US4092211A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Control of etch rate of silicon dioxide in boiling phosphoric acid
Assignee: Nortel Networks Ltd
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Filing: 1976-11-18
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Granted: 1978-05-30
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Expires: 1996-11-18
Abstract
Abstract The etch rate of silicon dioxide, particularly thermally grown silicon dioxide, in boiling phosphoric acid, can be controlled by deliberately adding additional silicate to the acid. For thermally grown silicon dioxide, the etch rate can be reduced from about 5A per minute with no added silicate, to about 0.5A/minute with 1 gram of added silicate to about 1 liter of acid.
Inventors
- 👤 John David Morris
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 09:00
CPC Classifications
H; H10; H10P; H10P50/00; H10P50/20; H10P50/28; H10P50/282; H10P50/283; H10P50/73
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
68 words
In a process for etching silicon nitride through apertures in a silicon dioxide mask in boiling phosphoric acid, the method of substantially reducing the etch rate of the silicon dioxide mask with substantially no reduction in the etch rate of the silicon nitride comprising adding material containing silicate to commercial quality phosphoric acid to add between about 0.30 and 1.25 grams of silicate per liter of phosphoric acid.
Claim 2
Dependent Claim
68 words
In a process for etching silicon nitride through apertures in a silicon dioxide mask in boiling phosphoric acid, the method of substantially reducing the etch rate of the silicon dioxide mask with substantially no reduction in the etch rate of the silicon nitride comprising adding material containing silicate to commercial quality phosphoric acid to add between about 0.30 and 1.25 grams of silicate per liter of phosphoric acid.
Claim 3
Dependent Claim
14 words
A method as claimed in claim 1, comprising the addition of a soluble silicate.
Claim 4
Dependent Claim
30 words
A method as claimed in claim 2, wherein the material added is sodium metasilicate, between about 0.7 gram and 2.5 grams of sodium metasilicate per liter of acid etch solution.
Claim 5
Dependent Claim
16 words
A method as claimed in claim 1, comprising the addition of finely divided silica containing material.
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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) | 1981-05-29 | 1981-11-28 | 1982-05-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-05-29 | 1985-11-28 | 1986-05-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-05-29 | 1989-11-28 | 1990-05-30 | $7700.00 | Window Closed / Lapsed |