The semiconductor industry is continually challenged to maintain the trend identified in 1965 by Gordon Moore of increasing the density of transistors on an integrated circuit. These advances have been achieved by increasing the resolution that can be printed with photolithography, traditionally by decreasing the exposure wavelength. Decreasing the exposure wavelength from 193 nm, the current state of the art, presents significant technical challenges. To circumvent these challenges, resolution can be increased by enabling increases in numerical aperture (without changing the exposure wavelength), using immersion lithography. In immersion lithography, the air gap between the photoresist-coated wafer and lens is replaced with a high refractive index fluid. Immersion lithography has been demonstrated with water as the immersion fluid. With water immersion lithography at 193 nm, the maximum resolution that can be printed can be decreased from 65 nm to 45 nm. To enable further resolution increases, immersion fluids with a higher index than water are needed. The requirements for next generation high index fluids are: an index of refraction higher than water, high transparency, and physical properties similar to water. A variety of methods to identify a high index fluid were completed. First, the optical properties of aqueous solutions of metal cations with varying anions were tested. A series of linear, cyclic, and polycyclic alkanes were also studied, since saturated systems have electronic transitions at wavelengths less than 200 nm, to provide the necessary transparency at 193 nm. Large alkane groups were also incorporated into either the cation or anion of a salt to develop an aqueous solution with the optical properties of a saturated hydrocarbon. In addition to these empirical surveys, a modeling approach was used to develop “designer” absorbance spectra that would correspond to fluids with a high index and low absorbance at 193 nm. Additionally, in Appendix D, the results of an electrochemical study of the diffusion coefficient of ferrocene methanol in poly(ethylene glycol) diacrylate hydrogels of varying molecular weight and water content will be presented. The results of these mass transport studies can be used to qualitatively understand the mass transport characteristics of additional species in the hydrogel. / text

Thesis (M.S.)--Rochester Institute of Technology, 2005. / Typescript. Includes bibliographical references (leaves 94-102).

The important roles of fluid dynamics in immersion lithography (IL) and step-and-flash imprint lithography (S FIL) are analyzed experimentally and theoretically. In IL there are many challenges with managing a fluid droplet between the lens and the wafer, including preventing separation of the fluid droplet from the lens and deposition of small droplets behind the lens. Fluid management is also critical in S FIL because the imprint fluid creates capillary and lubrication forces, both of which are primarily responsible for the dynamics of the template and fluid motion. The fluid flow and shape of the wafer determine how uniform the gap height between the wafer and the template is, and they affect the resistance during the alignment phase. IL was investigated as a methodology to improve laser lithography for making photomasks. The fluid flow in IL was investigated by building a test apparatus to simulate the motion of the fluid droplet during microlithographic production, and using this apparatus to conduct experiments on various immersion fluids and wafer topcoats to determine what instabilities would occur. A theoretical model was used to predict the fluid separation instabilities. Finite element simulations were also used to model the fluid droplet, and these simulations accurately predict the fluid instabilities and quantitatively agreed with the model and experiments. It is shown that the process is viable: capillary forces are sufficient to keep the fluid droplet stable, heating effects due to the laser are negligible, and other concerns such as evaporation and dissolution are manageable. Euler beam theory and the lubrication equation were used to model the bending of an S FIL template and the flow of the fluid between the template and a non-flat wafer. The template filling time, conformance of the template to the wafer, and the alignment phase are investigated with an analytical model and finite element simulations. Analysis and simulations show that uniformity of the residual film thickness and ease of proper alignment depend greatly on the planarity of the wafer, the properties of the template, and the surface tension of the fluid. / text