Grain Engineering in Polycrystalline Silicon Thin Films on Glass

Abstract

In this chapter, we present an overview of the state of the art in different deposition and processing techniques that can be used to obtain thin polycrystalline silicon (poly-Si) films on glass substrates. We discuss the direct deposition of poly-Si on glass by thermal CVD at intermediate temperatures, starting from chlorosilane precursors. We also present the ultimate advances to date related to the specific technique of metal-induced crystallization of amorphous silicon, which allows producing large crystalline grains (sizes over 100 microns) at low temperatures (below 600 ºC) by means of thermally activated solid phase transformations. Specifically, we focus on the use of nickel as the metallic mediator for inducing silicon crystallization, and its influence on grain nucleation and growth. We analyze the relevant concept of the solid phase epitaxial growth of a poly-Si film on a previously crystallized seed layer. The pre- or post-crystallization doping possibilities, together with their own advantages and/or disadvantages, are addressed. We also present results of different techniques for the structural characterization of thin poly-Si films. Raman spectroscopy, reflectance in the UV region, X-rays diffraction, optical microscopy, SEM and AFM are shown as valuable tools to follow the crystal growth and to test the crystalline quality of the resulting material. Finally, we discuss the application of the introduced techniques in the development and design of polycrystalline silicon thin film solar cells.