Link to wet etchants on UC Berkeley Microlab web site
 

Aluminum Etchants

• Aluminum Etchant Type A (Transene Co., Inc.) — For VLSI aluminum etching, there is available a pre-mixed phosphoric/acetic acid mixture. Etch rate: approx. 100 /sec at 50C. Corrosive. Avoid contact with eyes, skin and clothing. Avoid inhalation.
• Aluminum Etchant for VLSI — Etch rate: 2000 /min.
  • 16 parts phosphoric acid
  • 2 parts DI water
  • 1 part acetic acid
  • 1 part nitric acid
• Aluminum Etchants – Others
  • These will not etch gold, etc.
    • Phosphoric acid at 60C
    • Sodium hydroxide (10% solution)
    • Trisodium phosphate at 190C
  • These will not etch ZnO. Etch rate 100 /sec.
    • 10 g K3Fe(CN)6
    • 1 g Potassium hydroxide (KOH) in 100 ml water at room temperature.
       

Antimony Etchant

• Etch (off of silicon) : HNO3
• H2O : HCl : HNO3 (1:1:1)
• H2O : HF : HNO3 (90:1:10)
   

Aqua Regia

• HCl : HNO3 (3:1)
• Evaporation – removal:

**50% DI water **45% HCl **5% CuSO4 Dissolves gold. Never store in a tightly sealed container!
 

Bismuth Etchant

• 5 ml Sulfuric acid
• 5 ml Hydrogen peroxide
• 90 ml DI water

No heat necessary. Etches quickly.
• H2O : HCl (10:1)
Brass
• Use brass dip (Turco) for etching and cleaning. • Ferric chloride (etch) • Ammonium persulfate: 20 g to 100 ml H2O
Cadmium Sulfide Etchant (CdS)
• Dislocation pits on the (0001). Distinguishes between A and B faces. HNO3 : CH3COOH : H2O (6:6:1)
Cadmium Telluride (CdTe)
• Polishes 10 ml HNO3 20 ml H2O 4 g K2Cr2O7
• Pits 5% Br2 in methanol 5 mg AgNO3
Chromium Etchant
• HCl : H2O2 (3:1) – This will also etch gold film. • HCl : H2O (1:1) – Heat to 50C, immerse substrate and touch with aluminum wire.
Chromium/Nichrome Etchant
• HCl : H2O2 (3:1) – This will also etch gold film. • HCl and touch with aluminum wire.
Cobalt
• H2O : HNO3 (1:1) • HCl : H2O2 (3:1)
Columbium
• HF : HNO3 (1:1)
Copper
• Brass Dip, RT-2 Resist Stripper, FeCl solutions • H2O : HNO3 (1:5) • Oxide removal – cold solution of ammonium carbonate (slight etch)
Dislocation Etchants
• Sirtl Etchant 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 m/min. Good on {111}, poor on {100}, faceted pits. • Secco Etchant 2 parts conc. HF 1 part K2Cr2O7 (0.15 M) 44 g/L of solution Etch rate 1.5 m/min. Best with ultrasonic agitation. Good on all orientations. Non-crystallographic pits.
• Wright-Jenkins Etchant 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 m/min. Ultrasonic agitation not required. Good on all orientations. Faceted pits, good shelf life. • ASTM Dislocation Etchant 600 ml HF 30 ml HNO3 0.2 ml Br2 28 g Cu(NO3)2 + 3 H2O Dilute 1:10 with H2O Gallium Arsenide • 1-2% Br2 in ethanol H2SO4 : H2O2 : H2O (5:1:1) Good polishing etches • Fused KOH at 300C Good crystallographic dislocation pits on the (100) surfaces • 1 ml HF 2 ml H2O 8 mg AgNO3 1 g CrO3 Dislocation lines and striations Gallium Phosphide • 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 90C Etch rates: 100% Ge 4000 /min 80% Ge 1000 /min 60% Ge and less do not etch • H2O at 90C Etch rates: 100% Ge 200 /min < 60% Ge does not etch
• RCA SC-1 (NH4OH : H2O2 : H2O) at 75C
Etch rates: 100% Ge 4 um/min 80% Ge 9000 /min 60% Ge 500 /min 40% Ge 30 /min 20% Ge 10 /min 0% Ge 5 /min
Gold
• Aqua Regia: HCl : HNO3 (3:1) • Saturated solution of KI in H2O, 1 iodine crystal
Indium
• Reacts with acids (HCl) • Slow etch (1000 /min.) HNO3 : H2O (1:1) Hot HCl : HNO3 (3:1)
Indium Antimonide
• 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
Indium Phosphide
• 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.
Indium Tin Oxide (ITO)
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 50C.
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.
Iron Etchant
• H2SO4 : H2O (1:1) HCl : H2O (1:1) HNO3 : H2O (1:1)
• To remove rust: saturated oxalic acid solution.
Kovar
• Cleaner: Ferric ammonium sulfate 50 g H2SO4 125 ml HCl 150 ml
Heat to 60-80C
• Electrolysis: HCl and salt, alternating voltage. Kovar or carbon electrode 10% solution of HCl and a handful of salt
Lead
• Acetic acid : H2O (1:1) • Lead deposited on glass can be removed with dilute HNO3.
Lucite
• Softens with acetone • Acetone : formaldehyde
Magnesium
• Hot H2O : NaOH (10:1 by weight) Follow with H2O : CrO3 (5:1 by weight)
Magnesium Fluoride
• Dissolves (sometimes) in hot commercial ferric chloride.
Mercury
• Dissolves and reacts in HNO3. • To clean (purify), bubble air through mercury, filter and vacuum distill.
Molybdenum (Moly)
• Hot concentrated H2SO4 • Aqua Regia • HCl : H2O2 (1:1) (etches stainless steel) • Electrolysis 15 V ac moly or carbon electrode in pure H2SO4 • Dissolves in H2O : HNO3 : H2SO4 (1:1:1) cold • 45% formic acid : 45% H2O2 : 10% H2 Heat 2 min at 80C.
Monel
• Clean with 50% HNO3 : salt. Wash with water, then dip in 50% solution HNO3, then rinse in water, then dip in ammonium hydroxide and dry.
Nichrome
• HCl : copper chloride (1:1) • Ce(SO4)2 7.9 g Water 130 ml Add: 35 ml HNO3
Nichrome Etchant (Transene Co., Inc.)
• Contains nitric acid. Slightly irritating to skin. Wash area thoroughly if contacted.
Nickel
• HF : HNO3 (1:1) • Electrolysis: dc nickel electrode. H2SO4 or H3PO4. Reverse polarity several times, finish with nickel part as electrode.
Nickel Etchant (Transene Co., Inc.) • Contains nitric acid. Highly irritating to eyes, skin and mucous membranes, avoid inhalation of vapors. • Avoid contact with reducing agents.
Nickel Oxides
• HCl
Niobium
• HF: HNO3 (1:1)
P-Etchant (Phospho-Silicate Glass PSG Etchant)
• 3 parts HF 2 parts HNO3 60 parts DI water
Palladium
• HC l : HNO3 (3:1) Hot
Picein Wax
• Withstands all acids (including HF) • Thin/dissolve in trichloroethylene (TCE)
Piranha
• Excellent oxidant; removes most organic residues. 5 parts H2SO4 1 part H2O2 • Note: Always add peroxide to sulfuric acid, never vice versa! This is a self-heating solution.
Platinum
• HCl : HNO3 (3:1) Hot • Dissolves in Aqua Regia
Polish – Fairchild’s "Magic Polish"
• A – 2.5 g I2 in 1100 ml acetic acid B – HNO3 : HF (3:1) Add A to B (1:1) just prior to use.
Polysilicon Etchant (See also Silicon Etchant)
• 64% HNO3 / 33% H20 / 3% NH4F • 189 ml HNO3 / 96 ml H20 / 7.5 ml NH4F
Preferential Etch (See Dislocation Etchant Wright-Jenkins Etchant)
Rhodium
• HCl : HNO3 (3:1) Hot
Ruthenium
• HCl : HNO3 (3:1) Hot
Silicon Etchant – Polycrystalline Silicon (Bell Labs)
This solution is mixed and bottled by Microlab staff. Bottles are stored in the tall white acid cabinet next to sink 432C (old lab). • Etch rate 100 /sec 33% DI water / 3% NH4F / 64% HNO3 Bottle content: 960 ml DI water 75 ml NH4F (ammonium fluoride) 1890 ml HNO3 (nitric acid) Big Batch Silicon Etch (staff only) Big batch slicon etch is used by staff to rework Tylan dummies in the heated bath, left side of sink7. 48% DI water / 48% HNO3 / 2% HF at 50C Silicon Etchants – Single-Crystal (Sensors) • EDP Etchant for Single Crystal Silicon EDP etchant can be used on p-type wafers with <100> orientation, masked with either silicon dioxide or silicon nitride. It leaves a cleaner, smoother silicon surface with partial etch than KOH (see below). Heavy boron doping acts as an etch stop for EDP. Since EDP does not etch oxide, it is important to remember to dip off any native oxide from the silicon surfaces to be etched in HF solution. Etch rates and temperatures are given below. Complete instructions on the use of EDP are given in Chapter 1.3 of the lab manual. • Ethylenediamine N H2O(C H2)2N H2 1 mole = 50.10 g Pyrocatechol C6H4(O H2) 1 mole = 109.1 g Water H2O 1 mole = 18.02g • F&K Etchant – Finne & Klein, Bell Labs at Murray Hill. J. Electrochem. Soc., Vol. 114, No. 9, September 1967, pp. 965-970 Ethylenediamine 500 ml 35.1 mole% Pyrocatechol 88 g 3.7 mole% Water 234 ml 61.2 mole% Etch temp: 110C Etch Rate ratio: <100>:<110>:<111> 50:30:3 Initial Etch Rate: 28 m/hr Oxygen Exposure: up to > 50 m/hr Mask Resistance: SiO2 200 /hr This is the earliest reported EDP (or EPW) composition. It is generally used in the temperature range 100-118C. At lower temperatures it develops insoluble residues. This composition, as well as other uncatalyzed EDP compositions, tends to ‘age’ rapidly with exposure to oxygen. The etch rate increases with time to 50 m/hr and higher. The addition of pyrazine increases the <100> etch rate while making it less sensitive to oxygen expose. Pyrazine has a very small effect on the <111> etch rate so the <100>/<111> ratio increases with pyrazine content. The selectivity to boron content is reported by Reisman et al. to be similar for the F & K, B, and S etches. Also, the smoothness of the etching surface is improved by the addition of 0-6 g/L pyrazine. 8 g/> has shown some unevenness, <111> pyramids form, possibly due to the very high <100>/<111> etching ratio. IBM recommends 4 g of pyrazine to every liter of ethylene diamine for a smooth surface. • "B" Etchant – E. Bassous, IBM Research Center, Yorktown Heights, N.Y., U.S. Patent 3,921,916 (1975). Ethylenediamine 500 ml Pyrocatechol 80 g Water 160 ml Temperature Range: 100-118C Boiling Point: 18C <100> Etch Rate (with pyrazine added): Pyrazine per 500 ml Ethylenediamine 0 g 1.0 g 3.6 g at 100C 14 m/hr 42 m/hr 50 m/hr at 115C 26 m/hr 65 m/hr 75 m/hr • Mask Resistance: SiO2150 /hr Si3N4 80 /hr This composition with or without pyrazine provides residue-free etching above 100C. • "F" (Fast) Etchant – A. Reisman et al., IBM Research Center, Yorktown Heights, N.Y., J. Electrochemical Soc., Vol. 126, No. 8, August 1979, pp. 1406-1415. Ethylenediamine 500 ml Pyrocatechol 160 g Water 160 ml Temperature Range: 100-118C <100> Etch Rate (with pyrazine added): Pyrazine per 500 ml Ethylenediamine 0 g 1.0 g 3.0 g at 115C 27 m/hr 68 m/hr 81 m/hr • "S" (Slow) Etchant – A. Reisman et al., IBM Research Center, Yorktown Heights, N.Y., J. Electrochemical Soc., Vol 126, No. 8, August 1979, pp. 1406-1415. Ethylenediamine 500 ml Pyrocatechol 80 g Water 66 ml Temperature Range: 50-115C <100> Etch Rate (with pyrazine added): Pyrazine per 500 ml Ethylenediamine 3.6 g at 50C 4.5 m/hr at 75C 13 m/hr at 95C 26 m/hr at 105C 34 m/hr at 115C 45 m/hr • "M" (Medium) Etchant – Based on A. Reisman et al., as above. This etch is useful for etching below the boiling point in order to minimize agitation of the wafer. It etches at a rate between the "F" and "S" etches (hence "M" for medium). This etch prevents the formation of residues by the "F" etch by slowing oxidation of the surface through the reduction of the water content. Ethylenediamine 500 ml Pyrocatechol 160 g Water 125 ml Temperature Range: 105C <100> Etch Rate (with pyrazine added): Pyrazine per 500 ml Ethylenediamine 3.0 g at 115C 63 m/hr Other references: K.E. Petersen, Proc. IEEE, vol. 70, No. 5, May 1982, pp. 420-457. K.E. Bean, IEEE Trans. ED-25, No. 10, October 1978, pp.1185-1193. N.F. Raley etal., J. Electrochemical Soc., vol. 131, No.1, January 1984, pp.161-171. • KOH Etchant for Single Crystal Silicon KOH is a strongly anisotropic etch, preferring the 1-0-0 crystal plane. (The differential etch rate at 80C is on the order of 400:1.) Lines of rectangular areas to be etched must be parallel or perpendicular to the wafer flat. It is not possible to etch around rectangular geometries, i.e., leave islands of silicon, only to etch rectangular "cutouts" or windows, because the etchant rounds off inside corners. For this reason, if you are etching lines, they must not meet and form corners. 750 g KOH : 1500 ml H2O Temperature: 80C Etch Rate: 1 m/minute Silicon Dioxide Etchant (Buffered HF) • NH : HF4 (6:1) Etch rate: 1000 /min.
Silicon and Germanium Etchant
• CP-8 (fast) HNO3 : HF (5:3) CP-6 HNO3 : HF (5:1) CP-4 HNO3:HF : acetic acid (540 ml : 200 ml : 200 ml)
Silicon-Germanium (polycrystalline)
• H2O2 (30%) at 90C Etch rates: 100% Ge 4000 /min 80% Ge 1000 /min 60% Ge and less do not etch
• H2O at 90C Etch rates: 100% Ge 200 /min < 60% Ge doesn’t etch • RCA SC-1 (NH4OH: H2O2: H2O) at 75C Etch rates: 100% Ge 4 um/min 80% Ge 9000 /min 60% Ge 500 /min 40% Ge 30 /min 20% Ge 10 /min 0% Ge 5 /min Silicon Monoxide Etchant • Saturated solution of NaOH • THIN FILMS OF SiO REACT EXPLOSIVELY WILTH HF! Silicon Nitride Etchant • Hot phosphoric acid 150C
Silver
• NH4OH: H2O2 (1:1) • Remove with HNO3 • Clean with dilute HNO3 : NH4 (1:1)
Stainless Steel
• HF: HNO3 • Aqua Regia (depends upon grade of stainless steel) • HCl • Electrolytic in diluted HCl
Tantalum
• HF: HNO3 : H2O (1:1:1) 10 parts 30% KOH solution at 90C 1 part 30% H2O2
This mixture etches Ta2O5 and tantalum nitride at rates of 1000-2000 /min. Attacks photoresists and must therefore be used with a metal mask (e.g. gold).
Tin
• HF : HNO3 (1:1) • HF : HCl (1:1) • Clean with ammonium chloride • Remove with HCl
Titanium
• H2O : HF : HNO3 (50:1:1) • H2O : HF : H2O2 (20:1:1) • HF : H2O : ethylene glycol (20:10:220)
No heating necessary. Rate 1600 /min. • For evaporation, deposit Al before Ti to facilitate cleaning of glass cylinder. • Titanium dioxide is soluble in hot H2SO4. Titanium/Tungsten • Hydrogen peroxide Tungsten • 45% formic acid : 45% H2O2 : 10% H2O Heat 2 minutes at 80C. Bleach HNO3 : HF (1:10-15). This will not etch gold. Boiling hydrogen peroxide Fused NaOH (pellets, melted, 318C) • Electrolytic NaNO2 HF: HNO3 (1:1) 15 V ac with iron electrode (NaNO2 for polished finish) • Cleaning Boil in 20% solution NaOH for 15 minutes of HNO3 : HF (1:1) for a few seconds. • Potassium ferricyanide-based etch K H2PO4 34.0 grams KOH 13.4 grams K3Fe(CN)6 33.0 grams H2O 1.0 liter Etches tungsten without significantly attacking resist. You may use this for another application, and know it under a different name.
Turpentine
• Insoluble in water. Soluble in alcohol, chloroform, ether, acetic acid.
Vanadium
• H2 : HNO3 (1:1) • HF: HNO3 (1:1)

Westinghouse Etchant (Si Polish Etch)
• HF : acetic acid : HNO3 (3:5:15)
Zinc
• Reacts with HCl.
ZnO
• acetic acid : phosphoric acid : H2O (1:1:30)
The etch rate is approximately 5000 /min.
Zirconium
• H2O:HF : HNO3 (50:1:1) • H2O:HF : H2O2 (20:1:1)
See also: Dislocation Etches Secco Etch Silicon and Germanium Etchant, CP-4, 6 and 8
► Ref.: J. Electrochem. Soc. 119. 7, 1972.
12/90 K. Voros 9/97 K. Voros 10/99 J. Heck Rev. 00 10/03 S. Parsa Re. 01 12/06 K. Voros