Hydrogen and oxygen plasma effects on polycrystalline silicon thin films of various thicknesses

Abstract

This work studied the hydrogen and oxygen plasma effects on the resistivity, effective free carrier concentration, and mobility of As+- and BF2+-doped polycrystalline silicon (polysilicon) thin films of various thicknesses. It was found that the resistivity of a polysilicon thin film increased with the decrease of the thickness of the film. This was mainly due to the decrease of effective carrier concentration and the mobility through the decrease of the grain size since the thickness limited regrowth of the film. The hydrogen and/or oxygen plasma treatment decreased the effective carrier concentration of the film through the neutralization of boron and arsenic ions. This effect was more evident for the thinner (< 60 nm) film. The plasma treatment also decreased the mobility of the film, unless the thickness of the film was thinner than 50 nm, for which, the mobility instead increased since the plasma passivation effect became dominant.