Ghodssi R., Lin P., MEMS Materials and Processes Handbook
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524 D.W. Burns
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
51 Antimony (Sb) HF(49%):
HNO
3
(70%)
1:1
Room temperature; DI water rinse [156]
52 Antimony (Sb) HF(49%):
HNO
3
(70%):H
2
O
2:3:5
Room temperature; HNW etchant; DI water rinse [157]
53 Antimony (Sb) 4200 HF(49%):
HNO
3
(70%):Acetic
1:3:12
Room temperature; HNA etchant; also Dash etchant; DI water rinse
[158]
54 Arsenic (As) HCl(38%):
HF(49%):HNO
3
(70%):Acetic
1:2:2:12
Room temperature; DI water rinse [159]
55 Arsenic (As) HNO
3
(70%)
undiluted
DI water rinse [25]
56 Beryllium oxide
(BeO, beryllia),
single crystal
3 HCl(38%)
undiluted
120
◦
C; mildly anisotropic; stir or agitate; DI water rinse [160]
57 Beryllium oxide
(BeO, beryllia),
single crystal
H
3
PO
4
(85%)
undiluted
175
◦
C; also etches in HF vapor at 100
◦
C; DI water rinse [161]
58 Boron (B) H
2
SO
4
(96%):
HCl(38%):
HNO
3
(70%):H
2
O
2:5:10:50
Room temperature; DI water rinse [162]
59 Boron nitride (BN) H
2
SO
4
(96%)
undiluted
Boiling; DI water rinse [21]
8 MEMS Wet-Etch Processes and Procedures 525
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
60 Boron nitride (BN),
CVD
2.5 H
3
PO
4
(85%)
undiluted
180
◦
C; etches slightly in BHF (<0.2 Å/s), H
2
O
2
(3%) at 80
◦
C
(0.5 Å/s); DI water rinse [163]
61 Boron oxide (B
2
O
3
)H
2
O
undiluted
Room temperature [164]
62 Cadmium oxide
(CdO), thermally
grown
1 HCl(38%):H
2
O
1:10,000
Room temperature; 0.001 M HCl; also etches in dilute HF and
H
2
SO
4
:H
2
O
2
:H
2
Omixtures[165]; DI water rinse [166]
63 Cadmium tin oxide
(CdO-SnO
2
),
(CTO), sputtered
>330 HCl(38%):H
2
O
4:1
Room temperature; DI water rinse [167]
64 Cadmium selenide
(CdSe), single
crystal
HNO
3
(70%):
H
2
SO
4
(18 N):Acetic:
HCl(38%)
30:20:10:0.1
40
◦
C; preferential etch; DI water rinse [168]
65 Cadmium sulphide
(CdS), single
crystal
350 HCl(38%):H
2
O
1:2
Room temperature; etches cadmium-rich face 6x slower; DI water
rinse [169]
66 Cadmium sulphide
(CdS), single
crystal
HNO
3
(70%):
Acetic:H
2
O
1:6:1
25
◦
C; DI water rinse [168]
67 Cadmium telluride
(CdTe), ALE
H
3
PO
4
(85%):
HNO
3
(70%):H
2
O
71:1:29
Room temperature; avoid further dilution with H
2
O; can use H
2
O
2
in
place of HNO
3
; can use acetic acid in lieu of H
3
PO
4
; DI water rinse
[170]
68 Cadmium telluride
(CdTe), single
crystal
2000 HCl(38%):
HNO
3
(70%):H
2
O
2:2:1
23
◦
C; chemical polishing etchant; DI water rinse [171, 172]
526 D.W. Burns
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
69 Cadmium telluride
(CdTe), single
crystal
HF(49%):
HNO
3
(70%)
1:1
25
◦
C; also etches in concentrated hydrochloric acid; DI water rinse
[168]
70 Cadmium telluride
(CdTe), single
crystal
560 HF(49%):
H
2
O
2
(30%):H
2
O
3:2:1
25
◦
C; preferential etchant; DI water rinse [168, 172]
71 Cadmium telluride
(CdTe), single
crystal
10000 HF(49%):
HNO
3
(70%):Acetic
2:1:1
23
◦
C; HNA etchant; can form pits; agitate; DI water rinse [172]
72 Cadmium telluride
(CdTe), single
crystal
1300 HNO
3
(70%):
H
2
SO
4
(96%):
HCl(38%):Acetic
50:18:1:10
23
◦
C; polishes; DI water rinse [172]
73 Cadmium telluride
(CdTe), single
crystal
580 HNO
3
(70%)
undiluted
23
◦
C; can leave precipitate; DI water rinse [172]
74 Copper oxide (CuO) HCl(38%):H
2
O
1:2
Hot; little loss of Cu; DI water rinse [25]
75 Carbon (C), graphite H
2
SO
4
(96%)
undiluted
80
◦
C; DI water rinse [173]
76 Carbon (C), graphite HNO
3
(70%)
undiluted
Room temperature; DI water rinse [173]
77 Carbon (C), graphite KOH(50%) Hot; DI water rinse [173]
78 Diamond (C), SC
CVD
35 O
2
:Ar plasma
7 sccm:8 sccm
Dry etch; inductively coupled plasma (ICP); 2.5 mTorr; 600 W;
–160 V bias [174]
8 MEMS Wet-Etch Processes and Procedures 527
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
79 Fluorinated tin oxide
(FTO)
40 Proprietary 40
◦
C; Transene fluorinated tin oxide etchant FTO 100-FBA5; mask
with PR;
Etches Al, Cu, ITO, Ni, NiCr; strong agitation; DI water rinse [175]
80 Gallium (Ga) HCl(38%):
HNO
3
(70%)
3:1
Room temperature; aqua regia; DI water rinse [176]
81 Gallium (Ga) HNO
3
(70%)
undiluted
Hot; DI water rinse [176]
82 Gallium antimonide
(GaSb)
HCl(38%)
undiluted
Hot; DI water rinse [177]
83 Gallium antimonide
(GaSb)
HCl(38%):
H
2
O
2
(30%):H
2
O
1:1:2
Room temperature; DI water rinse [178]
84 Gallium antimonide
(GaSb), MBE
HF(49%):H
2
O
1:20
Room temperature; DHF etchant (20:1);
Etches AlSb;
Doesn’t significantly etch GaAs, InAs; DI water rinse [130]
85 Gallium antimonide
(GaSb)
HF(49%):
HNO
3
(70%):Acetic
1:2:1
25
◦
C; HNA etchant; DI water rinse [129]
86 Gallium antimonide
(GaSb)
HF(49%):
HNO
3
(70%):H
2
O
1:1:1
Room temperature; HNW etchant; DI water rinse [179]
87 Gallium antimonide
(GaSb)
HF(49%):
HNO
3
(70%):H
2
O
3:7:10
Room temperature; HNW etchant; p–n junction etchant; DI water
rinse [180]
528 D.W. Burns
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
88 Gallium antimonide
(GaSb), MBE
3 MF319
(TMAH-based
developer)
undiluted
Room temperature; also etches AlGaSb, AlSb (7 Å/s); doesn’t
significantly etch InAs; DI water rinse [133]
89 Gallium arsenide
(GaAs)
70 H
2
SO
4
(96%):H
2
O
5:1
Room temperature; consider citric acid and succinic acid etchants; DI
water rinse [25]
90 Gallium arsenide
(GaAs)
150 H
2
SO
4
(96%):
H
2
O
2
(30%)
4:1
21
◦
C; (001) surface; preferential etchant; rate increases with H
2
O
2
concentration; DI water rinse [181]
91 Gallium arsenide
(GaAs)
200 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
8:1:1
Room temperature; (100) face; etches (111) face more slowly; less
anisotropy with higher H
2
SO
4
concentrations; DI water rinse [8,
182–184]
92 Gallium arsenide
(GaAs)
210 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
1:1:8
Room temperature; (100) face; DI water rinse [182]
93 Gallium arsenide
(GaAs)
800 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
4:1:5
Room temperature; (100) face; preferential etchant; DI water rinse
[182]
94 Gallium arsenide
(GaAs)
2400 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
1:8:1
Room temperature; (100) face; etches (111) face more slowly; more
anisotropy with lower H
2
SO
4
concentrations; DI water rinse [182,
183]
95 Gallium arsenide
(GaAs)
15 H
3
PO
4
(85%):
H
2
O
2
(30%):H
2
O
3:1:50
20
◦
C; etch rate for (100) face; etch rate is less for (111) plane; higher
phosphoric acid c oncentrations produce smoother etch; mask with
PR, oxide, nitride; DI water rinse [8, 185]
96 Gallium arsenide
(GaAs)
450 H
3
PO
4
(85%):
H
2
O
2
(30%):H
2
O
1:1:3
30
◦
C; etch rate for (100) surface; mask with PR, oxide, nitride; DI
water rinse [185]
8 MEMS Wet-Etch Processes and Procedures 529
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
97 Gallium arsenide
(GaAs)
300 H
3
PO
4
(85%):
H
2
O
2
(30%):MeOH
1:1:3
Room temperature; direction dependent; DI water rinse [186]
98 Gallium arsenide
(GaAs)
75 HCl(38%):Acetic:
H
2
O
2
(30%)
1:2:1
20
◦
C; etch rate decreases with acetic acid dilution; smooth surfaces;
Etches In
0.48
Ga
0.52
P (45 Å/s), InP (60 Å/s) etch rate for In
0.48
Ga
0.52
P;
DI water rinse [187]
99 Gallium arsenide
(GaAs)
35 HCl(38%):
H
2
O
2
(30%):H
2
O
1:4:40
Room temperature; (100) face; anisotropy increases with lower HCl
concentration; DI water rinse [182]
100 Gallium arsenide
(GaAs)
800 HCl(38%):
H
2
O
2
(30%):H
2
O
40:4:1
Room temperature; smooth surfaces on As and Ga faces; anisotropy
decreases with higher HCl concentration; DI water rinse [182, 188]
101 Gallium arsenide
(GaAs)
15–1500 HF(49%):
H
2
O
2
(30%):H
2
O
varies
25
◦
C; low H
2
O
2
:H
2
O ratios are isotropic; high H
2
O
2
:H
2
Oratiosare
preferential; DI water rinse [189]
102 Gallium arsenide
(GaAs)
25 HF(49%):
H
2
O
2
(30%):H
2
O
1:16:450
25
◦
C; DI water rinse [189]
103 Gallium arsenide
(GaAs)
500 HF(49%):
H
2
O
2
(30%):H
2
O
1:2:25
Room temperature; rounds edges; DI water rinse [8, 190]
104 Gallium arsenide
(GaAs)
1600 HF(49%):
HNO
3
(70%):H
2
O
1:1:1
Room temperature; HNW etchant; (001) surface; DI water rinse [191]
530 D.W. Burns
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
105 Gallium arsenide
(GaAs)
3300 HF(49%):
HNO
3
(70%):
Acetic:H
2
O
1:3:5:5
24
◦
C; etch rate increases to 4000 Å/s at 30
◦
C; DI water rinse [192]
106 Gallium arsenide
(GaAs)
HNO
3
(70%):H
2
O
1:9
Room temperature; p–n junction etchant; delineate p and n regions; DI
water rinse [193]
107 Gallium arsenide
(GaAs)
1200 HNO
3
(70%):
H
2
O
2
(30%)
1:1
Room temperature; (001) surface; DI water rinse [191]
108 Gallium arsenide
(GaAs)
50 NH
4
OH(29%):
H
2
O
2
(30%)
1:700
Room temperature; etch rate for (111) Ga face; isotropic etchant; etch
rate is similar for As(100) and As(111) faces; mask with oxide,
nitride; doesn’t significantly etch AlGaAs [194]; DI water rinse [8,
177, 195]
109 Gallium arsenide
(GaAs)
650 NH
4
OH(29%):
H
2
O
2
(30%)
1:30
25
◦
C; etches Al
0.3
Ga
0.7
As (5 Å/s), Al
0.6
Ga
0.4
As (1 Å/s); selectivity to
AlGaAs increases with H
2
O
2
concentrations above 20:1 and
highest at 30:1; DI water rinse [196]
110 Gallium arsenide
(GaAs)
20 NH
4
OH(29%):
H
2
O
2
(30%):H
2
O
3:1:140
Room temperature; etch rate for n-type (100) Ga face; etch rate is
6 Å/s for Ga(111) and 33 Å/s for As(111) planes; etch rate is less
for p-type; mask with oxide, nitride; DI water rinse [8, 197]
111 Gallium arsenide
(GaAs)
250 NH
4
OH(29%):
H
2
O
2
(30%):H
2
O
1:1:8
Room temperature; (100) surface; anisotropic; DI water rinse [198]
112 Gallium arsenide
(GaAs), GaAIAs
and AlGaAs
22 Citric acid, hydrogen
peroxide
25
◦
C; Transene GA Etch-300; mask with PR, SiO
2
;
Etches GaAlAs and AlGaAs; Pyrex, HDPE, Teflon or quartz tank;
agitate for improved smoothness; store below 50
◦
F; DI water rinse
[199]
8 MEMS Wet-Etch Processes and Procedures 531
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
113 Gallium arsenide
antimony
(GaAsSb), MBE
H
3
PO
4
(85%):
H
2
O
2
(30%):H
2
O
1:1:40
22
◦
C; DI water rinse [142]
114 Gallium arsenide
phosphide
(GaAsP)
17 NH
4
OH(29%):
H
2
O
2
(30%):H
2
O
20:7:1000
Room temperature; DI water rinse [200]
115 Gallium nitride
(GaN), CVD
160 H
3
PO
4
(85%)
undiluted
180
◦
C; etches 30 Å/s at 50
◦
C; DI water rinse [201]
116 Gallium nitride
(GaN), deposited
1.3 Ortho-phosphoric
acid
180
◦
C; Transetch-N; SiO
2
mask (80:1); silicon selectivity (80:1);
Pyrex or quartz tank; add water to replace evaporated water; DI
water rinse [58]
117 Gallium phosphide
(GaP)
70 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
3:1:1
60
◦
C; etches p-type preferentially; DI water rinse [202]
118 Gallium phosphide
(GaP)
2400 H
3
PO
4
(85%)
undiluted
180
◦
C; (111) surface; anisotropic; etches (100) face at ∼120 Å/s;
(111) etch rate is 800 Å/s at 150
◦
C and 4000 Å/s at 200
◦
C; mask
with Au; DI water rinse [203]
119 Gallium phosphide
(GaP)
330 HCl(38%):
HNO
3
(70%):H
2
O
2:1:2
45
◦
C; P(111) face; P(111) etch rate is 800 Å/s at 50
◦
C; add HCL to
water first, then HNO
3
; DI water rinse [204]
120 Gallium phosphide
(GaP)
80 HF(49%):
H
2
O
2
(30%)
1:1
24
◦
C; preferential etch rate to p-type GaP with illumination; DI water
rinse [202]
121 Gallium phosphide
(GaP)
580 Potassium
hexacyanoferrate
80
◦
C; Transene Gallium Phosphide Etchant; mask with Ti, SiO
2
,Au
or KMER;
Etches SiC;
Doesn’t significantly etch Pd, Au or Pt; DI water rinse [205]
122 Germanium (Ge) See Table 8.7
532 D.W. Burns
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
123 Germanium dioxide
(GeO
2
)
H
2
O
undiluted
Room temperature;
Doesn’t significantly etch GeO [206]
124 Germanium dioxide
(GeO
2
), CVD
HF(49%)
undiluted
Room temperature; HF etchant (49 wt%); hexagonal form; also etches
in hydrochloric, phosphoric and sulfuric acids; t etragonal form is
etch resistant; DI water rinse [ 25]
125 Germanium dioxide
(GeO
2
)
HF(49%):H
2
O
1:4
Room temperature; DHF etchant (4:1);
Etches GeO [206]
126 Germanium nitride
(Ge
3
N
4
), CVD
HF(49%): NH
4
F
(40%)
1:5
Room temperature; BHF etchant (5:1); also etches in concentrated HF,
nitric or hot phosphoric acids; etches slightly in sulfuric acid; DI
water rinse [25]
127 Halfnium oxide
(HfO
2
), CVD
1 HF(49%):H
2
O
1:3
25
◦
C; DHF etchant (3:1); cracking may occur with higher HF
concentration; etch rate decreases with annealing; consider CP-4A
etch; DI water rinse [207]
128 Halfnium oxide
(HfO
2
), CVD
HF(49%): NH
4
F
(40%)
1:5
Room temperature; BHF etchant (5:1); also etches in concentrated HF
and slightly in hot phosphoric acids; DI water rinse [25]
129 Indium aluminum
arsenide (InAlAs),
MBE
110 HCl(38%):H
2
O
3:1
Room temperature; may have initial etch delay; lower HCl
concentrations will not etch InAlAs or InGaAlAs;
Etches AlGaAs, InGaAlAs (18 Å/s for AlAs mole fraction of 0.34),
InP;
Doesn’t significantly etch GaAs, InGaAs (<0.1 Å/s), InGaAlAs (for
AlAs mole fraction <0.2); DI water rinse [208]
130 Indium antiminide
(InSb)
HF(49%):
HNO
3
(70%):H
2
O
1:1:4
Room temperature; HNA etchant; DI water rinse [179]
131 Indium antiminide
(InSb)
3200 HF(49%):
H
2
O
2
(30%)H
2
O
1:1:8
25
◦
C; rate for In(111); preferential etchant; etches Sb(111) at
4800 Å/s; DI water rinse [209]
8 MEMS Wet-Etch Processes and Procedures 533
Table 8.18 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
132 Indium antiminide
(InSb)
2800 HF(49%):
HNO
3
(70%):Acetic
1:2:1
25
◦
C; HNA etchant; rate for In(111); similar rate for Sb(111) at this
temperature only; DI water rinse [129, 210]
133 Indium antiminide
(InSb)
HF(49%):
HNO
3
(70%):Acetic
3:5:3
Room temperature; HNA etchant; also CP-4A etchant; DI water rinse
[211]
134 Indium arsenide
(InAs)
HCl(38%)
undiluted
Room temperature; DI water rinse [179]
135 Indium arsenide
(InAs)
1400 HCl(38%)
undiluted
75
◦
C; DI water rinse [70]
136 Indium arsenide
(InAs)
HF(49%):
HNO
3
(70%):H
2
O
1:3:2
Room temperature; HNW etchant; p–n junction etchant; delineate p
and n regions; DI water rinse [70]
137 Indium arsenide
(InAs)
HNO
3
(70%):
H
2
O
2
(30%):H
2
O
1:1:4
Room temperature; DI water rinse [179]
138 Indium arsenide
phosphide
(InAsP), VPE
200 H
3
PO
4
(85%):
HCl(38%)
1:3
Room temperature; add 0–0.3 parts H
2
O
2
(30%) with increasing As
concentration; DI water rinse [212]
139 Indium gallium
antimonide
(AlGaSb),
sputtered
HCl(38%):
H
2
O
2
(30%):H
2
O
10:1:10
Room temperature; DI water rinse [213]
140 Indium gallium
arsenide
(InGaAs), MBE
22 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
1:1:50
25
◦
C; use citric acid system for higher selectivity to AlGaAs; DI
water rinse [136]