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8/7/2019 rca esquemaproceso
1/12
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Cleaning
1.Clean Factories
2.Wafer Cleaning
3.GetteringFrom Intel
75% of Yield loss due
to particles
3-pronged appraoch:
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
1. Clean Factories
Class of the clean room
From Middleman
Laminar
Flow
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
2. Wafer Cleaning It is important to have clean wafers at all stages of fabrication. Cleaning is especially important before any high temperature
process.
Improper cleaning can result in yield loss and process variability
Cleaning comprises roughly 1/4 of the IC process steps
Cleaning
solution
Wafers
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Typical Chemicals InvolvedChemical Name
H2O (DI) De-Ionized water
H2SO4 Sulfuric Acid
H2O2 Hydrogen Peroxide
H2O Water
HF Hydrofluoric Acid
NH4OH Ammonium Hydroxide
HCl Hydrochloric Acid
IPA Isopropyl alcohol
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Si SurfacesThe chemical nature of the Si surface affects reactivity with contaminants
Si Si Si Si
Si Si Si Si
Si Si Si Si
Bare Si
Si Si O
Si Si OO
O Si
Si SiO
O Si
O O O O
Si SiO Si SiO
O O O O
Si Si O
Si Si OO
O Si
Si SiO
O Si
O O O O
Si SiO Si SiO
O O O O O O O OH H H H H H H H
Silicon oxide Silanol on silicon oxide
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Generic Contaminated Si Surface
Silicon Wafer
Silicon Oxide
Water
Air
Absorbed gas
Particles
Nonpolar organics
Polar Organics
Water
Oxide
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
De-ionized (DI) Water Ions are reactive. They can make liquid products from solids. Theycan also bond to the solid.
Normal tap water has many different types of ions.
If we want to clean wafers without causing any reactions, we can notuse tap water. We need special water which is free of ions.
De-ionized waterTap water
Na+
Cl-
Na+
K +
K +
Cl- F-
F-
Ion free water is
called
De-ionized water
orDI water.
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Relative Strength of Binding Forces Important forAqueous Cleaning
Adsorption Type Energy (eV)
Chemical Bonds
Ionic
Covalent
Metallic
Physical Forces
H bonds
dipole-dipole
Despersion
6-11
0.6-7
1-3.5
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
General Scheme - RCA CleanH2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
Sulfuric Clean; Organics 10 to 1; Oxide Etch
SC 1; Particles SC 2; Surface Metals
100 to 1; Oxide Etch Wafer dry
W. Kern and D.A. Puotinen, Cleaning solutions based on hydrogen peroxide in
silicon semiconductor technology, RCA Rev. 31, 187-206 (1970).
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Individual Cleaning Processes Lets see the purpose of each
of these steps.
Sulfuric Clean(Piranha)
Recipe: H2SO4 /H2O2 /125oC
Removes: Organics
Hydrogen peroxide (H2O2) provides the chemical action for the
sulfuric clean.
H2O2 has two oxygens.
It easily gives up one of its oxygen atoms.
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
OHO
H Hydrogenperoxide
(H2O2)
OHO
H
(H2O2)H
O
H(H2O )
product formed byusing other oxygen
from H2O2
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Sulfuric Clean (Piranha) Action: Organics are mainly carbon (C) and hydrogen (H)
Hydrogen peroxide (H2O2) wants to give up one of its
oxygen atoms. It readily produces CO2( g ) and H2O( l ) on
reacting with organics.
CO2( g )
H2O( l )
OHO
H
O
HO
H
C C C
HHOH
O
H
Hydrogen
peroxide
(H2O2)
Organic Impurity OHO
H
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
DI Water Rinse Recipe: H2O* / Room Temperature
Removes: Cleaning chemicals
and reaction products from an
earlier wet clean.
Action:
Dissolves chemicals and reaction products
A DI water rinse may also be used to stop the action of
cleaning chemicals.
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Oxide Etch Recipe: H2O / HF Removes: Oxide (SiO2)
Action:
HF reacts with SiO2 to
make liquid products.
SiO2( s ) + 6HF( l )-> H2SiF6( l )+ 2H2O( l )
The etch rate (or reaction rate of HF with oxide) can be
slowed by adding more water. The lowers the concentration
of HF.
A DI water rinse is used to stop the action of acid after thiscleaning step.
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
P-Si
N-SiN-Si
(10:1) Oxide Etch The wafer goes through many processing steps before gate oxide
can be deposited.
A thick layer of poor quality oxide is grown in these steps to help ion
implant.
Now we need to remove this poor quality oxide before we can grow
high quality gate oxide.
This removal is done in the (10:1) Oxide Etch. A high concentration
of HF is used because we have a lot of oxide.
P-Si
N-SiN-Si
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
(100:1) Oxide Etch: Importance The silicon at the bottom of contact holes reacts with oxygen in theair. It forms a thin layer of oxide. This oxide is called native oxide.
We want to remove the native
oxide. This allows the metal to
make a good contact with the
source and drain.
The trick here is:
To remove the oxide at the bottom (native oxide)
Not to remove much of the oxide from the sides of the contact
holes.
This removal is done in the (100:1) Oxide Etch. A low concentrationof HF is used because we dont want to remove oxide from the sides.
Native oxide
Contact hole
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Particle Removal: SC-1 Particles from processing
steps, machinery or handling
can contaminate wafers.
These particles are removed
by the SC-1 clean.
The name of the solution used in this clean is Standard Clean -1
or SC-1 solution. Also called APM or RCA-1.
The cleaning solution is a mixture of five parts de-ionized
water(H2O*), one part ammonium hydroxide (NH4OH ) and one
part hydrogen peroxide(H2O2 ).
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
SC-1 Clean Recipe: H2O / NH4OH / H2O2 80oC(5:1:1)
Removes: Particulates
Action:
This works in two ways
1) By repulsion of like charges
Both the particle and the wafer get negatively charged when
dipped in the solution. The particle is repelled from the surface.
- - - - - - - - - - - - - - - - - -
- - -
- -
Negativelycharged
surface
Negatively
charged particle
moves away
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
SC-1 Clean - Electrochemistry!
Prefers
Re
duced
Form
Prefers
Ox id
ized
Form
Reduction Half reaction E0O 3+ 2H
++2e
-O2 +H2 2.07
H 2O2 + 2H+
+2e-2H2O 1.77
Cu2++ 2e
-Cu 0.34
Fe3++ 3e
-Fe -0.17
Ni2++ 2e
-Ni -0.25
Cr3++ 3e
- Cr -0.71
SiO2 + 4H++ 2e
-Si +2H2O -0.84
Mn2++ 2e
-Mn -1.05
Al3++ 3e
-Al -1.66
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
SC-1 Clean2) By chemical actioni) Hydrogen peroxide gives its extra oxygen to the silicon
substrate and makes a thin oxide film;
Si( s ) + 2 H2O2( l )-> SiO2( s )+ 2 H2O( l ).The oxide film lifts the particles.
ii) Ammonium Hydroxide etches the oxide and loosens theparticles; 2NH4OH( l ) + SiO2( s )-> (NH4)2SiO3( l ) + H2O( l )
iii) The loose particles are removed by shaking.
( i ) ( ii ) ( iii )
Substrate
Particle
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Surface Metal Removal: SC-2 Surface metal contaminants
are first oxidized
They are then removed by
reaction with hydrochloric
acid.
The name of the solution used in this clean is Standard Clean -2
or SC-2 solution. Also called HPM or RCA-2.
The cleaning solution is a mixture of six parts de-ionized
water(H2O*), one part hydrochloric acid (HCl) and one part
hydrogen peroxide(H2O2 ).
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
SC-2 Clean - Electrochemistry!
Prefers
Re
duced
Form
Pr
efers
Ox
idized
Fo
rm
Reduction Half reaction E0
O 3+ 2H+
+2e-O2 +H2 2.07
H 2O2 + 2H+
+2e-2H2O 1.77
Cu2++ 2e
-Cu 0.34
Fe3++ 3e
-Fe -0.17
Ni2++ 2e
-Ni -0.25
Cr3++ 3e
- Cr -0.71
SiO2 + 4H++ 2e
-Si +2H2O -0.84
Mn
2+
+ 2e
-
Mn -1.05
Al3++ 3e
-Al -1.66
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
SC-2 Clean Recipe: H2O / HCl / H2O2 80
oC
(6:1:1)
Removes: Surface metal ions
Action:
hydrochloric acid reacts with the ions and removes them.
Al +++Cl -
Cl -
Cl-
Chloride ions from HCl react with
aluminum ion and carry it away
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Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
Vapor Dry Recipe: Isopropyl Alcohol (IPA)
Removes: water from wafers
Action:
Alcohol vapors displace
water from surface
IPA Vapors
Drop of
water
IPA displaces water IPA evaporates
The alcohol evaporates more easily than water. It leaves a dry surface
H2SO4H2O2125oC
H2O Rinse
Room Temp
H2O / NH4OH /H2O2(5:1:1)
80oC
H2O Rinse
Room Temp
H2ORinse
H2O / HCl /H2O2(6:1:1)
80oC
H2O Rinse
Room Temp
Alcohol (IPA)
Dry
Room Temp
H2O : HF
(10 : 1)
Room Temp
H2O Rinse
Room Temp
H2O : HF
(100 : 1)
Room Temp
Prof. Milo Koretsky
Chemical Engineering Dept .
Cleaning
3. Gettering
Metals:
Traps on back
or in bulk
Alkali ions:
Dielectric layer
on topside SiO2 Precipitates
Damage induced