Abstract

As the photolithography field strives to obtain sub-half-micrometer geometries, the interrogation of latent images in photoresist is becoming increasingly important. A latent image is defined as the distribution of photoactive compound (PAC) concentration after exposure to radiation. The PAC concentration present in a photoresist layer after exposure determines the index of refraction of this layer. Photolithography simulation tools, such as PROLITH or SAMPLE, that model the PAC concentration can be utilized to provide a complete description of the index grating structure. Rigorous coupled-wave diffraction analysis is then used to model the scattered light from the latent image grating. The effects of focus and exposure conditions on the final line shape of the grating structure are of increasing importance in photolithography. By using the photolithography simulation tools, the effects of the focus and exposure conditions on the scat­tered light can now be considered. Also, processes that affect the latent image after the exposure step, such as post-exposure bake (PEB), can be considered. The theoretical results obtained illustrate how examination of scatter from a latent image grating enables the tracking of the effect of the focus, exposure, and PEB conditions.

© 1992 Optical Society of America