US4201623A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for making epitaxial silicon crystals with uniform doping levels
Assignee: United States Department of the Army
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Filing: 1978-05-23
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Granted: 1980-05-06
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Expires: 1998-05-23
Abstract
Abstract A crystal substrate of <111> silicon is doped by being exposed to a liquidetal solvent. The substrate is carried in a cavity in a refractory boat, and the solvent is carried in a perforation of a cover for the boat. The boat is heated to a certain temperature in a non-oxidizing atmosphere and is moved to place the substrate cavity under the cover perforation whereby the solvent and substrate come in contact. The temperature is raised and held to allow the desired substrate-solvent solution to form, then is reduced and held to allow supersaturation and eventually precipitation of the doped substrate. The boat is next moved to remove the cavity from beneath the perforation, is allowed to cool to room ambient, and is removed from the non-oxidizing atmosphere. The doped substrate is then cleaned as desired to remove any attached solvent.
Inventors
- 👤 Barbara E. Sumner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 08:09
CPC Classifications
C; C30; C30B; C30B31/00; C30B31/04
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
222 words
A method of making, in a refractory boat, an epitaxial silicon crystal layer on a silicon substrate, wherein said boat includes a base portion with a substrate cavity therein and a cover portion atop said base portion with a perforation therethrough, including the steps of: loading said cavity with a first material consisting of said substrate; loading said perforation with a second material consisting of a metal solvent; placing said boat in a non-oxidizing atmosphere; heating said boat to a first temperature; relatively moving said base and said cover portions with respect to each other to place said cavity under said perforation whereby said solvent contacts said substrate; raising said temperature at a controlled rate to a second temperature and holding for a first time whereby said substrate and said solvent diffuse into each other to form a saturated solution; reducing said temperature at a controlled rate to a third temperature and holding for a second time whereby said solvent first reaches an equilibrium solution, then supersaturation, then precipitation; relatively moving said base and said cover portions with respect to each other to remove said cavity from beneath said perforation. cooling said boat to ambient; and removing said boat from said non-oxidizing atmosphere, removing the substrate from said boat, and cleaning said substrate to remove any metal solvent on the surface thereof.
Claim 2
Independent Claim
222 words
A method of making, in a refractory boat, an epitaxial silicon crystal layer on a silicon substrate, wherein said boat includes a base portion with a substrate cavity therein and a cover portion atop said base portion with a perforation therethrough, including the steps of: loading said cavity with a first material consisting of said substrate; loading said perforation with a second material consisting of a metal solvent; placing said boat in a non-oxidizing atmosphere; heating said boat to a first temperature; relatively moving said base and said cover portions with respect to each other to place said cavity under said perforation whereby said solvent contacts said substrate; raising said temperature at a controlled rate to a second temperature and holding for a first time whereby said substrate and said solvent diffuse into each other to form a saturated solution; reducing said temperature at a controlled rate to a third temperature and holding for a second time whereby said solvent first reaches an equilibrium solution, then supersaturation, then precipitation; relatively moving said base and said cover portions with respect to each other to remove said cavity from beneath said perforation. cooling said boat to ambient; and removing said boat from said non-oxidizing atmosphere, removing the substrate from said boat, and cleaning said substrate to remove any metal solvent on the surface thereof.
Claim 3
Dependent Claim
76 words
The method as set forth in claim 1 wherein, in the case of <111> silicon and with indium as the metal solvent, said first temperature is approximately 300° C., said second temperature is approximately 950° C. and is raised thereto at 12° C. per minute, said first time is approximately 3.5 hours, said third temperature is approximately 700° C. and is reduced thereto at 0.4° C. per minute, and said second time is approximately 2.5 hours.
Claim 4
Dependent Claim
76 words
The method as set forth in claim 1 wherein, in the case of <111> silicon and with gallium as the metal solvent, said first temperature is approximately 35° C., said second temperature is approximately 600° C. and is raised thereto at 12° C. per minute, said fist time is approximately 3.5 hours, said third temperature is approximately 300° C. and is reduced thereto at 0.8° C. per minute, and said second time is approximately 2.5 hours.
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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) | 1983-05-06 | 1983-11-05 | 1984-05-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-05-06 | 1987-11-05 | 1988-05-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-05-06 | 1991-11-05 | 1992-05-06 | $7700.00 | Window Closed / Lapsed |