Effects of different processing conditions on line edge ... · Effects of different processing...

© imec 2004

Effects of different processing conditions on line edge roughness for

193nm and 157nm resistsM. Erckena), L.H.A. Leunissena), I. Pollentiera),

G.P. Patsisb), V. Constantoudisb) and E. Gogolidesb)

a) IMEC, Kapeldreef 75, B-3001 Leuven, Belgiumb) Institute of Microelectronics (IMEL), NCSR

“Demokritos”, P.O. Box 60228, Aghia Paraskevi, Attiki, Greece 15310

© imec 2004 Monique Ercken - Effects of different processing conditions on LER 2

Outline

IntroductionOverview of experimental resultsConclusionsAcknowledgements


Outline

Introductionn Classical definition of LER 3σn Inline versus offline LER analysisnMore complete LER description

Overview of experimental resultsConclusionsAcknowledgements


Classical LER/LWR 3σ definition

δW(zi) is the deviationfrom the average

line edge δWN is number of measurements points

2/1

1

2

1

))((33

−

−×=

∑=

N

WzWN

ii δδ

σ

Line Edge Roughness

CD variation over certainline length = Line WidthRoughness


Inline LER/LWR analysis

Standard SEM algorithms

LER/LWR measurements at n Fixed amount of effective

measurement positions n Changing measurement box length Lè Evaluation of full frequency spectrumn Sufficient averaging

A measurement procedure has been set up to give consistent results independent from the measurement tool (KLA8250XR or Hitachi9200S) used.

L


0

5

10

15

0 1 2 3

Measurement box length L (um)

LWR

3si

gma

(nm

)

measurement tool 1

measurement tool 2

2-parameter model (IMEC)

experimental data

• LWR is increasing with increasing box length

Plateau value ?

Curvature ?


0

5

10

15

0 1 2 3

Measurement box length L (um)

LWR

3si

gma

(nm

)

measurement tool 1

measurement tool 2

2-parameter model (IMEC)

( )[ ]2inf 2

)2exp(121)(

LWWLLW

L ccc −+−+−⋅= σσ

σinf = 11.3nmWc = 189nm(100nm poly line)0

5

10

15

0 1 2 3

Measurment box length L (um)

LWR

3si

gma

(nm

)

measurement tool 1

measurement tool 2

Theory

1st order autoregressive process

Plateau ð σinf

Curvature ð correlation length Wc

L.H.A. Leunissen et al., MNE 2003, to be published in Microelectronic Engineering


Offline image analysis

Generation of top-down SEM images of desired feature“Demokritos” software detects all edges present and automatically generates

n an averaging on LER 3σ versus edge length from each edge (ðonly LER)

n a correlation length ξ from the final average height-height correlation function (HHCF)

n a roughness exponent α

The program runs as an executable under MATLAB.

Edge detection on pixel base


3-parameter model (Demokritos)

1 10 100 10001

2

3

4

5

6

G(r

)

r(nm)

z(yi)

yi

height

G(r) is determined by:1. sigma value2. α : roughness exponent(relative contribution of high frequency fluctuations to roughness)3. ξ : correlation length(for r>ξ no height-height correlations)

rα

20.5sigma

[2(1-1/e)]0.5sigmaG(ξ)

ξ

spatial roughness: height-height correlation function

[ ]1/2N

1i

2ii )z(yr)z(y

N1

G(r)

−+= ∑

=


More complete description

A more complete description of the LER can be obtained by measuring the full spatial frequency dependence of the roughness.

2-parameter model (IMEC, MNE’03) :n Classical LER/LWR 3σn Correlation length Wc

n Inline measurements on top-down SEM

3-parameter model (Demokritos) :n Classical LER 3σ

n Correlation length ξ : the distance after which the edge points can be considered uncorrelated and the edge looks flat

n Roughness exponent α : the relative contribution of high frequency fluctuations to LER

n Offline analysis of top-down SEM pictures


Outline

IntroductionOverview of experimental results

1. Impact of changing SB and PEB temperature on LER (193nm & 157nm)

2. Impact of aerial image contrast (193nm)3. Introduction of a resist hardening step before the etch procedure

n Shallow trench isolation (STI) patterning for 193nmn Impact on 157nm resists

ConclusionsAcknowledgements


Outline

IntroductionOverview of experimental results

1. Impact of changing SB and PEB temperature on LER (193nm & 157nm)

2. Impact of aerial image contrast (193nm)3. Introduction of a resist hardening step before the etch procedure

n Shallow trench isolation (STI) patterning for 193nm processingn Impact on 157nm resists

ConclusionsAcknowledgements


110 115 120

110115

1204

6

8

LER

3si

gma

(nm

)

SB (C)PEB (C)

1. SB/PEB : impact on LER 3σ

193nm

Trends :• decreasing LER with decreasing SB• decreasing LER with increasing PEB

Offline analysis

100nm 1:1 L/S

85 9095

115120

1258

10

12

14

16

18

LER

3si

gma

(nm

)

SB (C)PEB (C)

157nm95nm IL


110 115 120

110115

1204

6

8

LER

3si

gma

(nm

)

SB (C)PEB (C)

1. SB/PEB : correlation length ξ

193nm

Offline analysis

100nm 1:1 L/S

110 115120

110

115120

0

10

20

30

40

corr

elat

ion

leng

th (n

m)

SB (C)PEB (C)

ξ


1. SB/PEB : roughness exponent α

193nm

Offline analysis

110 115120

110

115120

0

10

20

30

40

corr

elat

ion

leng

th (n

m)

SB (C)PEB (C)

ξ

110115120

110115

1200.3

0.4

0.5

0.6

roug

hnes

s ex

pone

nt

SB (C)PEB (C)

α

Trends :• ξ : decreasing with decreasing PEB and increasing SB• α : decreasing with decreasing SB and increasing PEB


1. SB/PEB : discussion

Trends seen for LER 3σ and correlation length with changing SB and PEB are opposite to each other

n decreasing LER / increasing correlation length with decreasing SBn decreasing LER / increasing correlation length with increasing PEB

Correlation length is believed to be related to acid diffusion (ð increases with larger acid diffusion lengths)

n Increasing PEB temperature will enhance acid diffusion, resulting in a smoothening of the final edge (less LER)

n Decreasing SB temperature will result in more residual solvent in the polymer matrix ð enhances also acid diffusion ð more smoothening of the edge (less LER)

Trend for roughness exponent not yet understood (needs further investigation)


3. Introduction of a resist hardening (RH) step prior to substrate etch

with resist hardeningwithout resist hardening

Top-down view STI patterning example (stack: Si/nitride/resist) after etch and resist strip


3. Impact of the RH on STI profile

without resist hardening with resist hardening

Significant reduced sidewall roughness

Due to particular shape of STI profile ð only offline LER analysis

• LER 3σ analysis (offline)

0

2

4

6

8

10

Resist RH

LER 3

sigma

[nm] DR

ISO INVISO

no RH + etch

RH + etch

110nm

no RH + etch

RH + etch

150nm

DR : 120nm active area width / 160nm field width ISO : 120nm iso active area INVISO : 160nm iso field width

2 different nitride


3. Verification with AFM

-800

-750

-700

-650

-600

-550

-500

-450

-400

-350

-3000 200 400 600 800 1000 1200

Profile width (nm)

Pro

file

hei

gh

t (n

m)

0

2

4

6

8

10

12

14

0 100 200 300 400 500

Depth from top (nm)

LER

3 (

nm)

AFM (no RH)

AFM (RH)

ISO structure, using 110nm nitridethickness

AFM scan

(with courtesy of Veeco)

Offline LER

approximate determinedoffline LER position


Outline



Conclusions

More complete characterization of LER including LER 3σ and correlation lengthGood agreement between inline and offline determined LER 3σ valueDemonstration and better understanding of parameters influencing LER

n SB and PEBn Aerial image contrastn Etch process

Definitely further improvement is needed3σ ~ 7.7nm

95nm 1:1 L/S

3σ ~ 9.1nm

e.g. impact of RHon 157nm resist


Outline



Thanks to …

Nadia Vandenbroeck, Christie Delvaux, Dieter Van Den Heuvel and Greet StormsDenis Shamiryan and Sabrina Locorotondo (IMEC etch)Johan Vertommen and Bart Coenegrachts (Lam Research, Leuven)Rita Rooyackers (IMEC integration)Ingo Schmitz (Veeco)European projects CRISPIES and UV2-LITHO

www.imec.beWorldwide collaboration with more than 500 companies and institutes.

IMEC – Kapeldreef 75 – B-3001 Leuven – Belgium – Tel. +32 16 281211 – Fax +32 16 229400 – www.imec.be

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