No abstract

Grown-in crystal-originated particles ͑COPs͒ on the surface of silicon nitride-doped Czochralski ͑CZ͒-grown silicon wafers were characterized using atomic force microscopy and scanning electron microscopy. These nanometer-scale COPs are categorized into kite-shaped, parallelepiped-plate and needle-shaped COPs, respectively, with unique features distinctively different from the octahedral voids commonly found in conventional CZ-grown silicon wafers. Based on the experimental data obtained, it is postulated that nitrogen dopants in the silicon crystals could influence the formation of these COPs with different morphologies and sizes. This may be supported by a simple analysis of the mapping distribution of COPs on the nitride-doped CZ-grown silicon wafer, which reveals that the densities of the smaller-size parallelepiped-plate and needle-shaped COPs are negligible at the center of the silicon wafer but increase to a significant proportion comparable to that of the kite-shaped COPs at the outer edges of the silicon wafer along the radial directions. These observations are thought to correlate well with the presence of nitrogen dopants and the radial concentrations of the excess free vacancy.

Iron impurities in bulk silicon are found to getter efficiently at the polysilicon layer by an electric field during isothermal annealing. Experimental results show that iron concentration at the polysilicon layer increases to the level that becomes detectable by total reflection x-ray fluorescence (TXRF) spectroscopy. The improved gettering efficiency for iron is attributed mainly to the directional drift of ionic iron interstitials toward the polysilicon gettering sites, under the influence of the applied potential gradient, thus presenting a more effective method for reducing the iron content in silicon.