S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Mechanical Aerospace Engineering (기계항공공학부) Theses (Ph.D. / Sc.D._기계항공공학부)
Correction of scanner errors using a capacitive sensor and phase compensation in White Light Phase Shifting Interferometry : 백색광 위상 천이 간섭계에서 정전센서와 위상 오차 보정 알고리즘을 이용한 스캐너 이송 오차 보정
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- 공과대학 기계항공공학부
- Issue Date
- 서울대학교 대학원
- White Light Phase Shifting Interferometry ; Modified Bucket Algorithm ; Compensated WSI Peak ; Capacitive sensor ; Phase error compensation
- 학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2016. 8. 박희재.
- 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.
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