1. 1
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Feature Profile Evolution and Microscopic Uniformity
during Polysilicon Gate Etching
in Cl2/O2 and Cl2/HBr/O2 Plasmas
ICRP / SPP
25 / Jan / 2006
Yugo Osano1
,
Masahito Mori2
, Naoshi Itabashi2
,
Kazuo Takahashi1
, Koji Eriguchi1
, Kouichi Ono1
1
Kyoto university, Japan
2
Central Research Laboratory, Hitachi Ltd., Japan

2. 2
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Outline
1. Objective
2. Simulation Model
3. Etching Experiments
4. Profile Evolution
5. Conclusions

3. 3
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Objective
 Development of a high precision, accurate
model to simulate the feature profile
evolution of sub-100 nm poly-Si gate etching
and shallow trench isolation (STI) process.
 Cl2/O2 and Cl2/HBr/O2 plasmas – poly-Si
substrate
Poly-Si gate etching
Modeling and Simulation
 Understand plasma-surface interactions
− Deposition of etch products, Surface oxidation
− Forward reflection of ions from surfaces
 Suppress profile anomalies
− Sidewall tapering
− Microtrench
mask
poly-Si
SiO2
sidewall tapering
microtrench
Profile anomalies

4. 4
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Outline
1. Objective
2. Simulation Model
3. Etching Experiments
4. Profile Evolution
5. Conclusions

5. 5
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Model: (1) Particle Transport and Surface Configuration
 Monte Carlo particle simulation
Cl+
Cl
SiCl4
Cl+
Cl
Cl
SiCl2
O
O
Desorption of etch products
Simulation domain
Mask
Si
SiCl4 Cl+
Cl
Vacuum
Solid(Si)
L = ρSi
－ 1/3
= 2.719 Å
( ρSi is atomic density)
 One cell represents One Si atom.
SiO2
L
L
SiCl2O
Cl+
Forward reflection
Adsorption
Ion penetration
Diffusive reflection

6. 6
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Model: (2) Surface reactions
 Adsorption
− Cl neutrals ： Si(s) + xCl(g) → SiClx(s)
− O neutrals (surface oxidation): Si(s) + yO(g) → SiOy(s)
− SiClx(s) + O(g) → SiClx–2O(s)
 Spontaneous chemical etching
− The etch rate is a function of substrate temperature Ts
− SiCl3(s) + Cl(g) → SiCl4(g) ↑
 Ion-enhanced etching
− Synergy of Cl+
ions and Cl neutrals
− SiCl4(s) [impact of Cl+
] → SiCl4(g) ↑
 Deposition of etch products (Sp: sticking probability)
− SiCl4(g) → SiCl4(s) [Sp ~ 0.02] (desorbed from surfaces)
− SiCl2(g) → SiCl2(s) [Sp ~ 0.1] (incident from the plasma)
 Deposition of (oxidized) etch by-products
− SiCl2O(g) → SiCl2O(s) [Sp ~ 0.1] (incident from the plasma)
Cl+
Cl
SiCl4
Cl+
SiCl2
O
SiCl2O
SiClx layers
(Surface reaction layers)
SiClxOy layers
(Sidewall passivation)

7. 7
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Model: (3) forward reflection of Cl+
ions from Si surfaces
Cl+
target Si atom
p : impact parameter
calculation of scattering angle ψ
ψ
v
p
∫
∞






−−
−=
min 21
2
2
2 )(
1
2
r
C r
p
E
rV
r
pdr
πψ
sidewall surface
L = 2.7 Å
Cl - Si :
Stillinger-Weber potential
rcutoff = 3.5 Å
rcutoff
z
x
y
3D-calculation
V(r)p

8. 8
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Sample trajectories of reflected ions
Si (solid)
Vacuum
Cl+
ion ： (Ei = 50
eV)
incident angle
θi = 75° θi
A part of ions penetrates into
the substrate.
feature sidewall
Width (nm)
Depth(nm)
Si atoms are allocated at 2D
lattices (for simplification).
The scattering angle is
determined by an impact
parameter on incidence.
z
x
y
3-dimensional deviation
leads to the dispersion of
reflected angles.

9. 9
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Outline
1. Objective
2. Simulation Model
3. Etching Experiments
4. Profile Evolution
5. Conclusions

10. 10
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Etching experiments
 Use an UHF-ECR plasma reactor
− pure Cl2, Cl2/O2, Cl2/HBr/O2
− total gas flow rate: 100 sccm
− gas pressure: 1.0 Pa
− 450 MHz UHF / 500 W incident power
Cl2/O2 = 100 / 0 (pure Cl2)
Cl2/O2 = 80 / 20
gas flow ratio dependence RF bias power dependence
10 W
80 W
0.2 Pa
5.0 Pa
gas pressure dependence
• substrate temperature
• total gas flow
• input power
......

11. 11
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Outline
1. Objective
2. Simulation Model
3. Etching Experiments
4. Profile Evolution
5. Conclusions

12. 12
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Profile evolution:
(1) effects of forward ion reflection
No reflection
With reflection
With reflection & etch products
mask
Si
SiO2
30nm 50nm 100nm 200nm 500nm
Space width
Γi ＝ 1.0×1016
cm–2
s–1
Γn ／ i ＝ 100
(Cl neutral reactant / C ｌ +
ion flux)
Ion incident energy Ei = 100 eV
Without O2 / etch products from the plasma
Round profiles at the corner are
suppressed.
Cl+
Deposition of etch products
Microtrenches formed by ions
reflected from sloped sidewalls
every 5 s
Sticking probability: Sp = 0.02

13. 13
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Profile evolution: (2) effects of additive O2
Mask
Si
SiO2
Cl2/O2 = 100 / 0 (pure Cl2)
Cl2/O2 = 80 / 20
50 nm
50 nm
Open
space
Open
space
200 nm
space
200 nm
space
pure Cl2
Γo
0
/ Γi
0
= 1.0 (O / Cl+
)
Γp
0
/ Γi
0
= 1.3 (SiCl2O / Cl+
)
every 5 s
O2 added
Inverse RIE lag
O
SiCl2O
inwardly bent
outwardly bent
200nm500nm

14. 14
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Formation of passivation layers
50nm
Open
Space
200nm
space
~11 nm
micro-
trenching
Cl2/O2=80/20
Passivation layers
~9 nm
mask
poly-Si
SiO2
mask mask
poly-Si poly-Si
poly-Si
vacuum
vacuum vacuum
Passivation layers (dense O)
red: O
green: Cl
Surface reaction layers (rich Cl, sparse O)
200nm500nm

15. 15
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Profile evolution:
(3) effects of rf bias power
Ei = 50 eV
Ei = 100 eV
Ei = 200 eV
Every 5 sec
Every 5 sec
Every 2.5 sec
Without O2 / etch products from the plasma
The microtrenches are deepest at
a middle Ei = 100 eV because of:
Significant sidewall tapering
at a lower Ei = 50 eV
– sloped sidewalls
– angular spread of incident ions

16. 16
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
(a) Ei = 50 eV, every 5 s
Mask
Si
SiO2
(b) Ei = 100 eV, every 5 s (c) Ei = 200 eV, every 2.5 s
Formation of microtrenches
(a) 10 W (b) 50 W (c) 80 W

17. 17
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Development of Cl2/HBr/O2 etching model
Jin, Vitale, Sawin (2002)
ExperimentsModeling
• gas flow ratio
• rf bias power
• gas pressure
......
Dependence of:
z
x
y
Br+
Si
• Forward reflection of Br+
ions
• Etch yield Y(Si/Br)
• Angular dependence of Y(Si/Br)
• Effects of H atoms
To be introduced:
Angular dependence of Y(Si/Br)

18. 18
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Outline
1. Objective
2. Simulation Model
3. Etching Experiments
4. Profile Evolution
5. Conclusions

19. 19
Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas
Conclusions
 A model has been developed to simulate the profile evolution of the nanometer-scale
gate etching in Cl2 / O2 plasma. The features are:
− The feature geometry presented by atomic size cells
− The binary collision model for forward reflection of ions
 The numerical results gave similar tendencies to the etching experiments, which were
performed by varying:
− The percentage of additive O2
− The rf bias power
 The model is expected in the fabrication of sub-100nm devices:
− to optimize etching recipes
− to predict profile anomalies