Chemical annealing, the periodic exposure of the growing amorphous silicon surface to H radicals, has evoked much interest because of its potential for modifying the film properties during the crucial process of sub-surface restructuring. We report the results of measurements of H content in chemically annealed a-Si:H and a-Si:H,F films.
We prepared a-Si:H and a-Si:H,F in a dc-triode reactor from SiH4 and SiF4 plus H2, respectively. We chemically anneal with a H2 discharge by switching off the Si bearing gas and switching on the H2 flow after 7 s of deposition. We measure the H content with a differential pressure effusion apparatus. We also report the opto-electronic properties of these films, including the defect density after light-soaking.
The key parameter of chemical annealing is the anneal duty cycle, which we specify as the fraction of the time that the H2 discharge is on. In the silane samples, we find that the H content is independent of chemical annealing. For the fluorinated samples we observe that the H content starts out at about 5 at.% without chemical annealing, rises to 10-15 at.% at 0.5 to 0.7 annealing duty cycle, and then decays to 6-7 at.% at 0.9 duty cycle. Although not fully understood, we offer evidence that these effects are due to the physics of the glow-discharge rather than surface reactions.