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.
A new, highly sensitive technique for measuring photothermal displacement using a laser heterodyne interferometric probe has been developed. This technique is based on the detection of phase changes in the probe beam and is very sensitive to the presence of lattice damage in semiconductors. It has been found that the phase change is caused by the thermal expansion of a sample surface induced by absorption of a modulated pump beam. The displacements of metals and semiconductors measured by this technique coincided with the results predicted by a thermal diffusion model. These displacements simply depended upon the ratio of the thermal expansion coefficient to the thermal conductlvity of a sample.
Subsurface lattice defects in silicon induced by ion implantation were studied by the use of the photo-acoustic displacement (PAD) method based on the sensitive measurements of the surface displacement due to the absorption of laser-light energy. A definite correlation between PAD and displaced atoms density (DAD) was found because PAD reflects the change in thermal conductivity associated with the net amount of displaced atoms in the crystal lattice beneath the surface. According to the linear dependence of 1/PAD on DAD, defects below a DAD of 1014/cm2 (corresponding to implant doses of 2×1011, 8×1010, and 6×1010 ions/cm2 for 100 keV B+, P+, and As+, respectively) were concluded to be point defects. After the DAD reached 1014/cm2, the PAD showed a gentle increase, and this can be attributed to the growth of point-defect clusters. A marked dependence of the PAD on the DAD was not observed beyond a DAD of 1016/cm2. In this region, the presence of an amorphous layer was observed by cross-sectional transmission electron microscopy. Annealing behavior due to low-temperature heating was studied by the change in temperature dependence curves of the PAD, and the results reflected the characteristics of the defects described above.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.