Surface Modification by Ion Beam Enhanced Deposition
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SURFACE MODIFICATION BY ION BEAM ENHANCED DEPOSITION
R. A. KANT AND B. D. SARTWELL U.S. Naval Research Laboratory,
Washington,
D.C.,
20375
ABSTRACT Copper films given multiple sequences of Ta implantation and Cu depositions were analyzed using electron microscopy, backscattering, and Auger spectroscopy. Ta retention is 92% following direct implantation, and 100% retention was achieved for the same Ta dose if sputtered Cu is replaced during implantation. Lateral migration of Ta and microroughness were observed for all cases studied. Evidence for TaC formation is presented.
INTRODUCTION The use of concurrent ion irradiation and vapor deposition to achieve enhanced thin film properties and to improve coating adherence has, for the most part, been studied using ion beams with energies less than 5 keV 11-3]. The reasons for using low-energy ions as opposed to beams of moderate-energy ions that are obtained from ion implantation systems include (1) energy deposition will be very near the surface, (2) low energy ion sources are readily available and reasonably inexpensive and (3) sputtering is reduced at low energies. If, however, the negative aspects of increased sputtering could be overcome, then there would be several advantages to using higher energy ion beams available from an implanter. Principle among these are that the ion beam can consist of any element and is not limited to gaseous species as is frequently the case for low energy ion guns. Because of the increased energy available, the dose required to produce the same energy deposition is reduced. In addition, the combined ion implantation and deposition technique offers a new approach for the study of sputtering phenomena. Ordinarily the measurement of a sputtering rate is complicated by an increase in concentration of the implanted element at the surface. If, however, the target material is continuously being replenished by vapor deposition during the sputtering process, the surface fraction of the implanted element can be kept arbitrarily low. Another interesting potential application of the combined technique is to use vapor deposition to precisely offset sputtering. If this can be done, then the maximum concentration of an implanted specie should no longer be fixed by the "sputtering limit" and the fraction of the implanted dose that is retained could be increased significantly. In the process, a completely new range of material compositions would become accessable via ion implantation. To establish the feasibility of combining vapor deposition techniques and moderate energy ion implantation, a long range systematic study has been initiated. The preliminary results of that study are reported here. An initial goal is to determine the extent to which conventional models for implanted systems are applicable to ion beam enhanced deposition (IBED) systems. For this initial phase of the study, copper was implanted with tantalum while copper was being deposited to replace the sputtered atoms. This system was selected because the sputtering rate for Ta on Cu
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