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

Roughening of the polished side of a silicon wafer caused by copper contami nation present on the unpolished side of the wafer was quantified by tappin g-mode atomic force microscopy (AFM). The copper contamination was introduc ed via a contaminated buffered hydrochloric acid solution on the unpolished side of the silicon wafer while the polished side was protected. The prote ction was then removed, and the wafer placed in a clean HF solution. As a r esult, the copper on the unpolished side catalyzed electrochemical dissolut ion 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 brea kdown measurements showed a significant decrease in oxide quality in these wafers. However, the introduction of HCl to the HF solution significantly r educed the roughening process. (C) 2001 Elsevier Science B.V. All rights re served.