Semiconductor device manufacturing method

Abstract

To provide a method of manufacturing a semiconductor device capable of suppressing variation in electrical characteristic.SOLUTION: A method of manufacturing a semiconductor device includes: a gate insulating film formation step of forming a gate insulating film 22 with a separation film 22a and an oxide film 22b on a first principal surface 1a of a GaN-based substrate 1 having the first principal surface and a second principal surface 1b, the separation film being deposited so as to be in contact with the first principal surface of the GaN-based substrate and being a material not containing oxygen, the oxide film being deposited so as to be opposed to the first principal surface of the GaN-based substrate via the separation film; and a laser irradiation step of emitting a laser 32 from the second principal surface of the GaN-based substrate toward the inside of the GaN-based substrate after the gate insulating film formation step.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Semiconductor devices manufactured using GaN-based substrates are being developed, and one example is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-14645 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of semiconductor device, gallium oxide may be generated at the interface between the GaN substrate and the gate insulating film during the manufacturing process. The presence of gallium oxide at the interface between the GaN substrate and the gate insulating film raises concerns about variations in electrical characteristics, such as a shift in threshold voltage. This specification provides a method for manufacturing a semiconductor device that suppresses variations in electrical characteristics. [Means for solving the problem]

[0005] The method for manufacturing a semiconductor device disclosed herein may include a gate insulating film forming step of forming a gate insulating film (22) having an isolation film (22a) and an oxide film (22b) on a first main surface of a GaN-based substrate (1) having a first main surface (1a) and a second main surface (1b), the isolation film being formed to contact the first main surface of the GaN-based substrate and being made of a material that does not contain oxygen, and the oxide film being formed to face the first main surface of the GaN-based substrate with the isolation film interposed therebetween; and a laser irradiation step of irradiating a laser (32) from the second main surface of the GaN-based substrate toward the interior of the GaN-based substrate after the gate insulating film forming step. Here, the GaN-based substrate is a nitride semiconductor containing gallium and nitrogen as constituent elements of a crystal, and may be, for example, GaN, AlGaN, InGaN, or InAlGaN. The type of the semiconductor device is not particularly limited and may be, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

[0006] In the above manufacturing method, the isolation film made of an oxygen-free material is formed between the GaN substrate and the oxide film. Therefore, the GaN substrate and the oxide film are not in direct contact with each other, thereby suppressing oxidation of gallium contained in the GaN substrate. Furthermore, in the above manufacturing method, the laser irradiation step is performed after the gate insulating film formation step. When the laser irradiation step is performed, at least a portion of the isolation film migrates toward the oxide film, and at least a portion of the oxide film migrates toward the isolation film. As a result, at least a portion of the interface between the GaN substrate and the gate insulating film is constituted by the interface between the GaN substrate and the oxide film. According to the above manufacturing method, generation of gallium oxide at the interface between the GaN substrate and the gate insulating film is suppressed, and a high-quality interface between the GaN substrate and the oxide film is formed at the interface between the GaN substrate and the gate insulating film. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing a flow of a MOS structure forming step, a laser irradiation step, a peeling step, and a dicing step in a manufacturing method of a semiconductor device. [Figure 2] 1A to 1C are diagrams each showing a cross section of a GaN-based substrate during the manufacturing process of a semiconductor device. [Figure 3] FIG. 2 is a diagram schematically showing a cross-sectional view of a unit cell of a device structure formed on the upper surface side of a GaN-based substrate. [Figure 4] 1A to 1C are diagrams each showing a cross section of a GaN-based substrate during the manufacturing process of a semiconductor device. [Figure 5] 1A to 1C are diagrams each showing a cross section of a GaN-based substrate during the manufacturing process of a semiconductor device. [Figure 6] 1A to 1C are diagrams each showing a cross section of a GaN-based substrate during the manufacturing process of a semiconductor device. [Figure 7] FIG. 2 is a diagram schematically showing the state of a laser irradiated into a GaN-based substrate in a laser irradiation step. [Figure 8] FIG. 1 is a diagram showing the element distribution near the interface between a GaN-based substrate and a gate insulating film before laser irradiation. [Figure 9] FIG. 10 is a diagram showing the element distribution in the vicinity of the interface between the GaN-based substrate and the gate insulating film after laser irradiation. [Figure 10] FIG. 1 is a diagram showing the relationship between the p-type impurity concentration in the channel region and the threshold voltage of a semiconductor device manufactured by the manufacturing method disclosed in this specification. DETAILED DESCRIPTION OF THE INVENTION

[0008] A method for manufacturing a semiconductor device using laser delamination technology will be described below. Note that the technology disclosed in this specification is not limited to the method for manufacturing a semiconductor device using laser delamination technology, and can also be applied to various other manufacturing methods.

[0009] As shown in Fig. 1, the method for manufacturing a semiconductor device using the laser delamination technique disclosed in this specification includes a MOS structure formation step (step S1), a laser irradiation step (step S2), a delamination step (step S3), and a dicing step (step S4). This manufacturing method can manufacture a plurality of semiconductor devices (also called chips) by performing these steps on a GaN-based substrate 1 shown in Fig. 2. Note that, although a detailed description will be omitted, a step of forming various semiconductor regions that constitute the device structure inside the GaN-based substrate 1 is carried out before the MOS structure formation step (step S1). The step for forming the device structure is not particularly limited, and known manufacturing techniques can be used.

[0010] As shown in FIG. 2 , the GaN substrate 1 has an upper surface 1a and a lower surface 1b, each of which is flat and extends parallel to each other. These upper surface 1a and lower surface 1b are also referred to as primary surfaces. The GaN substrate 1 is not particularly limited, but in this example, it may be a gallium nitride substrate. As will be described later, a surface 3 extending to a predetermined depth of the GaN substrate 1 is the surface onto which the laser is irradiated, i.e., the surface on which multiple focal points of the laser are gathered. In this specification, the portion of the GaN substrate 1 above the surface 3 onto which the laser is irradiated, i.e., the portion to be peeled off from the GaN substrate 1, is referred to as a device layer 2. A device structure is formed in the device layer 2 of the GaN substrate 1.

[0011] 3 shows a unit cell of a device structure 10 formed in the device layer 2 of the GaN-based substrate 1 after the MOS structure formation step (step S1 in FIG. 1) has been performed. The device structure 10 is not particularly limited, but may be, for example, a vertical MOSFET.

[0012] The device structure 10 is + a drain region 12 of n-type, a drift region 14 of n-type, a body region 16 of p-type, and + The semiconductor device includes a planar source region 18 and a planar MOS structure 20.

[0013] The drain region 12 is located at a position exposed on the bottom surface 1b of the GaN substrate 1. The drift region 14 is located between the drain region 12 and the body region 16. The part of the drift region 14 located at a position exposed on the top surface 1a of the GaN substrate 1 is called the JFET region 14a. The body region 16 is located at a position exposed on the top surface 1a of the GaN substrate 1, separating the drift region 14 from the source region 18. The part of the body region 16 located between the JFET region 14a and the source region 18 of the drift region 14 is called the channel region CH. The electron density of the inversion layer generated in the channel region CH of the body region 16 is controlled in response to the gate voltage applied to the MOS structure 20, thereby controlling the on / off state of the device structure. In this way, the channel region CH is defined as a region whose carrier density is controlled by the MOS structure 20. The source region 18 is located at a position exposed on the top surface 1a of the GaN substrate 1.

[0014] The MOS structure 20 is provided so as to cover a portion of the upper surface 1a of the GaN-based substrate 1, and includes a gate insulating film 22 and a gate electrode 24. The gate electrode 24 faces the channel region CH of the body region 16 via the gate insulating film 22. The gate insulating film 22 includes an isolation film 22a and an oxide film 22b. The isolation film 22a is formed so as to be in contact with the upper surface 1a of the GaN-based substrate 1. The oxide film 22b is stacked on the isolation film 22a and is formed so as to face the upper surface 1a of the GaN-based substrate 1 with the isolation film 22a interposed therebetween. Note that another film may be provided between the isolation film 22a and the oxide film 22b.

[0015] The MOS structure formation process (step S1 in FIG. 1) includes a gate insulating film formation process of forming a gate insulating film 22 having an isolation film 22a and an oxide film 22b on the upper surface 1a of the GaN-based substrate 1, and a gate electrode formation process of forming a gate electrode 24 on the gate insulating film 22.

[0016] The gate insulating film forming step is not particularly limited, but may include, for example, a step of using atomic layer deposition (ALD) to form an isolation film 22a on the upper surface 1a of the GaN-based substrate 1. The isolation film 22a is not particularly limited, but may be, for example, an aluminum nitride (AlN) film.

[0017] The gate insulating film forming step may further include a step of forming an oxide film 22b on the surface of the isolation film 22a by, for example, atomic layer deposition (ALD), although this is not particularly limited thereto. The oxide film 22b may be, for example, silicon oxide (SiO2), although this is not particularly limited thereto.

[0018] As shown in FIG. 4, in the laser irradiation step (step S2 in FIG. 1), a laser is irradiated onto the surface 3 of the GaN substrate 1, which extends to a predetermined depth. The laser is irradiated from the lower surface 1b of the GaN substrate 1, on which no device structure is formed, so as to be focused at a predetermined depth in the GaN substrate 1. The laser is a laser with a wavelength range that is transparent to the GaN substrate 1 (a gallium nitride substrate in this example). The laser is not particularly limited, but may be a visible light laser, for example, a green laser. At the position of the focusing point, the crystal (in this example, a gallium nitride single crystal) constituting the GaN substrate 1 is heated and decomposed. As a result, a modified layer composed of a precipitated layer of constituent atoms of the crystal constituting the GaN substrate 1 (in this example, a gallium precipitated layer) is formed at the position of the focusing point. The modified layer has a lower strength than the crystal constituting the GaN substrate 1. Therefore, the modified layer has a lower strength than the surrounding crystal.

[0019] As shown in FIG. 5, in the peeling step (step S3 in FIG. 1), the device layer 2 on which the device structure 10 is formed is peeled off from the remaining GaN-based substrate 1 along the laser-irradiated surface 3. Since the strength of the laser-irradiated surface 3 has been reduced by the formation of a modified layer, the device layer 2 is easily peeled off from the remaining GaN-based substrate 1. The GaN-based substrate 1 from which the device layer 2 has been peeled off is reused in the manufacture of semiconductor devices. For example, after polishing and etching the peeled surface of the GaN-based substrate 1, a device layer can be formed on the peeled surface using epitaxial crystal growth technology, thereby forming a device structure on the formed device layer.

[0020] As shown in FIG. 6, in the dicing process (step S4 in FIG. 1), the device layer 2 peeled off from the GaN-based substrate 1 is subjected to a polishing process, an electrode formation process, etc., and then a plurality of devices (also called dies) are cut out from the device layer 2, thereby completing the semiconductor device.

[0021] Next, the above-mentioned laser irradiation step (step S2 in FIG. 1) will be described in detail. FIG. 7 shows how a laser 32 is irradiated into the GaN substrate 1 from the lower surface 1b of the GaN substrate 1. The laser 32 is irradiated so as to be focused on a surface 3 extending to a predetermined depth in the GaN substrate 1. A portion of the laser 32 reaches the upper surface 1a of the GaN substrate 1 beyond the focusing point. Such escape light of the laser 32 is irradiated onto the gate insulating film 22.

[0022] The laser beam 32 is absorbed by the isolation film 22a of the gate insulating film 22. Assume now that the isolation film 22a is not provided. In this case, the GaN substrate 1 and the oxide film 22b are in direct contact with each other. In this example, the energy of the laser beam 32 causes oxygen contained in the oxide film 22b to promote oxidation of gallium contained in the GaN substrate 1, resulting in the formation of gallium oxide at the interface between the GaN substrate 1 and the gate insulating film 22. This formation of gallium oxide causes fluctuations in electrical characteristics, such as a shift in threshold voltage. In contrast, in the semiconductor device manufacturing method disclosed herein, the oxygen-free isolation film 22a is provided between the GaN substrate 1 and the oxide film 22b, thereby suppressing oxidation of gallium contained in the GaN substrate 1. Thus, the technology of providing the isolation film 22a between the GaN substrate 1 and the oxide film 22b can suppress fluctuations in electrical characteristics due to the laser beam 32 in semiconductor device manufacturing methods using laser delamination technology.

[0023] Furthermore, at least a portion of the isolation film 22a (AlN film) that absorbs the escape light of the laser 32 decomposes into aluminum and nitrogen. The aluminum generated by the decomposition diffuses as aluminum oxide and moves toward the oxide film 22b. Meanwhile, a portion of the oxide film 22b moves toward the interface between the GaN-based substrate 1 and the gate insulating film 22. In this manner, when the isolation film 22a is irradiated with the laser 32, the aluminum generated by the decomposition of the isolation film 22a moves along the direction of the laser 32, thereby exchanging positions of at least a portion of the isolation film 22a and at least a portion of the oxide film 22b, and at least a portion of the interface between the GaN-based substrate 1 and the gate insulating film 22 is constituted by the interface between the GaN-based substrate 1 and the oxide film 22b. A high-quality interface between the GaN-based substrate 1 and the oxide film 22b improves the carrier mobility in the channel region and the dielectric breakdown strength of the gate insulating film 22.

[0024] 8 and 9 show element distributions near the interface between the GaN-based substrate 1 and the gate insulating film 22 obtained using electron energy loss spectroscopy (EELS). FIG. 8 shows the element distribution before laser irradiation, and FIG. 9 shows the element distribution after laser irradiation. The horizontal axis indicates the distance along the thickness direction between the GaN-based substrate 1 and the gate insulating film 22, and the position of "5 nm" corresponds to the position of the interface between the GaN-based substrate 1 and the gate insulating film 22. In this example, the thickness of the isolation film 22a (shown as "AlN" in FIG. 8) formed before laser irradiation was 5 nm, and the thickness of the oxide film 22b (shown as "SiO2" in FIG. 8) formed before laser irradiation was 100 nm.

[0025] 8 and 9, aluminum generated by decomposition of the isolation film 22a migrates toward the oxide film 22b along the laser beam propagation direction after laser irradiation. In this example, the aluminum at the interface between the GaN substrate 1 and the gate insulating film 22 drops below the detection limit after laser irradiation. That is, it was confirmed that the isolation film 22a was completely replaced by the oxide film 22b at the interface between the GaN substrate 1 and the gate insulating film 22.

[0026] In this way, the technique of providing the isolation film 22a between the GaN substrate 1 and the oxide film 22b can be combined with laser irradiation to replace at least a part of the isolation film 22a with the oxide film 22b. As a result, a high-quality interface between the GaN substrate 1 and the oxide film 22b is formed at the interface between the GaN substrate 1 and the gate insulating film 22, and the carrier mobility in the channel region and the dielectric breakdown strength of the gate insulating film 22 can be improved.

[0027] Figure 10 shows the relationship between the p-type impurity concentration in the channel region, calculated from the threshold voltage of the semiconductor device manufactured by the above manufacturing method, and the threshold voltage. The measured value of the threshold voltage of the semiconductor device manufactured by the above manufacturing method is 6.5 V, and the p-type impurity concentration in the channel region is 5 × 10 17 cm -3 Furthermore, the thickness of isolation film 22a formed before laser irradiation was 5 nm, and the thickness of oxide film 22b formed before laser irradiation was 100 nm.

[0028] As shown in Figure 10, the p-type impurity concentration in the channel region is 6 × 10 16 cm -3 If the p-type impurity concentration in the channel region is 9×10 or more, the semiconductor device can operate in the enhancement mode. 17 cm -3 In order to achieve a practical threshold voltage of 2 to 3 V, the p-type impurity concentration in the channel region must be 1.4 × 10 or less. 17 ~2×10 17 cm -3 This can be done as follows.

[0029] This suggests that the semiconductor device manufactured by the above manufacturing method can operate in the enhancement mode even if the p-type impurity concentration in the channel region is low. Therefore, it is suggested that the semiconductor device manufactured by the above manufacturing method can operate in the enhancement mode and has low channel resistance.

[0030] The above manufacturing method can form a high-quality interface between the GaN-based substrate and the gate insulating film while suppressing the influence of laser light leakage for laser delamination. Alternatively, a laser for a purpose other than the laser for laser delamination or its light leakage may be used to form a high-quality interface between the GaN-based substrate and the gate insulating film. For example, a laser may be irradiated solely for the purpose of forming a high-quality interface between the GaN-based substrate and the gate insulating film. The technology disclosed in this specification can also be applied to manufacturing methods other than those using laser delamination technology.

[0031] The material of the separation film is not particularly limited as long as it does not contain oxygen. The material of the separation film may be selected from materials that can efficiently absorb laser light depending on the wavelength range of the laser. The material of the separation film may include, for example, at least one selected from the group consisting of nitrides, metal films, and Si. The nitride may be aluminum nitride (AlN) or silicon nitride (SiN). Separation films made of these materials can absorb visible laser light.

[0032] The thickness of the isolation film is not particularly limited as long as it can suppress oxidation of gallium contained in the GaN-based substrate. The isolation film is preferably thin so that the isolation film and the oxide film can be effectively replaced by laser irradiation. The thickness of the isolation film is not particularly limited, but may be, for example, 10 nm or less.

[0033] The features of the technology disclosed in this specification are summarized below. Note that the technical elements described below are independent technical elements that exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0034] (Feature 1) A method for manufacturing a semiconductor device, comprising: a gate insulating film forming step of forming a gate insulating film having an isolation film and an oxide film on a first main surface of a GaN-based substrate having a first main surface and a second main surface, the isolation film being formed so as to be in contact with the first main surface of the GaN-based substrate and being made of a material that does not contain oxygen, and the oxide film being formed so as to face the first main surface of the GaN-based substrate with the isolation film interposed therebetween; a laser irradiation step of irradiating a laser beam from the second main surface of the GaN-based substrate toward inside the GaN-based substrate after the gate insulating film formation step.

[0035] (Feature 2) a peeling step of peeling off a device layer of the GaN-based substrate on which the gate insulating film is formed from remaining layers of the GaN-based substrate, In the laser irradiation step, the laser is irradiated onto a surface of the GaN substrate extending from the second main surface to a predetermined depth of the GaN substrate, 2. The manufacturing method according to Feature 1, wherein in the peeling step, the device layer is peeled off from the remaining layers of the GaN-based substrate along the surface irradiated with the laser.

[0036] (Feature 3) the GaN-based substrate has a p-type channel region (CH) in a portion where the gate insulating film is in contact, The concentration of p-type impurities in the channel region is 6×10 16 ~9×10 17 cm -3 3. The method according to Feature 1 or 2,

[0037] (Feature 4) 4. The manufacturing method according to any one of Features 1 to 3, wherein the separation film includes at least one selected from the group consisting of a nitride, a metal film, and Si.

[0038] (Feature 5) 5. The method according to Feature 4, wherein the separation membrane is made of AlN or SiN.

[0039] (Feature 6) 6. The method according to any one of Features 1 to 5, wherein the oxide film is SiO2.

[0040] 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]

[0041] 1: GaN-based substrate, 2: device layer, 10: device structure, 12: drain region, 14: drift region, 14a: JFET region, 16: body region, 18: source region, 20: MOS structure, 22: gate insulating film, 22a: isolation film, 22b: oxide film, 24: gate electrode, 32: laser

Claims

1. A method for manufacturing a semiconductor device, comprising: a step of forming a gate insulating film (22) on a first main surface of a GaN-based substrate (1) having a first main surface (1a) and a second main surface (1b), each of which is planar and extends parallel to each other, the gate insulating film (22) having an isolation film (22a) and an oxide film (22b) constituting a planar MOS structure (20) extending parallel to the first main surface, the isolation film being formed parallel to the first main surface so as to be in contact with the first main surface of the GaN-based substrate and being made of a material that does not contain oxygen, and the oxide film being formed so as to face the first main surface of the GaN-based substrate via the isolation film; a laser irradiation step of irradiating a laser (32) from the second main surface of the GaN-based substrate toward inside the GaN-based substrate after the gate insulating film formation step, In the laser irradiation step, the laser is irradiated onto a surface (3) extending from the second main surface of the GaN-based substrate to a predetermined depth of the GaN-based substrate, The method for manufacturing a semiconductor device, wherein the isolation film has a thickness of 10 nm or less.

2. a peeling step of peeling off the device layer (2) on which the gate insulating film is formed of the GaN-based substrate from the remaining layers of the GaN-based substrate, The manufacturing method according to claim 1 , wherein in the peeling step, the device layer is peeled off from the remaining layers of the GaN-based substrate along the surface irradiated with the laser.

3. the GaN-based substrate has a p-type channel region (CH) in a portion where the gate insulating film is in contact, The concentration of p-type impurities in the channel region is 6×10 16 ~9 x 10 17 cm -3 The method according to claim 1, wherein

4. The method of claim 1 , wherein the isolation film comprises at least one selected from the group consisting of a nitride film, a metal film, and Si.

5. The method according to claim 4 , wherein the separation film is made of AlN or SiN.

6. The oxide film is SiO 2 The method according to claim 1, wherein

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