Dynamics of a pulsed DC discharge used for plasma-assisted chemical vapor deposition — a case study for titanium nitride deposition

Abstract

Abstract An investigation of the development of a pulsed DC discharge used for plasma-assisted chemical vapor deposition (PACVD) of titanium nitride was carried out in order to understand non-uniform depositions in larger PACVD systems. The temporal and spatial evolution of the plasma light emission was studied by a video camera. The time evolution of the plasma potential was studied by a single Langmuir probe and the discharge current by a current probe. In the presence of TiCl 4 for formation of the discharge across the reactor is slow, reaching some parts of the reactor with substantial delay. Our experiments show that the development of the discharge depends on the geometry of the cathode, which includes loading and placement of the substrates, gas mixture and waveform of the voltage supplied. The slow spreading of the discharge across the surface of the cathode, on which the substrates are placed, leads to a non-uniformity of plasma power density in front of the cathode as well as to a spatially varying exposure time of the surface to the plasma. The experiments revealed that the slow spreading of the discharge can be solved by measures which provide sufficient voltage for the cathode fall across the entire cathode surface whereby high average discharge currents have to be avoided.