# US 12,113,078 B2 · Photodetector > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,113,078 B2 - Document ID: US12113078B2 - Status: Granted - Kind: B2 - Application number: 17/479,835 - Filed: 2021-09-20 - Published: 2022-01-06 - Granted: 2024-10-08 - Earliest claimed: 2018-03-30 - Assignees: Panasonic Intellectual Property Management Co., Ltd. - Applicants: Panasonic Intellectual Property Management Co., Ltd. - Inventors: Akito Inoue; Yuki Sugiura; Yutaka Hirose - Web page: https://patentgrep.com/patent/US12113078B2 ## CPC - H10F 39/8033: {Photosensitive area} - H10F 39/807: {Pixel isolation structures} - H10F 30/225: the potential barrier working in avalanche mode, e.g. avalanche photodiodes - H10F 39/014: {of CMOS image sensors} - H10F 39/18: Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors - H10F 39/802: {Geometry or disposition of elements in pixels, e.g. address-lines or gate electrodes} - H10F 39/8037: {the integrated elements comprising a transistor} - H10F 39/813: {Electronic components shared by multiple pixels, e.g. one amplifier shared by two pixels} - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION ## Abstract A photodetector includes: a semiconductor substrate having a first main surface and a second main surface; a first semiconductor layer that is of a first conductivity type, and is included in the semiconductor substrate and closer to the first main surface than to the second main surface; a second semiconductor layer that is of a second conductivity type different from the first conductivity type, and is included in the semiconductor substrate and interposed between the first semiconductor layer and the second main surface; a multiplication region that causes avalanche multiplication to a charge generated in the semiconductor substrate through photoelectric conversion; a circuit region disposed alongside the first semiconductor layer in a direction parallel to the first main surface; at least one isolation transistor disposed in the circuit region; and an isolation region interposed between the first semiconductor layer and the circuit region. ## Claims ### Claim 1 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface; an epitaxial layer in the semiconductor substrate; a first semiconductor layer that is of a first conductivity type, and included in the semiconductor substrate and closer to the first main surface than to the second main surface; a multiplication region included in the epitaxial layer, and causes avalanche multiplication to a charge generated in the semiconductor substrate through photoelectric conversion, the multiplication region comprising at least two multiplication regions; and an isolation region that separates the at least two multiplication regions, wherein a gradient of an impurity concentration distribution of the epitaxial layer includes a first section where an impurity concentration of the epitaxial layer is substantially constant and a second section where the impurity concentration drastically increases from the first main surface toward the second main surface, the second section following the first section. ### Claim 2 (depends on 1) The photodetector according to claim 1, wherein the epitaxial layer includes a fourth semiconductor layer, the fourth semiconductor layer being of a second conductivity type different from the first conductivity type, an impurity concentration of the fourth semiconductor layer is less than an impurity concentration of the first semiconductor layer. ### Claim 3 (depends on 1) The photodetector according to claim 1, wherein the epitaxial layer includes: a fourth semiconductor layer that is of a second conductivity type different from the first conductivity type; and a photoelectric conversion layer that drifts the charge generated through the photoelectric conversion to reach the multiplication region, and an impurity concentration of the fourth semiconductor layer is greater than an impurity concentration of the photoelectric conversion layer. ### Claim 4 (depends on 1) The photodetector according to claim 1, wherein the epitaxial layer includes a fourth semiconductor layer, the fourth semiconductor layer being of a second conductivity type different from the first conductivity type, and an impurity concentration of the fourth semiconductor layer is less than a maximum value of the impurity concentration of the second section where the impurity concentration drastically increases. ### Claim 5 (depends on 1) The photodetector according to claim 1, wherein a coefficient of variation of an avalanche breakdown voltage is equal to or less than 0.015. ### Claim 6 (depends on 1) The photodetector according to claim 1, wherein a coefficient of variation of an avalanche breakdown voltage is equal to or less than 0.007. ### Claim 7 (depends on 1) The photodetector according to claim 1, wherein a coefficient of variation of an avalanche breakdown voltage ranges from 0.005 to 0.015, inclusive. ### Claim 8 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, the second semiconductor layer includes: a first region where an impurity concentration changes with a first gradient of impurity concentration distribution; and a second region where the impurity concentration changes with a second gradient of impurity concentration distribution, the second gradient of impurity concentration distribution is greater than the first gradient of impurity concentration distribution, the second region is closer to the second main surface than to the first main surface, and a width of the first region in a direction perpendicular to the semiconductor substrate is greater than a width of the second region in the direction perpendicular to the semiconductor substrate. ### Claim 9 (depends on 8) The photodetector according to claim 8, wherein the impurity concentration of the second semiconductor layer drastically increases in the second region. ### Claim 10 (depends on 9) The photodetector according to claim 9, wherein the first gradient of impurity concentration distribution of the second semiconductor layer is substantially constant in the first region. ### Claim 11 (depends on 10) The photodetector according to claim 10, wherein a maximum value of an impurity concentration of the fourth semiconductor layer is smaller than a maximum value of the impurity concentration in the second region. ### Claim 12 (depends on 11) The photodetector according to claim 11, wherein the photodetector is a backside illumination (BSI) photodetector including an avalanche photodiode. ### Claim 13 (depends on 8) The photodetector according to claim 8, wherein the second semiconductor layer consists of the first region and the second region. ### Claim 14 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, the second semiconductor layer includes: a first region where an impurity concentration changes with a first gradient of impurity concentration distribution; and a second region where the impurity concentration changes with a second gradient of impurity concentration distribution, the second gradient of impurity concentration distribution is greater than the first gradient of impurity concentration distribution, the second region is closer to the second main surface than to the first main surface, and an interface between the second region and the first region is closer to the second main surface than to the first main surface in the second semiconductor layer. ### Claim 15 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, and the second semiconductor layer includes a region where a gradient of impurity concentration distribution drastically increases, the region being closer to the second main surface than to the fourth semiconductor layer. ### Claim 16 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type, and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, the second semiconductor layer includes: a first region where an impurity concentration changes with a first gradient of impurity concentration distribution; and a second region where the impurity concentration changes with a second gradient of impurity concentration distribution, the second gradient of impurity concentration distribution is greater than the first gradient of impurity concentration distribution, the second region is closer to the second main surface than to the first main surface, and an impurity concentration of the fourth semiconductor layer is greater than an impurity concentration of the first region. ### Claim 17 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type, and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, the second semiconductor layer includes: a first region where an impurity concentration changes with a first gradient of impurity concentration distribution; and a second region where the impurity concentration changes with a second gradient of impurity concentration distribution, the second gradient of impurity concentration distribution is greater than the first gradient of impurity concentration distribution, the second region is closer to the second main surface than to the first main surface, and an impurity concentration of the fourth semiconductor layer is smaller than a maximum value of an impurity concentration of the second region. ### Claim 18 A photodetector, comprising: a semiconductor substrate that has a first main surface and a second main surface opposed to the first main surface, wherein the semiconductor substrate includes: a first semiconductor layer that is of an N type and closer to the first main surface than to the second main surface; a fourth semiconductor layer that is of a P type; and a second semiconductor layer that is of a P type and closer to the second main surface than to the first main surface, the first semiconductor layer, the fourth semiconductor layer, and the second semiconductor layer are stacked in the stated order, and the second semiconductor layer includes an inflection point of impurity concentration, the inflection point being closer to the second main surface than to the fourth semiconductor layer, and wherein the impurity concentration in a part closer to the fourth semiconductor layer than to the second main surface in the second semiconductor layer is smaller than a maximum value of impurity concentration of the fourth semiconductor layer, and the impurity concentration in a part closer to the second main surface than to the fourth semiconductor layer in the second semiconductor layer is greater than the maximum value of the impurity concentration of the fourth semiconductor layer.