Effects of Sputtering Variables on Film Structure

Because of the complex interaction of many of the variables, and the influence of the shape and size of the vacuum chamber and the sputtering module, no attempt will be made here to analyse or define all the effects of the variables. In practice it seems that different operators have established their own optimum operating conditions, and that these differ considerably between different operators, even after thirty years of experience. 

The influence of the substrate will be discussed later, but in general substrates for sputtered molybdenum disulphide films are very smooth, with surface textures of the order of 0.1 //m. The gross keying effect which has been found important for adhesion of bonded or burnished films is therefore not normally available. It has been 

Lavik and Campbell studied coatings sputtered at temperatures between 150°C and 427°C, and found a high degree of crystallinity. They estimated that about 30 per cent of the crystais were oriented with their basal planes parallel to the substrate surface, and 70 per cent perpendicular to the surface. Most workers now appear to assume that above 70°C an even higher proportion of the crystals have the perpendicular orientation and this is discussed later. 

By varying the sputtering parameters, coatings have been produced varying in composition from MoS,, to MoSj s factors have been shown to exert a strong influence on the stoichiometry of the films. The presence of small amounts of moisture has a major effect on stoichiometry as well as on crystallinity. The effect may be due to the incorporation of oxygen from the water into the films, and it has 

One final factor which can influence stoichiometry has been described by Stupp . He reported that fresh molybdenum disulphide compacts initially emit sulphur faster than molybdenum. As a result the target surface becomes molybdenum-rich. As sputtering continues, sulphur diffuses to the surface at a rate which balances the removal of sputtered atoms, so that an equilibrium is established and the composition of the sputtered material remains constant. The problem of the initial variation in composition is overcome by a preliminary sputtering of the target before the specimen substrate is exposed to the sputtered particles. 

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