Study of acid diffusion in a positive tone chemically amplified resist using an on-wafer imaging technique

Abstract

In this article, the acid diffusion coefficient of Shipley positive tone resist, UV-III, in an as-spin coated film is determined by using an on-wafer imaging technique. This technique involves incorporation of a pH-dependent fluorescence material, 5-aminofluorescence, into the resist. This fluorescence material images the acid distribution by generating fluorescence intensity contrast under a confocal microscope. Using a laser beam of 488 nm wavelength and an objective lens of 100× (with oil immersion), the nominal feature sizes of 0.20 μm can be resolved with a high signal-to-noise ratio. The acid diffusion coefficient is determined from 1 μm lines and spaces (1:9), which are generated by e-beam writing under different post exposure baking (PEB) times. The value obtained during the PEB is smaller than 3.5×10−13 cm2/s. The resist properties (e.g., sensitivity, resolution, and thermal stability) are not changed significantly by the low loading of the fluorophore because the dose to size and the printed linewidth are very close to the conditions for resist processing without the fluorophore.