ClassOne Technology of Kalispell, MT, USA, which manufactures wet-chemical processing equipment including Solstice electroplating systems (especially for emerging markets and other cost-conscious users of ≤200mm substrates), is reporting significant savings in the plating of gold in ≤200mm applications using its Solstice systems. The savings come from the elimination of gold waste, faster and simpler processing, and Solstice-enabled techniques that can substantially reduce gold usage.
"Many users have been spending millions of dollars on gold each year," says Byron Exarcos, president of ClassOne Group. "It's a major issue, especially in emerging markets such as lasers, LEDs, RF and MEMS which often require gold layers as thick as 3-35μm. That's why they are becoming keenly interested in Solstice to cut their gold spending," he adds.
"One fundamental advantage of Solstice electroplating is its elimination of gold waste," says ClassOne Technology president Kevin Witt. "Previously used CVD [chemical vapor deposition] and PVD [physical vapor deposition] methods deposited gold not just on the wafer but also on the entire chamber interior. That 'over-sprayed' gold was difficult to remove and inefficient to reclaim — which led to a considerable net loss of gold," he adds. "By contrast, Solstice deposits only on the wafer, so there is no gold waste, and no need for cleaning or gold reclamation efforts."
Witt adds that Solstice economies also come from its higher gold deposition speed. Plating at 150-300nm/min, it is roughly ten times faster than CVD and PVD methods. In addition, Solstice starts processing immediately, not requiring an hour or more for pump-down (as vacuum-based tools do). All of this translates to additional savings, from higher throughput and more cost-efficient production.
The unique eight-chamber design of the Solstice S8 enables it to readily replace a solid gold layer with a multi-metal stack — and reduce gold usage very substantially. For example, a feature that previously required a 5μm layer of solid gold can now be replaced with a 'sandwich' of 0.25μm Au, 1μm Ni, 2.5μm Cu, another 1μm Ni, topped with 0.25μm Au — to achieve equivalent functionality while reducing gold usage by a factor of ten, it is reckoned. Also, Solstice's multi-chamber design enables it to deposit all five layers in a single cycle. So, no additional process steps or time are required to gain very significant cost savings.
ClassOne notes that, over a year, total gold savings can grow quite large. For example, in the above case, if the solid gold 5μm layer covers 50% of a 150mm wafer area, and if the fab is running 1500 wafers per week through a metal lift-off process and gold costs of $1200 per troy ounce — even if all over-sprayed gold were recovered — the user's annual gold expenditure would be about $2,150,000. However, if the Solstice multi-metal layering technique were used, the total metal cost (for Au, Ni and Cu combined) would be reduced to about $108,000, yielding annual savings of over $2,042,000 (more than paying back the cost of a Solstice system).
