Network compaction and surface deformation in the hydrogenated silicon nitride film upon soft x-ray/VUV illumination

In the present study, modifications in a hydrogenated silicon nitride film by soft x-ray/VUV (vacuum ultra violet) radiations are investigated using in situ soft x-ray reflectivity measurements at Indus-1 synchrotron source. The illumination experiments are performed at 10 deg. grazing incidence angle at which the majority of incident radiation (belonging to 10 eV-250 eV) are restricted to ∼8.0 nm depth, except near the Si-L absorption edge (100 eV) where photons penetrate much deeper into the film and initiate photochemical changes. Resultantly, the film density has increased along with a change in surface morphology. Due to illuminations, hydrogen bonds responsible for voids and network deformation are more likely to break and pave the path for the formation of more compact Si3N4 network. Evolution of hydrogen changes the surface morphology significantly. Atomic force microscopy confirms the formation of nano clusters at the surface. The out diffusion of hydrogen near the surface is responsible for surface deformation. Probable mechanism of surface modification and network compaction is discussed