Resist Dissolution Kinetics And Submicron Process Control

The details of photoresist dissolution kinetics play a major role in image quality and process control, especially at sub-micron geometries. Kinetic parameters for photoresist dissolution are obtained using methods familiar to most lithography engineers. For example, activation energies can be extracted from the temperature dependence of dissolution rate while chemical reaction orders are obtained from the variation of dissolution rate with developer concentration. Taken together, these data provide valuable insight, not only about the mechanism of dissolution but also about the details of resist performance. Large chemical reaction orders and negative activation energies are observed at low to medium exposure doses, which prevail at the edges of lithographic features. The decrease in exposure selectivity at lower temperatures might suggest that higher resolution can be obtained at higher developer temperatures. Furthermore, a resist-developer combination which exhibits a strong dependence of reaction order on exposure energy is expected to show higher selectivity than a system with a lower reaction order-exposure dependence. Other desirable lithographic properties such as sidewall angle, latitude and resolution will follow the same trend. In this paper, the results of experiments in dissolution kinetics are tied to submicron lithography through semiempirical Prosim modeling. Activation energies are measured for various exposures and developer concentrations. Dissolution reaction orders are obtained for various developer temperatures and exposure energies. The computer modeling program, Prosim, is then used to model resist characteristics under various conditions. These include exposure, focus and mask-matching latitudes as well as resist profiles. Prosim calculations are verified by selected applications results which illustrate the influence of kinetic parameters on lithographic performance.