Roles of N₂O and O₂ Gas Additives

Dry etching of silicon using a radio frequency glow discharge in SF₆ + N₂0 and SF₆ + O₂ gas mixtures have been studied. Both N₂O and O₂ additives can significantly enhance the silicon etch rate. For low RF power, the same amount of N₂0 enhances silicon etch rate more than 0₂ does. When the RF power level is increased beyond a value, O₂ becomes more efficient in enhancing the silicon etch rate. The chemisorption model based on the competition between atomic fluorine and oxygen species for active silicon etching sites is applied to explain these etching characteristics. Optical emission spectroscopy is used to measure the relative concentrations of atomic oxygen and fluorine, which are subsequently applied to correlate the silicon etch rates. According to XPS characterization, there is no detectable sulfur contamination on silicon surface after being etched by either plasma.