Solid-Source Doping of Float-Zoned Silicon with B, N, O, and C: Preprint

We report on a solid-source method to introduce dopants or controlled impurities directly into the melt zone during float-zone growth of single- or multicrystalline ingots. Unlike the Czochralski (CZ) growth situation, float-zoning allows control over the levels of some impurities (O, C) that cannot be avoided in CZ growth or ingot casting. But aside from impurity studies, the method turns out tobe very practical for routine p-type doping in semicontinuous growth processes such as float-zoning, electromagnetic casting, or melt-replenished ribbon growth. Equations governing dopant incorporation, dopant withdrawal, and N co-doping are presented and experimentally verified. Doping uniformity and doping initiation and withdrawal time constants are also reported. The method uses nontoxicsource materials and is flexible with quick turnaround times for changing doping levels. Boron p-type doping with nitrogen co-doping is particularly attractive for silicon lattice strengthening against process-induced dislocation motion and also allows greater freedom from incorporation of Si self-interstitial cluster or A and B swirl-type defects and 'D'-type microdefects than nitrogen-freep-type material.