Reduction of surface roughening due to copper contamination prior to ultra-thin gate oxidation

Abstract

Roughening of the polished side of a silicon wafer caused by copper contamination present on the unpolished side of the wafer was quantified by tapping-mode atomic force microscopy (AFM). The copper contamination was introduced via a contaminated buffered hydrochloric acid solution on the unpolished side of the silicon wafer while the polished side was protected. The protection was then removed, and the wafer placed in a clean HF solution. As a result, the copper on the unpolished side catalyzed electrochemical dissolution of the polished side of the silicon. Power spectral density analysis of hundreds of AFM images showed a 10-fold increase in surface roughness with features between 30 and 300 nm in diameter. Time-dependant dielectric breakdown measurements showed a significant decrease in oxide quality in these wafers. However, the introduction of HCl to the HF solution significantly reduced the roughening process.