SAFE ARSENIC GAS PHASE DOPING

A method is described for safe gas phase doping a semiconductor with arsenic. The substrate including a semiconductor structure is exposed to arsine at elevated temperatures within a reaction chamber. Thereafter, prior to opening the reaction chamber, a sealant layer is formed over the semiconductor structure. The sealant layer inhibits outdiffusion of arsenic when the substrate is unloaded from the reaction chamber, enabling safe unloading at relatively high temperatures. In the illustrated embodiments, the sealant layer can be formed by oxidation, nitridation or chemical vapor deposition. Forming the sealant layer can be conducted prior to, during or after cooling the substrate to an unloading temperature. Preferably, a gettering step is conducted after gas phase doping and prior to forming the sealant layer, such as by exposing the substrate to HCl vapor.