Photomask technology has become a critical part of IC manufacturing in recent years. It is the link between IC design and IC manufacturing through lithography and etch image-transfer processes. The heart of the enabling lithography technology (in keeping with Moore’s law) involves transferring the pattern images from a mask to the wafer plane with acceptable distortion and maintaining reasonable pattern fidelity. Nearly all lithographic resolution enhancement techniques (RETs) involve masks in some degree. The exposure light path (OAI, immersion), light intensity (OPC), and phase (PSM) are all modified to increase the image information transfer through an optical system of scanners. Other areas, such as polarization and illumination shape adjustment to match the exposed mask patterns (SMOs), are also actively tapped to maximize the lithography process window. All of these techniques make the photomask production process and qualification process especially important. Furthermore, because a mask is used to expose every die on wafers, the quality of a mask directly affects pattern qualities on wafers and thus the product yield.
Online access to SPIE eBooks is limited to subscribing institutions.