Structural studies on the microcrystallization of Si:H network developed by hot-wire CVD

Effect of H-2-dilution to the SiH4 plasma, R(H-2), on the microcrystallization of Si:H network at a low substrate temperature (180 degrees C) has been studied by using hot-wire CVD. Structural characterization of the films has been performed by micro-Raman, ellipsometry, infrared absorption and X-ray diffraction studies. A dramatic structural transformation from amorphous to microcrystalline phase has been identified at an H-2-dilution beyond 92.0%, induced by high atomic H density in the plasma. A virtual saturation in overall crystallinity has been attained for H-2-dilution in the range 92.75 <= R(H-2) (%)<= 93.75, contributing crystalline volume fraction changing between 60% and 64%, the average crystalline grain size varying between 150 and 200 A and bonded hydrogen content maintaining between 3.3 and 2.6at%. A crystalline volume fraction of 86.6% was obtained along with a low bonded H-content of 1.76 at% at R(H-2) = 98.0%. However, at such extremely high H-2-dilution, overall crystallization is hindered due to enormous polyhydrogenation and formation of lesser dense network full of voids. Hence, microcrystallization in Si-network can be easily obtained in HWCVD, at a relatively low hydrogen dilution and low substrate temperature, without cornpromising much with the deposition rate arising out of those two stringent factors affecting in the conventional technique; and thereby, enhancing the technological acceptability of the deposition process presently dealt with. (c) 2005 Elsevier B.V. All rights reserved.