Sputtering: The User's Viewpoint

The invitation to talk about sputtering in a conference devoted to heating may seem incongruous. Sputtering is primarily a mechanical effect, a dislodging of material from a solid target by bombardment with gas ions. To be sure, a lot of heat is developed in the process, but this heat is usually unwanted and must be removed or limited. Wehner [1] estimates that 95 percent of ion energy appears as heat in the target. From the user's point of view, the exact classification of the process does not matter. Sputtering is competitive with many industrial processes that are purely thermal such as coating or bonding by evaporation or by melting. It is this competitive situation that should be of interest to the potential user of the sputtering process. His questions are likely to be: Can sputtering do what conventional heating cannot do? Can sputtering achieve a lower product cost or improved product quality, as compared with a purely thermal process? Is sputtering sufficiently simple and controllable to be used as a production process? These questions cannot be answered in detail by a short paper. Rather, an attempt is made to supply a generalized answer, derived from a rough simplistic description of the physical principle of sputtering. The gist of this answer is that in many specialized applications where purely thermal processes become difficult to control, sputtering can indeed be superior. The accurate control claimed for depositing materials by sputtering comes about mainly because sputtering is an ``atom by atom'' transfer process.