US4732648A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of preparing semiconductor substrates
Assignee: Max-Planck-Gesellschaft zur Förderung der Wissenschaften eV
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Filing: 1986-12-16
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Granted: 1988-03-22
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Expires: 2006-12-16
Abstract
Abstract A new method for GaAs substrate preparation which significantly reduces theormation of oval defects during MBE growth of selectively doped n-Al x Ga 1-x As/GaAs heterostructures. The method simply requires treatment in H 2 SO 4 after mechano-chemical polishing in NaOCl solution and generation of a protective surface oxide during in soldering. Routinely a density of oval defects of less than 200 cm -2 is achieved for 2-μm thick heterostructures. The efficiency of the new preparation procedure is demonstrated by 2DEG mobilities in excess of 10 6 cm 2 /Vs at 6K obtained with a spacer width as narrow as 18 nm.
Inventors
- 👤 Hans Fronius
- 👤 Albrecht Fischer
- 👤 Klaus Ploog
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 17:26
CPC Classifications
H; H10; H10P; H10P14/00; H10P14/20; H10P14/29; H10P14/2901; H10P14/2907; H10P14/2909; H10P14/22; H10P14/2911; H10P14/32; H10P14/3202; H10P14/3214; H10P14/3221; H10P14/34; H10P14/3402; H10P14/3414; H10P14/3421; H10P52/00; H10P52/40; H10P52/402
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
107 words
A method of preparing semiconductor substrates to reduce the formation, in particular of oval defects, during subsequent growth of semiconductor structures thereon, in particular growth of heterostructures by molecular beam epitaxy, wherein the substrates are chemically cleaned and are provided with a thin oxide layer as protection against contamination during handling prior to growth of a said semiconductor structure thereon, characterised in that the substrate is first subjected to mechano-chemical etch polishing using an abrasive free fabric or paper polishing lap soaked with an oxidising etching solution and is then treated by placing it in a concentrated acid, in particular H 2 SO 4 subjected to agitation.
Claim 2
Independent Claim
107 words
A method of preparing semiconductor substrates to reduce the formation, in particular of oval defects, during subsequent growth of semiconductor structures thereon, in particular growth of heterostructures by molecular beam epitaxy, wherein the substrates are chemically cleaned and are provided with a thin oxide layer as protection against contamination during handling prior to growth of a said semiconductor structure thereon, characterised in that the substrate is first subjected to mechano-chemical etch polishing using an abrasive free fabric or paper polishing lap soaked with an oxidising etching solution and is then treated by placing it in a concentrated acid, in particular H 2 SO 4 subjected to agitation.
Claim 3
Dependent Claim
38 words
A method in accordance with claim 1, characterised in that said oxidising etching solution is NaOCl, preferably with a concentration in the range 0.5 to 6.5 % active chlorine, and in particular with a concentration of 2.0 %.
Claim 4
Dependent Claim
26 words
A method in accordance with claim 1, characterised in that the substrate is GaAs and in that the concentrated acid is H 2 SO 4 .
Claim 5
Dependent Claim
25 words
A method in accordance with claim 1, wherein both said mechano-chemical etch polishing and said treatment in concentrated acid are carried out at room temperature.
Claim 6
Dependent Claim
52 words
A method in accordance with claim 1, characterised in that the substrate is sequentially placed in two separate baths of said concentrated acid and said baths are preferably subjected to ultrasonic agitation, with the duration of the treatment in the concentrated acid preferably lying between 5 and 10 minutes in each bath.
Claim 7
Dependent Claim
16 words
A method in accordance with claim 1, characterised in that the polishing lap comprises lens paper.
Claim 8
Dependent Claim
26 words
A method in accordance with claim 1, characterised in that the substrate is preheated under dust-free conditions in air prior to mounting to the substrate holder.
Claim 9
Dependent Claim
32 words
A method in accordance with claim 1, characterised in that, with a sawn substrate the sawn surface is first polished with diamond paste to remove saw-cut damage prior to mechano-chemical etch polishing.
Claim 10
Dependent Claim
24 words
A method in accordance with claim 1, characterised in that the treatment in the concentrated acid is effected for approximately 5 minutes or longer.
Claim 11
Dependent Claim
16 words
A method in accordance with claim 1, characterised in that said semiconductor substrate is indium phosphide.
Claim 12
Dependent Claim
16 words
A method in accordance with claim 1, characterised in that said oxidising-etching solution is bromium methanol.
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) | 1991-03-22 | 1991-09-21 | 1992-03-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-03-22 | 1995-09-21 | 1996-03-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-03-22 | 1999-09-21 | 2000-03-22 | $7700.00 | Window Closed / Lapsed |