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Vital Control in Fab Materials Supply-Chains – Part 2

Thursday, February 16th, 2017

By Ed Korczynski, Sr. Technical Editor

As detailed in Part 1 of this article published last month by SemiMD, the inaugural Critical Materials Council (CMC) Conference happened May 5-6 in Hillsboro, Oregon. Held just after the yearly private CMC meeting, the public CMC Conference provides a forum for the pre-competitive exchange of information to control the supply-chain of critical materials needed to run high-volume manufacturing (HVM) in IC fabs. The next CMC Conference will happen May 11-12 in Dallas, Texas.

At the end of the 2016 conference, a panel discussion moderated by Ed Korczynski was recorded and transcribed. The following is Part 2 of the conversation between the following industry experts:

  • Jean-Marc Girard, CTO and Director of R&D, Air Liquide Advanced Materials,
  • Jeff Hemphill, Staff Materials R&D Engineer, Intel Corporation,
  • Jonas Sundqvist, Sr. Scientist, Fraunhofer IKTS; and co-chair of ALD Conference, and
  • John Smythe, Distinguished Member of Technical Staff, Micron Technology.

FIGURE 1: 2016 CMC Conference expert panelists (from left to right) John Smyth, Jonas Sundqvist, Jeff Hemphill, and Jean-Marc Girard. (Source: TECHCET CA)

KORCZYNSKI:  We heard from David Thompson [EDITOR’S NOTE:  Director of Process Chemistry, Applied Materials presented on “Agony in New Material Introductions -  Minimizing and Correlating Variabilities”] today on what we must control, and he gave an example of a so-called trace-contaminant that was essential for the process performance of a precursor, where the trace compound helped prevent particles from flaking off chamber walls. Do we need to specify our contaminants?

GIRARD:  Yes. To David’s point this morning, every molecule is different. Some are very tolerant due to the molecular process associated with it, and some are not. I’ll give you an example of a cobalt material that’s been talked about, where it can be run in production at perhaps 95% in terms of assay, provided that one specific contaminant is less than a couple of parts-per-million. So it’s a combination of both, it’s not assay OR a specification of impurities. It’s a matter of specifying the trace components that really matter when you reach the point that the data you gather gives you that understanding, and obviously an assay within control limits.

HEMPHILL:  Talking about whether we’re over-specifying or not, the emphasis is not about putting the right number on known parameters like assay that are obvious to measure, the emphasis is on identifying and understanding what makes up the rest of it and in a sense trying over-specify that. You identify through mass-spectrometry and other techniques that some fraction of a percent is primarily say five different species, it’s finding out how to individually monitor and track and control those as separate parameters. So from a specification point of view what we want is not necessarily the lowest possible numbers, but it’s expanding how many things we’re looking at so that we’re capturing everything that’s there.

KORCZYNSKI:  Is that something that you’re starting to push out to your suppliers?

HEMPHILL:  Yes. It depends on the application we’re talking about, but we go into it with the assumption that just assay will not be enough. Whether a single molecule or a blend of things is supposed to be there, we know that just having those be controlled by specification will not be sufficient. We go under the assumption that we are going to identify what makes up the remaining part of the profile, and those components are going to need to be controlled as well.

KORCZYNSKI:  Is that something that has changed by node? Back when things were simpler say at 45nm and larger, were these aspects of processing that we could safely ignore as ‘noise’ but are now important ‘signals’?

HEMPHILL:  Yes, we certainly didn’t pay as close attention just a couple of generations ago.

KORCZYNSKI:  That seems to lead us to questions about single-sources versus dual-sourcing. There are many good reasons to do both, but not simultaneously. However, it seems that because of all of the challenges we’re heard about over the last day-and-a-half of this conference it creates greater burden on the suppliers, and for critical materials the fabs are moving toward more single-sourcing over time.

SMYTHE:  I think that it comes down to more of a concern over geographic risk. I’ll buy from one entity if that entity has more than one geographic location for the supply, so that I’m not exposed to a single ‘Act of God’ or a ‘random statistical occurrence of global warming.’ So for example I  need to ask if a supplier has a place in the US and a place in France that makes the same thing, so that if something bad happens in one location it can still be sourced? Or do you have an alternate-supply agreement that if you can’t supply it you have an agreement with Company-X to supply it so that you still have control? You can’t come to a Micron and say we want to make sure that we get at minimum 25% no matter what, because what typically happens with second-sourcing is Company-A gets 75% of the business while Company-B gets 25%. There are a lot of reasons that that doesn’t work so well, so people may have an impression that there’s a movement toward single-source but it’s ‘single flexible-source.’

HEMPHILL:  There are a lot of benefits of dual- or multiple-sourcing. The commercial benefits of competition can be positive and we’re for it when it works. The risk is that as things are progressing and we’re getting more sensitive to differences in materials it’s getting harder to maintain that. We have seen situations where historically we were successful with dual-sourcing a raw material coming from two different suppliers or even a single supplier using two different manufacturing lines and everything was fine and qualified and we could alternate sources invisibly. However, as our sensitivity has grown over time we can start to detect differences.

So the concept of being ‘copy-exactly’ that we use in our factories, we really need production lines to do that, and if we’re talking about two different companies producing the same material then we’re not going to get them to be copy-exactly. When that results in enough of a variation in the material that we can detect it in the factory then we cannot rely upon two sources. Our preference would be one company that maintains multiple production sites that are designed to be exactly the same, then we have a high degree of confidence that they will be able to produce the same material.

FIGURE 2: Jean-Marc Girard, Distinguished Member of Technical Staff of Micron Technology, provided the supplier perspective. (Source: SEMI)

GIRARD:  I can give you a supplier perspective on that. We are seeing very different policies from different customers, to the point that we’re seeing an increase in the number of customers doing single-sourcing with us, provided we can show the ability to maintain business continuity in case of a problem. I think that the industry became mature after the tragic earthquake and tsunami in Japan in 2011 with greater understanding of what business continuity means. We have the same discussions with our own suppliers, who may say that they have a dedicated reactor for a certain product with another backup reactor with a certain capacity on the same site, and we ask what happens if the plant goes on strike or there’s a fire there?

A situation where you might think the supply was stable involved silane in the United States. There are two large silane plants in the United States that are very far apart from each other and many Asian manufacturers dependent upon them. When the U.S. harbors went on strike for a long time there was no way that material could ship out of the U.S. customers. So, yes there were two plants but in such an event you wouldn’t have global supply. So there is no one way to manage our supply lines and we need to have conversations with our customers to discuss the risks. How much time would it take to rebuild a supply-chain source with someone else? If you can get that sort of constructive discussion going then customers are usually open to single-sourcing. One regional aspect is that Asian customers tend to favor dual-sourcing more, but that can lead to IP problems.

[DISCLOSURE:  Ed Korczynski is co-chair of the CMC Conference, and Marketing Director of TECHCET CA the advisory services firm that administers the Critical Materials Council (CMC).]

—E.K.

Vital Control in Fab Materials Supply-Chains

Wednesday, January 25th, 2017

By Ed Korczynski, Sr. Technical Editor

The inaugural Critical Materials Council (CMC) Conference, co-sponsored by Solid State Technology, happened May 5-6 in Hillsboro, Oregon. Held just after the yearly private CMC meeting, the public CMC Conference provides a forum for the pre-competitive exchange of information to control the supply-chain of critical materials needed to run high-volume manufacturing (HVM) in IC fabs. The next CMC Conference will happen May 11-12 in Dallas, Texas.

At the end of the 2016 conference, a panel discussion moderated by Ed Korczynski was recorded and transcribed. The following is an edited excerpt of the conversation between the following industry experts:

  • Jean-Marc Girard, CTO and Director of R&D, Air Liquide Advanced Materials,
  • Jonas Sundqvist, Sr. Scientist, Fraunhofer IKTS; and co-chair of ALD Conference, and
  • John Smythe, Distinguished Member of Technical Staff, Micron Technology.

KORCZYNSKI:  Let’s start with specifications: over-specifying, and under-specifying. Do we have the right methodologies to be able to estimate the approximate ‘ball-park’ range that the impurities need to be in?

GIRARD:  For determining the specifications, to some extent it doesn’t matter because we are out of the world of specs, where what matters is the control-limits. To Tim Hendry’s point in the Keynote yesterday [EDITOR’S NOTE:  Tim G. Hendrey, vice president of the Technology and Manufacturing Group and director of Fab Materials at Intel Corporation provided a conference keynote address on “Process Control Methods for Advanced Materials”], what was really interesting is instead of the common belief that we should start by supplying the product with the lowest possible variability, instead we should try to explore the window in which the product is working. So getting 10 containers from the same batch and introducing deliberate variability so that you know the process space in which you can play. That is the most important information to be able to reach the most reasonable and data-driven numbers to specify control limits. A lot of specs in the past were primarily determined by marketing decisions instead of data.

FIGURE 1: Jonas Sundqvist, Sr. Scientist of Fraunhofer IKTS, discusses collaboration with industry on application-specific ALD R&D. (Source: TECHCET CA)

SUNDQVIST:  Like the first introduction of what were called “super-clean” ALD precursors for the original MIS DRAM capacitors, Samsung used about 10nm of hafnium-aluminate and it would not matter if there was slight contamination in the precursors because you were not trying to control for a specific high-k phase. Whereas now you are doping very precisely and you have already scaled thinness so over time the specification for high-k precursors has become more important.

SMYTHE:  I think it comes down to the premise that when you are doing vapor transport through a bubbler that some would argue that that’s like a distillation column. So it’s a matter of thinking about what is transporting and what isn’t. In some cases the contaminant you’re concerned about is in the ampule but it never makes it to the process chamber, or the act of oxidizing destroys it as a volatile byproduct. So I think the bigger issue is change-management not necessarily the exact specification. You must know what you have, and agree that a single adjustment to improve the productivity of chemical synthesis requires that ‘fingerprinting’ must be done to show the same results. The argument is that you do not accept “less-than” as part of a specification, you only accept what it is.

AUDIENCE QUESTION:  The systems in which these precursors are used also have ‘memory’ based on the prior reactions in the chamber and byproducts that get absorbed on walls. When these byproducts come out in subsequent processing they can alter conditions so that you’re actually running in CVD-mode instead of ALD-mode. Chamber effects can wash-out a lot of value of having really pure chemicals moving through a delivery system into a chamber and picking up contaminants that you spent a whole lot of money taking out at the point of delivery. What do you think about that?

GIRARD:  Well, this is a ‘crisis!’ When something like this starts to happen in a fab or even during the development cycles, you can’t prioritize resources and approaches you just have to do everything. Sometimes it’s the tool, sometimes it’s the chemical, sometimes it’s the interaction of the two, sometimes it’s back-streaming from the vacuum sub-system…there are so many ways that things can go wrong. Certainly you have to clear up the chemistry part as early as possible.

SUNDQVIST:  We work with zirconium precursors for ALD, and you can develop a precursor that gives you a very pure ALD process that really works like an ALD process should. However, you can still use the TEMA-Zr precursor, that in processing has a CVD component which you can use that to gain throughput. So you can have a really good ALD precursor that gives low particle-counts and good process stability and ideal thermal processing range, but the growth rate goes down by 20% so you’re not very popular in the fab. Many things change when you make an ‘improved’ molecule to perfect the process, and sometime you want to use an imperfect part of the process.

FIGURE 2: John Smythe, Distinguished Member of Technical Staff of Micron Technology, explains approaches to controlling materials all the way to point-of-use. (Source: TECHCET CA)

SMYTHE:  What we’re doing a lot more these days is doing chamber finger-printing, where we’re putting a quad-filtered mass-spec on each chamber—not a cheap little RGA, but real analytical-grade—and it’s been enlightening. If you look at your chemistry moving through a delivery line using something like the Schrødenger software, it’s not a big deal to see that you can use the mass spec to see some synthesis happening in the line. We joke and call it ‘point of use synthesis’ but it’s not very funny. We are used to having spare delivery lines built-in so we can install tools to try to gain insights to prevent what we’ve been talking about.

KORCZYNSKI:  John, since Micron has fabs in Lehi and fabs in Singapore and other places, while they do run different product loads, do you have to worry about how long it takes things to travel on a slow boat to Singapore? Do you have to stockpile things more strategically these days, and does that effect your receiving department?

SMYTHE:  What we really need are a few good ocean-going hydrofoil ships! The most complete answer is we first identify which things need ‘batch-qual’ so if we do a batch-qual in Virginia and know that material is going to Taiwan that we have confidence it will pass batch-qual in Taiwan. There are certain materials that we require information on which synthesis batch, which production batch, and sometimes which bottling batch. Sometimes you take a yield hit because you didn’t have the right vision, and then you institute batch qual.

I think most of you are familiar with the concept of ‘ship-to-stock,’ when you have enough good statistical history and a good change management process with the supplier then you can do ship-to-stock and that reduces the batch-qual overhead. On a case by case basis you have to figure out how difficult that is. A small story I can tell is that with Block Co-Polymer (BCP) self-assembly we found one particular element that in concentration above 5 ppm prevented the poly-styrene from self-assembling in the same way, whereas other metal trace contaminants could be a hundred times higher and have no effect on the process. So this gets back to some of our earlier discussion that it’s not enough to know that your trace elements are below some level. Tell me the exact atoms and the exact counts and then we’ll talk about using them. The BCP R&D taught us that in some situations just changing from one batch to the next could increase defects a thousands times. So we will see a bigger push to counting atoms.

[DISCLOSURE:  Ed Korczynski is co-chair of the CMC Conference, and Marketing Director of TECHCET CA the advisory services firm that administers the Critical Materials Council (CMC).]

—E.K.

Fab Facilities Data and Defectivity

Monday, August 1st, 2016

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By Ed Korczynski, Sr. Technical Editor

In-the-know attendees at SEMICON West at a Thursday morning working breakfast heard from executives representing the world’s leading memory fabs discuss manufacturing challenges at the 4th annual Entegris Yield Forum. Among the excellent presenters was Norm Armour, managing director worldwide facilities and corporate EHSS of Micron. Armour has been responsible for some of the most famous fabs in the world, including the Malta, New York logic fab of GlobalFoundries, and AMD’s Fab25 in Austin, Texas. He discussed how facilities systems effect yield and parametric control in the fab.

Just recently, his organization within Micron broke records working with M&W on the new flagship Fab 10X in Singapore—now running 3D-NAND—by going from ground-breaking to first-tool-in in less than 12 months, followed by over 400 tools installed in 3 months. “The devil is in the details across the board, especially for 20nm and below,” declared Armour. “Fabs are delicate ecosystems. I’ll give a few examples from a high-volume fab of things that you would never expect to see, of component-level failures that caused major yield crashes.”

Ultra-Pure Water (UPW)

Ultra-Pure Water (UPW) is critical for IC fab processes including cleaning, etching, CMP, and immersion lithography, and contamination specs are now at the part-per-billion (ppb) or part-per-trillion (ppt) levels. Use of online monitoring is mandatory to mitigate risk of contamination. International Technology Roadmap for Semiconductors (ITRS) guidelines for UPW quality (minimum acceptable standard) include the following critical parameters:

  • Resistivity @ 25C >18.0 Mohm-cm,
  • TOC <1.0 ppb,
  • Particles/ml < 0.3 @ 0.05 um, and
  • Bacteria by culture 1000 ml <1.

In one case associated with a gate cleaning tool, elevated levels of zinc were detected with lots that had passed through one particular tool for a variation on a classic SC1 wet clean. High-purity chemistries were eliminated as sources based on analytical testing, so the root-cause analysis shifted to to the UPW system as a possible source. Then statistical analysis could show a positive correlation between UPW supply lines equipped with pressure regulators and the zinc exposure. The pressure regulator vendor confirmed use of zinc-oxide and zinc-stearate as part of the assembly process of the pressure regulator. “It was really a curing agent for an elastomer diaphragm that caused the contamination of multiple lots,” confided Armour.

UPW pressure regulators are just one of many components used in facilities builds that can significantly degrade fab yield. It is critical to implement a rigorous component testing and qualification process prior to component installation and widespread use. “Don’t take anything for granted,” advised Armour. “Things like UPW regulators have a first-order impact upon yield and they need to be characterized carefully, especially during new fab construction and fit up.”

Photoresist filtration

Photoresist filtration has always been important to ensure high yield in manufacturing, but it has become ultra-critical for lithography at the 20nm node and below. Dependable filtration is particularly important because industry lacks in-line monitoring technology capable of detecting particles in the range below ~40nm.

Micron tried using filters with 50nm pore diameters for a 20nm node process…and saw excessive yield losses along with extreme yield variability. “We characterized pressure-drop as a function of flow-rate, and looked at various filter performances for both 20nm and 40nm particles,” explained Armour. “We implemented a new filter, and lo and behold saw a step function increase in our yields. Defect densities dropped dramatically.” Tracking the yields over time showed that the variability was significantly reduced around the higher yield-entitlement level.

Airborne Molecular Contamination (AMC)

Airborne Molecular Contamination (AMC) is ‘public enemy number one’ in 20nm-node and below fabs around the world. “In one case there were forrest fires in Sumatra and the smoke was going into the atmosphere and actually went into our air intakes in a high volume fab in Taiwan thousands of miles away, and we saw a spike in hydrogen-sulfide,” confided Armour. “It increased our copper CMP defects, due to copper migration. After we installed higher-quality AMC filters for the make-up air units we saw dramatic improvement in copper defects. So what is most important is that you have real-time on-line monitoring of AMC levels.”

Building collaborative relationships with vendors is critical for troubleshooting component issues and improving component quality. “Partnering with suppliers like Entegris is absolutely essential,” continued Armour. “On AMCs for example, we have had a very close partnership that developed out of a team working together at our Inotera fab in Taiwan. There are thousands of important technologies that we need to leverage now to guarantee high yields in leading-node fabs.” The Figure shows just some of the AMCs that must be monitored in real-time.

Big Data

The only way to manage all of this complexity is with “Big Data” and in addition to primary process parameter that must be tracked there are many essential facilities inputs to analytics:

  • Environmental Parameters – temperature, humidity, pressure, particle count, AMCs, etc.
  • Equipment Parameters – run state, motor current, vibration, valve position, etc.
  • Effluent Parameters – cooling water, vacuum, UPW, chemicals, slurries, gases, etc.

“Conventional wisdom is that process tools create 90% of your defect density loss, but that’s changing toward facilities now,” said Armour. “So why not apply the same methodologies within facilities that we do in the fab?” SPC is after-the-fact reactive, while APC is real-time fault detection on input variables, including such parameters as vibration or flow-rate of a pump.

“Never enough data,” enthused Armour. “In terms of monitoring input variables, we do this through the PLCs and basically use SCADA to do the fault-detection interdiction on the critical input variables. This has been proven to be highly effective, providing a lot of protection, and letting me sleep better at night.”

Micron also uses these data to provide site-to-site comparisons. “We basically drive our laggard sites to meet our world-class sites in terms of reducing variation on facility input variables,” explained Armour. “We’re improving our forecasting as a result of this capability, and ultimately protecting our fab yields. Again, the last thing a fab manager wants to see is facilities causing yield loss and variation.”

—E.K.

Mentor Graphics U2U Meeting April 26 in Santa Clara

Monday, April 11th, 2016

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Mentor Graphics’ User2User meeting will be held in Santa Clara on April 26, 2016. The meeting is a highly interactive, in-depth technical conference focused on real world experiences using Mentor tools to design leading-edge products.

Admission and parking for User2User is free and includes all technical sessions, lunch and a networking reception at the end of the day. Interested parties can register on-line in advance.

Wally Rhines, Chairman and CEO of Mentor Graphics, will kick things off at 9:00am with a keynote talk on “Merger Mania.“ Wally notes that in 2015, the transaction value of semiconductor mergers was at an all-time historic high.  What is much more remarkable is that the average size of the merging companies is five times as large as in the past five years, he said. This major change in the structure of the semiconductor industry suggests that there will be changes that affect everything from how we define and design products to how efficiently we develop and manufacture them. Dr. Rhines will examine the data and provide conclusions and predictions.

He will be followed by another keynote talk at 10:00 by Zach Shelby, VP of Marketing for the Internet of Things at ARM. Zach was co-founder of Sensinode, where he was CEO, CTO and Chief Nerd for the ground-breaking company before its acquisition by ARM. Before starting Sensinode, Zach led wireless networking research at the Centre for Wireless Communications and at the Technical Research Center of Finland.

After user sessions and lunch, a panel will convene at 1:00pm to address the topic “Ripple or Tidal Wave: What’s driving the next wave of innovation and semiconductor growth?” Technology innovation was once fueled by the personal computer, communications, and mobile devices. Large capital investment and startup funding was rewarded with market growth and increased silicon shipments. Things are certainly consolidating, perhaps slowing down in the semiconductor market, so what’s going to drive the next wave of growth?  What types of designs will be staffed and funded? Is it IoT?  Wearables?  Automotive?  Experts will address these and other questions and examine what is driving growth and what innovation is yet to come.

Attendees can pick from nine technical tracks focused on AMS Verification, Calibre I and II, Emulation, Functional Verification, High Speed, IC Digital Implementation, PCB Flow, and Silicon Test & Yield Solutions. You’ll hear cases studies directly from users and also updates from Mentor Graphics experts.

These user sessions will be held at 11:10-12:00am, 2:00-2:50pm and 3:10-5:00pm.

A few of the highlights:

  • Oracle’s use of advanced fill techniques for improving manufacturing yield
  • How Xilinx built a custom ESD verification methodology on the Calibre platform
  • Qualcomm used emulation for better RTL design exploration for power, leading to more accurate power analysis and sign-off at the gate level
  • Micron’s experience with emulation, a full environment for debug of SSD controller designs, plus future plans for emulation
  • Microsoft use of portable stimulus to increase productivity, automate the creation of high-quality stimulus, and increase design quality
  • Formal verification at MicroSemi to create a rigorous, pre-code check-in review process that prevents bugs from infecting the master RTL
  • A methodology for modeling, simulation of highly integrated multi-die package designs at SanDisk
  • How Samsung and nVidia use new Automatic RTL Floorplanning capabilities on their advanced SoC designs
  • Structure test at AMD: traditional ATPG and Cell-Aware ATPG flows, as well as verification flows and enhancements

Other users presenting include experts from Towerjazz, Broadcom, GLOBALFOUNDRIES, Silicon Creations, MaxLinear, Silicon Labs, Marvell, HiSilicon, Qualcomm, Soft Machines, Agilent, Samtec, Honewell, ST Microelectronics, SHLC, ViaSat, Optimum, NXP, ON Semiconductor and MCD.

The day winds up with a closing session and networking reception from 5:00-6:00pm.

Registration is from 8:00-9:00am in the morning.

Many Mixes to Match Litho Apps

Thursday, March 3rd, 2016

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By Ed Korczynski, Sr. Technical Editor

“Mix and Match” has long been a mantra for lithographers in the deep-sub-wavelength era of IC device manufacturing. In general, forming patterns with resolution at minimum pitch as small as 1/4 the wavelength of light can be done using off-axis illumination (OAI) through reticle enhancement techniques (RET) on masks, using optical proximity correction (OPC) perhaps derived from inverse lithography technology (ILT). Lithographers can form 40-45nm wide lines and spaces at the same half-pitch using 193nm light (from ArF lasers) in a single exposure.

Figure 1 shows that application-specific tri-layer photoresists are used to reach the minimum resolution of 193nm-immersion (193i) steppers in a single exposure. Tighter half-pitch features can be created using all manner of multi-patterning processes, including Litho-Etch-Litho-Etch (LELE or LE2) using two masks for a single layer or Self-Aligned Double Patterning (SADP) using sidewall spacers to accomplish pitch-splitting. SADP has been used in high volume manufacturing (HVM) of logic and memory ICs for many years now, and Self-Aligned Quadruple Patterning (SAQP) has been used in HVM by at least one leading memory fab.

Fig.1: Basic tri-layer resist (TLR) technology uses thin Photoresist over silicon-containing Hard-Mask over Spin-On Carbon (SOC), for patterning critical layers of advanced ICs. (Source: Brewer Science)

Next-Generation Lithography (NGL) generally refers to any post-optical technology with at least some unique niche patterning capability of interest to IC fabs:  Extreme Ultra-Violet (EUV), Directed Self-Assembly (DSA), and Nano-Imprint Lithography (NIL). Though proponents of each NGL have dutifully shown capabilities for targeted mask layers for logic or memory, the capabilities of ArF dry and immersion (ArFi) scanners to process >250 wafers/hour with high uptime dominates the economics of HVM lithography.

The world’s leading lithographers gather each year in San Jose, California at SPIE’s Advanced Lithography conference to discuss how to extend optical lithography. So of all the NGL technologies, which will win out in the end?

It is looking most likely that the answer is “all of the above.” EUV and NIL could be used for single layers. For other unique patterning application, ArF/ArFi steppers will be used to create a basic grid/template which will be cut/trimmed using one of the available NGL. Each mask layer in an advanced fab will need application-specific patterning integration, and one of the rare commonalities between all integrated litho modules is the overwhelming need to improve pattern overlay performance.

Naga Chandrasekaran, Micron Corp. vice president of Process R&D, provided a fantastic overview of the patterning requirements for advanced memory chips in a presentation during Nikon’s LithoVision technical symposium held February 21st in San Jose, California prior to the start of SPIE-AL. While resolution improvements are always desired, in the mix-and-match era the greatest challenges involve pattern overlay issues. “In high volume manufacturing, every nanometer variation translates into yield loss, so what is the best overlay that we can deliver as a holistic solution not just considering stepper resolution?” asks Chandrasekaran. “We should talk about cost per nanometer overlay improvement.”

Extreme Ultra-Violet (EUV)

As touted by ASML at SPIE-AL, the brightness and stability and availability of tin-plasma EUV sources continues to improve to 200W in the lab “for one hour, with full dose control,” according to Michael Lercel, ASML’s director of strategic marketing. ASML’s new TWINSCAN NXE:3350B EUVL scanners are now being shipped with 125W power sources, and Intel and Samsung Electronics reported run their EUV power sources at 80W over extended periods.

During Nikon’s LithoVision event, Mark Phillips, Intel Fellow and Director of Lithography Technology Development for Logic, summarized recent progress of EUVL technology:  ~500 wafers-per-day is now standard, and ~1000 wafer-per-day can sometimes happen. However, since grids can be made with ArFi for 1/3 the cost of EUVL even assuming best productivity for the latter, ArFi multi-patterning will continue to be used for most layers. “Resolution is not the only challenge,” reminded Phillips. “Total edge-placement-error in patterning is the biggest challenge to device scaling, and this limit comes before the device physics limit.”

Directed Self-Assembly (DSA)

DSA seems most suited for patterning the periodic 2D arrays used in memory chips such as DRAMs. “Virtual fabrication using directed self-assembly for process optimization in a 14nm DRAM node” was the title of a presentation at SPIE-AL by researchers from Coventor, in which DSA compared favorably to SAQP.

Imec presented electrical results of DSA-formed vias, providing insight on DSA processing variations altering device results. In an exclusive interview with Solid State Technology and SemiMD, imec’s Advanced Patterning Department Director Greg McIntyre reminds us that DSA could save one mask in the patterning of vias which can all be combined into doublets/triplets, since two masks would otherwise be needed to use 193i to do LELE for such a via array. “There have been a lot of patterning tricks developed over the last few years to be able to reduce variability another few nanometers. So all sorts of self-alignments.”

While DSA can be used for shrinking vias that are not doubled/tripled, there are commercially proven spin-on shrink materials that cost much less to use as shown by Kaveri Jain and Scott Light from Micron in their SPIE-AL presentation, “Fundamental characterization of shrink techniques on negative-tone development based dense contact holes.” Chemical shrink processes primarily require control over times, temperatures, and ambients inside a litho track tool to be able repeatably shrink contact hole diameters by 15-25 nm.

Nano-Imprint Litho (NIL)

For advanced IC fab applications, the many different options for NIL technology have been narrowed to just one for IC HVM. The step-and-pattern technology that had been developed and trademarked as “Jet and Flash Imprint Lithography” or “J-FIL” by, has been commercialized for HVM by Canon NanoTechnologies, formerly known as Molecular Imprints. Canon shows improvements in the NIL mask-replication process, since each production mask will need to be replicated from a written master. To use NIL in HVM, mask image placement errors from replication will have to be reduced to ~1nm., while the currently available replication tool is reportedly capable of 2-3nm (3 sigma).

Figure 2 shows normalized costs modeled to produce 15nm half-pitch lines/spaces for different lithography technologies, assuming 125 wph for a single EUV stepper and 60 wph for a cluster of 4 NIL tools. Key to throughput is fast filling of the 26mmx33mm mold nano-cavities by the liquid resist, and proper jetting of resist drops over a thin adhesion layer enables filling times less than 1 second.

Fig.2: Relative estimated costs to pattern 15nm half-pitch lines/spaces for different lithography technologies, assuming 125 wph for a single EUV stepper and 60 wph for a cluster of 4 NIL tools. (Source: Canon)

Researchers from Toshiba and SK Hynix described evaluation results of a long-run defect test of NIL using the Canon FPA-1100 NZ2 pilot production tool, capable of 10 wafers per hour and 8nm overlay, in a presentation at SPIE-AL titled, “NIL defect performance toward high-volume mass production.” The team categorized defects that must be minimized into fundamentally different categories—template, non-filling, separation-related, and pattern collapse—and determined parallel paths to defect reduction to allow for using NIL in HVM of memory chips with <20nm half-pitch features.

—E.K.

Solid State Watch: November 13-19, 2015

Friday, November 20th, 2015
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Solid State Watch: July 31-August 6, 2015

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Solid State Watch: July 10-16, 2015

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CoorsTek Increases its Business with Covalent Acquisition, Organic Growth

Tuesday, July 14th, 2015

By Jeff Dorsch, Contributing Editor

CoorsTek made one of the biggest acquisitions of its century-long history late last year in purchasing Covalent Materials, formerly known as Toshiba Ceramics.

Jonathan Coors, CEO of the company’s Semiconductor and Medical Group, said Tuesday the Covalent acquisition was “really strategic for us. It enhanced the company as a whole.”

CoorsTek’s Japan market share in engineered ceramics  was “relatively small prior to Covalent,” Coors noted. Covalent broadened CoorsTek’s product portfolio in carbons, quartz, and silicon products, according to Coors.

CoorsTek plans to pursue both organic growth in its business and acquisition opportunities as they present themselves, the CoorsTek executive said.

Asked whether privately held CoorsTek may pursue a public offering, Coors said, “We enjoy being private.” That status offers some “regulatory ease,” he noted.

As a private company, CoorsTek is able to engage in a “long-term thought process, while maintaining focus on quarterly performance,” Coors added.

CoorsTek also provides orthopedic implants, such as hip and knee replacements. Medical products present “a demand on quality that is as high (as semiconductor products), if not higher,” Coors noted. There is a “similar supply chain” in the two product lines, he stated.

Coors and other CoorsTek executives are meeting this week with customers to learn “where the market is heading,” Coors said. Such information gleaned at SEMICON West 2015 can point to “the next generation of growth,” he said.

Micron Technology, in the news this week on reports of a rumored takeover bid by Tsinghua Unigroup, is a customer of CoorsTek, according to Coors.

Solid State Watch: March 20-26, 2015

Thursday, March 26th, 2015
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