Wet Chemical Etching

Safety
Material Selectivity
Etchant GaAs InP InGaAs InGaAsP GaInP GaAsP AlGaP AlGaAs AlInP InAlAs InGaAlAs SiO2
HCL : H3PO4 S E S S E       E      
H3PO4 : H2O2 : H2O E S E   S              
H2SO4 : H2O2 : H2O E S E E                
C6H8O7 : H2O2 CD S CD         CD   CD    
HCL : HNO3 : H2O E E         E   E      
HNO3 : H2SO4 : H2O E         E            
HCL : H2O2 : H2O E E       E            
HCL : H2O S E S           E CD CD  
BHF : H2O               CD       E
Legend
Etches Selective/Stops Composition Dependent No Data
E S CD  

Ga2O3 Etchants

References: (2 [sec. 4.3.2], 8, 98, 99).
Ga2O3 thickness typically ~<50 Å.
1:1 - HCL : H2O --- (10 sec.)
1:20 - H2SO4 : H2O --- (30 sec.)
1:40 - H3PO4 : H2O --- (20 sec.)

HCL : H3PO4

References: (4, 9, 10, 99).
Reaction rate limited.
InP etch rate with 1:1 ~2.5 µm/minute.
GaInP etch rate with 1:1 ~0.60 µm/minute.

H3PO4 : H2O2 : H2O

References: (13, 98, 99).
Reaction rate limited.
GaAs etch rate with 3:1:25 ~0.30 µm/minute.
InGaAs etch rate with 1:1:8 ~0.40 µm/minute.
InGaAs and InAlAs etch rates with 1:1:38 ~0.10 µm/minute.

H2SO4 : H2O2 : H2O

References: (1, 2, 3, 14).
Diffusion rate limited above ~33% H2SO4.
Reaction rate limited below ~ 33% H2SO4.
Etch rates proportional to Ga and As content.
InGaAsP etch rate with 1:1:10 ~0.10 µm/minute.

C6H8O7 : H2O2

References: (5, 6, 7, 16).
Reaction rate limited.

References (5, 16) prepares citric acid solution = 1 gram C6H8O7 (anhydrous) : 1 ml H2O. Various selective and non-selective etchants are obtained by varying the volume ratio of citric acid to hydrogen peroxide (after refs. 5, 16):

Etch Rate Å/min.
C6H8O7 : H2O2 GaAs Al0.3Ga0.7As In0.2Ga0.8As In0.53Ga0.47As In0.52Al0.48As InP InAs Al0.5Ga0.5Sb GaAs0.85Sb0.15 GaSb
1 : 2 60 27 346 1235 21 12 655 0 41 7
1 : 1 69 27 751 1116 22 11 826 0 47 6
2 : 1 85 24 1442 1438 26 9 n/a n/a n/a 9
3 : 1 2169 24 2318 n/a n/a n/a n/a n/a n/a n/a
4 : 1 2235 23 2777 n/a n/a n/a n/a n/a n/a n/a
5 : 1 3140 27 2588 1433 44 5 895 0 52 9
7 : 1 2882 89 2231 1421 63 3 n/a n/a 1523 n/a
10 : 1 2513 1945 1219 1020 154 4 727 0 1284 7
15 : 1 1551 1082 882 1013 n/a n/a n/a n/a n/a n/a
20 : 1 762 918 624 665 204 2 473 0 997 7
50 : 1 397 512 384 303 174 5 n/a n/a n/a n/a

References (6 & 7) employ citric acid monohydrate which results in different etch rates and selectivity thresholds than those in the table. Reference (16) gives a conversion of 1 gram C6H8O7 (monohydrate) : 0.829 ml H2O, which gives results within 10% of the table. Reference (7) reports AlGaAs etch rates to be a function of Al composition with no etching occuring for AlxGa 1-xAs (x > 0.7), and selective etching for AlxGa1-xAs / AlyGa1-yAs (x<0.5, y>0.7) with C6H8O7 : H2O2 / BHF : H2O. Results of experiments at LPS with 5:1 for GaAs over AlAs were similar to those in the table for GaAs / AlGaAs.

HCL : HNO3 : H2O

References: (10, 11)
Varying ratios produce selective and non-selective etchants for AlInP/GaAs and AlGaP/GaAs with etch rates dependent on material composition.

HNO3 : H2SO4 : H2O

References: (12)
Varying ratios produce selective and non-selective etchants for GaAsP over GaAs.

HCL : H2O2 : H2O

References: (2, 12)
Varying ratios produce selective and non-selective etchants for GaAs over GaAsP.

HCL : H2O

References: (10, 15).
AlInP etch rate with 1:2 ~0.45 µm/minute.
InAlAs etch rate with 3:1 ~0.65 µm/minute.
InGaAlAs (AlAs=0.34) etch rate with 3:1 ~0.11 µm/minute, and (AlAs=0.20) = no observable etching.

BHF : H2O

References: (7)
SiO2 etch rate with BHF(6:1) and no H2O ~0.10 µm/minute.
Guidelines for SiO2 / BHF Etching
AlGaAs etch rate in 1:25 BHF(7:1) : H2O varies with Al composition from ~0 µm/minute (Al<0.70) to 1.0 µm/minute (Al0.99).

References

1.
"Modern GaAs Processing Methods"

R.E. Williams, Chap. 5, 1990, Artech House.
2.
"InP HBTs: Growth, Processing, and Applications"

B. Jalali, S.J. Pearton, Chap. 3, 1995, Artech House.
3.
"Selective Etching of Gallium Arsenide Crystals in H2SO4-H2O2-H2O System"

S. Iida, K. Ito, J. Electrochem. Soc., 118-5, 1971, p. 768.
4.
"Material-Selective Chemical Etching in the System InGaAsP/InP"

S.B. Phatuk, G. Kelner, J. Electrochem. Soc., 126-2, 1979, p. 287.
5.
"Etch Rates and Selectivities of Citric Acid/Hydrogen Peroxide on GaAs, AlGaAs, InGaAs, InAlAs, and InP"

G.C. DeSalvo, W.F. Tseng, J. Comas, J. Electrochem. Soc., 139-3, 1992, p. 831.
6.
"Selective Etching of GaAs and AlGaAs with citric acid/hydrogen peroxide solutions"

C. Juang, K.J. Kuhn, R.B. Darling, J. Vac. Sci. Technol B, 8-5, 1990, p. 1122.
7.
"Selective etching of AlGaAs/GaAs structures using the solutions of citric acid/H2O2 and de-ionized H2O/buffered oxide etch"

J. Kim, D.H. Lim, G.M. Yang, J. Vac. Sci. Technol. B, 16-2, 1998, p. 558.
8.
"Wet Chemical Digital Etching of GaAs at Room Temperature"

G.C. DeSalvo, et al, J. Electrochem. Soc., 143-11, 1996, p. 3652.
9.
"Plasma and Wet Chemical Etching of InGaP"

J.R. Lothian, J.M. Kuo, F. Ren, S.J. Pearton, J. Elec. Mat., 21-4, 1992, p. 441.
10.
"Wet Chemical Etching of AlInP"

J.W. Lee, S.J. Pearton, C.R. Abernathy, et al, J. Electrochem. Soc., 142-6, 1995, p. L100.
11.
"Wet Chemical Etch Solutions for AlGaP"

J.W. Lee, C.J. Santana, C.R. Abernathy, S.J. Pearton, J. Electrochem. Soc., 143-1, 1996, p. L1.
12.
"Selective and Non-Selective Wet Chemical Etching of GaAsP"

J. Hong, S.J. Pearton, Solid-State Electronics, 39-11, 1996, p. 1675.
13.
"Selective Chemical Etching of InP Over InAlAs"

Y. He, B.W. Liang, N.C. Tien, C.W. Tu, J. Electrochem. Soc., 139-7, 1992, p. 2046.
14.
"A Slow Selective Etch for GaInAsP Grown on InP"

G.A. Ferrante, J.P. Donnelly, C.A. Armiento, J. Electrochem. Soc., 130-5, 1983, p. 1222.
15.
"A Selective Etch for InAlAs over InGaAs and for Different InGaAlAs Quaternaries"

N.J. Sauer, K.B. Chough, J. Electrochem. Soc., 139-1, 1992, p. L10.
16.
"Citric Acid Etching of GaAsSb, AlGaSb, and InAs for Heterostructure Device Fabrication"

G.C. Desalvo, R. Kaspi, C. Bozada, J. Electrochem. Soc., 141-12, 1994, p. 3526.
98.
Oliver King.
99.
Fred Seiferth.

Notes

All etch rates approximate at room (~20-25oC) temperature.

Generalizations concerning etch rate limiting processes are for the etchant solutions commonly used at LPS which contain relatively high proportions of diluents.

Etch rates and etch profiles are usually influenced by the specific crystal plane undergoing the etch process.

Etch rates can be influenced by dopants.