AVS 50th International Symposium
    Workshop on Sputtering Sunday Sessions
       Session WS-SuM

Invited Paper WS-SuM1
Basic Understanding of Reactive Sputtering Processes

Sunday, November 2, 2003, 10:00 am, Room Constellation C, Hyatt Regency

Session: Workshop on Sputtering (Morning Session)
Presenter: S. Berg, Uppsala University, Sweden
Authors: S. Berg, Uppsala University, Sweden
T. Nyberg, Uppsala University, Sweden
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Reactive sputtering is a mixed physical and chemical vapour deposition process. It is frequently used in a wide variety of industrial applications. It is not, however, a simple matter to combine high rate reactive sputter deposition and process stability. The reactive gas may easily poison the target causing the deposition rate to decrease sometimes as much as a 5-20 times. In addition the process exhibits a hysteresis behaviour in the relations between the primary processing parameters. In a large volume production situation this may cause serious problems. There must be some sort of built in control system to force the process to avoid being trapped in the hysteresis loop and entering too far into the target poisoned mode. Process modeling of the reactive sputtering process may serve to illustrate the influence of different processing parameters on the overall behaviour of the process. A quite successful model for the basic behaviour of the reactive sputtering process have been suggested by Berg and co-workers. It is frequently referred to as Berg´s model. This model enables to predict the general shapes of most experimental reactive sputtering processing observations. It may predict the complex realations between the partial pressure and supply of the reactive gas as well as the fraction of target poisoning and the composition and deposition rate of the growing film. Knowing the actual relations between these parameters significantly assists in designing reliable control systems for reactive sputtering processes. A detailed analysis suggests that there exist several ways of eliminating the hysteresis in reactive sputtering processes. Increasing the pumping speed of the system will ultimately result in elimination of the hysteresis. Decreasing the effective sputter erosion zone at the target may also result in elimination of the hystereis. Hysteresis or no hysteresis depend on a critical balance between the gettering of the reactive gas by compound formation of the growing film and the amount of the supplied reactive gas eliminated from the processing chamber by the external pump. There exists several ways of "twisting and turning" this balance. This will be shown in this presentation. Sputtering from more than one target (co-sputtering of different elements) and/or the use of more than one reactive gas in a reactive sputtering process will significantly increase the complexity of the process. Reproducing deposition rate and film composition under such conditions may be hazardous. Input processing parameters interact with each other in such a way that not only their absolute values are important but also the sequence in wich that they are varied must be taken into account. This makes process control quite problematic. We will illustrate how such conditions occur and suggest how to be in full control of the process. @FootnoteText@ 1. Computer modeling as a tool to predict deposition rate and film composition in the reactive sputtering process.: S. Berg, T.Nyberg, H-O.Blom and C.Nender; J.Vac.Sci.Technol.A16(3)May/June 1998,p1277-85 2. Modeling of the reactive sputtering process: S. Berg, T.Nyberg, H-O.Blom and C.Nender Handbook of thin film process technology, Edited by D.A.Glocker and S.I.Shah, Inst.of Physics, 1998, pp A5.3:1-15 3. Review article to appear in the journal Thin Solid Films in spring 2004.