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Proceedings Paper

An automatic angular positioning of mask with wafer using modified moire technique
Author(s): Brahm Pal Singh; Dr. Kowsalya; Rina Sharma; Ram Narain; Alok K. Kanjilal; Ramesh P. Singh; Vijay Trimbak Chitnis; Yoshihisa Uchida
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Paper Abstract

An automatic and accurate technique for angular positioning of mask with respect to wafer is reported.. Alignment marks are in the form of gratings and the moire signal is obtained by the relative displacement between the gratings. The higher slope region of the moire signal is used to obtain higher sensitivity and better position control accuracy. The experiments are performed with 25 micrometer pitch gratings and Piezo- Electric Transducer is used for the angular displacement. The angular -7 accuracy of the order of 2 x 10 radian is reported with a time constant of 0.2 sec. In the recent years, use of moire interference technique for mask to wafer alignment has attracted much attention especially in VLSI fabrication technology where a highly accurate linear and angular positioning is involved. In this technique the alignment marks are in the form of gratings. A laser beam is passed normally through a mask grating and reflected from the wafer grating. Intensity variation in the reflection mode due to relative angular rotation is detected by a photodetector and converted into the electrical signal, known as moire signal.

Paper Details

Date Published: 16 December 1992
PDF: 5 pages
Proc. SPIE 1622, Emerging Optoelectronic Technologies, (16 December 1992); doi: 10.1117/12.637260
Show Author Affiliations
Brahm Pal Singh, National Physical Lab. (India)
Dr. Kowsalya, National Physical Lab. (India)
Rina Sharma, National Physical Lab. (India)
Ram Narain, National Physical Lab. (India)
Alok K. Kanjilal, National Physical Lab. (India)
Ramesh P. Singh, National Physical Lab. (India)
Vijay Trimbak Chitnis, National Physical Lab. (India)
Yoshihisa Uchida, Aichi Institute of Technology (Japan)

Published in SPIE Proceedings Vol. 1622:
Emerging Optoelectronic Technologies
Krishna Shenai; Ananth Selvarajan; C. Kumar N. Patel; C. N. R. Rao; B. S. Sonde; Vijai K. Tripathi, Editor(s)

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