We present a new method for in situ monitoring of a grating profile during the development process to control the critical dimensions of surface-relief rectangular photoresist gratings on transparent substrates. A He–Ne laser of visible wavelength is employed as the monitoring light source. We determine the height of the grating ridges from the first minimum value of the diffraction intensity curve of the zeroth transmission order and then obtain the duty cycle of the grating from the diffraction intensity of the st transmission order. The effectiveness of our method has been demonstrated through the fabrication of rectangular photoresist gratings of 1200, 2200, and on glass substrates. The experimental results are statistically compared with results extracted from scanning electron micrographs. Good agreement between the online, real-time measured results and the scanning electron microscopy results is obtained.
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