Low-temperature polysilicon deposition by ionized magnetron sputtering

Abstract

Ionized magnetron sputtering was successfully applied to polycrystalline silicon thin-film deposition on glass substrate at temperatures lower than 250 °C maintaining a deposition rate of about 133 Å/min. Hydrogen mixing was effective up to Ar:H2=10:6 by mass flow rate. Prior to deposition, H2 inductively coupled plasma was used for precleaning the substrate with −40 V bias. During Si deposition, the substrate biasing scheme was in two steps; +20 V for an initial stage and +20 to −40 V bipolar pulse bias for the rest of the deposition time. The crystallinity was evaluated by both x-ray diffraction analysis and Raman spectroscopy; the average crystalline fraction was calculated as 70%. Grain size was measured in plan-view scanning-electron micrographs after selective etching of the amorphous phase by chemical solution. In 800-nm-thick samples, grains are 500–700 Å in diameter. Optical emission spectroscopy was used as real-time diagnostics, and ionization of sputtered silicon atoms distinctly increased as the hydrogen partial pressure increased. The successful deposition of polycrystalline silicon was explained as being due to enhanced ionization of sputtered and reflected neutrals and resultant energy control by bipolar substrate bias.