The present invention is directed toward a method of removing epitaxial substrates from host substrates. A sacrificial release layer of ternary material is placed on the substrate. A layer of InP is then placed on the ternary material. Afterward a layer of wax is applied to the InP layer to apply compressive force and an etchant material is used to remove the sacrificial release layer

Bailey, Sheila G.

DeAngelo, Frank L.

Wilt, David M.

English

NASA Technical Reports Server

United States Patent 1191 [ill Patent Number: 5,64 1,381 
Bailey et al. 1451 Date of Patent: Jun. 24,1997 
PREFERENTIALLY ETCHED EPITAXIAL 
LIFTOFF OF INF’ MATERIAL 
Inventors: 
Assignee: 
Appl. No.: 
Filed 
Sheila G. Bailey, Lakewood; David M. 
Wilt, Bay Village; Frank L. DeAngelo, 
Parma, all of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
411,357 
Mar. 27, 1995 
Int. CL6 ............................. B44C y22; HOlL 211306 
U.S. C1. ................................. 438/455; 21612; 216195; 
216196; 1171915; 4381745; 438197 
Field of Search .............................. 1561631.1, 633.1, 
1561655.1, 662.1; 21612, 95, 96 
References Cited 
US. PATENT DOCUMENTS 
4,686,001 8/1987 Okazaki .................................. 15G652 
4,846,931 7/1989 Gmitter et al. ........... 15G633.1 
5,073,230 1W1991 Maracas et al. ........... 1W633.1 
5,286,335 W1994 Drab& et al. ............ 156/631.1 
4,883,561 11/1989 Gmitter et al. ........... 156/633.1 
5,201,996 4/1993 Gmitter et al. ........... 15G655.1 
Primary Eraminer-John S. Chu 
Attorney, Agent, or FirnoKent N. Stone; Vernon E. Will- 
iams 
1571 ABSTRACT 
The present invention is directed toward a method of remov- 
ing epitaxial substrates from host substrates. A sacrificial 
release layer of ternary material is placed on the substrate. 
A layer of InP is then placed on the ternary material. 
Afterward a layer of wax is applied to the Inp layer to apply 
compressive force and an etchant material is used to remove 
the sacrificial release layer. 
13 Claims, 1 Drawing Sheet 
https://ntrs.nasa.gov/search.jsp?R=19970022002 2020-06-18T00:18:21+00:00Z
US. Patent Jun. 24,1997 5,641,38 1 
- 16 
14 
12 
5,@1,38 1 
1 2 
PREFERENTIALLY ETCHED EPITAXIAL 
LIFTOFF OF INP MATERIAL 
ORIGIN OF THE INVENTION 
of the United States Government and may be manufactured 
and used by or for the Government for governmental pur- 
therefor. 
DISCLOSURE OF THE INVENTION 
The aforementioned objects of the invention are achieved 
by using a method for preferential etching epitaxial liftoff 
(PEEL) of InP films by using an etchant based on HF,H,O,, 
The invention described herein was made by employees 5 H,O. The Inp films are lifted off a substrate removing an 
I n ~ a A s  layer without etching the ne method for lifting 
off the Inp layer black wax on the Inp film which 
undercut. 
poses without the Pament Of royalties thereon Or provides compression and causes the film to lift off as it is 
10 
TECHNICAL FIELD 
films from host substrates. The invention is particularly 
concerned with the removal of such a film from an indium 
phosphide (In€') substrate. 
The removal of epitaxial films from host substrates and 
the subsequent deposition on a new material has a wide 
variety of applications. In addition to the economic advan- 
tage of reusable substrates, the production of ultra-thin 
device layers has potential applications in optoelectronic 2o bonded to a 
devices, such as optical modulators or detectors, and thin 
The method comprises mixing trichlorethylene with wax 
layer is cured at room temperature for about 30 minutes, and 
then it is cured at 160" C. for about 30 minutes which 
15 generates the compressive forces for the peeling process. 
The edges are cleaned after curing. The substrate supporting 
the Inp film is submerged in an etchant solution which 
dissolves an indium release 
The etchant mixture solution is then diluted with 
deionized water. ne film is gently dtied and 
This invention is concerned with the removal of e p i w d  and 'praying the mixture On the Inp layer* This 
substrate. 
BREF DESCRZPTION OF THE DFAWJNG film solar cells. 
Preferentially etched epitaxial liftoff (PEEL) requires a 
release layer that can be removed using a selective etchant. 
is aluminum arsenide (us). Hydrofluoric acid (m 
Apiezon W, provides the tension required for undercutting 
as explained in Applied Physics Letter 51 which was pub- 3o 
lished in 1987. As explained in Electronics Letter 25 which 
was published in 1989 and TUG 4 which was published in 
1991, recent applications of this procedure have been h- 
ited to gallium arsenide (GaAs) thin film devices. 
applications involving indium phosphide c~np) devices. mS 
The Objects, advantages, and Of the inven- 
description when read in connection with the accompanying 
process Of the present invention. 
The sacrificial release layer which as been used thus far for 25 tion 
is used as the etchant. A black wax, known commercially as 
be more from the detailed 
drawing which is a Prospective View showing the IOp 
BEST MODE FOR CAF?RYJNG OUT THE 
INVENTION 
Referring now to the drawing, there is shown an indium 
phosphide [Inp] substrate 10. A sacrificial release layer of 
has not been utilized in any significant 35 indium gallium arsenide 12 is interposed between the sub- 
Strate 10 and indium phosphide cover layer 14. The 
indium gallium arsenide release layer 12 is a ternary mate- 
rial whose lattice constant can be varied by changing the 
WGa ratio. At a ratio of 0.53/0.47 the lattice constant is 
matched to W; thus, the InGaAs release layer may be as 
thick as desired without introducing any deleterious defects 
into the overlying Inp epaayers. By way of example7 the hE' 
substrate 10 may be about 300 um thick, the lattice matched 
InGaAs layer l2 has a thickness Of about 500 
Such a 
is attributed to the significant lattice mismatch bemeen the 
us and J,,~. me lattice mismatch requires a pseudomor- 
phic deposition of us to avoid dislocations in the ~np 
epitaxial film. Also, stringent control of the metal organic 
vapor phase (MOWE) is required to fabricate 
pseudomorphic layers. Thus, InP PEEL devices using u s  
have not been produced. 
It is, therefore, an object of the present invention to 
Another object of the invention is to provide an improved 
provi& for the preferentidy etched epitaxial liftoff of Inp. 
method for the removal of epitaxial films from Inp and the 
angstr0m7 and Ihe Iap ePilaYer l4 has a thickness Of about 
45 4um. 
structures Of the we shown in the require 
a highly selective etchant. By way of example, one such 
etchant is HF:H,0,:H20 (1:l:lO). This etchant has been 
used successfully to produce PEEL InP films. Under room 
subsequent deposition of the films on a new material. 
BACKGROUND 
50 
U.S. pat. No. 4,846,931 to Gmiwr et al discloses a 
method for selectively removing an epitaxial film from a 
t e m p w e  conditions, this etchant slowly removes the 
InGaAs layer 12 without etching the Inp eP*Yer 14 
single crystal substrate upon which it was grown. The 
method comprises the steps of selectively etching away a AcommflciallY available black Wax known as APiezon w 
release layer positioned between the film and the 55 provides compression in the Inp film. This compression 
substrate and causing the edges of the film to curl upwardly causes the film 14 to lift as it is undercut, thereby P e A ~ g  
as the release layer is etched away. This enchances an Complete etching Of the thin I&aAS release layer 12. 
outdiffusion of reaction products of the etching process from After the substrate 10 is covered by the sacrificial release 
the active etching area. A solution of support layer material layer 12 and the indium phosphide film 14 has been depos- 
is sprayed on the epitaxial film layer. 60 ited on the layer 12, preparation is made to remove the 
u.S. Pat. No. 4,686,001 to Okazaki discloses a method for indium phosphide film 14 and bond it to another substrate 
producing a semiconductor light emitting device that (not shown). In t h i s  manner the first substrate 10 may be 
includes a step of removing an Inp cover layer by a selective reused for a sizeable reduction in the cost of the process. 
etching process. The InP cover layer on an InGaAs contact The indium phosphide film 14 is covered with a layer of 
layer may be selectively removed by an etching process 65 wax. A black wax sold commercially as Apiezon W has been 
using HC1 or HBr as an etchant so that the previously formed satisfactory for this purpose. A mixture of trichlorethylene 
contact layer is exposed. (TCE) and Apiezon type W wax is prepared. This mixture 
Or the Inp substrate lo. 
5,641,38 1 
3 4 
has a ratio of 40 and of TCE: to log of wax. The indium While several embodiments of the invention have been 
phosphide film is contacted with thiskxture by spraying it 
with an air brush to create a thin layer 16 of wax. The layer 
16 of wax has a thickness of about 40 mil. 
The layer 16 of wax is then cured for about 30 minutes at 
room temperature. This is followed by a second curing of 30 
minutes at about 160" C. This curing process generates the 
compressive forces necessary for the peeling process. 
The aforementioned etchant solution is applied to the 
lattice matched InGaAs layer by submerging the substrate 
with the sacrificial release layer and indium phosphide film 
thereon in the aforementioned etchant solution. As the 
etchant solution dissolves the indium gallium arsenide, the 
sacrificial release layer 12 is removed from between the 
substrate 10 and the indium phosphide film 14. Once this 
separation occurs, the resulting free-floating thin indium 
phosphide film 14 is quite fragile even though it is supported 
by the wax layer 16. Thus, the InP film must be handled very 
carefully. 
After the etchant solution is diluted with deionized water, 
a filter paper (not shown) may be placed beneath this film 14. 
The filter paper and film 14 are then gently removed from 
the diluted etchant solution. An advantage of using the filter 
paper is that it enables the film 14 to dry. 
After drying, the film 14 is bonded to an appropriate 
substrate (not shown). Thus, the substrate 10 can be reused 
to produce additional InP films. 
After the InP film 14 is bonded to the new substrate, the 
wax layer 16 is removed from the indium phosphide film by 
sequential baths of trichlorethylene (TCE). 
DESCRIPTION OF THE A I I ' E F W ~  
EMBODIMENT 
Instead of removing the free-floating InP film 14 from the 
etchant solution by placing filter paper on the underside of 
this film, it is contemplated that the film 14 may be attached 
directly to the new substrate. In this embodiment, a Van der 
Waals bonding is utilized by the placement of the InP film 
onto the new substrate. The film 14 is transferred while still 
wet, and then dried slowly on the new substrate. 
Several organic-based etchants have proven to possess the 
required selectivity to be used for PEEL film development. 
These etchants may facilitate the use of alternate processing 
sequences which could eliminate the fragile. free-floating, 
film stage. It is also contemplated that the structure shown 
in  the drawing could be bonded to a cover glass superstate, 
tensioned to provide the required lifting force, and peeled. 
The use of the InP as the sacrificial release layer is also 
contemplated. This layer would be bounded on either side by 
GaInAs lattice matched layers to act as etch barrier layers. 
Devices based on this inversion of the PEELprocess include 
the InP/GaInAs monolithic cascade solar cell. 
The quality of the electronic structures produced by this 
method are superior and more reproducible than prior art. 
The technique does not require sophisticated deposition 
equipment, and therefore it has greater potential c o m e r -  
cialization. 
A variety of applications can be envisioned for a PEE%, 
structure. One of which is a PEEL InP top cell connected to 
a Si bottom cell to produce a highly efficient tandem solar 
cell structure. The PEEL technique also provides easy fab- 
rication of optoelectronic devices in which monolithic 
growth is often di€Ecult. Current use of thin InP has been in 
optoelectronic integrated circuits (OEIC) and Si-LsIs. A 
laser diode (LD) on a Si substrate is a key device for 
developing viable llI-V/Si OEICs. 
disclosed and described, it will be apparent that various 
structural modifications may be made without departing 
from the spirit of the invention or the scope of the subjoined 
5 claims. 
What is claimed 
1. Amethod of producing a preferentially etched epitaxial 
liftoff (PEEL) of InP comprising covering a first substrate 
with a sacrificial release layer of a ternary material whose 
lattice constant can be varied, depositing a film of InP on 
said release layer, contacting the InP film with a layer of 
wax, curing said layer of wax thereby providing compres- 
sive forces to said InP film. applying an etchant solution to 
15 said ternary material to undercut said InP film whereby said 
release layer is removed from between said fmt substrate 
and said InP film, bonding said InP film to a second 
substrate, andremoving saidlayer of wax from said InPfilm, 
wherein said ternary material of the sacrificial release layer 
2o is  lattice-matched InGaAs, and said etchant is  
HF:H,O,:H,O (1:l:lO). 
2. A method as claimed in claim 1 wherein the first 
substrate with the InP film thereon is submerged in said 
etchant solution to dissolve the sacrificial release layer. 
3. A method as claimed in claim 2 further comprising the 
step of diluting the etchant solution after the Inp film has 
separated from the first substrate. 
4. A method as claimed in claim 3 further comprising 
either the step of supporting the InP film on filter paper and 
3o drying said InP film after removal from the etchant solution, 
or the step of supporting the InP film in the etchant solution 
on the second substrate, and removing the second substrate 
with the film thereon from the etchant solution. 
5. Amethod as claimed in claim 4 wherein the InGaAs has 
35 a lattice constant that is matched to InP whereby the thick- 
ness of the InGaAs layer can be increased without introduc- 
ing deleterious defects into the overlaying InP layer. 
6. A method as claimed in claim 5 wherein the InGaAs 
material has an WGa ratio of 0.53/0.47. 
7. A method as claimed in claim 6 wherein the wax layer 
is provided by applying a mixture of trichlorethylene and 
waxtotheInPfilm. 
8. A method as claimed in claim 7 wherein the mixture is 
sprayed onto the InP fih 
9. A method as claim in claim 8 wherein a 40 mil thick 
layer of wax is sprayed onto the InP fih 
10. A method as claimed in claim 9 wherein the wax is 
cured for about 30 minutes at room temperature. 
11. A method as claimed in claim 10 wherein the wax is 
50 cured a second time for about 30 minutes at about 160" C. 
12. A method of producing a preferentially etched epi- 
taxial liftoff (PEEL) of InP comprising covering a first 
substrate with a sacrificial release layer of a ternary material 
whose lattice constant can be varied, depositing a film of InP 
55 on said release layer, contacting the InP film with a layer of 
wax, curing said layer of wax thereby providing compres- 
sive forces to said InP film, applying an etchant solution to 
said ternary material to undercut said InP film whereby said 
release layer is removed from between said fist substrate 
60 and said InP film, bonding said InP film to a second 
substrate, andremoving saidlayer of wax from said InPfilm, 
wherein said ternary material of the sacrificial release layer 
is A1InAs, and said etchant is HF:H,O,:H,O (1:l:lO). 
13. A method as claimed in claim 12 wherein the AlInAs 
25 
45 
65 material has an AvIn ratio of 0.48/0.52. 
* * * * *  


Preferentially Etched Epitaxial Liftoff of InP Material

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