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Birck Nanotechnology CenterPL SM RIE ETCHINGL SM RIE ETCHING
FUND MENT LS ND PPLIC TIONSUND MENT LS ND PPLIC TIONSUND MENT LS ND PPLIC TIONSUND MENT LS ND PPLIC TIONS
1
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u ne
.
2. Plasma Fundamentals
3. The Physics and Chemistry of Plasmas
. n so ropy ec an sms
5. The Etchin of Si and its Com ounds
6. The Etching of Other Materials
2
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Electron (e-)
Positive ion (Ar +, Cl+, SiF4+, CF3
+)
Positive ion mass in RIEs >>mass of electron
Radical (F, Cl, O, CF3)
bonding
3
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cont nue
Mean free ath avera e distance a article travels before collisions
(Dependent on the species)5
)(mT P
1atmosphere= 760 Torr = 1*105 Pascals
Pumping speed (S) [liters/sec]
Gas flow rate (Q) [Torr-liters/sec] or [sccm]
4
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asma acuum ystem
[Q]Mixed gasvalve
Gas lines
MFC box
Chamber Vacuum pump [S]
ga e
valve
V
Matching
network He backside
cooling
P tS-dP t ⋅V= chamber volume
PSQ:stateSteadyIn
Vdt
⋅=
=
5
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ec an ca umps
Pumping speed: 20-500 m3/hUltimate pressure: 1-10 mTorr
[BOC Edwards Dry Pump]
6
[Kurt J. Lesker]
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ur o umps
= -
Pumping speed: 50-3000 l/sUltimate pressure: 10-5-10-8 Torr
[Wiki]
7
[BOC Edwards Turbo Pump]
[TP controller]
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ass ow on ro er
Heater
Thermal-based flow meter
Q [sccm]
T1 T2
T2 – T1= Cp × Q
Cp is specific heat.
8
[HORIBASTEC]
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or as ox
Mixed gasline
as
lines
9
Panasonic MFC Box
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u oma c ressure on ro er& Gate Valve
Butterfly valvePendulum valve
P×=
10 [VAT]
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amp or ec ros a c uc
Electrostatic Chuck (ESC)Clamp
DielectricSi wafer
Base Plate
+++++ -------
------- +++++
+V -V+ -
He
11
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enera or a c ng e wor
RF Generator
NetworkPF PL
L
ZIn
PL=PF- PR
PR
ZS= 50Ω
In general: ZL≠ ZS
Purpose of Matching Network: Zin= ZS to
maximize power delivery from source.
Manual or Automatic
Matching NetworkZL
ZS C1L
12
[Gambetti]
ZIn
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u ne
.
2.2. Plasma FundamentalsPlasma Fundamentals
3. The Physics and Chemistry of Plasmas
. n so ropy ec an sms
5. The Etching of Si and its Compounds
6. The Etching of Other Materials
13 [Plasmas.org]
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a s asma
• Plasma is the fourth state of matter. It is an ionized gas, a gas
into which sufficient energy is provided to free electrons fromatoms or molecules and to allow both species, ions and
, .
14
.
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.
Vc=0 Vc= -100
XRed: n iBlack: ne
x
XVp
V(x)
XVp
-100v
16
Vp= a few vol ts
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.
VRF G p RF
G E
ZV (t) V (t)
Z Z
=
+
VRF(t)
ZE ZG
pE G G E
p RF
A A Z Z
V (t) V (t)
⇒
V(x)
X
VRF
17
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G
p RF
G E
Z
V (t) V (t)Z Z= + Actual RIE
E G G E
p RFV (t) V (t)VRF(t)
AEZGVp(t) ≈ 0
Ion transit time (Tion) is the time it takes the ion
to traverse the sheath.
1/Freq
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asc en s awDescribes how the breakdown voltage depends on electrode
separation and the pressure based on ideal gas law.
a (p.d)× V
l n(p.d) b=
+
600
800
p: Pressure
d: gap distance
a & b: constants
400
[Torr cm]100
10110-1
19
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n uc ve oup e asma
STS ASE and AOE systems
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y g ens y asmas Lower ion bombardment energies improve selectivity and reduce ion-
bombardment-induced physical damage of the wafer surface.
Lower ion ener ies however result in the lower etch rates and reduced
anisotropy!
,
due to high density plasmas.
.
21
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u ne
.
2. Plasma Fundamentals
3.3. The Physics and Chemistry of PlasmasThe Physics and Chemistry of Plasmas
. n so ropy ec an sms
5. The Etching of Si and its Compounds
6. The Etching of Other Materials
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ec ron- o ecu e o s ons An energetic electron colliding with a neutral etch gas molecule can
create any of the following processes:
Dissociation AB + e- A+B + e- CF4 + e- CF3+F+e
-
- - - -on za on e e r e r e
Often dissociation and ionization
Occur in one collision:
CF4 + e- CF3
++ F+ 2e-
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a ca s an ons n asmas Positive ions are very important for etching processes.
Radicals are more numerous than ions in gas glowdischarges because:
1. The electron energy required in order to break chemical bonds in themolecules is usually less than the energy required to ionize these
molecules.
2. Radicals have a longer lifetime in the plasma compared to ions becausean ion is almost always neutralized during a collision with a surfacewhile radicals often do not react with a surface and are reflected back
into the plasma.
24
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a s asma c ngCF4
Chamber
valveCF4
+ e- CF3
++ F+ 2e-
Si + 4F SiF4 (gas)Vacuum pump
Si Wafers
SiF4
CF3+, F
1- Need an etching gas
2- Establish a glow discharge
to form a volatile by-product
4- Pump away the volatile by-product
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y asma c ng
Compatible with automation
Anisotropic etching
rec se pattern trans er espec a y or ano-sca e eatures
Substrate
Isotropic etch Directional etch Vertical etch
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-Solid Etch Gas Etch Product
Silicon CF4,Cl2, SF6 SiF4, SiCl4, SiCl2SiO2, SiNx CF4, C4F8, SiF4, CO, O2, N2,
3, 6
Al BCl3/Cl2 Al2Cl6, AlCl3
Ti, TiN Cl2, CF4 TiCl4, TiF4
Organic Solids O2, O2/CF4 CO, CO2,
GaAs & III-V Cl2/Ar, BCl3 Ga2Cl6, AsCl3
2 2 2 2
27
Fe, Ni, Co, Au, Ag, Pt halides not volatile
Cu Cu3Cl3 is volatile above 200C
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z
28
[Handbook of Advanced Plasma Processing Techniques by Pearton]
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u ne.
2. Plasma Fundamentals
3. The Physics and Chemistry of Plasmas
..
5. The Etching of Si and its Compounds
6. The Etching of Other Materials
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• Etch rate Mask
e n on
• Mask (Photoresist, Metal, SiO2, …)
o
• Selectivity
Substrate
• Anisotropy degreeL
H
f A 1H≡ −
30
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eac ve e c ng s an so rop c process
Has very high selectivity!Si + 4F SiF4 (gas)
MaskSiF
4
Substrate
F
Isotropic etch
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process!Has lower selectivit and etch rate!
Si + Ar + Si + Ar +
Mask Ar +
Si
Substrate
32
Directional etch Vertical etch
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Has better selectivity and much higher etch rate!
Effect of Ions:
33[J. Appl. Phys. 50, 3189 (1979)]
Breaks bonds, raises temperature locally
on the surface and provides activation energy
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ewa ass va on
where:
(a) Either the carbon is provided by the feed gas through the chamber
3, 4 8.
(b) Or the carbon is provided by the erosion of the photoresist etch
mask.
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ewa ass va on
Oxidation of the sidewall by adding O2 gas.
35
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osc rocess
500um Silicon Etched by T.
Maleki using STS ASE
(8um/min etch rate)
Switching SF6 and C4F8
36
e s ewa m t c ness epen s to t e epos t on or pass vat on t me.
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empera ure e ec s n p asma e c ng
Wafer surface temp. depends on:- Chuck temperature
- on s energy an ens y
Reaction probability of radicals depends on substratetemperature.
or reducing reaction of F and Cl species with sidewalls.
37
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Notchin effect due to char in
oxide by ions
Can be reduced by using low
in pulsed modee-
+++++++
+
[J. Vac. Sci. Technol. B 19.5., Sep/Oct 2001]
RF biasoff
RF biason
38
STS ASE has LF pulsed generator!!
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Grass or micromaskin issue mainl
because of metal mask sputtered on
the wafer
spec a o epen en ec
Typically large open areas etch faster than
smaller features!
39
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Feature of the same size etch more slowly in dense patterns
Than in wide open areas!
c ng
Species
Density
x
40
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u.
2. Plasma Fundamentals
3. The Physics and Chemistry of Plasmas
4. Anisotro Mechanisms
5.5. The Etching of Si and its CompoundsThe Etching of Si and its Compounds
6. The Etching of Other Materials
41
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It’s a 6” ICP Bosch rocess dedicated
Gases:
for silicon etching!
66 44 88
OO22 ArAr
42
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Hi h etch-rate reci e:
Switchingtime
Pressure RF coil power RF bias power
Gas flow[sccm]
Etch 8.5 sec 40mTorr 2200W 40W 450 SF6
Passivation 3 sec 14mTorr 1500W 20W 200 C4F8
Etch rate ≈ 8µm/min for 500 µm feature
size with ~ 20% exposed area
High selectivity to PR≈ 75-100
43
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Low etch-rate reci e:
Switchingtime
Pressure RF coil power RF bias power
Gas flow[sccm]
Etch 13 sec 5mTorr 800W 25W 160 SF6
Passivation 7 sec 1mTorr 600W 20W 85 C4F8
Etch rate ≈ 2µm/min for 500 µm feature
size with ~ 20% exposed area
High selectivity to PR≈ 50Smooth side wall
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It’s a 6” ICP tool for etching of silicon,
oxide, nitrite, III-V, polymers, and some
metals!
SFSF66 CCHHFF33 ClCl22 OO22
CFCF44 ArAr BClBCl33 NN22
ases:
46
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ressure co
power
as
power 6 ow
[sccm]2 ow
[sccm]
Etch
Etch rate ≈ 1µm/min [Panasonic]
Pressure RF coil
power
RF bias
power
Cl2flow
[sccm]
O2 flow
[sccm]
SiEtch
0.8Pa 350W 50W 63 1.2
47
c ra e ≈ n m m n [Panasonic]
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power
power 3
[sccm]
Oxide 0.16 Pa 450W 50W 40
Etch rate ≈ 60 nm/min
2
Pressure RF coil
power
RF bias
power
CF4 flow
[sccm]
CHF3 flow
[sccm]
SiN 2 Pa 400W 30W 48 50 SiN3
Etch
Etch rate ≈ 100 nm/min
48
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It’s a simple RIE.
It can be used for etching silicon, oxide,nitrite, SiC, and polymers.
SFSF OO ArAr
Gases:
50
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power
power 2
[sccm] [sccm]
Ti 2 Pa 400W 100W 100 5
Etch rate ≈ 3 µm/min
52
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Pressure RF coil RF bias BCl3 flow Cl2 flow Ar flow
power power [sccm] [sccm] [sccm]
GaAs 3 Pa 900W 75W 50 150 20
Etch
Etch rate ≈ 5.3µm/minSelectivity to PR≈ 5
53 [Panasonic]
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Pressure RF coil RF bias BCl3 flow Ar flow
power power [sccm] [sccm]
GaAs 0.6 Pa 500W 50W 15 60
Etch
Etch rate ≈ 120 nm/min
54
[Panasonic]
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How to Increase Etch Rate?How to Increase Etch Rate?
Increasing Main Coil Power
Increasing Platen or Bias Power Increasing Process pressure
Increasing Etch cycle time (for Bosch process)
How to Reduce Sidewall Roughness/Scallops?How to Reduce Sidewall Roughness/Scallops?
Keep etch and deposition cycle times to minimum, (for Bosch process)
Reduce process pressure
Reduce etch gas flow
, , ,
How to Increase Selectivity?How to Increase Selectivity?
56
Reducing platen power
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How to Straighten the Profile?How to Straighten the Profile?
Using low pressure
Decreasing etch cycle time or increasing deposition cycle time (for Bosch process)
Optimizing platen power
57
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Trends for
Controllingprocess results
Etchrate
Profile Selectivity SidewallRoughness
Etch gas increase ↑↑ ↑ ↑
Pressure increase ↑↑ ↑ ↑
Etch Coil Powerincrease
↑ ↑ ↑
Platen Power
increase
↑↔ ↓ ↔
58
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c now e gmen
We would like to thank faculty members, staff, andstudents for their support.
Questions?Questions?
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