5/21/2018 Wet Etching
1/15
Etching
Basics of Etching technology
Wet etching-----dielectrics, semiconductors, & metal
----- so rop c an so rop c e c ng
Dry etching (RIE)
Electrochemical polishing
Etching
Three steps in etching process?
Two kinds of Etching?
5/21/2018 Wet Etching
2/15
(1) Diffusion (3) Diffusion
eac on
dry & wet etching
Gas phase(chemical, and physical)
Liquid phase(chemical)
Etching profiles
5/21/2018 Wet Etching
3/15
5/21/2018 Wet Etching
4/15
5/21/2018 Wet Etching
5/15
Profiles: isotropic & anisotropic
Applications: Si, Silicon nitride, silicon dioxide, metal
Controls: doping, electrochemical, film quality, mask materials
Wet Etching of Metals
Aluminum - Aluminum Etchant Type A from Transene Co., Inc. is a mixture ofphosphoric acid, acetic acid and nitric acid. Etch Rate is about 1 min for 2000 .
interlevel dielectric. When the underlying layer is aluminum and the insulatinglayer is glass the preferred etchant is 5 parts BOE and 3 parts Glycerin. (straightBOE etches aluminum
Copper - Ferric Chloride or mix Etchant from 533 ml water, add 80 ml Na2S2O3,Sodium Persulfate, (white powder, Oxidizer), prepare in glass pan, place pan on
~ .Copper Coated Board about 30 min.
Platinum7ml HCl, 1ml HNO3, 8 ml H2O at 85 C approximate etch rate 450/min.
Chromium - CR-9 Etch, Cyantek Corp.- o c .
5/21/2018 Wet Etching
6/15
Profiles: isotropic & anisotropic
Applications: Si, Silicon nitride, silicon dioxide, metal
Controls: doping, electrochemical, film quality, mask materials
Wet Etching of Dielectrics
Wet Etching of Silicon OxideWet Etching of Silicon Oxide
BY HF with or without the addition of ammonium flouride
(NH4F).
The addition of ammonium flouride creates a buffered HF solution (BHF) alsocalled buffered oxide etch (BOE).
The addition of NH4F to HF controls the pH value and replenishes the depletion oft e uor e ons, t us ma nta n ng sta e etc rate.
SiO2 + 6HF = H2SiF6 + 2H2O
Types of silicon dioxide etchants:
49% HF - fast removal of oxide, poor photoresist adhesion
BHF - medium removal of oxide, with photoresist mask
Dilute HF - removal of native oxide, cleans, surface treatments
HF/HCl or HF/Glycerin mixtures special applications
Buffered HF Etching
7:1 NH4F/HFgives about
1000 /min etch rateat room temperature
5/21/2018 Wet Etching
7/15
Etching tools - HF
SiO2 etching is performed on HF bench using Teflon tools
Teflon Chemical Process Wafer
Cassette & container
Fluoroware A182-60MB orPerFluoroAlkoxy (Teflon)
High resistance to chemicals and
temperatureCan be used in wet chemistryprocesses (RCA clean, BOE etch,
HF Bench
wet nitride etch, wet aluminumetch)
BOE (7:1) 20A/min,
1:1 HF:HCL 120A/min,
49% HF 140 A/min165C Phosphoric Acid 55A/min (BOE dip first to removeoxynitride layer), etches silicon dioxide at 10 /min ands con
Hot phosphoric acid etch of nitride can not use photoresist as an etchmask. One can use a thin patterned oxide (or oxynitride) to act as the etchmask. Etch rate for silicon is even lower than the etch rate of oxide.
Silicon Nitride Etching with Hot H3PO4
5/21/2018 Wet Etching
8/15
Etching tools Hot Phos
Warm up Hot Phosphoric Acid
pot to 175C
Use Teflon boat to lace wafers
Hot Phos Bench
in acid bath 3500 +/-500 50 minutes
1500 +/- 500 25minutes
Etch rate of ~80 /min
Rinse for 5 min.
Water rinse
Wet Etching of Silicon
Anisotropic etching
HNA (Hydrofluoric acid + Nitric acid + Acetic acid)
Base:
KOHetch
NaOH etch
EDP (Ethylene Diamine Pyrocatechol) etch
5/21/2018 Wet Etching
9/15
5/21/2018 Wet Etching
10/15
Orientation
Pr imary f lat or ien tat ion
Secondary flat locations--
p-type 90 clockwise from primary flat
n-type 45 clockwise from primary flat
n-type 180 clockwise from primary flat
5/21/2018 Wet Etching
11/15
Anisotropic Wet etching
Convex corners areundercut
Concave corners stopat [111] intersection
5/21/2018 Wet Etching
12/15
100
(100) Si Etching rate
5/21/2018 Wet Etching
13/15
Etching selectivity en 2 s use as a mas ng ayerwith a KOH solution both temperature
and concentration should be chosen as low
as ossible.
KOH etch rate is about 50 to 55 m/minat 72 C and KOH concentrations between
10 and 30 weight %.
The Si/SiO2 etch ratio is 1000:1 for 10%KOH at 60 C, at 30% it drops to 200:1.
lightly doped silicon decreases for doping
concentrations above 1E19 and at 1E20
the relative etch rate is 1/100 for 10%
concentration. (on (100) wafer the angle is50.6)
Si3N4 is the perfect masking material forKOH etch solution. The etch rate for
Silicon Nitride appears to be zero.
5/21/2018 Wet Etching
14/15
KOH etching rate on B-dopingDoping
Revisit:
- 2+ -
Si SiHO OH[ ] 2
4H2O + 4e- = 4(OH)- + 2H2
Si + 2 (OH)- = Si(OH)22+ + 4e- (1)
In Boron doped Si, particularly the degenerated doped Si (p++ - Si),Fermi level close to valance band and man , man holes in Ev
Ec
Transfer to conduction band
recombination
4H2O + 4e- = 4(OH)- + 2H2 (2)
5/21/2018 Wet Etching
15/15
Top Related