# US 11,908,898 B2 · Lateral bipolar transistor structure with base layer of varying horizontal width and methods to form same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,908,898 B2 - Document ID: US11908898B2 - Status: Granted - Kind: B2 - Application number: 17/456,943 - Filed: 2021-11-30 - Published: 2023-03-02 - Granted: 2024-02-20 - Earliest claimed: 2021-09-02 - Assignees: GlobalFoundries U.S. Inc. - Applicants: GlobalFoundries U.S. Inc. - Inventors: Haiting Wang; Hong Yu; Zhenyu Hu; Alexander M. Derrickson - Web page: https://patentgrep.com/patent/US11908898B2 ## CPC - H10D 62/184: {of lateral BJTs} - H10D 10/041: {of thin-film BJTs (of heterojunction BJTs H10D10/021)} - H10D 10/061: {of lateral BJTs (of heterojunction BJTs H10D10/021; of thin film BJTs H10D10/041)} - H10D 10/311: {Thin-film BJTs} - H10D 10/60: Lateral BJTs - H10D 64/231: {Emitter or collector electrodes for bipolar transistors} - H10D 62/134: {of lateral BJTs} - H10D 62/137: {Collector regions of BJTs} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract Embodiments of the disclosure provide a lateral bipolar transistor with a base layer of varying horizontal thickness, and related methods to form the same. A lateral bipolar transistor may include an emitter/collector (E/C) layer on a semiconductor layer. A first base layer is on the semiconductor layer and horizontally adjacent the E/C layer. The first base layer has a lower portion having a first horizontal width from the E/C layer. The first base layer also has an upper portion on the lower portion, with a second horizontal width from the E/C layer greater than the first horizontal width. A second base layer is on the first base layer and adjacent a spacer. The upper portion of the first base layer separates a lower surface of the second base layer from the E/C layer. ## Claims ### Claim 1 A lateral bipolar transistor structure comprising: an emitter/collector (E/C) layer on a semiconductor layer; a first base layer on the semiconductor layer and horizontally adjacent the E/C layer and including: an upper portion having a first horizontal width from the E/C layer, a lower portion under the upper portion and having a second horizontal width from the E/C layer less than the first horizontal width, and a sidewall adjacent the E/C layer including a concave surface; and a second base layer on the first base layer and adjacent a spacer, wherein the upper portion of the first base layer separates a lower surface of the second base layer from the E/C layer. ### Claim 2 (depends on 1) The lateral bipolar transistor structure of claim 1, further comprising a spacer adjacent the second base layer and on the upper portion of the first base layer, wherein a portion of the E/C layer is below the spacer. ### Claim 3 (depends on 2) The lateral bipolar transistor structure of claim 2, wherein the combined horizontal width of the spacer and the second base layer is the same as the first horizontal width. ### Claim 4 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein a second dopant concentration of the second base layer is greater than a first dopant concentration of the first base layer and the semiconductor layer. ### Claim 5 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein a height of the E/C layer over the semiconductor layer is greater than a height of the first base layer over the semiconductor layer. ### Claim 6 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein the second horizontal width of the lower portion of the first base layer is at most approximately five nanometers (nm), and wherein the first horizontal width of the upper portion of the first base layer is at most approximately one-hundred nm. ### Claim 7 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein the first base layer is substantially hourglass shaped. ### Claim 8 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein the first base layer is substantially I shaped. ### Claim 9 (depends on 1) The lateral bipolar transistor structure of claim 1, wherein the first base layer physically contacts the semiconductor layer. ### Claim 10 A lateral bipolar transistor structure comprising: a semiconductor layer on an insulator; an emitter/collector (E/C) layer on the semiconductor layer, the E/C layer having a first doping type; a first base layer on the semiconductor layer and horizontally adjacent the E/C layer, the first base layer having a second doping type opposite the first doping type and including: an upper portion having a first horizontal width from the E/C layer, a lower portion under the upper portion and having a second horizontal width from the E/C layer less than the first horizontal width, and a sidewall adjacent the E/C layer including a concave surface; a spacer on the upper portion of the first base layer and adjacent the E/C layer, wherein an upper portion of the E/C layer is adjacent the spacer and a lower portion of the E/C layer is below the spacer; and a second base layer on the first base layer and adjacent the spacer, the second base layer having the first doping type, wherein the upper portion of the first base layer separates a lower surface of the second base layer from the E/C layer. ### Claim 11 (depends on 10) The lateral bipolar transistor structure of claim 10, wherein a second dopant concentration of the second base layer is greater than a first dopant concentration of the first base layer and the semiconductor layer. ### Claim 12 (depends on 10) The lateral bipolar transistor structure of claim 10, wherein a lower surface of the second base layer does not physically interface with any portion of the E/C layer. ### Claim 13 (depends on 10) The lateral bipolar transistor structure of claim 10, wherein the second horizontal width of the lower portion of the first base layer is at most approximately five nanometers (nm). ### Claim 14 (depends on 13) The lateral bipolar transistor structure of claim 13, wherein the first horizontal width of the upper portion of the first base layer is at most approximately one-hundred nm. ### Claim 15 (depends on 10) The lateral bipolar transistor structure of claim 10, wherein the first base layer is substantially hourglass shaped. ### Claim 16 A method of forming a lateral bipolar transistor structure, the method comprising: forming a semiconductor layer on an insulator; forming an emitter/collector (E/C) layer on the semiconductor layer, the E/C layer having a first doping type; forming a first base layer on the semiconductor layer and horizontally adjacent the E/C layer, the first base layer having a second doping type opposite the first doping type and the first base layer including: an upper portion having a first horizontal width from the E/C layer, a lower portion under the upper portion and having a second horizontal width from the E/C layer less than the first horizontal width, and a sidewall adjacent the E/C layer including a concave surface, and forming a second base layer on the first base layer and adjacent a spacer, the second base layer having the first doping type, wherein the upper portion of the first base layer separates a lower surface of the second base layer from the E/C layer. ### Claim 17 (depends on 16) The method of claim 16, further comprising forming the spacer adjacent the second base layer and on the upper portion of the first base layer, wherein a portion of the E/C layer is below the spacer. ### Claim 18 (depends on 16) The method of claim 16, wherein forming the second base layer includes introducing dopants into the second base layer such that a dopant concentration of the second base layer is greater than a dopant concentration of the first base layer. ### Claim 19 (depends on 16) The method of claim 16, wherein forming the E/C layer causes a height of the E/C layer over the semiconductor layer to be greater than a height of the first base layer over the semiconductor layer. ### Claim 20 (depends on 16) The method of claim 16, wherein forming the first base layer includes forming the lower portion of the first base layer with the second horizontal width of at most approximately five nanometers (nm), and forming the upper portion of the first base layer to have the first horizontal width of at most approximately one-hundred nm.