Simulation Analysis of Defect Repair Methods for EUVL Mask Blanks Association of Super-Advanced Electronics Technologies (ASET) EUV Process Technology Research Laboratory Takeo Hashimoto and Iao Nishiyama
Contents Background Blanks repair methods Simulation method Results Amplitude defect repair Phase defect repair Defect covering by absorber pattern Conclusions
Background (1) -Critical issues for EUVL- Critical issues for EUVL 1. Source poer and lifetime including condenser optics lifetime 2. Availability of defect free masks 3. Reticle protection during storage, handling, and use 4. Projection and illumination optics lifetime and contamination Defect mitigation Patterning Repair Inspection 5. Resist resolution, sensitivity, and LWR Mo/Si Multilayer Mask Blanks 6. Optics quality for 32nm node
Background Defect mitigation SEMI P38 1102 Defect requirements for multilayer stack Class A B PSL equivalent range (nm) 25 30 Maximum defect count 0 0 Recent progress for defect mitigation Defect density ( /cm2) 10.0 1.00 0.10 IBS Helicon (DC) ASET(2003) [>120-70nm ] Others C 40 0 0.01 D 60 Agreed upon beteen user and supplier 0.001 Target 0.003/cm2
Blanks repair methods Scooped by FIB, EB Covering Amplitude defect Absorber Phase defect Depression by EB exposure substrate Schematic of multilayer defects
Simulation method Simulator: EM-Suite (TEMPESTpr) Absorber Buffer defect Substrate h substrate Defect Typical defect @ ASET h EUV 13.5nm Multilayer Mo/Si 40pair Multilayer Mo/Si pair: 40 d-spacing: 6.95nm(nominal) : 0.4 Exposure tool : 13.5nm NA/: 0.25/0.80 Incident angle: 6 Magnification: x4 Mask structure Buffer : Cr 10nm Absorber: TaGeN 70nm Cap : Non Contrast : More than 100
Amplitude defect repair Scooped ith FIB, EB and RAVE Defect50nm, Mo 200nm 50nm y Mo/Si Aerial image after scooping repair Crater depth dependency No repair The intensity degradation is small in case of crater depth less than 20nm.
Amplitude defect repair The effect of capping layer formation on a crater A. Barty et al. (SPIE 2002) Ar ion beam Cap material Si Thickness: t=5nm Sputtered cap 250nm 200nm y=20nm Mo/Si t No comformal Without cap
Phase defect repair by EB exposure EB No smoothing effect defect defect h h substrate p Initial d :6.95nm EB contraction Defect sizeh=10nm, =40nm h substrate Imin. is recovered by d-spacing contraction due to EB exposure.
Phase defect repair by EB exposure Imin. of aerial image after EB repair P h=10nm, =40nm, on substrate Defect size Before repair The reason for insufficient recover of Imin. Reflectivity loss accompanied by d-spacing reduction Structure distortion inside multilayer stack (even though the surface of multilayer is flat.)
Phase defect repair method taking account of d-spacing reduction Reflectivity loss No reflectivity loss Reflectivity Reflectivity loss No loss Wavelength (nm) Wavelength (nm) Reflectivity Initial d-spacing6.95nm After repair: 6.85nm Initial d-spacing7.01nm After repair: 6.92nm
Phase defect repair method taking account of d-spacing reduction Defect on substrate (at the bottom of multilayer) Defect sizeh=10nm, =40nm (on Mask) Initial d-spacing6.95nm Before repair After repair Imin. of aerial image recovers sufficiently by taking account of initial d-spacing. Initial d-spacing7.01nm Before repair After repair
Effect of EB repair for defects in multilayer Defect sizeh=10nm, =40nm EB 40th layer 30th layer 20th layer 10th layer Aerial image for optimized contraction of d-spacing Substrate 0.45 0.31 0.17 z (/2) z
Defect covering by absorber pattern Absorber 128 32nmL&S (x4 Mask) 128 128 128 Covering h=10nm h=10nm a) =80nm (20nm) b) =160nm (40nm) Not resolved Not resolved
Defect covering by absorber pattern Absorber 128 128 128 128 h=10nm =80nm intensity distibution (20nm on afer) CD CD (nm) 40 30 Defect size dependency of CD 2.5% 32nmL&S 10 20 30 40 /4(nm)
Conclusions 3 kinds of defect repair methods for multilayer mask blank ere evaluated through aerial image simulations. It as confirmed that they ere effective for amplitude and phase defect repair. If defect density of mask blank is close to the target value in future, the defect covering by absorber pattern ill be especially effective. Defect repair ill be a useful countermeasure for EUVL mask blank defect issues. Acknoledgement This ork as supported by NEDO.