Foundry Landscape Changes In 3D

Shifting strategies, a new foundry and lots of questions emerge as industry prepares for stacked die.

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By Mark LaPedus
Over the last year, leading-edge silicon foundries announced their new and respective strategies in the emerging 2.5D/3D chip arena. The ink is barely dry and now the foundry landscape is changing.

One new vendor, Tezzaron Semiconductor, is entering the market. The 3D DRAM supplier plans to provide select 2.5D/3D foundry services within its recently acquired fab in Austin, Texas.

In addition, Taiwan Semiconductor Manufacturing Co. Ltd. (TSMC) is tweaking its 2.5D/3D foundry strategy. Last year, TSMC announced a controversial turnkey solution. The company not only provides the front-end steps, but also the back-end work traditionally handled by the IC packaging houses. Now, instead of locking in customers with its front-to-back solution, TSMC is rethinking its position.

“We prefer to do it ourselves,” said Morris Chang, chairman and chief executive of TSMC, in a recent conference call. “We have become more flexible to partner with the OSATs.”

Two other vendors, GlobalFoundries and UMC, are sticking with their collaborative approaches. In that model, the foundries handle the front-end steps, but pass on the back-end work to the IC packaging houses.

Another foundry, IBM, has a slightly different strategy. Still to be seen, however, is what Intel and Samsung will do in the arena. And some of the IC packaging houses have given up the notion of doing fine-pitch interposers and through-silicon vias (TSVs). Instead, the OSATs are looking at doing course-pitch TSVs and interposers.

So, in general, there are two prevailing, leading-edge 2.5D/3D foundry models: TSMC’s turnkey solution and the rival collaborative approach. “I think both models will co-exist,” said David McCann, senior director of technical business operations for packaging and central engineering at GlobalFoundries.

Foundries go 3D
The memory bandwidth gap and resistivity problems in planar devices have fueled the development of 2.5D/3D chips. But advanced chip stacking has several challenges and is still a few years away from mass production. For example, TSMC will not see “significant revenue” in 2.5D/3D until 2015 or 2016, Chang said.

2.5D/3D technology and the associated supply chain are immature. Manufacturing costs are falling, but there is still a perception that the 3D devices will be prohibitively expensive, said Niranjan Kumar, product marketing manager for TSV programs at Applied Materials.

So far, only a few chipmakers have announced 3D chips. In 2010, Samsung rolled out one of the first 3D DRAMs using a 40nm process and TSVs. Then, last year, Samsung and Micron formed a consortium to develop a serial specification for a 3D DRAM technology called the Hybrid Memory Cube (HMC). Micron will sample HMC devices in 2013. Aimed at high-end applications, HMC will stack DRAM arrays on a logic chip. IBM is making the logic chip based on an SOI substrate.

Another 3D DRAM vendor, Tezzaron, recently has begun shipping its initial parts. But other 3D DRAM schemes, such as Wide I/O, have been delayed due to an assortment of technical issues. Still, the industry is making more progress on the 2.5D front. “The 2.5D era has arrived,” said E. Jan Vardaman, president of TechSearch International, a research firm.

To date, Altera, Cisco, IBM, Huawei and Xilinx have talked about or shipped 2.5D devices using interposers. In fact, Xilinx has shipped the Virtex-7 2000T FPGA, a product based on a 28nm process and a 65nm silicon interposer.

The device itself is built and assembled by TSMC, which refers to its 2.5D/3D turnkey solution as “Chip on Wafer on Substrate” (CoWoS). Using CoWoS, TSMC is also building a rival 2.5D FPGA for Altera. In CoWoS, the chip is attached to the substrate to form the final component. TSMC provides front-end manufacturing, TSV formation, interposers, chip-on wafer bonding, backside thinning, dicing and final test.

CoWoS has been given a lukewarm reception by the IC packaging houses, many of which believe that TSMC is taking a chunk of the backend business away from the OSATs. “For some customers, (CoWoS) works well. It doesn’t work for all customers,” Vardaman said.

TSMC has defended CoWoS, saying that the in-house, turnkey solution enables the foundry to ensure the quality of the chips and the production process. TSMC also assumes responsibility for the supply chain. “Technically, it is progressing well,” TSMC’s Chang said. “We are trying to reduce the costs.”

Beyond 2.5D FPGAs, TSMC recently taped out a Wide I/O device. To enable Wide I/O, the company requires DRAM from a third party. Originally, it was working with Elpida, which is being acquired by Micron. Now, TSMC is working with Micron and SK Hynix.

TSMC’s model may fall flat when customers ask for DRAM from Samsung. TSMC and Samsung are foundry competitors. It’s unlikely that Samsung will hand over DRAM wafers, along with its proprietary IP and test data to TSMC.

In some cases, it makes more sense to follow the collaborative model, where there are fewer conflicts. A customer can use its own logic and/or memory or buy it from a third party. The foundries do the front-end processing, while the OSATs collect and assemble the pieces.

With that scenario in mind, TSMC is warming up to the idea of working with OSATs to give customers more flexibility. TSMC also may be fending off its rivals, which are offering a collaborative approach.

More models

Others are moving full speed ahead with their strategies. Earlier this year, GlobalFoundries installed the tools to create 3D TSV devices on its 20nm platform within its fab in New York. It will handle the “via creation” steps. Then, it will hand off the traditional backend steps, such as temporary bonding/debonding, grinding and test, to the OSATs.

The foundry vendor also devised a low-volume, 2.5D line using 65nm interposers within its fab in Singapore. GlobalFoundries’ challenge is to demonstrate a smooth flow and good product yields at a competitive cost. “It’s going well,” said GlobalFoundries’ McCann. “The question is, can we make this collaborative supply chain model a one-to-one solution? We have to prove this to our customers.”

Another vendor, IBM, has been working on 2.5D/3D for years, including a specialized interposer technology. “IBM is working with Sematech to connect analog converter functions in a logic device with an interleaver IC in IBM’s BiCMOS SiGe technology,” said TechSearch’s Vardeman. “Applications are fiber optic telecom, high-performance RF, test equipment and processing for radar systems.”

The new kid on the foundry block is Tezzaron. In October, the company acquired the former SVTC fab in Austin. R&D foundry SVTC, which recently went bankrupt, originally acquired the fab from Sematech. Now, the fab operates under the name of Novati Technologies. Tezzaron is the sole shareholder in Novati. “We are going to become a 3D foundry,” said Robert Patti, chief technology officer at Tezzaron. “What we are trying to do is provide an open platform for 2.5D and 3D integration.”

Asked if Novati will compete against TSMC and GlobalFoundries, Patti said Novati can work with other foundries and will not compete against them. Novati will continue to serve SVTC’s customers. The Austin fab is a 200mm CMOS line, with 200mm/300mm backend capabilities.

As part of the plan, Tezzaron will shut down its current fab in Singapore and transfer the tools to the Austin fab by early 2013. By Q3 of next year, the company hopes to provide 3,000 wafer starts a week in Austin.

In the 2.5D/3D foundry arena, Novati will offer advanced stacking capabilities, TSVs and interposers. It can provide Tezzaron’s 3D DRAMs or procure third-party logic and memory chips. And Novati will offer both a turnkey and collaborative model. “We are willing to do a full turnkey solution,” Patti said. “I am willing to take the pieces and assemble them.”

The company prefers customers to use its so-called FaStack technology, which makes use of a proprietary bonding and tungsten process. Its 2.5D/3D technology is based on a 40nm process. By late 2013, it will offer a 28nm platform.

While the foundry landscape continues to evolve, several IC packaging houses are rethinking their plans. Some time ago, Taiwan’s Advanced Semiconductor Engineering (ASE) was looking at fine-pitch interposers and TSVs in a “via-last” production flow. “We have an interposer technology that we’ve promoted,” said Rich Rice, senior vice president of sales for North America at ASE. “We are not sure about the market acceptance.”

As it turns out, ASE discovered that leading-edge TSV and interposer work belongs in the foundries and not at the OSATs. “I think poking holes in silicon is mostly a foundry business,” he said at a recent event sponsored by the Microelectronics Packaging and Test Engineering Council (MEPTEC).

On the other hand, ASE and STATS are looking at course-pitch interposers and TSVs for niche applications like MEMS and RF. The OSATs will also play a major role in fine-pitch 2.5D/3D by offering the critical backend work.

TSMC and its turnkey model will not take all of the backend business away from the OSATs. TSMC is still going up the learning curve in the backend and may find the work a headache in the long run. “This is something we do day in and day out,” Rice added.