Carl A. Gogol

The effect of target power on the nitrogen partial pressure level and hardness of reactively sputtered titanium nitride coatings

Target power and deposition rate have a significant effect on the properties of titanium nitride (TiN) coatings prepared by high rate reactive sputtering. As the target power is increased from 2.3 to 10.0 kW and the deposition rate from 1000 to 4800 A min-1, the Vickers microhardness (50 gf) increases from 970 to 3160 kgf mm-2 and the crystallographic orientation goes from a very strong (111) texture to a more random orientation for the TiN coatings. The partial pressures of the argon and nitrogen gases measured through the target show an apparent drop as power is applied to the titanium target. This apparent drop in pressure is actually a density reduction of the gases in front of the target due to gas rarefaction and heating. In order to maintain stoichiometry in the coatings, the partial pressure of the nitrogen reactive gas must be increased as the target power is increased to offset the N2 density reduction and to compensate for the increase in density of the titanium atoms.

Advances in partial-pressure control applied to reactive sputtering

Summary High-rate reactive sputtering (HRRS) requires rapid and careful control of the reactive gas partial pressure to achieve high deposition rates and to maintain stoichiometry in the coating. HRRS of TiN was first achieved with feedback control of the N 2 utilizing a differentially pumped mass spectrometer system to sense the N 2 partial pressure. Recently, a new instrument called the optical gas controller (OGC) that operates at sputtering pressures became available for sensing the partial pressure of the gases in the sputtering atmosphere. The OGC was used during the reactive sputtering of TiO x with partial-pressure control, and the TiO x hysteresis loop exhibited a wide negative slope region which is much larger than the one found during the reactive sputtering of TiN x . Partial-pressure control, compared to mass flow control during oxide reactive sputtering, leads to better control of the process and to a 3.5 times higher deposition rate for highly resistive oxide coatings. With partial-pressure control, the anatase form of TiO 2 has been produced with lattice parameters of a 0 = 3.780 A and c 0 = 9.610 A.