Abstract

During efforts to produce multilayer high efficiency dielectric reflection gratings in oxides, 351nm high efficiency transmission gratings, and other development work, we required very high-contrast grating profiles in photoresist. High-contrast profiles are profiles with very steep sidewalls, greater than 80 degrees. It is quite difficult to achieve high-contrast profiles using interference lithography. The electric field distribution is sinusoidal. Therefore, one would conclude that the profile would resemble a sinusoid, as shown in Figure la. Early work with interference lithography produced grating profiles similar to the ones shown in Figure la.^1-3 We have learned that if great care is taken in the processing steps, very different profiles can be achieved. Figure 1b shows a very high-contrast, high-aspect ratio grating profile in photoresist. The difference between Figure 1a and Figure 1b is that 1) the photoresist profile in Figure 1b has completely developed through to the substrate, and 2) the contrast characteristics of the photoresist used in Figure 1b are superior over the photoresist used in Figure 1a.

© 1996 Optical Society of America