Large changes in refractive index by synchrotron-radiation-driven compaction of hydrogenated silicon nitride films

Abstract

When high-energy photons (hν>100 eV) irradiate films of hydrogenated silicon nitride (a-SiNx:H) that have been deposited by plasma-enhanced chemical-vapor deposition, the network of atoms in the material is photolytically rearranged. This reaction proceeds rapidly from the instance the radiation is applied and is almost completed within 200 s. This is in striking contrast with the continuing effect of such radiation on SiO2 (defect formation and decomposition). The result was a change (Δn) in the refractive index at 633 nm of as much as 0.04, and this effect was independent of the temperature of irradiation. By using an effective medium mixture of Si3N4, crystalline Si, and voids to model the dielectric function of a-SiNx:H films, the volumes of the voids and of crystalline Si components were found to be reduced by 44% and 49%, respectively, from their initial values. The resulting 9.8% reduction in the thickness (compaction) is the origin of the large Δn.

Phase stabilization by rapid thermal annealing in amorphous hydrogenated silicon nitride film

“…Our present investigations are consistent with previous reports of a-SiN x :H films processed using other annealing techniques, namely furnace annealing, soft x-ray/VUV and synchrotron radiation irradiation, wherein the densification of films with enhanced refractive index is reported [12,[21][22][23].…”

Influence of the high-temperature “firing” step on high-rate plasma deposited silicon nitride films used as bulk passivating antireflection coatings on silicon solar cells

“…Microscopic voids can, for example, represent the vacant space around H-terminated defects. 42 The loss of H atoms and decrease in microscopic voids lead to a rearrangement and restructuring of the atomic network in the films and as a consequence the average atomic distance between the atoms decreases. Therefore the total atomic density in the film increases while the ͓N͔/͓Si͔ ratio remains approximately constant.…”

Optical and structural characterization of rapid thermal annealed non-stoichiometric silicon nitride film

“…The short process cycle times and relatively high temperature may also induce structural changes in the dielectric films, which may result in modification of their refractive indices. Studies employing RTA [5][6][7][8][9] and/or exposure of dielectric films to light [10][11][12] to tailor their refractive indices are of great importance in optical waveguide applications to select appropriate material for core and cladding regions.…”