Etch rates of aluminum and “native aluminum oxide” films were studied as a function of substrate temperature in a parallel plate plasma etcher using CCl4 and BCl3 plasmas. Differences in the inhibition period for CCl4 vs. BCl3 etching were attributed to the relative abilities of these etchants to scavenge oxygen and water vapor and to etch native aluminum oxide. The temperature dependence of the etch rates suggested basic differences in the rate‐controlling steps for CCl4 vs. BCl3 plasma etching. The surface chemistry of the electrode materials played an important role in the etch rates observed with CCl4 and BCl3 .
The plasma‐assisted etching of aluminum in chlorine containing RF glow discharges has been studied. Use of a single parallel plate reactor permitted a direct comparison of etch results between BCl3 , BCl3/Cl2 , CCl4 , and SiCl4 . Separation of aluminum etching into native oxide reduction and water vapor/oxygen scavenging, and metal film etching allowed the likely rate‐limiting processes in the etch cycle to be ascertained for the different etch gases. The longer initiation period observed with CCl4 and SiCl4 compared to BCl3 appeared to be due to etch gas dissociation effects. Metal etching was believed to be limited by the removal of CClx and SiClx residues with CCl4 and SiCl4 and by etchant generation with BCl3 .
In order to quantify the contributions of atomic and molecular chlorine during the plasma etching of aluminum, a discharge-flow system was used to generate chlorine atoms upstream of a parallel-plate reactor in which aluminum samples were etched with the afterglow. Molecular dissociation in excess of 70% was achieved. Dissociation was measured in the parallel-plate reactor by gas-phase titration of the chlorine atoms with NOC1 using the chemiluminescent emission resulting from atom recombination as an end point indicator. Molecules etched aluminum at least four times faster than atoms and displayed an activation energy near zero (0.02–0.04 eV/molecule) between 35 and 150 °C. Below 25 °C etching was quenched due to the inability of products and/or contaminants to desorb. The higher molecular etch rate is believed to be the result of an enhanced sticking coefficient on the chlorinated surface. Calculation of molecular sticking coefficients based on the assumption of adsorption-limited etching are in good agreement with reported values. Temperature-dependent atom recombination on the in situ electrodes prevented accurate determination of the molecule/atom etch rate ratio and masked the activation energy for atom etching.
Nomenclature d = particle diameter, cm D, = liquid-liquid diffusion coefficient, cm2/s D, = diffusion coefficient (into pores), cmz/s F = bed porosity H = plate height, eq 1 and 2, cm K = distribution coefficient, taken as K = 1 / c + ( t u F / [ ( l -L = length of column, cm t = time (retention time), s u = carrier fluid velocity, mL/s W = width of chromatographic peak at half-heightGreek Letters e = pellet porosity, from the ratio of the density in mercury F)LH to that in helium Registry NO. A-15,9037-24-5; XE-397,100485-15-2; XN-1010, 54991-00-3; Dowex MSC-1-H, 70026-04-9; Biorad MP-50, 100040-56-0. Literature Cited Baltas, R. E.; Anderson, J. L. Chem. Eng. S d . 1983, 38, 1959. Bolt, B. A.; Innes, J. A. Fuel 1959, 38, 333. Bozlk, J. E.; Vogel, R. F.: Kissin, Y. V.; Beach, D. L. J . Appl. Polym. Sci. Conner, W. C.; Lane, A. M.; Ng, K. M.; Goldblatt, M. J . Catal. 1983, 83, 336. Eberly, P. E. Ind. Eng. Chem. Fundam. 1969, 8 , 25. Goring, R. L.; de Rosset, A. J. J . Catal. 1964, 3 , 341. Jewell, D. M.; Weber, J. H.; Bunger, J. W.; Plancher, H.; Latham, D. R. Anal. Kolk, J. F. M.; Matulewicz, E. R. A.; Moulljn. J. J . Chromafogr. 1978, 160, Prasher, B. D.; Ma. Y. H. AIChE J . 1977, 23, 303. Prudich, M. E.; Cronauer, D. C.; Vogei, R. F.; Solash, J. Ind. Eng. Chem. Ruberto, R. C.; Jewell. D. M. NSF Workshop Aug 21-23, 1974. Shimura, M.; Shiroto, Y.; Takeuchl, C.The jet, diesel, and gas oil distillate fractions from raw and hydrotreated shale oils are characterized by column chromatography, FTIR, carbon-13 and proton NMR, and GC/MS techniques. Nitrogen concentrates from the ion-exchange treatment of these shale oils are characterized in the same manner. The nitrogen-containing components in the raw jet fuel primarily consist of alkylpyridines with minor levels of alkyl-substituted indoles, quinolines, and hydroquinolines. While catalytic hydrodenitrogenation serves to reduce the nitrogen content of the distillates, the type of nitrogencontaining compounds that remain is the same as that of the feed with the exception that quinolines are converted to hydroquinoiines. The spectral characteristics of the nitrogen concentrates isolated from the higher boiling distillates are essentially the same as those derived from the jet with the differences being related to the molecular weight, namely degree of substitution, chain length, and aromaticity.
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