Abstract

To obtain higher optical performance in semiconductor lithography or metrology systems, inclination control of the wafer substrate surface is becoming more important. An inclination measurement monitor attached to these systems requires high measurement accuracy, ability to deal with patterned and resist coated wafer, and compact size. The linear grating coupler of the optical waveguide element is sensitive to the incident beam angle. This characteristic was considered a weakness when used in a conventional optical measurement system. However, for the inclination measurement, this becomes a valuable characteristic. To verify inclination measurement ability of the linear grating coupler (TiO₂) formed on the optical waveguide device (Ti-diffused LiNbO₃), an experimental system was produced. A collimated s-polarized He-Ne laser illuminated the wafer surfaces (incident angle = 60°) and coupled light intensity of the reflected or scattered light from the tested surface was detected. Inclination of the substrate was obtained from the maximum intensity position. Standard deviation of the measurement accuracy of the order of < 10^-6 radian(σ) was confirmed even when a patterned and resist coated wafer was measured. The experimental results fit the numerically simulated results.

© 1991 Optical Society of America