I n d . Eng. Chem. Res. 1991,30, 1461-1468 Kondo, K.; Sonoda, N.; Tsutaumi, S. New Selenium-triethylamine Catalyzed Synthesis of Arylureaa from Carbon Monoxide and Aromatic Amines. J. C h " SOC.,Chem. Commun. 1972,307-308. Lee, S. M.; Lee, C. W.; Lee, J. S. Manufacture of N,N'-substituted Ureas. Korean Patent Application 89-15880, 1989. Macho, V.; Hudec, J.; Polievka, M.; Filadelfyova, M. One-Step Synthesis of N,N'-diphenyl Urea. Chem. h u m . 1975,25, 140-144. Nefedov, B. K.; Sergeeva, N. S.;Eidus, Ya. T. CarbonylationReactions. 9. Carbonylation of Amines by Carbon Monoxide in the Presence of Mercury(I1) Acetate. Zzu. Akad. Nauk SSSR, Ser. Khim. 1973,807-808. Nefedov, B. K.; Sergeeva, N. S.; Eidus, Ya. T. CarbonylationReactions. 21. Synthesis of N,N'-substituted Urea by Carbonylation
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of Amines by Carbon Monoxide at Atmospheric Pressure. Izu. Akad. Nauk SSSR, Ser. Khim. 1976,349-353. Tkatchenko, I. In Comprehensive Organometallic Chemiatry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, p 173. Tsuii, J. Organic Synthesis with Palladium Compounds:. Swingerverlag: Berlin, i9aO; p 81. Tsuji, Y.; Takeuchi, Y.; Watanabe, Y. Platinum Complex Catalyzed Synthesis of Urea Derivatives from Nitroarena and Amiiea under C-arbon Monoxide. J. Organomet. Chem. 1981, 290, 249-255.
Receiued for reuiew July 30, 1990 Accepted January 3,1991
Kinetic Study of NH3-CatalyzedImage Reversal in Positive Photoresist Gary L. Wolk* and David H. Ziger AT&T Bell Laboratories, P.O. Box 900,Princeton, New Jersey 08540 Ammonia-catalyzed image reversal of a positive photoresist was studied by investigating the kinetics of thermal reactions, in air and NH3 ambients, by using in situ UV/vis and FTIR spectroscopic techniques. Kinetic data indicate that the photoactive compound, a substituted 1,Bnapthoquinone diazide, decomposes three times faster in ammonia than in air and that an azo compound is formed during thermal treatment in NH3. Activation energies for thermal decomposition in air- and ammonia-catalyzed azo dye formation are calculated to be 32 f 1and 29.7 f 3.6 kcal/mol, respectively. FTIR data obtained before and after treatment with amine indicate that rapid decarboxylation is observed a t temperatures lower than typically used for ammonia-catalyzed image reversal. This discrepancy is attributed to either ammonia mass transport limitations or other, as yet undefined, secondary reactions that may be important to the reversal process. 1. Introduction
Advances in microelectronic circuit fabrication have been accelerated by the availability of photopolymer materials used for submicron pattern definition. Positiveworking photoresists, materials that faithfully reproduce an object pattern upon exposure and development, have been the mainstay of the semiconductor industry for some time (Bowden, 1984). This type of resist consists of a photolabile material, typically a substituted 1,2-napthoquinone diazide (I),
additional photoactive moieties tied to a benzophenone backbone. The lithographic utility of this combination of materials depends on the solubility, in basic aqueous developer, of irradiated material: the photoactive compound I (hereafter PAC) inhibits the base solubility of the acidic novolac resin I1 (hereafter NOV). Photolysis of the PAC leads to the formation of an indenecarboxylic acid 111, which is base soluble (Pacanksy and Lyerla, 1979) 0
0
I
R
R
and a phenolic (novolac) polymer backbone (11) (Willson, 1983): OH
OH
I
R
I11
I
r
c
1
I1
Commercial photoresists oftan employ poly(diazoquinone) compounds with the R group in I possessing two or more 0888-5885191/ 2630-1461$02.50/ 0
thereby allowing the exposed material to be removed with a basic developer. Numerous methods (Burggraff, 1987) have been proposed to extend the lithographic resolution of these materials, including amine-catalyzed image reversal (Moritz and Pall, 1978; Moritz, 1986; Takahashi et al., 1980). While image reversal adds processing steps to the simple positive process, it can extend the resolution of an exposure tool by 30% (Alling and Stauffer, 1986; Ziger and Reightler, 1988b). The image reversal process involves heating a photoresist film, in which a latent image has been created, in the presence of base. The base can be part of the photoresist formulation (the monazoline process) (MacDonald et al., 1982) or may be supplied as a gaseous amine such as anhydrous ammonia or ammonium hydroxide vapors (MacDonald et al., 1982; Long and Newman, 1984; Kloee et al.,
ca 1991 American Chemical Society
1462 Ind. Eng. Chem. Res., Vol. 30, No. 7, 1991
1986). With model compounds (MacDonald et al., 1982), it has been shown that the carboxy acid group in I11 decomposes in the presence of amine at temperatures between 70 and 80 OC, leading to formation of the base insoluble substituted indene, I V
I
IV
R I11
After amine treatment the initially exposed areas (latent image) have been converted to nonphotoactive, base-insoluble regions. Subsequent flood exposure (i.e. no masking of the resist takes place) converts the PAC in the initially unexposed (masked) areas to base-soluble indenecarboxylic acid 111. Upon development the resist now yields the negative, or reversed, image of the originally exposed material. Applications and mechanisms of ammonia-catalyzed image reversal have been investigated extensively because the technique is applicable to any napthoquinone diazide-based positive photoresist and avoids shelf-life concerns when amines are added directly to the photoresist formulation (Ziger, 1989; Ziger and Mack, 1988a). While the mechanism shown above is consistent with observations concerning ammonia-catalyzed image reversal, kinetic parameters required to optimize both resolution and processing time have not been previously reported. In particular, the reversal bake can decompose the PAC in the unexpmed areas,limiting process resolution (Ziger and Reightler, 1988b). The purpose of this study was to investigate ammonia-catalyzedimage reversal kinetics in a commercial napthoquinone diazide-novolac photoresist mixture to determine the thermal degradation rates of the unexposed PAC in air and NH3, and the thermal degradation rate of indene carboxylic acid in NH3, i.e. the reversal reaction. These data can then be used to reproducibly control the reversal bake (Ziger and Reightler, 1988b3, by integrating the kinetics over measured time-temperature profiles (Ziger and Mack, 1988a). 2. Experimental Section Waycoat HPR 206 positive photoresist (Olin Hunt, W. Paterson, NJ) was used for this investigation. Anhydrous ammonia (99.99%)and dry air were obtained from commercial sources. In situ ultraviolet/visible (UV/vis) spectroscopy was used to measure the degradation rate of the PAC in air and ammonia. The UV/vis apparatus consisted of a Harrick high-temperature transmission cell (HTC-100) that was modified to accept an unsheathed thermocouple placed in contact with the film under study. The transmission cell was placed onto a modified holder that fit directly into a Perkin-Elmer 330 UV/vis spectrometer. Sample temperature was controlled by heating the water-cooled cell with three 50-W cartridge heaters, which were powered by an Omega 4001 proportional controller. The cell temperature and gas pressure were continuously monitored via an HP9816 computer and an HP3497A data acquisition unit, The computer also controlled the vacuum/process gas sequence automatically. The cell was evacuable to
