Hidehisa Hashizume

Dose and Damage Measurements in Low Dose Ion Implantation in Silicon by Photo-Acoustic Displacement and Minority Carrier Lifetime

Photo-acoustic displacement (PAD) generated with a modulated laser beam pumping is studied for As+ or B+ implanted Si. At doses above 1×1013 ions/cm2, the PAD has a close relationship to damage density. An ion implantation dose down to 2×109 ions/cm2 can be detected by the PAD measurement. Doses below 2×1010 ions/cm2 can be monitored by minority carrier lifetime measurement. A non-destructive high-sensitive dose monitor can be achieved by the PAD and minority carrier lifetime measurements. This monitoring leads to tight control of the threshold voltage of a MOS transistor.

Carrier Lifetime Measurements by Microwave Photoconductive Decay Method at Low Injection Levels

The minority carrier lifetime of Si wafers has been measured at very low injection levels by employing a newly developed microwave photoconductive decay (µ-PCD) technique. It is found that the effective lifetime is dramatically increased for the case of p-type Si when the injection level is reduced to two orders of magnitude less than the equilibrium value. In contrast to this, the n-type wafer lifetime remains almost un-changed even upon lowering the injection level. Also, it is shown that the different contamination levels of Fe in Si wafers are clearly discriminated by the measured lifetime.

Comparison of Silicon-on-Insulator Wafer Mappings between Photoluminescence Intensity and Microwave Photoconductivity Decay Lifetime

We characterized the nonuniformities of state-of-the-art ultrathin silicon-on-insulator (SOI) wafers by photoluminescence (PL) intensity mapping and microwave photoconductivity decay (µ-PCD) lifetime mapping. Both mapping techniques revealed characteristic patterns with extreme sensitivity. The PL and µ-PCD mapping patterns on the substrate were almost exactly alike for all the measured wafers. There was also a strong resemblance between the two mapping patterns on the top Si layer for most wafers. A higher PL intensity region corresponded to a longer lifetime area. The quantitative relationship between the PL intensity and µ-PCD lifetime was obtained not only for comparison within a wafer but also for wafer-to-wafer comparison. The mapping pattern on the substrates varied greatly depending on the wafer fabrication method. We believe that the pattern on the top Si layer originates in the distribution of microdefects such as HF defects in the layer, the variation in layer thickness, and/or the nonuniformity produced during the thermal process for surface passivation.

Excess Carrier Lifetime Mapping for Bulk SiC Wafers by Microwave Photoconductivity Decay Method and Its Relationship with Structural Defect Distribution

Excess carrier lifetime in commercially available bulk 2 in. 4Hand 6H-SiC wafers were characterized by the microwave photoconductivity decay (μ-PCD) method. We obtained maps of the lifetime in the entire wafer. In each wafer, we observed several small regions in which the lifetime is relatively longer than the rest of the wafer. We also observed the birefringence and X-ray Lang topograph for the wafers in order to see structural defect distribution and measured net donor concentrations within the wafers. From comparison of the lifetime maps with structural defect observation, the long lifetime regions was found to correspond to regions with high density of structural defects.