Chapter 1.10
Miscellaneous Etchants
Table of Contents
(Click on the
name of the etchant to go to its description.)
Aluminum Etchant
►
Type A (Transene Co., Inc.)
►
for VLSI
►
Others
Cadmium
► Sulfide Etchant (CdS)
► Telluride (CdTe)
Dislocation Etchants
►
Sirtl
►
Secco
►
ASTM
Gallium
►
Arsenide
Germanium
Etchant (and Germanium-Silicon)
► Tin Oxide (ITO)
Molybdenum
(Moly)
Polish –
Fairchild’s “Magic Polish”
Polysilicon
Etchant (see also Silicon Etchant)
Preferential
Etch (see Dislocation Etchant
Wright Jenkins Etchant)
Silicon
►
Polycrystalline Silicon
(Bell Labs)
►
Big Batch Silicon Etch (staff only)
► Single-Crystal (Sensors)
►
EDP
►
F & K (Finne &
Klein)
►
“B” (Bassous)
►
“F” (Fast)
►
“S” (Slow)
►
“M” (Medium)
►
KOH
►
Dioxide Etchant (Buffered HF)
►
Silicon and Germanium Etchant
►
Silicon-Germanium
(polycrystalline)
Westinghouse
Etchant (Si Polish Etch)
Aluminum Etchant Type A (Transene Co.,
Inc.)
►
For VLSI aluminum etching, there is available a pre-mixed
phosphoric/acetic acid mixture. Etch rate: ~ 100 Å/sec at 50ºC.
►
Corrosive. Avoid contact with eyes, skin and clothing. Avoid inhalation.
► Etch rate ~ 2000
Å/min.
16
parts phosphoric acid
2
parts DI water
1
part acetic acid
1 part nitric acid
► These will not
etch gold, etc.
► Phosphoric acid
at 60ºC
► Sodium hydroxide
(10% solution)
► Trisodium
phosphate at 190ºC
► These will not
etch ZnO. Etch rate ~ 100 Å/sec.
► 10 g K3Fe(CN)6
►
1 g Potassium hydroxide (KOH) in 100 ml water at room temperature.
► Etch (off of
silicon) : HNO3
H2O : HCl : HNO3 (1:1:1)
H2O : HF : HNO3 (90:1:10)
► HCl : HNO3 (3:1)
► Evaporation -
removal:
50% DI water
45% HCl
5%
CuSO4
► Dissolves gold.
►
Never store in a tightly sealed container!
► 5 ml Sulfuric
acid
5 ml Hydrogen
peroxide
90 ml DI water
No heat necessary. Etches quickly.
►
H2O : HCl
(10:1)
► Use brass dip
(Turco) for etching and cleaning.
► Ferric chloride
(etch)
► Ammonium
persulfate: 20 g to 100 ml H2O
► Dislocation pits
on the (0001). Distinguishes between A and B faces.
HNO3 : CH3COOH : H2O (6:6:1)
► Polishes
10
ml HNO3
20
ml H2O
4 g K2Cr2O7
► Pits
5%
Br2 in methanol
5 mg AgNO3
► HCl : H2O2
(3:1) - This will also etch gold film.
►
HCl : H2O (1:1) - Heat to 50ºC, immerse substrate and
touch with aluminum wire.
► HCl : H2O2
(3:1) - This will also etch gold film.
►
HCl and touch with aluminum wire.
► H2O :
HNO3 (1:1)
►
HCl : H2O2
(3:1)
►
HF : HNO3 (1:1)
► Brass Dip, RT-2
Resist Stripper, FeCl solutions
► H2O :
HNO3 (1:5)
►
Oxide removal - cold solution of ammonium carbonate (slight etch)
Dislocation Etchants
1 part conc. HF or 50
g CrO3 in 100 ml H2O
1 part CrO3 (5 M) 1:1 = HF : CrO3
solution
500 g/L of solution
Etch rate ~ 3.5 µm/min.
Good on {111}, poor on {100}, faceted pits.
2
parts conc. HF
1
part K2Cr2O7 (0.15 M)
44 g/L of solution
Etch rate ~ 1.5 µm/min.
Best with ultrasonic agitation. Good on all orientations. Non-crystallographic
pits.
2 parts
conc. HF
2
parts conc. acetic acid
1
part conc. nitric acid
1
part CrO3 (4M)
400 g/L of solution
2
part Cu(NO3)2 + 3 H2O (0.14 M)
33 g/L of solution
Etch rate ~ 1.7 µm/min. Ultrasonic agitation not required. Good on
all orientations. Faceted pits, good shelf life.
600 ml HF
30
ml HNO3
0.2 ml Br2
28
g Cu(NO3)2 + 3 H2O
Dilute 1:10 with H2O
► 1-2% Br2
in ethanol
H2SO4 : H2O2 : H2O (5:1:1)
Good polishing etches
►
Fused KOH at 300ºC
Good crystallographic dislocation pits on
the (100) surfaces
► 1 ml HF
2 ml H2O
8 mg AgNO3
1 g CrO3
Dislocation lines and striations
► Behaves similarly
to GaAs and the above etches may be used.
►
HF : Acetic Acid : Saturated KMn2O4
sol'n (1:1:1)
Good striations, free from pits on (110) surfaces
Germanium Etchant (and Germanium-Silicon)
►
H2O2 (30%) at 90ºC
Etch rates:
100% Ge 4000 Å/min
80% Ge 1000 Å/min
60% Ge and less do not
etch
►
H2O at 90ºC
Etch rates:
100% Ge ~ 200 Å/min
< 60% Ge does not etch
►
RCA SC-1 (NH4OH : H2O2 : H2O)
at 75ºC
Etch rates:
100% Ge ~ 4 um/min
80% Ge ~ 9000 Å/min
60% Ge ~ 500 Å/min
40% Ge ~ 30 Å/min
20% Ge ~ 10 Å/min
0% Ge ~
5 Å/min
► Aqua Regia: HCl : HNO3 (3:1)
►
Saturated solution of KI in H2O, 1 iodine crystal
► Reacts with acids
(HCl)
► Slow etch (1000
Å/min.)
HNO3 : H2O
(1:1)
Hot HCl : HNO3 (3:1)
► HNO3 : HF : Acetic Acid (5:3:3)
Polishes rapidly as it does most semiconductors, but bubble
formation can ruin the polish.
► 0.2N solution of
FeCl3 in HCl
Develops pits.
► HF : Acetic Acid
: 2N HMnO4 (1:1:1)
Good pit-free striations of (211) surfaces
►
Cut on diamond saw using slow feed. Lap using 5u powder. Degrease
in acetone, then methanol. Chemical etch using 5% bromine by weight for about 2
minutes using a swirling motion. Rinse in methanol, DI water, N2
dry.
In order to etch ITO it is needed to reduce it to a metallic
state. The reactions are:
Zn + HCl = H2 + ZnCl2
H2 reduces ITO
SnO2 + H2 = Sn or
SnOx with x smaller than 1
Sn + HCl = H2 + SnCl4 which is soluble
► The procedure:
conc. HCl: H2O=1:1 at 50ºC.
Add a small amount of Zn powder (on edge of a spatula). Put the wafer in the solution for about 1
min. Watch for turbidity of the ITO. Transfer the wafer to another beaker
containing conc. HCl (no dilution), for about 1 min.
Take the wafer out and check if all the film was etched. Return to first solution if needed, at 50
degrees.
► H2SO4 : H2O (1:1)
HCl
: H2O (1:1)
HNO3 : H2O (1:1)
►
To remove rust: saturated oxalic acid solution.
► Cleaner:
Ferric ammonium
sulfate 50 g
H2SO4 125 ml
HCl 150
ml
Heat to 60-80ºC
► Electrolysis:
HCl
and salt, alternating voltage. Kovar or carbon electrode
10% solution of HCl and a handful of salt
► Acetic acid : H2O (1:1)
►
Lead deposited on glass can be removed with dilute HNO3.
► Softens with
acetone
►
Acetone : formaldehyde
► Hot H2O
: NaOH (10:1 by weight)
Follow with H2O : CrO3 (5:1 by weight)
►
Dissolves (sometimes) in hot commercial ferric chloride.
► Dissolves and
reacts in HNO3.
►
To clean (purify), bubble air through mercury, filter and vacuum
distill.
► Hot concentrated
H2SO4
► Aqua Regia