Tetrahydropyranyl‐ and furanyl‐protected polyhydroxystyrene in chemical amplification systems

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Abstract
Tetrahydropyranyl‐ (THP) and furanyl‐ (THF) protected polyhydroxystyrene (PHS) polymers have been investigated for their potential use in conjunction with onium salt acid precursors to yield high‐sensitivity resist systems. The synthesized polymers have high transmittance at 248 nm (the wavelength used in next‐generation excimer laser, KrF exposure tools). At 248 nm the transmittance for a 1‐μm thick film is ∼ 80% (Abs = 0.097 μm−1). The acid sensitivity of the acetal functionality at room temperature is high, requiring careful handling of all materials to prevent any premature deprotection of the hydroxy group. The highest lithographic sensitivities obtained so far with a system consisting of poly(p‐tetrahydropyranyl‐oxy‐styrene) base resin and 1 mol % of bis (p‐tert‐butyl phenyl) iodinium triflate (TBIT) was ∼ 2 mJ / cm2. High‐resolution line and space patterns (0.35 μm) were obtained with a system comprising PHS‐p‐THP and an acid precursor, using an excimer laser step and repeat exposure at 248 nm.