Semiconductor Processing Technique Based On Faraday Rotation Measurement Using A CO 2 Laser

Abstract

A non-destructive technique for processing semiconductor material based on Faraday Rotation (FR) measure-ment has been developed and successfully utilized for evaluation of single crystal Cadmium Sulfide (CdS) wafers. We have extended the technique to the infrared region of the spectrum by utilizing a CO2 laser, thus significantly enhancing wafer mapping capability of the technique. Since homogeneity becomes a serious problem for large size wafers, considerable cost savings are realized if the wafer is screened prior to array fabrication. CdS Schottky barrier detectors are presently used in the two-color STINGER-POST missile system. In the band edge region, FR was found to vary as λ-2, where X is the wavelength of the incident radiation, as predicted by the theory for interband transitions. In the infrared, e.g., at 10.6 microns, FR is primarily due to free carriers and varies as λ 2. Free carrier concentration calculated from FR measurements agrees well with results obtained by Hall measurements. Advantages of the FR method are: 1) no contacts need be alloyed, hence no material contamination, 2) surface preparation such as etching/polishing is not required, 3) it is a rapid technique and does not require a skilled operator, and 4) by the use of the CO2 laser, auto-mated wafer mapping is possible. This technique, used here for CdS, is applicable for any semiconductor material where rapid measurement of carrier concentration and a determination of material homogeneity is desired. Development of a self-contained, automated and computer controlled wafer mapping system based on carrier concentration measurement by FR will be described. Results obtained for CdS wafers will be presented© (1986) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.