No abstract

No abstract

Previous publications have shown that the absorption coefficient of silicon in the near infrared depends on the carrier concentration of the material considered. Consequently, determination of the absorption coefficient enables the carrier concentration to be deduced. Unfortunately the absorption is generally small for the doping levels used in integrated circuits, and therefore normal absorption methods require thick samples for accurate measurements. For measuring material with low absorption, an emissivity method is better. Such a technique is presented which enables carrier concentrations in standard integrated circuit diffusions to be evaluated with a spatial resolution approaching 20 pm. The samples are heated to approximately 373 K so that there is a net emission of thermal radiation, the amount emitted depending on the carrier concentration. A review of the main factors involved in the emission is presented, together with experimental verification on standard bipolar diffusions. The basic technique is applicable in most cases where observation of carrier distribution is required.