BIMODAL CRYSTAL SIZE DISTRIBUTION IN ANNEALED RF MAGNETRON SILICON FILMS - A MEMORY EFFECT OF THE LOCAL ORDER INHOMOGENEITIES IN THE INITIAL AMORPHOUS STATE

Microcrystalline silicon( mu c-Si) layers have been obtained by therma l annealing of amorphous films prepared by radio frequency (r.f.) magn etron sputtering. X-ray diffraction (XRD) and Raman spectra were measu red. A systematic effect has been observed in these samples on both th e diffraction lines and the Raman spectrum profiles, i.e., a distribut ion of the crystal size peaking at two different means. The diffractio n pattern has tails superimposed on the 111, 220, 311 powder lines, wh ile the Raman spectra have a shoulder on the low wave number side of t he 520-cm(-1) band at about 500 cm(-1). A relationship is established between this effect and the local order inhomogeneities observed in th e initial amorphous state by XRD. The first halo of the diffraction pa ttern can be reproduced by two components, one being located on the lo w angle side (left side) of the theoretical 111 line of c-Si (relaxed domains), the other one on its right side (disordered domains). This b imodal size distribution is the result of heterogeneous nucleation and crystal growth process during the amorphous-crystalline transition. R elaxed domains favor a nucleation rate leading to small crystals, whil e disordered domains increase the nucleation activation energy, i.e., yield fewer nuclei and larger crystals. (C) 1998 Elsevier Science B.V. All rights reserved.