The experimental results of examination of the optical emission of microwave plasma discharge in oxygen, performed in order to determine the spectral lines, peculiar to the process of the plasma chemical removal of the photoresist masks, are submitted. It is determined, that due to the specific manifestation of the “loading” effect when processing the silicon substrates in the microwave plasma discharge, the control of the process of removing photoresist from small batches of substrates should be performed by controlling the intensity fluctuations of the strip CO (λ=519,82 nm), and in case of processing the large quantity of substrates - as per the line OI (λ=777,7 nm; λ=844,6 nm).