Alchimer Ready to Tackle TSV Seed Layer

David Lammers, News Editor -- Semiconductor International, 5/28/2008 8:40:00 AM

Following an IP licensing business model, Alchimer SA (Massy, France) said it is ready to do business in the 3-D interconnect sector, offering its unique electrografting (eG) process on available electroplating tools. The company’s target for the “eG ViaCoat” solution is the creation of copper seed layers in high-aspect-ratio through-silicon vias (TSVs).

Alchimer's eG ViaCoat tackles the challenge of conformal copper seed layers in deep TSVs.

Alchimer CEO Steve Lerner said eG ViaCoat will serve to reduce the costs associated with TSVs by replacing the physical vapor deposition (PVD) steps now used for seed deposition with eG, a wet coating process first developed at a French national laboratory to create anti-corrosion layers in nuclear reactors. Alchimer’s technology can be implemented on existing electroplating equipment, and the company is in licensing discussions with the major electroplating vendors, as well as several chemical companies, to provide the chemical formulation. Lerner said its relationship with electroplating vendor NEXX Systems Inc. (Billerica, Mass.) is public knowledge. Two other licensing agreements with electroplating vendors will “become clear very soon.” On the chemical side, Alchimer has an existing relationship with the OM Group Inc. (OMG, Cleveland), and discussions are underway with other chemical suppliers, he said.

“We offer a solution used in existing electroplating equipment. We use 10-year-old legacy electroplating tools to plate resolutions of 5 nm films. There is a huge savings in the investments required,” Lerner said.

Vias with a high aspect ratio are needed to reduce TSV costs.

Alchimer’s main target is high-aspect-ratio devices, with 10:1 aspect ratio vias that Alchimer claims are too deep for existing PVD equipment. Much of the cost of creating TSVs is in grinding the wafer thin enough to reduce the aspect ratio to the 5:1 range that PVD equipment is comfortable with, Lerner said. By enabling deeper vias with eG ViaCoat, the wafers can be thicker, thus reducing wafer thinning costs, improving yields and cutting wafer handling costs.

“Due to its ability to cope with even the most aggressive TSV aspect ratios, eG ViaCoat is the only copper seed layer technology that enables TSVs to keep up with the 3-D IC packaging roadmap,” said Dan Marx, vice president of business development at Alchimer.

Lerner said memories and MEMS beckon as two large markets. Memory companies are on the verge of implementing 3-D TSVs in a big way, connecting, for example, nine NAND devices to create high-density solutions for thumb drives and other markets. Rather than rely solely on expensive 45 nm and beyond technologies, memory vendors will soon use TSVs to vertically connect memory die, he argued, predicting that memory adoption of TSVs will escalate by 10-20× in the next few years. Logic will come later.

MEMS vendors are also studying the application of Alchimer’s eG solution to vertically connect logic and MEMS devices. At the International Interconnect Technology Conference (IITC), to be held June 1-4 in San Francisco, Alchimer and NXP Semiconductors (Eindhoven, Netherlands) are scheduled to present a paper on the use of TSVs to connect a MEMS RF device with embedded passives. Lerner said many MEMS vendors do not own the required dry deposition tools and are attracted to employing electroplating equipment for the TSV seed creation step.

Jagged edges on deep TSVs require a conformal seed layer.

From a business perspective, Lerner said Alchimer’s process will essentially halve the cost of depositing the seed layer. “The whole picture of TSVs is in bringing down the costs. A TSV is just a dumb wire, and one cannot be paying $400 a wafer to create them. When TSVs become very low cost with high reliability, then they will become real. Our view is that directional gas processes will most likely not be players in TSVs because of the overheads and capital costs,” Lerner said.

On the technical side, he said the Alchimer solution has the conformal properties required for TSVs. “The process of etching holes is an iterative process: etching, laying down a resist, then etching again. The long and short of it is that you end up with a very scalloped, jagged wall that doesn’t readily accept the subsequent barrier and seed. This product adheres directly to the barrier on the high-aspect-ratio walls. That is where the conformal nature of our product comes in,” he said.

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