Correction of scanner errors using a capacitive sensor and phase compensation in White Light Phase Shifting Interferometry

Abstract

The research in this dissertation aims at improvement of measurement results by correcting scanner errors in White Light Phase Shifting Interferometry (WLPSI). WLPSI is widely used to get surface profiles of inspection targets in Liquid Crystal Displays and semiconductor industries nowadays. WLPSI is a non-contact type inspection system, therefore it does not destruct target samples. WLPSI is one of the fastest measurement system, additionally it satisfies the measurement accuracy and repeatability. But, there always occurs phase errors due to irregular and non-linear scanner movement, and these factors affect the measurement stability. There is a limitation to reduce movement errors of a vertical scanner by changing hardware. It is impossible to terminate mechanical delay of scanner movement due to inertia entirely. Errors caused by electrical delay cannot be avoidable either. In this thesis, a modified WLPSI system is suggested to correct phase errors without any changes in optics. It is very important not to make a complicated optics system and optical path, because it can make the lower measurement performance and cause the cost increases. Compensated White light Scanning Interferometry (WSI) Peak and Modified Bucket Algorithm are proposed to compensate phase errors caused by irregular and non-linear scanner movement. By using the proposed system, the position of the vertical scanner can be directly acquired, and it is possible to correct phase errors by applying proposed methods with the acquired position data. Different scan speed measurement and different scan start position measurement test are conducted to verify the proposed measurement system and algorithms. The measurement accuracy and the maximum difference between the results are under 0.4%. The measurement repeatability is also examined by 20 times repeat measurement for different measurement conditions. The target repeatability is 3σ 10 nm of the repeat measurement. The proposed method satisfies both the measurement accuracy and the measurement repeatability.