Stability Improvement of Nickel Silicide with Co Interlayer on Si, Polysilicon and SiGe
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Stability Improvement of Nickel Silicide with Co Interlayer on Si, Polysilicon and SiGe Jer-shen Maa, Douglas J. Tweet, Yoshi Ono, Lisa Stecker, and Sheng Teng Hsu, Sharp Laboratories of America, 5700 NW Pacific Rim Blvd. Camas, WA 98607 ABSTRACT Thermal stability of nickel silicide is improved by adding a thin Co interlayer at Ni/Si interface. After high temperature anneal, the low sheet resistance of silicide and the low junction leakage of the ultra-shallow junction show the lack of film degradation. The transformation to disilicide phase occurred at a lower temperature. At 850°C, interface shows the truncated facet structure extended 100Å to 200Å below silicide/Si interface. With Co addition, nickel silicide formed on polysilicon and on SiGe films also show improved thermal stability and low sheet resistance. Formation temperature of disilicide phase occurred at lower temperature in all these cases. INTRODUCTION Nickel silicide is a candidate material for use in future CMOS device generations. [1-4] Besides the advantages of low resistivity and reduced Si consumption of the monosilicide, very low junction leakage has been demonstrated in ultra-shallow junctions. The major drawback of nickel silicide is its poor thermal stability. [5,6] Enhancement of the thermal stability of nickel silicide has been reported previously by the addition of Pt. [7,8] Electrically active defects were detected on the ntype silicon. Improved thermal stability on (100) Si is achieved by adding a thin interlayer before Ni deposition. [9] Nickel silicide films formed with Ir interlayer can withstand a RTA temperature of 850°C and still maintain a low junction leakage in ultra-shallow junctions. Films with Co interlayer show significant improvement in sheet resistance stability, but there is a gradual increase of leakage at RTA temperature higher than 800°C. The purpose of this work is to further understand this temperature effect and to determine thermal stability of silicide formed on polysilicon and SiGe films. EXPERIMENTS Wafers used for this study were p-type (100) Si wafers. Blank 2000Å amorphous Si films were deposited by LPCVD at 560°C on (100) Si covered with 1000Å thermal oxide. Blanket SiGe layers were grown on p-type (100) Si wafers at 640°C in a commercial RTCVD reactor using H2, SiH2Cl2, and GeH4. The films contained 21% Ge and were about 220Å thick. These wafers were subject to a pre-metal dip in dilute buffered HF, DI water rinse and spin dry before loading into an e-beam evaporation chamber. Ni and Co were deposited by sequential e-beam evaporation. The thickness of Co was in the range of 14Å to 20Å. The Ni thickness was in the range of 60Å to 130Å. The film structure includes: (1) pure Ni film deposited directly on (100) Si, a-Si film, or SiGe film without Co interlayer, (2) Ni/Co on (100) Si, a-Si, or SiGe, here Co was at the interface, and (3) Ni/Co/Ni on (100) Si, a-Si or SiGe. Here the Co layer was not at the interface, but sandwiched between Ni films. The rapid thermal anneals were performed in Ar ambient at a tempe
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