Minimizing Costs of Precious Metals

Precious metals, such as Gold (Au) and Platinum (Pt), are commonly employed in the manufacture of compound semiconductor devices. These precious metals are chosen because they offer high electrical conductivity and resistance to corrosion necessary for superior performance. However, Au and Pt represent a significant cost to the manufacturer due to the high percentage of the metal that is deposited onto the surfaces of the chamber and internal fixtures during the evaporation or sputtering process.  Although this material is recoverable, the choice of recovery techniques can directly impact the precious metal recovery yields. 

It is important to recover the maximum amount of Au and Pt from the shield kit to minimize total cost of ownership. Materion has developed proprietary chemical processes that offer distinct advantages over traditional shield kit cleaning. The comparative advantages and disadvantages of the cleaning methods will be discussed in this article.

Unrecovered Output Increases Costs

The output from evaporation or sputtering processes ends up on a variety of surfaces inside the vacuum chamber.  Most of the evaporated Au and Pt is not deposited on the final production wafers. The majority of the precious metal can be found in a variety of places including: shield kits; shutters; Cu parts such as hearths/turrets, e-gun inserts, V plates; spent crucibles; chambers; vacuum bags; etch tools, viewing windows, etc.  In most current evaporator tools, only a small portion (3%-8%) of the evaporated Au and Pt ends up coated onto the wafer substrate.

A similar challenge exists for precious metal utilization during the sputtering process. Only around 10-15% of the Au and Pt ends up coated onto the wafer substrate.  Precious metal will be found on spent targets, shield kits, chamber flakes, vacuum bags, scrap wafers, etch tools, etc. While the majority of Au and Pt in sputter tools is recovered as spent targets, the amount transferred onto the shield is significant.

Minimizing Costs

Critical to minimizing costs for either of these processes is recovering the maximum amount of Au and Pt output from the PVD tools.  This can be achieved through precision parts cleaning using traditional cleaning processes or Materion’s advanced chemical method.  The following data is for Evaporation and Sputter tools.

Even a 1% improvement in Evaporator Tools cleaning return would equate to $1,000-$2,100 savings for a low end user and as much as $322,000-$697,000 for a high end user. (With Jan 2014 gold price at $1250/ozt). For sputter tools, a 1% return improvement would mean potential savings of $482-$1,045 for low usage and $4,019-$8,707 for high usage.

The typical range of coatings on Sputter Kits is 300-2500 grams of precious metal for a cost of approximately $12K-$100K per Kit. With Planned Maintenance added, this equates to a broad range of $48K to $850K annually per tool. Thus, even a 1% improvement in Shield Kit Cleaning, Precious Metal Reclaim and Refine would equate to an annual savings of $500-$8500 per sputter tool.

Traditional Shield Kit Cleaning vs. Chemical Cleaning – Pros and Cons

Scraping and Bead Blasting
Scraping involves the physical removal of the metal deposition using a scraping tool and manual force.  It usually must be followed by bead blasting which involves removal of the deposition employing a media and a carrier gas. The disadvantage of these recovery techniques is the lower precious metal yield and possible damage to the shields parts and reduced part life times. They do have the advantage of being easy to perform with no special training and relatively low capital investment. The problem is that they may not fully remove the deposition, therefore do not provide an efficient return of precious metal.  In addition, the physical impact of scraping can damage shields or run the risk of igniting the dust.

Chemical Etch  
Materion has developed proprietary chemical shield kit cleaning processes that offer distinct advantages over traditional scraping and bead blasting technologies. They return the highest precious metal yields. We also offer a chemical process for cleaning Copper and Aluminum parts which is unique in the industry. Our processes:

• Provide the highest quality cleaning
• Avoid the problem of shield damage
• Lower the frequency at which shields need to be replaced
• Produce optimal Au and Pt reclaim and refine yields
• Customized cleaning solutions for difficult to clean parts such as: for Au on Aluminum or Copper parts

In addition, the reclaim material from Materion’s chemical etch processes contain concentrated Au and Pt and thus are easier to refine.

Maximizing Metal Return

In summary, to increase refine yield and minimize costs, chemical etch cleaning is Materion’s  recommended choice.  It produces the highest quality of cleaning and can be used to effectively remove a variety of depositions:

• Single stack Au and Pt depositions
• Stacks containing Au and Pt along with base metals
• Thick stacks containing Au and Pt along with base metals

The Materion chemical cleaning technology also delivers above industry returns for platinum along with faster settlement times.

To learn more about Materion’s removal technologies and other services, please contact Matthew Waz, Product Manager - Precision Parts Cleaning, at Matthew.Waz@Materion.com.