Hydrogen evolution from plasma-deposited amorphous silicon films

The temperature dependence of hydrogen evolution from amorphous silicon films prepared by plasma deposition using a silane–argon mixture was studied by line-of-sight mass spectrometry. The structure changes accompanying hydrogen evolution were simultaneously studied with reflection high-energy electron diffraction (RHEED). Mass spectrometric analysis during linear temperature sweeps showed that H2 was the evolving species indicating that hydrogen atom recombination occurs prior to desorption. H or SiHx were not detected. The evolution spectrum consisted of two broad peaks. The temperature corresponding to the initiation of evolution, the maximum evolution rate and the termination of evolution were dependent on deposition parameters. Attempts at depopulating specific hydrogen binding states by isothermal heat treatments indicated the existence of a broad range of states. The amorphous to crystalline transition was initiated subsequent to hydrogen depletion and at 760° C+10° independent of deposition parameters.