Abstract
Noncontact displacement measurement is generally based on the interferometry method. In the semiconductor industry, a technique for measuring small features is required as circuit integration becomes denser and the wafer size becomes larger. An interferometric system known as a three-longitudinal-mode heterodyne interferometer (TLMI) is made of two main parts: optical setup and electronic sections. In the optical part, the base and measurement signals having 500-MHz frequency are produced, resulting from interfering three longitudinal modes. The secondary beat frequency to measure the displacement in the TLMI is about 300 kHz. To extract the secondary beat frequency, wide-band amplifiers, doublebalanced mixers (DBMs), band-pass filters (BPFs), and low-pass filters (LPFs) are used. In this paper, we design the integrated circuit of a super-heterodyne interferometer with total gain of 56.9 dB in size of 1030 μm×1030 μm.
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