Study of Near Surface Structure and Composition for High Dose Implantation of Cr + into Si
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STUDYt OF NEAR SURFACE STRUCTURE AND COMPOSITION FOR HIGH DOSE IMPLANTATION OF Cr+ INTO Si
F. NAMAVAR,* J. I. BUDNICK,* H. C. HAYDEN,* F. A. OTTER,** AND V. PATARINI** *The University of Connecticut, Storrs, CT 06268; **United Technologies Research Center, East Hartford, CT 06108
ABSTRACT The dependence of the implanted layer composition on total dose, dose rate and target chamber environment for Cr + implanted Si have been studied by means of Rutherford Back Scattering (RBS) and Auger Electron Spectroscopy (AES). ions/cm and a Implantation of Cr+ for doses up to 2 x 10 fixed dose rate and energy were carried out in an ultra high vacuum (UHV) system as well as in a diffusion pumped vacuum (DPV) system. For the former, the maximum Cr concentration was about 42%. On the other hand, implantation of Cr in a DPV system resulted in a much higher peak concentration (86%) and retention. Both the RBS and AES results positively demonstrate the existence of extensive surface carbon for a Si-rich surface and a chromium oxide layer for the Cr-rich surface. This result suggests that the interaction of oxygen or carbon occurs preferentially and depends on the surface composition. No surface compositional variation could be observed by the RBS experiments for Cr implanted in a UHV system for different dose rates. In contrast, for implantation in a DPV system, higher concentrations can be achieved for lower dose rates.
INTRODUCTION In this work we are interested in: (i) investigating silicide formation by means of the high dose implantation technique for the Cr-Si system, (ii) obtaining information concerning the saturation concentration of implanted Cr into Si in an ultra high vacuum as well as in a DPV system, and (iii) determining the nature of the final products for different vacuum conditions as well as understanding the effect of oxygen and carbon impurities on compound formation or precipitation. The maximum achievable concentration in ion implanted systems is governed by the sputtering of the near surface region of the target syste• [1]. Implantation in a vacuum system with a pressure of the order of 10 Torr may, in some cases, result in the production of an oxide or carbide layer where generally such a layer can reduce the sputtering rate. Armenian et al. [2] reported the production of a very high concentration of Cu for Cu implantation in Al as a result of the creation of an oxide layer on their target. Introduction of elements of residual adsorbed gases by recoil implantation [3] or any other means [4] has two facets: (1) a detrimental effect, i.e., the target becomes contaminated with unwanted impurities; and
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(2) a beneficial effect, i.,e., the production of a protective layer from sputtering. Indeed, because of this protective layer, we have been able to achieve a very high concentration (86%) of Cr for the Cr-Si system.
EXPERIMENTAL PROCEDURES Polished single crystals of Si with (111) and (100) orientations were implanted with
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