High energy pulsed laser deposition of ohmic tungsten contacts on silicon at room temperature

Tungsten-on-n+ silicon ohmic contacts were obtained by depositing 100 nm-thick W coatings on silicon substrates using pulsed laser deposition at room temperature, without native oxide removal. The high energy of the impinging species (about 10–100 eV per atom) led to sputtering phenomena and to the implantation of W atoms through the Si oxide. W coatings were characterized, as-deposited and after performing rapid thermal annealing steps. The morphology and crystallinity were characterized by scanning electron microscopy, X-ray diffraction and reflectometry. The interdiffusion of W and Si was shown by scanning Auger microscopy. The ohmic character of the contacts and contact resistance were investigated by the transfer length method. Fast annealing at moderate temperatures (450 °C) remarkably improved contact performance without significant variation of the features of either W film or Si substrates. The ohmic character of the contact was preserved even after annealing at high temperature (1000 °C) at which a complete interdiffusion of Si into the W film takes place.