A study of deposition conditions and hydrogen motion in rf sputtered hydrogenated amorphous silicon
Three series of a-Si:H films were prepared by r.f. sputtering in He/H(,2), Ar/H(,2), and Xe/H(,2) atmospheres. The r.f. power used for deposition was varied from 0.27 W/cm('2) to 3.3 W/cm('2) for each of these three series. The films were characterized using mechanical thickness, optical transmission, infrared, and electron spin resonance measurements;The deposition rates of these films were found to vary linearly with deposition rates predicted from known sputtering yields. The total hydrogen concentration of the films as a function of deposition rate was found to agree with the predictions of a kinematic model for hydrogen incorporation. The concentration of silicon atoms bonded to more than one hydrogen atom was found to agree with a random statistical model, although, there were fluctuations away from this model's predictions when high r.f. powers were used for deposition;The density of weak Si-Si bonds and the value of the Urbach edge coefficient were used to judge the quality of the films. It was found that samples prepared in an Ar/H(,2) atmosphere at high r.f. powers (>2.2 W/cm('2)) were of the highest quality;Samples consisting of alternating layers of high and low hydrogen concentration were also prepared. These samples were confirmed to be multilayers through the use of x-ray, optical transmission, and reflected electron loss spectroscopy depth profiling measurements. Thermal annealing experiments performed on these samples demonstrated that hydrogen does not diffuse, but rather effuses out of the sample, at elevated temperatures. These experiments also;indicated that silicon-hydrogen bonds in r.f. sputtered a-Si:H are stronger than silicon-hydrogen bonds in glow discharge produced a-Si:H; *DOE Report IS-T-1309. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.