MICROSTRUCTURAL AND ELECTRICAL CHARACTERIZATION OF ION-BEAM-SPUTTERED POLYSILICON FILMS FOR MICROELECTRONIC APPLICATIONS

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-degrees-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 cm2 V-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 cm2 V-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 x 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 x 10(4) p.p.m.-degrees-C-1 has been obtained for a typical n-type doped resistor with a concentration of 8 x 10(19) cm-3.