New inductively coupled plasma system using divided antenna for photoresist ashing

We have developed an inductively coupled plasma (ICP) system with a small chamber for 300-mm-diameter-wafer processes, and a good uniformity of ashing, and both low substrate temperature and low pressure were achieved. The features of this ICP system are substrate temperatures lower than 60°C in order to suppress chemical reactions, and low pressures of 3-5 Pa to suppress the both oxidation of Cu wiring and the degradation of low-k films. Furthermore, the antenna is divided plurally and capacitively coupled. This new antenna can achieve good uniformity in a small chamber because the capacitive coupling to the chamber through a quartz glass window can be easily controlled by reducing series impedance, even when the radio frequency (rf) power is very high. Moreover, the damage to the quartz glass window can be decreased by controlling the series impedance of the antenna, resulting in a long-lasting quartz window. The chamber structure was also optimized by performing an original plasma simulation to improve the uniformity of ashing rate. As results for 300-mm-diameter wafers in the 460-mm-diameter chamber, an average ashing rate of 848 nm/min with a uniformity of ±5.5% was obtained for photoresist films under the following conditions: an O₂ gas flow rate of 200 seem, a substrate temperature of 60°C, a gas pressure of 3 Pa and an rf power of 4kW.