Published in Semiconductor International, April 2007

By Tuan Le

INTRODUCTION
Automated edge inspection has revealed several immersion-specific defectivity modes. Defects related to the activity of the immersion fluid, interactions with resists and topcoats, and edge bead removal processes can have a significant effect on process yield.

The availability of high-speed automated edge inspection has created a growing awareness of the impact of the wafer-edge defects on process yield. Some manufacturers estimate that 30% or more of killer defects originate from wafer-edge regions. Increased focus on edge defectivity during the development of advanced processes and materials for 300 mm manufacturing has revealed a number of edge-specific mechanisms that will require careful monitoring and control as new processes move into production. Developing and qualifying new processes require sensitive detection and detailed characterization capabilities.

Controlling these processes at high volume demands production-worthy inspection capability -- adding such requirements as high throughput and robust automatic classification of a broad range of physical- and process-related defects. The imminent introduction of immersion lithography is an excellent case in point -- interactions of the wafer and scanner through the immersion medium introduces a number of novel defectivity modes, several of which are edge-specific. Although edge defects typically do not cause yield loss directly, they are often precursors to killer defects in the wafer's active area. Real-time edge inspection ensures that edge defects can be detected, and their causes can be corrected, thereby minimizing yield impact.

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