Christian Linke¹, Hennrik Schmidt¹, Enrico Franzke¹, Thomas Scherer¹, Paul Rudnik^2
1Plansee SE, Reutte, Austria
²Plansee USA LLC, Franklin, MA
Molybdenum (Mo) and tungsten (W) are important materials in thin film applications. For many semiconductor and microelectronic devices, these materials are used because of their specific properties. The high density and good electrical resistivity of Mo and W thin films are important in MEMS components, RF filters (SAW/BAW) or piezoelectric sensors. In semiconductor manufacturing Mo and W play a crucial role as thin film materials for achieving smaller nodes and device structures due to the long mean free path of electrons at small critical dimensions. PVD is one of the key processes to deposit such thin films and the availability of high-quality sputtering target materials is a major requirement. Process and design modifications such as seed layer stack or HiPIMS can be applied to further improve refractory thin film performance.
The powder metallurgical manufacturing process for Mo and W offers opportunities to develop sputtering targets with tailor made properties. Using high-purity raw materials and appropriate consolidation processes, the grain size and texture of the materials can be tuned to achieve homogeneous deposition rates and lowest defect densities. For bonding of target assemblies with different backing plate materials solder or diffusion bonding must be applied. Such processes require specific material knowledge and control of parameters to guarantee a stable utilization of the targets especially in high power or high temperature deposition processes.
Besides metal Mo and W sputtering targets, the use of electrically conductive oxide sputtering targets allows to apply films with tunable work function and wide range of optical properties. Doping of such targets with other oxides or metals can improve chemical resistance or wet etching rate which is crucial for structuring and stability of the deposited oxide films.