Effect of the species of sputtering gas on the composition of multi-component glass film: A new approach to control the composition of multi-component glass film

Abstract

Glass thin films are expected to be used for various purposes such as micro-optics, coating and microbatteries and so on. Sputtering is a convenient method to prepare films, and the new type of multi-component glass films such as non-linear optical materials and solid electrolytes have been successfully prepared in the last decade [1–5]. In these studies, it is reported that the composition of the obtained film is not the same as that in the target when the multi-component one is used. In particular, the concentration of alkali in the sputtered film has a strong tendency to deviate from that in the target [5]. Alkali is one of the important elements in multi-component glass, and therefore, a method to control the alkali concentration is necessary. To control the composition of the glass film, the sputtering power is usually varied. However, it is found that the change of the sputtering power is not very effective in changing the alkali concentration in the film [5]. The variation of the species of the sputtering gas should, in principle, affect the concentration of the film dramatically, and it is expected to be a good method to control the composition of the film. Such an attempt has been done in the case of alloys, but never has been attempted in the case of multi-component glass [6]. For the purpose of investigating the possibility of controlling the composition of the film by this method, we have studied the effect of species of the sputtering gas on the composition of the multi-component films from multicomponent glass target. The glass films were deposited with the same condition except for the species of inert gas (He, Ne, Ar, Xe, Kr), and the variation of the compositions of the obtained film is examined. The glass chosen for this study is K2O-BaO-SiO2 glass system which is one of the basic components in optical lenses. The target used for the sputtering is 20K2O-10BaO70SiO2 glass disk the diameter of which is 40 mm. Sputtering was carried out by a conventional RF-apparatus. After evacuating a chamber below 10−6 Torr, the inert gas (He, Ne, Ar, Kr or Xe) was introduced up to the pressure of 1.0 × 10−2 Torr. Then, the sputtering was carried out for 2 h at the power of 30 W and 60 W. The substrate used was non-alkali glass (Corning #7059). The chemical compositions of the films were analyzed by XPS with a PHI ESCA 550E. The excitation source was Mg Kα . The relative atomic concentration of K, Ba and Si was estimated from K2s,