Platinum silicide ohmic contacts to shallow junctions in silicon

Ohmic contact to shallow pn+ and np+ junctions in silicon were studied. Thin layers (∼200 Å) of platinum were sputter deposited and reacted with the silicon substrate at 590 °C to result in the stable PtSi silicide. In a self-registered process, aqua regia was used to etch the unreacted platinum. An Al-0.9% Si alloy has been used for final metallization. A small contact area of 3×3 μm2 was chosen so as to be in accordance with the current level of integration. A four-terminal Kelvin-resistor structure has been utilized to accurately measure the contact resistance. The effect due to the dopant concentration was studied at the implant dose range of 1–8×1015 cm−2. Van der Pauw sheet resistance measurements, secondary ion mass spectroscopy, and Rutherford backscattering experiments were all performed in order to characterize the shallow junctions and the silicide-silicon interface. Predeposition and in-situ etching resulted in considerable improvement in the measured specific contact resistance. Values well within the range required for very large scale integration applications were obtained.