AssigneeInternational Business Machines Corporation
InventorsVlasta Brusic, Robert O. Lussow
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Abstract
Chromium is passivated by forming a chromium oxide layer thereon by heating at temperatures of about 450.degree.C in an atmosphere containing oxygen. While useful, per se, the process finds particular application as an integral part of overall processing schemes where thermal cycles are used.
Drawings
Claims11
A process for passivating chromium which comprises contacting chromium at a temperature of from about 425.degree.C to about 475.degree.C with O.sub.2 for a period of time greater than twenty minutes to grow a passivating chromium oxide film thereon.
17 Feb 1993Estimated · howhidePre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.
#In the drawings, FIG. 1 illustrates the variation of the chromium oxide thickness with time in dry air, on a logarithmic scale, on the upper Cr layers of Cr/Cu/Cr films;
#FIG. 2 shows the oxide thickness on the upper Cr layers of Cr/Cu/Cr films after the heating thereof for about 4 hours at 550.degree.C as a function of primary oxidation temperature, there being a pre-oxidation time of about 2 hours;
#FIG. 3 depicts oxide growth on Cr/Cu/Cr films at 550.degree.C, these films having been pre-oxidized at 400.degree. and 450.degree.C; and
Detailed description3,656 words
#In considering the chromium passivation process, according to the invention, it is to be noted that an important parameter therein is the range of temperature, viz., 425.degree. to 475.degree.C in which the oxidizing step is carried out, the best temperature being at about the mid-point of this range, i.e., 450.degree.C.
#To understand the importance of this range, there are considered the results which ensue when chromium is oxidized both at temperatures outside of and within this range.
#Thus, for example, when bulk, and thin film, polycrystalline chromium are oxidized at atmospheric pressure in atmospheres containing oxygen in a range of 400.degree.C to 750.degree.C, Cr.sub.2 O.sub.3 is the main product which is formed at all of these temperatures. With regard to the nature of the surfaces formed during these oxidations, the oxides produced at 400.degree.C and 450.degree.C show a texture which is not present in oxides formed at temperatures of 500.degree.C and greater. In this connection, chromium thin films exhibit more pronounced changes of surface morphology relative to length of oxidation period, temperature and ambient atmosphere than does bulk chromium. Thus, where thin films of chromium are employed, the oxidation reaction causes roughening of the original surface with a pronounced formation of hillocks of oxides interconnected by a thin layer of the oxidation reaction product. The number of hillocks which are formed can be related to the residual stress in the metallic films which in turn results from the temperature at which the films are evaporated. During the oxidation at elevated temperatures, the sizes of the hillocks increase proportionately with time, their number increases with temperature, and their shape is influenced by the ambient atmosphere.