Stresses in thin films can affect phase transformation temperatures. We show, however, that stress relief and grain growth in Co thin films occur at temperatures below the hcp to fcc phase transformation. Temperature ramped (10 °C/min) in situ stress, differential scanning calorimetry, and resistivity were measured on evaporated 56–275 nm Co films, and microstructure was examined with transmission electron microscopy. As-deposited films are under tensile stress, ≊1×109 Pa, which is relieved between 120 and 275 °C. The as-deposited small grains (15–20 nm) undergo secondary grain growth at 230–350 °C, giving a mixed phase bimodal grain size distribution with the smallest grains (both hcp and fcc) 20–25 nm in diameter and the largest grains (〈0001〉 hcp) 150–200 nm in diameter. The hcp grain growth is signalled by an exothermic calorimetric peak at 282 °C with an enthalpy of 0.15±0.04 kJ/mol and a resistivity decrease. The hcp to fcc phase transformation is signaled by an endothermic calorimetric peak with an enthalpy of 0.27 ±0.07 kJ/mol at 380 °C although transmission electron microscopy reveals that the transformation is incomplete. There is no indication of a reverse transformation on cooling. Additional heat treatment to 736 °C, on the thinner 56 nm Co film on SiO2 substrates, results in agglomeration and an accompanying decomposition of SiO2 catalyzed by Co. The results indicate that as-deposited tensile stress does not control the phase transformation temperature in Co thin films.

In situ resistance measurements, x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, isothermal and constant heating rate differential scanning calorimetry and Auger electron spectrometry depth profiles have been used to investigate the interactions in copper and magnesium thin films leading to the growth of Cu2Mg and CuMg2 intermetallics. The effect of exposing the reacting interfaces to controlled exposure of oxygen on the nucleation and growth kinetics of such intermetallics was also investigated. It is found that the first phase to form is CuMg2, at about 200–215 °C. It is determined that the formation of CuMg2 occurs by a two step process consisting of nucleation and growth. The nucleation of CuMg2 takes place in a region composed of a Cu/Mg solid solution. The nuclei form at certain preferred sites and grow in directions both parallel and perpendicular to the surface, eventually leading to a continuous CuMg2 layer. The growth of CuMg2 nuclei in the plane of the original interface occurs at a constant rate, whereas the growth in a direction perpendicular to the original interface is found to be diffusion limited. In the presence of excess copper Cu2Mg forms at higher temperatures, with complete conversion to Cu2Mg occurring at about 380 °C. When the Cu surface is dosed with oxygen prior to Mg deposition, ramp rate differential scanning calorimetry (DSC) shows that the nucleation and growth of CuMg2 as well as the growth of Cu2Mg are not disturbed. Dosing the Mg surface with oxygen results in significant changes in the growth of the two phases. In this case a thin MgO layer is formed at the oxygen dosed surface, lateral growth of CuMg2 is unaffected, but vertical growth of CuMg2 across the oxygen dosed interfaces is delayed by 25–30 °C. The growth of Cu2Mg is also shown to be delayed, by 22–54 °C due to the interfacial oxygen dose.

The interdiffusion of Cu and Sn, and the formation and dissolution of Cu-Sn precipitates have been examined for Cu alloy films. Cu͑Sn͒ films were deposited by electron beam evaporation either as Sn/Cu bilayers or Cu/Sn/Cu trilayers, with overall Sn concentrations from 0.1 to 5 at. %. In situ resistance, calorimetry, electron, and x-ray diffraction measurements indicate that -Cu 6 Sn 5 forms during film deposition. Upon heating, ⑀-Cu 3 Sn forms at 170°C, then this phase dissolves into the Cu matrix at approximately 350°C. Finally, -Cu 10 Sn 3 forms and precipitates after thermal cycling to 500°C. The final resistivity of Cu/Sn/Cu films with more than 2 at. % Sn exceeds 3.5 ⍀ cm. However, resistivities from 1.9 to 2.5 ⍀ cm after annealing were reached in Cu/Sn/Cu films with less than 2 at. % Sn. Auger and Rutherford backscattering analysis of Cu/Sn bilayers ͑1 mm thick͒ showed that the homogenization of Sn in Cu requires annealing in excess of 350°C for 30 min; after annealing, the Sn concentration at the surface is approximately 20 at. %. The interdiffusion of Sn and Cu is inhibited by contamination at the Sn/Cu interface caused by air exposure.

The reliability of copper multilevel interconnections requires good adhesion and the prevention of copper diffusion into the interlevel dielectric. Magnesium is a candidate for an adhesion layer and diffusion barrier for copper due to the high heats of formation of magnesium oxides, fluorides and sulfides and the formation of low resistivity compounds of Mg with copper. An investigation of the interactions in thin films of copper and magnesium has been carried out in the temperature range of 25°C to 500'C. The results of these reactions leading to phase formation in Cu/Mg bilayers deposited on Si 3 N 4 or SiO 2 using X-ray diffraction, in situ sheet resistance, and Rutherford backscattering measurements are presented in this paper. It was found that the Mg-rich phase CuMg 2 is the first phase to form on annealing to approximately 215'C, followed by the formation of the Cu-rich phase Cu 2 Mg at about 380°C in the presence of excess Cu.

Copper with its high conductivity, specific heat and melting point (compared to Al), is being investigated as the interconnection metal for applications both on and off the chip. Such interconnection wirings will be seperated by the dielectric layers which could be either polymers or inorganic oxides like SiO2. In such applications an adhesion promoter, which may also work as a diffusion barrier, maybe used between the dielectric and the metal film. An investigation of the diffusion and interaction of Copper with such dielectrics and insulators has been carried out in the temperature range of 200 – 500 ºC. Specifically, interactions of Copper with SiO2'P—glass, Polyimidesiloxane and Magnesium are investigated. Results of these studies will be presented and discussed.