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MRAM Takes Center Stage at IEDM 2016

Monday, December 12th, 2016

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By Dave Lammers, Contributing Editor

The IEDM 2016 conference, held in early December in San Francisco, was somewhat of a coming-out party for magneto-resistive memory (MRAM). The MRAM presentations at IEDM were complemented by a special MRAM-focused poster session – organized by the IEEE Magnetics Society in cooperation with the IEEE Electron Devices Society (EDS) – with 33 posters and a lively crowd.

And in the opening keynote speech of the 62nd International Electron Devices Meeting, Seok-hee Lee, executive vice president at SK Hynix (Seoul), set the stage by saying that the race is on between DRAM and emerging memories such as MRAM. “Originally, people thought that DRAM scaling would stop. Then engineers in the DRAM and NAND worlds worked hard and pushed out the end further in the future,” he said.

While cautioning that MRAM bit cells are larger than in DRAM and thus more more costly, Lee said MRAM has “very strong potential in embedded memory.”

SK Hynix is not the only company with a full-blown MRAM development effort underway. Samsung, which earlier bought MRAM startup Grandis and which has a materials-related research relationship with IBM, attracted a standing-room-only crowd to its MRAM paper at IEDM. TSMC is working with TDK on its program, and Sony is using 300mm wafers to build high-performance MRAMs for startup Avalanche Technology.

And one knowledgeable source said “the biggest processor company also has purchased a lot of equipment” for its MRAM development effort.

Dave Eggleston, vice president of emerging memory at GlobalFoundries, said he believes GlobalFoundries is the furthest along on the MRAM optimization curve, partly due to its technology and manufacturing partnership with Everspin Technologies (Chandler, Ariz.). Everspin has been working on MRAM for more than 20 years, and has shipped nearly 60 million discrete MRAMs, largely to the cache buffering and industrial markets.

GlobalFoundries has announced plans to use embedded STT-MRAM in its 22FDX platform, which uses fully-depleted SOI technology, as early as 2018.

Future versions of MRAM– such as spin orbit torque (SOT) MRAM and Voltage Controlled MRAM — could compete with SRAM and DRAM. Analysts said today’s spin-transfer torque STT-MRAM – referring to the torque that arises from the transfer of electron spins to the free magnetic layer — is vying for commercial adoption as ever-faster processors need higher performance memory subsystems.

STT-MRAM is fast enough to fit in as a new memory layer below the processor and the SRAM-based L1/L2 cache layers, and above DRAM and storage-level NAND flash layers, said Gary Bronner, vice president of research at Rambus Inc.

With good data retention and speed, and medium density, MRAM “may have advantages in the lower-level caches” of systems which have large amounts of on-chip SRAM, Bronner said, due in part to MRAM’s smaller cell size than six-transistor SRAM. While DRAM in the sub-20nm nodes faces cost issues as its moves to more complex capacitor structures, Bronner said that “thus far STT-MRAM) is not cheaper than DRAM.”

IBM researchers, which pioneered the spin-transfer torque approach to MRAM, are working on a high-performance MRAM technology which could be used in servers.

As of now, MRAM density is limited largely by the size of the transistors required to drive sufficient current to the magnetic tunnel junction (MTJ) to flip its magnetic orientation. Dan Edelstein, an IBM fellow working on MRAM development at IBM Research, said “it is a tall order for MRAM to replace DRAM. But MRAM could be used in system-level memory architectures and as an embedded memory technology.”

PVD and etch challenges

Edelstein, who was a key figure in developing copper interconnects at IBM some twenty years ago, said MRAM only requires a few extra mask layers to be integrated into the BEOL in logic. But there remain major challenges in improving the throughput of the PVD deposition steps required to deposit the complex material stack and to control the interfacial layers.

The PVD steps must deposit approximately 30 layers and control them to Angstrom-level precision. Deposition must occur under very low base pressure, and in oxygen- and water-vapor free environments. While tool vendors are working on productization of 300mm MRAM deposition tools, Edelstein said keeping particles under control and minimizing the maintenance and chamber cleaning are all challenging.

Etching the complex materials stack is even harder. Chemical RIE is not practical for MRAMs at this point, and using ion beam etching (IBE) presents challenges in terms of avoiding re-deposition of material sputtered off during the IBE etch steps for the high-aspect-ratio MTJs.

For the tool vendors, MRAMs present challenges as companies go from R&D to high-volume manufacturing, Edelstein said.

A Samsung MRAM researcher, Y.J. Song, briefly described IBE challenges during an IEDM presentation describing an embedded STT-MRAM with a respectable 8-Mbit density and a cell size of .0364 sq. micron. “We worked to optimize the contact etching,” using IBE etch during the patterning steps, he said. The short fail rate was reduced, while keeping the processing temperature at less than 350°C, Song said.

Samsung embedded an STT-MRAM module in the copper back end of the line (BEOL) of a 28nm logic process. (Source: Samsung presentation at IEDM 2016).

Many of the presentations at IEDM described improvements in key parameters, such as the tunnel magnetic resistance (TMR), cell size, data retention, and read error rates at high temperatures or low operating voltages.

An SK Hynix presentation described a 4-Gbit STT-MRAM optimized as a stand-alone, high-density memory. “There still are reliability issues for high-density MRAM memory,” said SK Hynix’s S.-W. Chung. The industry needs to boost the TMR “as high as possible” and work on improving the “not sufficiently long” retention times.

At high temperatures, error rates tend to rise, a concern in certain applications. And since devices are subjected to brief periods of high temperatures during reflow soldering, that issue must be dealt with as well, detailed by a Bosch presentation at IEDM.

Cleans and encapsulation important

Gouri Sankar Kar, who is coordinating the MRAM research program at the Imec consortium (Leuven, Belgium), said one challenge is to reduce the cell size and pitch without damaging the magnetic properties of the magnetic tunnel junction. For the 28nm logic node, embedded MRAM would be in the range of a 200nm pitch and 45nm critical dimensions (CDs). At the IEDM poster session, Imec presented an 8nm cell size STT-MRAM that could intersect the 10nm logic node, with the MRAM pitch in the 100nm range. GlobalFoundries, Micron, Qualcomm, Sony and TSMC are among the participants in the Imec MRAM effort.

Kar said in addition to the etch challenges, post-patterning treatment and the encapsulation liner can have a major impact on MTJ materials selection. “Some metals can be cleaned immediately, and some not. For the materials stack, patterning (litho and etch) and clean optimization are crucial.”

“Chemical etch (RIE) is not really possible at this stage. All the tool vendors are working on physical sputter etch (IBE) where they can limit damage. But I would say all the major tool vendors at this point have good tools,” Kar said.

To reach volume manufacturing, tool vendors need to improve the tool up-time and reduce the maintenance cycles. There is a “tail bits” relationship between the rate of bit failures and the health of the chambers that still needs improvement. “The cleanup steps after etching are very, very critical” to the overall effort to improving the cost effectiveness of MRAM, Kar said, adding that he is “very positive” about the future of MRAM technology.

A complete flow at AMAT

Applied Materials is among the equipment companies participating in the Imec program, with TEL and Canon-Anelva also heavily involved. Beyond that, Applied has developed a complete MRAM manufacturing flow at the company’s Dan Maydan Center in Santa Clara, and presented its cooperative work with Qualcomm on MRAM development at IEDM.

In an interview, Er-Xuan Ping, the Applied Materials managing director in charge of memory and materials technologies, said about 20 different layers, including about ten different materials, must be deposited to create the magnetic tunnel junctions. As recently as a few years ago, throughput of this materials stack was “extremely slow,” he said. But now Applied’s multi-cathode PVD tool, specially developed for MRAM deposition, can deposit 5 Angstrom films in just a few seconds. Throughput is approaching 20 wafers per hour.

Applied Materials “basically created a brand-new PVD chamber” for STT-MRAM, and he said the tool has a new e-chuck, optimized chamber walls and a multi-cathode design.

The MRAM-optimized PVD tool does not have an official name yet, and Ping said he refers to it as multi-cathode PVD. With MRAM requiring deposition of so many different metals and other materials, the Applied tool does not require the wafer to be moved in and out, increasing efficiency. The shape and structure of the chamber wall, Ping said, allow absorption of downstream plasma material so that it doesn’t come back as particles.

For etch, Applied has worked to create etching processes that result in very low bit failure rates, but at relatively relaxed pitches in the 130-200nm range. “We have developed new etch technologies so we don’t think etch will be a limiting factor. But etch is still challenging, especially for cells with 50nm and smaller cell sizes. We are still in unknown territory there,” said Ping.

Jürgen Langer, R&D manager at Singulus Technology (Frankfurt, Germany), said Singulus has developed a production-optimized PVD tool which can deposit “30 material layers in the Angstrom range. We can get 20 wafers per hour throughputs, so I would say this is not a beta tool, it is for production.”

Jürgen Langer, R&D manager, presented a poster on MRAM deposition from Singulus Technology (Frankfurt, Germany).

Where does it fit?

Once the production challenges of making MRAM are ironed out, the question remains: Where will MRAM fit in the systems of tomorrow?

Tom Coughlin, a data storage consultant based in Atascadero, Calif., said embedded MRAM “could have a very important effect for industrial and consumer devices. MRAM could be part of the memory cache layers, providing power advantages over other non-volatile devices.” And with its ability to power on and power off without expending energy, MRAM could reduce overall power consumption in smart phones, cutting in to the SRAM and NOR sectors.

“MRAM definitely has a niche, replacing some DRAM and SRAM. It may replace NOR. Flash will continue for mass storage, and then there is the 3D Crosspoint from Intel. I do believe MRAM has a solid basis for being part of that menagerie. We are almost in a Cambrian explosion in memory these days,” Coughlin said.

Directed Self Assembly Hot Topic at SPIE

Wednesday, February 25th, 2015

By Jeff Dorsch, contributing editor

At this week’s SPIE Advanced Lithography Symposium in San Jose, Calif., the hottest three-letter acronym is less EUV and more DSA, as in directed self-assembly.

Extreme-ultraviolet lithography continues to command much attention, yet this conference is awash in papers about DSA, which dominates the “Alternative Lithographic Technologies” track of technical sessions. The two-day poster sessions feature 15 posters about DSA. Thursday’s conference sessions include three separate sessions devoted to “DSA Design for Manufacturability” and one for “DSA Modeling.”

With semiconductor industry anxiety rising at the prospect of quadruple-patterning and the slow yet steady progress of EUV technology, directed self-assembly is being hailed and recognized as a way to simplify chip manufacturing at the low end of the nanoscale era.

Before the conference got under way, imec reported on making significant progress in DSA technology, specifically reducing the defectivity associated with the process. Working with Tokyo Electron Ltd. (TEL) and Merck, which acquired AZ Electronic Materials last year, imec has come up with a DSA solution for a via patterning process that they say is compatible with the 7-nanometer process node. The partners are targeting the manufacture of DRAMs using 193nm immersion scanners.

“Over the past few years, we have realized a reduction of DSA defectivity by a factor 10 every six months,” imec’s An Steegen said in a statement. “Together, with Merck and Tokyo Electron, providing state-of-the-art DSA materials and processing equipment, we are looking ahead at two different promising DSA processes that will further improve defectivity values in the coming months. Our processes show the potential to achieve single-digit defectivity values in the near future without any technical roadblocks lying ahead.”

Kurt Ronse of imec describes DSA as utilizing two polymers to get molecules to array in lines or spaces. The issue has been to avoid the creation of holes that don’t fit the guided pattern, resulting in defects.

“All the big [chip] companies are having their internal developments on DSA,” Ronse said at SPIE. “All the memory companies are interested; Micron is in our program.”

While DSA is being implemented with 193 immersion equipment at the outset, there is the possibility of working with EUV scanners in the future, according to Ronse, and imec has an extensive EUV research and development program, he noted.

DSA started to emerge as a technology of note at the 2011 SPIE Advanced Lithography conference, Ronse said, which resulted in imec initiating its program in the field. There has been a significant amount of progress in the past two years, he added.

The momentum behind DSA R&D led to the establishment of the 1st International Symposium on DSA, scheduled for October 26-27, 2015, in Leuven, Belgium. Partnering with imec on the conference are CEA-Leti, EIDEC, and Sematech.

DSA – it’s one TLA you’ll hear a lot about in the years to come.

Applied Materials Q4 Report

Friday, November 14th, 2014

By Jeff Dorsch, contributing editor

Applied Materials reported in a fourth quarter earnings call  that its long-pending merger with Tokyo Electron Ltd. may not close until the first quarter of 2015.

Gary Dickerson, Applied’s president and CEO, told analysts that the combination with TEL has just received unconditional approval from Germany’s competition authority. Without disclosing details, he added that the regulatory process is potentially pushing closing of the transaction into the new year.

Applied and TEL previously said that they expected to complete the mega-merger during the second half of calendar 2014. Shareholders of both companies have approved the transaction, leaving the process in the hands of antitrust regulators in several countries.

Last July, the two companies announced that the combined company will be called Eteris B.V.

Applied also reported today the financial results of its fiscal fourth quarter and fiscal year ended October 26. In Q4, Applied posted net income of $290 million on revenue of $2.26 billion, compared with the year-ago figures of $183 million in net income and revenue of $1.99 billion.

For the full year, Applied posted net income of $1.1 billion on revenue of $9.07 billion, compared with fiscal 2013’s net income of $256 million on revenue of $7.51 billion.

Applied had orders of $2.26 billion in the fourth quarter and of $9.65 billion in the fiscal year.

For its fiscal first quarter, the company is forecasting its net sales will be flat to up 5 percent from the fiscal fourth quarter.

Blog review December 16, 2013

Monday, December 16th, 2013

Randhir Thakur of Applied Materials wishes the transistor a happy 66th birthday, noting that the transistor is truly one of the most amazing technological innovations of all time! He says it’s estimated that more than 1200 quintillion transistors will be manufactured in 2015, making the transistor the most ubiquitous man-made device on the planet.

Phil Garrou writes that 3DIC memory, and therefore all of 2.5/3D technology, took one step closer to full commercialization last week with the High Bandwidth Memory HBM joint development announcement from AMD and Hynix at the RTI 3D ASIP meeting in Burlingame CA.

Zhihong Liu, Executive Chairman of ProPlus Design Solutions is celebrating 20 years of BSIM3v3 SPICE models. He notes that with continuous geometry down-scaling in CMOS devices, compact models became more complicated as they needed to cover more physical effects, such as gate tunneling current, shallow trench isolation (STI) stress and well proximity effect (WPE).

Applied Materials and Tokyo Electron held a media roundtable in Japan to discuss the merger of equals announced on September 24, 2013. Tetsuro Higashi, Chairman, President and CEO of Tokyo Electron, who will become Chairman of the new company, and Mike Splinter, Executive Chairman of Applied Materials, who will serve as Vice-Chairman, addressed the audience of more than 20 members of the Japanese media. Kevin Winston blogs about the event.

Pete Singer is freshly back from the International Electron Devices Meeting (IEDM). “A dream for the device engineer could be a nightmare for a process integration engineer,” said Frederic Boeuf of ST Microelectronics in the opening talk. That seemed to be echoed throughout the conference, where the potential of new devices such as tunnel FETs or materials such as graphene were always tempered with a dose of reality that materials had to be deposited, patterned, annealed to create devices, and those devices had to be connected.