Oxide etch behavior in a high-density, low-pressure, inductively coupled C2F6 plasma: Etch rates, selectivity to photoresist, plasma parameters, and CFx radical densities

Silicon dioxide and photoresist substrates were etched in a gaseous electro nics conference inductively coupled plasma reference cell using C2F6 feed g as. The power/pressure/bias parameter space of the study generated a plasma which has plasma and ion current densities, plasma potential, ion energy, and etch rate characteristics typical of commercial high density plasma (HD P) etch tools. Absolute number density trends of CF and CF2 were measured u sing wavelength-modulated infrared spectroscopy in situ with etch rate expe riments. For nonreactive surfaces such as Si and photoresist, typical CF an d CF2 number densities varied around 4.9 X 10(12) and 4.8 X 10(13) cm(-3), respectively. Over an SiO2 surface, these values decreased and evidence of the reaction of CFx, radicals with an oxide surface to form COF2, was obser ved. Source and bias powers were mapped into ion current densities and ion energies, and correlations were made with etch rate, which was in the 0-150 A/s range. Selectivity ranged from 1 to 6. Typical plasma density was 8 X 10(11) cm(-3), typical ion current density was 30 mA/cm(2), and typical ion energy was 50-160 eV. Both ion current density (source power) and ion ener gy (bias power) primarily controlled etch rate and selectivity. Transition from net etch to net deposition of fluorocarbon occurred near 30 W bias pow er. Increasing substrate temperature decreased the polymer growth rate, and increased the etch rate. This data is expected to be important for develop ing computer simulation plasma models of the HDP oxide etch process. (C) 20 01 American Vacuum Society.