Continued advances in microelectronic fabrication are trying the limits of conventional lithographic technologies [1]. The traditional diazonaphthoquinone/novolac resist materials are not suitable for use with the deep-UV exposure tools both from the absorption and sensitivity considerations [2]. New resist materials and processes are necessary to fully utilize the potential of deep-UV microlithography, a more promising technology for the production of sub-0.5µm geometries. The advent of resist materials based on chemical amplification principle [3,4], where one photochemical event leads to a cascade of subsequent events causing a solubility differential, exhibit high resolution, excellent sensitivity and good etch selectivity required for deep-UV lithography. While process sequence for chemically amplified materials is similar to conventional positive resist process sequence, post-exposure bake (PEB) assumes the role of effecting a solubility differential by means of thermally activating the acid catalyzed crosslinking or deblocking reaction. The PEB parameters, the delay time between exposure and post exposure bake (post exposure delay time, PED) and the inherent chemistry of the resist system greatly effect the process performance. This paper summarizes the process characteristics of select positive and negative deep-UV resists, and attempts to correlate the results to the chemical design of the individual resists.
When used in conjunction with a nitrobenzylester photoacid generator, poly(t-butoxycarbonyloxystyrene-sulfone) deep-UV resist films exhibit high contrast, good resolution and linewidth stability. Use of overcoat materials dramatically reduce the surface inhibition problems, improve the latent image stability (time delay) and enhance the sensitivity by isolating the resist surface from environmental contaminants that react with the photogenerated acid. The photospeed of the all organic CAMP formulation is lower compared to the arsenate based system but can be improved by using more aggressive PEB conditions. Coded, 0.35 tm 1/s pairs could be resolved in 1 im thick resist films at a dose of 20-30 mJ/cm2. The exposure latitude is 25% for 0.5 p.m features, upon exposure with a GCA prototype deep-UV exposure tool with a NA = 0.35 and 5x reduction optics. This paper will discuss the resolution, depth-of-focus, exposure latitude and processing characteristics obtained during the evaluation of this chemically amplified resist. INTRODUCTIONNew resist materials and processes must be developed in order to introduce deep-UV lithography into manufacturing1 . The current conventional positive resist materials based on a novolac resin and diazonaphthoquinone dissolution inhibitors have limited use for the deep UV region (240-270 nm) due to their strong and non-bleachable absorbance. We recently reported a chemically amplified resist systern comprised of a transparent, poly(t-butoxycarbonyloxystyrene-sulfone)2 (TBSS) copolymer resin (OD 0. 1/jim) and triphenylsulfonium hexafluoroarsenate as the photo-acid-generator (PAG) which demonstrated 0.35 jim resolution in 1j.tm thick films at a dose of 10 mJ/cm2. While this resist exhibits * currently with National Semiconductor, 2900 Semiconductor Drive, Santa Clara, CA 95051 O-8194-Q565-5/91/$4.QQ SPIE Vol. 1466 Advances in Resist Technology and Processing VIII (1991) / 13 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspxgood process latitude, its performance is critically dependent on controlling the elapsed time between the exposure and post-exposure bake (PEB) steps (post-exposure time delay). In addition, the presence of arsenic, a potential device contaminant, in the PAG may limit its acceptance by industry, especially as metal-ion free resist formulations become available.The chemistry and preliminary lithographic characteristics of chemically amplified resist formulations consisting of metal ion free, non-ionic and non-volatile PAG materials has been reported3 . These PAG materials are structural variants of 2,6-dinitrobenzyl tosylate and have been shown to be effective acid generators upon deep-UV irradiation. The photogenerated benzene sulfonic acids are sufficiently strong to effect the deblocking of the tert-butoxycarbonyl (t-boc) group significantly below the Tg (glass transition temperature) of the matrix polymer, and hence are practical alternatives for onium salt resist formulations for...
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