Microstructural and electrical characterisation of ion-beam-sputtered polysilicon films for microelectronic applications

Abstract

Microcrystalline silicon films of grain size 50–80 nm have been deposited by ion beam sputtering from a crystalline silicon target and processed by subsequent annealing. The X-ray diffraction analysis has shown the growth of 〈420〉, 〈200〉 and 〈331〉 principal crystal textures with annealing at temperatures up to 1050°C. Films of sheet resistance ranging from tens of ohms to tens of kiloohms per square have been formed by the thermal diffusion of dopants. The electron mobility of phosphorus-doped films varied from 3 to 87 cm 2V −1 s −1 for carrier concentrations of 5 x 10 18 to 10 21 cm −3. A typical boron-doped film showed a carrier mobility of 38 cm 2V −1 s −1 at a concentration of 3 x 10 19 cm −3. Compact resistors of different sizes and aspect ratios have been fabricated to test the suitability of the ion-beam-sputtered polysilicon film as a microelectronic material. The measured current-voltage characteristics over a wide range of electric field up to 7 kV cm −1 and current density up to 1.3 × 10 6 A cm −2 fit well with the theoretical plots obtained using an improved physical model of polysilicon conduction valid for large bias condition. A TCR of −4 × 10 4 p.p.m.°C −1 has been obtained for a typical n-type doped resistor with a concentration of 8 × 10 19 cm −3.