1. Metrology-characterization and simulation
of Line Width Roughness (LWR)
Evangelos Gogolides,
Vassilios Constantoudis,
George Patsis
Institute of Microelectronics
NCSR "Demokritos"
Attiki - Greece
(in affiliation with lithographic materials team of P. Argitis)
More Moore-Excite Joint meeting, Athens May 12, 2005

2. Outline
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

3. SEM image after noise smoothing Intensity profile for a pixel row
A. LWR metrology-characterization methodology
Off line software for the detection of line edges from top down
CD-SEM images
middle
inner outer
threshold
Normalized pixel intensity
SEM image after noise smoothing
Determine the pixel size in nm and the noise smoothing parameters
Intensity profile for a pixel row
Edge detection algorithm at each
pixel row using a threshold value
Obtain the line edges of the image
(outer,inner or middle)
A line edge
LER : yi,R(L) of all the edges
line width
or gate length
LWR : δyi of all the lines
Line length or gate width
For uncorrelated and parallel edges :
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): MAY-JUN 2003

4. A. LWR metrology-characterization methodology
2. Characterization of LWR: The importance of sigmaLWR(L) curve
Why sigmaLWR(L) curve : sigma not a value BUT a function, sigma(L) curve
100
200
300
400
500 50
150
250
350
450
x (pixels)
y (pixels) L
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
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): (2003)

5. A. LWR metrology-characterization methodology
The physical meaning of α, Ls
Influence of α, Ls on:
a) sigmaLWR(L) curve
b) edge morphology
1. Different α, the same sigma, Ls
α=0.2
α=0.8
3. Different Ls , the same sigma,α
LS=300
LS =600

6. A. LWR metrology-characterization methodology
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)
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 V. Constantoudis et al. in Metrology Session of SPIE 2005

7. B. Simulation of material and process effects on LWR
Schematic flowchart of simulator
Side
LER
(Accurate)
Front
View
Top -
Down
LER in 2D
Resist
Mask
Exposure
Molecular
structure
Deprotected
Developer

8. SIMULATION OF ACID DIFFUSION AND MOLECULAR WEIGHT EFFECTS ON LER

9. SIMULATION OF ACID DIFFUSION AND MOLECULAR WEIGHT EFFECTS ON LER
Side
LER
(Accurate)
Front
View
Top -
Down
LER in 2D