Recovering Precious Metal
Shield Kit Cleaning Returns Value
Many precious metals, such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh) and ruthenium (Ru) are used in Physical Vapor Deposition (PVD) technologies. These precious metals are chosen for advantages such as high electrical conductivity and corrosion resistance, and for a variety of applications including Memory (hard disk drive) and Low E Glass.
However, they represent a significant cost in two ways: one is that precious metals are in themselves expensive; and second, manufacturers can “lose” a high percentage of metal that is deposited onto chamber surfaces and internal fixtures during the evaporation or sputtering process. Although this material is recoverable, the choice of technical methods employed can directly impact the yield of precious metal return.
Materion has developed proprietary chemical processes that offer distinct advantages over traditional shield kit cleaning. Our chemical removal of depositions without aggressive mechanical procedures:
- Shortens cleaning time, thus enabling a faster return of parts & less downtime for our customers
- Reduces parts damage & extends the effective life of the components; and most importantly,
- Reclaims the maximum amount of precious metal from the shield kit.
Together, these factors represent a total lower cost-of-ownership that more than off-sets the cost of chemical processing. They also provide for a high quality return with parts that are contamination-free and ready for immediate installation.
Unrecovered Output Increases Costs
Much of the output from PVD processes ends up on a variety of surfaces inside the vacuum chamber. Only 3%-8% of precious metals used in a typical evaporation process are actually deposited on the product wafer. The remainder can be found in a variety of places and can be recovered from: shield kits; shutters; hearths/turrets, e-gun inserts, V plates; spent crucibles; chambers; vacuum bags; etch tools, viewing windows and more.
Similarly, the same challenge exists for sputter processes. Only around 10%-15% of the precious metal ends up coated onto the wafer substrate. The rest can be found on spent targets, shield kits, chamber flakes, vacuum bags, scrap wafers, etch tools, etc. While the majority of precious metal in sputter tools is recovered as spent targets, the amount transferred onto the shield is significant.
Precious Metal Recovery & Controls
Critical for the best return on your precious metal investment is cradle-to-grave metals management. This is a unique industry service offered by Materion. It starts with the creation of a broad range of precious metal products and customized alloy development, through precision parts cleaning, on toward refining & recycling and ultimately flexible settlement plans. Throughout these stages, Materion’s tight process controls ensure that the maximum amount of precious metal is recovered from the PVD tools, that the recovered material is refined to its purest form, and that a consistent level of quality is maintained for returned shield kits.
For gold (Au) evaporation processes, the average Au recovery from shield kits is approximately 14.5Kg (471 troy ounces) with an April 2015 value of approximately $565K. For sputter processes, the average weight per shield kit is 1.4Kg (45 troy ounces) with a value of approximate value of $54K. Other precious metal (PM) values can be calculated according to the PM usage and the PM market value. This high value of PM recovered from PVD shield kits demonstrates the importance of selecting a recovery process with stringent controls in place in order to ensure optimal returns.
Shield Kit Cleaning Methods
Shield kits essentially consist of all components that are coated during the deposition process including the chamber liners and all parts that support the PVD tool and wafers. At certain intervals, it is necessary for shield kits to be removed and replaced with a fresh, deposition-free kit. The interval is usually determined by the level of deposition present and its potential for particle generation. Once removed, the shield kit is processed to remove the deposition, reclaim the deposition for refine, and return the shield kit to a standard where it can be re-used.
A variety of methods are used for the removal of precious metal from shield kits. Physical methods such as scraping and bead blasting are relatively straightforward and require less investment and training. However, they have some serious disadvantages. Both produce lower precious metal yield; scraping because of residue left on the shields, and bead blasting because of deposition rendered into a high volume dust. In addition, the physical impact of these methods causes damage to the shields parts and thus reduces their “life.”
Materion has selected an alternative process - chemical etching. It offers a far greater yield of precious metal and delivers superior quality cleaning. We specialize in chemical etch technologies and have developed a unique process for precious metal shield kits. Data indicates a 1%-7% increase in metal returns from our method over conventional chemical etch technologies.
Shield Kits - Additional Quality Processes
Following the removal of the deposition, the shield kit is processed to remove any contamination that would be detrimental to the thin film deposition process and to optimize its performance. Other processes performed include:
- Texturing: Metal shield kits are textured to achieve surface roughness appropriate to the particular customer PVD process. Improving the surface roughness will increase adhesion of the deposition to the individual shield thus reducing deposition flaking and the related particle generation in the PVD tool.
- Aluminum Twin Wire Arc Spraying (Al TWAS): The application of a coating of aluminum on shield kit components using TWAS further enhances the surface roughness. This process is recommended for problematic depositions that flake easily and where tool uptime is especially critical.
- Clean Room Processing: Following the texturing and Al TWAS operations, shield kits receive a final cleaning to restore the high quality expected for PVD processes. Processes include ultrasonic cleaning baths, high purity water and air, dimensional and performance checks, baking to remove residues and clean room packaging to stringent standards.
Materion Precious Metal Assistance
With over a century experience with precious metals, we excel at all stages of metals management. We offer a one-stop solution for precious metal products, shield kit cleaning, and reclaim & refine. We also advise customers on the best handling and management of precious metals onsite, from receiving to storage to shipment. We can assist with establishing controls for the recovery of precious metals from shield kits, such as Weight Logs and Trending Data that can be targeted to meet customer requirements and monitor yields.
To learn more about Materion’s shield kit cleaning and other precious metal services, please contact: Matthew Waz, Product Manager - Precision Parts Cleaning, Matthew.Waz@Materion.com.