Carrier Lifetime Measurements for Process Monitoring During Device Production

Carrier lifetime measurements were performed in silicon crystals in order to characterize the quality of the material and to control the device production process. For process monitoring, floating-zone n-type silicon of high resistivity was used, since p-type silicon in general exhibits pronounced axial and radial profiles of carrier lifetime.

The influence of various atmospheres during heat treatment on the final carrier lifetime in n-type silicon was investigated. Oxygen with and without additional hydrochloric acid increased the carrier lifetime, while hydrogen, in comparison with inert gas atmospheres, decreased it. Gold, copper, and iron were found to be the main heavy metal impurities introduced into silicon specimens by heat treatment. The iron content varied considerably with the atmosphere used during annealing, showing the highest concentrations for hydrogen. Fast cooling of specimens after heat treatment produced carrier lifetimes that were unstable with the time elapsed after quenching.