HIGH SELECTIVITY PLASMA-ETCHING OF SILICON DIOXIDE WITH A DUAL-FREQUENCY 27 2 MHZ CAPACITIVE RADIO-FREQUENCY DISCHARGE/

A 27 MHz/2 MHz Ar/CO/CFx rf capacitive discharge was used to selective ly etch submicron SiO2/Si, SiO2/TiSi2 and SiO2/TiN structures. The bor ophosphosilicate glass etch rate (similar to 1.0 mu m/min) was observe d to decrease with bottom electrode temperature, whereas etch selectiv ity to TiSi2 (>50:1) was found to increase with temperature, with a ph otoresist selectivity >50:1. Plasma emission of the dual frequency dis charge indicated the presence of an abundant concentration of the CF2 radical (249 nm) as compared to a lower frequency (400 kHz) rf dischar ge with low etch selectivity (<20:1). Langmuir probe measurement indic ated an enhancement of ion density of an order of magnitude (similar t o 5x10(10) cm(-3)) as compared to the low frequency (400 kHz) rf disch arge. Particle-in-cell simulation was used to calculate plasma density as a function of excitation frequency. Plasma density scales with the square of the source frequency while it remains relatively independen t of the substrate frequency. (C) 1995 American Vacuum Society.