Study of the Carry-over Layer and Its Importance for Wet Processing of Semiconductor Substrates

Abstract

In this paper we investigate the entrainment of a liquid film by a solid as the latter is removed from a bath (referred to as the carry-over layer). This is done theoretically as well as experimentally with emphasis on its role in immersion-based processing of flat substrates such as semiconductor wafers. Existing models calculating liquid withdrawal by infinite substrates are modified to take gravitational drainage into account. The latter is important when substrates of a finite size (such as semiconductor wafers) are considered. Experiments using metal salts as tracer elements are performed to evaluate the thickness of the carry-over layer as a function of withdrawal speed and postwithdrawal drainage time. A good agreement with the drainage models is obtained, leading us to draw some qualitative conclusions concerning liquid carry-over during semiconductor wafer processing.