Experimental measurement of E to H mode transition in O2, N2 and O2-N2 gases in cylindrical ICP source for photoresist dry-strip applications

Abstract

Summary form only given. Inductively coupled plasmas (ICP) have attracted widespread interest in semiconductor fabrication processes due to attractive properties including high plasma density and low contamination that are available under low-pressure. We report the characteristics of E-H mode transition changes at various gas mixtures in the pressure controlled chamber. Our discharge chamber, which was designed for photoresist dry-strip process, had 200mm diameter and consisted of three-turn external cylindrical antenna coil which sustained 13.56 MHz RF power through pi-type matching network. Generation of O radical is of great interest for dry-strip process in semiconductor industry in order to remove photoresist (PR) deposited on wafer. Mixture of N2 in the O2 plasma increases portion of O radical due to collision of two molecules 1. It is of interest to evaluate the EH mode transition power at various gas mixture for better understand the process tool. The voltage and current on the coil are measured with a high voltage probe and a current sensor. The preliminary results show that the transition from E to H mode occurs at relatively low power for pure oxygen than pure nitrogen and gas mixture. The energy loss via collision and electron-neutral collision frequency for N2 molecules are greater than O2 which requires higher transition ICP power. Moreover PR strip rate was compared at different gas mixture in order to compare O radical generation. Total PR strip amount was compared for changing the ratio of two gas mixture. The experimental results show the total PR strip amount is increased for mixing N2 among O2 plasma. These results will be considered to operate efficient ICP source and to optimize the process condition for PR dry-strip process.