Chromeless phase shift mask

Abstract

A photolithographic mask for receiving light at a wavelength, phase, and intensity and printing a desired image on a substrate with an optical system. The mask is formed on an optically transmissive substrate, called a mask blank. The mask blank is preferably one hundred percent transmissive of the light intensity at the wavelength. At least one layer of an attenuated material that is at least partially transmissive to the wavelength of the light is formed on the optically transmissive substrate. The at least one layer of the attenuated material preferably blocks from about fifty percent to about ninety-four percent of the intensity of the light at the wavelength, whereas the prior art masks use materials that block about six percent of the intensity of the light at the wavelength. The attenuated material defines three feature types on the mask, including a primary image having edges, a scattering bar disposed near the edges of the primary image, and a background region. The primary image represents the desired image to be printed on the substrate. The scattering bar is adapted to enhance a contrast of the primary image and to at least reduce the intensity of the light at the edges of the primary image. The background region is adapted to block the light without using a material that is non transmissive to the light, such as chrome. By 'block the light' it is meant that the background region substantially and preferably reduces the intensity of the light passing through the background region to about zero.