JP7650461B2 - Semiconductor device manufacturing method - Google Patents

Description

The technology disclosed in this specification relates to a method for manufacturing a semiconductor device.

The manufacturing process of semiconductor devices 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. For the sake of convenience, hereinafter, wafers and ingots whose main component is gallium nitride are referred to as "semiconductor chunks." According to the technique of Patent Document 1, a laser beam focused on the inside of the semiconductor chunk is irradiated to generate modified spots distributed in a planar shape inside the semiconductor chunk. Gallium precipitates in the modified spots and nitrogen gasifies. The modified spots become weaker than other parts. When force is applied to the semiconductor chunk, the semiconductor chunk breaks along the modified spots distributed in a planar shape. The high nitrogen gas pressure inside the modified spots helps to divide the semiconductor chunk.

JP 2020-1202520 A

If the nitrogen gas pressure in the modification spot is too high, cracks may occur not only in the in-plane direction in which the modification 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 in areas other than the division surface.

The manufacturing method disclosed in this specification includes a gas flow path forming step, an altered layer forming step, and a division 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 division 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.

According to the above manufacturing method, some of the nitrogen gas that has accumulated in the altered layer is released outside the semiconductor mass through the gas flow path. This prevents the gas pressure in the altered layer from becoming excessively high, making it difficult for cracks to occur outside the altered layer.

In the manufacturing method disclosed in this specification, when viewed along the depth direction of the gas flow path, the altered layer is deeper than the bottom of the gas flow path at positions away from the gas flow path. In other words, the bottom surface of the altered layer is raised directly below the gas flow path. Gas pressure is likely to be high at the contact point between the altered layer and the gas flow path. However, because the bottom surface of the altered layer is raised directly below the gas flow path, cracks are less likely to occur in the semiconductor mass on the bottom side of the altered layer.

When viewed along the depth direction of the gas flow path, the laser light can be focused at a position deeper than the gas flow path at a position away from the gas flow path, and the laser light can be scanned so that the focal position of the laser light becomes 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 mass on the bottom side.

The surface of the semiconductor block may be flat, with multiple semiconductor elements formed on that surface, and a 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 to surround the semiconductor elements. The gas flow path also serves as a guide when cutting out the semiconductor elements.

Similar to the process of generating the altered layer, the gas flow path may be formed by irradiation with laser light. In other words, the gas flow path may be of the same quality as the altered layer. The gas flow path can be formed by a process similar to the process of forming the altered layer.

Details and further improvements of the technology disclosed in this specification are explained in the "Description of Embodiments" below.

1A to 1C are diagrams illustrating a manufacturing method according to an embodiment (element formation process). 5A to 5C are diagrams illustrating the manufacturing method according to the embodiment (gas flow path forming step). FIG. 2 is a plan view of an ingot in which a plurality of semiconductor elements are formed. 5A to 5C are diagrams illustrating the manufacturing method according to the embodiment (deteriorated layer forming step). FIG. 4 is a diagram illustrating the manufacturing method of the embodiment (division step). 4A to 4C are diagrams illustrating the manufacturing method of the embodiment (a back electrode forming step). 4A to 4C are diagrams illustrating the manufacturing method according to the embodiment (dicing process).

The manufacturing method of the embodiment will be described with reference to the drawings. The manufacturing method of the embodiment is a method for manufacturing a semiconductor device from an ingot 3 whose main component is gallium nitride. The ingot 3 is cylindrical and has a flat top surface.

(Element formation process) First, multiple semiconductor elements 4a are formed on the flat upper surface 3a of the ingot 3 (Figure 1). The semiconductor elements are formed through multiple processes, such as thin-film crystal growth, various ion implantations, etching, and the formation of insulating films. Since the semiconductor elements are made using known processes, a detailed explanation is 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.

(Gas flow path forming process) A laser is irradiated from the bottom surface 3b side of the ingot 3 to form a gas flow path 5 (Figure 2). A laser irradiator 10 is placed on the bottom surface 3b side of the ingot 3, and the laser is focused inside the ingot 3. When the laser is applied to the ingot 3, which is mainly composed of gallium nitride, gallium precipitates at the focus and nitrogen gasifies. As the nitrogen gasifies, many vacancies are created inside the ingot 3. The area where many 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 the gas flow path 5.

When the focus of the laser is changed from the top 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 top surface 3a. The gas flow path 5 is formed from the top surface 3a to a depth that passes through the element region 4. The laser irradiator 10 is also 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 appears as 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 top 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.

(Affected layer formation process) Next, the laser light is scanned while being focused on the inside of the ingot 3, forming an altered layer 6 in which gallium is precipitated and nitrogen is gasified (Figure 4). The laser irradiator 10 is placed on the bottom surface 3b side of the ingot 3, and the laser is irradiated from the bottom surface 3b side and scanned parallel to the top 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 top surface 3a of the ingot 3 (the surface on which the semiconductor element 4a is formed).

The altered layer 6 and the gas flow path 5 are generated by the same laser, so the altered layer 6 and the gas flow path 5 have the same composition. A green laser with a wavelength of about 530 μm is typically used to form the gas flow path 5 and the altered layer 6.

The altered 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 at a position deeper than the gas flow path 5. Reference symbol 10a in FIG. 4 indicates a laser irradiator located at a position away from the gas flow path 5, and reference symbol 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 bottom right of FIG. 4).

In the altered layer formation 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 altered 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 altered layer 6.

The lower right of Figure 4 shows an enlarged view of the vicinity of the bottom 5a of the gas flow path 5. The altered layer 6 rises at the position of the gas flow path 5. In other words, the bottom surface 6a of the altered layer 6 rises directly below the gas flow path 5.

As mentioned above, gallium is precipitated in the altered layer 6 and nitrogen is gasified. Because gallium is precipitated and nitrogen is gasified, the altered layer 6 becomes more brittle than the surrounding material. The altered layer 6 is also filled with nitrogen gas. The altered layer 6 is connected to the gas flow path 5, which reaches the upper surface 3a of the ingot 3. Therefore, some of the nitrogen gas in the altered layer 6 is released outside the ingot 3 through the gas flow path 5.

(Dividing process) Force is applied to the part above the altered layer 6 and the part 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 (Figure 5). The altered layer 6, where gallium is precipitated and nitrogen is gasified, is weaker than other parts. 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 of the altered layer 6 does not become excessively high, cracks are less likely to occur around the altered layer 6.

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 concentrate 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.

The bottom surface 6a side 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 contributes to suppressing the occurrence of cracks in the remaining ingot 7. If cracks remain in the remaining ingot 7, that part 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.

(Back electrode generation 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, completing the multiple semiconductor elements 4a (semiconductor device 4a) (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.

The remaining ingot 7 shown in FIG. 5 does not have a flat upper surface (the bottom surface 6a of the altered layer 6). The upper surface of the remaining ingot 7 is polished to make it flat, and then reused in the formation of a new semiconductor element.

Notes regarding the technology described in the examples are as follows. 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 with a cutter. When the gas flow path is a groove, it is advisable to form discrete gas flow paths around the semiconductor element 4a when the ingot 3 is viewed in a plan view.

The embodiment shows a method for dividing a semiconductor ingot 3, but the technology disclosed in this specification can also be used when dividing a wafer.

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 exert 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 can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful.

3: Ingot 3a: Top surface 3b: Bottom 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 (5)

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. 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 the focal position of the laser light becomes shallower toward the bottom of the gas flow path as the laser light approaches the gas flow path. The manufacturing method according to claim 1 or 2, wherein a plurality of semiconductor elements (4a) are formed on the surface, and the gas flow path is formed between adjacent semiconductor elements. The manufacturing method according to claim 3, wherein the gas flow path is formed to surround the semiconductor element. The manufacturing method according to any one of claims 1 to 4, in which the gas flow path is formed by irradiating with laser light.

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