Influence of chemical mechanical polishing of copper on the inherently selective atomic layer deposition of zirconia

Abstract

Copper is a highly used material for making interconnects in complementary metal-oxide-semiconductor devices in today's semiconductor industry. In this process, chemical mechanical polishing (CMP) is performed on silicon (Si) wafers patterned with electroplated (EP) copper (Cu) whereby further processing by selective atomic layer deposition (SALD) of zirconia on Si only is highly desirable. Although there have been previous studies of the selectivity on Si over Cu, inherent selectivity of an ALD process on post-CMP Cu was not discussed. CMP can modify the Cu surface and leave residual contaminants which can influence the selectivity of deposition. To understand the impact of CMP treated Cu surface on SALD, this study, first, examines the chemical surfaces of three forms of Cu: electron-beam deposited, EP, and post-CMP Cu and then evaluates the selectivity of the ALD process by altering process parameters. X-ray photoelectron spectroscopic surface analysis and atomic force microscopy reveal post-CMP Cu having a slightly different chemical composition and lower surface roughness than EP Cu. SALD of zirconia was performed using ethanol both as the pre-deposition surface treatment agent and the oxygen source for the zirconium precursor used - tris(dimethylamino)cyclopentadienyl zirconium under variable process parameters. Since CMP of Cu is a necessary component of semiconductor manufacturing, assessing selectivity of this process on this form of Cu was necessary. In this study, we show a ∼2 nm ZrO2 layer on Si via ALD was possible with no deposition on post-CMP Cu under a less robust process window than that observed for other forms of Cu.