The reactive sputtering of thin films of TiN at low target voltages

Abstract

Thin films of titanium nitride have been made on low-temperature substrates by the dc reactive sputtering of titanium. An unbalanced magnetron source was used in an enclosed volume, within a vacuum chamber, into which nitrogen gas was admitted. The admission of the reactive nitrogen gas was controlled from an observation of the partial pressure of it within the box, provided with a fast response time by observation of the spectral line emission of the sputtering titanium. Films of specular quality could be produced onto glass substrates at room temperature, having properties close to those reported for bulk material and those for thin films made at elevated temperatures. A straightforward observation of the flow of the nitrogen into the reaction volume allows the stoichiometry of the film that is being made to be easily controlled. The unbalanced magnetron caused the substrate and growing film to be subjected to an ion bombardment from the dense plasma incident upon them, this was in addition to the energy provided by the depositing metal particles. The plasma incident on the system was controlled by the magnetic field given by a coil behind the substrate. The energy of the incident particles could be adjusted by operating the magneton at different potentials, allowed by using electron injection into the race-track of the magnetron from a resistance-heated filament. It is reported that operation of the process at low magnetron potentials and under conditions that provide considerable ion bombardment of the growing film leads to TiN of better quality, where this is assessed by improved specular selectivity in their reflectivity and lower resistivity.