Macro-effects of resputtering due to negative ion bombardment of growing thin films
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Bombardment of a growing thin film by negative ions can lead to changes in the film through the process of resputtering. Macro-effects of resputtering (effects on the film thickness) include a slowing of the film growth rate and, in some cases, a complete suppression of the film growth as well as an etching of the substrate materials. To study this result of resputtering, rf-diode sputtering was used to deposit BaTiO3 films under a variety of conditions, varying deposition time, rf-power level, substrate-to-target distance, total gas pressure, and argon, oxygen, and hydrogen partial pressures. The effect resputtering had on the thickness was seen to be a result of the competition between deposition and etching of the thin film material. The relative influence of the various sputtering parameters and the effect each of these has on the thickness distribution were examined. It was found that the greatest influence was system geometry, followed by rf-power level. Various methods of controlling resputtering are discussed.
I. INTRODUCTION A growing thin film being deposited through sputtering may be subject to bombardment by negative ions formed at the target and accelerated away from it and toward the growing film. If this bombardment is of sufficient flux and energy, previously deposited atoms may be ejected from the growing film. This is one of the processes known as resputtering. One of the most studied results of resputtering is the effect that it has on the film composition. Resputtering will affect the different constituents of a compound film in different amounts, leading to nonstoichiometric films.1"3 Two other effects resputtering has on a film are what we have termed the macro-effects, which are the effects on the overall thickness of the film, and the microeffects, which are the effects resputtering has on the surface morphology of the thin film. In a related paper4 we look in detail at the micromorphology development due to the resputtering process and suggest a general mechanism of sputter erosion. This paper will examine the macro-effects of resputtering. It will be seen that if the resputtering rate is high enough in relation to the deposition rate of material, the growth rate of the film may be noticeably decreased. In some cases it may even prevent film growth and lead to etching of the substrate material. It will also be seen that what is critical is not the amount of actual resputtering,
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'Present address: Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695.
1928
http://journals.cambridge.org
J. Mater. Res., Vol. 8, No. 8, Aug 1993
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but the balance between the amount of material deposited and the amount resputtered. One of the earliest reports of resputtering effects was by Jones, Standley, and Maissel in 1967, on sputtered SiO2 and Si films.5 They found resputtering due to positive ions from the glow discharge bombarding a negatively charged film. In this case the film was an insulator, SiO2, which became neg
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