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157 CRISPIES157 CRISPIES

Etching mechanisms of POSS Copolymers

David EON, Gilles CARTRY, Vanessa RABALLAND, Christophe CARDINAUDand CRISPIES PARTNERS


Aim of the present work

POSS etching in oxygen plasmas

v Measurement of etch rates and selectivityv Determination of the etch mechanismsv Surface roughness – Line Edge Roughnessv Dimension control during pattern transfer

Experiment

v ICP plasmav O2, 800W, 10 mTorr, 40 sccm – Bias voltage: 0 V or –100Vv In-situ ellipsometryv Quasi in-situ XPS


O2 plasma - Bias voltage: 0V

Ä The etch resistance decreases with the silicon content

Ellipsometric measurements (I)

0 1 2 3 4 5 6 7 8

80

100

120

140

160

180

200

220

PDMS

40%

40% MA20

ICP O2 plasma, 800 W, 10 mTorr, 0 V

20%

30% MA20

60%

100%

N

orm

aliz

ed th

ickn

ess

(nm

)

Etching time (min)


Ellipsometric measurements (II):Etch resistance

0

20

40

60

80

100

120

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.21 / (weight percentage of silicon)

Th

ickn

ess

loss

20%

30%(S69)40%

40% (S53)

60%

100%

10 min

7 min

5 min

3 min

1 min

12 s PDMSPMSQ

ICP O2 plasma, 800W, 10 mTorr, 0 V

Ä Si content (or Si-O) controls the etch resistance to oxygen plasma

O2 plasma - Bias voltage: 0V


Ellipsometric measurements (III):Fluorinated materials

O2 plasma - Bias voltage: 0V – Fluorinated materials

0 1 2 3 4 5 6 7 8

80

100

120

140

160

180

200

220

20%

30% MA20


30% F-tBMA (S106)

30% FA30

(S83)

100%

N

orm

aliz

ed th

ickn

ess

(nm

)

Etching time (min)

Ä Fluorine significantly reduces material consumption


Ellipsometric measurements (IV):Addition of a photo-acid generator

O2 plasma - Bias voltage: 0V – S47(40%POSS) / 5%PFOS

Ä PFOS slightly modify etch rates (19% at maximum)

0 1 2 3 4 5 6 7 8

130

140

150

160

170

180

190

200

210

S47 - S47PFOS


40% PFOS

40%

N

orm

aliz

ed th

ickn

ess

(nm

)

Etching time (min)

0

2

4

6

8

10

12

14

16

18

20

Difference (%

)


Ellipsometric measurements (V):Bias effect

0 2 4 6 8 10 1220

40

60

80

100

120

140

160

180

200

220

100 % POSS

30%MA20%

40%MA20%

23 nm/min

7 nm/min

3 nm/min

1.6 nm/min

20 % POSS

40 % POSS

60 % POSS

PDMS

Thic

knes

s (n

m)

Etching time (min)

PDMS presents a different behavior

O2 plasma - Bias voltage: -100V

Ä POSS mat. present higher resistance to ion bombardment compared to PDMS


0 2 4 6 8 10 1220

40

60

80

100

120

140

160

180

200

220

100 % POSS

30%MA20%

40%MA20%

23 nm/min

7 nm/min

3 nm/min

1.6 nm/min

20 % POSS

40 % POSS

60 % POSS

PDMS

Thic

knes

s (n

m)

Etching time (min)

O2 plasma - Bias voltage: -100V

Hydrocarbonresist (Novolac

AZ5214):630 nm/min

Selectivity:390

210

90

27

16

8

6

2

Ellipsometric measurements (VI):Selectivity

Ä 30% POSS is sufficient to ensure a satisfactory etch resistance


v High initial etch rates suggest a surface oxidation of POSS copolymersv XPS is used to monitor surface atomic percentages versus etching time

0 2 4 6 8 10 12 14 16 18 20 22

10

20

30

40

50

60

70 S48 (40% POSS):

CARBON

SILICON

OXYGEN

Etching time (s)

Ato

mic

per

cent

ages

0 2 4 6 8 10 12 14 16 18 20 2210

20

30

40

50

60

S41 (100% POSS)

CARBON

SILICON

OXYGEN

Etching time (s)

Ato

mic

per

cent

ages

Oxidation of the surface !

Oxidation of the top surface (I): XPS measurements


100 % POSS material before and after 5 min etching

800 1200 1600 2000 2400 2800 3200

0.00

2.50x105

5.00x105

7.50x105

1.00x106

1.25x106

1.50x106

1.75x106

Pure POSS monomer (S41)

After 5 min etching (0V)

Before etching

Wavenumber (cm-1)

abso

rban

ce (m

-1)

Oxidation of the top surface (II): FTIR measurements

Oxidation of the surface !


Copolymer layerCarbon - Oxygen - Silicon

SiO2 layer No carbon

Top layer (I)

v We use a two layers model for XPS analysis

v The decrease of the carbon peak through the oxide layer is used to determine the oxide thickness versus etching time

v Once the oxide layer is determined it is possible to distinguish the oxygen and silicon peak contribution coming only from the oxide layer

Ä The chemical composition of the oxide layer can be determined

XPS analysis


v There is oxidation of thetop surface during first seconds

v The chemical composition is closed to silicon oxide in all cases

v Ion bombardment seems to favor oxidation

Top layer (II)

Material 100% 60% 40%MA20 40% 30% IA10 30% IA20 30% MA20 30% FA30 30% IA10FA20 20%

Oxide thickness (nm) 2.4 2.0 1.7 1.7 1.5 1.6 1.6 1.4 1.5 1.4

Oxide thickness (nm) 3.2 2.7 2.4 2.2 2.4 2.5 2.2 2.4 2.5 1.8

O/Si ratio 1.9 1.7 1.9 1.8 1.6 1.7 1.8 1.7 1.8 1.9

O/Si ratio 2.2 2.1 2.0 2.0 1.9 2.0 2.0 1.9 2.0 2.0

Oxide thickness versus etching time

0 2 4 6 8 10 12 14 16 18 20 22

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5Estimation of SiO2 thickness using C1s peak

S41 - 100% S48 - 60% S71 - 30% IA20 S83 - 30% FA30

Etching time (s)

SiO

2 thi

ckne

ss (n

m)

0 V

100 V

0 V

100 V


Silicon oxidation

Balance of Si atoms

F. Watanabe, Y. Onishi, JVSTB 4(1), Jan/Feb 1986, p422

dt

de

dtde polSi

poloxinSi

ox ρ−=ρ

Chemicals reaction with C and H forms volatiles compounds

Oxygen plasma

eox

Sputtering

Diffusion

SiXX

SiX pρ=ρ

Xρ Material densitySiXp Weight percent of

silicon

Oxidation model (I)


Thickness loss with sputtering (bias: -100V)

( )tete ox)( +λ=∆

Sputtering of silicon dioxideLayer densification

Without sputtering (No bias: 0V)

( ) tktete sox )1()( λ++λ=∆

Oxidation model (II)

v To calculate λ, we need copolymers densities and silicon contentv Silicon content is always knownv Copolymer densities have been taken equal to 1.0 g/cm3

Sipol

Sipol

Siox

ρ

ρ−ρ=λ

SipolρSi

oxρ >


0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

35

40

20%30%

40%

60%

100%

Oxide thickness (nm)

Lost

thic

knes

s (n

m)

( )tete ox)( +λ=∆ : theoretical values

Ä Thickness loss is measured by ellipsometry

Ä Oxide thickness have been measured by XPS

for 5s, 10s and 20s etching time

Ä Experimental curves ofthickness loss versus oxide thickness can be plotted

Oxidation model (III):Without ion bombardment


0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

35

40

10s 20s5s

20%30%

40%

60%

100%

Oxide thickness (nm, XPS)

Lost

thic

knes

s (n

m)

( )tete ox)( +λ=∆ : theoretical and experimental values

Ä The model fits very well with the 100% POSS

material

Ä Thickness loss of the 100% POSS material is

due to layer densification following oxidation of the

top surface

Oxidation model (IV):Without ion bombardment


( )tete ox)( +λ=∆ : theoretical and experimental values

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

35

40

10s 20s5s

20%30%

40%

60%

100%


Lost

thic

knes

s (n

m)

Ä The model fits well with the experiments: Thickness losses seem

to come from layer densification

Ä The model points out the effect of surface

segregation on plasma etching

Oxidation model (V):Without ion bombardment



Oxidation model (VI)With ion bombardment

v A second term is added to the material densification term

v This second term is positive and takes into account the sputtering

v For a sake of clarity, we present results only after 10 seconds etching


0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

35

40

45

50

55

60

100V0V

100V

0V

10 seconds

20%

30%

40%

60%

100%


Lost

thic

knes

s (n

m)

Ä No sputtering is observed !

(except for S43)

Ä Ion bombardment seems to favor oxidation

Oxidation model (VII)With ion bombardment



Main ideas of the model

v The flux of oxidant species at the interface between silicon oxide and polymer is equals to the oxidation flux:

v This gives the layer growth function f(eoxide)The oxide layer is then determined by the following differential equation:

v Its solution give the oxidised layer growth function

Oxidised layer growth: Deal & Grove model

sputteringoxideoxide kef

te

−=∂

∂)(

1

cF D

z∂

= −∂ ( )2

Si Cox ox i ox iF k k c k c= + ==

( )1ln 1 expox s

s s

B Be k At

A k k

= − − +

Three free parameters: A, B, ks


0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8Temps (min)

Epa

isse

ur t

otal

e pe

rdue

(nm

) 20%

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8Temps (min)

Ep

aiss

eur

tota

le p

erd

ue

(nm

) 100%

Results of the oxidation layer growth model

Ä A, B and kS parameters are the fitting parameters

Ä kS, the sputtering rate is assumed independant of the material

Ä kS is found lower than for silicon oxide !

Ä B is determined for all copolymers.Ä B could give the reaction coefficient between Oand Si at interface if Oplasma is measuredÄNeed for mass spectrometry and optical actinometry

ÄA is determined for all copolymersÄA could give the carbon etching coefficient if DO-SiO2 is known

If these coefficients are known, the Demokritos profile simulator may be applied to POSS copolymer pattern

transfers


Conclusions

Ä Etch rates and selectivity have been measured for a all the copolymers (>30% for good selectivity)

ÄWe have shown that the copolymer top surface is converted into an oxide like layer during first plasma seconds

ÄWe have developped an oxidation model:ØWithout bias, thickness loss comes from layer densificationØ The ion bombardment favors the formation of the oxide layer but do not induce a strong sputtering

ÄWe have determined for all copolymers the oxidised layer growth function and we may be able to estimate rate coefficient of atomic oxygen at interface

ÄWe want to apply all these results to:Ø The developement of an etching strategy without LERØ The control of dimension during pattern transferØ The study of new materials

ÄWe still need:Ø New etching conditionsØ Plasma measurements (ion flux, oxygen concentration)Ø Pattern transfer experiments


0 2 4 6 8 10 12 14 16 18 20 221.0

1.5

2.0

2.5

3.0

3.5

Surface segregation effect ?

Estimation of SiO2 thickness using C1s peak

S41 - 100% S48 - 60% S47 - 40% S43 - 20%

Etching time (s)

SiO

2 thi

ckne

ss (n

m)

Silicon oxide thickness versus time

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