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

Abstract

Platinum (Pt)-incorporation (5 -10%) into nickel silicide films is a promising approach to reduce the contact resistance (RC) at the silicide/Si interface. One key issue during this silicide step is converting Ni-Pt silicide at different rapid thermal annealing (RTA) temperatures. The first RTA is performed to form Ni Silicide at a controllable thickness, followed by a Ni strip to remove access materials, lastly a second RTA is performed to drive Pt into the NiSi network at a higher temperature. This process results in finer crystal grain and enriches the Pt of Ni-Pt silicide, thereby suppressing the increase in resistivity in Ni-Pt silicide. After NiPtSi formation, the final step is to remove the Pt residues with aqua regia (AR). A High Productivity Combinatorial (HPC) materials/process screening technique was used to reduce the number of product wafers needed for the evaluation process development. Using this technique, the etch rates of all materials of interest were tested on blanket wafers. The defectivity was tested using full flow product wafers. Complete NiPt residues removal was achieved using dilute nitric acid and dilute aqua regia at low process temperature. Also, aqua regia shelf-life and queue time before and after RTA were shown to effect the Pt residues removal.