The Role of Implant Temperature in the Formation of Thin Buried Oxide Layers
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THE ROLE OF IMPLANT TEMPERATURE IN THE FORMATION OF THIN BURIED OXIDE LAYERS
Alice E. White, K. T. Short, L. N. Pfeiffer, K. W. West, and J. L. Batstone AT&T Bell Laboratories, Murray Hill, NJ 07974
ABSTRACT From the early work on high dose oxygen implantation for buried Si0 2 formation, it is apparent that the temperature of the Si substrate during the implant has a strong influence on the quality of both the Si0 2 layer and the overlying Si. This, in turn, can be related to the damage from the oxygen implant. For substrate temperatures < -- 300 C, amorphous Si is created during the implant and leads to the formation of twins or polycrystalline Si during the subsequent high temperature (>1300*C) anneal. At higher substrate temperatures (>--400°C), dynamic annealing eliminates the amorphous Si, but the implanted oxygen appears to segregate during the implant leading to oxygen-rich amorphous regions imbedded in regions of crystalline material. As the amorphous regions start to coalesce and form Si0 2 during the high temperature anneal, they trap crystalline Si which cannot escape by diffusion. This process can be circumvented by using a randomizing Si implant to change the damage structure from the oxygen implant before annealing. We have seen these effects clearly in sub-stoichiometric implants, and believe they are also operative during stoichiometric implants.
INTRODUCTION High dose oxygen implantation and high temperature (T) annealing to form buried Si0 2 layers has shown promise as a viable Silicon-on-Insulator (SOI) technology. In particular, it has the advantage that it is completely compatible with conventional processing techniques and does not involve a melt. Most of the work to date in high dose implantation to form buried layers has involved oxygen doses large enough to form a stoichiometric layer during the implantation [11. However, the details of how these layers form are not entirely understood. Since the minimum dose required to reach stoichiometry (67 at.% oxygen) is -- 1.4X1018 0/cm 2 at 200keV, the layer that forms is -3000A thick. There is, however, considerable practical as well as fundamental interest in thinner layers which require sub-stoichiometric doses. Not only is it easier to observe the process of formation of these layers, but the single crystal Si overlayer has reduced defect densities because of the lower dose. Our previous observations of the differences in buried oxide layers due to different substrate temperatures [2] led us to perform a more carefully controlled experiment, the results of which we report here. In order to investigate in detail the role of substrate temperature during the implant, it is necessary to address the Mat. Res. Soc. Symp. Proc. Vol. 74. 1987 Materials Research Society
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problem of beam heating, which can raise the substrate temperature several hundred degrees above that of the holder [3]. We are using a new arrangement which allows us to independently vary the beam current and substrate temperature of a 4 inch Si wafer target during the implant
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