Germanium doping for improved silicon substrates and devices

Abstract

During the last decade, the 300 mm silicon wafer has been optimized and one is studying the move to 450 mm crystals and wafers. The ever increasing silicon crystal diameter leads to two important trends with respect to substrate characteristics: the interstitial oxygen concentration decreases while the size of grown in voids (COP's) in vacancy-rich crystals is increasing.The first effect is due to the large melt in which movements have to be controlled and partly suppressed by the use of magnetic fields. This magnetic confinement leads to a more uniform dopant incorporation but at the same time to a more limited transport of oxygen from the quartz crucible to the melt and the growing crystal. The reduced interstitial oxygen concentration and the lower thermal budget of modern device processing leads to strongly reduced oxygen precipitation and thus internal gettering capacity.The increasing COP size (accompanied by a decreasing density) is caused by the decreasing pulling rate and thermal gradient that have to be used in order to avoid dislocation formation. The slower cooling of the crystal leads to a decreased void nucleation rate and at the same time to an increased thermal budget for void growth as well as a larger number of vacancies available per void. Journal of Crystal Growth November 9, 2010 In the present paper the effect of germanium doping in the range between 10 16 cm −3 and 10 19 cm −3 on COP formation and oxygen precipitation is discussed and illustrated. Also the beneficial effect of germanium doping with respect to wafer breakage during processing, with respect to the suppression of thermal donor formation and with respect to improving device radiation hardness is addressed. Preprint submitted to

2 MeV e‐irradiation UHVEM study on the impact of O and Ge doping on {113}‐defect formation in Si

“…These impurities interact with vacancies and interstitials, and can therefore be used to affect interactions of point defects during crystal growth, during device processing as well as under irradiation. Although a huge amount of experimental and theoretical data have been collected during the last decades, our understanding of intrinsic point defect‐impurity reactions is not yet definitive, see, for example 1–9 and references therein.…”

On the assumed impact of germanium doping on void formation in Czochralski-grown silicon

“…Due to the nucleation of oxide precipitates at lower temperatures and the slower oxygen diffusion, oxide precipitates can indeed only grow to a maximum size of about 20 nm during a crystal pulling process. The previously reported differences in COP size between silicon wafers with and without Ge doping, 9,15 are most probably due to the fact that only the tail of the COP size-density distribution with the largest defects can be observed with the surface inspection tools. 14 The void data in Table I suggest also that with respect to defect size/density distribution, no significant differences exist between the crystals with and without Ge doping and even not between the 4 and 6 in.…”

Density functional theory study of the impact of tin doping on oxygen diffusion in Czochralski silicon

“…It has been widely accepted that O i atom migrates via jumping between neighboring SiSi bond centers, which is strongly influenced by high concentrations of dopant atoms in silicon. It has been reported that the oxygen diffusion can be retarded or enhanced by dopant atoms such as arsenic (As) , antimony (Sb) , boron (B) , carbon (C) , and germanium (Ge) . The mechanism underpinning such influence is usually understood as dopant trapping or vacancy‐mediated dopant trapping .…”