The size effect of liftoff metallization of sputtered aluminum films

Liftoff metallization of sputtered aluminum films successfully produces small patterns with tapered sidewalls. In this metallization, a size effect occurs wherein pattern height is influenced by pattern width. This article reports experiments regarding size effect dependences on liftoff parameters of pattern width, film thickness, photoresist thickness, and sputtering argon pressure. The size effect is favorably suppressed by reducting photoresist thickness and sputtering argon pressure. In addition, the effect is discussed by a model taking into account shadowing of sputtered atoms due to photoresist patterns and aluminum film itself deposited on the photoresist patterns.