Process to Etch Ni and Pt Residues during Silicide Contact Electrode Processing Using Low Temperature Aqueous Solutions

Abstract

During NiPtSi contact electrode processing and after the first thermal treatment to form Ni rich silicide, excessive Ni is removed by a strong acid mixture such as piranha (mixture of sulfuric acid and hydrogen peroxide. The post salicidation clean process has to be selective to all exposed materials: Si3N4, SiO2, NiPtSi, and NiPtSiGe (contact electrodes of source/drain for strain applications)). Performing a partition process with RTA1 (rapid thermal annealing) followed by Ni strip, followed by RTA2, and then with Pt strip is one method to check for NiPt removal. The Ni strip was performed using dilute nitric acid (20:1) and dilute aqua regia (1:5:4) and showed completed NiPt removal. A queue time study was also investigated after the Ni strip and after RTA2 for defect formation. Also, Pt removal using aqua regia solutions of various shelf-lives were tested. The result led to the conclusion that solutions of aqua regia with longer shelf-lives were also shown to be less effective in Pt residue removal. Using a High Productivity Combinatorial materials/process screening technique to reduce the number of product wafers used for evaluation process development, the etch rates of all the materials of interest were tested on blanket wafers. The chemistry consists of varying acid and base types and the relative combinations of these chemistries. Process conditions that consisted of various process chemistries, process temperatures, and degrees of fluid agitation (e.g. stirrer speed) were done on the same substrate.