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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, Japan2 Central Research Laboratory, Hitachi Ltd., Japan

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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

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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-SiSiO2

sidewall tapering

microtrench

Profile anomalies

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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

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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 domainMask

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

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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+

SiCl2O

SiCl2O

SiClx layers(Surface reaction layers)

SiClxOy layers(Sidewall passivation)

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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

v

p

min 21

2

22 )(

1

2r

C r

pE

rVr

pdr

sidewall surface

L = 2.7 Å

Cl - Si : Stillinger-Weber potential

rcutoff = 3.5 Å

rcutoff

z

xy

3D-calculation

V(r)p

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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 i = 75° i

A part of ions penetrates into the substrate.

feature sidewall

Width (nm)

Dep

th (

nm)

Si atoms are allocated at 2D lattices (for simplification).

The scattering angle is determined by an impact parameter on incidence.

z

xy

3-dimensional deviation leads to the dispersion of reflected angles.

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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

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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......

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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

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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 500nmSpace width

i ＝ 1.0×1016 cm–2 s–1

n ／ 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

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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

Γo0 / Γi

0 = 1.0 (O / Cl+)Γp

0 / Γi0 = 1.3 (SiCl2O / Cl+

)

every 5 s

O2 added

Inverse RIE lag

O SiCl2O

inwardly bent

outwardly bent

200nm500nm

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Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 and Cl2/HBr/O2 Plasmas

Formation of passivation layers

50nm

OpenSpace

200nmspace

~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

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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

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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

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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

xy

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)

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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

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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