# US 11,908,928 B2 · Field plate anchoring structure for trench-based semiconductor devices > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,908,928 B2 - Document ID: US11908928B2 - Status: Granted - Kind: B2 - Application number: 17/534,495 - Filed: 2021-11-24 - Published: 2023-05-25 - Granted: 2024-02-20 - Earliest claimed: 2021-11-24 - Assignees: Infineon Technologies Austria AG - Applicants: Infineon Technologies Austria AG - Inventors: Ling Ma - Web page: https://patentgrep.com/patent/US11908928B2 ## CPC - H10D 30/668: {having trench gate electrodes, e.g. UMOS transistors} - H10D 30/0297: {using recessing of the gate electrodes, e.g. to form trench gate electrodes} - H10D 62/115: {Dielectric isolations, e.g. air gaps} - H10D 62/127: {of cellular field-effect devices, e.g. multicellular DMOS transistors or IGBTs} - H10D 64/01: Manufacture or treatment - H10D 64/117: {Recessed field plates, e.g. trench field plates or buried field plates} - H10D 64/252: {for vertical or pseudo-vertical devices} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract A semiconductor device includes: a semiconductor substrate; a first gate trench and a second gate trench both extending from a first main surface of the semiconductor substrate into the semiconductor substrate; a semiconductor mesa delimited by the first and second gate trenches; and a field plate trench extending from the first main surface through the semiconductor mesa. The field plate trench includes a field plate separated from each sidewall and a bottom of the field plate trench by an air gap. The field plate is anchored to the semiconductor substrate at the bottom of the field plate trench by an electrically insulative material that occupies a space in a central part of the field plate, the electrically insulative material spanning the air gap to contact the semiconductor substrate at the bottom of the field plate trench. Methods of producing the semiconductor device are also described. ## Claims ### Claim 1 A semiconductor device, comprising: a semiconductor substrate; a first gate trench and a second gate trench both extending from a first main surface of the semiconductor substrate into the semiconductor substrate; a semiconductor mesa delimited by the first and second gate trenches; and a field plate trench extending from the first main surface through the semiconductor mesa, wherein the field plate trench comprises a field plate separated from each sidewall and a bottom of the field plate trench by an air gap, wherein the field plate is anchored to the semiconductor substrate at the bottom of the field plate trench by an electrically insulative material that occupies a space in a central part of the field plate, the electrically insulative material spanning the air gap to contact the semiconductor substrate at the bottom of the field plate trench. ### Claim 2 (depends on 1) The semiconductor device of claim 1, wherein the field plate comprises polysilicon, and wherein the electrically insulative material comprises nitride. ### Claim 3 (depends on 1) The semiconductor device of claim 1, wherein the first and second gate trenches are stripe-shaped in a lengthwise direction of the first and second gate trenches, wherein the field plate trench is needle-shaped in a lengthwise direction of the field plate trench, wherein the lengthwise direction of the first and second gate trenches is parallel to the first main surface of the semiconductor substrate, and wherein the lengthwise direction of the field plate trench is perpendicular to the first main surface of the semiconductor substrate. ### Claim 4 (depends on 1) The semiconductor device of claim 1, further comprising: a contact structure having a first part in electrical and physical contact with one or more device regions formed in the semiconductor mesa, and a second part in electrical and physical contact with the field plate, wherein the second part of the contact structure is laterally spaced inward and separated from the first part of the contact structure. ### Claim 5 (depends on 4) The semiconductor device of claim 4, wherein the space between the second part of the contact structure and the first part of the contact structure is aligned with the air gap in the field plate trench such that no part of the contact structure covers the air gap. ### Claim 6 (depends on 4) The semiconductor device of claim 4, wherein the second part of the contact structure has an opening aligned with the electrically insulative material that occupies the space in the central part of the field plate. ### Claim 7 (depends on 4) The semiconductor device of claim 4, wherein the electrically insulative material that occupies the space in the central part of the field plate is recessed below the first main surface of the semiconductor substrate such that the electrically insulative material has a recess, and wherein the second part of the contact structure occupies the recess in the electrically insulative material. ### Claim 8 (depends on 4) The semiconductor device of claim 4, wherein the first part of the contact structure has a square cross-section in a direction parallel to the first main surface of the semiconductor substrate, and wherein the second part of the contact structure has a circular cross-section in the same direction. ### Claim 9 (depends on 4) The semiconductor device of claim 4, wherein the first part of the contact structure has a rectangular cross-section in a direction parallel to the first main surface of the semiconductor substrate, and wherein the second part of the contact structure has a circular cross-section in the same direction. ### Claim 10 (depends on 4) The semiconductor device of claim 4, wherein the first part of the contact structure has a rectangular cross-section in a direction parallel to the first main surface of the semiconductor substrate, and wherein the second part of the contact structure has a rectangular cross-section in the same direction. ### Claim 11 (depends on 4) The semiconductor device of claim 4, further comprising: an interlayer dielectric on the first main surface of the semiconductor substrate and sealing the air gap in the field plate trench; and a metallization layer on the interlayer dielectric, wherein the first part of the contact structure extends through the interlayer dielectric to electrically connect the metallization layer to the one or more device regions formed in the semiconductor mesa, wherein the second part of the contact structure extends through the interlayer dielectric to electrically connect the metallization layer to the field plate in the field plate trench. ### Claim 12 A semiconductor device, comprising: a semiconductor substrate; a gate trench extending from a first main surface of the semiconductor substrate into the semiconductor substrate; a field plate trench extending from the first main surface into the semiconductor substrate and laterally spaced apart from the gate trench, the field plate trench having one or more sidewalls and a bottom; a field plate in the field plate trench; an air gap separating the field plate from the one or more sidewalls and the bottom of the field plate trench; a space in a central part of the field plate; and an electrically insulative material occupying the space in the central part of the field plate and anchoring the field plate to the semiconductor substrate by spanning the air gap at the bottom of the field plate trench. ### Claim 13 A method of producing a semiconductor device, the method comprising: etching a first gate trench and a second gate trench into a first main surface of a semiconductor substrate, the first and second gate trenches delimiting a semiconductor mesa; etching a field plate trench into the first main surface, the field plate trench extending through the semiconductor mesa; forming a field plate in the field plate trench, the field plate being separated from each sidewall and a bottom of the field plate trench by an air gap, the field plate having a space in a central part of the field plate; and anchoring the field plate to the semiconductor substrate at the bottom of the field plate trench by an electrically insulative material that occupies the space in the central part of the field plate, the electrically insulative material spanning the air gap to contact the semiconductor substrate at the bottom of the field plate trench. ### Claim 14 (depends on 13) The method of claim 13, wherein forming the field plate comprises: lining each sidewall and the bottom of the field plate trench with an oxide; forming polysilicon on the oxide without closing the space in the central part of the field plate; and removing the polysilicon and the oxide from a central part of the bottom of the field plate trench such that a corner part of the bottom of the field plate trench remains covered by both the oxide and the polysilicon. ### Claim 15 (depends on 14) The method of claim 14, wherein removing the polysilicon and the oxide from the central part of the bottom of the field plate trench comprises: anisotropically etching the polysilicon and the oxide at the central part of the bottom of the field plate trench. ### Claim 16 (depends on 14) The method of claim 14, wherein anchoring the field plate to the semiconductor substrate at the bottom of the field plate trench comprises: after removing the polysilicon and the oxide from the central part of the bottom of the field plate trench, filling the space in the central part of the field plate with nitride; and after filling the space in the central part of the field plate with the nitride, removing the oxide from each sidewall and the corner part of the bottom of the field plate trench. ### Claim 17 (depends on 13) The method of claim 13, further comprising: forming a contact structure having a first part in electrical and physical contact with one or more device regions formed in the semiconductor mesa, and a second part in electrical and physical contact with the field plate, wherein the second part of the contact structure is laterally spaced inward and separated from the first part of the contact structure. ### Claim 18 (depends on 17) The method of claim 17, wherein forming the contact structure comprises: forming an interlayer dielectric on the first main surface of the semiconductor substrate, the interlayer dielectric sealing the air gap in the field plate trench; forming, in the interlayer dielectric, one or more first openings aligned with the semiconductor mesa and one more second openings aligned with the field plate; and depositing an electrically conductive material in each first opening and each second opening formed in the interlayer dielectric. ### Claim 19 (depends on 18) The method of claim 18, further comprising: recessing the electrically insulative material that occupies the space in the central part of the field plate below the first main surface of the semiconductor substrate, wherein after depositing the electrically conductive material, the second part of the contact structure occupies the recess in the electrically insulative material. ### Claim 20 (depends on 18) The method of claim 18, further comprising: forming a metallization layer on the interlayer dielectric, wherein the first part of the contact structure extends through the interlayer dielectric to electrically connect the metallization layer to the one or more device regions formed in the semiconductor mesa, wherein the second part of the contact structure extends through the interlayer dielectric to electrically connect the metallization layer to the field plate in the field plate trench.