Metrology-characterization and simulation

of Line Width Roughness (LWR)

Evangelos Gogolides, Evangelos Gogolides, Vassilios ConstantoudisVassilios Constantoudis,,

George PatsisGeorge Patsis

Institute of Microelectronics Institute of Microelectronics NCSR "Demokritos" NCSR "Demokritos"

Attiki - GreeceAttiki - Greece

(in affiliation with lithographic materials team of P. Argitis)

More Moore-Excite Joint meeting, Athens May 12, 2005

Outline

A. LWR metrology-characterization methodology

1. Off line detection of line edges and line widths from top down CD-SEM images 2. Characterization of LWR :The importance of sigma(L) curve 3. LWR and CD variation - LWR descriptors

B. Simulation of lithography material and process effects on LWR

A. LWR metrology-characterization methodology

1. Off line software for the detection of line edges from top down CD-SEM images

LER : yi,R(L) of all the edges

A line edge

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500

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x (pixels)

y (p

ixel

s)

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0.0

0.2

0.4

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0.8

1.0

κατώφλι φωτεινότητας

εσωτερικής ή εξωτερικής ακμήςσημείο της

Εντ

ασ

η φ

ωτε

ινότ

ητα

ς ει

κονο

στο

ιχεί

ων

x (pixels)

Nor

mal

ized

pix

el in

tens

ity

threshold

inner outermiddle

SEM image after noise smoothing

Determine the pixel size in nm and the noise smoothing parameters

Intensity profile for a pixel rowEdge detection algorithm at each pixel row using a threshold value

Obtain the line edges of the image (outer,inner or middle)

LWR : δyi of all the lines

N

1i

2)L(R,i

2)L(R,LER yN

1sigma

N

1i

2i

2LWR y

N

1sigma

For uncorrelated and parallel edges :

LERLWR sigma2sigma Patsis GP, Constantoudis V, Tserepi A, et al. Quantification of line-edge roughness of photoresists. I. A comparison between off-line and on-line analysis of top-down

scanning electron microscopy images J. VAC SCI TECHNOL B 21 (3): 1008-1018 MAY-JUN 2003

Lin

e l

en

gth

or

ga

te w

idth

line widthor gate length

2. Characterization of LWR: The importance of sigmaLWR(L) curve

• Why sigmaLWR(L) curve : sigma not a value BUT a function, sigma(L) curve

Parameters for sigma(L) curve determination:

• 1) sigma(inf): the sigma for the infinite line length

• 2) LS: sigma-correlation length sigma(LS)=0.9*sigma(inf). For L>Ls the line edges look flat (no correlations) and sigma(L)sigma(inf)

• 3) α : roughness exponent giving the relative contribution of high frequency roughness to LWR. It is related to fractal dimension d=2-α

A. LWR metrology-characterization methodology

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500

0 50 100 150 200 250 300 350 400 450 500x (pixels)

y (p

ixel

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L

L

L

Constantoudis V, Patsis GP, Tserepi A, et al. Quantification of line-edge roughness of photoresists. II. Scaling and fractal analysis and the best roughness descriptorsJ. VAC SCI TECHNOL B 21 (3): 1019-1026 (2003)

• Influence of α, Ls on:

A. LWR metrology-characterization methodology

1. Different α, the same sigma, Ls

α=0.2 α=0.8

3. Different Ls , the same sigma,α

LS=300 LS =600

The physical meaning of α, Ls

a) sigmaLWR(L) curve b) edge morphology

3. LWR and CD variation : estimating sigmaLWR(inf) using finite line lengths

The key relationship :

sigmaLWR 2(inf)= sigmaLWR 2(L)+ CDvariation 2(L)+ rmssigma 2(L)

A. LWR metrology-characterization methodology

variation of sigmaLWR values

sigmaLWR(inf): a line length independent parameter that can be estimated using any line length A new parameter for LWR definition ?Also,A new meaning for α,Ls : control the partition of sigmaLWR(inf) in LWR and CD variation as line length L decreases (L<Ls)See paper 5752-141- V. Constantoudis et al. in Metrology Session of SPIE 2005

B. Simulation of material and process effects on LWR

SideLER

(Accurate)

Front ViewLER

Top-DownViewLER

Top-DownViewLER in 2D

Resist

Mask

Exposure

Molecular structure

Deprotected Deprotected

Developer

Schematic flowchart of simulator

SIMULATION OF ACID DIFFUSION AND MOLECULAR WEIGHT EFFECTS ON LER

10 1000

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CR CAR,C

PAG=2.5,

RD=90steps

FC=0.3

DF=0.7AIC=13D

LE

R (

3 s

igm

a)

(~n

m)

CR, CAR,C

PAG=2.5,

RD=90steps CAR,C

PAG=10%,

RD=22steps

FC=0.3

DF=0.9AIC=13D

Average polymerization length, <L>

10 1000

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9

10F

C=0.5

DF=0.9AIC=13D

CR, CAR,C

PAG=10%,

RD=22steps

10 1000

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9

10

CR, CAR,C

PAG=2.5,

RD=90steps CAR,C

PAG=10%,

RD=22steps

FC=0.3

DF=0.9AIC=13D

Average polymerization length, <L>

10 1000

1

2

3

4

5

6

7

8

9

10Obtained from 1st row

of edge data (top-down view)

CR, CAR,C

PAG=2.5,

RD=90steps CAR,C

PAG=10%,

RD=22steps

LER

(~

nm)

Average polymerization length, <L>

SIMULATION OF ACID DIFFUSION AND MOLECULAR WEIGHT EFFECTS ON LER

SideLER

(Accurate)

Front ViewLER

Top-DownViewLER

Top-DownViewLER in 2D