We have developed a two-dimensional nano-displacement measuring system utilizing a combined optical and x-ray interferometer (COXI). The system consists of optical interferometers for two-dimensional displacements and an x-ray interferometer. The x-ray interferometer was used to calibrate the non-linearity of the optical interferometers. The x-ray interferometer can subdivide the optical interference signal with 0.2 nm linear scales. The measured non-linearity of the heterodyne optical interferometer was less than 2 nm. The calibrated optical interferometers were used to measure two dimensional nanoscale displacements, and the accuracy of the optical interferometers was reduced to sub-nanometer after the compensation. To demonstrate the application of the system, we have measured the non-linearity of capacitive sensors using the calibrated optical interferometers.
We have calibrated an LVDT using an optical and x-ray interferometer. We have calibrated optical interferometer using x-ray interferometer. The LVDT has calibrated by the optical interferometer. We made the monolithic x-ray interferometer with a double parallel spring structure for the translation of an analyzer lamella. One period of the x-ray interference fringe corresponds to the lattice parameter, 0.192 nm. The nonlinearity of optical interferometer has been calibrated by an x-ray interferometer. We have used a phase modulation optical interferometer. This calibration using the x-ray interferometer is directly traceable to primary standards. We have achieved the resolution of an x-ray interferometer and optical interferometer better than 0.01 nm. The optical phase stability of the interferometer is less than ± 150 pm. For the control of environmental temperature, we have used PID method. PID controller controlled the temperature inside chamber. Temperature drift was less than ± 3 mK (k = 2).
A monolithic x-ray interferometer manufactured at KRISS has been used to provide a means for the calibration of transducers with the traceability to the standards of length in the sub-nanometer region. Such calibration by the monolithic x-ray interferometer using the lattice spacing of silicon is directly traceable to primary standards. The lattice plane used for diffraction was (220) with lattice parameter of 0.192 nm. One period of the x-ray interference fringe corresponds to the lattice parameter. We could achieve a resolution of less than 0.01 nm by detecting the phase of the x-ray interference signal. A monolithic x-ray interferometer was made from a silicon single crystal. It comprises three thin lamellas called splitter, mirror, and analyzer, and it incorporates a double parallel spring structure for the translation of the analyzer lamella. The x-ray interferometer has been applied to the measurements of displacements at sub-nanometer levels. The displacements of linear transducers have been measured using the x-ray interferometer. Several capacitive sensors were also calibrated and the results of these measurements are reported in the paper.
As design rule shrinks down, the role of CMP process is important for obtaining available depth of focus margin in optical lithography. However, the alignment mark deformed by CMP process contributes to the total overlay error budget. This study examines the effect of alignment accuracy with various CMP polishing targets in STI process and optimizes for stable overlay control in gate pattering. At first, polishing uniformity was monitored as polishing targets in STI process and results show that uniformity is getting worse as increasing polishing target. Also, the signal contrast of alignment mark becomes lower and thus, modeled alignment residual is increased. The investigations of modeled alignment residual with signal profile and overlay result as alignment mark type show that convex alignment mark is more sensitive than concave in varying a polishing target. And, the effect of Tungsten gate film stack was considered. In order to make alignment topology, oxide between alignment marks was removed by wet etching process. Then, gate film stack materials, poly, Tungsten, Nitride, oxide, were successively deposited over alignment mark. For stable overlay control, alignment mark type and the optimization of the width of segment alignment mark with concave was examined using modeled alignment residual with signal profile and overlay result. From this study, it is found that narrow width with segment alignment mark and concave type is better than normal bar alignment mark with convex type for overlay control in Tungsten gate patterning.
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