Temperature coefficient of resistivity in heavily doped oxygen-rich polysilicon

Oxygen, boron, and phosphorus additions to polysilicon films were followed up to 23% oxygen. Above 500 Omega/square, oxygen resulted in temperature co efficients of resistivity (TCR) magnitudes a factor of two smaller than wit hout oxygen. For p-type films, the TCR saturated at similar to0.05% for low resistivities. Surface energy considerations show that the oxygen atoms ar e likely to attach to the surface of the growing grains. This explains the dependence on oxygen concentration of grain size, boron segregation, and tu nneling barrier. A model for polysilicon resistivity was used to study chan ges with added oxygen and dopants. The potential barrier was followed down to a saturation region. The latter was found to be independent of oxygen, b ut to depend on carrier concentration and type according to the U-shaped tr ap distribution in oxygen-free films. This is also responsible for the satu ration in the TCR. The f factor showed temperature-independent tunneling to gradually outweigh the temperature-dependent contribution from the potenti al barrier. A dopant-dependent f factor showed that dopant scattering begin s to dominate over tunneling. Boron segregation in oxygen-rich films was 30 -35%. Boron gave rise to a slight increase in grain size and phosphorus gav e rise to a large increase. There were significantly more charged traps in films containing oxygen, where they exceeded 10(13) cm(-2). (C) 2001 The El ectrochemical Society.