Improved ion implantation masking through photoresist fluorination

Abstract

As semiconductor gate lengths shrink, photoresist trends toward thinner films. Thick photoresist films are not desirable because they tend to absorb more light, require higher energies to pattern, increase pattern collapse, and subtract from depth of focus and exposure latitude. The minimum thickness of implant photoresist is governed by the stopping power of the photoresist for the ion type and the energy of the implant. Relatively high energy implants and/or lower ion stopping power in the photoresist require thicker photoresist films. These problems can be mitigated through a novel photoresist fluorination process. The fluorination process results in the replacement of H atoms by heavier F atoms effectively increasing the molecular weight of the fluorinated film and its ability to block ion implantation. This straightforward and cost-effective process is investigated for use with a standard 248 nm dyed photoresist. Substrate damage probe measurements and Secondary Ion Mass Spectrometry depth profiles show species-dependent ion implant masking improvements of up to 40 % for fluorinated photoresist versus as-developed photoresist. Geometric and process margin arguments are discussed for thinning photoresist where angled implants are needed or process capability is insufficient. Finally, electrical data is presented that demonstrates the manufacturability of these fluorinated and thinned photoresist films.