APPLICATIONS OF DOPING AND DEDOPING OF TEFLON AF FILMS IN MICROFABRICATION USING KRF AND ARF EXCIMER LASERS

Teflon films in amorphous forms have many advantageous features for electronic applications such as low dielectric constant (from 1.89 to 1.93), low refractive index (from 1.29 to 1.31), complete transparency at 190 nm, good adhesion to substrates, high thermal and chemical stabilities. The unique feature of amorphous Teflon is its solubility in selected solvents which makes it possible to have uniformly doped Teflon films. Teflon AF films doped with tris(perfluoroalkyl)-s-triazine exhibit an UV absorption at wavelengths shorter than 330 nm: the maximum at 278 nm, the minimum at 236 nm, and an absorption coefficient of 1200 cm-2 at 248 nm for a dopant concentration of 6 wt% in the solid. With 10 pulses of a KrF laser a 10 μm thick doped Teflon film was etched completely with a 1 μm/pulse etch rate at a fluence of 428 mJ/cm2. With an ArF laser the doped Teflon film was etched completely in the same way. No photoablation was observed in the absence of a dopant in the same laser exposure condition. The tris(perfluoroalkyl)-s-triazine was readily removed from microfabricated films by heating the wafers on a hot plate at 200°C for 5 min. At this dedoping temperature no deformation of the images was observed. UV irradiation of the doped Teflon film made the dopant persist in the film at the dedoping temperature, suggesting imagewise doping. © 1990.