Dry Etching Using NF3/Ar and NF3/He Plasmas

Abstract

Dry etching of silicon, silicon dioxide and photoresist has been studied using NF3 plasmas diluted with helium and argon in both reactive ion etch and plasma etch modes. NF3 concentrations in Ar and He ranged from 10 to 80% for these experiments. Power densities varied from 0.02 to 0.8W/cm2 and pressure from 15 to 500 μm depending on the etching mode selected. Etch rates increased with power density in both PE and RIE modes. Si etch rates as high as 14800Å/min. were obtained with an 80% NF3/Ar mixture at 0.8W/cm2 and 500 μm pressure. Oxide etch rates varied from 30 to 1500Å/min. depending on mode selected. Silicon over oxide selectivity tended to be higher for low power densities for all mixtures studied in either PE or RIE mode. Values obtained were ∼ 30 to 40 for low power densities (0.12 W/cm2) and ∼ 5 for the highest power density used. Selectivities were higher in PE than RIE mode. X-ray photoelectron spectroscopy analysis of etched Si, SiO2, and photoresist coated samples indicated that the surface layer had become fluorinated. Photoresist etch rates of ∼ 500Å/min. were measured for positive photoresist etched in a 40% NF3/He plasma. Loading experiments indicated 10 and 13% decreases in Si and SiO2 etch rates respectively, as the area being etched doubled and, the uniformity of etch rate was approximately 7% over the entire batch.