A new technique for preparing PSG film using RF magnetron sputtering

Abstract

In the present work, we report a new technique for preparing phospho-silicste-glass (PSG) films using RF magnetron sputtering process. For this, purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. Since P₂O₅is hygroscopic in nature, special care was taken to prevent lump formation due to moisture incorporation during the target making process. The PSG films were prepared in a RF (13.56 MHz) magnetron sputtering system at 200-300 watt RF power, 10-20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. The thickness, refractive index (n) and the absorption coefficient (k) of the films were measured using a thin-film analyzer. To confirm the presence of phosphorus in the deposited films, hot-probe test and the sheet resistance measurements were performed. As a final confirmatory test, a p-n diode was fabricated in a p-type Si wafer using the deposited film as a source of phosphorus diffusion. The phosphorus concentration in the target and the deposited film were analyzed using energy dispersive X-rays (EDAX) tool. The etch rate of the PSG film in buffered HF was measured to be about 30 times higher as compared to that of thermally grown SiO₂ films. The issues related to the use of RF sputtered PSG films as sacrificial layer in surface micromachining technology have been addressed.