High Productivity Combinatorial Analysis of Cu Post-CMP Cleans: Corrosion Protection and Queue Time

Abstract

High Productivity Combinatorial (HPC) technology was used to evaluate post-CMP clean chemistries and their impact on copper surface corrosion protection and queue time performance. Cleaning formulations at low pH and high pH, both with and without functional additives, were used to produce a wide range of surface conditions typical in semiconductor processing. X-ray photoelectron spectroscopy (XPS) results show that low pH cleans remove most oxides, but that within 20 hrs copper oxide re-growth occurs in the form of Cu (I) and Cu (II) oxide species. Electrochemical analysis is a simpler and higher throughput method to study oxide growth over time. Good agreement existed between electrochemical and XPS techniques when both were used to study copper surfaces for 0 to 20 hours after clean. The electrochemical tests were continued after 48 hours of queue time to develop a better understanding of oxide growth trends, and showing continued oxidation of Cu surfaces treated with low pH cleans. For extremely long queue times, SEM analysis shows growth of visible copper oxide nodules on Cu lines and pads for low pH treated M1 test structures. Leakage of comb structures monitored as a function of queue time was inconsistent, indicating that standard leakage measurements at 1V for comb structures with 0.125 / 0.175 line/space dimensions are not sensitive to the copper surface instability of oxidation.