Study On Texture And Internal Stress Of Electrodeposited Copper Film

The technology of electrodeposited copper film has been widely used in electronic industry because of its economy, selectivity and deepening plating ability. With the development of ULSI especially the copper interconnection technology, the electrodeposition process and microstructure of copper film receive more and more attention. The texture and internal stress of the copper film influenced greatly the physical and chemical properties and the reliability of electronic component. So, it is very necessary to characterization and study on preferred orientation and internal stress of copper film.The textures of electrodeposited copper film were investigated with X-ray diffraction technique, such as pole figure, inverse pole figure and ODF methods. According to observation of the preferred orientation of copper films, the film has strong (220) fiber texture at low current density (2A/dm~2). At high current density (16A/dm~2), the film has strong (111) fiber texture in sulfate solution. The extent of texture increased with the film thickness. The preferred orientation was changed when the cerium was added into the plating bath. The cationic of the rare earth will adsorb on the activity place of growth. It results in inhibition of grain growth. When the polyethylene glycol was added into the plating bath, the preferred orientation was changed also. It is because that the polyethylene glycol will form selective adsorption on different crystal plane. The ethylene diamine tetraacetate was added into bath and complexing reaction occurred with copper ions. It caused the change of the nucleation mechanism from three-dimensional to two-dimensional nucleation. In citrate solution, the citrate has strong complexation with copper ions.For reducing the effect of substrate materials on microstructure of copper films, the Ni-P amorphous deposits were used as the substrate for electrodeposited copper films. The initial nucleation of copper film electrodeposition process was studied in sulfate electrolyte. It was found that the mechanism of initial nucleation was three dimensions instantaneous nucleation. With the enhancing of overpotential, the mechanism of nucleation in the electrodeposited copper film preferred to three dimensions instantaneous nucleation. When added a little of cerium, the potential of dispersion layer in electrode interface enhanced because of the rare earth cationic adsorption. This enhancement resulted that the overpotential of cathode reaction in copper electrodeposited increased, and the energy of nucleation in film decreased. When a little of polyethylene glycol was added, the polyethylene glycol adsorbed the surface of metal electrode because of its surface-active action. This absorption produced the additional energy barrier which strongly barred the nucleation of copper electrodeposited. With the enhancement of potentials, the mechanism of nucleation in the electrodeposited copper film transferred from continuous nucleation to instantaneous nucleation.The X-ray diffraction is the uppermost method for measuring films stress. However, the effect of preferred orientation caused the non-linear of measure curve. It leads to unreasonable results of stress measurement. In this thesis, the different preferred orientation that affect elastic constant and X-ray elastic constant of copper films were investigated. The influence of preferred orientation on the elastic constants of copper film was calculated using Voigt and Reuss models. The results showed that the symmetry of the elastic matrix changed and a large difference of the elastic constants exited between the textured film and the isotropic. The distribution of the X-ray elastic constants of copper film vs.ψangle was also calculated. The results showed that the difference could be introduced when the measured direction of the residual stress was different, though the diffraction plane did not change. The calculated method for copper film stress was improved considering the influence of theψangle.The following regulation found in the research of internal stress of copper film. In copper sulfate solution, the electrodeposited copper film was tensile, and then the internal stress was higher with the increasing of the current. When the copper film was thin, the thickness was obviously decreasing with the increasing of the thickness. When the copper film was thick, the thickness was slowly increasing with the increasing of the thickness. The ultrasound and the low temperature treatment have been used for modifying the stress of the film in this paper. The effect of ultrasound can decrease the stress of the copper film. Similarly, the low temperature treatment can reduce the stress of the film, and the stress decreased with the drop of the treatment temperature.