The authors have developed a compact monitoring probe for measuring the spatial distribution of the atomic radical densities of hydrogen and nitrogen, employing a vacuum ultraviolet absorption spectroscopy with a high pressure microdischarge hollow cathode lamp as a light source. In order to achieve the high performance of measuring the spatial distribution of atomic radical densities, they have tried to realize spatially nonuniform plasma discharge by parallel plates with respective different sizes. It was confirmed that the compact radical monitoring probe enabled one to measure the spatial distribution of atomic radical densities in the plasma precisely. In addition, the etching characteristics of a low-k film were analyzed in H-2/N-2 mixture plasma by internal parameters such as radical and ion fluxes coming to the substrate.