The Development of Chemically Amplified Positive- and Negative-tone Resists for DUV Lithography

Abstract

The development of robust, high resolution, positive- and negative-tone resists is necessary for the eventual implementation of DUV lithography in a manufacturing environment. Great progress has been made in the last two years in the area of chemically amplified resists. Environmentally stable, high resolution and high thermal resistance negative-tone resists have been commercially available for three years. Prototype DUV positive-tone resists are now achieving better environmental stability through the use of partially blocked poly(p-vinyl)phenol polymer and photoacid generators (PAG) based on organic onium salts. In this paper, our studies of various PAG structures in positive-tone DUV resists are reported. The PAG structure, M+X- was varied such that M+ was either triphenylsulfonium (TPS+) or diphenyliodonium (DPI+), and X-was trifluoromethanesulfonate (TFA-), toluenesulfonate (TSA-), camphorsulfonate(CSA-), and hexadecylsulfonate (HDSA). The relative photospeed of these resists corresponded to the pKa of the photogenerated acid generated from the anion, TFA>TSA>HDSA>CSA. The TPSTSA-based resist showed the lowest diffusion coefficient, D = 2.7 × 10-5 µm2/s, as estimated from linewidth vs. postexposurebake(PEB) time plots. This paper also shows a unique advantage of onium salts in that they can show a maximum dissolution rate ratio, Rp /Rmin at less blocked polymer levels, where Rp is the dissolution rate of the blocked polymer, and Rmin is the dissolution rate of the unexposed blocked polymer/5% onium salt. The dissolution rate ratio was 250 using a 10% blocked polymer, which approaches the inhibition capability of PAC/Novolak systems. This work on PAG structural variation has led to the development of XP-9402 positive DUV resist, which is linear to 0.225 µm on a 0.53 NA excimer laser stepper at a photospeed of 46 mJ/cm2. This resist shows good postexposure delay stability for up to two hours, without the use of a covercoat. The second part of this paper discusses our work on negative DUV resists, where low molecular weight poly(p-vinyl)phenol (PVP) provides highest resolution performance in negative DUV resists. The PVP-based resists suffer from microbridging in 0.26 N TMAH developer. Finally, it is shown that with altered PVP, high resolution with negative DUV resists without microbridging in 0.26 N TMAH developer can be achieved. © 1994, The Society of Photopolymer Science and Technology(SPST). All rights reserved.