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.