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US5545580A
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Multi-state read-only memory using multiple polysilicon selective depositions
Assignee: United Microelectronics Corp
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Filing: 1995-09-19
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Granted: 1996-08-13
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Expires: 2015-09-19
Abstract
Abstract A multi-state read-only-memory device and a method for fabricating the same is suitable for forming on a semiconductor substrate. The read-only memory device is provided with bit lines and word lines which are mutually intersecting. In accordance with the present invention, multiple polysilicon selective deposition procedures are utilized to form a plurality of protrusion portions onto the word lines but with multiple thicknesses. Then, one implantation procedure is applied to program the device into multiple states at the same time without incurring misalignment problems that result in inaccuracy.
Inventors
- 👤 Yi-Chung Sheng
- 👤 Chen-Hui Chung
- 👤 Kuan-Cheng Su
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 09:49
CPC Classifications
H; H10; H10B; H10B20/00
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
124 words
A method for fabricating a multi-state read-only memory device on a semiconductor substrate, comprising: (a) defining a first direction and a second direction above said substrate; (b) forming a plurality of bit lines spaced apart in said substrate along said first direction; (c) forming a dielectric layer overlying said substrate; (d) forming a plurality of word lines on said dielectric layer along said second direction whereby channel regions are disposed between each pair of bit lines below said word lines striding thereover, wherein each said word line above each said corresponding channel region has a thickness selected from a series of thicknesses through a plurality of selective deposition steps; and (e) implanting impurities into said substrate for programming said channel regions into multiple states.
Claim 2
Independent Claim
124 words
A method for fabricating a multi-state read-only memory device on a semiconductor substrate, comprising: (a) defining a first direction and a second direction above said substrate; (b) forming a plurality of bit lines spaced apart in said substrate along said first direction; (c) forming a dielectric layer overlying said substrate; (d) forming a plurality of word lines on said dielectric layer along said second direction whereby channel regions are disposed between each pair of bit lines below said word lines striding thereover, wherein each said word line above each said corresponding channel region has a thickness selected from a series of thicknesses through a plurality of selective deposition steps; and (e) implanting impurities into said substrate for programming said channel regions into multiple states.
Claim 3
Dependent Claim
97 words
The method as in claim 1, wherein the step (d) comprises: forming a plurality of polysilicon lines spaced apart on said dielectric layer along said second direction; forming a silicon oxide layer covering said polysilicon lines; subsequently and repeatedly the following steps, comprising: forming a mask layer on said silicon oxide layer; etching said silicon oxide layer by utilizing said mask layer as masking; removing said mask layer; selectively depositing polysilicon on portions of said word lines not covered by said silicon oxide layer; until said word lines have thicknesses that correspond to said series of thicknesses.
Claim 4
Dependent Claim
21 words
The method as in claim 2, wherein each said polysilicon line has a thickness ranging from about 1500Å to about 2000Å.
Claim 5
Dependent Claim
21 words
The method as in claim 2, wherein the selectively deposited polysilicon has a thickness ranging from about 500Å to about 800Å.
Claim 6
Dependent Claim
17 words
The method as in claim 2, wherein said mask layer is a photoresist layer formed by photolithography.
Claim 7
Dependent Claim
21 words
The method as in claim 1, wherein said series of thicknesses have an increment ranging from about 500Å to about 800Å.
Claim 8
Dependent Claim
28 words
The method as in claim 1, wherein the step (e) is performed at an energy of about 130-150 KeV with a dosage of about 1E14-1E15 cm -2 .
Claim 9
Dependent Claim
16 words
The method as in claim 1, wherein the step (b) is achieved by a photolithography procedure.
Claim 10
Dependent Claim
15 words
The method as in claim 1, wherein said dielectric layer is made of silicon oxide.
Claim 11
Dependent Claim
17 words
The method as in claim 1, wherein said first direction is approximately orthogonal to said second direction.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1999-08-13 | 2000-02-12 | 2000-08-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-08-13 | 2004-02-12 | 2004-08-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-08-13 | 2008-02-12 | 2008-08-13 | $7700.00 | Window Closed / Lapsed |