Microstructure and grain growth of polycrystalline silicon grown in fluidized bed reactors

Fluidized bed technology is being implemented commercially to produce polycrystalline silicon that is used as a precursor for silicon ingot growth for the photovoltaic industry. The fluidized bed reactor produces polysilicon in a granular form, usually at lower temperatures than the traditional Siemens process. This current study documents for the first time grain growth and mechanical properties of polysilicon grown via a fluidized bed. In the as-grown state the granules produced by the fluidized bed reactor consist of equiaxed grains that are approximately 30 nm in diameter. Annealing at temperatures above 1000 °C causes significant grain growth to occur resulting in grains up to 300 nm. The hardness of the granular material was 10% less than that of single crystal silicon, which can be attributed to grain boundary sliding. Understanding the effect of annealing on microstructure, grain growth, and mechanical properties of the granules is critical for establishing appropriate techniques for handling the material.