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 and crystal originated particles (COPs) 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. In the present paper the effect of germanium doping in the range between 10 16 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.