Semiconductor device manufacturing method

Abstract

To provide a method for manufacturing a semiconductor device, the method for manufacturing a semiconductor device preventing, in dividing a semiconductor block, generation of cracks in portions of the semiconductor block other than a parting plane.SOLUTION: A manufacturing method includes a gas passage forming step, an altered layer forming step, and a division step. The gas passage forming step includes forming gas passages 5 extending from a surface of a semiconductor block having gallium nitride as a main component in a depth direction of the semiconductor block. The altered layer forming step includes scanning a laser beam focused on the inside of the semiconductor block and forming an altered layer 6 in which gallium is precipitated and nitrogen is gasified. The division step includes dividing the semiconductor block along the altered layer 6. Here, in the altered layer forming step, the altered layer 6 is in contact with bottoms 5a of the gas passages 5, and when seen along the depth direction, the altered layer 6 is deeper than the bottoms 5a of the gas passages 5 at positions separated from the gas passages 5. Since a bottom face 6a of the altered layer 6 rises immediately below the gas passages 5, cracks are hardly generated in the semiconductor block facing the bottom face 6a of the altered layer 6.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] The manufacturing process of a semiconductor device includes a step of dividing a wafer or an ingot. Patent Document 1 discloses a technique for dividing a wafer or an ingot whose main component is gallium nitride. In the following, for convenience of explanation, the wafer and the ingot whose main component is gallium nitride are referred to as "semiconductor block". According to the technique of Patent Document 1, a laser beam focused on the inside of the semiconductor block is irradiated to generate modified spots distributed in a planar shape inside the semiconductor block. Gallium precipitates in the modified spots and nitrogen gasifies. The modified spots become weaker than other parts. When a force is applied to the semiconductor block, the semiconductor block breaks along the modified spots distributed in a planar shape. High nitrogen gas pressure in the modified spots helps to divide the semiconductor block. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-1202520 A Summary of the Invention [Problem to be solved by the invention]

[0004] If the nitrogen gas pressure in the modified spot is too high, cracks may occur not only in the in-plane direction in which the modified spot is distributed, but also in other directions. If cracks remain in the remaining semiconductor block, the area where the cracks occurred becomes unusable, resulting in waste. This specification provides a technology that suppresses the occurrence of cracks in the semiconductor block other than on the division surface. [Means for solving the problem]

[0005] The manufacturing method disclosed in this specification includes a gas flow path forming step, an altered layer forming step, and a dividing step. In the gas flow path forming step, a gas flow path is formed extending from the surface of a semiconductor block mainly composed of gallium nitride in the depth direction of the semiconductor block. In the altered layer forming step, a laser beam is focused on the inside of the semiconductor block and scanned to form an altered layer in which gallium is precipitated and nitrogen is gasified. The altered layer corresponds to the modified spot described above. In the dividing step, the semiconductor block is divided along the altered layer. Here, in the altered layer forming step, the altered layer is in contact with the bottom of the gas flow path, and the altered layer is deeper than the bottom of the gas flow path at a position away from the gas flow path when viewed along the depth direction.

[0006] According to the above manufacturing method, a part of the nitrogen gas accumulated in the affected layer is released to the outside of the semiconductor block through the gas flow passage. The gas pressure in the affected layer does not become excessively high, and cracks are unlikely to occur outside the affected layer.

[0007] In the manufacturing method disclosed in this specification, when viewed along the depth direction of the gas flow path, the affected layer is deeper than the bottom of the gas flow path at a position away from the gas flow path. In other words, the bottom surface of the affected layer is raised directly below the gas flow path. Gas pressure is likely to be high at the contact point between the affected layer and the gas flow path. However, since the bottom surface of the affected layer is raised directly below the gas flow path, cracks are unlikely to occur in the semiconductor block on the bottom side of the affected layer.

[0008] When viewed along the depth direction of the gas flow path, the laser light may be focused at a position deeper than the gas flow path at a position away from the gas flow path, and the focus position of the laser light may be made shallower toward the bottom of the gas flow path as the laser light approaches the gas flow path. This causes the bottom surface of the altered layer directly below the gas flow path to gradually rise, making it even more difficult for cracks to occur in the semiconductor block on the bottom side.

[0009] The surface of the semiconductor block may be flat, with a plurality of semiconductor elements formed on the surface, and the gas flow path may be formed between adjacent semiconductor elements. After the semiconductor elements are formed on the flat surface of the semiconductor block, the layer on which the semiconductor elements are formed is cut out from the semiconductor block. In this case, the gas flow path is formed between adjacent semiconductor elements. Alternatively, the gas flow path is formed so as to surround the semiconductor elements. The gas flow path also serves as a guide when cutting out the semiconductor elements.

[0010] The gas flow passage may be formed by irradiation with a laser beam in the same manner as the process of generating the denatured layer. In other words, the gas flow passage may be of the same quality as the denatured layer. The gas flow passage can be formed in the same process as the process of forming the denatured layer.

[0011] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0012] [Figure 1] 1A to 1C are diagrams for explaining a manufacturing method according to an embodiment (element formation process). [Diagram 2] 5A to 5C are diagrams illustrating the manufacturing method according to the embodiment (gas flow path forming step). [Diagram 3] FIG. 2 is a plan view of an ingot in which a plurality of semiconductor elements are formed. [Figure 4] 4A to 4C are diagrams illustrating the manufacturing method according to the embodiment (deteriorated layer forming step). [Diagram 5] FIG. 2 is a diagram for explaining the manufacturing method of the embodiment (division step). [Figure 6] 4A to 4C are diagrams illustrating the manufacturing method of the embodiment (rear electrode forming step). [Figure 7] 1A to 1C are diagrams for explaining a manufacturing method according to an embodiment (dicing process). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A manufacturing method according to the embodiment will be described with reference to the drawings. The manufacturing method according to the embodiment is a method for manufacturing a semiconductor device from an ingot 3 containing gallium nitride as a main component. The ingot 3 has a cylindrical shape and a flat upper surface.

[0014] (Element Formation Process) First, a plurality of semiconductor elements 4a are formed on the flat upper surface 3a of an ingot 3 (FIG. 1). The semiconductor elements are formed through a plurality of processes, such as thin-film crystal growth, various ion implantations, etching, and formation of an insulating film. Since the semiconductor elements are produced through known processes, detailed explanations are omitted. For ease of explanation, the region of the ingot 3 where the semiconductor elements 4a are formed is referred to as the element region 4.

[0015] (Gas flow path forming process) A laser is irradiated from the side of the bottom surface 3b of the ingot 3 to form a gas flow path 5 (Figure 2). A laser irradiator 10 is placed on the side of the bottom surface 3b of the ingot 3, and the laser is focused inside the ingot 3. When the laser is aimed at the ingot 3, which is mainly composed of gallium nitride, gallium precipitates at the focus and nitrogen is gasified. As the nitrogen gasifies, a large number of vacancies are created inside the ingot 3. The area where a large number of vacancies are created becomes a gas flow path. Therefore, the layer where gallium is precipitated can become a gas flow path. In this process, the area irradiated with the laser is called a gas flow path 5.

[0016] When the focus of the laser is changed from the upper surface 3a of the ingot 3 to the depth direction of the ingot 3, a gas flow path 5 extending in the depth direction is obtained. The gas flow path 5 reaches the upper surface 3a. The gas flow path 5 is formed from the upper surface 3a to a depth that passes through the element region 4. In addition, the laser irradiator 10 is moved between adjacent semiconductor elements 4a. The gas flow path 5 extends along the boundary between adjacent semiconductor elements 4a. FIG. 3 shows a plan view of the ingot 3 on which multiple semiconductor elements 4a are formed. As described above, the ingot 3 has a cylindrical shape, so that the ingot 3 is a circle in the plan view. In the gas flow path forming process, the gas flow path 5 is formed so as to surround each of the multiple semiconductor elements 4a when the upper surface 3a of the ingot 3 is viewed in plan. "Viewing the ingot 3 in plan" is equivalent to viewing the ingot 3 along the depth direction of the gas flow path 5.

[0017] (Affected layer forming process) Next, the laser light is scanned while being focused on the inside of the ingot 3, forming an affected layer 6 in which gallium is precipitated and nitrogen is gasified (FIG. 4). The laser irradiator 10 is disposed on the lower surface 3b side of the ingot 3, and the laser is irradiated from the lower surface 3b side and scanned parallel to the upper surface 3a. The affected layer 6 is formed so as to spread in a direction intersecting the depth direction of the gas flow path 5. In other words, the affected layer 6 is formed so as to spread parallel to the upper surface 3a of the ingot 3 (the surface on which the semiconductor element 4a is formed).

[0018] The affected layer 6 and the gas flow passage 5 are generated by the same laser, and therefore have the same composition. A green laser with a wavelength of about 530 μm is typically used to form the gas flow passage 5 and the affected layer 6.

[0019] The affected layer 6 is formed at a position deeper than the bottom of the gas flow path 5. More specifically, at a position away from the gas flow path 5 when viewed along the depth direction of the ingot 3, the laser light is scanned with a focus set at a position deeper than the gas flow path 5. Reference numeral 10a in FIG. 4 indicates a laser irradiator located at a position away from the gas flow path 5, and reference numeral Fc1 indicates the focal position of the laser at that time. The focal position Fc1 of the laser at this time is deeper than the bottom 5a of the gas flow path 5 (see the enlarged view at the lower right of FIG. 4).

[0020] In the affected layer forming process, the laser light is scanned parallel to the upper surface 3a of the ingot 3, and the focal position of the laser light is gradually made shallower toward the depth of the bottom 5a of the gas flow path 5 as it approaches the gas flow path. Reference numeral 10 in FIG. 4 indicates a laser irradiator positioned directly below the gas flow path 5. Directly below the gas flow path 5, the focal position Fc2 coincides with the bottom 5a of the gas flow path 5. The affected layer 6 is in contact with the bottom 5a of the gas flow path 5. In other words, the gas flow path 5 does not penetrate the affected layer 6.

[0021] 4 shows an enlarged view of the vicinity of the bottom 5a of the gas flow passage 5. The affected layer 6 bulges at the position of the gas flow passage 5. In other words, the bottom surface 6a of the affected layer 6 bulges immediately below the gas flow passage 5.

[0022] As described above, in the affected layer 6, gallium is precipitated and nitrogen is gasified. Because gallium is precipitated and nitrogen is gasified, the affected layer 6 becomes more brittle than the surrounding materials. The affected layer 6 is also filled with nitrogen gas. The affected layer 6 is connected to the gas flow passage 5, which reaches the upper surface 3a of the ingot 3. Therefore, part of the nitrogen gas in the affected layer 6 is released to the outside of the ingot 3 through the gas flow passage 5.

[0023] (Dividing step) Force is applied to the portion above the altered layer 6 and the portion below the altered layer 6 to divide the ingot 3. The ingot 3 is separated into the element region 4 and the remaining ingot 7 (Fig. 5). The altered layer 6, where gallium is precipitated and nitrogen is gasified, is weaker than other portions. Therefore, when force is applied above and below the altered layer 6, the ingot 3 cracks along the altered layer 6. The pressure of the nitrogen gas inside the altered layer 6 also contributes to the division of the ingot 3. If the internal pressure of the altered layer 6 is too high, cracks may also occur around the altered layer 6. However, because part of the nitrogen gas in the altered layer 6 is released to the outside through the gas flow path 5, the internal pressure of the altered layer 6 is maintained at an appropriate level. Since the gas pressure in the altered layer 6 does not become excessively high, cracks are unlikely to occur around the altered layer 6.

[0024] As mentioned above, the gas flow path 5 does not penetrate the altered layer 6. In other words, the gas flow path 5 does not intersect with the bottom surface 6a of the altered layer 6. If the gas flow path 5 and the bottom surface 6a intersect, stress will be concentrated at the intersection point, making it easier for cracks to occur in the bottom surface 6a. Since the gas flow path 5 does not intersect with the bottom surface 6a of the altered layer 6, cracks are less likely to occur in the bottom surface 6a. Furthermore, the bottom surface 6a of the altered layer 6 is raised directly below the gas flow path 5. The raised bottom surface 6a increases the pressure resistance of the bottom surface 6a. The raised bottom surface 6a also contributes to suppressing cracks.

[0025] The side of the bottom surface 6a of the ingot 3 (remaining ingot 7) is reused as a substrate for a semiconductor device. The fact that the bottom 5a of the gas flow path 5 is in contact with the altered layer 6 (in other words, the gas flow path 5 does not penetrate the altered layer 6) and that the bottom surface 6a of the altered layer 6 is raised directly below the gas flow path 5 contribute to suppressing the occurrence of cracks in the remaining ingot 7. If cracks remain in the remaining ingot 7, that portion must be polished. In other words, the remaining ingot 7 is wasted. In the manufacturing method of the embodiment, cracks are unlikely to occur in the remaining ingot 7, so the remaining ingot 7 can be reused without waste.

[0026] (Back electrode generating process and dicing process) After polishing the back surface 3c of the element region 4 flat, a back electrode 8 is formed (FIG. 6). Finally, the element region 4 is cut along the boundaries between the multiple semiconductor elements 4a, and multiple semiconductor elements 4a (semiconductor device 4a) are completed (FIG. 7). A gas flow path 5 is provided to surround the semiconductor elements 4a. The gas flow path 5 is of the same type as the altered layer 6, and is more fragile than the surrounding areas. When cutting the multiple semiconductor elements 4a along their boundaries, the fragile gas flow path 5 functions as a guide when separating adjacent semiconductor elements 4a.

[0027] The upper surface (bottom surface 6a of the altered layer 6) of the remaining ingot 7 shown in Fig. 5 is not flat. The upper surface of the remaining ingot 7 is polished to be flattened, and then reused for forming a new semiconductor element.

[0028] Points to note regarding the technology described in the embodiment are described below. The gas flow path 5 is an area where nitrogen is gasified and many voids are generated. Nitrogen gas flows through the voids. The gas flow path may be a groove formed by a cutter. When the gas flow path is a groove, it is preferable to form discrete gas flow paths around the semiconductor element 4a when the ingot 3 is viewed in a plan view.

[0029] Although the embodiment shows a method for dividing a semiconductor ingot 3, the technology disclosed in this specification can also be used when dividing a wafer.

[0030] Although specific examples of the present invention have been described above in detail, 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. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0031] 3: ingot 3a: upper surface 3b: lower surface 3c: back surface 4: element region 4a: semiconductor element (semiconductor device) 5: gas flow path 5a: bottom 6: affected layer 6a: bottom surface 7: remaining ingot 8: back electrode 10: laser irradiator Fc1, Fc2: focal position

Claims

1. a gas flow passage forming step of forming a gas flow passage (5) extending from a surface of a semiconductor block (3) mainly composed of gallium nitride in a depth direction of the semiconductor block; a deteriorated layer forming step of scanning a laser beam focused on the inside of the semiconductor block to form an deteriorated layer (6) in which gallium is precipitated and nitrogen is gasified; a dividing step of dividing the semiconductor block along the affected layer; Equipped with In the affected layer forming step, the affected layer is in contact with a bottom (5a) of the gas flow passage, and the affected layer is deeper than the bottom of the gas flow passage at a position away from the gas flow passage when viewed along the depth direction. A method for manufacturing a semiconductor device.

2. 2. The manufacturing method according to claim 1, wherein at a position away from the gas flow path when viewed along the depth direction, the laser light is focused at a position deeper than the gas flow path, and as the laser light approaches the gas flow path, the focal position of the laser light becomes shallower toward the bottom of the gas flow path.

3. 3. The method according to claim 1, wherein a plurality of semiconductor elements (4a) are formed on the surface, and the gas flow path is formed between adjacent ones of the semiconductor elements.

4. The manufacturing method according to claim 3 , wherein the gas flow path is formed so as to surround the semiconductor element.

5. The method according to claim 1 , wherein the gas flow passage is formed by irradiation with a laser beam.

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