| dc.description.abstract |
In this study, a high-precision displacement measurement system: sinusoidal phase modulation grating interferometer, is developed by integrating heterodyne grating interferometry and digital lock-in technique.
In the 21st century, high-precision displacement measurement technology plays an important role in a wide range of industries, especially in the industry of semiconductor. Currently, production of semiconductor has achieved nanoscale dimensions, therefore it is essential that measurement system attains nanometer or even sub-nanometer resolution, in order to meet the demand of semiconductor industry. Thus, this study presents a high-precision displacement measurement system developed using optical technology.
The measurement system utilizes sinusoidal phase modulation as heterodyne light source, which is passed through a grating to generate 1st order light by diffraction and 0th order light by reflection. A mirror is used to direct the 0th order light to the grating so that -1st order light can be generated by diffraction. As the mirror moves, displacement signals are stored within the interferometry signals, and the relative phase can be retrieved using digital lock-in technique. Conventional heterodyne grating interferometry requires many polarizing elements, nevertheless fabrication flaws of polarizing elements increase the chances of nonlinear inaccuracies during measurement. Furthermore, conventional method requires analogue lock-in amplifier, which is big in volume and expensive, in order to extract signal from a noisy environment. In contrast, the sinusoidal phase modulation grating interferometer presented in this study is able to achieve high resolution in displacement measurement with a simple set-up. Displacement measurement can be performed by utilizing a laser, a grating fixed on moving stage, a mirror and a photodetector. This system uses digital lock-in technique, eliminating the need for a conventional lock-in amplifier, and thus reducing the measurement cost and size of measurement system in a great scale. The sinusoidal phase modulation grating interferometer proposed in this study is able to achieve resolution of 2 nm and sensitivity of 1.14 ˚/nm with measurement speed at 2.85 μm/s. | en_US |