Structure and electrical properties of polysilicon films doped with ammonium tetraborate tetrahydrate

Here, p-type polysilicon films are fabricated by ex-situ doping method with ammonium tetraborate tetrahydrate (ATT) as the boron source, named ATT-pPoly. The effects of ATT on the properties of polysilicon films are comprehensively analyzed. The Raman spectra reveal that the ATT-pPoly film is composed of grain boundary and crystalline regions. The preferred orientation is the (111) direction. The grain size increases from 16−23 nm to 21−47 nm, by ~70% on average. Comparing with other reported films, Hall measurements reveal that the ATT-pPoly film has a higher carrier concentration (>10²⁰ cm⁻³) and higher carrier mobility (>30 cm²/(V·s)). The superior properties of the ATT-pPoly film are attributed to the heavy doping and improved grain size. Heavy doping property is proved by the mean sheet resistance (R _sheet,m) and distribution profile. The R _sheet,m decreases by more than 30%, and it can be further decreased by 90% if the annealing temperature or duration is increased. The boron concentration of ATT-pPoly film annealed at 950 °C for 45 min is ~3 × 10²⁰ cm⁻³, and the distribution is nearly the same, except near the surface. Besides, the standard deviation coefficient (σ) of R _sheet,m is less than 5.0%, which verifies the excellent uniformity of ATT-pPoly film.