Resolving Integration Issues from Bump Metal Processing

Abstract

Bump processing is a very common, cost-effective packaging technique which requires thick (>1 µm) AlCu top metal deposition. Use of this thicker metal has led to numerous process integration and defect inspection challenges. Several problems lurk at the edges of the multidimensional process window for this thick metal module. They include inducing soft shorts through metal spires or metal residuals, enhancing copper precipitates, and the anomalies generated from these precipitates. These anomalies lead to challenges obtaining useful defect inspection data and also adverse effects post fab bump processing [1]. Bump photo processing often experiences severe alignment problems due to inability to discern alignment marks. The primary cause for alignment fails is the copper precipitate anomalies. There are additional variables discussed as well in deposition and etch processes.In this paper, we detail this multi-variable fab integration problem initiated by challenges with thick metallization processing and outline the ways to minimize the negative effects.