Semiconductor device manufacturing method

Abstract

To provide a technique capable of manufacturing a semiconductor device with a good yield.SOLUTION: A method for manufacturing a semiconductor device comprises the steps of: forming a recess for degasification along an interface of an element region on a first surface of a compound semiconductor substrate including a first surface having a plurality of element regions and a second surface located on the rear side of the first surface; forming a modified layer extending along the first surface of the compound semiconductor substrate inside the compound semiconductor substrate and within a depth range of the recess for degasification by irradiating the computer semiconductor substrate with a laser; dividing the compound semiconductor substrate into a first portion of the first surface side and a second portion of the second surface side along the modified layer of the compound semiconductor substrate; and forming a meal film covering a division surface of the first portion so as to expose the recess for degasification.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In the method for manufacturing a semiconductor device disclosed in Patent Document 1, a compound semiconductor substrate is irradiated with a laser to form an affected layer inside the compound semiconductor substrate. The affected layer is formed so as to extend along the surface of the compound semiconductor substrate. By forming the affected layer in this manner, the compound semiconductor substrate can be processed. For example, thinner compound semiconductor substrates can be obtained by dividing the compound semiconductor substrate along the affected layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-102520 Summary of the Invention [Problem to be solved by the invention]

[0004] When an altered layer is formed inside a compound semiconductor substrate, gas is generated in the altered layer. The pressure of the generated gas can cause cracks in the compound semiconductor substrate in unintended directions. To avoid this, a venting portion that reaches the depth at which the altered layer will be formed may be formed in the first surface of the compound semiconductor substrate before the altered layer is formed. Here, consider a situation in which a compound semiconductor substrate is divided along the altered layer, and then a metal film that functions as an electrode or the like is formed on the dividing surface of the first portion on the first surface side. Because the venting portion extends from the first surface to a depth that reaches the altered layer, a recess formed by the venting portion exists on the dividing surface of the first portion. Therefore, when the metal film is formed on the dividing surface, the metal film is deposited across the dividing surface and within the venting portion. Therefore, when the first portion is divided into semiconductor devices along the venting portion, stress is applied to each semiconductor device by the metal film formed in the venting portion, which can cause cracks in the semiconductor devices. This specification proposes a technology for manufacturing semiconductor devices with a high yield. [Means for solving the problem]

[0005] A method for manufacturing a semiconductor device disclosed in this specification includes the steps of: forming a degassing recess (14) on a first surface of a compound semiconductor substrate (12) having a first surface (12a) with a plurality of element regions (40) and a second surface (12b) located on the back side of the first surface, along the interface of the element regions; forming an affected layer (16) extending along the first surface of the compound semiconductor substrate within the compound semiconductor substrate and within a depth range of the degassing recess by irradiating the compound semiconductor substrate with a laser (112); dividing the compound semiconductor substrate along the affected layer into a first portion (61) on the first surface side and a second portion (62) on the second surface side; and forming a metal film (71, 81, 91) covering a dividing surface (61a) of the first portion so that the degassing recess is exposed.

[0006] In this manufacturing method, after dividing the compound semiconductor substrate into a first portion and a second portion along the altered layer, a metal film is formed covering the dividing surface of the first portion so that the vent recesses are exposed. Therefore, when the first portion is divided into semiconductor devices along the vent recesses, stress caused by the metal film is not applied to each semiconductor device. As a result, cracks are less likely to occur in the semiconductor devices, and semiconductor devices can be manufactured with a high yield. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. [Figure 2] FIG. 1 is a cross-sectional view of a GaN substrate 12. [Figure 3] FIG. [Figure 4] FIG. 1 is a plan view of a GaN substrate 12 in which recesses for venting gas are formed. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. 3 is an explanatory diagram of an electrode forming step in Example 1. [Figure 9] FIG. 3 is an explanatory diagram of an electrode forming step in Example 1. [Figure 10] FIG. 3 is an explanatory diagram of an electrode forming step in Example 1. [Figure 11] FIG. 3 is an explanatory diagram of an electrode forming step in Example 1. [Figure 12] 1 is a bottom view of a semiconductor device manufactured by the manufacturing process of Example 1. FIG. [Figure 13] FIG. 10 is an explanatory diagram of an electrode forming step in Example 2. [Figure 14] FIG. 10 is an explanatory diagram of an electrode forming step in Example 2. [Figure 15] FIG. 10 is an explanatory diagram of an electrode forming step in Example 2. [Figure 16] FIG. 10 is an explanatory diagram of an electrode forming step in Example 3. [Figure 17] FIG. 10 is an explanatory diagram of an electrode forming step in Example 3. [Figure 18] FIG. 10 is an explanatory diagram of an electrode forming step in Example 3. [Figure 19] 10 is a bottom view of a semiconductor device manufactured by a manufacturing process of a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] In one example manufacturing method disclosed in the present specification, the step of forming the metal film may include a step of forming a resist that covers the inner surface of the vent recess and the peripheral portion of the parting surface around the vent recess and has a first thickness in the peripheral portion; a step of forming the metal film that has a second thickness thinner than the first thickness so as to cover the parting surface and the resist; and a step of removing the resist after the step of forming the metal film that has the second thickness.

[0009] In this configuration, the second thickness, which is the thickness of the metal film, is thinner than the first thickness, which is the thickness of the resist around the vent recess, so the metal film covering the top surface of the resist can be separated from the metal film covering the dividing surface. Therefore, the metal film formed on the top surface of the resist can be removed together with the resist, preventing the metal film from being formed inside the vent recess. Furthermore, the resist can be formed with high precision. This allows for the manufacture of semiconductor devices with minimal variation.

[0010] In one example manufacturing method disclosed in the present specification, the step of forming the metal film may include a step of placing a mask having a third thickness so as to cover the vent recess and a peripheral portion of the parting surface of the vent recess; a step of forming the metal film having a fourth thickness thinner than the third thickness so as to cover the parting surface and the mask; and a step of removing the mask after the step of forming the metal film having the fourth thickness.

[0011] In this configuration, the fourth thickness, which is the thickness of the metal film, is thinner than the third thickness, which is the thickness of the mask around the vent recess, so the metal film covering the upper surface of the mask can be separated from the metal film covering the dividing surface. Therefore, the metal film formed on the upper surface of the mask can be removed together with the mask, preventing the metal film from being formed inside the vent recess. Furthermore, since the mask is simply positioned and placed to cover the vent recess and its periphery, it can be physically removed. This allows semiconductor devices to be manufactured regardless of the metal film material.

[0012] In one example manufacturing method disclosed in the present specification, the step of forming the metal film may include the steps of: forming the metal film so as to cover the parting surface and the venting recess; forming a resist on the surface of the metal film, the resist having openings above the venting recess and the peripheral area of ​​the venting recess; and removing the metal film inside the venting recess via the resist.

[0013] In this configuration, a metal film is formed over the entire surface of the parting surface and the inside of the vent recess, and then the metal film inside the vent recess is removed via the resist. This allows the vent recess to be exposed. Furthermore, the resist can be formed with high precision. This allows semiconductor devices to be manufactured with minimal variation.

[0014] In one example of the manufacturing method disclosed herein, the compound semiconductor substrate may be made of gallium nitride or gallium oxide.

[0015] Example 1 In the manufacturing method of Example 1, a semiconductor device is manufactured from a gallium nitride substrate 12 (hereinafter referred to as GaN substrate 12) shown in FIGS. 1 and 2. As shown in FIG. 1, the GaN substrate 12 has a central region 42 and a peripheral region 44. The central region 42 has a plurality of element regions 40. In the central region 42, the element regions 40 are arranged in a matrix. Although not shown, an element structure is formed in each element region 40 in an area facing the first surface 12a of the GaN substrate 12. The element structure formed in each element region 40 may be a MOSFET, an IGBT, a diode, or the like. The peripheral region 44 is located around the central region 42. The peripheral region 44 is the region of the GaN substrate 12 excluding the central region 42. The GaN substrate 12 is optically transparent.

[0016] (Gas vent recess formation process) When manufacturing a semiconductor device from a GaN substrate 12, a degassing recess forming process is first performed. In this process, degassing grooves 14 are formed in the first surface 12a of the GaN substrate 12. Here, as shown in FIG. 3, a laser 110 is irradiated onto the GaN substrate 12 from the first surface 12a side. The laser 110 is irradiated so as to form a focal point S1 within the GaN substrate 12. The degassing grooves 14 are formed at the positions irradiated by the laser 110. Here, by moving the irradiation position of the laser 110, the degassing grooves 14 are formed along the interfaces of the element regions 40, as shown in FIG. 4. The degassing grooves 14 are also formed in the peripheral region 44. In the peripheral region 44, the degassing grooves 14 are formed on extensions of the interfaces of the element regions 40. That is, here, the degassing grooves 14 are formed so that the entire first surface 12a of the GaN substrate 12 is divided into a lattice pattern, as shown in FIG. 4. In the gas vent recess forming step, the gas vent grooves 14 may be formed in the first surface 12a of the GaN substrate 12 by irradiating the GaN substrate 12 with a laser 110 from the second surface 12b side.

[0017] (Deteriorated layer formation process) Next, an affected layer forming step is performed to form an affected layer 16 inside the GaN substrate 12. In the affected layer forming step, as shown in FIG. 5, a laser beam 112 is irradiated onto the GaN substrate 12 from the second surface 12b side. The laser beam 112 is irradiated so as to form a focal point S2 inside the GaN substrate 12. At the position of the focal point S2, GaN (i.e., gallium nitride) is heated and decomposed. As a result, an affected layer 16 composed of a gallium precipitate layer or the like is formed at the position of the focal point S2. The strength of the affected layer 16 is lower than that of the original gallium nitride single crystal. Therefore, the strength of the affected layer 16 is lower than that of the surrounding gallium nitride single crystal. Here, the irradiation position of the laser beam 112 is moved in a direction parallel to the first surface 12a and the second surface 12b of the GaN substrate 12, thereby forming the affected layer 16 extending along the first surface 12a and the second surface 12b. Here, the affected layer 16 is formed so that the affected layer 16 and the degassing grooves 14 overlap in depth. In other words, the affected layer 16 is formed so that the range 16a of the affected layer 16 in the thickness direction of the GaN substrate 12 overlaps with the range 14a of the gas vent grooves 14 in the thickness direction of the GaN substrate 12. Herein, the affected layer 16 is formed over the entire lateral direction of the GaN substrate 12 (i.e., the direction parallel to the first surface 12a and the second surface 12b of the GaN substrate 12). Hereinafter, the portion of the GaN substrate 12 closer to the first surface 12a than the affected layer 16 will be referred to as a first portion 61, and the portion of the GaN substrate 12 closer to the second surface 12b than the affected layer 16 will be referred to as a second portion 62.

[0018] When GaN is decomposed by irradiating the GaN substrate 12 with the laser 112 (i.e., when the affected layer 16 is formed), nitrogen gas (i.e., N2 gas) is generated. As described above, the affected layer 16 is formed in a depth range that overlaps with the gas vent groove 14. Therefore, as shown by arrow 100 in FIG. 6, the nitrogen gas generated at the formation position of the affected layer 16 is discharged to the outside of the GaN substrate 12 through the gas vent groove 14. This prevents the pressure of the nitrogen gas from increasing inside the GaN substrate 12. This prevents cracks from occurring in the GaN substrate 12 due to the pressure of the nitrogen gas.

[0019] (Support member attachment process) Next, a support member attaching step is performed. In this support member attaching step, as shown in FIG. 6, a support member 22 is attached to the first surface 12a of the GaN substrate 12. The support member 22 may be a hard plate material or a flexible sheet-like member. This prevents the first surface 12a of the GaN substrate 12 from being scratched by the support member 22 in a subsequent step. The support member 22 may be attached to the GaN substrate 12 before the degassing recess forming step or before the affected layer forming step. In this case, the support member 22 is preferably optically transparent so that the GaN substrate 12 can be irradiated with the laser 110, and is also preferably breathable so that the nitrogen gas generated in the affected layer forming step can be exhausted.

[0020] (splitting process) Next, as shown in FIG. 7 , a force is applied to the second portion 62 in a direction away from the first portion 61, thereby dividing the GaN substrate 12 along the affected layer 16. That is, the second portion 62 is separated from the first portion 61. As described above, the strength of the affected layer 16 is lower than that of the gallium nitride single crystal, so the GaN substrate 12 can be divided at the affected layer 16. Thereafter, the upper surface 61a of the first portion 61 (i.e., the dividing surface 61a) is polished and cleaned as necessary. Note that the first portion 61 has gas release grooves 14 formed in a lattice pattern that penetrate from the first surface 12a to the dividing surface 61a, so that the first portion 61 is divided into a plurality of device regions 40. Each device region 40 is supported by a support member 22, and therefore each device region 40 is fixed on the support member 22.

[0021] (Electrode formation process) Next, an electrode formation process is performed. First, a resist liquid is applied to the dividing surface 61a of the first portion 61 and the inside of the vent groove 14, and then exposure and development are performed to selectively form a resist 70 on the first portion 61, as shown in FIG. 8. Here, as shown in FIG. 9, the resist 70 is formed so as to cover the inside of the vent groove 14 and the peripheral portion 40a of the vent groove 14 on the dividing surface 61a (i.e., the periphery 40a of each element region 40). The resist 70 is not formed on the central portion 40b of each element region 40 on the dividing surface 61a. Furthermore, as shown in FIG. 8, the resist 70 is formed so that the thickness in the peripheral portion 40a (i.e., the height from the dividing surface 61a to the upper surface of the resist 70) is t1.

[0022] 10, a metal film 71 is formed to cover the dividing surface 61a and the resist 70. The metal film 71 can be formed by a known method such as sputtering or vapor deposition. Here, the metal film 71 is formed so that the thickness t2 of the metal film 71 is thinner than the thickness t1. Because the thickness t2 is thinner than the thickness t1, the metal film 71 formed on the upper surface of the resist 70 is separated from the metal film 71 formed on the dividing surface 61a.

[0023] 11, the resist 70 is removed. Since the metal film 71 formed on the upper surface of the resist 70 is separated from the metal film 71 formed on the dividing surface 61a, removing the resist 70 leaves the metal film 71 on the dividing surface 61a. Each metal film 71 remaining on the dividing surface 61a functions as an electrode of the semiconductor device.

[0024] Next, the support member 22 is peeled off from the first portion 61 to obtain a plurality of element regions 40 on which electrodes (metal films 71) are formed. Thereafter, an insulating layer, an electrode, etc. are formed on the first surface 12a of each element region 40 to complete a plurality of semiconductor devices.

[0025] In this embodiment, in the electrode formation process, a resist 70 is formed so as to cover the gas vent grooves 14 and the peripheral portion 40a. Therefore, the metal film 71 is not formed over the entire parting surface 61a. That is, as shown in FIG. 12, the completed semiconductor device has a part of the parting surface 61a (i.e., the peripheral portion 40a) exposed.

[0026] The second portion 62 may be subsequently reused in the manufacture of a semiconductor device. For example, the split surface 62a (see FIG. 7) of the second portion 62 may be polished, etched, or the like, and then a GaN layer may be epitaxially grown on the split surface 62a, thereby increasing the thickness of the second portion 62 to the thickness of the original GaN substrate 12. The second portion 62 with increased thickness may be reused as the GaN substrate 12 to manufacture a semiconductor device.

[0027] In the manufacturing method of Example 1, the thickness t2 of the metal film 71 is thinner than the thickness t1 of the resist 70 in the peripheral portion 40a of the vent groove 14, so that the metal film 71 covering the upper surface of the resist 70 can be separated from the metal film 71 covering the dividing surface 61a. Therefore, the metal film 71 formed on the upper surface of the resist 70 can be removed together with the resist 70 (so-called lift-off), and the metal film 71 can be prevented from being formed inside the vent groove 14. Because the metal film 71 is not formed inside the vent groove 14 provided along the interface between each element region 40, stress due to the metal film 71 is not applied to each element region 40 when the support member 22 is peeled off to extract the multiple element regions 40. Therefore, cracks are less likely to occur in the manufactured semiconductor device, and semiconductor devices can be manufactured with a high yield.

[0028] Furthermore, in the first embodiment, the resist 70 prevents the metal film 71 from being formed inside the gas vent groove 14. Since the resist 70 can be formed with high precision, it is possible to manufacture a semiconductor device in which the dimensional precision of the metal film 71 has little variation.

[0029] Example 2 The manufacturing method of Example 2 differs from Example 1 in the electrode formation process. In Example 2, after dividing the GaN substrate 12 into a first portion 61 and a second portion 62, a mask 80 is first arranged as shown in FIG. 13. Here, as in Example 1, the mask 80 is arranged so as to cover the inside of the gas vent grooves 14 and the peripheral portions 40a (see FIG. 9) of the dividing surface 61a around the gas vent grooves 14. The mask 80 is not formed on the central portions 40b of each element region 40 on the dividing surface 61a. In addition, here, the mask 80 having a thickness t3 (i.e., the height from the dividing surface 61a to the upper surface of the mask 80) is arranged.

[0030] 14, a metal film 81 is formed to cover the dividing surface 61a and the mask 80. The metal film 81 can be formed by a known method such as sputtering or vapor deposition. Here, the metal film 81 is formed so that the thickness t4 of the metal film 81 is thinner than the thickness t3. Because the thickness t4 is thinner than the thickness t3, the metal film 81 formed on the upper surface of the mask 80 is separated from the metal film 81 formed on the dividing surface 61a.

[0031] Next, as shown in Fig. 15, the mask 80 is removed. Since the metal film 81 formed on the upper surface of the mask 80 is separated from the metal film 81 formed on the dividing surface 61a, removing the mask 80 leaves the metal film 81 on the dividing surface 61a. Each metal film 81 remaining on the dividing surface 61a functions as an electrode of the semiconductor device. Thereafter, multiple semiconductor devices are completed by going through the same process as in Example 1.

[0032] In the manufacturing method of Example 2, the thickness t4 of the metal film 81 is thinner than the thickness t3 of the mask 80 in the peripheral portion 40a of the gas vent groove 14, so that the metal film 81 covering the upper surface of the mask 80 can be separated from the metal film 81 covering the dividing surface 61a. Therefore, the metal film 81 formed on the upper surface of the mask 80 can be removed together with the mask 80 (so-called mask vapor deposition), and the metal film 81 can be prevented from being formed inside the gas vent groove 14.

[0033] Furthermore, in Example 2, the mask 80 prevents the metal film 81 from being formed inside the gas vent groove 14. The mask 80 is simply positioned and placed so as to cover the gas vent groove 14 and its surrounding area 40a, and can therefore be physically removed. Therefore, in Example 2, a semiconductor device can be manufactured regardless of the material of the metal film 81.

[0034] Example 3 The manufacturing method of Example 3 differs from Examples 1 and 2 in the electrode formation step. In Example 3, after dividing the GaN substrate 12 into a first portion 61 and a second portion 62, as shown in Fig. 16, first, a metal film 91 is formed so as to cover the dividing surface 61a and the gas vent grooves 14. Here, the metal film 91 is formed in an area extending from the inside of the gas vent grooves 14 to the entire dividing surface 61a. The metal film 91 can be formed by a known method such as sputtering or vapor deposition.

[0035] Next, as shown in Fig. 17, a resist 90 having openings 90a above the vent grooves 14 and the peripheral portions 40a of the vent grooves 14 (see Fig. 9 of Example 1) is formed on the surface of the metal film 91. That is, the resist 90 is selectively formed on the surface of the metal film 91 in an area that covers only the upper portion of the central portion 40b of the element region 40. Then, as shown in Fig. 18, the metal film 91 inside the vent grooves 14 is removed via the resist 90 by, for example, dry etching or wet etching. Thereafter, the resist 90 is removed, and multiple semiconductor devices are completed through the same steps as in Example 1.

[0036] In the manufacturing method of Example 3, after forming a metal film 91 on the dividing surface 61a and the entire inside of the gas vent groove 14, the metal film 91 inside the gas vent groove 14 is removed via the resist 90. This makes it possible to expose the gas vent groove 14. Also, in Example 3, the metal film 91 inside the gas vent groove 14 is removed via the resist 90. Because the resist 90 can be formed with high precision, it is possible to manufacture a semiconductor device in which the dimensional precision of the metal film 91 has little variation.

[0037] In each of the above-described examples, in the gas vent recess formation step, grooves (gas vent grooves 14) extending along the interface of the element region 40 are formed. However, in the gas vent recess formation step, for example, holes may be formed intermittently along the interface of the element region 40. That is, a plurality of gas vent holes may be formed at predetermined intervals in the first surface 12a of the GaN substrate 12 along the interface of the element region 40. In this case, after forming the metal film, dicing is performed along the interface of the element region 40, thereby dividing the first portion 61 into a plurality of element regions 40. Note that, in the semiconductor device obtained by the manufacturing method of this modification, as shown in FIG. 19 , a part of the dividing surface 61a is exposed at the periphery of the element region 40 in a shape corresponding to the shape of the gas vent hole (for example, a circle).

[0038] In addition, in each of the above-described examples, a GaN substrate 12 was used. However, a semiconductor device may be manufactured using a compound semiconductor substrate other than a GaN substrate, such as a gallium oxide substrate.

[0039] 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]

[0040] 12: Gallium nitride substrate, 14: Gas vent groove, 16: Deteriorated layer

Claims

1. A method for manufacturing a semiconductor device, comprising: a step of forming a gas vent groove (14) in a compound semiconductor substrate (12) having a first surface (12a) having a plurality of element regions (40) and a second surface (12b) located on the back side of the first surface, the gas vent groove (14) extending along the interface of the element regions and reaching an end face of the compound semiconductor substrate; forming an affected layer (16) extending along the first surface of the compound semiconductor substrate within the compound semiconductor substrate and within a depth range of the gas release groove by irradiating the compound semiconductor substrate with a laser (112); Dividing the compound semiconductor substrate along the altered layer into a first portion (61) on the first surface side and a second portion (62) on the second surface side; a step of forming a metal film (71) covering the dividing surface (61 a) of the first portion so that the gas vent groove is exposed; Equipped with The step of forming the metal film (71) forming a resist (70) that covers the inner surface of the gas vent groove and a peripheral portion (40a) of the dividing surface around the gas vent groove and has a first thickness (t1) in the peripheral portion; forming the metal film having a second thickness (t2) thinner than the first thickness so as to cover the dividing surface and the resist; removing the resist after the step of forming the metal film having the second thickness; A manufacturing method comprising:

2. 2. The manufacturing method according to claim 1, wherein the compound semiconductor substrate is made of gallium nitride or gallium oxide.

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