Structure and properties of Al-1%Si thin films on Si as a function of gas impurities during DC magnetron-sputtered deposition

Thin films of Al-l%Si were sputter deposited on Si under a variety of pressures of atmospheric impurity gases. The effect of the impurity gases (oxygen, nitrogen, and water), and deposition temperature (15° and 300° C), on the microstructure and properties of the aluminum thin films were studied. The gas pressures introduced during deposition varied from 5 × 10s−6 Torr (6.7 × 10s−4 Pa) to 1 × 10s-10 Torr (1 × 10s−8 Pa). The thin films were investigated by transmission electron microscopy and were found to have a columnar microstructure with an even distribution of silicon precipitates. Both the grain size and silicon precipitate size increased at the higher deposition temperature. A smaller grain size was found in samples that were deposited under the higher impurity gas pressures tested. The specular reflectance of the films was found to be dependent upon the amount of impurity gases present during deposition, the greater the partial pressure the greater the surface roughness. This study also investigated the possibility of using a Resistivity Ratio (RR) measurement to evaluate the grain size of the Al thin films. It has been previously observed that a small Al grain size has poor electromigration resistance. This study found that the correlation between Al grain size and RR values was good indicating that RR tests may be used as a quick, non-destructive measure of film quality.