# US 2014/0191251 A1 · Silicon carbide semiconductor device and method of manufacturing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191251 A1 - Document ID: US20140191251A1 - Status: Published application - Kind: A1 - Application number: 14/240,017 - Filed: 2011-09-21 - Published: 2014-07-10 - Earliest claimed: 2011-09-21 - Assignees: Mitsubishi Electric Corporation - Inventors: Yoichiro Tarui; Eisuke Suekawa; Naoki Yutani; Shiro Hino; Naruhisa Miura; Masayuki Imaizumi - Web page: https://patentgrep.com/patent/US20140191251A1 ## CPC - H10D 62/153: {Impurity concentrations or distributions} - H10D 12/031: {of IGBTs} - H10D 30/021: {of FETs having insulated gates [IGFET]} - H10D 30/0291: {of vertical DMOS [VDMOS] FETs} - H10D 30/60: Insulated-gate field-effect transistors [IGFET] (H10D30/40 takes precedence) - H10D 30/66: Vertical DMOS [VDMOS] FETs - H10D 62/8325: {Silicon carbide} - H10D 64/0115: {to silicon carbide} - H10P 14/3408: {Silicon carbide} - H10P 30/2042: {into crystalline silicon carbide} - H10P 30/21: {of electrically active species} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract It is expected that both reduction of the resistance of a source region and reduction of a leakage current in a gate oxide film be achieved in an MOSFET in a silicon carbide semiconductor device. A leakage current to occur in a gate oxide film of the MOSFET is suppressed by reducing roughness at an interface between a source region and the gate oxide film. If an impurity concentration is to become high at a surface portion of the source region, the gate oxide film is formed by dry oxidation or CVD process. If the gate oxide film is formed by wet oxidation, the impurity concentration at the surface portion of the source region is controlled at a low level. ## Claims ### Claim 1 A silicon carbide semiconductor device comprising an MOSFET that includes: a well region formed in an upper surface portion of a silicon carbide semiconductor layer; a source region formed in an upper surface portion of said well region; a gate oxide film formed on said well region and said source region; and a gate electrode formed on said gate oxide film, wherein an impurity concentration at an upper surface portion of said source region is 1×1018 cm−3 or less. ### Claim 2 (depends on 1) The silicon carbide semiconductor device according to claim 1, wherein the impurity concentration at the upper surface portion of said source region is 5×1017 cm−3 or less. ### Claim 3 (depends on 1) The silicon carbide semiconductor device according to claim 1, wherein a peak of the impurity concentration in said source region is 1×1018 cm−3 or more. ### Claim 4 (depends on 1) The silicon carbide semiconductor device according to claim 1, wherein said gate oxide film is formed by one or more of wet oxidation, dry oxidation, and CVD process. ### Claim 5 (depends on 1) The silicon carbide semiconductor device according to claim 1, wherein nitrogen is introduced into an interface between said well region and said gate oxide film. ### Claim 6 (depends on 1) The silicon carbide semiconductor device according to claim 1, wherein impurities forming said source region are nitrogen or phosphorous. ### Claim 7 A silicon carbide semiconductor device comprising an MOSFET that includes: a well region formed in an upper surface portion of a silicon carbide semiconductor layer; a source region formed in an upper surface portion of said well region; a gate oxide film formed on said well region and said source region; and a gate electrode formed on said gate oxide film, wherein an impurity concentration at an upper surface portion of said source region is 1×1018 cm−3 or more, and said gate oxide film is formed by performing at least dry oxidation or CVD process first. ### Claim 8 (depends on 7) The silicon carbide semiconductor device according to claim 7, wherein said gate oxide film is formed by performing dry oxidation first and then CVD process. ### Claim 9 (depends on 7) The silicon carbide semiconductor device according to claim 7, wherein said gate oxide film is formed by performing CVD process first and then wet oxidation or dry oxidation. ### Claim 10 (depends on 7) The silicon carbide semiconductor device according to claim 7, wherein nitrogen is introduced into an interface between said well region and said gate oxide film. ### Claim 11 (depends on 7) The silicon carbide semiconductor device according to claim 7, wherein impurities forming said source region are nitrogen or phosphorous. ### Claim 12 A method of manufacturing a silicon carbide semiconductor device, comprising the steps of: (a) forming a well region of an MOSFET by ion-implanting impurities of a first conductivity type into an upper surface portion of a silicon carbide semiconductor layer; (b) forming a source region of said MOSFET by ion-implanting impurities of a second conductivity type into an upper surface portion of said well region; (c) forming a gate oxide film of said MOSFET on said well region and said source region; and (d) forming a gate electrode of said MOSFET on said gate oxide film, wherein a concentration of said impurities of said second conductivity type ion-implanted in said step (b) is 1×1018 cm−3 or less at an upper surface portion of said source region. ### Claim 13 (depends on 12) The method of manufacturing a silicon carbide semiconductor device according to claim 12, wherein the concentration of said impurities of said second conductivity type ion-implanted in said step (b) is 5×1017 cm−3 or less at the upper surface portion of said source region. ### Claim 14 (depends on 12) The method of manufacturing a silicon carbide semiconductor device according to claim 12, wherein the concentration of said impurities of said second conductivity type ion-implanted into said source region in said step (b) peaks at 1×1018 cm−3 or more. ### Claim 15 (depends on 12) The method of manufacturing a silicon carbide semiconductor device according to claim 12, wherein in said step (c), said gate oxide film is formed by one or more of wet oxidation, dry oxidation, and CVD process. ### Claim 16 (depends on 12) The method of manufacturing a silicon carbide semiconductor device according to claim 12, further comprising the step of: (e) performing thermal process using nitrogen oxide gas or dinitrogen oxide gas, the step (e) being performed after said step (c). ### Claim 17 (depends on 12) The method of manufacturing a silicon carbide semiconductor device according to claim 12, wherein said impurities of said second conductivity type are nitrogen or phosphorous. ### Claim 18 A method of manufacturing a silicon carbide semiconductor device, comprising the steps of: (a) forming a well region of an MOSFET by ion-implanting impurities of a first conductivity type into an upper surface portion of a silicon carbide semiconductor layer; (b) forming a source region of said MOSFET by ion-implanting impurities of a second conductivity type into an upper surface portion of said well region; (c) forming a gate oxide film of said MOSFET on said well region and said source region; and (d) forming a gate electrode of said MOSFET on said gate oxide film, wherein a concentration of said impurities of said second conductivity type ion-implanted in said step (b) is 1×1018 cm−3 or more at an upper surface portion of said source region, and in said step (c), said gate oxide film is formed by performing at least dry oxidation or CVD process first. ### Claim 19 (depends on 18) The method of manufacturing a silicon carbide semiconductor device according to claim 18, wherein in said step (c), said gate oxide film is formed by performing dry oxidation first and then CVD process. ### Claim 20 (depends on 18) The method of manufacturing a silicon carbide semiconductor device according to claim 18, wherein in said step (c), said gate oxide film is formed by performing CVD process first and then wet oxidation or dry oxidation. ### Claim 21 (depends on 18) The method of manufacturing a silicon carbide semiconductor device according to claim 18, further comprising the step of: (e) performing thermal process using nitrogen oxide gas or dinitrogen oxide gas, the step (e) being performed after said step (c). ### Claim 22 (depends on 18) The method of manufacturing a silicon carbide semiconductor device according to claim 18, wherein said impurities of said second conductivity type are nitrogen or phosphorous.