Ghodssi R., Lin P., MEMS Materials and Processes Handbook
Подождите немного. Документ загружается.
564 D.W. Burns
Table 8.20 Silicide etchants and etch processes
Material
Etch rate
(Å/s) Etchant Remarks and references
1 Chrome–silicon
(CrSi)
10–15 H
3
PO
4
(85%):
HF(49%):
HNO
3
(70%)
60:1:5
Room temperature; DI water rinse [16]
2 Chrome–silicon
(CrSi), thin film
on Cu, Ni or Au
15–20 Potassium
hexacyanoferrate
50
◦
C; Transene chromium cermet etchant TFE; mask with negative
PR; etches CrO;
Doesn’t significantly etch Au, Cu, Ni; glass tank; stirring helpful; DI
water rinse [349]
3 Chromium silicide
(CrSi
2
)
H
2
SO
4
(96%):
H
3
PO
4
(85%):
H
2
O
1:4:2
Room temperature; DI water rinse [21]
4 Chromium silicide
(CrSi
2
)
HF(49%):
HNO
3
(70%)
1:1
Room temperature; DI water rinse [21]
5 Cobalt silicide
(CoSi
2
)
H
3
PO
4
(85%)
undiluted
155
◦
C; DI water rinse [17, 21, 125, 127, 350]
6 Cobalt silicide
(CoSi
2
), sputtered
Co on Si and
sintered
6 HF(49%):H
2
O
1:20
Room temperature; DHF etchant (20:1); DI water rinse [351]
7 Copper–Silicon
(CuSi)
H
3
PO
4
(85%):
HCl(38%):
HNO
3
(70%):Acetic
1:1:3:5
70–80
◦
C; DI water rinse [53]
8 Hafnium silicide
(HfSi
2
)
HF(49%):H
2
O Resistant to aqueous alkali and inorganic acids except HF, aqua regia
and sulfuric-peroxide mixtures; DI water rinse [125, 127]
8 MEMS Wet-Etch Processes and Procedures 565
Table 8.20 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
9 Iron silicide (FeSi
2
) HCl(38%):
HF(49%): HNO
3
(70%):H
2
O
50:1:5:44
Room temperature; ternary alloys with Cr and V; DI water rinse [352]
10 Iron silicide (FeSi
2
) HF(49%)
undiluted
Room temperature; HF etchant (49 wt%); DI water rinse [21]
11 Iron silicide (FeSi
2
) HF(49%):
HNO
3
(70%)
1:1
Room temperature; DI water rinse [21]
12 Magnesium silicide
(Mg
2
Si)
Acetic
undiluted
Room temperature; DI water rinse [21]
13 Magnesium silicide
(Mg
2
Si)
HF(49%):
HNO
3
(70%)
5:1
Room temperature; DI water rinse [26]
14 Manganese silicide
(MnSi
2
)
HCl(38%):
HNO
3
(70%)
3:1
Room temperature; DI water rinse [21]
15 Manganese silicide
(MnSi
2
)
HF(49%):
HNO
3
(70%)
1:1
Room temperature; DI water rinse [21]
16 Molybdenum
silicide (MoSi
2
)
H
2
SO
4
(96%):
H
3
PO
4
(85%):H
2
O
1:4:2
Room temperature; doesn’t significantly etch Mo
5
Si
3
;DIwaterrinse
[21]
17 Molybdenum
silicide (MoSi
2
)
3.3 HF(49%):
HNO
3
(70%)
1:1
Room temperature; DI water rinse [21, 45, 127]
566 D.W. Burns
Table 8.20 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
18 Nickel silicide
(NiSi
2
), sintered
HF(49%):H
2
O
1:10
Room temperature; DHF etchant (10:1); reduce etch rate with
cathodic protection; DI water rinse [127, 353]
19 Nickel silicide
(NiSi
2
)
HF(49%):
HNO
3
(70%)
1:3
Room temperature; agitate ultrasonically; DI water rinse [354]
20 Nickel silicide
(NiSi
2
), sintered
6 Phosphoric, acetic,
nitric and
fluoroboric acids
with water
Room temperature; Freckle etch, Arch Chemicals; etches silicon (100
surface at 3 Å/s), AlSi (1%) (9 Å/s); DI water rinse [355]
21 Niobium silicide
(NbSi
2
)
H
2
SO
4
(96%):
H
3
PO
4
(85%):H
2
O
1:4:2
Room temperature; DI water rinse [21]
22 Niobium silicide
(NbSi
2
)
HF(49%):
HNO
3
(70%):H
2
O
4:10:86
Room temperature; HNW etchant; also Kroll’s reagent; DI water rinse
[356]
23 Niobium silicide
(NbSi
2
)
HF(49%): NH
4
F
(40%)
1:10
Room temperature; BHF etchant (10:1); DI water rinse [127]
24 Palladium silicide
(Pd
2
Si)
HF(49%)
undiluted
Room temperature; HF etchant (49 wt%); DI water rinse [26]
25 Palladium silicide
(Pd
2
Si)
HF(49%):
HNO
3
(70%)
Room temperature; DI water rinse [127]
26 Platinum silicide
(PtSi), sintered
HCl(38%):
HNO
3
(70%)
3:1
85
◦
C; aqua regia; precede with BHF etch; DI water rinse [328, 329]
8 MEMS Wet-Etch Processes and Procedures 567
Table 8.20 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
27 Platinum silicide
(PtSi), sintered
HCl(38%):
HNO
3
(70%):H
2
O
3:1:4
60
◦
C; also etches Pt; DI water rinse [357]
28 Platinum silicide
(PtSi)
HF(49%):
HNO
3
(70%)
Room temperature; DI water rinse [127]
29 Platinum silicide
(PtSi)
HF(49%):
HNO
3
(70%):Acetic
1:3:4
Room temperature; HNA etchant; DI water rinse [45]
30 Rhenium silicide
(ReSi)
HF(49%):
HNO
3
(70%):H
2
O
Room temperature; HNW etchant; DI water rinse [358]
31 Rhodium silicide
(RhSi), sintered
HF(49%):
HNO
3
(70%):Acetic
4:9:7
Room temperature; HNA etchant; etches Rh and Si; DI water rinse
[359]
32 Ruthenium Silicide
(Ru
2
Si
3
)
23 HF(49%): KOCl
(11%):H
2
O
1:3:50
Room temperature; nonstandard chemical; DI water rinse [360]
33 Tantalum silicide
(TaSi
2
)
H
2
SO
4
(96%):
H
3
PO
4
(85%):H
2
O
1:4:2
Room temperature; DI water rinse [21]
34 Tantalum silicide
(TaSi
2
), LPCVD
HF(49%)
undiluted
40
◦
C; HF etchant (49 wt%); DI water rinse [361]
35 Tantalum silicide
(TaSi
2
), LPCVD
HF(49%):
HNO
3
(70%)
1:25
Room temperature; also etches Si; DI water rinse [362]
568 D.W. Burns
Table 8.20 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
36 Tantalum silicide
(TaSi
2
), sintered
3.3 HF(49%): NH
4
F
(40%)
1:10
Room temperature; BHF etchant (10:1); DI water rinse [127, 363]
37 Tantalum silicide
(TaSi
2
)
50 Proprietary 20
◦
C; Transene; DI water rinse [364]
38 Titanium silicide
(Ti
2
Si
3
)
H
2
O
2
(30%)
undiluted
20
◦
C; etches Ti
2
Si
3
, other compositions unknown; DI water rinse [21]
39 Titanium silicide
(TiSi
2
)
25 HF(49%):H
2
O
1:100
Room temperature; DHF etchant (100:1); insoluble i n aqueous alkali
and most inorganic acids; DI water rinse [127, 128, 365]
40 Titanium silicide
(TiSi
2
)
45 HF(49%):H
2
O
1:40
Room temperature; DHF etchant (40:1); DI water rinse [128]
41 Titanium silicide
(TiSi
2
), sintered
25 HF(49%): NH
4
F
(40%)
1:10
Room temperature; BHF etchant (10:1); DI water rinse [363]
42 Titanium silicide
(TiSi
2
),
evaporated
0.7 KOH:H
2
O
500 g:1000 mL
70
◦
C; KOH etchant (30 wt%); etches silicon (100 surface at 85 Å/s);
DI water rinse [366]
43 Titanium-tungsten
silicide (TiWSi),
sintered
HCl(38%):
HNO
3
(70%)
3:1
Room temperature; Ti
0.3
W
0.7
Si
2
;Diwaterrinse[367]
44 Tungsten silicide
(WSi
2
), sintered
HF(49%):
HNO
3
(70%):H
2
O
4:10:86
Room temperature; HNW etchant; also Kroll’s reagent; insoluble in
aqua regia and most inorganic acids; DI water rinse [127, 365, 368,
369]
45 Tungsten silicide
(WSi
2
), CVD
HF(49%):
HNO
3
(70%):H
2
O
2:60:40
Room temperature; HNW etchant; etches Si; DI water rinse [370]
8 MEMS Wet-Etch Processes and Procedures 569
Table 8.20 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
46 Tungsten silicide
(WSi
2
)
HNO
3
(70%): NH
4
F
(40%)
49:1
Room temperature; DI water rinse [45]
47 Vanadium silicide
(VSi
2
)
HF(49%): NH
4
F
(40%)
1:10
Room temperature; BHF etchant (10:1); DI water rinse [127]
48 Vanadium silicide
(VSi
2
)
H
2
SO
4
(96%):
H
3
PO
4
(85%):H
2
O
1:4:2
Room temperature; DI water rinse [21]
49 Vanadium silicide
(V
3
Si)
HF(49%):
HNO
3
(70%)
1:6
Room temperature; DI water rinse [371]
50 Vanadium silicide
(V
3
Si)
HF(49%):
HNO
3
(70%):
H
2
O
2
(30%)
1:1:4
Room temperature; DI water rinse [372]
51 Zirconium silicide
(ZrSi
2
)
HF(49%):H
2
O Room temperature; DHF etchant; DI water rinse [127]
52 Oxides of (CoSi
2
),
(CrSi
2
), (Ir
3
Si
5
),
(NiSi
2
), (Ru
2
Si
3
),
(Si), (WSi
2
),
thermally grown
2.5–4 HF(49%): NH
4
F
(40%)
1:50
Room temperature; BHF etchant (50:1); thermally grown oxides; DI
water rinse [373]
570 D.W. Burns
masking materials are limited to low temperatures to avoid excessive cross-linking,
melting, or burning of the underlying polymer. Polymers that are photosensitive
such as PMMA, SU-8, photo-sensitive polyimide, BCB, and commercial photore-
sists may need no masking layer. Etch rates and etchants for some plastics and
polymers are listed in Table 8.21. Typically, polymers may be etched in an oxygen
plasma. Particularly stubborn thin materials may be sputter-etched with an argon
plasma. Chemical resistance of polymers varies widely and assessments can be
found in the literature [374].
8.5.3 Examples: Wet Chemical Etching of Nonstandard Materials
Plastic and polymeric thin films may be desirable in an IC or MEMS process
for passivation, corrosion resistance, overmolding, chip-scale packages, chemical
specificity, expansion with absorption, and relatively low elastic moduli. Modern
plastics provide a wide variety of properties that can be favorably exploited for
small lightweight sensors and ICs. Bio-MEMS devices utilize biocompatible poly-
mers with relatively large feature sizes. Photoresponsive polymers can be patterned
directly with submicron features and used directly or as molds for other polymer
processes. Epoxies and solvent bonding techniques can be used to assemble smaller
sections of a system. Traditional micromachining of silicon substrates is greatly
expanded and in some cases supplanted by the use of these alternative materials in
a variety of optical, electrical, chemical, and mechanical sensors and actuators. The
appropriate selection of materials is governed largely by cost, performance, and
availability. Several examples for wet chemical etching of nonstandard materials
follow.
8.5.3.1 Example 1: BCB Patterning and Etching
Negative-acting BCB resist is equilibrated to room temperature, hand-dispensed at
100 RPM on a borosilicate glass wafer and spun at ∼2500 RPM in a well-ventilated
hood to produce a 5 µm-thick layer. The wafer is pretreated with an adhesion pro-
moter before BCB application, and a Q-tip soaked with developer is placed against
the wafer periphery near the end of the high-speed spin to remove excess resist. The
wafer is prebaked on an in-line hot plate for 90 s at 65
◦
C; exposed within the day
to form seal-ring patterns using a contact aligner; and then puddle-developed on a
wafer-track using a commercial developer until unexposed areas are cleared, rinsed
with a DI water spray at 10 s at 500 RPM, spun dry at 3000 RPM for 30 s, and
postbaked for 60 s at 90
◦
C. The wafer is then diced and each cap die is flip-chip
bonded to an underlying silicon RF-MEMS wafer using a 250 g force for 3 min in
air at 120
◦
C. A nonhermetic seal is made by reflowing and curing the BCB in the
flip-chip assembly at 250
◦
C for 20 min. The cap wafer may be reworked if needed
using a commercial stripper at 80
◦
C to remove the BCB after exposure and before
curing (the developer may be used if the wafer has not been exposed), using the
commercial stripper at 95
◦
C for partially cured BCB, dry etching the cured film in
8 MEMS Wet-Etch Processes and Procedures 571
Table 8.21 Plastics and polymer etchants and etch processes
Material
Etch rate
(Å/s) Etchant Remarks and references
1 Benzocyclo-butene
(BCB), spun and
cured
H
2
SO
4
(96%):
H
2
O
2
(30%)
4:1
120
◦
C; exothermic mixture; DI water rinse [375, 376]
2 Benzocyclo-butene
(BCB), spun and
cured
180 SF
6
:O
2
plasma
15:95 sccm
Dry etch; cured material; 260 W, 1000 mTorr; also etches in CF
4
:O
2
plasma or straight O
2
for BCB without silicon [377]
3 Cyclic olefin
copolymer (COC)
Heptane
undiluted
Room temperature; nonstandard solvent; DI water or isopropyl
alcohol rinse [378]
4 Cyclic olefin
copolymer (COC)
Hexadecane:IPA
1:12
Room temperature; nonstandard chemical; solvent bonding; isopropyl
alcohol rinse [378]
5 Epoxy,
aluminum-filled
H
2
SO
4
(96%)
undiluted
Hot; DI water rinse [26]
6 Epoxy, gold-filled HNO
3
(70%):
HCl(38%):H
2
O
3:1:10
Room temperature; DI water rinse [26]
7 Epoxy, silver-filled HF(49%):
HNO
3
(70%)
1:3
Room temperature; DI water rinse [26]
8 Fluorinated ethylene
propylene (FEP,
Teflon-FEP), film
THF
undiluted
Warm; nonstandard solvent; surface modifier; DI water or isopropyl
alcohol rinse [379]
9 Liquid crystal
polymer (LCP),
plastic packages
H
2
SO
4
(96%):
HNO
3
(70%)
1:9
60
◦
C; less attack on metallurgy; rinse with acetone while part is hot;
finish with DI water rinse then isopropyl alcohol with ultrasonic
agitation [45]
10 Liquid crystal
polymer (LCP),
plastic packages
HNO
3
(70%)
undiluted
60–70
◦
C; etches nonferrous metals; rinse with acetone while part is
hot; finish with DI water rinse then isopropyl alcohol with
ultrasonic agitation [45]
572 D.W. Burns
Table 8.21 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
11 Liquid crystal
polymer (LCP),
sheet
40 O
2
RIE Dry etch; mask with Al; 350 W, 500 mTorr [380]
12 Novolak (PR) 80 Isopropyl alcohol
undiluted
50
◦
C; etch rate is 40 Å/s at 27
◦
C; DI water or isopropyl alcohol rinse
[381]
13 Octadecyltri-
chlorosilane
(OTS)
HCl(38%):H
2
O
1:10
Room temperature; pretreated surface; DI water rinse [382]
14 Photoresist (PR),
vexing
Air
ambient
450–650
◦
C; negative and positive resists [383, 384]
15 Photoresist (PR),
vexing
H
2
SO
4
(96%):
H
2
O
2
(30%)
1:1
160
◦
C; negative and positive resists; mix fresh; DI water rinse [383]
16 Photoresist (PR),
vexing
O
2
plasma Dry ashing; negative and positive resists; removal rate increases with
wafer temperature; high selectivity to SiO
2
and Si [383, 385]
17 Photoresist (PR) 50 Ozone:H
2
O95
◦
C; ozone-rich water; add ammonium hydroxide to remove etch
residues; DI water rinse [386]
18 Photoresist (PR),
thick negative or
positive resist
110–750 Ozone:Solvent Room temperature; solvent selected for high ozone solubility; DI
water rinse [387]
19 Polyaniline (PANI) H
2
SO
4
(96%)
undiluted
Room temperature; DI water rinse [388]
20 Polyaniline (PANI) NMP
undiluted
Room temperature; nonstandard solvent; DI water or isopropyl
alcohol rinse [389, 390, 391, 392]
21 Polycaprolactone
(PCL)
Acetone
undiluted
Room temperature; also reacts with isopropyl alcohol and gold etchant
(type TFA); DI water rinse [393]
22 Polycarbonate (PC),
sheet film
Acetone
undiluted
Room temperature; DI water rinse [394]
8 MEMS Wet-Etch Processes and Procedures 573
Table 8.21 (continued)
Material
Etch rate
(Å/s) Etchant Remarks and references
23 Polycarbonate (PC) MEK
undiluted
Room temperature; nonstandard solvent; solvent bonding; DI water or
isopropyl alcohol rinse [395]
24 Polydimethyl-
siloxane
(PDMS)
Acetone
undiluted
Room temperature; swells film [396]
25 Polydimethyl-
siloxane
(PDMS)
55 CF
4
:O
2
RIE
3:1
Dry etch; 270 W; 47 mTorr [397]
26 Polydimethyl-
siloxane
(PDMS)
HCl(38%):H
2
O
1:5
Room temperature; surface treatment; DI water rinse [398]
27 Polydimethyl-
siloxane
(PDMS)
1600 TBAF:NMP
1:1
Room temperature; nonstandard chemicals; DI water rinse [399]
28 Polydimethyl-
siloxane
(PDMS)
TBAF:THF
1g:1mL
Room temperature; 1.0 M solution; non-standard chemicals; DI water
rinse [400]
29 Polyester, substrate H
2
SO
4
(96%):
H
2
O
2
(30%)
7:3
90
◦
C; surface modification; DI water rinse [401]
30 Polyethylene (PE) H
2
SO
4
(96%):
K
2
Cr
2
O
7
:H
2
O
150:7:12 by
weight
70
◦
C; chromic acid; nonstandard chemical; slightly etches
polypropylene (PP); DI water rinse [402]
31 Polyethylene (PE) H
2
SO
4
(96%):CrO
3
:
H
2
O
29:29:42 by
weight
75
◦
C; chromic acid; nonstandard chemical; follow with HNO
3
at
50
◦
C or HCl:H
2
O 1:1 (6 N) at 50
◦
C; DI water rinse [403]