Measurement of microchannels inside transparent substrate based on confocal microscopy

In this paper an efficient method is proposed to measure the geometric dimensions of a microchannel bonded by a transparent top plate by employing the techniques of quick vertical scan of featured surfaces, detailed multi-layer sampling of depth response curves (DRC), and measurement of the refractive index of transparent top plate. The featured surfaces with profile fluctuation in the micro scale are scanned with high vertical resolution. The absolute height of each surface is determined by the peak point of the corresponding DRC. Since the DRCs are only sampled in the central area the processing speed is acceptable even with a large scanning length. The results of the measured depth should be corrected by the refractive index. Only in the same material does the focal point move at the same speed during the scanning motion. In this study an inverse measurement scheme is proposed to calculate the refractive index of a transparent plate without prior calibration. Any measurable steps on the sample surface can be used as the sampling area. By scanning the same area from both sides different sectional profiles can be extracted. The ratio of the different steps is the refractive index.