PULSE-TIME-MODULATED ELECTRON-CYCLOTRON-RESONANCE PLASMA-ETCHING FOR HIGHLY SELECTIVE, HIGHLY ANISOTROPIC, AND NOTCH-FREE POLYCRYSTALLINE SILICON PATTERNING

Highly selective, highly anisotropic, and notch-free etching for polycrystalline silicon is achieved in a few tens of us pulse-time-modulated electron cyclotron resonance plasma. In the pulsed plasma, the selectivity ratio of polycrystalline silicon etching rate to the SiO2 etching rate is drastically improved with high etching rate, as compared with the ratio with a continuous discharge. Furthermore, vertical and notch-free phosphorus-doped polycrystalline silicon etching profiles can be achieved even with 100% over etching. These etching characteristics are achieved by controlling ion energy distributions through the duty ratio, maintaining a high ion current density, generating a collimated ion flux and eliminating surface charging with a pulsed discharge of a few tens of mus.