US4718973A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Process for plasma etching polysilicon to produce rounded profile islands
Assignee: STMicroelectronics NV
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Filing: 1986-05-19
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Granted: 1988-01-12
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Expires: 2006-05-19
Abstract
Abstract In a silicon integrated circuit manufacturing process a layer of polysilicon is ion implanted with an n-type dopant and etched through a mask with a fluorine:chlorine mixture. The etchant undercuts at the mask to an extent dependent on the ratio of chlorine:fluorine and on the dopant level. By appropriately selecting that ratio and dopant level, polysilicon islands having a rounded profile can be achieved, this being most efficacious for subsequent deposition onto the polysilicon.
Inventors
- 👤 Thomas Abraham
- 👤 Robert E. Theriault
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 05:06
CPC Classifications
H; H10; H10P; H10P50/00; H10P50/20; H10P50/26; H10P50/264; H10P50/266; H10P50/267; H10P50/268; Y; Y10; Y10S; Y10S438/00; Y10S438/978
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
79 words
In a silicon integrated circuit fabrication process the steps in order of: depositing a layer of polysilicon; forming a thin oxide layer on said polysilicon; implanting an n-type dopant within said polysilicon layer so that the dopant is heavily concentrated at the polysilicon surface; removing the oxide layer; and plasma etching through a mask to form islands of polysilicon wherein the n-type dopant concentration profile is selected to produce a rounded upper outer edge profile in said polysilicon islands.
Claim 2
Dependent Claim
79 words
In a silicon integrated circuit fabrication process the steps in order of: depositing a layer of polysilicon; forming a thin oxide layer on said polysilicon; implanting an n-type dopant within said polysilicon layer so that the dopant is heavily concentrated at the polysilicon surface; removing the oxide layer; and plasma etching through a mask to form islands of polysilicon wherein the n-type dopant concentration profile is selected to produce a rounded upper outer edge profile in said polysilicon islands.
Claim 3
Dependent Claim
22 words
A process as claimed in claim 1 in which an etchant gas used to plasma etch the polysilicon contains fluorine and chlorine.
Claim 4
Dependent Claim
16 words
A process as claimed in claim 2 wherein the fluorine is derived from SF 6 .
Claim 5
Dependent Claim
19 words
A process as claimed in claim 2 in which the chlorine is derived from C 2 ClF 5 .
Claim 6
Dependent Claim
30 words
A process as claimed in claim 2 in which the fluorine and the chlorine are produced from a gas etchant mixture of SF 6 and C 2 ClF 5 .
Claim 7
Dependent Claim
29 words
A process as claimed in claim 2 further comprising tailoring the profile by selecting a flow rate ratio of fluorine to chlorine in the range from 1:1 to 1:9.
Claim 8
Dependent Claim
22 words
A process as claimed in claim 1 further comprising thermally annealing the polysilicon after introduction of dopant and prior to plasma etching.
Claim 9
Dependent Claim
33 words
A process as claimed in claim 1 in which the dopant concentration is a maximum at an upper surface of the polysilicon and decreases as a function of depth within the polysilicon layer.
Claim 10
Dependent Claim
22 words
A process as claimed in claim 1 in which the n-type dopant is one of the group consisting of phosphorus and arsenic.
Claim 11
Dependent Claim
45 words
A process as claimed in claim 1 further comprising thermally growing an oxide layer on a silicon substrate prior to deposition of said polysilicon layer and thermally growing a second gate oxide layer on the polysilicon islands after exposure thereof by removal of the mask.
Claim 12
Dependent Claim
45 words
A process as claimed in claim 10 further comprising low pressure chemical vapour depositing a layer of dielectric over the second oxide layer said dielectric having an upper surface characterized by smoothly curving regions conforming to the rounded upper edge profile of said polysilicon islands.
References Cited (Backward Citations)
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Cited
JPS5923522A
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JPS59141232A
Cited
US4473435A
Cited
JPS59232443A
Cited
US4554728A
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-01-11 | 1991-07-13 | 1992-01-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-01-11 | 1995-07-13 | 1996-01-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-01-11 | 1999-07-13 | 2000-01-12 | $7700.00 | Window Closed / Lapsed |