Optimization of Metal Photo Rework Dry Strip Scheme for Yield Improvement : YE: Yield Enhancement/Learning

Abstract

Photolithography is one of the most critical operations in semiconductor manufacturing. Due to increasing complexity and stricter limits on CD control, rework routes exist that involve plasma-based resist ash, wet clean and send back again to coat, expose and develop. Yield loss was observed on rework of metal layer wafers where the critical dimensions were out of control on inspection post lithography. The cause of the yield loss was primarily due to formation of Al2Cu precipitates due to heat cycling of 0.5wt.% Cu below 293°C. This paper describes the development of a metal-layer photo rework scheme that involved a reduction of amount of temperature cycling steps in a dry strip chamber and changing process temperature from 270°C to 300°C (from precipitation to anneal region of Al2Cu) to significantly improve die yield on reworked wafers between 90-130nm technology nodes.