Thermodynamic stability of SiO2 in contact with thin metal films

Solid-state compound phase formation has been investigated between thin metal films (Cu, Ir, Mo, Pt, Re, Y, Yb, and Zr) and SiO2 substrates using Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) techniques. The thin-film couples were annealed for time periods ranging from 30 min to 3 h between 320 and 900 °C. It was found that Y, Yb, and Zr react with SiO2 whereas Cu, Ir, Pt, Re, and Mo do not. Heats of reaction were calculated for all possible combinations of silicide and metal-oxide reaction products. Comparisons with experimental results obtained from this study and the literature show in all cases that metal-SiO2 reactions only take place when the calculated heat of reaction is negative. This study shows that the results obtained as well as those which could be found from the literature correlate well with the electronegativity of the metal, which offers a convenient empirical method of predicting whether a metal will react with SiO2 or not. Only metals with a Miedema electronegativity parameter less than 4.45 V reacted with SiO2.