Fabrication of phase masks and microlenses using binary optics

A process for the fabrication of binary optics at the Rochester Institute of Technology was established and tested. A sacrificial aluminum layer was used to provide both a conductive substrate for electron beam exposure, and a clean highly resistant etch stop for reactive ion etching. This enabled the use of a low pressure CF4 RE process that minimized the rates of polymerization during etch and provided stable etch rates necessary to achieve 100 angstrom etch depth control. Alignment errors of up to 1 micron were attributed to stage drifts on the electron beam exposure system. No systematic errors were found to indicate problems with the MEBES alignment system and alignment mark detection. Simulations of multiphase PSMs were performed using a program developed as a part of this work capable of simulating a 1024 pixel array of arbitrary magnitude and phase under conditions of partially coherent illumination. Cases of annular (off-axis) illumination and defocus are also allowed. The program has demonstrated rapid calculation as well as flexibility of user input using a graphical user interface. A three-etch, 8-phase level binary optic process was used to produce phase shifting masks and a quartz microlens array. Submicron chromeless phase mask features were demonstrated and gradient phase transitions were successfully used to eliminate unwanted lines at phase boundaries. Although photoresist process limitations prevented the realization of significant benefits from phase shifting, the electrical metrology structures demonstrated the ability to rapidly gather CD data useful in identifying problem areas