Novel Properties of a-Si:H Prepared by Dual Ion Beam Sputtering
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ION BEAM SPUTTERING DUAL BY PREPARED a-SI:H OF NOVEL PROPERTIES Oil Co. Standard The Cavese, J.M. Collins, R.W. H.Windischmann, (Ohio),Cleveland ,Ohio 44128 ABSTRACT Films of a-Si:H were deposited by dual ion beam sputtering using a new configuration in which both the argon and hydrogen beam sources are directed at the silicon target. This geometry also permits independent control of the hydrogen and argon energy and particle flux. Infrared absorption mealurents Si-H hydrogen concentrations, the 2000 cm show that even for high This result is in contrast with the more stretching band is dominant. conventional configuration in which the H soyrce is directed at the substrate, mode. This suggests that the resulting in films with dominant 2100 cmfor the two are different precursors resulting in H-incorporation configurations. In fact, IR reflectance and SIMS analysis of the silicon sputtering target reveal hydrogen is incorporated, peaking at about 30 A A strong increase in the photo and dark dc below the target surface. conductivity occurs as the hydrogen ion enery is reduced below 30 eV, suggesting the importance of preventing high energy back-scattered H ioR bombardment of thS film. At1 a H ion energy of 8eV, the values are 2x10 (ohm-cm-), respectively. Spectroscopic ellipsometry (AM1) and 2x10measurements of films reveal a Si-Si bond packing greater than that of low Hcontent a-Si prepared by LPCVD even up to H contents as high as 249. Above 25% a microstructural transition is observed, verified by SEM, resulting in an (which appears to be responsible for a increase in the density of voids, sudden drop in the hydrogen-induced compressive stress) and accompanied by a shift in the dominant stretching mode energy. INTRODUCTION Early studies of by
sputtering
tetrahedrally-bonded
crystalline
targets
in
amorphous semiconductors prepared Ar/H2
mixtures
have
provided an
understanding of the effect of hydrogen incorporation on the electronic These findings also provided insight into properties of these materials(l]. the interpretation of the properties of glow discharge prepared a-Si:H. The difficulty with both of these techniques, however, is that the energy and flux of the plasma constituents are not controlled independently so that cause and effect are difficult to establish when trying to explain the role of Ion beam sputtering[2] has the potential of energetic particle bombarment. accomplishing this. The early work on ion beam sputtered a-Si:H[3], however, was performed with a single ion gun operated with an Ar/ H2 mixture so that the hydrogen flux and energy was not decoupled from the argon. By using two guns, the argon aimed at the silicon target while the hydrogen is directed at The work reported here the substrate(4] independent control was achieved. also uses the two gun configuration with the added feature that the hydrogen gun can be directed either at the substrate or target. Furthermore, the hydrogen source was operated at voltages down to 10 eV, which is lower than The results show a significant incre
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