Electromagnetically Dual-Axis Driven MEMS Grating and Its Application to 3D Profiling with Near-Infrared Low-Coherence Interferometry

摘要

We have investigated 3D profiling of the objects by a low-coherence optical interferometer using MEMS grating. This system, constructed with optical fibers and MEMS devices, is a Fourier domain interferometer, which can discriminate distance to the object by wavelength analysis of the interference spectra. A MEMS mirror gives the object 2D optical scanning, and a MEMS grating permits spectroscopy of interference spectra. The MEMS grating can tilt to dual axis with electromagnetic force induced by planar coils and a permanent magnet. One axis tilting enables near-infrared spectroscopy and another axis tilting functions as optical axis alignment in an interferometer. Fabricated MEMS grating could tilt ±3.5° (mech.)/less than ± 10 mA in both directions at low frequency, which were equivalent to approximately 1400 to 1700 nm in wavelength. The interferometer, whose S/N was 50 dB and vertical standard deviation was 0.6 μm, could scan full wavelength width (1400 to 1700 nm) in 25 ms. Finally, we could realize 3D profiling which was not only surface reflection profiling of 1-μm step, but also transparent profiling of IC process layer from the wafer backside.