The effect of silicon ion implantation on the structure of tantalum-silicon contacts.

The effect of ion beam mixing on the formation of tantalum-silicon contacts was studied. Silicon implantation into 50 nm Ta layers on n+-Si (100) was carried out at temperatures from 150 to 500°C and fluences between 1x1015 and 1x1017 Si/cm². To characterize the microstructural changes Auger electron spectroscopy (AES), X-ray diffraction and cross-sectional transmission electron microscopy (TEM) were used. The contact resistance was measured before and after implantation using the four-point Kelvin method. Implantation at low temperature (~150°C) leads to the formation of an amorphous Ta-Si interface-layer. The width of the mixed layer increases linearly with implanted dose and temperature. Substrate amorphisation up to a depth of about 200 nm results in an increase of the contact resistance. An improved contact resistance was achieved by implantation with 5x1016 Si/cm² at 400°C. TaSi2 formation at the interface was observed in this case.