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Copper is known to diffuse in dielectrics subjected to high electrical bias at temperatures as low as 100 degree(s)C. Also, it does not adhere to the interlayer dielectrics like SiO2 and polymers. In addition, copper corrodes readily in the corrosive environments. These properties of copper have inhibited the early acceptance of copper as the interconnection metal in the high performance integrated electronic circuit/devices. We have investigated the use of possible diffusion barrier (DB) and adhesion promoter (AP) materials in the conventional layered structures which lead to an increase in the total interconnection resistance negating the advantages of copper. Also, since the subquarter micron circuits necessitates the need of < 10 nm thick DBAP material, such layered structures are generally not stable under the interconnection processing, chip packaging, and/or actual use conditions. In this paper, we present results of our study of the electrically stable and corrosion resistant doped copper as the interconnection material. Al, Mg, and Ta, all of which have considerably higher free energy of formation for their oxides compared to that for Cu or Si oxides, have been added as the dopant in concentration range of 0.5 - 10 atomic percent in copper. Resistivity, adhesion to dielectric surfaces, effect of annealing to temperatures as high as 800 degree(s)C on such properties, corrosion resistance in air, and I-V/C-V characteristics of the metal/SiO2/Si capacitors have been investigated. It is found that addition of such dopants provides the necessary passivation. Doped films are very smooth even after anneals to temperatures as high as 800 degree(s)C. They did not lose adherence to SiO2 substrates after such anneals as demonstrated by the adhesive tape-peel tests. Preliminary indications are that doping has reduced the overall stress in the film. There is a small increase in the resistivity of copper, caused by the addition of these dopants. For example, for Cu with Mg (less than 2 atomic percent) the resistivity remains at or below 2 (mu) (Omega) cm. These results are compared with layered Al/Cu, Mg/Cu, Ti/Cu and TiN/Cu and show that doped films of copper satisfy all the reliability requirements at a small sacrifice of the resistivity in a manner similar to Al containing small amounts of copper.
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