1. Field of the Invention
This invention relates generally to functionalized carbosilane polymers and photoresist compositions containing the same.
2. Description of Background
Dry 193 nm resist materials are generally limited to indices of refraction near or below 1.7. It has been predicted that using a high refractive index resist in immersion lithography can significantly enhance the depth of focus, exposure latitude and mask error enhancement factor (MEET) at numerical apertures (Nas) >1.0. The higher the refractive index, the greater the enhancements. It is expected that immersion lithography at 193-nm complemented by techniques such as double exposure would be the main lithography solution for 32-nm node manufacturing. This will place stringent requirements on 193-nm photoresists, among others.
Several polymers having a retractive index n as high as 1.9 have been identified as potential candidates. These materials include thioacrylates and thiazolines, but share the property of having a high sulfur content. Unfortunately, however, the 193-nm absorption of these polymers has also progressively increased with the increase in sulfur content and has made them unsuitable for photoresist applications. Some of the polymers that have been prepared for resist applications have absorbance values [A=(α10/μm)] greater than 5.
A few functional polycarbosilanes have been reported previously. For, example, Interrante et. al., (I. L. Rushkin and L. V. Interrante, Macromolecules, 1996, 29, 5784) have reported the synthesis of several functional polycarbosilanes including a phenol containing polycarbosilane. The US patents and patent publications listed below have also reported the use of functional polycarbosilanes for various applications: U.S. Patent Publication No. 2005/0042538 to Babich et al; U.S. Pat. No. 7,172,849 to Babich et al.; U.S. Pat. No. 6,660,230 to McGill et al.; U.S. Pat. No. 7,157,052 to McGill et al.; U.S. Patent Publication No. 2007/0003440 to McGill et al.; U.S. Patent Publication No 2006/0063905 to Nakagawa et al.; and U.S. Patent Publication No. 2007/0020467 to Nakagawa et al.
Babich et al, describe polycarbosilanes with cross-linkable pendant groups for hard-mask applications. McGill et al. describe the use of fluoroalcohol containing polycarbosilanes for analytical and purification applications. Nakagawa et al. have reported the synthesis and utilization of polycarbosilanes for insulating films. None of the publications or patents mentioned above describes the use of polycarbosilanes for photoresist applications, or polycarbosilanes with acid functionalities. Furthermore, no report has attributed higher refractive index to polycarbosilanes.
Accordingly, there remains a need for high refractive index polymers suitable for use in photoresist compositions employed in immersion lithography.