Effect of acid anion on the behavior of single component molecular resists incorporating ionic photoacid generators

A series of single component chemically amplified molecular resists were made using an onium salt cation core of tris(4-(tert-butoxycarbonyloxy)-3,5-dimethylphenyl)sulfonium (TAS) with five different acid anions: chloride (Cl), hexafluoroantimonate (SbF6), triflate (Tf), nonaflate (Nf), and tosylate (Ts). The counter-ion had a large effect on both the performance and physical characteristics of the resists. TAS-SbF6 and TAS-Tf imaged as positive tone resists with good LER, but suffered from acid diffusion problems which limited resolution. TAS-Ts and TAS-Cl had high water solubility that prevented their use as positive tone resists. TAS-Nf had poor wetting and adhesion that prevented it from being spin-coated into films. Using onium salts as single molecule resists places great restriction on the choice of anion used because of the large effect it has on the properties of the resist. Using extreme ultraviolet lithography, TAS-SbF6, the best performing derivative, was able to resolve 50nm 1:1 line/space patterns with LER ([email protected]) of 5.2nm.