# US 12,225,738 B2 · Method for manufacturing nitride semiconductor device and nitride semiconductor device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,225,738 B2 - Document ID: US12225738B2 - Status: Granted - Kind: B2 - Application number: 17/787,945 - Filed: 2021-01-15 - Published: 2023-02-09 - Granted: 2025-02-11 - Earliest claimed: 2020-01-24 - Assignees: Rohm Co., Ltd. - Applicants: Rohm Co., Ltd. - Inventors: Hirotaka Otake; Kentaro Chikamatsu - Web page: https://patentgrep.com/patent/US12225738B2 ## CPC - H10D 30/4732: {using Group III-V semiconductor material} - H10D 30/475: {having wider bandgap layer formed on top of lower bandgap active layer, e.g. undoped barrier HEMTs such as i-AlGaN/GaN HEMTs} - H10D 30/015: {of FETs having heterojunction interface channels or heterojunction gate electrodes, e.g. HEMT} - H10D 30/6738: {Schottky barrier electrodes} - H10D 30/675: {Group III-V materials, Group II-VI materials, Group IV-VI materials, selenium or tellurium} - H10D 62/824: comprising only Group III-V materials heterojunctions, e.g. GaN/AlGaN heterojunctions - H10D 62/85: being Group III-V materials, e.g. GaAs - H10D 62/8503: {Nitride Group III-V materials, e.g. AlN or GaN} - H10D 64/0125: {characterised by the sectional shape, e.g. T or inverted T} - H10D 64/64: Electrodes comprising a Schottky barrier to a semiconductor - H10P 50/267: {using plasmas} - H10P 50/695: {characterised by the process involved to create the mask, e.g. lift-off masks or sidewalls or to modify the mask} - H10D 62/343: {Gate regions of field-effect devices having PN junction gates} - H10D 64/111: {Field plates} - H10D 64/411: {for FETs} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract A method for manufacturing nitride semiconductor device includes a second step of forming, on a gate layer material film, a gate electrode film that is a material film of a gate electrode, a third step of selectively etching the gate electrode film to form the gate electrode 22 of a ridge shape, and a fourth step of selectively etching the gate layer material film to form a semiconductor gate layer 21 of a ridge shape with the gate electrode 22 disposed at a width intermediate portion of a front surface thereof. The third step includes a first etching step for forming a first portion 22A from an upper end to a thickness direction intermediate portion of the gate electrode 22 and a second etching step being a step differing in etching condition from the first etching step and being for forming a remaining second portion 22B of the gate electrode. ## Claims ### Claim 1 A method for manufacturing nitride semiconductor device comprising: a first step of forming a first nitride semiconductor layer that constitutes an electron transit layer, a second nitride semiconductor layer that constitutes an electron supply layer, and a gate layer material film that is a material film of a nitride semiconductor gate layer containing an acceptor type impurity in that order above a substrate; a second step of forming, on the gate layer material film, a gate electrode film that is a material film of a gate electrode; a third step of selectively etching the gate electrode film to form the gate electrode of a ridge shape; a fourth step of selectively etching the gate layer material film to form the semiconductor gate layer of a ridge shape with the gate electrode disposed at a width intermediate portion of a front surface thereof; and a fifth step of forming a passivation film such as to cover an exposed front surface of the second nitride semiconductor layer, side surfaces and an exposed front surface of the nitride semiconductor gate layer, and side surfaces of the gate electrode; and wherein the third step includes a first etching step for forming a first portion from an upper end to a thickness direction intermediate portion of the gate electrode and a second etching step being a step differing in etching condition from the first etching step and being for forming a remaining second portion of the gate electrode and the exposed front surface of the second nitride semiconductor layer, the side surfaces and the exposed front surface of the nitride semiconductor gate layer, and the side surfaces of the gate electrode are covered by the same passivation film. ### Claim 2 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, wherein a thickness of the gate electrode film removed by the first etching step is greater than a thickness of the gate electrode film removed by the second etching step. ### Claim 3 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, wherein if inclination angles of both side surfaces of the first portion with respect to the front surface of the semiconductor gate layer when a width of the first portion becomes narrower as the second portion is approached are expressed by angles of not less than 90 degrees and inclination angles of both side surfaces of the first portion with respect to the front surface of the semiconductor gate layer when the width of the first portion becomes wider as the second portion is approached are expressed by angles of not more than 90 degrees, an average inclination angle of the respective side surfaces of the first portion with respect to the front surface of the semiconductor gate layer is within a range of not less than 80 degrees and not more than 95 degrees. ### Claim 4 (depends on 1) The method for manufacturing nitride semiconductor device according to any claim 1, wherein an etching rate in a vertical direction per unit time of the second etching step is slower than an etching rate in the vertical direction per unit time of the first etching step. ### Claim 5 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, wherein a lateral direction amount that is etched in the second etching step is greater than a lateral direction amount that is etched in the first etching step. ### Claim 6 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, wherein the second etching step is dry etching. ### Claim 7 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, wherein the second etching step is wet etching. ### Claim 8 (depends on 6) The method for manufacturing nitride semiconductor device according to claim 6, wherein the first etching step is dry etching. ### Claim 9 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, further comprising: a step between the third step and the fourth step of forming a first insulating film on the gate layer material film such as to cover the gate electrode and thereafter etching back the first insulating film to form side walls that cover the side surfaces of the gate electrode. ### Claim 10 (depends on 9) The method for manufacturing nitride semiconductor device according to claim 9, further comprising: a step between the second step and the third step of forming a second insulating film on a front surface of the gate electrode film layer and thereafter selectively etching the second insulating film to form a mask on the front surface of the gate electrode film layer; and wherein in the third step, the gate electrode film is etched using the mask. ### Claim 11 (depends on 9) The method for manufacturing nitride semiconductor device according to claim 9, further comprising: a step between the fourth step and the fifth step of removing the side walls. ### Claim 12 (depends on 10) The method for manufacturing nitride semiconductor device according to claim 10, further comprising: a step between the fourth step and the fifth step of removing the mask and the side walls. ### Claim 13 (depends on 1) The method for manufacturing nitride semiconductor device according to claim 1, further comprising after the fifth step: a step of forming a barrier metal on the passivation film; a step of forming a source contact hole and a drain contact hole that penetrate through the barrier metal and the passivation film at positions opposing each other across the semiconductor gate layer; a step of forming, on the barrier metal, a source/drain electrode film that covers at least the source contact hole and the drain contact hole; and a step of selectively etching the source/drain electrode film and the barrier metal to form a source electrode and a drain electrode are further included after the fifth step. ### Claim 14 A nitride semiconductor device comprising: a substrate; a first nitride semiconductor layer that is formed above the substrate and constitutes an electron transit layer; a second nitride semiconductor layer that is formed on the first nitride semiconductor layer, is greater in bandgap than the first nitride semiconductor layer, and constitutes an electron supply layer; a semiconductor gate layer of ridge shape that is formed on the second nitride semiconductor layer and contains an acceptor type impurity; a gate electrode of ridge shape that is formed on a width intermediate portion of a front surface of the semiconductor gate layer; a passivation film that is formed such as to cover an exposed surface of a front surface of the second nitride semiconductor layer and side surfaces and a front surface of the gate electrode; and a source electrode and a drain electrode that are disposed on the second nitride semiconductor layer to oppose each other across the semiconductor gate layer; and wherein the gate electrode, in a sectional view in a ridge width direction, is constituted of a first portion of rectangular shape and a second portion that projects downward from a width intermediate portion of a lower surface of the first portion, and the exposed surface of the front surface of the second nitride semiconductor layer and the side surfaces and the front surface of the gate electrode are covered by the same passivation film. ### Claim 15 (depends on 14) The nitride semiconductor device according to claim 14, wherein if inclination angles of both side surfaces of the first portion with respect to the front surface of the semiconductor gate layer when a width of the first portion becomes narrower as the second portion is approached are expressed by angles of not less than 90 degrees and inclination angles of both side surfaces of the first portion with respect to the front surface of the semiconductor gate layer when the width of the first portion becomes wider as the second portion is approached are expressed by angles of not more than 90 degrees, an average inclination angle of the respective side surfaces of the first portion with respect to the front surface of the semiconductor gate layer is within a range of not less than 80 degrees and not more than 95 degrees. ### Claim 16 (depends on 14) The nitride semiconductor device according to claim 14, wherein the first nitride semiconductor layer is constituted of a GaN layer, the second nitride semiconductor layer is constituted of an AlxGa1-xN (0