sio 2 etch rate and profile control using pulse power in capacitively coupled plasmas* sang-heon...

SiO2 ETCH RATE AND PROFILE CONTROL USING PULSE POWER IN CAPACITIVELY

COUPLED PLASMAS*

Sang-Heon Songa) and Mark J. Kushnerb)

a)Department of Nuclear Engineering and Radiological Sciences University of Michigan, Ann Arbor, MI 48109, USA

[email protected]

b)Department of Electrical Engineering and Computer ScienceUniversity of Michigan, Ann Arbor, MI 48109, USA

[email protected]

http://uigelz.eecs.umich.edu

September 21st, 2011

* Work supported by DOE Plasma Science Center and Semiconductor Research Corp.

AGENDA

Motivation for controlling f()

Description of the model

Typical Ar/CF4/O2 pulsed plasma properties

Etch property with different PRF

Constant Power with DC Bias

Constant Voltage with DC Bias

Without DC Bias

Concluding remarks

University of MichiganInstitute for Plasma Science & Engr.

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CONTROL OF ELECTRON KINETICS – f() Controlling the generation of reactive species for technological

devices benefits from customizing the electron energy (velocity) distribution function.


, , , , ,, , ,

df v r t qE r t f v r tv f r v f v r t

dt m tx ve c

1 2

0

2, , ,ij

ek r t f r t d

m

,

,,k

e ij ji j

dN r tn k r t N

dt

e + CF4 CF3 + F + ek

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ETCH RATE vs. FLUX RATIOS


Ref: D. C. Gray, J. Butterbaugh, and H. H. Sawin, J. Vac. Sci. Technol. A 9, 779 (1991)

Flux Ratio (F/Ar+) Flux Ratio (CF2/Ar+)

Etc

hin

g Y

ield

(S

i/Ar+

)

Etc

hin

g Y

ield

(S

i/Ar+

)

Large fluorine to ion flux ratio enhance etching yield of Si.

Large fluorocarbon to ion flux ratio reduce etching yield of Si.

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Ref: K. Ono, M. Tuda, H. Ootera, and T. Oomori, Pure and Appl. Chem. Vol 66 No 6, 1327 (1994)

Large chlorine radical to ion flux ratio makes undercut in etch profile due to too much chemical reactions.

Etch profile result in ECR Cl2 plasma after 200% over etch with different flux ratios

p-Si p-Si


ETCH PROFILE vs. FLUX RATIOS

Flux Ratio (Cl / Ion) = 0.3 Flux Ratio (Cl / Ion) = 0.8

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HYBRID PLASMA EQUIPMENT MODEL (HPEM)

Fluid Kinetics Module: Heavy particle and electron continuity, momentum,

energy Poisson’s equation

Electron Monte Carlo Simulation: Includes secondary electron transport Captures anomalous electron heating Includes electron-electron collisions

E, Ni, ne

Fluid Kinetics ModuleFluid equations

(continuity, momentum, energy)Poisson’s equation

Te, Sb, Seb, kElectron Monte Carlo Simulation


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MONTE CARLO FEATUREPROFILE MODEL (MCFPM) The MCFPM resolves the surface

topology on a 2D Cartesian mesh.

Each cell has a material identity. Gas phase species are represented by Monte Carlo pseuodoparticles.

Pseuodoparticles are launched with energies and angles sampled from the distributions obtained from the HPEM

Cells identities changed, removed, added for reactions, etching deposition.

PCMCM

Energy and angular distributions for ions

and neutrals

MCFPM

Etch rates and profile


Poisson’s equation solved for charging

HPEM

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REACTOR GEOMETRY: 2 FREQUENCY CCP

2D, cylindrically symmetric

Ar/CF4/O2 = 75/20/5, 40 mTorr, 200 sccm

Base conditions

Lower electrode: LF = 10 MHz, 500 W, CW

Upper electrode: HF = 40 MHz, 500 W, Pulsed


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PULSE POWER

Time = 1/PRF

Duty Cycle

Power(t)

Pmin

0

1dttPPave

Pmax


Use of pulse power provides a means for controlling f().

Pulsing enables ionization to exceed electron losses during a portion of the ON period – ionization only needs to equal electron losses averaged over the pulse period.

Pulse power for high frequency.

Duty-cycle = 25%, PRF = 50, 100, 200, 415, 625 kHz

Average Power = 500 W

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Typical Plasma Properties

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PULSED CCP: ne, Te, f()


Pulsing with a PRF and moderate duty cycle produces nominal intra-cycles changes [e] but does modulate f().

[e]

Te

MIN MAX

f()

ANIMATION SLIDE-GIF

40 mTorr, Ar/CF4/O2=75/20/5 LF = 10 MHz, 500 W HF = 40 MHz, pulsed 500 W PRF = 100 kHz, Duty-cycle = 25%

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ELECTRON DENSITY CW


Duty = 50%

Duty = 25%

MIN MAX

ANIMATION SLIDE-GIF

At 50% duty, the electron density is not significantly modulated by pulsing, so the plasma is quasi-CW.

At 25% duty, modulation in [e] occurs due to electron losses during the longer inter-pulse period.

The lower duty cycle is more likely to reach higher value of electron density.

40 mTorr, Ar/CF4/O2=75/20/5 LF = 10 MHz, 500 W HF = 40 MHz, 500 W (CW or pulse)

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ELECTRON SOURCES BY BULK ELECTRONS


CW

Duty = 50%

Duty = 25%

The electrons have two groups: bulk low energy electrons and beam-like secondary electrons.

The bulk electron source is negative due to electron attachment and dissociative recombination.

At the start of the pulse-on cycle, is there a impulsive positive electron source due to the overshoot of E/N.

MIN MAX

40 mTorr, Ar/CF4/O2=75/20/5 LF 500 W, HF 500 W

ANIMATION SLIDE-GIFSHS_MJK_ISPC

ELECTRON SOURCES BY BEAM ELECTRONS


CW

Duty = 50%

Duty = 25%

MIN MAX

40 mTorr, Ar/CF4/O2=75/20/5 LF = 10 MHz, 500 W HF = 40 MHz, 500 W (CW or pulse)

The beam electrons result from secondary emission from electrodes and acceleration in sheaths.

The electron source by beam electron is always positive.

The electron source by beam electrons compensates the electron losses and sustains the plasma.

ANIMATION SLIDE-GIFSHS_MJK_ISPC

Etch Properties

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0.0

1.0

2.0

3.0

4.0

5.0

625 415 200 100 kHz

F / POLY FLUX RATIO: CONSTANT POWER

F to polymerizing flux ratio is largest at 200 kHz of PRF.

40 mTorr, Ar/CF4/O2=75/20/5, 200 sccm LF 10 MHz 500 W, Pulsed HF 40 MHz 500 W


ETCH PROFILE IN SiO2 & IEAD: CONST. POWER


40 mTorr, Ar/CF4/O2=75/20/5, 200 sccm LF 10 MHz 500 W, Pulsed HF 40 MHz 500 W

Angle (degree)

En

erg

y (

eV

)

Etch rate is fastest at 200 kHz PRF with larger ion energy and F to polymerizing flux ratio.

Cycle Average IEAD

He

igh

t (

m)

Width (m)

100 kHz CW 415 200 415 200 100 CW

ANIMATION SLIDE-GIF

Etch Profile (300 sec)

CD70 nm

-64 V -92 V -107 V -134 VBias:

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0.0

1.0

2.0

3.0

4.0

5.0

CW 625 415 200 50 kHz

0.0

1.0

2.0

3.0

4.0

5.0

CW 625 415 200 100 kHz

F / POLY FLUX RATIO: CONSTANT VOLTAGE F to polymerizing flux ratio is controlled not only by PRF, but also

by DC bias.

DC bias is manipulated by the blocking capacitor on the substrate.

Without DC Bias With DC Bias


40 mTorr, Ar/CF4/O2=75/20/5, 200 sccm LF 10 MHz 250 V, Pulsed HF 40 MHz 500 W

ETCH PROFILE IN SiO2 & IEAD: CONST. VOLTAGE

Etch rate is fastest at 415 kHz having larger fluorine flux.

Cycle Average IEAD

100 kHz CW 415 200 415 200 100 CW


CD70 nm

-88 V -103 V -116 V -129 VBias:

Angle (degree)Width (m)ANIMATION SLIDE-GIF



ETCH PROFILE IN SiO2 & IEAD: NO BIAS Etch rate is fastest at CW excitation due to continuously delivered

power. Cycle Average IEAD

100 kHz CW 415 200 415 200 100 CW


CD70 nm



POWER NORMALIZED ETCH RATE

Power normalized etch rate is dependant on the pulse repetition frequency and DC bias of the substrate.


40 mTorr, Ar/CF4/O2=75/20/5, 200 sccm LF 10 MHz, Pulsed HF 40 MHz, Duty 25%

CONCLUDING REMARKS

Extension of tail of f() beyond that obtained with CW excitation produces a different mix of fluxes to substrate.

Ratios of fluxes and IEADs are tunable using pulsed excitation.

Ratios of fluxes are IEADs are tunable using blocking capacitor.

Consequently, etch rate can be controlled by pulsed power with different blocking capacitors.

With constant power operation, fastest etch rate is achieved at 200 kHz having larger F to polymerizing flux ratio.

With constant voltage operation, fastest etch rate is achieved at 415 kHz having larger fluorine flux.

Without DC bias, the etch rate decrease as pulse repetition frequency decreases.

University of MichiganInstitute for Plasma Science & Engr.SHS_MJK_ISPC

sio 2 etch rate and profile control using pulse power in capacitively coupled plasmas* sang-heon...

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