Use of diffracted light from latent images in photoresist for optimizing image contrast

摘要

The present invention includes a method and apparatus for the rapid, nondestructive evaluation of the contrast of a latent image in a photoresist. More particularly, the contrast of the latent image is directly monitored by measuring the intensity of the light diffracted from a pattern in the exposed, undeveloped photoresist known as the latent image. The proper exposure tool parameters, such as exposure tool time and focus, is suitably determined based on the intensity of different orders of diffracted light, namely the 2nd-order diffracted from the latent image. In a preferred embodiment, a test pattern consisting of a periodic pattern, or a pattern of the device associated with the particular lithographic step, is employed to provide well-defined diffraction orders.