Growth of Single Crystal type A and type B Co x Ni 1-x Si 2 Layers on Si(111)
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GROWTH OF SINGLE CRYSTAL TYPE A AND TYPE B CoxNilIxSi2 LAYERS ON Si(111) R. T. TUNG, F. HELLMAN, J. M. GIBSON & T. BOONE AT&T Bell Laboratories, Murray Hill, NJ 07974 ABSTRACT Single crystal type A and type B Co xNil 1xSi 2 layers have been grown on Si(111) by deposition of Co-Ni alloy in UHV and annealing. The dependence of CoxNil 1xSi2 layer orientation on the thickness of deposited metal is similar to that observed for pure nickel reaction. Silicon deposition along with the Co-Ni alloy allows the growth of type B oriented Co xNi ixSi 2* Auger, LEED, RBS and TEM analyses suggest that the composition of the ternary silicide layers is inhomogeneous. The advantages and disadvantages of this material in device application will be briefly discussed. INTRODUCTION Near perfect epitaxial structures of NiSi 2 and CoSi 2 have recently been demonstrated on Si substrates, using the template growth technique.[1l 12]Both NiSi 2 and CoSi 2 have cubic fluorite lattice structure and small lattice mismatches to Si. The orientation of the silicide, as well as the layer uniformity, was found to be sensitive to a slight variation in growth parameters. This phenomenon has led to the fabrication of single crystal NiSi 2 layers of either type A or type B orientation on Si(411).Il1 Type A NiSi 2 has the same orientation as the silicon substrate, while type B NiSi 2 shares the surface normal axis with the Si, but is rotated 1800 about this axis with respect to the Si. Because the NiSi 2 lattice usually contains a significant density of point defects, 13]the residual resistivity of CoSi 2 is much lower than that of NiSi . [4] The long 2 mean free path of CoSi 2 makes it an ideal material for the base of a metal base 5 transistor (MBT).Y] However,
difficulties with fabricating pinhole-free epttaxial CoSi 2 layers have thus far hindered such efforts. Because of a smaller lattice mismatch, NiSi 2 layers and multi-layered structures can be grown with much higher quality than the corresponding structures based on CoSi 2 . Attempts to use CoSi 2 to fabricate an MBT have thus far been unsuccessful because of material problems, and NiSi 2 is deemed unsuitable because of the short electron mean free path. The purpose of this paper is to point out that ternary epitaxial silicides (CoxNilxSi 2 ) may prove to be a better choice than either pure NiSi 2 or CoSi 2 . There have been
Mat. Rep. Soc. Symp. Proc. Vol. 91. c 1987 Materials Research Society
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some recent reports on the growth of non-epitaxial structures of these silicides.[6] The bulk material of the ternary silicide (Co Ni Si 2 , 0.5 < x < 1 ) has electrical resistivites nearly identical to that of CoSi 2 ,[3 a surprising result for an alloy which would be expected to have a resistivity considerably higher than the end members due to alloy scattering.[6] The smaller lattice mismatch of CoxNi 1xSi 2 to Si compared to CoSi 2 should make fabrication of high quality structures easier. The present work shows that single crystal type A and type B ternary silicide layers can be grown on Si(l11
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