X-Ray Techniques for Silicides
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X-Ray Techniques for Silicides
Douglas J. Tweet, Jer-shen Maa and Sheng Teng Hsu Sharp Laboratories of America 5700 NW Pacific Rim Blvd Camas, WA 98607, U.S.A.
ABSTRACT Previously we have found that the addition of a thin layer of Co between Ni and the Si substrate dramatically improves the thermal stability of the resulting silicide. Here we describe the use of four different x-ray techniques to obtain complementary information on film structure, providing a possible explanation for the observed thermal stability.
INTRODUCTION Nickel silicide is a candidate material for use in future CMOS device generations [1,2]. Besides the advantages of low resistivity and reduced Si consumption of the monosilicide NiSi, very low junction leakage has been demonstrated in conjunction with plasma doped ultrashallow junctions [3]. The major drawback to using nickel silicide is its poor thermal stability at temperatures above 650°C, where it undergoes a transition to a disilicide phase [4]. This limitation restricts its use in typical CMOS applications. NiSi2 is known to have an epitaxial relationship with (001), (011), and (111) silicon substrates [5]. However, NiSi2 grown on (100) Si exhibits facets along Si(111). This will cause an increase of junction leakage and present serious challenges to device application. Successful formation of epitaxial NiSi2 on (100) Si by using co-deposition or by molecular beam epitaxy (MBE) techniques have been reported previously [6]. Cobalt silicides have attracted a good deal of attention, as well. Single crystal CoSi2 growth on Si(100) has been achieved by special MBE techniques. In this method, nucleation of CoSi2 at the Co/Si interface must be carefully controlled through the use of template layers [7,8]. It would be a great advantage to produce epitaxial Ni(Co)Si2 by a more conventional salicide process for CMOS device fabrication. Recently we have shown that the thermal stability of Ni silicide on Si(100) can be significantly improved by the addition of a thin layer of Ir or Co between the Ni and the Si substrate [3,9]. In particular, it was found that the sheet resistance of blanket films was stable up to at least 850°C. Furthermore, the junction leakage of ultra-shallow junctions with 40 nm junction depths was also considerably reduced. A Co interlayer also improves the thermal stability of Ni silicides grown on SiGe films [10]. Here we describe the x-ray analysis of Ni and Ni/Co films using four different methods. Sheet resistance and other results have been reported elsewhere [3,9,11].
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EXPERIMENT To prepare the films, patternless p-type (100) Si wafers underwent a pre-metal dip in dilute buffered HF, DI water rinse and spin dry before loading into an e-beam evaporation chamber. Nickel and the interlayer cobalt were deposited by sequential e-beam evaporation. The Co thickness was in the range of 14Å to 16Å as measured by a quartz crystal monitor. For the Ni only films the Ni thickness was ~85Å. For the Ni/Co films, the Ni thickness was ~69Å. The rapid thermal anneals were per
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