Key Photolithographic Outputsmyplace.frontier.com/~stevebrainerd1/PHOTOLITHOGRAPHY/Week … ·...

3/28/03 PHOTOCLASS/ECE580/Overview/plots.ppt Brainerd

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Key Photolithographic Outputs

• Exposure latitude • Depth of Focus• Exposure latitude Vs DOF plot• Linearity and MEEF• Isolated-Dense Bias• NILS• Contrast• Swing Curve• Reflectivity Curve


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• Exposure latitude:The range of exposure energies (usually expressed as a percent variation from the nominal) which keeps the linewidth within specified limits.

• Example:A minimum exposure latitude of 10% is needed for this process in order to get adequate CD control.

• % = [Exposure for low CD spec - Exposure for high CD spec]/ Exposure dose for Target CD

D U V P hotores is t FEM

y = -0 .0 3 8 1 x + 1 .5 0 6 4R 2 = 0 .9 9 1 5

0 .7 50 .7 60 .7 70 .7 80 .7 9

0 .80 .8 1

0 .8 20 .8 30 .8 40 .8 50 .8 60 .8 70 .8 80 .8 9

0 .90 .9 1

0 .9 20 .9 30 .9 40 .9 50 .9 60 .9 70 .9 80 .9 9

11.0 1

1.0 21.0 31.0 41.0 51.0 61.0 71.0 81.0 9

1.11.11

1.121.131.141.151.161.171.18

1 0 1 0 .5 1 1 1 1 .5 1 2 1 2 .5 1 3 1 3 .5 1 4 1 4 .5 1 5 1 5 .5 1 6 1 6 .5 1 7 1 7 .5 1 8 1 8 .5 1 9

Ex pos ure Dos e (m J /c m 2 )

Phot

ores

ist l

inew

idth

CD

(um

)

T arg et CD

U p p er S p ec CD

L o w er S p ec C D


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• Depth of Focus 200 nm spacewidth: Focus range for target CD +/- 10%

DUV: UV6 ( 6275A) on SiON on Polysilicon

0

100

200

300

400

500

600

-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Focus microns

Spac

ewid

th C

D n

m (

1:1

200n

m)

8 mj/cm29 mj/cm210 mj/cm211 mj/cm212 mj/cm213 mj/cm214 mj/cm215 mj/cm216 mj/cm217 mj/cm218 mj/cm219 mj/cm22 0 mj/cm22 1 mj/cm22 2 mj/cm22 3 mj/cm22 4 mj/cm22 5 mj/cm2


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• Depth of Focus 250nm linewidth: Prolith setup with TARC ( JSR NFC-540) and BARC ( SiON)


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Key Photolithographic Outputs• Depth of Focus 250nm linewidth: Focus range for target CD +/- 10%

248nm DUV UV6 with TARC/BARC 250nm L/S

200205210215220225230235240245250255260265270275280285290295300

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Focus Microns

Phot

ores

ist C

D n

m (

1:1=

250n

m)

5.5 mj/cm26 mj/cm26 .5 mj/cm37 mj/cm27.5 mj/cm48 mj/cm28 .5 mj/cm59 mj/cm29 .5 mj/cm610 mj/cm210 .5 mj/cm711 mj/cm211.5 mj/cm812 mj/cm212 .5 mj/cm913 mj/cm213 .5 mj/cm1014 mj/cm2

DOF = 1.0u

best focus = -0.35u


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Key Photolithographic Outputs• Depth of Focus 250nm linewidth: Sidewall angle ( >80 degrees) and

CD spec range( CD target +/-10%) specs are met!


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Key Photolithographic Outputs• “Best” Focus 250nm linewidth: Optimal focus = centered in focal

range for best dose to achieve maximum sidewall angle and target CD


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Key Photolithographic Outputs• Exposure latitude Vs DOF plot from Prolith example: Depth of Focus

250nm linewidth:Exposure latitude Vs DOF 300nm dense

Linewidth from Prolith

0123456789

1011121314151617181920

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

DOF microns

% E

xpso

ure

Latit

ude

Taken from CD Vs Focus plot ( FEM) Maximum process rectangle that contains CDs and sidewall angles meeting the specified criteria. The Exposure latitude is taken as the height of the rectangle and the DOF as the base of the rectangle.

Maximum DOF = single dose( 0% exposure latitude) , while Maximum exposure latitude = 0 DOF (1 focus setting)


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Key Photolithographic Outputs• Linearity and MEEF(Mask Error Enhancement Factor): Slope of Wafer

CD Vs Reticle CD (scaled to 1X): Ideal MEEF =1.00. See plot at right. For small CDs the change in the wafer CD is greater than the reticle CD.

• MEEF = δCD image /δCD mask


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• Isolated-Dense Bias: Caused by diffraction differences

• CDS are same size on reticle scaled to 1X• ISO-DENSE BIAS = Isolated wafer CD - Dense wafer CD


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• Isolated-Dense Bias: Caused by diffraction differences

• CDS are same size on reticle scaled to 1X• ISO-DENSE BIAS = Isolated wafer CD - Dense wafer CD


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Key Photolithographic Outputs NILS

The slope of the image intensity as a function of position (dI/dx) measures the steepness of the image at the transition from bright to dark


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NILS : Normalized image log slope: slope of aerial image intensity (NILS) pattern multiplied by the feature width. This is a metric for the quality of the aerial image. Values between 6 – 8 are good! Can use inProlith for quick Simulations to investigate OPTICAL effects. NILS saysnothing about Photoresist patterns.


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NILS : Normalized image log slope:


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16




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NILS : Normalized image log slope: As image goes out of focus the image slope (NILS) decreases


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PROLITH Simulation NILS : Normalized image log slope: Typical NILS Vs Defocus curve


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PROLITH Simulation NILS : Normalized image log slope: Typical NILS Vs Defocus curve with multiple wavelengths ( Run simulation usingwavelenth min, max step, then Use Prolith’s Multi-line function. Focus = X axis; NILS = Y axis; wavelength = Z axis)


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Key Photolithographic Outputs: Contrast

Photoresist Contrast definition


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Image edge Partially exposed defines sidewall angle


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• Swing Curve: Thin films interference Effect:• Key photoresist CD variation Effects:

• Swing Curve: Interference of r1 and r12

• Standing Waves: Interference of i1 and r1

Swing CurveSpace width CD nm

600

625

650

675

700

725

750

775

800

825

850

800 850 900 950 1000 1050 1100 1150 1200

Photoresist Thickness nm

Spac

ewid

th C

D n

m

Space width CD nm

Reflective substrate ns

Medium no

i1

r1

r12


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• Reflectivity Curve: Prolith set up


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• Reflectivity Curve: Prolith

SiON Reflectivity: 248nm Wavelength on Polysilicon : SiON k effect

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

0.36

0.38

0.4

0.42

0.44

0.46

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

SiON thickness nm

Phot

oesi

st R

efle

ctiv

ity %

n= 2.15; k = 0.72n= 2.15; k = 0.22n= 2.15; k = 0.92n= 2.15; k = 1.10

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