Oxidation and thermal stability of thin film copper layers

The authors present several aspects of the thermal stability of thin-film copper layers. The copper oxidation experiment and the copper reaction with silicon and barrier layers were conducted separately. Copper oxidation has been characterized and its seems to be a major source of reliability problems. A qualitative model can be assigned to the copper oxidation which assumes an initial Cu₂O growth at random sites. The coalescence of those sites to form an oxide layer occurs after certain time. The formed oxide may limit the oxidation to the underlying copper and the process becomes diffusion controlled. At high temperatures (>255°C) the oxide nucleation consumes most of the copper layer and no diffusion regime is observed. TiN, Cr, and Co were found to be non-reacting at typical processing temperatures. TiN seems to be superior since it does not react with copper and even at 550°C