Investigation into the processes of plasmachemical etching of a photoresist with the help of in situ optical monitoring

The peculiarities of photoresist etching in inductively coupled plasma in various modes, including the mode using to etch the GaN-based structures are investigated. The continuous in situ monitoring of the photoresist thickness, surface morphology, and substrate temperature was performed with the help of the optical reflectometry and low-coherent interferometry. It is shown that the etch rate of photoresist is not constant but decreases in the course of the process, which is in addition associated with the substrate heating. It is revealed that the pulsed etching mode makes it possible to exclude the development of the roughness observed in the continuous mode. The comparison of the new data with the etch rates of the photoresist with the characteristic rates of GaN etching performed under the same conditions made it possible to determine the process parameters and photoresist thickness necessary to perform the mentioned etching process in the optimal mode.