SELECTIVE ELECTROLESS PLATED NI CONTACTS TO CMOS JUNCTIONS WITH COSI2

We use selective electroless plated nickel alloys for filling high-aspect-ratio (height/width > 1) windows before sputtering aluminum for the first-level metallization. After briefly discussing the electroless plating process, we describe the physical analysis (cross-section transmission electron microscopy and Auger electron spectroscopy) of the Al(1%Cu)/electroless NiP/CoSi2/Si materials interaction as a function of anneal temperature. We then describe the electrical properties of contact resistance and diode leakage. Here, we study several complimentary metal-oxide-silicon (CMOS) processes with junctions 500-2500 angstrom deep, below 700 angstrom CoSi2. The Al/Ni plug metallization does not degrade CMOS devices with nominally 2500-angstrom-deep junctions, when the subsequent processing temperatures is < 400-degrees-C. Both Al/Ni and Ni/Si (through CoSi2) interact at above 400-degrees-C. At 450-degrees-C, the Ni/Si interacts to form enough Ni2Si below CoSi2 to degrade < 2000-angstrom-deep junctions. The Al/Ni interacts to form Al3Ni with discontinuities at window steps. Physical analysis does not indicate interaction between Al, Ni, and Si at 330-degrees-C. However, the reverse-bias diode leakage of the ultrashallow junctions 500 angstrom below CoSi2 severely degrades after the Al/Ni metallization is annealed at 330-degrees-C.