Abstract

Our goal is to use the light diffracted from a latent image grating to improve CD uniformity. The experimental technique involves using a laser at a non-exposing wavelength to illuminate a grating pattern in exposed, undeveloped resist (a latent image). Photodiodes are employed to measure the intensity in the orders diffracted from the image. Data has been taken on a latent image focus-exposure matrix produced on Si. The data indicates that the first order is a function of both exposure and focus, and the second order is more strongly effected by focus. The zeroth order is a function of the thickness of the resist and any underlying films. The effects of post exposure bake (PEB) temperature have also been investigated. The zeroth order changes as a function of PEB temperature because of the resist thickness shrinking, and the first and second orders are also functions of PEB temperature. We have generated a program that uses rigorous diffraction theory to predict the intensity in the diffracted orders as a function of exposure, focus, and PEB. This modeling program is discussed in a separate paper.

© 1992 Optical Society of America