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Tuesday, June 21, 2016

Future EUV/FEL Strategy – The Beam Line Approaches



As many of you know, I've been following the progress of EUV lithography over the years, observing and commenting on the program's many engineering successes as well as the delays in the convergence of EUV lithography and the anticipated HVM time line (High Volume Manufacturing). In spite of improvements in laser technology and the availability of low dose photoresists, the development of high power LPP (Laser Produced Plasma) EUV source technology >100 watts remains problematic. EUV HVM insertion remains elusive and unpredictable. The source power limitations and MTBF (Mean Time Between Failure) of LPP technology have gated the program. A few years ago many in the SPIE community sought to explore the potential of a FEL source for high power EUV applications. At the time, Free Electron Laser [1] Technology was not yet a topic for dinner table discussion so in September, 2014 I published Future FEL/EUV Strategy – The Light at the End of the Beam Line. [2] On-going FEL developments at SLAC and recent related commentary from companies like GLOBALFOUNDRIES have generated new interest in FEL technology. As many new engineers and investors have joined our ranks, I thought a more comprehensive review was in order, so I've excerpted portions of my 1994 primer on FEL/EUV strategy to point out the enabling feature/benefits of a high power, high reliability light source for EUV lithography.

What are the current obstacles to high power EUV?

In ASML's current LPP source designs, a solid state "pre-pulse" laser and a second, high energy CO2 laser are fired at micron sized tin (Sn) pellets, evaporating them and releasing EUV light as a byproduct. Knowledgeable sources have informed me that the currently employed CO2 lasers are at or near the maximum of their pulse rate capabilities, effectively limiting further power output. As more CO2 laser power becomes available, there may still be practical limitations on the scaling and feed rate of Sn (tin) target material. As determined by physics, the inherent energy conversion factor for tin approximates 4%, and further incremental improvements in efficiency are obtained with diminishing returns. Assuming additional laser power becomes available for ASML, further complications can result from higher LPP source power levels as the rate of residual particulate contamination from evaporated tin increases in approximate proportion with increased laser power. Critical beam line mirror surfaces and other source components rapidly lose their efficiencies as tin contamination accumulates, reducing the available up time of the stepper (MTBF). It was originally anticipated that an optimal LPP EUV source design would provide 13.5nm light at power levels >200 watts, providing current and future lithography requirements. However, more recent demands for even higher EUV power levels have been identified. ASML and Carl Zeiss acknowledged in an invited paper at SPIE Advanced Lithography 2015, that higher resolutions will require 60mJ/cm2 for half pitch nodes <8nm. [3] ASML's recent (2015) collaboration with Carl Zeiss has produced an optical system with a numeric aperture (NA) of 0.55 vs. ASML's current EUV NA of 0.33. The higher NA system will require 500 watts of EUV power to achieve the estimated 60 mJ/cm2 dosimetry required for throughput of 150 wafers/hour. While this concept extends the viability of 13.5nm lithography, the delivery of a reliable 500 watt EUV source remains a critical item on the agenda, meaning the availability of free electron laser technology will probably gate related programs. A recent article appearing in the SPIE News Room, Extending extreme-UV lithography technology, [4] suggests that power levels of 500 – 1000 watts may be required for a single stepper necessitating a large scale central source EUV FEL.

A Primer on Free Electron Lasers

What is a free electron laser and how is it different from conventional lasers and LPP systems? To answer this question we must entertain the convergence of the US DOE's high energy physics community with the semiconductor industry and discuss recent innovations in technology. In previous and current generation stepper and scanner systems, it's been common to utilize laser light sources producing the desired wavelengths required for semiconductor photolithography. In current 193nm lithography systems, an argon fluoride (ArF) laser produces the light. The laser light produced is monochromatic, of sufficient brilliance and provides many hours of trouble free uptime. It would seem this simplistic approach might be applied to EUV lithography. Why not build an EUV laser with a wavelength of 13.5 nanometers? This has not been possible due to limitations in physics. The highly reflective optics required for laser efficiencies have yet to be created for EUV spectra. Current Bragg cell mirrors reflect EUV with a closely approximated 90% efficiency. However, FEL is a game changer. Some history and an analogy:


The term LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. The first solid state, 694nm synthetic ruby laser produced at Hughes Research in 1960, [5] utilized xenon flash lamps to inject high energy photons throughout the core of a ruby rod, stimulating the emission of photons from its lattice structures. Lasers operate at specific wavelengths which are determined by the seed (or lazing) material's inherent spectral signature. The 694nm wavelength is derived from the band gap emissions of the ruby's crystalline composition. We might compare the ruby crystal in this laser with a quartz crystal in a radio which determines its operational frequency. Accordingly, we might otherwise assign “channel I” as an identifier of I-line photolithography operating at 365nm.

The Foundation Physics of FEL
 A Radio Logical Analogy

A radio transmitter's frequency has historically been controlled by quartz crystal elements. Y-cut quartz crystals oscillate (vibrate) at specific frequencies which are dependent upon their thickness. The thinner the crystal, the higher the frequency obtained. Inversely, the thicker the crystal, the lower the frequency obtained. Passing an electric current through a quartz crystal induces it to oscillate at its inherent resonant frequency, so determined by its thickness. The frequency produced is extremely stable and the resulting wave form is of high purity, providing an excellent medium for control of radio frequencies and instrumentation. Crystals also produce harmonic frequencies. A harmonic is a multiple of the crystal's fundamental resonant frequency. As such, a crystal oscillating at 3 MHz will also produce a weaker signal at 6MHz (its second harmonic frequency), and a still weaker third harmonic at 9MHz and so on. When impractical to manufacture crystals at their desired fundamental frequencies, "third overtone" crystals are often utilized to provide a harmonic frequency which can be sufficiently amplified and utilized as an effective fundamental frequency, thus extending the upper limits (and our usage) of the radio spectrum. Even with clever engineering, over the years radio frequency control became problematic as multi-channel communication systems evolved, requiring large banks of crystals to span a given range of frequencies; one crystal required for each channel frequency. Rather than utilize thousands of crystals to span the radio spectrum, communications equipment evolved to employ a frequency control device called a VFO: a Variable Frequency Oscillator. In this scenario, several fundamental frequency crystals and specially designed varactor diode/phased locked loop circuits comprise a heterodyne oscillator, sometimes known as an IF (Intermediate Frequency) mixer. Such an oscillator can generate a wide range of possible frequency combinations by mixing (heterodyning) the output obtained from the crystals to produce the desired sum/difference of their frequencies by way of constructive or destructive interference. As a VFO radio tuning dial is manipulated, it changes one of the mixing frequencies to produce the desired sum/difference operational frequency for both transmitter and receiver. The advantage to such a design is the elimination of separate transmitter/receiver controls, and thousands of individual crystals normally assigned for each desired radio channel. The conceptual use of both harmonic and sum/difference frequency synthesis has found its way into many applications in physics and electronics.

Free Electron Laser Fundamentals

Imagine that we might adjust and control a laser's wavelength using a concept similar to a radio's Variable Frequency Oscillator but with a different set of physics. By electronically tuning a laser's wavelength, we can eliminate the need for specialized crystalline, gaseous or other lazing materials and operate outside the spectral wavelength segments they are physically limited to. FEL technology can produce tunable wavelengths of light throughout the microwave, visible spectrum and x-ray regime. A free electron laser is comprised of a large beamline/electron source which accelerates electrons to near the speed of light. On opposite sides of the electron beam line are interposed field coils of opposing polarity called undulators or "wigglers", which when energized establish a transverse sinusoidal field across the beam path. Electrons accelerated into the transverse field produce incoherent photons in a mixed assortment of sinusoidal wavelengths sometimes referred to as “bunches”, emitting photons at wavelengths determined by their acceleration and the transverse field strength (synchrotron radiation). By adjusting the electron beam energy or the magnetic field strength of the undulators, the wavelength of the emitted photons can be tuned selectively to produce coherent light. Variations on this concept have evolved as follows:

A Tunable SASE FEL

A SASE FEL is able to produce laser light over a broad range of spectrum without the requirement for conventional lazing materials such as ruby crystal or argon fluoride etc. In a tunable SASE (Self Amplified Spontaneous Emission) FEL, high energy source electrons passing through an undulator can produce an assortment of incoherent photons (initially at randomly different wavelengths) which become bunched in the transverse sine wave and interact via constructive or destructive interference, producing incidental derivative wavelengths (spontaneous emission). That is to say the bunched photons add and subtract their wavelength values from one another producing new sum/difference valued photons at the mathematically resulting wavelengths. When tuned to a specific wavelength of interest by adjusting the electron beam energy or the magnetic field strength of the undulators, such subsequently produced photons arrive in phase (at the same wavelength) and cumulatively intensify to release high energy coherent laser light (self amplification). While a very useful concept for a variety of applications, the spontaneous emission in a SASE FEL can propagate statistical artifacts resulting from the inherent mathematical sum/difference phenomenon, and consequently can produce a beam exhibiting limited shot to shot reproducibility. As such, the utility of a SASE FEL might be limited in applications which require extremely accurate dosimetry. The limited shot to shot reproducibility might also contribute to the dosimetry phenomenon known as “shot noise”.

A Tunable HGHG FEL

FEL performance can be modified and improved by utilizing an external seed laser as a source wavelength. The seed laser is a conventional laser utilizing a material such as ruby crystal (one example) to produce a monochromatic feed source of photons. In an HGHG (High Gain Harmonic Generation) FEL, the seed laser interacts with the electron beam as it propagates through the first undulator (called a modulator), tuned to the seed laser's wavelength. The resulting interaction with the seed laser induces coherent modulation of the electron beam energy, creating photon bunching as well as consequential harmonic propagation (photons which are the mathematical multiples of the seed laser's wavelength). The micro-bunched beam of photons are then injected into a long undulator tuned to the desired harmonic wavelength. The desired wavelength comprised of harmonically produced photons arrive in phase and cumulatively intensify to release high energy coherent light at the newer, shorter wavelength of interest. A recent FERMI paper illustrates 500 shot reproducibility of 8th harmonic spectra at 32.5nm (obtained from a 260nm seed laser) exhibiting normalized photon/energy stability in the order of 7x10^-5 (root mean square), a marked improvement over previous SASE FEL data obtained over the same photon energy range. The high purity monochromatic spectra of an HGHG seed laser improves the system's shot to shot repeatability as its mode of operation does not incur the statistical deviation phenomena found in spontaneous emission spectra typically observed in a SASE FEL. As such, an HGHG FEL might be more advantageous for use in EUV applications requiring highly precise dosimetry, possibly reducing shot noise phenomenon. 

The EUV Source Challenge Ahead

Large scale projects are underway to build FEL systems to accommodate a wide range of wavelengths and scientific applications. FEL is next generation laser technology which is perhaps the best candidate to replace the LPP/EUV source designs currently offered by ASML.

Known for its work in actinic inspection at the 13.5 nm EUV wavelength, Lawrence Berkeley CXRO Lab [6] is also part of a DOE consortium currently working on LCLS-II (Linac Coherent Light Source-II) [7] at Lawrence Livermore and SLAC. Last June at the 2015 International Workshop on EUV Lithography in Maui, Aaron Tremaine of SLAC presented a comprehensive review of possible FEL designs that might be considered for EUV lithography and identified the consortium of DOE laboratories participating in the EUV FEL program. The Who's Who list of DOE participants includes SLAC, Lawrence Berkeley National Labs, Fermilab, Argonne National Lab, Cornell, UCLA, RadiaBeam, AES and Radiasoft. In order to appreciate the scale and capital intensity of this project it becomes necessary to review Aaron Tremaine's 2015 EUV Litho, Inc. Workshop presentation, LCLS-II and Free electron laser drivers for EUV Lithography [8]. The report describes FEL design considerations and recommends a “Straight Shooter” beamline configuration for semiconductor EUV lithography applications. The report addresses Erik R. Hosler's (GLOBALFOUNDRIES) 2015 SPIE publication, “Considerations for a free-electron laser based extreme-ultraviolet lithography program”, (Proc. of SPIE Vol. 9422, 94220D, 2015). The good news is that many new FEL programs are in progress [9] and the LCLS-II at SLAC might provide a viable, solution for HVM/EUV lithography. More recently, visible collaboration between GLOBALFOUNDRIES and SLAC has established the ground work for possible in-fab FEL source designs. The subsequent challenge for any future FEL/EUV initiative, is that once again the convergence of the semiconductor industry and our national laboratory community will be required to deliver future lithography source technology for EUV and beyond.

ASML has taken the lead in providing viable interim EUV technology permitting the characterization of materials, resists, masks and process precision required for future generation lithography. Double patterning techniques utilizing 193i lithography will continue to enable CDs =<10nm. We can also speculate how 13.5nm multiple patterning might enable future nodes and continued process development. In the interim, the current ASML LPP/EUV initiative has enabled the ground work our industry requires for future precision nanometer scale lithography.

Let's continue working together to secure next generation EUV and the preservation of Moore's Law.

During the course of researching this article I digested many components of the SLAC Conceptual Design Report for the LCLS-II (Linear Coherent Light Source).  Among many, two components of the LCLS-II are the SXR (Soft X-Ray) and HXR (Hard X-Ray) undulators and their respective beam lines.  It is with some amusement that my FCC designated amateur radio call sign is WA2HXR which I acquired in 1970. It should be noted that my amateur radio operations are restricted to applicable licensed amateur radio frequency spectra which excludes X-Ray wavelengths.  
CQ SLAC CQ SLAC CQ SLAC DE WA2HXR K.     73   

Click here to download this article.

Thomas D. Jay
Semiconductor Industry Consultant
Thomas.Dale.Jay@gmail.com
https://ThomasDaleJay.blogspot.com
Thomas D. Jay YouTube Channel

Visit my new Amateur Radio blog at:
www.WA2HXR.blogspot.com


















Corporate, private entities or publications referenced or linked in this article are the respective owners of their logos, trademarks, service marks, media content and intellectual property. Unless otherwise disclosed, Thomas D. Jay has no financial interest in companies referenced in blog articles or other published media communications. Thomas D. Jay is not a registered financial advisor. No representation is made to either buy or sell securities. Opinions expressed by Thomas D. Jay are his own. Thomas D. Jay does not employ or otherwise utilize/authorize third party agents to express his opinions, represent his interests or conduct business on his behalf except where formally contractually designated. Thomas D. Jay does not agree to indemnify or hold harmless vendors, clients or third parties to related contractual agreements and reserves the right to applicable legal remedies in lieu of arbitration. These terms are subject to change. Concerned parties should check this blog site for periodic updates.

Acknowledgments and Reference Links

[1] Free Electron Laser
Wikipedia

[2] Future FEL/EUV Strategy – The Light at the End of the Beam Line
Thomas D. Jay, Blog Publication, September 20, 2014

[3] ASML and Carl Zeiss acknowledged in an invited paper at SPIE Advanced Lithography 2015, that higher resolutions will require 60mJ/cm2 for half pitch nodes <8nm
SPIE Proceedings

[4] Extending extreme-UV lithography technology
SPIE News Room, Erik R. Hosler, Obert R. Wood II, Moshe E Preil

[5] The first solid state, 694nm synthetic ruby laser produced at Hughes Research in 1960
Wikipedia

[6] Lawrence Berkeley CXRO Lab
Lawrence Berkeley National Labs CXRO Web Site

[7] Linac Coherent Light Source-II
Stanford Linear Accelerator Web Site

[8] LCLS-II and Free electron laser drivers for EUV Lithography
Aaron Tremaine Presentation, SLAC
EUV Litho, Inc. Web Site, 2015 Program, Maui

[9] many new FEL programs are in progress
University of California, Santa Barbara FEL Web Site
Site Maintained by G. Ramian


Friday, December 18, 2015

A Photonic Finish to the International Year of Light 2015 (updated)


The month of December 2015 concludes UNESCO's proclaimed International Year of Light. The National Photonics Initiative and its affiliates have sponsored and coordinated many educational and cultural programs during the year, all of them focused on the impact light based technologies have made on our social/global population.

As we conclude 2015 in the weeks ahead, we might pause to behold our handy work. Those of us in the semiconductor industry and broader electronic market place have delivered a multitude of miracles worth mention. New break throughs in LED/OLED and AMOLED display technologies have yielded 4K HD video resolution, four times the resolution of the 1080P video we thought so revolutionary. Quantum Dots are now being mass produced, extending both the efficiency and spectrum of available colors. Hang on, 16K HD video is not far down the road. Resultingly, our global Internet must be upgraded rapidly to accommodate throughputs required for bandwidth intensive applications.

IBM [1] and Intel's CL4 Alliance [2] will soon provide on-chip silicon photonic routers and switches to boost the speed and efficiency of server farms and cloud infrastructure. New techniques in the manufacture of optical fiber have boosted propagation speeds approaching 99% the velocity of light. [3] High power lasers with femtosecond pulse rates are enabling advanced imaging techniques.


Aixtron [4] and Veeco Instruments, Inc. [5] continue as key enabing equipment suppliers of MOCVD and related technologies for the manufacture of LEDs as the growth curve for this market segment continues.

On the semiconductor front, EUV progress at ASML [6] remains stalled until a more powerful source is developed. Although pilot line and limited production runs are possible, available up time remains problematic. In the interim, 193nm steppers will enable multiple patterning techniques. While viable, multiple patterning is a more costly path to nanometer scale lithography. Work continues on many fronts to enable increasingly demanding lithography requirements.

That said, the new year is rapidly approaching and we might shift gears to observe our handy work enabling its celebration. Everyone enjoys a great light show and new years eve is a great opportunity to show off the latest in illumination technology. High intensity LEDs and lasers have enabled large scale video display screens and special effect lighting while high power xenon strobes have become the norm. A company called Martin [7] manufactures a 3 kilowatt xenon strobe which can be mounted in arrays. Each strobe is numerically bus addressable and can be controlled by a master computer which "manages" the light show. When the strobes are integrated along side high intensity LEDs and video panels the resulting visual display is stunning and must be seen to be appreciated.

A great demonstration of these technologies took place at the Ultra Music Festival, an annual international event held in Miami during March of this year (2015). A segment of the festival featured a musical program by Armin van Buuren, an award winning Dutch pop music composer and DJ. During his performance Armin is perched on top of an enormous stage structure of metal girders and beams housing a monstrous array of high intensity LEDs and video displays. Arrays of Martin's Atomic 3000 DMX high intensity strobes are added to the mix. The strobes are so powerful that safety precautions must be observed at close quarters. In close proximity a three thousand watt xenon flash can cause burns and start fires. When the strobes are combined in cluster arrays the effect is multiplied but their remote positioning on the stage's superstructure assures the safety of the audience. I wondered what the EUV output might be (but I digress). I studied images of the festival on YouTube and estimated the power requirement for the lighting and sound systems on the massive stage must easily approach megawatt scaling.

The light show accompanying Armin van Buuren's performance at the Ultra Music Festival was nothing short of a super nova. Armin combined his many pop music compositions with improvised programming unique to the festival, all of which was synchronized with a computer system controlling the accompanying lighting and video effects. On stage, Armin can be seen wearing large black wrist bands on his forearms. The wrist bands are actually near field sensors which track the movement of his arms enabling him to physically control lighting effects during the show. Armin can be seen "pointing" beams of light into the crowd below. Later his arm motions direct waves of light and energy bolts over the massive stage and video screens. The best way to visualize what I'm describing is to watch Armin's Miami Ultra Music Festival performance on UMF TV as featured on YouTube.  [8]  Equally impressive is Dash Berlin's 2015 performance at the Ultra Music Festival in Tokyo [9]. Best viewing of the festival experience requires a large screen HD display with a good low end performance sound system or head phones.  Ultra Music Festival composures are referred to as "Trance Music" and for good reason. The bolts of sound and light are energizing and soon have everyone partying in a trance like state of euphoria. As for a new years celebration, I can't think of a better photonic finish to 2015 than the Ultra Music Festival in Miami earlier this year. During your off time over the holiday and new year, give it a look/listen on YouTube. The video's run time approximates 54 minutes
 and fits nicely in any one's holiday break schedule (it gets frequent rerun on my play list).

As we know, science fiction more frequently becomes science fact. The future's bright and you're gonna need shades.


Happy new year every one!


Thomas D. Jay
Semiconductor Industry Consultant

Thomas.Dale.Jay@gmail.com 
www.ThomasDaleJay.blogspot.com
Thomas D. Jay YouTube Channel


Visit my new Amateur Radio blog at:
www.WA2HXR.blogspot.com


http://www.linkedin.com/in/thomasdjay/

https://www.youtube.com/watch?v=vIiqAcGr614
www.npi.org











www.spie.org













https://youtu.be/-R8jJ0wPM2Q












Corporate, private entities or publications referenced or linked in this article are the respective owners of their logos, trademarks, service marks, media content and intellectual property.  Unless otherwise disclosed, Thomas D. Jay has no financial interest in companies referenced in blog articles or other published media communications. Thomas D. Jay is not a registered financial advisor.  No representation is made to either buy or sell securities. Opinions expressed by Thomas D. Jay are his own.  Thomas D. Jay does not employ or otherwise utilize/authorize third party agents to express his opinions, represent his interests or conduct business on his behalf except where formally contractually designated.  Thomas D. Jay does not agree to indemnify or hold harmless vendors, clients or third parties to related contractual agreements and reserves the right to applicable legal remedies in lieu of arbitration. These terms are subject to change. Concerned parties should check this blog site for periodic updates.

Acknowledgements and Reference Links

[1] https://www-03.ibm.com/press/us/en/pressrelease/46839.wss
IBM Press release, IBM web site May 12, 2015

[2] http://www.pcworld.com/article/2879152/intel-delays-part-for-highspeed-silicon-photonic-networking.html
PC World web site, Agam Shah, IDG News Service
February 2, 2015


[3] http://www.nature.com/nphoton/journal/v7/n4/full/nphoton.2013.45.html
Nature Photonics

[4] Aixtron
www.aixtron.com

[5] Veeco Instruments, Inc.
www.veeco.com

[6] ASML
www.ASML.com

[7] Martin Atomic 3000 DMX
http://www.martin.com/en-us/product-details/atomic-3000-dmx

[8] Armin van Buuren live at Ultra Music Festival Miami 2015 UMF TV
https://youtu.be/PbfSULQV9co

[9] Dash Berlin live at Ultra Music Festival Tokyo UMF TV
https://youtu.be/5YfWoVnAS_I

Thursday, May 28, 2015

Silicon Photonics in the Year of Light


https://www.youtube.com/watch?v=vIiqAcGr614
As we celebrate UNESCO's International Year of Light 2015, it is with some irony that earlier this month on May 12, 2015 IBM announced [1] it had fully fabricated and tested an integrated wavelength, multiplexed 100 Gb/sec silicon CMOS nano-photonic optical tranceiver chip whose design concept was first announced in December 2010 [2]. IBM's effort is echoed by consortiums of major players in the semiconductor industry, all in hot pursuit of silicon photonics [3] technology, and for good reason. The silicon photonics market is estimated to be worth $975 Million by the year 2020 [4]. Key players in this market include IBM, Intel Corporation and the CLR4 Innovators, PETRA (Japan's Photonics Electronics Technology Research Association), Hamamatsu Photonics, Finisar Corporation, Luxtera, Inc., ST Microelectronics, 3S Photonics, Oclaro Inc., Mellanox technologies, and Infinera Inc. The Optical Fiber Communication Conference and Exposition (OFC) [5] took place in Tokyo in March this year where many of these companies presented reports on their silicon photonic technologies.

IBM's recent announcement places emphasis on its compact device package and process proven fabrication techniques which will enable larger scale manufacturing of the devices for use in cloud computing and data centers in anticipation of “Big Data” network scaling. While IBM's most recent announcement is coincident with the International Year of Light, silicon photonics have been a glimmer in the eyes of semiconductor engineers for the past thirty years. In a recent SPIETV video presentation on silicon photonics, Yurii A. Vlasov of IBM [6] stated that during the past ten years over $1.5 B has been spent in the global quest for light based chip technology.  A portion of this investment resulted in an IBM silicon nano-photonic device design in which interconnected beams of wave guided light replace traditional electrical signals carried on copper circuit paths. Data carried by electrical signals on copper circuits propagate at only 66-70% of the speed of light as determined by dielectric properties near conductors and other physical factors. Device design engineers anticipated the day when this speed limitation would slow network server systems, as well as chip to chip intra-device data flow, and eventually singular on chip communications. To most smart phone owners, it's difficult to imagine a scenario in which electrical signals traveling at 66 to 70% of the speed of light becomes a limiting factor in computer chip design and performance, but in a world where global communications servers are linked by fiber optics, satellites and GPS navigation systems, cumulative device delay times have already created bottle necks in our global networks.

Interestingly, many original glass fiber optic cables transported light at about 70% of light's velocity in a vacuum.  New research and development in fiber optics and materials have resulted in the fabrication of optical fibers which can transport light at better than 99% of its vacuum velocity (186,282 miles/sec).  New silicon photonic devices are being optimized to provide maximum light velocity [7] while simultaneously implementing WDM (Wave Division Multiplexing) to maximize data speeds and throughput.  As such, silicon photonic devices might vary in performance as per the designs of their manufacturers.  

Why are silicon photonics important? I'll review some important observations I've made in my November 2013 blog article, “The Cloud of Nations” [8].

On a global scale we observe that in a vacuum, light travels approximately 186,282 miles per second and can circle the earth in 134 milliseconds (about one tenth of a second). If we consider the earth as a large computer, the continents might be compared to microprocessors interconnected by our global Internet, milliseconds apart. If we observe our immediate, personal photometric sphere of existence, we find that in one nanosecond light travels one foot. How precise must our world be?

Chip Level Clock Skew

In the metrics of semiconductors nanosecond measurements are woefully imprecise and we must calibrate metrology in picoseconds in order to measure the speed of data traversing millimeter sized computer chips. In the semiconductor industry we refer to differences in data arrival time on a computer chip as clock skew. On a real semiconductor device, electrical signals on copper conductors travel at approximately 66-70% of light speed. An acceptable clock skew range approximating 20 to 200 picoseconds (pico = 10^-12) usually provides acceptable device performance but this specification can vary across device types and circuit designs. For each tick of the chip's master system clock, billions of transistor gates must be switched on and off in precise unison. A microprocessor operating at a 2 gigahertz clock speed must have sufficient temporal uniformity across the device so that the arrival time of gate switching signals are all within an acceptable time window. If the switching signal's arrival time falls outside this window, the microprocessor and the program it's running will crash. Careful design considerations go into device fabrication technique and wafer processing to ensure product and performance quality. More information on computer chip clock skew can be found in the paper “Skew Variability in 3-D ICs with Multiple Clock Domains” [9] Hu Xu, Vasilis F. Pavlidis, and Giovanni De Micheli, LSI - EPFL, CH-1015, Switzerland Email: {hu.xu, vasileios.pavlidis, giovanni.demicheli}@epfl.ch

As clock speeds increase and device geometries decrease, the <10nm design node will pose additional technical challenges in device timing and data throughput. The evolution of light speed photonic interconnects for on and off chip communication will minimize concerns with clock skew across chips and networks as device structures shrink to critical dimensions (CD) <10nm and become stacked in dense arrays. As the integration of CMOS silicon nano-photonics matures, we may eventually see microprocessors, memory chips and 3D devices structured on photonics instead of conventional copper conductors. In the interim, IBM anticipates that the more immediate advantages afforded by silicon nano-photonic inter-chip speeds could dramatically improve cloud server/network performance, and advance its Exascale super computer initiative which could potentially perform over a thousand times the speed of currently available systems. While the initial focus of silicon nano-photonics targets network centers and cloud servers, the wider proliferation of the technology can profoundly effect our evolving Internet.

IBM's silicon photonic chip will address concerns across networks as four 25 Gb/sec optical tranceivers operating on as many different wavelengths will combine to provide a throughput of 100Gb/sec. Installed in server systems, these optical chips could dramatically improve data throughput, reducing network latency and clock skew by eliminating delays inherent in copper conductors found in servers and data center network interfacing. Using sub 100nm design rules (typically 90nm), electrical and optical device structures are formed on the same substrate to maximize efficiency. IBM estimates the device's bandwidth can accommodate the transfer of a high definition movie (approximately 1.5 to 2 Gigabytes) in two seconds.

To achieve maximum bandwidth over distance, most of today's data centers employ Vertical Cavity Surface Emitting Lasers (VCSEL) distributed on multi-mode optical fiber. Remotely located cloud servers have placed new demands on network resources as even larger bandwidths over greater distances are required. To illustrate the importance of IBM's initial 2010 achievement, note that IBM's on-chip silicon photonic wavelength multiplexing emulates the initial success of dense wave multiplexing utilized in early generation fiber optic networks, the major difference being that IBM has achieved this capability at the chip level.  Previous dense wave fiber optic implementations utilized bulky hardware to enhance long haul fiber optic bandwidth. In 1998, AT&T researchers transmitted 100 simultaneous optical signals, each at a data rate of 10 gigabits per second over a distance of 400 km utilizing dense wavelength-division multiplexing (DWDM) technology [10], allowing multiple wavelengths to be combined into one optical signal. This technique increased the total data rate on one fiber to one terabit per second. Although IBM's current silicon photonic chip design utilizes 4 discreet channel wavelengths providing 100Gbit/sec, data throughput is scalable and could be configured to accommodate many demanding applications. While IBM's silicon nano-photonic initiative is impressive, significant global competition is not far behind.

Intel's CLR4 Silicon Photonic Initiative

The silicon photonic initiative is also being pursued by Intel [11] who has helped form a consortium of companies to agree upon product designs and industry standards. The CLR4 Innovators [12] are an alliance of 27 companies inclusive of Intel, HP, Dell, MACOM and SEMATECH (see the above CLR4 link for a complete list).  In April 2014, Intel outlined its silicon photonic initiative in a presentation [13] which addresses the common requirements of the CLR4. The 100 Gb/sec silicon photonics under development utilizes 4X25 Gb/sec tranceivers which can span 1000 meters to link server centers.

Unfortunately, Intel's initiative was set back in February this year as a key component in its silicon photonic module did not meet specifications and quality control standards. [14] The new modules will not ship till the end of 2015 which means they won't be installed till early 2016. Intel's customers (and possibly CLR4 Innovator members) intending to integrate its silicon photonic technology are in a holding pattern till next year.


PETRA's Silicon Photonic Demonstration

Japan's Photonics Electronics Technology Research Association (PETRA), recently demonstrated [15] 100 Gb/sec transmissions over 300 meters using its silicon photonics device technology. The device's 5mm x 5mm package containing 4x25 Gbp/sec transceivers, can be expanded to 12 or more channels to obtain throughputs greater than 300 Gbp/sec.  This scalability enables accommodation of future demands and upgrades of installed network infrastructure.  


Silicon Photonic Research at IMEC

IMEC is also active in silicon photonic research. In February 2015 this year at the International Solid State Circuits Conference, IMEC and its collaborators released results of recent developments in their laboratories [16] demonstrating a 4x20 Ghz/sec wavelength division multiplexing hybrid CMOS silicon photonics tranceiver.  The larger global effort to standardize silicon photonic performance specifications sets the stage for future implementation over many platforms.


Silicon Photonics and The "Internet of Things"

Silicon photonics can assist us in resolving a potential net neutrality dilemma. Much has been debated regarding the FCC's recent adaption of a net neutrality policy which precludes Internet service providers from charging premiums for high speed commercial traffic on the web while intentionally throttling speeds on their networks. Conspicuous consumption of bandwidth by consumers is now the norm given HD and 4K video programming available on the web. If you travel frequently and patronize fast food establishments or coffee shops and use their complementary Wi-Fi systems, you become acutely aware of the limitations on available bandwidth. Many fast food restaurants preface their Wi-Fi login screens with disclaimers of suitability for a particular use, proclaiming “intended for text and email only” and “not intended for video streaming”. All too often, email and other essential services are slow when compared with Asian and European networks. The intentional throttling of Wi-Fi bandwidth often lowers video resolutions to “wax paper” quality. It's disheartening to see 1080P video rendered at resolutions below that of 1960s era analog broadcast quality. Will the FCC's net neutrality policy effectively address these concerns? Should the concept of net neutrality also accommodate the anticipated “Internet of Things” (IoT)? The IoT envisions the interconnection of “things” on the web to include household utility monitors, appliances, cars, watches, and any imaginable “thing” assigned an IP address. A few months ago I read a story describing hackers launching malware they had placed on someone's refrigerator sporting an on board computer. The fridge's door featured an HD flat screen providing an interactive family kiosk in the kitchen, but connected to the web it also kept malware in cold storage. Should ISP's be required to provide equal bandwidth and network routing for email, video conferencing, refrigerators and toasters? A humorous question, but if you're video conferencing from the fridge while snacking in the kitchen, net neutrality/equality for appliances becomes a pertinent IoT policy discussion. That said, the new IPv6 Internet protocol will provide an exponential increase in available URL's required for new email addresses, web sites and “things” attached to the web. Accordingly, the projected increase in Internet traffic can only be accommodated by enhancing routing systems and cloud services, ensuring network speeds are optimized and remain viable as global connectivity escalates.

In this regard we might agree that from both consumer and enterprise perspectives, silicon photonic solutions are long overdue and will enjoy rapid acceptance when available for shipment and implementation.

Closing Thoughts

- It will be interesting to track the evolution of silicon photonics as market demands are met with the delivery of Intel's technology to the CLR4 group of companies.

- IBM will seek to optimize its positioning in the enterprise markets, leveraging its silicon nano-photonics, cloud server infrastructure and possible ramp of MRAM technology for strategic product applications. IBM's advances could also provide “warp speed” for networks if additionally optimized with its fasp (TM) Aspera [17] file transfer platform.

- IMEC could leverage its own silicon photonic designs as its partnered R&D effort yields finished products ready for deployment.

- PETRA and its member companies have demonstrated competitive silicon photonic technology with the ability to scale for future throughput demands. 

- Possible additions to the silicon photonic market equation are prospects for more efficiently deployed Software Defined Networking (SDN) [18] which could reduce traditional hardware and infrastructure costs while enhancing network speed, efficiency and reliability.

- Lucent Bell Labs has introduced an ultra-dense network architecture designed for silicon photonics at the optical network unit. [19] A proof of principal experiment demonstrated an FDMA architecture providing up to eight 300-MBd 16QAM (Quadrature Amplitude Modulation) subbands providing a bidirectional data rate of 9.6 Gb/sec.

As silicon photonic infrastructure expands to enhance our global networks, we may eventually see the migration of this technology to microprocessor and memory devices for use in super computing and consumer products.  Congratulations to IBM, Intel and the global technology alliance members who are working to enlighten our future with photonics.

Please join me in supporting SPIE and the International Year of Light 2015 [20] (click on the icons below for additional site links).

Thomas D. Jay
Semiconductor Industry Consultant

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Corporate, private entities or publications referenced or linked in this article are the respective owners of their logos, trademarks, service marks, media content and intellectual property.  Unless otherwise disclosed, Thomas D. Jay has no financial interest in companies referenced in blog articles or other published media communications. No representation is made to either buy or sell securities. Opinions expressed by Thomas D. Jay are his own. Thomas D. Jay does not employ or otherwise utilize/authorize third party agents to express his opinions, represent his interests or conduct business on his behalf except where formally contractually designated.  Thomas D. Jay does not agree to indemnify or hold harmless vendors, clients or third parties to related contractual agreements and reserves the right to applicable legal remedies in lieu of arbitration.  These terms are subject to change. Concerned parties should check this blog site for periodic updates.

Acknowledgements and Reference Links

[1] https://www-03.ibm.com/press/us/en/pressrelease/46839.wss
IBM Press release, IBM web site May 12, 2015

[2] https://www-03.ibm.com/press/us/en/pressrelease/33115.wss
IBM Press Release, IBM web site, December 1, 2010

[3] http://en.wikipedia.org/wiki/Silicon_photonics
Wikipedia

[4] http://electronics.wesrch.com/paper-details/press-paper-EL1GP94JCLEHH-silicon-photonics-market-worth-497-53-million-by-2020
WeSRCH web site, MarketsandMarkets press release uploaded May 27, 2015

[5] http://www.ofcconference.org/en-us/home/about/
OFC web site

[6] https://www.youtube.com/watch?v=KRY53sEXyNI
Yurii A. Vlasov, SPIETV, YouTube

[7] http://www.nature.com/nphoton/journal/v7/n4/full/nphoton.2013.45.html
Nature Photonics

[8] http://www.thomasdalejay.blogspot.com/2013/11/the-cloud-of-nations.html
ThomasDaleJay.blogspot.com

[9]http://infoscience.epfl.ch/record/173534/files/ISCAS_11_1.pdf?version=1
InfoScience web site, Hu Xu, Vasilis F. Pavlidis, and Giovanni De Micheli, LSI - EPFL, CH-1015, Switzerland Email: {hu.xu, vasileios.pavlidis, giovanni.demicheli}@epfl.ch

[10] http://www.fiber-optics.info/history/P3/
Fiber Optics History web site

[11] http://www.intel.com/content/www/us/en/research/intel-labs-silicon-photonics-research.html
Intel web site

[12] http://www.intel.com/content/www/us/en/research/intel-labs-clr4-adopter-listing.html
Intel web site

[13] http://www.intel.com/content/www/us/en/research/intel-labs-clr4-presentation.html
Intel web site

[14] http://www.pcworld.com/article/2879152/intel-delays-part-for-highspeed-silicon-photonic-networking.html
PC World web site, Agam Shah, IDG News Service
February 2, 2015

[15] http://www.ofcconference.org/en-us/home/news-and-press/exhibitor-press-releases/petra-demonstrates-low-power-silicon-photonics-i-o/
OFC website

[16] http://www2.imec.be/be_en/press/imec-news/imec-ugent-tyndall-silicon-photonics-transceiver.html
IMEC web site

[17] http://asperasoft.com/resources/white-papers/ultra-high-speed-transport-technology/?gclid=Cj0KEQjw1pWrBRDuv-rhstiX6KwBEiQA5V9ZoXa1_o6T48KX_XxsJ95irqG6EuLgXtaJmB7fkHAFaNsaAnzj8P8HAQ
IBM Aspera web site

[18] https://en.wikipedia.org/wiki/Softwaredefined_networking
Wikipedia

[19] http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6997998
IEEE Xplore web site


[20] https://www.youtube.com/watch?v=-R8jJ0wPM2Q
International Year of Light 2015, Official Trailer, YouTube

Thursday, April 23, 2015

A Defining Inflection in the EUV Continuum


https://www.youtube.com/watch?v=vIiqAcGr614An April 22, 2015 ASML press release [1] announced an agreement with one of its major US customers (believed to be Intel) to purchase a minimum quantity of fifteen of its NXE:3350B EUV lithography systems with two of the units slated for delivery year end 2015. Intel has previously invested over $4 Billion in ASML. Given the size of the order, it would appear that Intel will proceed with a large scale strategic commitment to EUV lithography for future production process nodes =<10nm, with a path to 7nm and smaller CDs.

Although financial details of the purchase were not released, a sizable capital equipment expenditure has been made after many years of delay and uncertainty in the EUV program. This purchase transaction represents a large scale, high profile commitment to what has been a capital intensive development program delayed by uncooperative laws of physics, semiconductor sector business cycles, and capital market dynamics. It seems that the semiconductor production road map has been sufficiently refined, concomitant with related process technologies, and that confidence has been restored in long term EUV/HVM convergence/insertion forecasting. Although Intel's eventual commitment to production EUV had been anticipated, the waiting game is over. The remaining field of industry players who have withheld their commitments to EUV might now be motivated to secure anticipated purchase positioning with ASML before delivery date extensions become a concern.

SPIE Advanced Lithography 2015 was likely a key catalyst triggering this defining inflection point as process experts from around the globe converged to announce new and encouraging breakthroughs in lithography and related technologies which have heretofore gated the EUV program. We might review some of the important observations and breakthroughs which comprise the critical mass of the inflection:


EUV Inflection Triggers
Probable Key Factors in Intel's EUV Decision

- While lithographers have entertained DSA and electron beam lithography as developmental candidates for 7nm scaling, given current evolution, only 13.5nm stepper/scanners can provide the image resolution and throughput required for both pilot line and future HVM.

- SEMATECH recently announced the development of a metal oxide based photoresist which reduces the EUV power output required for EUVL dosimetry (typically 15 – 20 mJ/cm2) to less than 2 - 3 mJ/cm2. [2] The new resist enables process development at reduced EUV power levels, but will not eliminate the future requirement for higher HVM source power. In the interim, it's possible that process solutions can be built around this low dose resist, enabling further, accelerated development of EUV HVM.

- During SPIE Advanced Lithography on February 24, ASML announced TSMC's confirmation that it had processed 1022 wafers in twenty four hours [3] on its NXE:3300B with a sustained source power of 90 watts. There is encouraging new data illustrating improved MTBF while sustaining EUV source operation at higher power levels.

- ASML has made significant over all progress in EUV development and has recently updated its time line for implementation of key milestones. ASML released many new updates on their EUV program at SPIE Advanced Lithography 2015 which were quite voluminous (see the post conference SPIE abstract summary).

- Obstacles to 7nm and future nodes have been addressed. ASML and Carl Zeiss acknowledged in an invited paper at SPIE Advanced Lithography 2015, that higher resolutions will require 60mJ/cm2 for half pitch nodes <8nm. [4] ASML's work with Carl Zeiss has produced an optical system with a numeric aperture (NA) of 0.55 vs. ASML's current EUV NA of 0.33. The higher NA system will require 500 watts of EUV power to achieve the estimated 60 mJ/cm2 dosimetry required for throughput of 150 wafers/hour. While this ASML/Carl Zeiss achievement paves the way for =<7nm process nodes, current R&D programs are also under way to provide a visible path to a >500 watt free electron laser EUV source, identifying one of the last major puzzle pieces in ASML's EUV endeavor. While ASML continues to refine Laser Produced Plasma source technology, the future availability of a >500 watt free electron laser EUV source remains a critical item on the agenda, and will probably gate the time lines of related programs.

- ASML has entered the pellicle business in the self interest of providing viable protection for EUV photomasks from particulate contamination. The polysilicon based pellicles are transparent to EUV with a one pass transmission loss approximating 14% and seem to exhibit sufficient durability for use in production. Previous uncertainty in EUV pellicle viability and availability have been resolved.

- As a key semiconductor industry supplier, Veeco Instruments has been successful in providing ion beam deposition tooling enabling EUV mask fabrication for advanced process nodes within acceptable defect limits. Defect free mask fabrication for advanced nodes has been a gating factor in the EUV program.

- Advancements in actinic inspection are progressing. Lawrence Berkeley National Laboratory's CXRO has been developing the SHARP EUV microscope in cooperation with SEMATECH . [5] A progress report on mask inspection was made at SPIE Advanced Lithography 2015. The SHARP EUV microscope is illuminated by an EUV synchrotron light source within the CXRO complex. The commercial availability of EUV obtained from free electron laser technology could enable the emulation of SHARP's capabilities given comparable optical and analytical performance.

- Future commercial availability of free electron laser EUV sources could also offset concerns gating the development of actinic inspection tools by KLA-Tencor and others. Given proper design, it's possible that a single free electron source beamline could provide EUV source illumination for both stepper/scanner clusters and in-line actinic inspection tools.

- Recent successes at TSMC with ASML's NXE:3300B EUV systems have prompted an additional order for two newer model NXE:3350B tools. As foundry commitments to EUV lithography continue, Intel has taken a major strategic step to ensure its competitive leadership positioning in the global wafer fabrication market.


No doubt there were many other considerations factored into Intel's EUV purchase decision. Ultimately the achievement and convergence of key process and equipment performance concerns have prompted a major commitment to both lithography and investment strategy over the longer term. In doing so, Intel has set a defining course for the semiconductor industry.


Please join me in supporting SPIE and the International Year of Light 2015 (click on the icons below for additional site links).

Thomas D. Jay
Semiconductor Industry Consultant

Thomas.Dale.Jay@gmail.com
www.ThomasDaleJay.blogspot.com
Thomas D. Jay YouTube Channel



http://www.linkedin.com/in/thomasdjay/


https://www.youtube.com/watch?v=vIiqAcGr614
www.npi.org











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Corporate, private entities or publications referenced or linked in this article are the respective owners of their logos, trademarks, service marks, media content and intellectual property.  Unless otherwise disclosed, Thomas D. Jay has no financial interest in companies referenced in blog articles or other published media communications. No representation is made to either buy or sell securities. Opinions expressed by Thomas D. Jay are his own. Thomas D. Jay does not employ or otherwise utilize/authorize third party agents to express his opinions, represent his interests or conduct business on his behalf except where formally contractually designated.

Acknowledgements and Reference Links

[1] ASML press release