Highly selective oxide to nitride etch processes on BPSG/nitride/oxide structures in a MERIE etcher

This study is on oxide etch selective to nitride using a C/sub 4/F/sub 8/-CO-Ar-O/sub 2/ chemistry in a RIE chamber. It has been tested in a manufacturing environment on several applications for 16 and 64 megabit DRAM chips. Film stacks tested included a BPSG/nitride self-aligned contact type of application and a BPSG/nitride/oxide application. Aspect ratios ranged from 4:1 to 8:1. Critical dimensions were typically 0.4 /spl mu/m and 0.3 /spl mu/m, but for one application, oxide etch had to finally occur in a 0.09 /spl mu/m wide space. Process development started with a design of experiments on patterned wafers in order to understand the major trends of the chemistry. The wafers were analysed by SEM. Fine tuning of processes for each application involved optical emission spectroscopy (OES) and electrical test yield analysis.