Technologically important silicon nitride is generally grown by chemical vapor deposition (CVD) in NH3 gas environment at elevated temperatures of 1000-1100°C. This high temperature process can cause undesirable problems, such as dopant diffusion, structural transformation, etc. We have monitored photon or e-beam-induced nitridation process in detail from synchrotron radiation photoemission spectroscopy (SRPES) results obtained at the 2B1 beamline of Pohang Light Source in Korea. In this work, we find that one can make an ultra-thin silicon nitride film by non-thermal method, i.e. by synchrotron radiation (SR) or electron beam (EB) irradiation even at room temperature (RT).
There are two surface components at 0.31 and 0.72 eV higher binding energies than a bulk peak in Si 2p core level spectra from a NH3 exposed Si surface at RT. This indicates that ammonia dissociates into NH2 and H species upon adsorption on the surface. In valence band photoemission spectra, two peaks due to the Si-NH2 and the N-H bonds are observed at the binding energies of about 5 and 10 eV, respectively. These structures become weak and a new feature from silicon nitrides (SiNx) appears at about 7.5 eV upon SR or EB irradiation. N 1s core-level shifts also confirm the non-thermal silicon nitride formation by SR/EB. When the NH3/Si(100) surface is exposed to SR/EB, N 1s single peak at 398.4 eV attributed to Si-NH2 configurations is shifted towards higher binding energies by about 0.82 eV. The valence band and N 1s core level spectra clearly show that the ammonia adsorbed Si surface can transform to a silicon nitride even at RT. These SRPES results provide clear evidences about the non-thermal formation of ultra-thin silicon nitride film by SR or EB.
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