Melt or Powder Processing
Sputtering targets are typically manufactured at Materion using either melt or powder processing. Each approach offers unique capabilities and manufacturing advantages. Here we will concentrate on powder processing, a technique that offers significant advantages in the manufacture of targets. Advantages include microstructural tailoring that can significantly improve sputtering performance, as well as the manufacture of targets from materials that do not lend themselves to other processing methods. Powder processing also allows high material utilization - an important cost factor when processing high cost material systems.
Image of Titanium-Tungsten sputter target material produced by powder processing.
Advantages of Powder Processing
In powder processing, articles are manufactured by the sintering and densification of powder starter materials at elevated temperatures. The driving force for this process is minimization of the energy of the material by reduction of the large surface area associated with powders.
Powder processing has a number of advantages over complementary processing techniques such as melt processing. For example, powder metallurgy allows the production of sputtering targets from materials with high melting points, including refractory metals and ceramic materials. In addition, it allows microstructural tailoring of the sputter target material that is difficult to achieve using any other technique. This tailoring can include fine grain sizes, random crystallographic orientation (the elimination of preferred crystallographic orientation, also known as texture), suppression of undesirable phases, and production of materials with immiscible materials.
Powder processing also allows the usage of extremely brittle materials which do not lend themselves to more traditional casting technologies. Finally, powder processing also significantly increases material utilization by facilitating the production of near-net-shape articles, reducing the cost of the material, which is a very important cost factor when processing precious metals and alloys.
Powder Processing Procedures
Depending on the material and its properties, different sintering conditions are needed to make a high quality part. For many ceramic materials, including many oxides, powder processing can be done by sintering the material in air at elevated temperatures followed by final machining of the target. However, for many other materials a more complex processing route is required. For example, for many metallic alloy systems powder processing can include powder manufacture and blending, room temperature powder compaction, sintering of the compact under protective atmosphere (typically inert gas of Argon or Nitrogen) or under vacuum, and finally machining of a sputter target.
The powders used can either be elemental materials, pre-alloyed, or a blended mixture of elemental powders. The powders are typically produced by gas atomization, mechanical comminution, or by wet chemical techniques. The powders are blended, and then poured into a die and cold pressed into a compact. During pressing the neighboring powder particles are cold welded together to give the compact sufficient “green strength” to be handled. The powder compacts are then typically sintered under a protective atmosphere to produce the densified product. The sintering temperature is typically kept below the melting point of the constituent of the powder with the lowest melting point. Sintering is typically done under pressure to reduce processing times and temperatures, and to increase the density of the final product. For oxygen sensitive powders vacuum hot pressing (VHP) is recommended. In addition vacuum processing can improve the overall purity of the product by eliminating (volatilizing) impurities from the material during heating.
Range of Applications
For low volume applications, sintering is typically done under uniaxial pressure in a die between two plungers. For high volume applications, sintering is done in a hot isostatic press (HIP). During HIP-ing the powder compact is placed in a metallic can which is then sealed and subsequently subjected to hydrostatic pressure at elevated temperatures. The pressing medium used is an inert gas. The resulting HIP-ed material is close to fully dense, mechanically robust and is subsequently machined to final shape.
More Information on Powder Processing
In addition to these processes, Materion has developed hybrid processes to make high purity targets from more challenging materials. We work with customers to produce sputtering targets that will meet their unique application needs at the lowest possible cost. For more information on powder processing and sputtering targets, please contact: Dejan Stojakovic, Technical Manager (Brewster), Dejan.Stojakovic@materion.com.