experimental validation of full-field compensation for …€¦ · experimental validation of...

G-Number

1

Experimental validation of full-field compensation for

EUV flare and mask shadowing

Manish Chandhok, Sang H. Lee, Todd R. Younkin, Michael Leeson

Intel Corporation

10/18/11

G-Number

2

Motivation EUV lithography has specific issues

that induce CD variation such as –Mask shadowing due to off-normal angle of

incidence

–Flare created by scattering due to mirror roughness

–Mask reflectivity variation

These effects need to be properly

characterized to enable methods

such as OPC to compensate for them

G-Number

3

Flare compensation

G-Number

4

Flare REflectivity Shadowing COmpensation (FRESCO) mask

Having both compensated and uncompensated on the same mask reduces mask-to-mask & wafer-to-wafer variation

26 mm

22 mm

No

compensation

With

compensation

Separator

distance

(6 mm)

8 rows x 26

columns of

1 mm x 1 mm

Micro-cell

with H& V

OCD

structures

8 mm

G-Number

5

Micro-cell layout (FRESCO)

OCD area

Alternate

rows of H

(red) & V

(orange)

Window to measure

reflectivity (0.5 mm x 0.15

mm)

Row

column

label

Features:

L40P80,

L40P120,

L40P160

L50P100,

L50P150,

L50P200

L60P120,

L60P180,

L60P240

15 combinations of

pitch and CD in

column

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

L40 P80 only for uniformity



L40 P80, L40 P120, L40 P160

repeated 5X

L50 P100, L50 P150, L50

P200 repeated 5X

L60 P120, L60 P180, L60 P240 repeated 5X

Feature sizes were selected to be much larger than resolution limit to minimize CD variation

G-Number

6

OCD pattern layout details

OCD structures were used to minimize local CD variation

60 x 60 micron OCD pads

Label is on top of the H-V pair

0.5 m

line to

measure

flare

H

V

G-Number

7

FRESCO after dummification

Pattern density as drawn is too uniform

Clear and dark dummies added to induce density variation and hence flare variation

As drawn

Additional

Dummies: Green = Clear

Blue = Dark

Final Density map

No dummies

G-Number

8

Principle of rule based FVC (Flare Variation Compensation)

All regions within the orange boundary get a bias depending on flare as per the equation below (rule based)

FVC Rules

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

L4

0P

80

L4

0P

12

0

L4

0P

16

0

L4

0P

20

0

L5

0P

10

0

L5

0P

15

0

L5

0P

20

0

L5

0P

25

0

L6

0P

12

0

L6

0P

18

0

L6

0P

24

0

L6

0P

30

0

Slo

pe

of

CD

Vs

. F

lare

Fit

(b

lue

), R

2 f

or

Lin

ea

r F

it (

red

)

Slope

R2

Sample CD sensitivity to

flare “rules”

G-Number

9

CD sensitivity to flare and MEEF for SEVR-59

SEVR-59 sensitivity to flare and MEEF all appear to be close to 1 for FRESCO structures

Calibrated values from IMEC as seen in SEVR-59 simulations were ultimately used for the rule based FVC

Flare rules for FRESCO SEVR-59 simulations SEVR59 measured

VARIABLE meef_l40_p80 0.93 1.15

VARIABLE meef_l40_p120 0.9



VARIABLE meef_l50_p150 1



VARIABLE meef_l60_p180 1


VARIABLE slope_flare_l40_p80 0.97 1.3nm/%Flare change



VARIABLE slope_flare_l50_p100 0.94






G-Number

10

FRESCO mask flare variation

0

1

2

3

4

5

6

7

8

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

Flar

e (%

,)

Location in Y (um)

X=13 mm, Top, Compensated H

X=13 mm, Bottom, Uncompensated H



X = 3 mm X = 13 mm

With CD sensitivity to flare ~1 nm/% flare and expected flare range of ~3%, ~3 nm CD change is expected

G-Number

11

Mask Shadowing Compensation

G-Number

12

EUV mask shadowing

Effective CD from

geometric optics

Reflective

Multi-layers

Absorber

Shadowing effect for EUV masks

Absorber height

of ~ 51-87 nm

Incident angle = 0

Parallel

No shadowing

Incident angle = 6

Perpendicular

Shadowing

Produces H-V bias (varies across the slit), distorts 2D features

Center shift

Tilted Bossungs

Difference in best focus for H & V

E-field at mask

G-Number

13

Shadowing variation across the slit

The angle of incidence at the same radius along the curved slit is the same

However, the structures on the mask may be rotated with respect to plane of incidence of the light1

1U. Mickan and M. Lowisch, “Discussion of a simple EUV reticle model,” Proc. EMLC, pp. 243 (2005)

CRAO = 6, varies by slit location, & = 0 for

vertical structures & 90 for horizontal structures

G-Number

14

Rule based shadowing compensation

Use rigorous mask simulations to estimate the

Horizontal and Vertical CD variation with respect to

effective shadowing angle across the slit

Obtain compensated CDs by scaling the predicted CD

difference with respect to center vertical CD, with

appropriate MEEF

Location

at 1X (x)

Compensation

H (nm)

Compensation

V (nm)HV bias (nm)

-13 to -11 1.94 0.26 1.68

-11 to -9 2.05 0.20 1.85

-9 to -7 2.14 0.15 1.99

-7 to -5 2.21 0.08 2.13

-5 to -3 2.25 0.05 2.21

-3 to -1 2.30 0.02 2.28

-1 to +1 2.33 0.00 2.33 Center

+1 to +3 2.30 0.02 2.28

+3 to +5 2.25 0.05 2.21

+5 to +7 2.21 0.08 2.13

+7 to +9 2.14 0.15 1.99

+9 to +11 2.05 0.20 1.85

+1 to +13 1.94 0.26 1.68

-4

-3

-2

-1

0

1

2

3

4

5

6

7

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40

Effe

ctiv

e S

ha

do

win

g A

ng

le (

°)

Slit position given by azimuth angle (°)

ESA Horizontal Structures

ESA Vertical Structures

G-Number

15

Mask Reflectivity Variation Compensation

G-Number

16

Reflectivity measurements on FRESCO

Reflectivity variation < 0.1% (absolute); so no compensation for reflectivity variation (sensitivity in model is ~1 nm per 1% reflectivity change)

Reflectivity optimized for 6 angle of incidence which has the right d-spacing for uniform reflectivity through incidence angle

No reflectivity variation worth correcting for

-15 -10 -5 0 5 10 1564.08

64.10

64.12

64.14

64.16

64.18AGC 071214-1

Re

fle

ctivity (

%)

Measurement

A

12.5 13.0 13.5 14.0 14.50.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

AGC 071214-1

Re

fle

cta

nce

Wavelength (nm)

4 deg

6 deg

8 deg

G-Number

17

Experiments on the ADT

G-Number

18

FRESCO compensation experiments on Alpha Demo Tool(ADT)

ADT#2 (IMEC): 0.25 NA, =0.5

80 nm FT SEVR-59 resist on 20 nm underlayer

7 x 7 shot map, 26 mm x 22 mm with 4 mm spacing (non–touching die)

38.00

40.00

42.00

44.00

46.00

48.00

50.00

10 11 12 13 14 15 16 17 18 19

DC

CD

(n

m)

Dose (mJ/cm2)

V L40P80 at X=13 mm, Y= 8mm

L40P80

18 mJ/cm2, 3.3 nm LWR

31.00

33.00

35.00

37.00

39.00

41.00

43.00

45.00

-0.15 -0.1 -0.05 0 0.05 0.1 0.15

DC

CD

(n

m)

Focus(um)

L40P80 FE V uncompensated, X=13 mm, Y = 0.01 mm

12

13

14

15

16

17

18

Wafers were targeted to print 40 nm HP features at 18 mJ/cm2; LWR was low (~3.3 nm)

G-Number

19

CD-SEM measurements

Automated CD-SEM jobs were created to measure the CD at 9 points separated by 2 m centered at the center of the OCD pads (spread over a 4 m x 4 m region in the center of the OCD pad)

The average standard deviation of the 9 measurements was < 0.2 nm (see sample below)

The measurements were done at 26 x 16 locations or 3744 measurements/die

G-Number

20

L40P80 CDU across the slit

CDU shows that there is a strange slit signature on the ADT which could be from illumination non-uniformity, lens aberrations (astigmatism, & coma/trifoil), apodization, and source shape

Mask CD variation appears to be negligible

Comparing HV-bias across the slit eliminates the illumination non-uniformity but not lens aberrations etc

33.00

34.00

35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

0 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000

DC

CD

(n

m)

Location in X (um)

V L40P80 CDU at Y = 5 mm

Vertical

Horizontal

Mask CD V

Mask CD H

G-Number

21

L40P80 HV-bias across the slit

Predicted HV-bias was ~ 1 nm less than experiment (bottom, uncompensated) – Predicted HV-bias (using 87 nm mask absorber thickness) was 2.3

nm at the center (X=13 mm), and 1.68 nm at the edges (X= 1 mm) whereas the experimental data shows center HV-bias is 3.5 nm & 2.5 nm at the edges

The measured HV bias across the slit for the compensated region varies from 0 to 1 nm – There is a strange effect at the edges of the slit (at X values of 0, 1,

24, and 25 mm)

The residual trend in the compensated HV-bias could be due to aberrations, apodization, &/or source shape

0.000.501.001.502.002.503.003.504.00

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000 26000

HV

-bia

s (n

m)

Location in X (um)

L40P80 HV bias averaged in Y (across all density/flare levels)

HV bias, Top (compensated)HV bias, Bottom (uncompensated)Predicted optical HV bias

G-Number

22

Reminder: flare variation

0

1

2

3

4

5

6

7

8

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

Flar

e (%

,)

Location in Y (um)





X = 3 mm X = 13 mm

With CD sensitivity to flare ~1 nm/% flare and expected flare range of ~3%, ~3 nm CD change is expected

G-Number

23

Mask CD variation

Mask CD deviation from design increases with increased “chrome” loading during the mask making process

0

0.5

1

1.5

2

0 2000 4000 6000 8000

∆FC

CD

mas

k (n

m,

1X

)

Location in Y (um, 1X)

∆ Mask CD Vs design CD at the bottom (uncompensated) Vs location in Y at X = 13,100 (1X)

Delta V mask CD bottom center

Delta H mask CD bottom center

0

0.5

1

1.5

2

13000 15000 17000 19000 21000

∆FC

CD

mas

k (n

m,

1X

)

Location in Y (um, 1X)

∆ Mask CD Vs design CD at the top (compensated for flare and shadowing) Vs location in Y at X = 13,100

(1X)

Delta H mask CD

Delta V mask CD

0

1

2

3

4

5

6

7

8

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

Flar

e (%

,)

Location in Y (um)





G-Number

24

L40 P80 V CD variation at X = 13 mm

CD variation was reduced from 3 nm to 2 nm after compensation

If we include the effect of mask CD variation, then the compensated CD variation would be 0.75 nm – Almost all of the CD variation is at the first location (close to

edge of the die)

35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)

CD variation on FRESCO at X = 13 mm

Compensated: Wafer CD V

Uncompensated: Wafer CD V

Designed V (compensated)

Compensated+corrected for mask CD: V

Note: X-axis for compensated data was transposed to make comparison with uncompensated data

G-Number

25

L40 P80 V CD variation at X = 3 mm

CD variation was reduced from 3.75 nm to 2 nm after compensation

If we include the effect of mask CD variation, then the compensated CD variation would be 1 nm

– Almost all of the CD variation is at the first 2 locations (close to edge of the die)


35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)




Designed V (compensated)

Compensated+corrected for mask CD: V

G-Number

26

L40 P80 H CD variation at X = 13 mm


If we include the effect of mask CD variation, then the compensated CD variation would be 1 nm – Part of the CD variation is due to the 1st point at the edge of the die

– However, the compensated CD variation observed at Y = 4 mm and 5 mm is due the designed CD variation based on the rule based compensation

– Due to relatively large discretization of flare levels in the rule based FVC, the flare values at those locations (6.6% and 6.1%) were barely above the previous lower flare bin


35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)


Compensated: Wafer CD H

Uncompensated: Wafer CD H

Designed H (compensated)

Compensated+corrected for mask CD: H

G-Number

27

L40 P80 H CD variation at X = 3 mm


If we include the effect of mask CD variation, then the compensated CD variation would be 1.5 nm – Most of the CD variation is due to the 1st point at the edge of

the die


35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)




Designed H (compensated)

Compensated+corrected for mask CD: H

G-Number

28

L40 P160

Even without accounting for mask CD variation, the CD variation reduced from 3 nm to 1 nm after FVC for L40 P160

35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)




35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)

L40 P160 CD variation on FRESCO at X = 3 mm



35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)




35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

0 1000 2000 3000 4000 5000 6000 7000 8000

DC

CD

(n

m)

Location in Y (um)




G-Number

29

Summary & conclusions Observed significant CD variation due to mask

shadowing on the ADT exposure tool

– H-V bias decreases from the center to the edge of the slit

– Shadowing compensation reduced H-V bias from 3.5 nm to <1 nm across the slit

Demonstrated up to 67% reduction in CD variation by Flare Variation Compensation (FVC)

– Nearly half of the residual after FVC was due to mask CD variation; the remaining half was due to flare modeling errors at the edge of the die

Reflectivity variation across the field is < 0.1% (absolute); no variation worth correcting for

OPC for EUV must include effects such as flare and

mask shadowing

G-Number

30

Acknowledgements

Intel EUV lithography team & IMO

IMEC

experimental validation of full-field compensation for …€¦ · experimental validation of...

Documents