Defect structures in cosputtered thin films of transition-metal disilicides with C11 b , C40 and C54 structures
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Defect Structures in Cosputtered Thin Films of TransitionMetal Disilicides with C11b, C40 and C54 Structures HARUYUKI INUI, TAKASHI HASHIMOTO, AKIHIRO FUJII, HIROKI SAKAMOTO, NORIHIKO L. OKAMOTO, KATSUSHI TANAKA, and MASAHARU YAMAGUCHI Defect structures in crystallites of the stable phases in thin films of transition-metal (TM) disilicides (C11b MoSi2, C40 TaSi2, and C54 TiSi2) produced by cosputtering and subsequent annealing have been investigated by transmission electron microscopy (TEM). Crystallites in thin films of MoSi2, TaSi2, and TiSi2 all contain planar faults parallel to hexagonally arranged TMSi2 planes, which are a characteristic feature commonly observed in all three crystal structures. These planar faults are twin boundaries in all cases. Twins in thin films of these disilicides, thus, have a common characteristic that the twin habit plane is parallel to hexagonally arranged TMSi2 stoichiometric planes. For twins in thin films of C11b MoSi2, and C54 TiSi2, the twining elements can be deduced and the twin habit plane is found not to be parallel to the twinning (K1) plane, but to be perpendicular to it. Twins formed in C40 TaSi2 thin films are different from those formed in C11b MoSi2 and C54 TiSi2 thin films, in that the crystal orientation of the twin is exactly the same as that of the matrix, since they are racemic twins that are only enantiomorphically (space groups of P6222 or P6422) related to each other. I. INTRODUCTION
TRANSITION-METAL (TM) disilicides are extensively used in thin-film form for submicron complementary metal-oxide semiconductor (CMOS) gates in the semiconductor industry, because the resistance of CMOS gates is significantly reduced when compared to structures without these silicides.[1,2,3] Titanium, molybdenum, and tantalum disilicides have been the most widely used silicides for submicron gate-conductor applications, because of their low electrical resistivity and excellent thermal stability. Because of the technological importance, phase transformations of thin films of these TM disilicides have been the subject of extensive studies in the last two decades.[4,5,6] Many transmission electron microscopy (TEM) studies have indicated that the metastable phases with the C49 and C40 structures are formed first at low temperatures prior to the stable phases with the C54 and C11b structures, respectively, for TiSi2[7–12] and MoSi2[13–19] thin films. For TaSi2 thin films, on the other hand, some X-ray diffraction studies have reported that only the stable C40 phase is formed when cosputtered amorphous thin films are annealed.[20–23] Defect structures in crystallites of these metastable phases (C40 MoSi2 and C49 TiSi2) have been intensively investigated, since the high resistivity of these metastable phases should be avoided for the practical application of these TM disilicide thin films in Si large-scale integrated (LSI) devices. Many TEM studies have indicated that crystallites of these HARUYUKI INUI, Associate Professor, TAKASHI HASHIMOTO, AKIHIRO FUJII
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