrogen gas is more easily discharged to the outside of the semiconductor substrate 12. Therefore, according to the configuration of Example 2, cracks in the semiconductor substrate 12 can be suppressed more effectively during the second modified layer formation process.

In Example 3, during the second modified layer formation process, the focal point X is moved as shown in Figure 12. Specifically, the focal point X is moved in a spiral pattern from the outer periphery of each element region 20 towards the center. With this configuration, regardless of the position of the focal point X, the shortest distance from the focal point X to the nearest groove 30 ensures a nitrogen gas discharge path, making it easier for nitrogen gas to be discharged to the outside of the semiconductor substrate 12. Therefore, according to the configuration of Example 3, cracks in the semiconductor substrate 12 can be more effectively suppressed during the second modified layer formation process.

In Example 4, the third modified layer formation step is performed after the first modified layer formation step and before the second modified layer formation step. In the third modified layer formation step, a laser is irradiated onto the semiconductor substrate 12 so that a focal point is formed inside the semiconductor substrate 12. This forms a modified layer inside the semiconductor substrate 12. Here, the modified layer formed in the third modified layer formation step is called the third modified layer 63. Here, the third modified layer 63 is formed in a region that overlaps with the region where the first modified layer 61 exists in the thickness direction of the semiconductor substrate 12. More specifically, the third modified layer 63 is formed at the same depth as the first modified layer 61. Here, as shown in Figure 13, the third modified layer 63 is formed linearly (in other words, in a grid pattern) so that when viewed from above, the third modified layer 63 intersects with the first modified layer 61. Note that because the width of the third modified layer 63 is narrow, gas reservoirs are less likely to form inside the semiconductor substrate 12 when forming the third modified layer 63. Therefore, cracks are less likely to occur in the semiconductor substrate 12 when forming the third modified layer 63.

Following the third modification layer formation process, the second modification layer formation process is performed. During the second modification layer formation process, nitrogen gas generated at the formation location of the second modification layer 62 (i.e., the location of focal point X) flows to the groove 30 via the first modification layer 61 or the third modification layer 63. Since the element region 20 is finely divided by the first modification layer 61 and the third modification layer 63, the distance from the formation location of the second modification layer 62 to the first modification layer 61 or the third modification layer 63 is short. In other words, the distance of the path through which the nitrogen gas flows is short. Thus, in Example 4, the discharge path for the nitrogen gas generated during the formation of the second modification layer 62 can be shortened, making it easier for the nitrogen gas to be discharged to the outside of the semiconductor substrate 12. Therefore, according to the configuration of Example 4, cracks in the semiconductor substrate 12 can be more effectively suppressed during the second modification layer formation process.

In the embodiments described above, the first modified layer 61 was formed at the depth of the lower end of the groove 30. However, as shown in Figure 14, the first modified layer 61 may also be formed at an intermediate depth in the groove 30.

Furthermore, in the embodiments described above, grooves 30 were formed as decomposition regions. However, instead of grooves 30, a modified layer (hereinafter referred to as the fourth modified layer) may be formed. That is, the laser focus may be moved to a depth range corresponding to the grooves 30 (i.e., the range from the top surface to a predetermined depth) along the boundary of each element region 20, thereby forming a fourth modified layer extending along the boundary of each element region 20. In this configuration, nitrogen gas generated inside the semiconductor substrate 12 is discharged to the outside through the fourth modified layer. Note that if a fourth modified layer is formed as a decomposition region, after the splitting process, the upper part 12a of the semiconductor substrate 12 can be further split along the fourth modified layer by an expansion process to manufacture the semiconductor element.

The configurations of the technology disclosed herein are listed below.
(Composition 1)
A method for manufacturing semiconductor devices,
A semiconductor substrate preparation step is to prepare a semiconductor substrate (12) having a plurality of element regions (20) provided on the upper surface layer, wherein the plurality of element regions are arranged in a matrix on the upper surface,
The process of forming a decomposition region (30) on the upper surface, which extends linearly along the boundaries of the plurality of element regions,
A first modified layer formation step comprising: a step of forming a first modified layer (61) inside the semiconductor substrate by irradiating the semiconductor substrate with a laser, wherein when viewed from above, the first modified layer extends along the decomposition region in a state overlapping the decomposition region, the first modified layer exists in a part of the range where the decomposition region exists in the thickness direction of the semiconductor substrate, and the first modified layer is formed such that it has a wider width than the decomposition region;
A step of forming a second modified layer (62) inside the element region by irradiating the element region with a laser so as to scan the element region, wherein the range in which the second modified layer exists and the range in which the first modified layer exists overlap in the thickness direction of the semiconductor substrate, and the second modified layer is formed such that the second modified layer is connected to the first modified layer.
A splitting step of dividing the semiconductor substrate along the first modified layer and the second modified layer,
A manufacturing method having the following characteristics.
(Structure 2)
A step of forming a third modified layer (63) inside the semiconductor substrate by irradiating the semiconductor substrate with a laser after the first modified layer formation step and before the second modified layer formation step, wherein the third modified layer intersects with the first modified layer when viewed from above, and the third modified layer is formed such that the area where the third modified layer exists and the area where the first modified layer exists overlap in the thickness direction of the semiconductor substrate.
The manufacturing method according to configuration 1, further comprising the above.
(Composition 3)
The element region is rectangular,
The manufacturing method according to configuration 1 or 2, wherein in the second modified layer formation step, the process of moving the laser focal point parallel to the short side of the rectangle is repeatedly performed while shifting the position in a direction parallel to the long side of the rectangle.
(Composition 4)
The manufacturing method according to configuration 1 or 2, wherein in the second modified layer formation step, the focus of the laser is moved in a spiral shape from the outer periphery towards the center within the region demarcated by the first modified layer.
(Composition 5)
In the above decomposition region formation step, grooves are formed on the upper surface by a dicing blade.
The groove is the decomposition region.
A manufacturing method described in any one of the components 1 to 4.

The embodiments described above are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical utility individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical utility.

12: Semiconductor substrate, 20: Device region, 30: Groove, 61: First modified layer, 62: Second modified layer

Claims (5)

A method for manufacturing semiconductor devices,
A semiconductor substrate preparation step is to prepare a semiconductor substrate (12) having a plurality of element regions (20) provided on the upper surface layer, wherein the plurality of element regions are arranged in a matrix on the upper surface,
The process of forming a decomposition region (30) on the upper surface, which extends linearly along the boundaries of the plurality of element regions,
A first modified layer formation step comprising: a step of forming a first modified layer (61) inside the semiconductor substrate by irradiating the semiconductor substrate with a laser, wherein when viewed from above, the first modified layer extends along the decomposition region in a state overlapping the decomposition region, the first modified layer exists in a part of the range where the decomposition region exists in the thickness direction of the semiconductor substrate, and the first modified layer is formed such that it has a wider width than the decomposition region;
A step of forming a second modified layer (62) inside the element region by irradiating the element region with a laser so as to scan the element region, wherein the range in which the second modified layer exists and the range in which the first modified layer exists overlap in the thickness direction of the semiconductor substrate, and the second modified layer is formed such that the second modified layer is connected to the first modified layer.
A splitting step of dividing the semiconductor substrate along the first modified layer and the second modified layer,
A manufacturing method having the following characteristics. A step of forming a third modified layer (63) inside the semiconductor substrate by irradiating the semiconductor substrate with a laser after the first modified layer formation step and before the second modified layer formation step, wherein the third modified layer intersects with the first modified layer when viewed from above, and the third modified layer is formed such that the area where the third modified layer exists and the area where the first modified layer exists overlap in the thickness direction of the semiconductor substrate.
The manufacturing method according to claim 1, further comprising: The element region is rectangular,
The manufacturing method according to claim 1 or 2, wherein in the second modified layer formation step, the process of moving the laser focal point parallel to the short side of the rectangle is repeatedly performed while shifting the position in a direction parallel to the long side of the rectangle. The manufacturing method according to claim 1 or 2, wherein in the second modified layer formation step, the laser focus is moved in a spiral pattern from the outer periphery towards the center within the region demarcated by the first modified layer. In the decomposition region formation step, grooves are formed on the upper surface by a dicing blade.
The groove is the decomposition region.
The manufacturing method according to claim 1 or 2.