Failure Analysis of Resist Pattern Collapse: Surface Tension Influences

Cyrus TaberyMay 29, 2000

Problem: Resist Feature Collapse

• Resist features collapse upon formationat high aspect ratios.

• What are important parameterscontrolling this phenomena?

• What is required to design around thisproblem?

Shear and Bending Model• Beam is treated as

elastic solid

• Young-Laplacepressure

• Aspect Ratio

Substrate

E

R

γz

x

y

L

Pitch P

ThicknessεP/2

2

2zPLM y ∆=

96

3LPI y =

RnP

γγ =⋅∇=∆

Moment of Inertia

Bending Moment

PLdz

vdEI y ∆=

4

4

HalfPitch

Thickness=ε

Shear and Bending Model Cont.• Shear Stress is linear

with ε

• Tensile stresses isquadratic in ε

)2

(P

zPxy −∆= ετ

2max

3

2

12

48

εγσ

σ

P

P

Pxzx

I

M

y

yz

=

∆==

z

x

Perturbation in Spacing• Stress field in resist

beam causesdeformation

• Deformationinfluences Laplacepressure

Ev

γε 4max 3=

max

4

vPP

−=∆ γ

R

R

Elastic Deformation

An Illustrative Example

Perturbation in Spacing Cont.• Updated Laplace

pressure gives newelastic problem.

• Several iterationsreveals a seriesconvergence fordeformation and stress

• Note: Rigid Model isrecovered in limit E 8

∑=

−

−=

i

m

mi

EPEv

0

44)(max 63

γεγε

−−=

22

2842

max183

1

112

EPPE

P γεγεεγσ

( ) 10

+=−∑∞

=

− xxm

m

+

Feature Collapse Comparison• Consider the

system– E~109 Pa

γ~70 mJ/m2

• High stressescause adhesive orplastic deformationfailure, thus criticalaspect ratio existsfor each pitch. 100 101 102

10-4

10-2

100

102

104

106

Aspect Ratio

Fai

lure

Pitc

h (m

icro

ns)

Uns table Region

Stable Region

Elas tic ModelRigid Model

Models Conflict

Conclusions• Elastic deformation is important in

considering failure of resist beams– Rigid model significantly overestimates

stable region

–

• Length scale for deformation isγ/Eε4~0.07ε4nm for glassy polymer/H2O

• Supercritical develop would eliminateinterfacial tension induced failure

scaleFeature

scalenDeformatio

PENTa _

_4

== γε