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Edge Placement Error Control in Multi-Patterning

Thursday, March 2nd, 2017

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By Ed Korczynski, Sr. Technical Editor

SPIE Advanced Lithography remains the technical conference where the leading edge of minimum resolution patterning is explored, even though photolithography is now only part of the story. Leading OEMs continue to impress the industry with more productive ArFi steppers, but the photoresist suppliers and the purveyors of vacuum deposition and etch tools now provide most of the new value-add. Tri-layer-resist (TLR) stacks, specialty hard-masks and anti-reflective coatings (ARC), and complex thin-film depositions and etches all combine to create application-specific lithography solutions tuned to each critical mask.

Multi-patterning using complementary lithography—using argon-fluoride immersion (ArFi) steppers to pattern 1D line arrays plus extreme ultra-violet (EUV) tools to do line cuts—is under development at all leading edge fabs today. Figure 1 shows that edge placement error (EPE) in lines, cut layers, and vias/contacts between two orthogonal patterned layers can result in shorts and opens. Consequently, EPE control is critical for yield within any multi-patterning process flow, including litho-etch-litho-etch (LELE), self-aligned double-patterning (SADP) and self-aligned quadruple-patterning (SAQP).

Fig.1: Plan view schematic of 10nm half-pitch vertical lines overlaid with lower horizontal lines, showing the potential for edge-placement error (EPE). (Source: Y. Borodovsky, SPIE)

Happening the day before the official start of SPIE-AL, Nikon’s LithoVision event featured a talk by Intel Fellow and director of lithography hardware solutions Mark Phillips on the big picture of how the industry may continue to pattern smaller IC device features. Regarding the timing of Intel’s planned use of EUV litho technology, Phillips re-iterated that, “It’s highly desirable for the 7nm node, but we’ll only use it when it’s ready. However, EUVL will remain expensive even at full productivity, so 193i and multi-patterning will continue to be used. In particular we’ll need continued improvement in the 193i tools to meet overlay.”

Yuichi Shibazaki— Nikon Fellow and the main architect of the current generation of Nikon steppers—explained that the current generation of 193i steppers, featuring throughputs of >200 wafers per hour, have already been optimized to the point of diminishing returns. “In order to improve a small amount of performance it requires a lot of expense. So just improving tool performance may not decrease chip costs.” Nikon’s latest productivity offering is a converted alignment station as a stand-alone tool, intended to measure every product wafer before lithography to allow for feed-forward tuning of any stepper; cost and cost-of-ownership may be disclosed after the first beta-site tool reaches a customer by the end of this year.

“The 193 immersion technology continues to make steady progress, but there are not as many new game-changing developments,” confided Michael Lercel, Director of Strategic Marketing for ASML in an exclusive interview with SemiMD. “A major theme of several SPIE papers is on EPE, which traditionally we looked at as dependent upon CD and overlay. Now we’re looking at EPE in patterning more holistically, with need to control the complexity with different error-variables. The more information we can get the more we can control.”

At LithoVision this year, John Sturtevant—SPIE Fellow, and director of RET product development in the Design to Silicon Division at Mentor Graphics—discussed the challenges of controlling variability in multi-layer patterning. “A key challenge is predicting and then mitigating total EPE control,” reminded Sturtevant. “We’ve always paid attention to it, but the budgets that are available today are smaller than ever. Edge-placement is very important ” At the leading edge, there are multiple steps within the basic litho flow that induce proximity/local-neighbor effects which must be accounted for in EDA:  mask making, photoresist exposure, post-exposure bake (PEB), pattern development, and CD-SEM inspection (wherein there is non-zero resist shrinkage).

Due to the inherent physics of EUV lithography, as well as the atomic-scale non-uniformities in the reflective mirrors focusing onto the wafer, EUV exposure tools show significant variation in exposure uniformities. “For any given slit position there can be significant differences between tools. In practice we have used a single model of OPC for all slit locations in all scanners in the fab, and that paradigm may have to change,” said Sturtevant. “It’s possible that because the variation across the scanner is as much as the variation across the slit, it could mean we’ll need scanner-specific cross-slit computational lithography.” More than 3nm variation has been seen across 4 EUVL steppers, and the possible need for tool-specific optical proximity correction (OPC) and source-mask optimization (SMO) would be horrible for managing masks in HVM.

Thin Films Extend Patterning Resolution

Applied Materials has led the industry in thin-film depositions and etches for decades, and the company’s production proven processing platforms are being used more and more to extend the resolution of lithography. For SADP and SAQP MP, there are tunable unit-processes established for sidewall-spacer depositions, and chemical downstream etching chambers for mandrel pull with extreme material selectivity. CVD of dielectric and metallic hard-masks when combined with highly anisotropic plasma etching allows for device-specific and mask-specific pattern transfers that can reduce the line width/edge roughness (LWR/LER) originally present in the photoresist. Figure 2 from the SPIE-AL presentation “Impact of Materials Engineering on Edge Placement Error” by Regina Freed, Ying Zhang, and Uday Mitra of Applied Materials, shows LER reduction from 3.4 to 1.3 nm is possible after etch. The company’s Sym3 chamber features very high gas conductance to prevent etch byproducts from dissociation and re-deposition on resist sidewalls.

Fig.2: 3D schematics (top) and plan view SEM images (bottom) showing that control of plasma parameters can tune the byproducts of etch processes to significantly reduce the line-width roughness (LWR) of minimally scaled lines. (Source: Applied Materials)

TEL’s new SAQP spacer-on-spacer process builds on the work shown last year, using oxide as first spacer and TiO2 as second spacer. Now TEL is exploring silicon as the mandrel, then silicon-nitride as the first spacer, and titanium-oxide as second spacer. This new flow can be tuned so that all-dry etch in a single plasma etch chamber can be used for the final mandrel pull and pattern transfer steps.

Coventor’s 3D modeling software allows companies to do process integration experiments in virtual space, allowing for estimation of yield-losses in pattern transfer due to variations in side-wall profiles and LER. A simulation of 9 SRAM cells with 54 transistors shows that photoresist sidewall taper angle determines both the size and the variability of the final fins. The final capacitance of low-k dielectric in dual-damascene copper metal interconnects can be simulated as a function of the initial photoresist profile in a SAQP flow.

—E.K.

Photonics in Silicon R&D Toward Tb/s

Tuesday, January 3rd, 2017

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By Ed Korczynski, Sr. Technical Editor

The client:server computing paradigm colloquially referred to as the “Cloud” results in a need for extremely efficient Cloud server hardware, and from first principles the world can save a lot of energy resources if servers run on photonics instead of electronics. Though the potential for cost-savings is well known, the challenge of developing cost-effective integrated photonics solutions remains. Today, discrete compound-semiconductor chips function as transmitters, multiplexers (MUX), and receivers of photons, while many global organizations pursue the vision of lower-cost integrated silicon (Si) photonics circuits.

Work on photonics chips—using light as logic elements in an integrated circuit—built in silicon (Si) has accelerated recently with announcements of new collaborative research and development (R&D) projects. Leti, an institute of CEA Tech, announced the launch of a European Commission Horizon 2020 “COSMICC” project to enable mass commercialization of Si-photonics-based transceivers to meet future data-transmission requirements in data centers and super computing systems.

The Leti-coordinated COSMICC project will combine CMOS electronics and Si-photonics with innovative fiber-attachment techniques to achieve 1 Tb/s data rates. These scalable solutions will provide performance improvement an order of magnitude better than current VCSELs transceivers, and the COSMICC-developed technology will address future data-transmission needs with a target cost per bit that traditional wavelength-division multiplexing (WDM) transceivers cannot meet. The project’s 11 partners from five countries are focusing on developing mid-board optical transceivers with data rates up to 2.4 Tb/s with 200 Gb/s per fiber using 12 fibers. The devices will consume less than 2 pJ/bit. and cost approximately 0.2 Euros/Gb/s.

Figure 1: Schematic of COSMICC on-board optical transceiver at 2.4 Tb/s using 50 Gbps/wavelength, 4 CWDM wavelengths per fiber, 12 fibers for transmission and 12 fibers for reception. (Source: Leti)

A first improvement will be the introduction of a silicon-nitride (SiN) layer that will allow development of temperature-insensitive MUX/DEMUX devices for coarse WDM operation, and will serve as an intermediate wave-guiding layer for optical input/output. The partners will also evaluate capacitive modulators, slow-wave depletion modulators with 1D periodicity, and more advanced approaches. These include GeSi electro-absorption modulators with tunable Si composition and photonic crystal electro-refraction modulators to make micrometer-scale devices. In addition, a hybrid III-V on Si laser will be integrated in the SOI/SiN platform in the more advanced transmitter circuits.

Meanwhile in the United States, Coventor, Inc. is collaborating with the Massachusetts Institute of Technology (MIT) on photonics modeling. MIT is a key player in the AIM Photonics program, a federally funded, public-private partnership established to advance domestic capabilities in integrated photonic technology and strengthen high-tech U.S.-based manufacturing. Coventor will provide its SEMulator3D process modeling platform to model the effect of process variation in the development of photonic integrated components.

“Coventor’s technical expertise in predicting the manufacturability of advanced technologies is outstanding. Our joint collaboration with Coventor will help us develop new design methods for achieving high yield and high performance in integrated photonic applications,” said Professor Duane Boning of MIT. Boning is an expert at modeling non-linear effects in processing, many years after working on the semiconductor industry’s reference model for the control of chemical-mechanical planarization (CMP) processing.

—E.K.

Air-Gaps for FinFETs Shown at IEDM

Friday, October 28th, 2016

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By Ed Korczynski, Sr. Technical Editor

Researchers from IBM and Globalfoundries will report on the first use of “air-gaps” as part of the dielectric insulation around active gates of “10nm-node” finFETs at the upcoming International Electron Devices Meeting (IEDM) of the IEEE (ieee-iedm.org). Happening in San Francisco in early December, IEDM 2016 will again provide a forum for the world’s leading R&D teams to show off their latest-greatest devices, including 7nm-node finFETs by IBM/Globalfoundries/Samsung and by TSMC. Air-gaps reduce the dielectric capacitance that slows down ICs, so their integration into transistor structures leads to faster logic chips.

History of Airgaps – ILD and IPD

As this editor recently covered at SemiMD, in 1998, Ben Shieh—then a researcher at Stanford University and now a foundry interface for Apple Corp.—first published (Shieh, Saraswat & McVittie. IEEE Electron Dev. Lett., January 1998) on the use of controlled pitch design combined with CVD dielectrics to form “pinched-off keyholes” in cross-sections of inter-layer dielectrics (ILD).

In 2007, IBM researchers showed a way to use sacrificial dielectric layers as part of a subtractive process that allows air-gaps to be integrated into any existing dielectric structure. In an interview with this editor at that time, IBM Fellow Dan Edelstein explained, “we use lithography to etch a narrow channel down so it will cap off, then deliberated damage the dielectric and etch so it looks like a balloon. We get a big gap with a drop in capacitance and then a small slot that gets pinched off.

Intel presented on their integration of air-gaps into on-chip interconnects at IITC in 2010 but delayed use until the company’s 14nm-node reached production in 2014. 2D-NAND fabs have been using air-gaps as part of the inter-poly dielectric (IPD) for many years, so there is precedent for integration near the gate-stack.

Airgaps for finFETs

Now researchers from IBM and Globalfoundries will report in (IEDM Paper #17.1, “Air Spacer for 10nm FinFET CMOS and Beyond,” K. Cheng et al) on the first air-gaps used at the transistor level in logic. Figure 1 shows that for these “10nm-node” finFETs the dielectric spacing—including the air-gap and both sides of the dielectric liner—is about 10 nm. The liner needs to be ~2nm thin so that ~1nm of ultra-low-k sacrificial dielectric remains on either side of the ~5nm air-gap.

Fig.1: Schematic of partial air-gaps only above fin tops using dielectric liners to protect gate stacks during air-gap formation for 10nm finFET CMOS and beyond. (source: IEDM 2016, Paper#17.1, Fig.12)

These air-gaps reduced capacitance at the transistor level by as much as 25%, and in a ring oscillator test circuit by as much as 15%. The researchers say a partial integration scheme—where the air-gaps are formed only above the tops of fin— minimizes damage to the FinFET, as does the high-selectivity etching process used to fabricate them.

Figure 2 shows a cross-section transmission electron micrograph (TEM) of what can go wrong with etch-back air-gaps when all of the processes are not properly controlled. Because there are inherent process:design interactions needed to form repeatable air-gaps of desired shapes, this integration scheme should be extendable “beyond” the “10-nm node” to finFETs formed at tighter pitches. However, it seems likely that “5nm-node” logic FETs will use arrays of horizontal silicon nano-wires (NW), for which more complex air-gap integration schemes would seem to be needed.

Fig.2: TEM image of FinFET transistor damage—specifically, erosion of the fin and source-drain epitaxy—by improper etch-back of the air-gaps at 10nm dimensions. (source: IEDM 2016, Paper#17.1, Fig.10)

—E.K.

3D-NAND Deposition and Etch Integration

Thursday, September 1st, 2016

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By Ed Korczynski, Sr. Technical Editor

3D-NAND chips are in production or pilot-line manufacturing at all major memory manufacturers, and they are expected to rapidly replace most 2D-NAND chips in most applications due to lower costs and greater reliability. Unlike 2D-NAND which was enabled by lithography, 3D-NAND is deposition and etch enabled. “With 3D-NAND you’re talking about 40nm devices, while the most advanced 2D-NAND is running out of steam due to the limited countable number of stored electrons-per-cell, and in terms of the repeatability due to parasitics between adjacent cells,” reminded Harmeet Singh, corporate vice president of Lam Research in an exclusive interview with SemiMD to discuss the company’s presentation at the Flash Memory Summit 2016.

“We’re in an era where deposition and etch uniquely define the customer roadmap,” said Singh,“and we are the leading supplier in 3D-NAND deposition and etch.” Though each NAND manufacturer has different terminology for their unique 3D variant, from a manufacturing process integration perspective they all share similar challenges in the following simplified process sequences:

1)    Deposition of 32-64 pairs of blanket “mold stack” thin-films,

2)    Word-line hole etch through all layers and selective fill of NAND cell materials, and

3)    Formation of “staircase” contacts to each cell layer.

Each of these unique process modules is needed to form the 3D arrays of NVM cells.

For the “mold stack” deposition of blanket alternating layers, it is vital for the blanket PECVD to be defect-free since any defects are mirrored and magnified in upper-layers. All layers must also be stress-free since the stress in each deposited layer accumulates as strain in the underlying silicon wafer, and with over 32 layers the additive strain can easily warp wafers so much that lithographic overlay mismatch induces significant yield loss. Controlled-stress backside thin-film depositions can also be used to balance the stress of front-side films.

Hole Etch

“The difficult etch of the hole, the materials are different so the challenges is different,” commented Singh about the different types of 3D-NAND now being manufactured by leading fabs. “During this conference, one of our customer presented that they do not see the hole diameters shrinking, so at this point it appears to us that shrinking hole diameters will not happen until after the stacking in z-dimension reaches some limit.”

Tri-Layer Resist (TLR) stacks for the hole patterning allow for the amorphous carbon hardmask material to be tuned for maximum etch resistance without having to compromise the resolution of the photo-active layer needed for patterning. Carbon mask is over 3 microns thick and carbon-etching is usually responsive to temperature, so Lam’s latest wafer-chuck for etching features >100 temperature control zones. “This is an example of where Lam is using it’s processes expertise to optimize both the hardmask etch as well as the actual hole etch,” explained Singh.

Staircase Etch

The Figure shows a simplified cross-sectional schematic of how the unique “staircase” wordline contacts are cost-effectively manufactured. The established process of record (POR) for forming the “stairs” uses a single mask exposure of thick KrF photoresist—at 248nm wavelength—to etch 8 sets of stairs controlled by a precise resist trim. The trimming step controls the location of the steps such that they align with the contact mask, and so must be tightly controlled to minimize any misalignment yield loss.

A) Simplified cross-sectional schematic of the staircase etch for 3D-NAND contacts using thick photoresist, B) which allows for controlled resist trimming to expose the next “stair” such that C) successive trimming creates 8-16 steps from a single initial photomask exposure. (Source: Ed Korczynski)

Lam is working on ways to tighten the trimming etch uniformity such that 16 sets of stairs can be repeatably etched from a single KrF mask exposure. Halving the relative rate of vertical etch to lateral etch of the KrF resist allows for the same resist thickness to be used for double the number of etches, saving lithography cost. “We see an amazing future ahead because we are just at the beginning of this technology,” commented Singh.

—E.K.

Applied Materials Releases Selective Etch Tool

Wednesday, June 29th, 2016

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By Ed Korczynski, Sr. Technical Editor

Applied Materials has disclosed commercial availability of new Selectra(TM) selective etch twin-chamber hardware for the company’s high-volume manufacturing (HVM) Producer® platform. Using standard fluorine and chlorine gases already used in traditional Reactive Ion Etch (RIE) chambers, this new tool provides atomic-level precision in the selective removal of materials in 3D devices structures increasingly used for the most advanced silicon ICs. The tool is already in use at three customer fabs for finFET logic HVM, and at two memory fab customers, with a total of >350 chambers planned to have been shipped to many customers by the end of 2016.

Figure 1 shows a simplified cross-sectional schematic of the Selectra chamber, where the dashed white line indicates some manner of screening functionality so that “Ions are blocked, chemistry passes through” according to the company. In an exclusive interview with Solid State Technology, company representative refused to disclose any hardware details. “We are using typical chemistries that are used in the industry,” explained Ajay Bhatnagar, managing director of Selective Removal Products for Applied Materials. “If there are specific new applications needed than we can use new chemistry. We have a lot of IP on how we filter ions and how we allow radicals to combine on the wafer to create selectivity.”

FIG 1: Simplified cross-sectional schematic of a silicon wafer being etched by the neutral radicals downstream of the plasma in the Selectra chamber. (Source: Applied Materials)

From first principles we can assume that the ion filtering is accomplished with some manner of electrically-grounded metal screen. This etch technology accomplishes similar process results to Atomic Layer Etch (ALE) systems sold by Lam, while avoiding the need for specialized self-limiting chemistries and the accompanying chamber throughput reductions associated with pulse-purge process recipes.

“What we are doing is being able to control the amount of radicals coming to the wafer surface and controlling the removal rates very uniformly across the wafer surface,” asserted Bhatnagar. “If you have this level of atomic control then you don’t need the self-limiting capability. Most of our customers are controlling process with time, so we don’t need to use self-limiting chemistry.” Applied Materials claims that this allows the Selectra tool to have higher relative productivity compared to an ALE tool.

Due to the intrinsic 2D resolutions limits of optical lithography, leading IC fabs now use multi-patterning (MP) litho flows where sacrificial thin-films must be removed to create the final desired layout. Due to litho limits and CMOS device scaling limits, 2D logic transistors are being replaced by 3D finFETs and eventually Gate-All-Around (GAA) horizontal nanowires (NW). Due to dielectric leakage at the atomic scale, 2D NAND memory is being replaced by 3D-NAND stacks. All of these advanced IC fab processes require the removal of atomic-scale materials with extreme selectivity to remaining materials, so the Selectra chamber is expected to be a future work-horse for the industry.

When the industry moves to GAA-NW transistors, alternating layers of Si and SiGe will be grown on the wafer surface, 2D patterned into fins, and then the sacrificial SiGe must be selectively etched to form 3D arrays of NW. Figure 2 shows the SiGe etched from alternating Si/SiGe stacks using a Selectra tool, with sharp Si corners after etch indicating excellent selectivity.

FIG 2: SEM cross-section showing excellent etch of SiGe within alternating Si/SiGe layers, as will be needed for Gate-All-Around (GAA) horizontal NanoWire (NW) transistor formation. (Source: Applied Materials)

“One of the fundamental differences between this system and old downstream plasma ashers, is that it was designed to provide extreme selectivity to different materials,” said Matt Cogorno, global product manager of Selective Removal Products for Applied Materials. “With this system we can provide silicon to titanium-nitride selectivity at 5000:1, or silicon to silicon-nitride selectivity at 2000:1. This is accomplished with the unique hardware architecture in the chamber combined with how we mix the chemistries. Also, there is no polymer formation in the etch process, so after etching there are no additional processing issues with the need for ashing and/or a wet-etch step to remove polymers.”

Systems can also be used to provide dry cleaning and surface-preparation due to the extreme selectivity and damage-free material removal.  “You can control the removal rates,” explained Cogorno. “You don’t have ions on the wafer, but you can modulate the number of radicals coming down.” For HVM of ICs with atomic-scale device structures, this new tool can widen process windows and reduce costs compared to both dry RIE and wet etching.

—E.K.

79 GHz CMOS RADAR Chips for Cars from Imec and Infineon

Tuesday, May 24th, 2016

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By Ed Korczynski, Sr. Technical Editor

As unveiled at the annual Imec Technology Forum in Brussels (itf2016.be), Infineon Technologies AG (infineon.com) and imec (imec.be) are working on highly integrated CMOS-based 79 GHz sensor chips for automotive radar applications. Imec provides expertise in high-frequency system, circuit, and antenna design for radar applications, complementing Infineon’s knowledge from the many learnings that go along with holding the world’s top market share in commercial radar sensor chips. Infineon and imec expect functional CMOS sensor chip samples in the third quarter of 2016. A complete radar system demonstrator is scheduled for the beginning of 2017.

Whether or not fully automated cars and trucks will be traveling on roads soon, today’s drivers want more sensors to be able to safely avoid accidents in conditions of limited visibility. Typically, there are up to three radar systems in today’s vehicle equipped with driver assistance functions. In a future with fully automated cars, up to ten radar systems and ten more sensor systems using cameras or lidar (https://en.wikipedia.org/wiki/Lidar) could be needed. Short-range radar (SRR) would look for side objects, medium-range radar (MRR) would scan widely for objects up to 50m in front and in back, and long-range radar (LRR) would focus up to 250m in front and in back for high-speed collision avoidance.

“Infineon enables the radar-based safety cocoon of the partly and fully automated car,” said Ralf Bornefeld, Vice President & General Manager, Sense & Control, Infineon Technologies AG. “In the future, we will manufacture radar sensor chips as a single-chip solution in a classic CMOS process for applications like automated parking. Infineon will continue to set industry standards in radar technology and quality.”

The Figure shows the evolution of radar technology over the last decades, leading to the current miniaturization using solid-state silicon CMOS. Key to the successful development of this 79 GHz demonstrator was choosing to use 28 nm CMOS technology. Imec has been refining this technology as shown at ISSCC (isscc.org) for many years, first showing a 28nm transmitter chip in 2013, then showing a 28nm transmit and receive (a.k.a. “transceiver”) chip in 2014, and finally showing a single-chip with a transceiver and analog-digital converters (ADC) and phase-lock loops (PLL) and digital components in 2015. Long-term supply of eventual commercial chips should be ensured by using 28nm technology, which is known as a “long lived” node.

“We are excited to work with Infineon as a valuable partner in our R&D program on advanced CMOS-based 77 GHz and 79 GHz radar technology,” stated Wim Van Thillo, program director perceptive systems at imec. “Compared to the mainstream 24 GHz band, the 77 GHz and 79 GHz bands enable a finer range, Doppler and angular resolution. With these advantages, we aim to realize radar prototypes with integrated multiple-input, multiple-output (MIMO) antennas that not only detect large objects, but also pedestrians and bikers and thus contribute to a safer environment for all.”

Since the aesthetics are always important for buyers, automobile companies have been challenged to integrate all of the desired sensors into vehicles in an invisible manner. “The designers hate what they call the ‘warts’ on car bumpers that are the small holes needed for the ultrasonic sensors currently used,” explained Van Thillo in a press conference during ITF2016.

In an ITF2016 presentation, CEO Reinhard Ploss, discussed how Infineon works with industrial partners to create competitive commercial products. “When we first developed RADAR, there was a collaboration between the Tier-1 car companies and ourselves,” explained Ploss. “The key lies in the algorithms needed to process the data, since the raw data stream is essentially useless. The next generation of differentiation for semiconductors will be how to integrate algorithms. In effect, how do you translate ‘pixels’ into ‘optics’ without an expensive microprocessor?”

Evolution of radar technology over time has reached the miniaturization of 79 GHz using 28nm silicon CMOS technology. Imec is now also working on 140 GHz radar chips. (Source: imec)

—E.K.

IoT Demands Part 2: Test and Packaging

Friday, April 15th, 2016

By Ed Korczynski, Senior Technical Editor, Solid State Technology, SemiMD

The Internet-of-Things (IoT) adds new sensing and communications to improve the functionality of all manner of things in the world. Solid-state and semiconducting materials for new integrated circuits (IC) intended for ubiquitous IoT applications will have to be extremely small and low-cost. To understand the state of technology preparedness to meet the anticipated needs of the different application spaces, experts from GLOBALFOUNDRIES, Cadence, Mentor Graphics and Presto Engineering gave detailed answers to questions about IoT chip needs in EDA and fab nodes, as published in “IoT Demands:  EDA and Fab Nodes.” We continue with the conversation below.

Korczynski: For test of IoT devices which may use ultra-low threshold voltage transistors, what changes are needed compared to logic test of a typical “low-power” chip?

Steve Carlson, product management group director, Cadence

Susceptibility to process corners and operating conditions becomes heightened at near-threshold voltage levels. This translates into either more conservative design sign-off criteria, or the need for higher levels of manufacturing screening/tests. Either way, it has an impact on cost, be it hidden by over-design, or overtly through more costly qualification and test processes.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

We need to make sure that the testability has also been designed to be functional structurally in this mode. In addition, sub-threshold voltage operation must account for non-linear transistor characteristics and the strong impact of local process variation, for which the conventional testability arsenal is still very poor. Automotive screening used low voltage operation (VLV) to detect latent defects, but at very low voltage close to the transistor threshold, digital becomes analog, and therefore if the usual concept still works for defect detection, functional test and @speed tests require additional expertise to be both meaningful and efficient from a test coverage perspective.

Korczynski:  Do we have sufficient specifications within “5G” to handle IoT device interoperability for all market segments?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

The estimated timeline for standardization availability of 5G is around 2020. 5G is being designed keeping three classes of applications in mind:  Enhanced Mobile Broadband, Massive IoT, and Mission-Critical Control. Specifically for IoT, the focus is on efficient, low-cost communication with deep coverage. We will start to see early 5G technologies start to appear around 2018, and device connectivity,

interoperability and marshaling the data they generate that can apply to multiple IoT sub-segments and markets is still very much in development.

Korczynski:  Will the 1st-generation of IoT devices likely include wide varieties of solution for different market-segments such as industrial vs. retail vs. consumer, or will most device use similar form-factors and underlying technologies?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

If we use CES 2016 as a showcase, we are seeing IoT “Things” that are becoming use-case or application-centric as they apply to specific sub-segments such as Connected Home, Automotive, Medical, Security, etc. There is definitely more variety on the consumer front vs. industrial. Vendors / OEMs / System houses are differentiating at the user-interface design and form-factor levels while the “under-the-hood” IC capabilities and component technologies that provide the atomic intelligence are fairly common. ​

Steve Carlson, product management group director, Cadence

Right now it seems like everyone is swinging for the fence. Everyone wants the home-run product that will reach a billion devices sold. Generality generally leads to sub-optimality, so a single device usually fails to meet the needs and expectations of many. Devices that are optimized for more specific use cases and elements of purchasing criteria will win out. The question of interface is an interesting one.

Korczynski:  Will there be different product life-cycles for different IoT market-segments, such as 1-3 years for consumer but 5-10 years for industrial?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

That certainly seems to be the case. According to Gartner’s market analysis for IoT, Consumer is expected to grow at a faster pace in terms of units compared to Enterprise, while Enterprise is expected to lead in revenue. Also the churn-cycle in Consumer is higher / faster compared to Enterprise. Today’s wearables or smart-phones are good reference examples. This will however vary by the type of “Thing” and sub-segment. For example, you expect to have your smart refrigerator for a longer time period compared to smart clothing or eyewear. As ASPs of the “Things”come down over time and new classes of products such as disposables hit the market, we can expect even larger volumes.​

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

The market segments continue to be driven by the same use cases. In consumer wearables, short cycles are linked to fashion trends and rapid obsolescence, where consumer home use has longer cycles closer to industrial market requirements. We believe that the lifecycle norms will hold true for IoT devices.

Korczynski:  For the IoT application of infrastructure monitoring (e.g. bridges, pipelines, etc.) long-term (10-20 year) reliability will be essential, while consumer applications may be best served by 3-5 year reliability devices which cost less; how well can we quantify the trade-off between cost and chip reliability?

Steve Carlson, product management group director, Cadence

Conceptually we know very well how to make devices more reliable. We can lower current densities with bigger wires, we can run at cooler temperatures, and so on.  The difficulty is always in finding optimality for a given criterion across the, for practical purposes, infinite tradeoffs to be made.

Korczynski:  Why is the talk of IoT not just another “Dot Com” hype cycle?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

​​I participated in a panel at SEMICON China in Shanghai last month that discussed a similar question. If we think of IoT as a “brand new thing” (no pun intended), then we can think of it as hype. However if we look at the IoT as as set of use-cases that can take advantage of an evolution of Machine-to-Machine (M2M) going towards broader connectivity, huge amounts of data generated and exchanged, and a generational increase in internet and communication network bandwidths (i.e. 5G), then it seems a more down-to-earth technological progression.

Nicolas Williams, product marketing manager, Mentor Graphics

Unlike the Dot Com hype, which was built upon hope and dreams of future solutions that may or may not have been based in reality, IoT is real business. For example, in a 2016 IC Insights report, we see that last year $63.4 billion in revenue was generated for IoT systems and the market is growing at about 20% CAGR. This same report also shows IoT semiconductor sales of over $15 billion in 2015 with a CAGR of 21.1%.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

It is the investment needed up front to create sensing agents and an infrastructure for the hardware foundation of the IoT that will lead to big data and ultimately value creation.

Steve Carlson, product management group director, Cadence

There will be plenty of hype cycles for products and product categories along the way. However, the foundational shift of the connection of things is a diode through which civilization will only pass through in one direction.

IoT Demands Part 1: EDA and Fab Nodes

Thursday, April 14th, 2016

The Internet-of-Things (IoT) is expected to add new sensing and communications to improve the functionality of all manner of things in the world:  bridges sensing and reporting when repairs are needed, parts automatically informing where they are in storage and transport, human health monitoring, etc. Solid-state and semiconducting materials for new integrated circuits (IC) intended for ubiquitous IoT applications will have to be assembled at low-cost and small-size in High Volume Manufacturing (HVM). Micro-Electro-Mechanical Systems (MEMS) and other sensors are being combined with Radio-Frequency (RF) ICs in miniaturized packages for the first wave of growth in major sub-markets.

To meet the anticipated needs of the different IoT application spaces, SemiMD asked leading companies within critical industry segments about the state of technology preparedness:

*  Commercial IC HVM – GLOBALFOUNDRIES,

*  Electronic Design Automation (EDA) – Cadence and Mentor Graphics,

*  IC and complex system test – Presto Engineering.

Korczynski:  Today, ICs for IoT applications typically use 45nm/65nm-node which are “Node -3″ (N-3) compared to sub-20nm-node chips in HVM. Five years from now, when the bleeding-edge will use 10nm node technology, will IoT chips still use N-3 of 28nm-node (considered a “long-lived node”) or will 45nm-node remain the likely sweet-spot of price:performance?

Timothy Dry, product marketing manager, GLOBALFOUNDRIES

In 5 years time, there will be a spread of technology solutions addressing low, middle, and high ends of IoT applications. At the low end, IoT end nodes for applications like connected smoke

detectors, security sensors will be at 55, 40nm ULP and ULL for lowest system power, and low cost. These applications will be typically served by MCUs <50DMIPs. Integrated radios (BLE, 802.15.4), security, Power Management Unit (PMU), and eFlash or MRAM will be common features. Connected LED lighting is forecasted to be a high volume IoT application. The LED drivers will use BCD extensions of 130nm—40nm—that can also support the radio and protocol-MCU with Flash.

In the mid-range, applications like smart-meters and fitness/medical monitoring will need systems that have more processing power <300DMIPS. These products will be implemented in 40nm, 28nm and GLOBALFOUNDRIES’ new 22nm FDSOI technology that uses software-controlled body-biasing to tune SoC operation for lowest dynamic power. Multiple wireless (BLE/802.15.4, WiFi, LPWAN) and wired connectivity (Ethernet, PLC) protocols with security will be integrated for gateway products.

High-end products like smart-watches, learning thermostats, home security/monitoring cameras, and drones will require MPU-class IC products (~2000DMIPs) and run high-order operating systems (e.g. Linux, Android). These products will be made in leading-edge nodes starting at 22FDX, 14FF and migrating to 7FF and beyond. Design for lowest dynamic power for longest battery life will be the key driver, and these products typically require human machine Interface (HMI) with animated graphics on a high resolution displays. Connectivity will include BLE, WiFi and cellular with strong security.

Steve Carlson, product management group director, Cadence

We have seen recent announcements of IoT targeted devices at 14nm. The value created by Moore’s Law integration should hold, and with that, there will be inherent advantages to those who leverage next generation process nodes. Still, other product categories may reach functionality saturation points where there is simply no more value obtained by adding more capability. We anticipate that there will be more “live” process nodes than ever in history.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

It is fair to say that most IoT devices will be a heterogeneous aggregation of analog functions rather than high power digital processors. Therefore, and by similarity with Bluetooth and RFID devices, 90nm and 65nm will remain the mainstream nodes for many sub-vertical markets, enabling the integration of RF and analog front-end functions with digital gate density. By default, sensors will stay out of the monolithic path for both design and cost reasons. The best answer would be that the IoT ASIC will follow eventually the same scaling as the MCU products, with embedded non-volatile memories, which today is 55-40nm centric and will move to 28nm with industry maturity and volumes.

Korczynski:  If most IoT devices will include some manner of sensor which must be integrated with CMOS logic and memory, then do we need new capabilities in EDA-flows and burn-in/test protocols to ensure meeting time-to-market goals?

Nicolas Williams, product marketing manager, Mentor Graphics

If we define a typical IoT device as a product that contains a MEMS sensor, A/D, digital processing, and a RF-connection to the internet, we can see that the fundamental challenge of IoT design is that teams working on this product need to master the analog, digital, MEMS, and RF domains. Often, these four domains require different experience and knowledge and sometimes design in these domains is accomplished by separate teams. IoT design requires that all four domains are designed and work together, especially if they are going on the same die. Even if the components are targeting separate dice that will be bonded together, they still need to work together during the layout and verification process. Therefore, a unified design flow is required.

Stephen Pateras, product marketing director, Mentor Graphics

Being able to quickly debug and create test patterns for various embedded sensor IP can be addressed with the adoption of the new IEEE 1687 IP plug-and-play standard. If a sensor IP block’s digital interface adheres to the standard, then any vendor-provided data required to initialize or operate the embedded sensor can be easily and quickly mapped to chip pins. Data sequences for multiple sensor IP blocks can also be merged to create optimized sequences that will minimize debug and test times.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

From a testing standpoint, widely used ATEs are generally focused on a few purposes, but don’t necessarily cover all elements in a system. We think that IoT devices are likely to require complex testing flows using multiple ATEs to assure adequate coverage. This is likely to prevail for some time as short run volumes characteristic of IoT demands are unlikely to drive ATE suppliers to invest R&D dollars in creating new purpose-built machines.

Korczynski:  For the EDA of IoT devices, can all sensors be modeled as analog inputs within established flows or do we need new modeling capability at the circuit level?

Steve Carlson, product management group director, Cadence

Typically, the interface to the physical world has been partitioned at the electrical boundary. But as more mechanical and electro-mechanical sensors are more deeply integrated, there has been growing value in co-design, co-analysis, and co-optimization. We should see more multi-domain analysis over time.

Nicolas Williams, product marketing manager, Mentor Graphics

Designers of IoT devices that contain MEMS sensors need quality models in order to simulate their behavior under physical conditions such as motion and temperature. Unlike CMOS IC design, there are few standardized MEMS models for system-level simulation. State of the art MEMS modeling requires automatic generation of behavioral models based on the results of Finite Element Analysis (FEA) using reduced-order modeling (ROM). ROM is a numerical methodology that reduces the analysis results to create Verilog-A models for use in AMS simulations for co-simulation of the MEMS device in the context of the IoT system.

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.

Comfortable Consumer EEG Headset Shown by Imec and Holst Centre

Thursday, August 27th, 2015

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By Ed Korczynski, Sr. Technical Editor

A new wireless electroencephalogram (EEG) headset that is comfortable while providing medical-grade data acquisition has been shown by the partnership of imec, the Holst Centre, and the Industrial Design Engineering (IDE) department of TU Delft. The 3D-printed low-volume product enables early research and self-monitoring of emotions and mood in daily life situations using a smartphone application. Consumer applications include games that monitor relaxation and/or concentration, and medical applications that help with sleep disorders and treatment of Attention Deficit Hyperactivity Disorder (ADHD).

Figure 1 shows the new headset with novel elastic electrode arrays in an elegant uni-body assembly to optimize both comfort and signal quality. The electronics package in the middle of the headset fits on the back of the user’s neck. Each electrode is a small array of elastic polymer fingers which allow for dry contact—without needing a conductive liquid or gel—to skin for long-term comfortable use.

Figure1: Comfortable EEG headset developed by imec and Holst Centre and TU Delft in 2015, providing medical-quality data tracing of emotions and mood in daily life situations using a smartphone application. (Source: imec)

“Leveraging imec’s strong background in EEG sensing, dry polymer and active electrodes, miniaturized and low-power data acquisition, and low-power wireless interfaces to smartphones, we were able to focus on the ergonomics of this project. In doing so, we have successfully realized this unique combination of comfort and effectiveness at the lowest possible cost to the future user,” stated Bernard Grundlehner, EEG system architect at imec.

In 2011, imec and Holst Centre created an 8-channel ultra-low-power analog readout application-specific integrated circuit (ASIC) that consumes only 200µW and features high common mode rejection ratio (CMRR) of 120dB and signal to noise ratio of 25dB on real EEG signals. This ASIC is tuned to high input impedance (1GΩ) for compatibility with the use of dry electrodes. That system—including ASIC, radio, and controller chips— could be integrated in a package of 25mmx35mmx5mm dimensions for easy of integration in headsets, helmets, or other accessories. That system consumes only 3.3mW for continuous recording and wireless transmission of 1 channel—9.2mW for 8 channels—allowing for 1.5 to 4 days of functionality when powered by a 100mAh Li-ion battery.

In 2009, imec and Holst Centre showed off a rough mobile EEG prototype to partners and journalists at the yearly imec Technology Forum. Figure 2 shows that the prototype was bulky and a bit awkward to wear, while the figure does not show that sintered silver/silver-chloride electrodes are very hard such that dry contact to the human scalp tends to be uncomfortable.

Figure2: Ed Korczynski tests an imec EEG headset rough prototype, using uncomfortable hard silver/silver-chloride electrodes, at the 2009 Imec Technology Forum. (Source: Ed Korczynski)

The 2015 model uses new flexible electrodes arrays which are inherently more comfortable than hard silver/silver-chloride electrodes. A team of six master students from IDE of TU Delft led the design optimization of the 3D unibody for the new headset using 3D printing for short-loop prototyping and testing of different shapes for stability and comfort. Iterative tests with users for multiple applications led to this design which is intended for long-term comfortable use by consumers outside of a controlled research environment.

The new EEG headset is manufactured in one piece using 3-D printing, after which the electronic components are placed, connected, and covered by a 3-D-printed rubber inlay. The EEG electrodes are situated at the front of the headset for optimal acquisition of signals related to emotion and mood variations. A mobile app can then tie the user’s emotional state to environmental information such as location, time, agenda, and social context to track possible unconscious effects.

—E.K.

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