Monitoring processes in photoresist using infrared optical fibers and tunable diode lasers

A novel approach for the problem of in-situ and real time monitoring processes in thin film photoresists is presented. The approach is based on the fact that all the essential processing steps, such as softbaking, exposure, hardbaking, and development, can be monitored by the induced spectral modifications in the infrared spectrum of the resist film. The technique of fiber-optic-based evanescent field spectroscopy, is proposed as the method for measuring these spectral changes. The technique is demonstrated using a silver halide infrared transmitting optical fiber coated with thin photoresist film, as the sensing element, and a tunable lead salt diode laser, as the infrared monochromatic source. As an example, immense changes in the resist IR spectrum, induced by thermolysis, are measured. The advantages of using all-fiber technology for remote real time sensing is further discussed, and the possibility to monitor the resist film temperature and thickness, using the same silver halide fibers, is emphasized.