Grain growth and mechanical properties in bulk polycrystalline silicon

The grain structure of bulk polycrystalline silicon has been examined as a function of annealing temperatures and times between 1000 and 1400°C and 6 to 24 hours, respectively. The initial high aspect grain structure decomposes into roughly equiaxed grains at 1000°C over the course of 24 hours. The grains proceed to grow via Oswald ripening with an activation energy for grain growth of 1.49 eV. The hardness increases slightly during annealing and the subsequent transformation to an equiaxed grain structure, from a Vickers hardness of 964 to 1160 kg/mm². The fracture toughness is 0.8 MPa(m)^1/2in the as grown structure, and increases to 1 MPa(m)^1/2in annealed samples. The hardness and fracture toughness are independent of grain size for grain diameters between 2.7 and 4 m.