Formation of a Positive Photoresist Thin Film by Spin Coating: Influence of Atmospheric Humidity

Experimental film formation of a positive photoresist by spin coating at various atmospheric humidities was investigated. The temperature of the photoresist solution outside of the wafer increases during the intermediate stages of the spinning process in proportion to the humidity and decreases during the later stages. The baked films formed at higher humidities are thinner than those formed at lower humidities during the first stage of the spinning process due to the initial high outflow rate, but thick films are formed during the later stages of the spinning process due to the low outflow rate. The minimum thickness deviation, which is in the intermediate stage of the spinning process, increases at a high humidity with increased distinction at lower spin speeds.