Proceedings Article | 9 June 1995
KEYWORDS: Deep ultraviolet, Polymers, Absorbance, Lithography, Diffusion, Tin, Temperature metrology, Excimer lasers, Photoresist processing, Semiconducting wafers
The development of a new DUV positive resist, XP-9493, is reported. XP-9493 was designed for the Micrascan II exposure system. Its absorbance over the 245 - 252 nm wavelength range is 0.48/micrometers , substantially higher than that of APEX-E, which is approximately 0.2/micrometers . The dissolution selectivity, tan ((phi) ), of XP-9493, 7.7, is much higher than that of APEX-E, 4.1. Thus, XP-9493 is capable of higher resolution than APEX-E with better swing curve control. It is shown that the deprotection rate of this resist is proportional to the pKa of the photogenerated acid. This result leads to the prediction that protonation of the protected polymer may determine the rate of the deprotection reaction. Further study of the photospeed vs PEB temperature showed a two-tier activation energy for the deprotection reaction. At high PEB temperatures, >= 95 degree(s)C, the deprotection reaction is diffusion-limited, where the protonation step is rate limiting. The activation energy, Ea, under diffusion limited conditions is only 7.6 kJ/mole. At lower PEB temperatures, < 95 degree(s)C, the deprotection reaction is reaction-limited, where the deprotection of the protonated protected polymer is rate-limiting. Ea under these conditions is 26.3 kJ/mole. This behavior leads to lower linewidth shifts per unit PEB temperature change, (Delta) CD/(Delta) T, at the recommended process conditions. For XP-9493, (Delta) CD/(Delta) T is approximately 6 nm/ degree(s)C for 300 nm line/space pairs. XP- 9493 resolves 0.225 micrometers line/space pairs at 19 mJ, and 0.25 micrometers contact holes at 27 mJ. The 0.25 micrometers process window for XP-9493 is >= 1.0 micrometers depth-of-focus, with 25% exposure latitude on a MSII exposure tool.
