AVS 2002 Nov 3 - Nov 8, 2002 Denver, Colorado INTEGRATED MODELING OF ETCHING, CLEANING AND BARRIER...

AVS 2002Nov 3 - Nov 8, 2002Denver, Colorado

INTEGRATED MODELING OF ETCHING, CLEANING AND BARRIER COATING PVD FOR POROUS AND

CONVENTIONAL SIO2 IN FLUOROCARBON BASED

CHEMISTRIES*

Arvind Sankaran1 and Mark J. Kushner2

1Department of Chemical Engineering2Department of Electrical and Computer Engineering

University of Illinois, Urbana,

IL 61801, USAemail: [email protected]

[email protected]

http://uigelz.ece.uiuc.edu

*Work supported by SRC, NSF and SEMATECH

University of IllinoisOptical and Discharge Physics

AGENDA

Low dielectric constant materials

Surface reaction mechanism and validation Fluorocarbon etching of SiO2/Si

Ar/O2 etching of organic polymer

High aspect ratio etching of porous and non porous SiO2

Integrated Modeling: Ar/O2 strip of polymer and IMPVD

Concluding Remarks

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LOW DIELECTRIC CONSTANT MATERIALS

The increase in the signal propagation times due to RC delay has brought the focus onto low dielectric constant (low-k) materials (inorganic and organic)

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Inorganics such as porous silica (PS) are etched using fluorocarbon chemistries; organics are etched using oxygen chemistries.


GOAL FOR INTEGRATED MODELING

Plasma processing involves an integrated sequence of steps, each of which depends on the quality of the previous steps.

CFDRC_0503_05


SURFACE REACTION MECHANISM - ETCH

CFx and CxFy radicals are the precursors to the passivation layer which regulates delivery of precursors and activation energy.

Chemisorption of CFx produces a complex at the oxide-polymer interface. 2-step ion activated (through polymer layer) etching of the complex consumes the polymer.

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CFx Ion+

I*, CF2

SiO2CxFy SiOCFy

CxFy

Ion+

CO2Ion+

CO2

Polymer

SiF3

Ion+,FSiF3

CFx

Polymer

F

SiF SiF2 SiF3

Ion+,F

SiF3

SiO2

Plasma

Si

CxFy

Plasma

PassivationLayer

CxFyPassivation

Layer

Activation scales as 1/L and the L scales as 1/bias.

In Si etching, CFx is not consumed, resulting in thicker polymer layers.

Si reacts with F to release SiFx.


SURFACE REACTION MECHANISMS - STRIP

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Ar/O2 is typically used for polymer stripping after fluorocarbon etching and resist removal.

Little polymer removal is observed in absence of ion bombardment suggesting ion activation.

)()()(*

)(*)()(

gCOFgIsP

sPgOsP

x

For SiO2 etching in mixtures such C4F8/O2, the fluorocarbon polymer is treated as an organic. Resists are treated similarly.


MONTE CARLO FEATURE PROFILE MODEL (MCFPM)

The MCFPM predicts time and spatially dependent profiles using energy and angularly resolved neutral and ion fluxes obtained from equipment scale models.

Arbitrary chemical reaction mechanisms may be implemented, including thermal and ion assisted, sputtering, deposition and surface diffusion.

Energy and angular dependent processes are implemented using parametric forms.

INTELTALK_AS_17

Mesh centered identity of materials allows “burial”, overlayers and transmission of energy through materials.


MODELING OF POROUS SILICA

MCFPM may include “two phase” materials characterized by porosity and average pore radius.

Pores are incorporated at random locations with a Gaussian pore size distribution. Pores are placed until the desired porosity is achieved with/without interconnects.

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deviation standard:

radius pore average:

)(

0

)(

)(2

20

r

r

erP r

rr

Interconnected structures can be addressed.


TYPICAL PROCESS CONDITIONS

Process conditions Power: 600 W Pressure: 20 mTorr rf self-bias: 0-150 V C4F8 flow rate: 40 sccm

The fluxes and energy distributions are obtained using the HPEM.

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0 1 2 3 4 5 60123456 F + (1 0 1 7 )

C F 2+ (1 0 1 7 )C F3 + (1 0 1 6 )

02468 F (1 0 1 7 )

C F 2 (1 0 1 7 ) H (1 0 1 8 )C F (1 01 7 )

R a d iu s (cm )

Ion Fluxes (cm-2 s-1 )

Neutral Fluxes (cm-2 s-1 )

0 5 105100

5

10

15 Coils

SubstrateWafer

Feed ring

Pump port

Radius (cm)

Hei

ght (

cm)


BASE CASE ION AND NEUTRAL FLUXES

Self-bias = - 120 V. Decrease in neutral and ion fluxes along the radius have compensating effects.

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Ions have a narrow energy and angular distribution, in contrast to neutrals.

0 1 2 3 4 5 60

1

2

3

4

5

6

7F ( 1 0 1 5 )

C F 2 ( 1 0 1 7 )

C F ( 1 0 1 6 )

R a d i u s ( c m )

Ne

utr

al

Flu

xe

s (

cm

-2s

-1)

C 2 F 4 ( 1 0 1 7 )

C 2 F 3 ( 1 0 1 6 )

0 1 2 3 4 5 60

1

2

3

4

5

6

C F + (1 0 1 4 )

C F 2+ (1 0 1 5 )

C F 3+ (1 0 1 4 )

R a d i u s ( c m )

Ion

Flu

xe

s (

cm

-2s

-1)

C 2 F 4+ ( 1 0 1 5 )


VALIDATION OF REACTION MECHANISM: C4F8

The mechanism was validated with experiments by Oehrlein et al using C4F8, C4F8/Ar and C4F8/O2.1

Threshold for SiO2 etching was well captured at self-bias -40 V. Polymer formation is dominant until the threshold bias

As polymer thins at higher biases, the etching proceeds.

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1 Li et al, J. Vac. Sci. Technol. A 20, 2052, 2002.

0 50 100 150 2000

100

200

300

400

500

600

Model - MExperiment - E

SiO2 - E

SiO2 - M

Self Bias (-V)

Etc

h R

ate

(nm

/min

)

C4F8


VALIDATION: C4F8/Ar and C4F8/O2

Larger ionization rates result in larger ion fluxes in Ar/C4F8 mixtures. This increases etch rates.

With high Ar, the polymer layers thins to submonolayers due to less deposition and more sputtering and so lowers etch rates.

O2 etches polymer and reduces its thickness. Etch rate has a maximum with O2, similar to Ar addition.

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0 20 40 60 80 1000

100

200

300

C4F8/O2

SiO2 - E

SiO2 - M

Etc

h R

ate

(nm

/min

)

O Content (%)2

0 20 40 60 80 1000

100

200

300

400

500

C4F8/Ar

SiO2 - E

SiO2 - M

Etc

h R

ate

(nm

/min

)

Ar Content (%)


PROFILE COMPARISON: MERIE REACTOR

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Process conditions Power: 1500 W CCP Pressure: 40 mTorr Ar/O2/C4F8: 200/5/10 sccm

V. Bakshi, Sematech

CF2Density

MERIE Reactor Experiment Model


VALIDATION OF POROUS SiO2 ETCH MODEL

Two porous substrates 2 nm pore radius, 30% porosity 10 nm pore radius, 58% porosity

Process conditions Power: 1400 W (13.56 MHz) Pressure: 10 mTorr rf self-bias: 0-150 V 40 sccm CHF3

Etch rates of P-SiO2 are higher than for NP-SiO2 due to lower mass densities of P-SiO2.

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Exp: Oehrlein et al, J. Vac. Sci.Technol. A 18, 2742 (2000)

0 20 40 60 80 100 120 1400

100

200

300

400

500

6000

100

200

300

400

500

600

Self Bias (-V)

E-PSM-PS

2 nm, 30%Et

ch R

ate (n

m/mi

n)

E-PSM-PS

10 nm, 58%

Etch

Rate

(nm/

min)

= Porous= Solid SiO2

PSSS

= Experiment= Model

EM

CHF3

CHF3

E-SS

M-SS

E-SSM-SS


WHAT CHANGES WITH POROUS SiO2?

The “opening” of pores during etching of P-SiO2 results in the filling of the voids with polymer, creating thicker layers.

Ions which would have otherwise hit at grazing or normal angle now intersect with more optimum angle.

INTELTALK_AS_30

An important parameter is L/a (polymer thickness / pore

radius).

Adapted: Standaert, JVSTA 18, 2742 (2000)


EFFECT OF PORE RADIUS ON HAR TRENCHES

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With increase in pore radius, L/a decreases causing a decrease in etch rates.

Thicker polymer layers eventually lead to mass corrected etch rates falling below NP-SiO2. There is little variation in the taper.

4 6 8 10 12 14 160

200

300

400

500

ER - PS

ER - SS

CER - PS

50%

Pore Radius (nm)

Etc

h D

epth

(nm

)

CHF3

4 nm 16 nm10 nm


HAR PROFILES: INTERCONNECTED PORES

INTELTALK_AS_40

60% 100%0%

Interconnectivity


EFFECT OF PORE RADIUS ON CLEANING

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Larger pores are harder to clean due to the view angle of ion fluxes.

Unfavorable view angles lead to a smaller delivery of activation energy, hence lower activated polymer sites.

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

16

4 nm

710

13

Time (Arb Units)

Frac

tion

of R

esid

ual P

olym

er

4 nm 16 nm

ANIMATION SLIDE

Ar/O2=99/1, 40 sccm, 600 W, 4 mTorr


CLEANING INTERCONNECTED PORES

CHEME_AS_19

Cleaning is inefficient with interconnected pores.

Higher interconnectivity leads to larger shadowing of ions.

60% 100%0%

ANIMATION SLIDE

Interconnectivity Ar/O2=99/1, 40 sccm,

600 W, 4 mTorr


EFFECT OF ASPECT RATIO ON STRIPPING

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Cleaning decreases with increasing aspect ratios.

Pores at the top of the trench are stripped better due to direct ions (view angle).

Pores near the bottom see ions reflected from the bottom of the trench and are cleaned better.

3

5

1

ANIMATION SLIDE

Aspect Ratio

Ar/O2=99/1, 40 sccm, 600 W, 4 mTorr

4 nm 16 nmNP 10 nm


EFFECT OF PORE RADIUS ON Cu DEPOSITION

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Surrogate study for seed layer deposition and barrier coating.

Larger pores require longer deposition times for conformal coverage.

This produces thicker bottom and open field films.

Voids are created or initiated by larger pores.


EFFECT OF INTERCONNECTIVITY ON Cu IMPVD

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Interconnected pores need to be sealed to avoid pin-hole formation.

Pore sealing by Cu IMPVD ineffective at larger interconnectivities.

Thicker layers to seal pores produces trench narrowing, which can lead to pinch off.

30% 100%0% 60%

Interconnectivity


CONCLUSIONS

Etching of PS obeys scaling laws as that of SS. Etch rate increases for smaller pores and slows for larger pores (at high porosities).

L/a determines etch rate variation of P-SiO2. Polymer filling increases the net thickness.

Stripping is inefficient for interconnected pore networks and for larger pores due to the unfavorable view angles for the ion fluxes. Low aspect ratio pores are better cleaned.

Cu IMPVD is non-conformal for closed pore networks with larger pores. Pin-hole formation and trench narrowing is seen for interconnected networks.

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AVS 2002 Nov 3 - Nov 8, 2002 Denver, Colorado INTEGRATED MODELING OF ETCHING, CLEANING AND BARRIER...

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