Neutron transmutation doping of silicon single crystals

摘要

A working recipe for NTD CZ and MCZ silicon wafer production is provided. It teaches that a neutron-enhanced S-curve can be constructed by noting that a silicon interstitial (Si.sub.I), emitted due to volume change during the traditional oxygen precipitation, can join a neutron- created vacancy in facilitating further oxygen loss via precipitation. The former relation is: 2Si+2O.sub.I →SiO.sub.2 +Si. sub.i the latter is: vacancy+Si .sub.I +2O.sub.I →SiO ..sub.2 The total loss of oxygen interstitials is:PP[O.sub.I ]=Max([O .sub.I ]. sub.0 [O .sub.I ].sub.s +min{2([Si .sub.I ].sub.s +[Si .sub.I ]. sub.0). [vacancy]}),PPwith subscripts 0 and s standing for initial state and S-curve prediction, respectively; [Si.sub.I ].sub.s equal to 0.5[O .sub. I ].sub.s, and [vacancy] readily obtainable by computer simulation. [vacancy] is a function of the cadmium ratio (CR), silicon sample thickness, and total neutron fluence. The final oxygen interstitial content is: [0.sub.I ].sub.f =max{[O.sub.I ].sub.0 -[O.sub.I ],0}. Evidence for the effectiveness of the recipe taught by the present invention is provided in the form of characterization results derived from MOS capacitors and PN junctions built upon wafers produced according to the recipe. These show that the nominal minority carrier lifetime, interface density, and leakage currents under reverse bias are the same as those from a blank prime wafer.