A study has been performed to determine the viability of phosphoric acid as a high-index fluid for immersion lithography. The ability to image in the immersion fluid, and the compatibility of the fluid with photoresist were examined. Samples were soaked in the fluid before and after exposure in water to demonstrate no significant damage to the imaging capability of the resist. The refractive index of photoresist samples soaked in various immersion fluids was measured with a variable angle spectroscopic ellipsometer (VASE), and results did not show a significant variation from photoresist that was not soaked. Sixty-eight nanometer lines were imaged through phosphoric acid in 193nm photoresist without a topcoat layer.
Wolf, Karen R.
"Phosphoric Acid as a High-Index Immersion Fluid,"
Journal of the Microelectronic Engineering Conference: Vol. 14
, Article 8.
Available at: http://scholarworks.rit.edu/ritamec/vol14/iss1/8