Ghodssi R., Lin P., MEMS Materials and Processes Handbook
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544 D.W. Burns
Table 8.19 Nonstandard metal etchants and etch processes
Material
Etch rate
(Å/s) Etchant Remarks and references
1 Aluminum (Al) See Table 8.8
2 Beryllium (Be) H
2
SO
4
(96%)
undiluted
Room temperature; DI water rinse [271]
3 Beryllium (Be) HCl(38%)
undiluted
Room temperature; DI water rinse [272]
4 Beryllium (Be) HF(49%):H
2
O
1:7
Room temperature; DHF etchant (7:1); DI water rinse [273]
5 Bismuth (Bi) H
2
SO
4
(96%)
undiluted
Hot; DI water rinse [25]
6 Bismuth (Bi) HCl(38%):H
2
O
1:10
Room temperature; DI water rinse [98]
7 Bismuth (Bi), MBE HCl(38%):
HNO
3
(70%):H
2
O
1:1:1
Room temperature; DI water rinse [274]
8 Bismuth (Bi) 4200 HNO
3
(70%):Acetic:
H
2
O
6:6:1
Room temperature; DI water rinse [275]
9 Brass (CuZn) H
3
PO
4
(85%):
HNO
3
(70%):Acetic
1:1:4
50
◦
C; PAN etchant; DI water rinse; see also copper [53]
10 Cadmium (Cd) HNO
3
(70%):H
2
O
3:1
DI water rinse [25]
11 Cadmium (Cd) HNO
3
(70%):Acetic:
H
2
O
2
(30%)
1:2:2
DI water rinse [26]
12 Chromium (Cr) 25 HCl(38%)
undiluted
Room temperature; DI water rinse
[276, 277]
8 MEMS Wet-Etch Processes and Procedures 545
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
13 Chromium (Cr) HCl(38%):H
2
O
1:1 to 1:20
Room temperature; DI water rinse [26]
14 Chromium (Cr) HCl(38%): H
2
O
2
(30%)
3:1
Room temperature; DI water rinse [26, 45]
15 Chromium (Cr) HNO
3
(70%):H
2
O
3:1
80
◦
C; DI water rinse [92]
16 Chromium (Cr),
deposited
25 Ceric ammonium
nitrate, perchloric
acid
20
◦
C; Cyantek CR-7; mask with PR, oxide, Au, polyimide;
Etches Ag (75 Å/s), Al (0.6 Å/s), Cu (45 Å/s), Ge(poly) (45 Å/s),
Ti(0.3 Å/s), Va (10 Å/s);
Etches slightly graphite (0.1 Å/s), Mo (0.5 Å/s), Ni (0.3 Å/s), NiCr
(2 Å/s), Pyrex (roughens), quartz (<0.1 Å/s), SiGe(poly) (<0.1 Å/s),
SiO
2
(thermal) (<0.01 Å/s), Ta (0.1 Å/s), TiW (0.1 Å/s), W
(0.5 Å/s);
Doesn’t significantly etch Au, Nb (roughens), nitride, oxide, Pd,
poly-Si, Pt, sapphire (roughens), Si; DI water rinse [28]
17 Chromium (Cr),
deposited
40 Ceric ammonium
nitrate, nitric acid
40
◦
C; Transene chromium etchant 1020; mask with PR, Au, Si
3
N
4
,
SiO
2
, Ti, W; etches Al, Cu, GaAs, Ni; glass t ank; DI water rinse
[278]
18 Cobalt (Co) H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
1:14:15
Room temperature; DI water rinse [279, 280]
19 Cobalt (Co), sputtered 40 H
2
SO
4
(96%):
H
3
PO
4
(85%):
HNO
3
(70%):Acetic
1:1:3:5
40
◦
C; doesn’t significantly etch CoSi
2
;DIwaterrinse[281]
20 Cobalt (Co), deposited 1.5 HCl(38%):H
2
O
1:3
35
◦
C; slows with etch time; doesn’t significantly etch TiN; DI water
rinse [282]
546 D.W. Burns
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
21 Cobalt (Co), sputtered HCl(38%): H
2
O
2
(30%)
3:1
Room temperature; doesn’t significantly etch CoSi
2
; DI water rinse
[97, 101]
22 Cobalt (Co), deposited 13 HCl(38%):
H
2
O
2
(30%):H
2
O
1:1:100
30
◦
C; doesn’t significantly etch TiN (<0.02 Å/s); DI water rinse [282]
23 Cobalt (Co), deposited HCl(38%):
H
2
O
2
(30%):H
2
O
3:1:3
80
◦
C; etches cobalt oxide; doesn’t significantly etch CoSi
2
; DI water
rinse [283, 284]
24 Cobalt (Co) HNO
3
(70%):Acetic
1:1
Room temperature; DI water rinse [53]
25 Cobalt (Co), evaporated HNO
3
(70%): H
2
O
1:1
Room temperature; doesn’t significantly etch CoSi
2
; DI water rinse
[285]
26 Cobalt (Co), MBE HNO
3
(70%):
H
2
O
2
(30%)
1:3
Room temperature; doesn’t significantly etch CoSi
2
; DI water rinse
[286]
27 Copper (Cu) 110 H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
1:5:19
Also etches with H
3
PO
4
, HCl or HNO
3
; DI water rinse [287]
28 Copper (Cu) H
2
SO
4
(96%):
HNO
3
(70%):Acetic
2:3:3
Room temperature; etches Ni and Ni alloys at similar rate; dilute with
H
2
O for reduced rate; DI water rinse [288]
29 Copper (Cu), Brass
(CuZn)
H
3
PO
4
(85%):
HNO
3
(70%):Acetic
55:20:25
55–80
◦
C; PAN etchant; DI water rinse [53]
30 Copper (Cu), Cu–Al–Si
Alloy (CuAlSi)
H
3
PO
4
(85%):
HNO
3
(70%):Acetic
1:1:1
60–70
◦
C; PAN etchant; DI water rinse [53]
8 MEMS Wet-Etch Processes and Procedures 547
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
31 Copper (Cu) HCl(38%): HNO
3
(70%)
3:1
Room temperature; aqua regia; DI water rinse [289]
32 Copper (Cu), deposited 100 HCl(38%):
HNO
3
(70%):H
2
O
3:1:2
30
◦
C; dilute aqua regia; mask with PR;
Etches Ag, Al (100 Å/s), AlSi(2%), Au (115 Å/s), Mo (110 Å/s), Ni
(17 Å/s), Pd (65 Å/s), Pt (0.6 Å/s), W (1 Å/s);
Etches slightly Al
2
O
3
(0.2 Å/s), SiO
2
(PECVD) (0.1 Å/s), Ta
(0.3 Å/s), Ti (0.1 Å/s), TiW (0.6 Å/s);
Doesn’t significantly etch Cr, Nb, polyimide, quartz, sapphire, Si,
Si(poly), Si
3
N
4
,SiO
2
, Ta; water added to reduce PR attack;
self-heating; DI water rinse [28]
33 Copper (Cu) HF(49%): HNO
3
(70%)
1:1
Room temperature; rapid dissolution; DI water rinse [289]
34 Copper (Cu) HNO
3
(70%):H
2
O
5:1
Room temperature; dilute with H
2
O for slower etch; DI water rinse
[98, 289]
35 Copper (Cu) NH
4
OH(29%):H
2
O
1:1
Room temperature; rapid dissolution; can substitute H
2
O
2
for H
2
O;
DI water rinse [289]
36 Copper (Cu) NH
4
OH(29%):
H
2
O
2
(30%):H
2
O
1:1:1
Room temperature; DI water rinse [290]
37 Copper (Cu) 80 Ammonium persulfate 40
◦
C; Transene Copper Etchant APS-100; mask with PR;
Etches Ni;
Etches slightly W;
Doesn’t significantly etch Al, Au, Cr, Si, Si
3
N
4
,SiO
2
,Ta,TaN,Ti;
PVC, glass or epoxy-coated tank; continuous agitation; DI water
rinse [291]
548 D.W. Burns
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
38 Copper (Cu), deposited 480 H
3
PO
4
(85%):
HNO
3
(70%):Acetic:
H
2
O
16:1:1:2
50
◦
C; Transene aluminum etchant type A; mask with PR, Si
3
N
4
(>1000:1), Si
3
N
4
(low-stress) (>1000:1), SiO
2
(LTO) (>1000:1), Ti
(>1000:1);
Etches Al (90 Å/s), AlSi(2%) (110 Å/s), Ge(poly) (2 Å/s), Ni (5 Å/s);
Etches slightly Al
2
O
3
(1–10 Å/s), sapphire (0.3 Å/s), Si(poly)
(0.2 Å/s);
Doesn’t significantly etch Cr, quartz, Si, SiGe(poly), SiO
2
; heated
bath; DI water rinse [28]
39 Copper (Cu), deposited 45 Ceric ammonium
nitrate, nitric acid
20
◦
C; Cyantek CR-7; mask with Au, polyimide, PR, SiO
2
;
Etches Ag (75 Å/s), Al (0.6 Å/s), Cr (25 Å/s), Ge(poly) (45 Å/s),
Ti(0.3 Å/s), Va (10 Å/s);
Etches slightly graphite (0.1 Å/s), Mo (0.5 Å/s), Ni (0.3 Å/s), NiCr
(2 Å/s), Pyrex (roughens), quartz (<0.1 Å/s), SiGe(poly) (<0.1 Å/s),
SiO
2
(<0.01 Å/s), Ta (0.1 Å/s), TiW (0.1 Å/s), W (0.5 Å/s);
Doesn’t significantly etch Au, Nb (roughens), Pd, Si, Si(poly), Si
3
N
4
,
SiO
2
, sapphire (roughens), Pt; DI water rinse [28]
40 Dysprosium (Dy) HNO
3
(70%): Acetic
2:3
Room temperature; DI water rinse [292]
41 Erbium (Er) H
2
SO
4
(96%):
H
2
O
2
(30%)
1:1
DI water rinse [293]
42 Gold (Au), deposited 1600–2500 HCl(38%): HNO
3
(70%)
3:1
Room temperature; aqua regia; DI water rinse [26, 294]
43 Gold (Au), deposited 4000–8000 HCl(38%): HNO
3
(70%)
3:1
32–38
◦
C; aqua regia; DI water rinse [92]
8 MEMS Wet-Etch Processes and Procedures 549
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
44 Gold (Au), deposited 115 HCl(38%):
HNO
3
(70%):H
2
O
3:1:2
30
◦
C; dilute aqua regia; mask with PR;
Etches Ag, Al (100 Å/s), AlSi (2%), Cu (100 Å/s), Mo (110 Å/s), Ni
(17 Å/s), Pd (65 Å/s), Pt (0.6 Å/s), W (1 Å/s);
Etches slightly Al
2
O
3
(0.2 Å/s), SiO
2
(PECVD) (0.1 Å/s), Ta
(0.3 Å/s), Ti (0.1 Å/s), TiW (0.6 Å/s);
Doesn’t significantly etch Cr, Nb, polyimide, quartz, sapphire, Si,
Si(poly), Si
3
N
4
,SiO
2
, Ta; water added to reduce PR attack;
self-heating; DI water rinse [28]
45 Gold (Au), deposited 165 KI:I
2
:H
2
O4g:1g:40
mL
Room temperature; doesn’t significantly etch Al; DI water rinse [22,
45]
46 Gold (Au), deposited 1270 KI:I
2
:H
2
O 1 g:4 g:4 mL 55
◦
C; DI water rinse [26]
47 Gold (Au), deposited 28–150 KI, I
2
25–60
◦
C; Transene gold etchant TFA; mask with PR;
Etches Al, Cu (corrodes), GaAs;
Etches Ni slightly;
Doesn’t significantly etch Cr, Si, Si
3
N
4
,SiO
2
,Ta,TaN,Ti,W;glass
tank; DI water rinse [295]
48 Hafnium (Hf) 1.5 H
2
SO
4
(96%):
HNO
3
(70%)
1:1
35
◦
C; DI water rinse [296, 297]
49 Hafnium (Hf) 1 HCl(38%): HNO
3
(70%)
1:1
35
◦
C; DI water rinse [296]
50 Hafnium (Hf) HF(49%):H
2
O
1:50
Room temperature; DHF etchant (50:1); DI water rinse [16]
51 Hafnium (Hf) HF(49%):
H
2
O
2
(30%):H
2
O
1:1:20
Room temperature; DI water rinse [98]
550 D.W. Burns
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
52 Hafnium (Hf) HF(49%): HNO
3
(70%):
H
2
O
2
(30%)
10:45:45
Room temperature; DI water rinse [298]
53 Indium (In) HCl(38%)
undiluted
Room temperature; heat for faster etch rate; DI water rinse [299, 300,
301]
54 Indium (In) HCl(38%): HNO
3
(70%)
3:1
40
◦
C; aqua regia; DI water rinse [98, 300]
55 Indium (In) HNO
3
(70%):H
2
O
1:1
Room temperature; DI water rinse [302]
56 Indium (In) IPA, EtOH, then MeOH Room temperature; DI water rinse [26]
57 Invar (FeNi) HCl(38%):
HNO
3
(70%):Acetic:
H
2
O
2:2:5:1
Room temperature; DI water rinse [25]
58 Iridium (Ir) HCl(38%): HNO
3
(70%)
3:1
40
◦
C; aqua regia; DI water rinse [26, 98]
59 Iron (Fe) HCl(38%):H
2
O
1:1
Room temperature; DI water rinse [98]
60 Iron (Fe) HCl(38%):
HNO
3
(70%):H
2
O
7:3:30
60–70
◦
C; Di water rinse [25]
61 Iron (Fe), Steel
(low-carbon)
HF(49%): H
2
O
2
(30%)
3:97
Room temperature; DI water rinse [53]
62 Iron (Fe), Iron–silicon
alloy (FeSi)
HF(49%): H
2
O
2
(30%)
6:94
Room temperature; DI water rinse [53]
63 Iron (Fe), Steel
(low-carbon)
HF(49%):
HNO
3
(70%):H
2
O
7:3:30
60
◦
C; HNW etchant; DI water rinse [53]
8 MEMS Wet-Etch Processes and Procedures 551
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
64 Iron (Fe) HNO
3
(70%)
undiluted
Hot; can be diluted or used at room temperature; DI water rinse [303]
65 Kovar (FeNiCo) HCl(38%):H
2
O
1:1
70
◦
C; DI water rinse [26]
66 Kovar (FeNiCo) HCl(38%):
HNO
3
(70%):Acetic
15:1:3
Room temperature; DI water rinse [26]
67 Lead (Pb) Acetic:H
2
O
2
(30%)
1:4
Room temperature; DI water rinse [25]
68 Lead (Pb) Acetic:H
2
O
2
(30%)
3:1
Room temperature; DI water rinse [53]
69 Lead (Pb) Acetic:H
2
O
2
(30%):
MeOH
2:3:5
Room temperature; DI water rinse [53]
70 Lead (Pb) Acetic:H
2
O
2
(30%):
H
2
O
2:2:5
Room temperature; DI water rinse [98]
71 Lead (Pb) HNO
3
(70%):H
2
O
3:17
Room temperature; DI water rinse [25]
72 Lithium (Li) HNO
3
(70%)
undiluted
Room temperature; DI water rinse [26]
73 Lithium (Li) MeOH
undiluted
Room temperature; DI water rinse [304]
74 Magnesium (Mg) H
2
SO
4
(96%):
H
2
O
2
(30%):H
2
O
15:90:10
25
◦
C; DI water rinse [53]
75 Magnesium (Mg) HNO
3
(70%):H
2
O
1:19 to 3:17
Room temperature; DI water rinse [25]
552 D.W. Burns
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
76 Magnesium (Mg) HNO
3
(70%):MeOH
1:9
20
◦
C; DI water rinse [53]
77 Manganese (Mn) HCl(38%):H
2
O
1:1
Room temperature; DI water rinse [25, 305]
78 Molybdenum (Mo),
deposited
H
2
SO
4
(96%):
HNO
3
(70%)
1:4
Room temperature; DI water rinse [98]
79 Molybdenum (Mo),
deposited
4000 H
2
SO
4
(96%):
HNO
3
(70%):H
2
O
1:1:3
55
◦
C; DI water rinse [10]
80 Molybdenum (Mo),
sputtered
H
3
PO
4
(85%):
HNO
3
(70%):H
2
O
5:3:2
25
◦
C; DI water rinse [91]
81 Molybdenum (Mo),
deposited
80 H
3
PO
4
(85%):
HNO
3
(70%):Acetic:
H
2
O
5:2:4:150
Room temperature; PAN etchant; mask with PR; DI water rinse [8, 22]
82 Molybdenum (Mo),
deposited
115 H
3
PO
4
(85%):
HNO
3
(70%):
Acetic:H
2
O
180:11:11:150
20
◦
C; PAN etchant; mask with PR (3:1); etches Al (3 Å/s);
Doesn’t significantly etch Cr, TiW; Di water rinse [28]
83 Molybdenum (Mo),
deposited
HCl(38%): H
2
O
2
(30%)
1:1
Room temperature; DI water rinse [76]
84 Molybdenum (Mo),
deposited
110 HCl(38%):
HNO
3
(70%):H
2
O
3:1:2
30
◦
C; dilute aqua regia; mask with PR;
Etches Ag, Al (100 Å/s), AlSi(2%), Au (115 Å/s), Cu (100 Å/s), Ni
(17 Å/s), Pd (65 Å/s), Pt (0.6 Å/s), W (1 Å/s);
8 MEMS Wet-Etch Processes and Procedures 553
Table 8.19 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
Etches slightly Al
2
O
3
(0.2 Å/s), SiO
2
(PECVD) (0.1 Å/s), Ta
(0.3 Å/s), Ti (0.1 Å/s), TiW (0.6 Å/s);
Doesn’t significantly etch Cr, Nb, polyimide, quartz, sapphire, Si,
Si(poly), Si
3
N
4
,SiO
2
, Ta; water added to reduce PR attack;
self-heating; DI water rinse [28, 306]
85 Molybdenum (Mo) HF(49%): HNO
3
(70%)
1:1
Room temperature; DI water rinse [307]
86 Molybdenum (Mo),
deposited
55–85 Ferricyanide 30–60
◦
C; Transene moly etch TFM; mask with negative PR, KMER,
KTFR, or KPR; DI water rinse [308]
87 Molybdenum carbide
(Mo
2
C)
HNO
3
(70%)
undiluted
Room temperature; DI water rinse [26]
88 Monel (NiCuFe) HNO
3
(70%):
H
2
SO
4
(96%):Acetic
5:2:5
Room temperature; DI water rinse [288]
89 Nichrome (NiCr),
deposited
H
2
SO
4
(96%)
undiluted
100
◦
C; DI water rinse [76]
90 Nichrome (NiCr) HCl(38%):H
2
O
4:1
Room temperature; DI water rinse [25]
91 Nichrome (NiCr),
sputtered
HCl(38%): HNO
3
(70%)
3:1
Room temperature; aqua regia; DI water rinse [309]
92 Nichrome (NiCr) HCl(38%):
HNO
3
(70%):H
2
O
1:1:3
Room temperature; DI water rinse [16]