US-12622190-B2 - Method of manufacturing semiconductor device

Abstract

A method of manufacturing a semiconductor device includes: injecting an inert element or an electron beam into a GaN-based semiconductor substrate; implanting magnesium into the GaN-based semiconductor substrate; and performing a heat treatment after the injecting and the implanting. A first implantation range of inert element or electron beam and a second implantation range of magnesium overlap with each other. A reference depth Dref (nm) calculated using a formula of Dref=D1+140 and a deepest injection depth D1 (nm) in the injecting is deeper than a deepest implantation depth D2 (nm) in the implanting. After the heat treatment, a concentration of magnesium decreases toward a deeper side at a predetermined decrease rate at a position of the reference depth Dref. The predetermined decrease rate is smaller than a decrease rate at which a concentration of magnesium becomes 1/10 per depth of 300 nm.

Inventors

• Takashi Okawa
• Kenta WATANABE

Assignees

• DENSO CORPORATION
• TOYOTA JIDOSHA KABUSHIKI KAISHA
• MIRISE Technologies Corporation

Dates

Publication Date

20260505

Application Date

20230731

Priority Date

20220802

Claims (8)

1. 1 . A method of manufacturing a semiconductor device comprising: injecting an inert element or electron beam into a GaN-based semiconductor substrate; implanting magnesium into the GaN-based semiconductor substrate; and performing a heat treatment on the GaN-based semiconductor substrate after the injecting and the implanting, wherein a first implantation range, which is an injection range of inert element or electron beam, and a second implantation range, which is an implantation range of magnesium, overlap with each other on a surface of the GaN-based semiconductor substrate, a reference depth Dref (nm) calculated using a formula of Dref=D1+140 and a deepest injection depth D1 (nm) in the injecting is deeper than a deepest implantation depth D2 (nm) in the implanting, after the heat treatment, a concentration of magnesium decreases toward a deeper side at a predetermined decrease rate at a position of the reference depth Dref in a distribution of magnesium concentration in a depth direction within a range where the first implantation range and the second implantation range overlap with each other, the predetermined decrease rate is smaller than a decrease rate at which a concentration of magnesium becomes 1/10 per depth of 300 nm, the second implantation range is included in the first implantation range on the surface, and a dose amount DS1 in the injecting, an area S1 of the first implantation range, a dose amount DS2 in the implanting, and an area S2 of the second implantation range satisfy a relationship of DS1·S1>DS2·S2.
2. 2 . The method according to claim 1 , wherein the injecting includes implanting at least one of N, Ga, Ar, H, and He into the GaN-based semiconductor substrate.
3. 3 . The method according to claim 1 , wherein a heat treatment temperature is higher than or equal to 1300° C. in the heat treatment.
4. 4 . The method according to claim 1 , further comprising forming a gate electrode, after the heat treatment, such that a region of the surface outside the second implantation range and inside the first implantation range becomes a channel region.
5. 5 . The method according to claim 1 , further comprising removing a region where magnesium is implanted in the implanting after the heat treatment so as to expose a p-type region below the region; and forming a gate electrode so that the p-type region becomes a channel region.
6. 6 . A method of manufacturing a semiconductor device comprising: injecting an inert element or electron beam into a GaN-based semiconductor substrate; implanting magnesium into the GaN-based semiconductor substrate; and performing a heat treatment on the GaN-based semiconductor substrate after the injecting and the implanting, wherein a first implantation range, which is an injection range of inert element or electron beam, and a second implantation range, which is an implantation range of magnesium, overlap with each other on a surface of the GaN-based semiconductor substrate, a reference depth Dref (nm) calculated using a formula of Dref=D1+140 and a deepest injection depth D1 (nm) in the injecting is deeper than a deepest implantation depth D2 (nm) in the implanting, after the heat treatment, a concentration of magnesium decreases toward a deeper side at a predetermined decrease rate at a position of the reference depth Dref in a distribution of magnesium concentration in a depth direction within a range where the first implantation range and the second implantation range overlap with each other, the predetermined decrease rate is smaller than a decrease rate at which a concentration of magnesium becomes 1/10 per depth of 300 nm, the method of manufacturing the semiconductor device further comprises forming a gate electrode, after the heat treatment, such that a region of the surface outside the second implantation range and inside the first implantation range becomes a channel region, and a concentration of magnesium in the channel region is 10% or more of a concentration of magnesium in a region where magnesium is implanted in the implanting.
7. 7 . The method according to claim 6 , wherein the injecting includes implanting at least one of N, Ga, Ar, H, and He into the GaN-based semiconductor substrate.
8. 8 . The method according to claim 6 , wherein a heat treatment temperature is higher than or equal to 1300° C. in the heat treatment.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is based on Japanese Patent Application No. 2022-123354 filed on Aug. 2, 2022, the disclosure of which is incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a method of manufacturing a semiconductordevice. BACKGROUND A p-type semiconductor layer is formed in a GaN-based semiconductor substrate. The GaN-based semiconductor substrate is subjected to heat treatment after magnesium is implanted into the GaN-based semiconductor substrate. When the heat treatment is performed, magnesium is activated inside the GaN-based semiconductor substrate. SUMMARY A method of manufacturing a semiconductor device includes: injecting an inert element or an electron beam into a GaN-based semiconductor substrate; implanting a magnesium into the GaN-based semiconductor substrate; and performing a heat treatment on the GaN-based semiconductor substrate after the injecting and the implanting. A first implantation range, which is an injection range of an inert element or an electron beam, and a second implantation range, which is an implantation range of a magnesium, overlap with each other on a surface of the GaN-based semiconductor substrate. A reference depth Dref (nm) calculated using a formula of Dref=D1+140 and a deepest injection depth D1 (nm) in the injecting is deeper than a deepest implantation depth D2 (nm) in the implanting. After the heat treatment, a concentration of magnesium decreases toward a deeper side at a predetermined decrease rate at a position of the reference depth Dref in a distribution of magnesium concentration in a depth direction within a range where the first implantation range and the second implantation range overlap with each other. The predetermined decrease rate is smaller than a decrease rate at which a concentration of magnesium becomes 1/10 per depth of 300 nm. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a semiconductor device. FIG. 2 is an explanatory view illustrating a step of forming a drift layer. FIG. 3 is an explanatory view illustrating a step of implanting N. FIG. 4 is a graph showing a relationship between a concentration of N and a depth. FIG. 5 is an explanatory view illustrating a step of implanting Mg according to a first embodiment. FIG. 6 is a plan view illustrating an Mg implantation range and an N implantation range when a GaN-based semiconductor substrate is viewed from the upper side. FIG. 7 is an explanatory view illustrating a heat treatment step of the first embodiment. FIG. 8 is a graph showing a relationship between a concentration of Mg and a depth before the heat treatment step. FIG. 9 is a graph showing a relationship between a concentration of Mg and a depth after the heat treatment step. FIG. 10 is an explanatory view illustrating a step of forming a gate insulating film and a gate electrode. FIG. 11 is a graph showing a relationship between a concentration of Mg and a depth when a temperature of a heat treatment is changed. FIG. 12 is an explanatory view illustrating a step of implanting Mg according to a second embodiment. FIG. 13 is an explanatory view illustrating a heat treatment step of the second embodiment. FIG. 14 is an explanatory view illustrating a step of removing an Mg implantation range of the second embodiment. DESCRIPTION OF EMBODIMENTS There is a technique for forming a p-type semiconductor layer in a GaN-based semiconductor substrate. In this technique, after magnesium is implanted into a GaN-based semiconductor substrate, the GaN-based semiconductor substrate is subjected to heat treatment. When the heat treatment is performed, magnesium is activated inside the GaN-based semiconductor substrate. As a result, a p-type semiconductor layer is formed inside the GaN-based semiconductor substrate. In the heat treatment for activating magnesium, magnesium diffuses inside the GaN-based semiconductor substrate. Since the diffusion distance of magnesium greatly changes depending on the conditions of the heat treatment, it is difficult to control the diffusion distance of magnesium, such that it is difficult to control the shape of the p-type semiconductor layer. The present disclosure provides a technique for controlling the diffusion distance of magnesium in a GaN-based semiconductor substrate more accurately. A method of manufacturing a semiconductor device includes: injecting inert element or electron beam into a GaN-based semiconductor substrate; implanting magnesium into the GaN-based semiconductor substrate; and performing a heat treatment on the GaN-based semiconductor substrate after the injecting and the implanting. A first implantation range, which is an injection range of an inert element or an electron beam, and a second implantation range, which is an implantation range of magnesium, overlap with each other on a surface of the GaN-based semiconductor substrate. A reference depth Dref (nm) calculated using a formula of Dref=D1+140