Modern ohmic contacts to silicon such as titanium-tungsten disilicide are usually silicides made by CVD. Contacts are often made by depositing the transition metal and forming the silicide by annealing with the result that the silicide may be non-stoichiometric. Silicide contacts can also be deposited by direct sputtering of the compound or by ion implantation of the transition metal followed by annealing. Aluminum is another important contact metal for silicon which can be used with either the n-type or p-type semiconductor. As with other reactive metals, Al contributes to contact formation by consuming the oxygen in the native oxide. Silicides have largely replaced Al in part because the more refractory materials are less prone to diffuse into unintended areas especially during subsequent high-temperature processing.