VERY-HIGH-RATE REACTIVE SPUTTERING OF ALUMINA HARD COATINGS

A very-high-rate reactive magnetron sputtering deposition process for alumina hard coatings at substrate temperatures less than or equal to 250 degrees C has been developed. Utilizing pulsed DC power to sputter Al+AlOx, off the target surface and partial pressure control of the r eactive gas to maintain a certain partial pressure value (accuracy of better than 0.005 mtorr), fully dense. transparent alumina coatings co uld be produced at 76% of the metal deposition rate. The coatings have an elastic modulus of 140 GPa, a hardness of 12 GPa, a chemical compo sition close to stoichiometric, and a refractive index of 1.65. The in fluence of the O-2 partial pressure on the deposition rate, optical an d mechanical properties is discussed. (C) 1997 Elsevier Science S.A.