Deposition of thin films using the ionised cluster beam method

Abstract

For over a decade, the use of the ionised cluster beam (ICB) technique to deposit thin films of materials with applications in microelectronics has been explored. These films have been shown to be of superior quality compared to films deposited by conventional methods. With the ICB technique there is greater control over growth behaviour because there are more process parameters which influence film growth than are found in other methods. The evaporant material is heated in an almost closed crucible with a small aperture. Clusters can be produced when the gas pressure inside the crucible rises so that the evaporant expands adiabatically through the aperture into a region of low pressure. The clusters are passed through an electron beam and some of the clusters are ionised by impact. The ionised clusters are then accelerated towards the substrate, which is held at a variable potential. By altering the beam conditions, such as the ionisation current and acceleration potential, the kinetics of film growth can be modified resulting in improved film quality. This paper presents a brief review of the ICB method of thin film deposition. This is followed by review of some of the properties of films deposited by the ICB technique which have useful applications in microelectronics. Finally, some work carried out at the Cavendish Laboratory in this area is presented, including the deposition of thin (<or=120 AA) continuous gold films and thin films of titanium (<or=500 AA) on single crystal silicon, subsequently reacted to form TiSi2 layers.