Photochemical reactions in silicon nitride with ArF excimer laser

Exposure of silicon nitride to above-bandgap 6.5-eV photons from an ArF excimer laser drives both the dissociation of silicon-nitrogen bonds and the desorption of nitrogen atoms and/or molecules over a wide fluence range. Crystalline silicon precipitates are also generated on laser exposed surfaces, however, only for fluences exceeding 0.2 J/cm(2). The rates of nitrogen desorption and the concentration of silicon precipitation were found to depend strongly on laser fluence, rising rapidly above 0.2 J/cm(2), and saturating at similar to 0.5 J/cm(2). This saturation was also observed in the thickness of the silicon precipitate layer, which peaked at 35 nm depth for fluences >0.5 J/cm(2). Such saturation phenomena can be explained by the onset of laser ablation at similar to 0.5 J/cm(2) fluence which removes material in the laser affected zone. The formation of silicon precipitates is discussed in the context of photochemical reactions that follow band-to-band electronic transitions.