US5858840A
Expired / Lapsed
US
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Method of forming sharp beak of poly by nitrogen implant to improve erase speed for split-gate flash
Assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
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Filing: 1997-12-22
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Granted: 1999-01-12
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Expires: 2017-12-22
Abstract
Abstract A method is provided for forming a short and sharp gate bird's beak in order to increase the erase speed of a split-gate flash memory cell. This is accomplished by implanting nitrogen ions in the first polysilicon layer of the cell and removing them from the area where the floating gate is to be formed. Then, when the polysilicon layer is oxidized to form polyoxide, the floating gate region without the nitrogen ions oxidizes faster than the surrounding area still having the nitrogen ions. Consequently, the bird's beak that is formed at the edges of the polyoxide assumes a sharper shape with smaller size than that is found in prior art. This results in an increase in the erase speed of the memory cell.
Inventors
- 👤 Chia-Ta Hsieh
- 👤 Hung-Cheng Sung
- 👤 Yai-Fen Lin
- 👤 Di-Son Kuo
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 14:36
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/01; H10D30/021; H10D30/0411; H10D30/60; H10D30/68; H10D30/6891
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
167 words
A method of forming a bird's beak in a split-gate flash memory cell comprising the steps of: providing a semiconductor substrate having a gate oxide layer; forming a first polysilicon layer over said gate oxide layer; performing ion implantation on said first polysilicon layer to form a layer of impurity in said polysilicon layer; forming a mask layer over said first polysilicon layer; patterning said mask layer to define a floating gate region in said first polysilicon layer; removing said layer of impurity using said mask layer only in said floating gate region; forming a bird's beak by thermal oxidation in said floating gate region whereby the floating gate region oxidizes faster than other areas of said first polysilicon layer containing said impurity layer; etching said first polysilicon layer to form said floating gate; forming an oxide layer over said floating gate; forming a second polysilicon layer over said oxide layer; and patterning said second polysilicon layer to form a control gate to complete said memory cell.
Claim 2
Independent Claim
167 words
A method of forming a bird's beak in a split-gate flash memory cell comprising the steps of: providing a semiconductor substrate having a gate oxide layer; forming a first polysilicon layer over said gate oxide layer; performing ion implantation on said first polysilicon layer to form a layer of impurity in said polysilicon layer; forming a mask layer over said first polysilicon layer; patterning said mask layer to define a floating gate region in said first polysilicon layer; removing said layer of impurity using said mask layer only in said floating gate region; forming a bird's beak by thermal oxidation in said floating gate region whereby the floating gate region oxidizes faster than other areas of said first polysilicon layer containing said impurity layer; etching said first polysilicon layer to form said floating gate; forming an oxide layer over said floating gate; forming a second polysilicon layer over said oxide layer; and patterning said second polysilicon layer to form a control gate to complete said memory cell.
Claim 3
Dependent Claim
11 words
The method of claim 1, wherein said semiconductor substrate is silicon.
Claim 4
Dependent Claim
19 words
The method of claim 1, wherein said gate oxide has a thickness between about 70 to 90 angstroms (Å).
Claim 5
Dependent Claim
19 words
The method of claim 1, wherein said first polysilicon layer has a thickness between about 1000 to 1200 Å.
Claim 6
Dependent Claim
43 words
The method of claim 1, wherein said performing ion implantation on said first polysilicon layer is accomplished by implanting nitrogen ions at a dosage level between about 5×10 15 to 9×10 18 atoms/cm 2 and energy level between about 50 to 90 KeV.
Claim 7
Dependent Claim
22 words
The method of claim 1, wherein said mask layer is silicon nitride and has a thickness between about 700 to 800 Å.
Claim 8
Dependent Claim
26 words
The method of claim 5, wherein said patterning said mask layer is accomplished by using an etch recipe comprising gases SF 6 and O 2 .
Claim 9
Dependent Claim
31 words
The method of claim 1, wherein said removing said layer of impurity in said polysilicon layer is accomplished with a nitride overetch recipe comprising gases SF 6 and O 2 .
Claim 10
Dependent Claim
35 words
The method of claim 1, wherein said forming a bird's beak in said floating gate region is accomplished by wet oxidizing said first polysilicon layer at a temperature between about 850° C. to 900° C.
Claim 11
Dependent Claim
28 words
The method of claim 1, wherein said etching said first polysilicon layer is accomplished with a recipe comprising gases HBr, C1 2 , He and O 2 .
Claim 12
Dependent Claim
23 words
The method of claim 1, wherein said oxide layer over said first polysilicon layer has a thickness between about 200 to 300 Å.
Claim 13
Dependent Claim
24 words
The method of claim 1, wherein said second polysilicon layer has a thickness between about 2000 to 2500 Å to form said control gate.
References Cited (Backward Citations)
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