[OPTICAL REVIEW Vol. 7, No. 6 (2000) 525-534]
Investigation of High-Precision Lithography Lens AberrationMeasurement Based on Three-Beam Interference Theory: Sensitivityversus Coherent Factor and Variations with Dose and Focus
Process & Manufacturing Engineering Center, Semiconductor Company, Toshiba Corporation, 8, Shinsugita-cho, Isogo-ku, Yokohama, 235-8522 Japan
(Received April 18, 2000; Accepted July 18, 2000)
The three-beam interference technique with high coherent illumination is considered promising for application to the measurement of lens aberrations due to its ease of use and convertibility of the results to Zernike coefficients. The coefficients widely describing the characteristics of aberrations are crucially important for the prediction of aberration impacts on a specific pattern, and are expected to minimize the impacts. Furthermore, intensive study of the three-beam interference technique is necessary for highly accurate prediction. This paper discusses the expected characteristics of three-beam interference based on theoretical considerations and experimental results. In one experiment, a krypton fluoride excimer laser scanner with a numerical aperture of 0.68 was used. Having practicable highly coherent illumination affects sensitivity in detecting aberrations, and makes results independent of exposure dose and focus. Such characteristics improve repeatability under realistic conditions that the exposure dose is not uniform and the wafer surface is not flat.
Key words : photolithography, wavefront, aberration, Zernike polynomials, coherent factor