Manufacturing Metal/Alloy Sputtering Targets Presentation
International Symposium on Sputtering & Plasma Processes
Presented by David Sanchez
I was privileged to speak at the 14th International Symposium on Sputtering and Plasma Processes (ISSP 2017) at the Kanazawa Institute of Technology in Japan. My presentation and poster delved a bit deeper and took a more critical look at the technologies central to metal sputtering targets. The Technical Paper (“Reactive Deposition – Enabling Enhanced Thin Film Performance”), based on the presentation, explores various aspects of reactive deposition.
Recap of Some Key Points
Since metal targets enable the formation of metal films, fully reacted oxide, nitrides and even exotic carbides and selenides are central to thin film technology. In order to meet the demands for high density, high performance coatings – there are challenges to the production of metal targets that must be met that influence process control and repeatability. Beyond the extraction, purification and raw material source technologies, macroscopic failure modes are as varied as the formation technologies themselves.
When a metal or alloy is well-behaved, it will melt evenly, outgas volatile impurities, and allow thermo-mechanical processing to refine the grain structure and minimize residual stress. For these materials Vacuum Induction Melting (VIM) is the most common and flexible technique for producing viable target plate stock from high purity starting rod, bar, turnings and foils. The metal or alloy is melted and cast into a target mold. Subsequent thermo-mechanical processing including hot rolling, annealing and machining, further refine the structure as shown in Figure 1.
Figure 1. Refined grain structure of FeCo Target
As one would expect, the point at which the grain structure of the target influences the process stability is strongly dependent on the sputtering approach and the number of heat/roll/anneal cycles (rolling schedule). It is also true that different materials and compositions have different thermo-mechanical recipes or may require a hybrid or powder process to yield the most appropriate performance. The powders themselves can be produced from chemical synthesis as well as grinding, atomization and RF plasma technology.
For good consolidation, the starting powder density and flow characteristics are critical for a homogeneous product. Care is taken to control voids between particles which otherwise may survive sintering and increase arcs and contamination. Aside from ultimate density, the most important difference between conventional hot and cold press technologies and cast/rolled targets, is the oxygen/absorbed gases associated with the high surface area of the powder. Depending on the material, conventional hot pressing densities range from 65% - 99%. The more costly Hot Isostatic Press (HIP) process yields a more consistent 99%+ density product.
Materion has invested considerable time in completing the most cogent line of sputtering targets for the different thresholds of performance and price. Raw materials control, VIM Casting and advanced thermo-mechanical processing are perhaps the most notable differences between Ion Beam and Magnetron Sputtering targets. They also impact Optical and Semiconductor grade products.
Hot Pressing creates the best grain structure but risks from oxygen (for metal mode), anomalous erosion and particles must be monitored closely. VIM cast and rolled targets offer the advantages of scale, low oxygen and strength but are limited to well behaved metals and stable alloys that remain intact after successive thermo-mechanical processing. The intense bombardment and activity of a reactive process causes a host of common failures in targets. For example, fragile metals like Silicon and Germanium can crack; hard metals like Niobium and Zirconium can deform; and de-bond, complex alloys can change composition, melt or become brittle. For these reasons, Materion uses an ever growing host of powder and plate manufacturing/handling technologies, plus years of professional expertise in working with thin film deposition materials to help industry address challenging applications.