Papers by Keyword: Focus Error Signal

Abstract: An innovative high precision optical focus probe has been developed to measure the grating pitches. This probe uses characteristics of FES (focus error signal) of the modified DVD pickup head. Experimental tests showed the linear range of FES of this probe to the gratings was 5μm, the resolution was less than 1nm, the time stability was 5nm in 10 minutes, and positioning repeatability was better than 12nm. This system was applied to measure the grating pitch of 1200 lines per 1mm. The quality of the grating was assessed by the average of sampled pitches and its standard deviation. The inspected results can be an index to improve the process control of the grating fabrication.

Abstract: The primary purpose of this research is to adopt a commercially available DVD pickup head and modify it to become a high-speed scanning nano-measurement probe. With the principle of astigmatism the probe can execute the autofocusing motion by an imbedded voice coil motor (VCM) following the height change of the tested object in the vertical Z-direction. Given high precision triangular current signal with appropriate frequency to the input ports of tracking, the same VCM can be moved along the lateral X-direction for profile scanning. Firstly this paper presents the structure of DVD pickup head, the theory of autofocusing and auto scanning, and the developed controller. Then experimental setups and accuracy calibration will be introduced. In order to achieve a bi-directional precision measurement in autofocusing and scanning, this study has developed a hysteresis error compensation scheme by a DSP-32 integrated system. In association with a high precision linear stage in Y-direction, this high precision micro/nano optical probe can measure the 3D profile of the miniature object successfully at fast speed.