US3859178A
Expired / Lapsed
US
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Multiple anodization scheme for producing gaas layers of nonuniform thickness
Assignee: AT&T Inc
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Filing: 1974-01-17
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Granted: 1975-01-07
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Expires: 1994-01-17
Abstract
Abstract A multiple anodization technique is described for producing GaAs layers of nonuniform thickness; that is, GaAs layers having substantially rectangular steps or grooves of the type capable of guiding light. The technique includes the following steps: (1) growing a native oxide layer on a major surface of the GaAs layer by submersing the GaAs layer in an anodization bath of concentrated H2O2 having a pH less than 6; (2) removing selected portions of the oxide layer so as to expose the GaAs layer adjacent to the desired step region; and (3) immersing the surface again in an anodization bath of concentrated H2O2 having a pH less than 6. Also described are techniques for growing by liquid phase epitaxy an AlGaAs layer over the resultant GaAs step structure in a manner which alleviates two problems: the formation of deleterious oxides on the GaAs layer and the dissolving of the step configuration while in contact with the AlGaAs growth solution.
Inventors
- 👤 Ralph Andre Logan
- 👤 Barry Irwin Miller
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 01:31
CPC Classifications
H; H01; H01S; H01S5/00; H01S5/20; H01S5/22; H01S5/227; C; C25; C25D; C25D11/00; C25D11/02; C25D11/32; H01S5/2275; Y; Y10; Y10S; Y10S148/00; Y10S148/051; Y10S148/056; Y10S148/072; Y10S148/106; Y10S148/107; Y10S148/117; Y10S148/118; Y10S148/145
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
127 words
A METHOD OF FABRICATING A SUBSTANTIALLY RECTANGULAR STEP IN A PRESELECTED REGION OF A GAAS LAYER COMPRISING THE STEPS OF: A. GROWING A NATIVE OXIDE LAYER ON A MAJOR SURFACE OF SAID GAAS LAYER BY SUBMERSING SAID GAAS LAYER IN AN ANODIZATION BATH COMPRISING H2O2 HAVING A PH LESS THAN ABOUT 6 B. REMOVING SELECTED PORTIONS OF SAID OXIDE LAYER SO AS TO EXPOSE SAID GAAS LAYER ADJACENT SAID PRESELECTED REGION, A NATIVE OXIDE MASK REMAINING OVER SAID REGION; AND C. IMMERSING SAID GAAS LAYER IN AN ANODIZATION BATH COMPRISING H2O2 HAVING A PH LESS THAN ABOUT 6 SO THAT THE EXPOSED PORTIONS OF SAID GAAS LAYER ARE CONSUMED IN THE FORMATION OF A NATIVE OXIDE LAYER THEREON, THEREBY TO FORM SAID STEP IN SAID GAAS LAYER.
Claim 2
Independent Claim
127 words
A METHOD OF FABRICATING A SUBSTANTIALLY RECTANGULAR STEP IN A PRESELECTED REGION OF A GAAS LAYER COMPRISING THE STEPS OF: A. GROWING A NATIVE OXIDE LAYER ON A MAJOR SURFACE OF SAID GAAS LAYER BY SUBMERSING SAID GAAS LAYER IN AN ANODIZATION BATH COMPRISING H2O2 HAVING A PH LESS THAN ABOUT 6 B. REMOVING SELECTED PORTIONS OF SAID OXIDE LAYER SO AS TO EXPOSE SAID GAAS LAYER ADJACENT SAID PRESELECTED REGION, A NATIVE OXIDE MASK REMAINING OVER SAID REGION; AND C. IMMERSING SAID GAAS LAYER IN AN ANODIZATION BATH COMPRISING H2O2 HAVING A PH LESS THAN ABOUT 6 SO THAT THE EXPOSED PORTIONS OF SAID GAAS LAYER ARE CONSUMED IN THE FORMATION OF A NATIVE OXIDE LAYER THEREON, THEREBY TO FORM SAID STEP IN SAID GAAS LAYER.
Claim 3
Dependent Claim
44 words
The method of claim 1 wherein a first anodization voltage is applied in step (c) which is less than or equal to a second anodization voltage applied in step (a), so that the height of said step is proportional to said second anodization voltage.
Claim 4
Dependent Claim
63 words
The method of claim 1 wherein a second anodization voltage is applied in step (c) which is greater than a first anodization voltage applied in step (a), so that during step (c) GaAs is consumed not only in the exposed portions of said GaAs layer but also beneath said oxide mask, the height of said step being proportional to said first anodization voltage.
Claim 5
Dependent Claim
21 words
The method of claim 1 wherein the anodization baths of steps (a) and (c) each have a pH of about 2.
Claim 6
Dependent Claim
42 words
The method of claim 4 wherein said GaAs layer is grown by liquid phase epitaxy and wherein during said anodization steps (a) and (c) about 11 Angstroms of native oxide is grown and about 7 Angstroms of GaAs is consumed per volt.
Claim 7
Dependent Claim
40 words
The method of claim 4 wherein said GaAs layer is ingot grown and wherein during said anodization steps (a) and (c) about 18 Angstroms of native oxide is grown and about 12 Angstroms of said GaAs is consumed per volt.
Claim 8
Dependent Claim
197 words
The method of claim 1 where step (b) includes the additional steps of: applying a layer of photoresist over said oxide layer, irradiating with ultraviolet radiation the portions of said photoresist layer adjacent the desired oxide mask; submersing said photoresist layer in a caustic developer solution so as to dissolve the irradiated portions thereof and, in addition, to dissolve the native oxide layers under said irradiated portions, the unirradiated portion of said photoresist layer over said oxide mask remaining thereon, heating said remaining photoresist layer at an elevated temperature for a time period effective to harden said photoresist layer and to render it more chemically inert, said hardened photoresist layer and the oxide mask thereunder forming a composite mask for subsequent processing steps, performing anodization step (c) to grow a native oxide layer on the exposed portions of said GaAs layer and to consume GaAs in said portions so as to form said step, submersing said last grown native oxide layer in a solvent which removes said oxide layer but not said composite mask, and repeating the last mentioned two steps so as to increase the height of said step without the need for remasking said step.
Claim 9
Dependent Claim
47 words
The method of claim 1 wherein anodization voltages are applied in steps (a) and (c) which are less than approximately 150 volts so as to maintain within tolerable limits the roughness produced in the surface of said GaAs layer during the growth of the native oxide layers.
Claim 10
Dependent Claim
17 words
The method of claim 1 wherein all native oxide layers grown on said GaAs layer are removed.
Claim 11
Dependent Claim
21 words
The method of claim 9 including the additional step of growing by liquid phase epitaxy of AlGaAs on said GaAs layer.
Claim 12
Dependent Claim
39 words
The method of claim 10 including prior to the growth of said AlGaAs layer the additional step of submersing said GaAs layer in a solution of bromine methanol containing bromine in the approximate range of 0.01 to 0.1 percent.
Claim 13
Dependent Claim
78 words
The method of claim 10 wherein the solution used to grow said AlGaAs layer is allowed to equilibriate at about 800*C for several hours, bringing said solution into contact with a sacrificial GaAs seed to allow said solution to equilibriate for a time in the range of approximately 15 to 30 minutes, cooling said solution at a relatively slow rate to reduce its temperature by several degrees and then bringing said solution into contact with said GaAs layer.
Claim 14
Dependent Claim
77 words
The method of claim 10 including the steps of growing on a GaAs substrate a first AlGaAs layer by liquid phase epitaxy, growing said GaAs layer on said first AlGaAs layer by liquid phase epitaxy, controlling the amount of solution dragged over from the solution used to grow said first AlGaAs layer to the solution used to grow said GaAs layer so that the mole fraction of AlAs in said GaAs layer is less than approximately 0.008.
Claim 15
Dependent Claim
154 words
The method of claim 13 performed in conjunction with apparatus including a solution holder having at least three wells, a slider having at least two recesses, one for carrying said substrate and one for carrying a sacrificial GaAs seed, placing Ga solutions in each well, a first one of which contains AlGaAs, and the second and third of which contain GaAs, instituting a controlled cooling program, bringing said first solution into contact with said substrate to grow said first AlGaAs layer thereon, bringing said substrate into contact with said second solution of GaAs in order to dilute any solution dragged over from the well containing AlGaAs and concurrently bringing the third solution of GaAs into contact with said sacrificial seed so as to equilibriate said third solution, and bringing said substrate into contact with said third solution, thereby to grow a GaAs layer having a mole fraction of AlAs which is less than 0.008.
Claim 16
Dependent Claim
30 words
The method of claim 14 wherein the temperature of said second solution is decreasing at a rate of about 0.05*C per minute while it is in contact with said substrate.
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) | 1978-01-06 | 1978-07-08 | 1979-01-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-01-06 | 1982-07-08 | 1983-01-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-01-06 | 1986-07-08 | 1987-01-07 | $7700.00 | Window Closed / Lapsed |