Characteristics of a Stabilized Pulsed Plasma via Suppression of Side-Band Modes

Abstract

The instabilities caused by the reflected rf power in a pulsed-plasma operation employing modulated rf power was studied. By suppressing the side-band modes in the frequency domain, the pulsed plasma became more stable and produced less reflected power. The mode-suppressed pulsed plasma showed almost the same plasma characteristics as the conventional step-function-modulated pulsed plasma. The mode-suppressed plasma was applied to etch a polysilicon pattern. The etched polysilicon profile showed no charge-up defects, suggesting that the mode-suppressed plasma can be utilized for controlling the electron temperature in a more stable operation.

Plasma-etching processes for ULSI semiconductor circuits

“…Keller, Coultas, and Zhang'' have shown that the T^ of the negative-ion plasma over the wafer may be reduced by a factor of 3 or more compared to that of a conventional inductive plasma source. This means that etching would occur with a T^ of the order of 1 eV, or similar to that measured by Hahm et al [18], for 25 /us or more into the "off" part of a pulsed plasma. Visually such a plasma has the normal luminosity of an inductive plasma source below the dielectric window between the rf coil and the plasma.…”

“…During the off pulse, the electron temperature decreases to the order of 1 eV [18] through inelastic collisions and surface losses. Subsequently, the negative ion density increases relative to the electron density.…”

“…The polymer created during the etch accumulated on the resist, helping provide resist selectivity. This accumulation of polymer effectively prevented volatile by-products from the resist 18 and underlying substrate from escaping. After an extended period of time, heating of the wafer caused these byproducts to erupt.…”