<title>Evaluation of practical properties of a spin-on-glass for a shifter of phase-shift masks</title>

Abstract

Spin-on-glasses(SOGs) are excellent candidates for a shifter of phase shift masks. Four kinds of commercially available SOGs have been evaluated for use in i-line exposure. Each SOG had a high optical transmittance, and an adequate refractive index (ca. 1.44). However, only one of them, referred to as SOG: A hereafter, had enough durability against immersion in sulfuric acid for cleaning. The film cured at 200°C showed the above durability whereas that cured at 450°C did not The cause of the degradation was speculated from the FT-IR analysis. SOG:A also had (i) a low tensile stress( less than 5x108dyn/cm2 ) in its film, (ii) enough durability against scrubbing for cleaning, and (iii) good pattern profiles when fabricated by a dry-etching process. But, it had the two shortcomings; (i) poor durability against irradiation (at 200kJ/cm2) with i-line light, although this statement is based on the results of our preliminary experiment, (ii) poor step-coverage when its film was spin-coated over chrome patterns (because the thickness variation up to 20-30nm within a shifter pattern was observed). Implication of these shortcomings is discussed.