Effects of Thin Interposing Layers on the Epitaxial Growth of FeSi 2 on Silicon
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2
ON SILICON
H.C. CHENG*, T.R. YEW+ AND L.J. CHEN Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China. ABSTRACT Thin interposing Ni or Co layers between Fe thin films and Si have been shown to be very effective in inducing the growth and improving the quality of epitaxial FeSi 2 on silicon. The formation of a transition layer with graded concentration is conceived to facilitate the epitaxial growth of FeSi2 on silicon. The thin interposing layer scheme may be extended to promote the epitaxial growth of a number of refractory silicides on silicon. I.
INTRODUCTION
Recent interests in epitaxial silicides have been stimulated by their potential applications in high speed and high frequency as well as optoelectronic devices. Epitaxial silicides are known to possess low resistivity, low stress, and high thermal stability. In addition, regular atomic arrangement of epitaxial silicide-silicon interfaces permits basic understanding of the electronic properties associated with the contact interface. [1,2] The growth of a number of refractory silicides, FeSi2 and MnSil.7 epitaxially on silicon have raised the exciting prospect that the growth of epitaxial silicides with desirable characteristics tailored to the needs of the devices may be incorporated into very large scale integrated circuits (VLSI) technology to fabricate novel classes of devices. [3] One of the difficulties encountered in the epitaxial growth of FeSi2, MnSil.7 or the refractory silicides by solid phase epitaxy is their relatively high growth temperatures (generally about lOOOOC) compared to those below 800 0 C for the epitaxial growth of PtSi, Pd2Si, NiSi2 or CoSi2. [4] To avoid degradation of the devices at high temperature, it is desirable to find a scheme to lower the temperature for epitaxial growth. Previous investigations found that for Fe/Si samples with (lll)Si substrate, about 40% of the surface area was covered by epitaxial regions of FeSi2 after 9750C annealing in N2 furnace. For samples with (001) substrate, only polycrystalline FeSi2 grains were found after 900-1100 0 C annealings. [5] In contrast, epitaxial growth of NiSi2 was found to be complete after annealings at 8000C. [6] CoSi2 was transformed to epitaxial 0 silicide after 300-650 C two-step annealing. [7] The quality of epitaxial silicides are considerably better in NiSi2/Si and CoSi 2 /Si than those in FeSi2/Si systems. Fe, Co and Ni have similar atomic radii, belong to the same group and same period and occupy the neighbouring positions in the periodic table. Solubility data also indicated that these ferromagnetic elements and Si are all highly soluble in one another. [8] Both NiSi2 and CoSi2 are of cubic CaF2 structure. Orthorhombic FeSi2 (ý-FeSi2) is of deformed CaF 2 structure. CaF2 structure is similar to diamond cubic Si structure. The lattice mismatches between ý-FeSi2 and Si are small. Crystal structure analysis revealed an even better lattice match between *
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