Comparison of advanced plasma sources for etching applications .5. Polysilicon etching rate, uniformity, profile control, and bulk plasma properties in a helical resonator plasma source

Etching of polysilicon features using a helical resonator plasma source is evaluated. Performance metrics consist of etching rate, etching rate uniformity, and profile control using HBr/O-2-He gas-phase chemistry. The effect of source power, rf-bias power, and reactor pressure on etching rate and uniformity is examined using a response surface experiment. Feature profile control is determined by examining nested and isolated lines and trenches using oxide mask/polysilicon/oxide structures. Good uniformity and vertical profiles are obtained at low reactor pressures, high source power, and rf-bias between 50 and 60 W. The operating point for best uniformity is at 3.5 mTorr, 3000 W source power, and 53 W rf-bias power. At this point, the etching rate is 3700 Angstrom/min and the nonuniformity is less than 1.0%, over 125-mm-diam wafers. Radial profiles of electron temperature and ion density near the wafer surface are presented as a function of source power, rf-bias power, and reactor pressure. The ion density was found to be in the mid-10(11) cm(-3) range and electron temperatures were 5-7 eV. An increase in source power and reactor pressure results in an increase in ion density; however, the electron temperature shows a weaker dependence. Finally, these results are compared to those using helicon and multipole electron cyclotron resonance plasma sources evaluated in previous studies. We found that all three plasma sources provide high ion density at low pressures to meet performance demands for polysilicon etching; however, the helical resonator source offers somewhat higher etching rate and better bulk plasma uniformity. (C) 1996 American Vacuum Society.