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

抄録

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 pK_a of the photogenerated acid generated from the anion, TFA>TSA>HDSA>CSA. The TPSTSA -based resist showed the lowest diffusion coefficient, D=2.7 x 10-5μm²/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, R_p/R_min, at less blocked polymer levels, where R_p is the dissolution rate of the blocked polymer, and R_min is the dissolution rate of the unexposed blocked polyrner/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 0.225μm on a 0.53NA excimer laser stepper at a photospeed of 46mJ/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 0.26N TMAH developer. Finally, it is shown that with altered PVP, high resolution with negative DUV resists without microbridging in 0.26N TMAH developer can be achieved.