Fluorinated silicon nitride film for the bottom antireflective layer in quarter micron optical lithography

Abstract

Fluorinated silicon nitride thin film as a bottom antireflective layer (BARL) material, being suitable for line-patterning in 0.25 mu m KrF excimer laser (248 nm) lithography, has been studied by film fabrication/characterization and computer simulation, Three-dimensional reflectance simulation process suggests that the 0% reflectance between photoresist (PR) and BARL can be achieved by selecting proper combinations of film optical properties such as refractive index (n), extinction coefficient (k) and thickness (d). For the PR/300 Angstrom BARL/c-Si or PR/300 Angstrom BARL/W-Si structure at a wavelength of 248 nm, the simulation process reveals that nearly 0% reflectance could be obtained when the n and k values of the film are 2.109 and 0.68 or 2.052 and 0.592 respectively. The fluorinated silicon nitride films prepared by ICP enhanced CVD have been evaluated with the variations of NF3 flow rates under the two conditions of SiH4:N-2 = 2:15 and 3:20 (seem). The film n and k values at 248 nm vary in the ranges of 1.665-2.352 and 0.007-0.695 respectively, depending on gas flow ratio. As it is very sensitive to the film thickness, the reflectance could be reduced, using compoter simulation, to almost 0% by changing the film thickness. Furthermore, the ARL performance for 0.25 mu m line/space processed by the KrF excimer laser stepper and the stripping ability/selectivity show this material to be a superior candidate for deep-UV microlithography applications.