Failure Analysis of Resist Pattern Collapse: Surface Tension ...

Failure Analysis of Resist Pattern Collapse:Surface Tension InfluencesCyrus 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 aselastic solidEI y• Young-Laplacepressure∆P= γ ∇ ⋅ n =• Aspect Ratioε =d4dzv4= ∆PLγRThicknessHalfPitchzLyI y=ELP963M y= ∆PLxR2z2γPitch PSubstrateMoment of InertiaBending MomentThicknessεP/2

Perturbation in Spacing• Stress field in resistbeam causesdeformationv=max3ε 4γE• Deformationinfluences LaplacepressureRElastic DeformationR∆P=P4γ− vmax

An Illustrative Example

Perturbation in Spacing Cont.• Updated Laplacepressure gives newelastic problem.• Several iterationsreveals a seriesconvergence fordeformation and stress• Note: Rigid Model isrecovered in limit E8vγi( i)⎛ =4max3ε∑⎜− 6E m=0σmax∑ ∞m=0γ= 12 εP2⎝+⎛⎜⎜⎜⎜1−⎝ε441γEP−m( − x) = x + 1⎞⎟⎠−m83εγ 18εγ−PE2 2P E2⎞⎟⎟⎟⎟⎠

Feature Collapse Comparison• Consider thesystem– E~10 9 Paγ~70 mJ/m 2Failure Pitch (microns)10 6 Elastic ModelRigid Model10 410 2Stable RegionAs pect Ratio• High stressesModels Conflictcause adhesive or 10 0plastic deformationfailure, thus critical10 -2Unstable Regionaspect ratio exists1010for each pitch. 0 10 1 10 2

Conclusions• Elastic deformation is important inconsidering failure of resist beams– Rigid model significantly overestimatesstable region–N Ta4ε γ=PE=Deformation _ scaleFeature _ scale• Length scale for deformation isγ/Eε 4 ~0.07ε 4 nm for glassy polymer/H 2 O• Supercritical develop would eliminateinterfacial tension induced failure