Yasuhide Nakai

Photodisplacement Measurement by Interferometric Laser Probe

A highly sensitive optical heterodyne interferometer was developed for the purpose of measuring the photodisplacement of a sample induced by the absorption of modulated light. The sensitivity is 1 pm in the 1 Hz bandwidth, sufficient to measure the photodisplacement. A good correlation was obtained between the amplitude of the photodisplacement and the subsurface structures of aluminum thin-film samples. The experimental results revealed that this technique is applicable to thickness measurement and to imaging of subsurface structures for opaque thin films.

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.