Oxidation Resistance Of Copper Alloys At High Temperature

Copper has been both used in cooling systems of petrochemicals orchemical plant good due to its good conductivity and used as an alternatematerial for aluminum-based interconnects in ultra-large-scale-integration(ULSI) metallization, because of its high resistance to electromigration and lowelectrical resistivity. Cu₂O or/and CuO will be produced when Cu reacts withoxygen during working, however, Cu₂O or CuO is not protective as Al2O3, then,the Cu alloys will be oxidized continually and lead to increase it'selectric-resistance. Cu oxidized fast at higher temperature leading to poorconductivity and high electrical resistivity, even make parts of an apparatusunable to work in safety. On the other hand, the core of (ULSI) was developingat small, high speed and high electrical current. So high purity Copper andnano-crystalline Copper were more and more studied. It is that Copper willreact with oxygen inevitably when working. Alloying elements andre-annealing will be helpful to the xoidation resistance of copepr at hightemperature.Based on the above two points, the following research work wasconducted in this doctoral dissertation and the resultant conclusions arepresented as the following:1 The oxidation kinetics of 6N Cu, Cu-0.12 wt% Mg, Cu-0.34 wt% Mg andCu-1.0 wt% Mg alloys which were annealed at 600℃for 24 h in H2atmosphere oxidized under 1 atm O2 from 600℃-900℃was studied. Andthe transtion of surface morphology of three alloys during initial oxidation at 400℃and 800℃was analyzed respectively. The results of surfacemorphology and of the didtribution of alloying elements in/near the surface,combined with the oxidation kinetics results, show that the MgO sacleformed during annealing. When the content of Mg is too low, the MgOsacle was too thin and discontinual to cover the alloy surface leading toimproved OR a little. On the contrary, if the Mg content is so high that theoxide scale formed during annealing was so thick that will be exfoiledduring cooling , which lead to poor OR. The order of oxidation rate of fouralloys as 6N Cu Cu-0.12 wt% Mg Cu-1.0 wt% Mg and Cu-0.34 wt% Mg.2 The oxidation kinetics of Cu-0.2 /1.0 wt % Al under 1 atm O2 at 700℃for4h were tested by Thermogravimetric Analyzerand and compared theresults to that of 6N Cu(99.9999%). before this, all the samples wereannealed in H2 or Ar atmosphere with various annealing processing. TheElectron Probe Micro Analyzer (EPMA) and Secondary Ion MassSpectroscopy(SIMS) were used to analysis the distribution of alloyingelements on/near the surface of Cu-0.2 /1.0 wt % Al annealed. The resultsshow that Al2O3 scale formed on the surface of Cu-Al alloys duringannealing. Annealing in hydrogen with high temperature and slow coolingrate, the Al2O3 scale formed was densed and with good adherence to thesubstrate. The results of oxidation kinetics show that the oxidationresistance(OR) of all the Cu-Al alloys were improved remarkably comparedto that of 6N Cu. The good OR was achieved with annealing compared tothat without annealing and pre-annealing in hydrogen compared to that invacuum or Argon atmosphere. The ORs of Cu-0.2 /1.0 wt % Al annealed inhydrogen atmposphere at 900℃,for 12h and at 0.6℃/min coolingrate toroom temperture was good. And the oxidation kinetics of Cu-(0.2 -2.0 wt %)Al annealed in hydrogen oxidized under 1 atm O2 from 600℃to 800℃wasstudied, the results show that with increasing Al content, the oxidation ratewas slow and the OR was good. 3 The oxidation kinetics of Cu-S, Cu-Se, Cu-Te and 6N Cu under 1 atm O2 at300-900℃was studied. The surface morphology and the crossing -sectionmorphology were analyzed. The effects of S, Se and Te on the oxidationkinetics of Cu alloys were discussed. Among three alloys, the alloyingelement content was desigened as 0.1%. the oxidation rate of Cu-S, Cu-Seand Cu-Te was slower than that of 6N Cu at 300-600℃the ORs wasimproved and the Cu-Se alloy's was best. The main reasons were themechanism of the oxide scale growth mainly on the outer diffusion of Cuand inenr diffusion of O through grainboundary of alloy or oxide scale. At300-600℃, an obstructive layer was formed by the alloying elements S, Seor Te and some compounds such as Cu₂S, Cu₂Se and Cu₂Te in Cu₂O/Cuinterface. The layer hinders the diffusion of both Cu and O. The high Secontent and thick hinderence in Cu-Se alloy decreased the diffusion andimproved the dense oxide scale, which has the best OR. However, theoxidation rate ofCu-S, Cu-Se and Cu-Te alloys were higher than that of 6NCu at 700-900℃mainly on following three reasons: first, the obstructivelayer can not hinder the diffsuion for the mechanism of oxide growth islattice diffusion; second, at high temperature range, some compounds willreact with O , such as Cu₂Se, then Cu₂O and CuO formed during oxidation;third, the compound of Cu₂Te will melt at high temperature that formedholes in the alloy.4 The oxidation kinetics of coarse grain Cu(CC Cu) and nanocrystallineCu(NC Cu) produced by by electrical brush-plating technique under 1atmO2 at 300-600℃for 6h was investigated by TG.. SEM was used toanalysethe surface morphology and cross-section morphology afteroxidation. Thetransformation of surface morphology of CC Cu and NC Cuduring initial oxidation in 1atm O2 at 500℃was studied. The resultsclaimed the oxidation rate of NC Cu faster than that of CC Cu. The reasonis that the content of grainboundary in NC Cu is higherthan that of CC Cu. During oxidation at high temperature, the grainboundary diffusioncoefficient is large compared to that of CC Cu, leading to improve thediffusion of Cu and O, acceleratethe growth of oxide of Cu and decreas theOR. With increasing the temperature, the OR of NC Cu is poorer that thatof CC Cu remarkably.