Kostas Adam, Andrew Neureuther Characterization of Phase Defects in Phase Shift Masks and a New Model for Mask Edges SFR Workshop November 8, 2000 Kostas Adam, Andrew Neureuther Berkeley, CA 2001 GOAL: complete simulations for polarization masks and multi-parameter test structures by 9/30/2001 11/8/2000

Motivation Phase Shift Masks are finding their way into the production of ICs. However, the impact of phase defects needs to be carefully characterized: The inspection of phase defects is a difficult task. New approaches in locating defects in the quartz need to be explored Ideal mask simulations although speedier are known to suffer in accuracy. Taking into account edge diffraction effects the accuracy can be significantly improved 11/8/2000

An Isolated Quartz Post is Different than a Void l=248nm x y Observation plane 200nm x y Observation plane 1 2 Normalized |Ey| 1.0 1.2 1.4 1.6 1.8 -120 -80 -40 40 Mask Position (mm) Phase (deg) Mask Position (mm) Phase (deg) 100 120 140 160 180 200 220 1.0 1.2 1.4 1.6 1.8 11/8/2000

E-field Phase and Average Intensity vs. Defect Size 11/8/2000

Example: Alternating Phase Shift Mask defect-free APSM post defect phase defects void defect defect height underetch 0o 180o d size 0o 180o CDmask Illumination: Linearly polarized plane wave (TE/TM), l=248nm Imaging: Demagnification=4X, s=0.3, NA=0.68 160x160nm (4X) post |E| Phase of E Glass posts and voids have different near-field characteristics 160 x 160nm (4X) void |E| Phase of E 11/8/2000

CD Variations Caused by Phase Defects %DCDaerial=(CDdef-CDref)/CDref 11/8/2000

Inspection of Phase Defects: Approach The defect proximity to the feature affects both its inspectability and its printability Isolated quartz defect: Spatial variations of EM field (modes) 0o 180o Approach (similar to Socha’s contact hole inspection): - Excite a spatial mode within the defect and find the EM field outside - Time reversal: Use the calculated EM field as new illumination resulting EM field excite defect mode 11/8/2000

New Model for Mask Edges: Approach Goal: Model the bias between ideal and rigorous simulations to allow use of the thin mask approximation in the design of OPC etc. geometrical position of edge Illumination: E Quartz clear level (1) Stack middle level Air gray level (.265) New edge location for ideal simulation New Model: Modify mask geometry that is input in an ideal SPLAT simulation. This can be done by extracting information from the near-field diffraction pattern of 2D rigorous simulations (TEMPEST). 50nm So far: New Model: In SPLAT Mask In SPLAT Mask a+Da a a a b b b b +Db 11/8/2000

Conclusions and Goals Isolated quartz voids are seen to behave more like Cr defects - isolated quartz posts behave more like phase defects Voids (of equal size) are less than 50% as harmful to the aerial image than posts (first reported by Friedrich et al., SPIE2000, see also Adam et al., EIPBN2000 ) Vertical propagation programs (SPLAT) underestimate the effect of a defect by 25%-50%, when the insufficient 1/180o model for phase defects is used Establish guidelines for 3D defect sizing and feature interactions (Goal for 9/2002) Propose alternative inspection approach for phase defects and demonstrate its limits (Goal for 9/2002) 11/8/2000