Patent US5504022A successfully refreshed from Google Patents.
US5504022A
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Method of making a semiconductor memory device having a floating gate
Assignee: Fujitsu Ltd
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Filing: 1993-12-23
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Granted: 1996-04-02
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Expires: 2013-12-23
Abstract
Abstract A method of forming a non-volatile semiconductor memory device includes the steps of forming a generally periodical undulation on a surface of a silicon substrate with a pitch of 1-20 nm, by cleaning the surface of the substrate by a cleaning solution to form a native silicon oxide film that covers the surface of the silicon substrate with a thickness that changes generally periodically, followed by a selective etching process applied to the native silicon oxide film thus formed to expose the surface of the silicon substrate, and forming a tunneling oxide film on the undulated surface of the substrate by applying a thermal oxidation such that the tunneling oxide film has a thickness that changes generally periodically with a pitch of 1-20 nm.
Inventors
- 👤 Toshiro Nakanishi
- 👤 Yasuhisa Sato
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 13:58
CPC Classifications
H; H10; H10B; H10B41/00; Y; Y10; Y10S; Y10S148/00; Y10S148/138; Y10S438/00; Y10S438/964
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
142 words
A method for fabricating a non-volatile semiconductor memory device having an isolated floating gate for storing information in the form of electric charges, which comprises: oxidizing the upper surface of a silicon substrate by reaction with an oxidizing agent to form a silicon oxide film having a thickness varying from 1-20 nm on said surface, and simultaneously selectively etching the silicon substrate surface having the silicon oxide film thereon with an etchant, which reacts with silicon more rapidly than with silicon oxide, until the silicon oxide film is removed, with an aqueous solution that contains both the oxidizing agent and the etchant; thermally oxidizing the silicon substrate to form a tunneling oxide film of silicon oxide having a pitch varying from 1-20 nm on the upper surface of the silicon substrate; and providing a floating gate electrode on the silicon oxide film.
Claim 2
Independent Claim
142 words
A method for fabricating a non-volatile semiconductor memory device having an isolated floating gate for storing information in the form of electric charges, which comprises: oxidizing the upper surface of a silicon substrate by reaction with an oxidizing agent to form a silicon oxide film having a thickness varying from 1-20 nm on said surface, and simultaneously selectively etching the silicon substrate surface having the silicon oxide film thereon with an etchant, which reacts with silicon more rapidly than with silicon oxide, until the silicon oxide film is removed, with an aqueous solution that contains both the oxidizing agent and the etchant; thermally oxidizing the silicon substrate to form a tunneling oxide film of silicon oxide having a pitch varying from 1-20 nm on the upper surface of the silicon substrate; and providing a floating gate electrode on the silicon oxide film.
Claim 3
Dependent Claim
17 words
A method as claimed in claim 1, wherein the oxidizing agent is a solution of nitric acid.
Claim 4
Dependent Claim
19 words
A method as claimed in claim 1, wherein the etchant is a solution of hydrofluoric acid and nitric acid.
Claim 5
Dependent Claim
19 words
A method as claimed in claim 1, wherein the etchant is chlorine gas in the presence of ultraviolet radiation.
Claim 6
Dependent Claim
29 words
A method as claimed in claim 1, which additionally comprises covering the floating gate electrode with an insulating film and providing a control gate electrode on the insulating film.
Claim 7
Independent Claim
127 words
A method for forming an insulating film of varying thickness on the upper surface of a silicon substrate, which comprises: oxidizing the upper surface of a silicon substrate by reaction with an oxidizing agent to form a silicon oxide film having a thickness varying from 1-20 nm on said surface, and simultaneously selectively etching the silicon substrate having the silicon oxide film thereon with an etchant, which reacts with silicon more rapidly than with silicon oxide until the native silicon oxide film is removed, with an aqueous solution that contains both the oxidizing agent and the etchant; and thermally oxidizing the silicon substrate to form a tunneling oxide film of silicon oxide having a pitch varying from 1-20 nm on the upper surface of the silicon substrate.
Claim 8
Independent Claim
127 words
A method for forming an insulating film of varying thickness on the upper surface of a silicon substrate, which comprises: oxidizing the upper surface of a silicon substrate by reaction with an oxidizing agent to form a silicon oxide film having a thickness varying from 1-20 nm on said surface, and simultaneously selectively etching the silicon substrate having the silicon oxide film thereon with an etchant, which reacts with silicon more rapidly than with silicon oxide until the native silicon oxide film is removed, with an aqueous solution that contains both the oxidizing agent and the etchant; and thermally oxidizing the silicon substrate to form a tunneling oxide film of silicon oxide having a pitch varying from 1-20 nm on the upper surface of the silicon substrate.
Claim 9
Dependent Claim
17 words
A method as claimed in claim 6, wherein the oxidizing agent is a solution of nitric acid.
Claim 10
Dependent Claim
19 words
A method as claimed in claim 6, wherein the etchant is a solution of hydrofluoric acid and nitric acid.
Claim 11
Dependent Claim
19 words
A method as claimed in claim 6, wherein the etchant is chlorine gas in the presence of ultraviolet radiation.
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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) | 1999-04-02 | 1999-10-02 | 2000-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-04-02 | 2003-10-02 | 2004-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-04-02 | 2007-10-02 | 2008-04-02 | $7700.00 | Window Closed / Lapsed |