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Showing posts with label z-pinch. Show all posts
Showing posts with label z-pinch. Show all posts

Wednesday, August 7, 2013

The Continuing Evolution of Extreme Ultra Violet Lithography


On July 17, 2013 in a qualified safe harbor statement, an ASML press release (NASDAQ:ASML) announced its second quarter earnings and also indicated that its EUV platform, scanner imaging and overlay performance improved to levels enabling engagement with customers on a strategy targeting insertion at the 10nm logic node.  Additional discussions concerned strategies in which the first NXE:3300B systems running at currently available EUV power levels are utilized for production of future nodes at reduced throughput in place of mask strategies utilizing 193i multi-patterning techniques. Customers will be able to upgrade their systems as higher power levels become available and avoid a costly process transition from 193i to EUV HVM.  Combined with currently available multiple-patterning capabilities on existing 193i platforms, ASML could provide the best possible options for customers.  In the second quarter, ASML achieved good performance, stability and reliability of the pre-pulse source concept at power levels up to 55 Watts, and remains confident of targeted throughput of 70 wafers per hour in 2014.  ASML projects availability of upgraded systems with 125 wafer per hour throughput in 2015 provided further development of EUV power output progresses as planned. Additional strategies are being considered for continued funding of additional R&D on EUV.   450mm HVM insertion is anticipated in 2018.  News Source: Seeking Alpha.com 7/17/2013.

The semiconductor equipment industry participants driving the evolution of EUV (Extreme Ultra Violet) and nanometer scale lithography might be characterized as "tag team" players as process enabling technologies provided by an interactive vendor base will often trigger a cascade of new concepts and innovation frequently spawning “disruptive technologies”  The semiconductor lithography market is technologically unique, supporting many diverse products demanding application specific process solutions.  Although this market place can seem extraordinarily complex it is commonly bound by the semiconductor industry phenomenon known as Moore's Law which states that the number of transistors on semiconductor devices doubles approximately every two years, reducing costs.  During the past several years semiconductor lithographers have been pursuing the means to create a sufficiently powerful source of EUV (Extreme Ultra Violet) light for use in next generation lithography stepper/scanners.  These complex machines are used to mass produce semiconductor “computer chips” utilizing a photolithography process similar to conventional film photography, the difference being the “photo negative” is actually comprised of many individual photo masks (as many as 50 or more), providing the discrete image negatives required for each process layer in a complex semiconductor device.  EUV light source technology is being pursued as the emitted 13.5nm light's wavelength is short enough to produce high resolution circuit imaging for present and future 14, 10 and 7 nanometer scale device structures. Although several well established companies in the field of semiconductor lithography have participated in the development of EUV technology the expense and diminishing returns on investment have narrowed the playing field to a few.  Lithography giant ASML based in the Netherlands recently purchased a key lithography light source supplier, Cymer, in an effort to consolidate EUV development efforts and secure the timely delivery of critical source components.  Underscoring the strategic value of EUV lithography are recent investments made in ASML by Intel, Samsung, and TSMC which total more than $6 Billion. To date, ASML and Cymer have produced excellent EUV lithography imaging with an available light source power output approximating 55 watts.  This is about half the power required to support the throughput of high volume manufacturing (HVM).  After years of industry anticipation, delayed development of EUV power output has put some semiconductor industry professionals in an uneasy holding pattern.  Although multiple patterning techniques for 193i lithography provide feasible lithography solutions in the interim, most would prefer a simplified EUV lithography process solution requiring fewer mask levels at reduced cost.  In light of ASML's recent announcements some are reconsidering the current status of EUV lithography development and the implementation of available alternatives such as double patterning and Directed Self Assembly (DSA) techniques.  In an effort to gain additional insight and inspiration from established experts in the EUV community my inquiries revealed that many are reluctant to speak to the current situation and perhaps for good reason. It is difficult to speculatively comment on the efforts of lithography industry experts who have diligently achieved the excellent results obtained thus far.  It appears we've hit a physical wall which has temporarily stalled EUV development and delayed the HVM insertion time line.  As we have learned over the years, difficult tasks sometimes take longer to complete.

In the interim 24 months ahead we must also realize that the semiconductor industry will assimilate a new crop of scientists, electrical engineers, sales, marketing and application specialists along with the traditional complement of Wall Street industry analysts and investors.  To the new and uninitiated intelligentsia, EUV technology might require some explanation.  Educating new entrants to our industry is always a challenge.  As a technologist you might have a friend or relative who've asked about your work in semiconductors and observed their eyes glaze over as you explain.  As we pause to await news of higher EUV output power, I will utilize the available “dwell time” to provide an EUV primer for new industry participants and observers and hopefully fill in the blanks for our current, friends and colleagues.  Where to begin?                    


Plasma 101

Unlike solid, liquid or gas, plasma, the fourth state of matter exists within a narrow, low pressure domain approximating 1/760th of our atmosphere at sea level.  Positively ionized plasma can be created in this low pressure regime by inducing high energy electron collisions with gas molecules displacing orbital electrons normally found in the stable atoms comprising the gas.  The imparted electrical imbalance causes the gas molecules to gain a net positive charge as there are more positive protons remaining in the atoms/molecules than negatively charged electrons.  The resulting plasma is a glowing cloud of charged particles and gas molecules having a positive electrical potential and the conductivity of copper while simultaneously emitting light comprised of photons with the characteristic color of its elemental spectra.  Utilizing Italian physicist Torricelli’s scale, the pressure of the air at sea level is 760 Torr.  More specifically, the pressure at which electrical gas plasma can be created and sustained approximates 5x10-4 Torr, a near vacuum at less than 1/760th of the pressure of our atmosphere.  At an altitude of 84 kilometers above the earth and well below the international space station, the pressure in near outer space falls within this range and is conducive to the natural creation of plasma known as the aurora borealis.  This phenomenon occurs when high energy “solar wind” from the sun ionizes oxygen, nitrogen and other gases in the upper atmosphere in the presence of earth's magnetic field.  Back on terra firma, high vacuum technologists design and maintain carefully engineered process chambers simulating pressures ranging from ambient atmosphere to the ultra high vacuum of deep outer space.  Scientists and electrical engineers utilize these physical phenomena and resources to generate, contain and control high energy plasma by electrically ionizing specially selected process gases at precise pressures in high vacuum systems. Plasma etchers utilized in semiconductor wafer fabs were among the first process tools to adapt this technology.  In this application, plasma is generated to produce ions for etching semiconductor wafers.  The incidental light emitted from the plasma can be utilized to monitor the process.  The primary methods for ionizing these gases include hot cathode/filament electron discharge, microwave excitation, and RF (Radio Frequency) energy excitation.  Interestingly the Federal Communications Commission has designated special radio frequencies for use in plasma etch systems.   A common frequency utilized for RF plasma etchers is 13.56 MHz.  As a ham radio operator I am more spectrum conscious than most and when near a wafer fab I sometimes tune in with my mobile transceiver to listen for “etchers on the air”.  The received signal is not particularly exciting and is usually a continuous uninterrupted carrier wave sometimes producing a loud heterodyne when tuned in the single side band mode.

In this semiconductor manufacturing application of physics, positively charged high energy ions are created in these special plasma systems and utilized to etch semiconductor circuits on silicon wafers.  The ions having mass and kinetic energy bombard the surface of product wafers and selectively etch surfaces to form intricate device structures and circuit patterns from the metal film and materials left behind.  A variety of gases are utilized to etch process specific materials on product wafers.  Some of the gases utilized are also chemically reactive and can selectively enhance the etch rate of specific materials on a wafer's surface.  Other noble gases are chemically inert (non-reactive) and advantageous for a wide range of etch applications.  Plasma etch chambers emit a characteristic light whose primary color/wavelength is determined by the elemental composition of the process gas.  Argon gas for example emits a purple glow which is pleasing to the eye. This spectral phenomenon is often utilized as a process indicator to determine when a critical etch step must stop. While etching a thin film metal, a faint light emitting plasma with the metal's signature color/wavelength is also produced. Using optical end point detectors, process engineers can sample the spectrum of light emitted from the plasma to detect the metal's specific signature wavelength.  When this spectral signature disappears the metal etch process is deemed complete as there is no remaining metal being ionized.  This “end point” signal is typically used to automatically stop the etch cycle providing highly accurate process control and negates any manual intervention by wafer fab engineers.  A key observation of these phenomena are that elementally specific positively charged particle ions (mass specific) and photons (wavelength specific light) are created during the ionization process.  The science of plasma physics for etching semiconductor circuits has been refined over the years by companies like Applied Materials, Lam Research and Veeco Instruments (there are many others) however, the plasma physics required to produce 13.5nm EUV for lithography are quite different and much more challenging.  

Producing Extreme Ultra Violet Light With Plasma

For several years the semiconductor industry has been engaged in the research and development of next generation nanometer scale lithography requiring a precision stepper/scanner equipped with a 13.5nm light source.  For lithography applications, plasma is created for the purpose of generating light at specific wavelengths.  The production of ions and other charged particles is incidental and sometimes suppressed to avoid etching and erosion of sensitive components in the source and wafer stage. Utilizing the most current methods for producing this light, lithography research engineers create a plasma which emits 13.5nm EUV from the resulting ionization of xenon gas (Xe), or the solid metal tin (Sn).  As a gas, xenon ionizes easily but has a lower energy Conversion Efficiency (CE) than tin.  ASML has chosen solid tin as the plasma feed material for its EUV light source because of its higher energy conversion efficiency.  Creating an ionized tin plasma is more difficult and also creates unwanted particulates which can potentially contaminate EUV masks and product wafers. Although the 13.5nm spectra has been dubbed EUV (Extreme Ultra Violet) it can also be described as “soft x-ray” radiation or “vacuum EUV” as it is absorbed by many gases and propagates most efficiently in a high vacuum environment.  Extremely short wavelength EUV light will enable semiconductor lithographers to print ever smaller transistors and associated circuitry on computer chips reducing CD features (Critical Dimensions) down to nanometer scales and below.  Utilizing a current 22nm fabrication process, a state of the art Intel Quad core i7 microprocessor introduced in the year 2012 contains 1.4 billion transistors.  Moore's law marches on and future process nodes will soon shrink to 14, 10 and 7nm.  Imagine your smart phone's chip sets with the processing power of another billion or so transistors.


A Best Of Breed EUV Source?

As there has been significant wide ranging research on the subject of EUV source technology, I will focus on the most current technology utilized by ASML and will discuss possible alternately efficient means of EUV production. Having conducted research on past experimentation and published papers, I will direct attention to recent prior work having potential to enhance EUV source performance.  By “borrowing” concepts from the most promising efforts I will propose a possible “best of breed” hybrid EUV source design.  I suspect similar dialogue and debate has been conducted previously.  My intention is to foment new discussion which might yield solutions providing the EUV power output and performance required for HVM lithography (High Volume Manufacturing).   


ASML's EUV Source Design

ASML/Cymer's current technique for production of EUV light utilizes Laser Produced Plasma (LPP).  In this different approach to producing plasma, small droplets of tin approximating 30 microns in diameter are injected into an ionization source and targeted by a solid state “pre-pulse” laser.  The imparted energy from the pre-pulse laser enlarges the tin droplet and raises its energy state, providing a larger cross sectional profile for a more powerful 20 kilowatt CO2 laser.  After pre-pulse conditioning, the tin droplet is targeted with the larger CO2 laser resulting in the high energy evaporation and ionization of the tin, releasing 13.5nm EUV light as a result.  A continuous stream of tin droplets and sustained laser interaction produces stable EUV light output commensurate with requirements for precision lithography and dosimetry.  Utilizing this technique, current EUV power output levels of 55 watts have been achieved, about half the power required for HVM (High Volume Manufacturing).  In the quest for more EUV power output, I suspect ASML and Cymer will experiment with larger, more powerful lasers while optimizing other coincidental parameters.  While successfully producing EUV light, an Sn/LPP source produces a large number of tin particulates as the targeted tin droplet residue collects on exposed surface areas in the ion source and wafer stage. Reflective EUV optical mirror surfaces can lose efficiency (reflectivity) when coated with tin, while EUV masks and product wafers can be compromised if contaminated with particles as small as one nanometer.  A more recent technique for keeping surfaces clean is to direct a beam of hydrogen ions from a small, integral ion source at critical optics and wafer stage components.  Experiments implementing a hydrogen plasma clean cycle as part of a periodic maintenance regimen have also been suggested. The challenges in the design and implementation of EUV technology for high volume manufacturing are formidable.  


Z-Pinch Discharge Produced Plasma Source Technology

A Z-pinch source, consists of an insulated containment cylinder with electrodes attached on either end, mounted inside a vacuum chamber.  For the creation of EUV light emitting plasma, a gas such as SnH4 (Stannane) or xenon (Xe) is fed into the cylinder and pre-ionized with the resulting plasma having the electrical conductivity approximating that of copper.  A large pulse of electrical energy stored in a bank of capacitors or from a power supply is applied to the electrodes at the ends of the cylinder.  As a result, a large current flows through the electrically conductive plasma causing it to contract as a phenomenon known as the Lorentz force compels the mutual attraction of the ions flowing uniformly along the z-axis of the plasma. The term z-pinch is derived from the fact that the current flows along the z-axis of the plasma as it is being compressed and pinched. The contraction continues until the plasma becomes highly dense and further compression is resisted by the gas pressure comprising the plasma. Ultimately, the maximized “pinch” density releases a large burst of energy comprised of ions and characteristic spectral light.  In the case of SnH4 and Xe, Discharge Produced Plasma EUV light with a wavelength of 13.5 nanometers is emitted in the process.  A continuous, controlled flow of source gas and carefully timed high current pulses through the source cylinder repeat this cycle, sustaining the plasma and output of EUV light.  This is achieved by pulsing the power supply and the resulting high current flow through the conductive plasma between 6 and 8 thousand times a second.   A power supply pulsed at approximately 7 Khz usually delivers maximum output for this design.  Z-pinch operation can be further optimized by controlling the power supply frequency, pulse width and amplitude providing effective wave form control and regulation of power fed to the source.   With the power supply operating at a the relatively low frequency of 7 Khz, a computer operating at 1.5 to 2.0 GHz can be utilized to sample the sinusoidal/waveform input power and resulting EUV output at the wafer stage making it possible to close loop control associated lithography dosimetry and related functions.


Ushio's Sn/DPP EUV Source Design

At the SPIE 2007 International EUVL Symposium, Ushio published a paper on results obtained from experimentation conducted on a Discharge Produced Plasma EUV source utilizing SnH4 (Stannane) as the feed material: Development of Sn-fueled high-power DPP EUV Source Enabling HVM.  In this design a Z-pinch DPP source was fed with gaseous SnH4 providing the energy conversion efficiency of tin while affording the simplicity of source gas handling with conventional mass flow controllers and pressure measurement instruments.  Interestingly, Ushio's Discharge Produced Plasma (DPP) source produced 62 watts of EUV output utilizing gaseous SnH4 as compared with ASML's recently quoted EUV power output of 55 watts obtained with a Laser Produced Plasma sustained with source fed solid tin droplets.  A power output comparison of the two technologies builds a case for continued development of an SnH4 Discharge Produced Plasma EUV source with a more simplistic design.  An additional benefit of using SnH4 as a source feed material is it minimizes the erosion of electrodes and critical surfaces in the z-pinch tube.  

Zplasma's Xe/Stable DPP Z-Pinch Source With
Sheared Flow Stabilization (SFS)®

In my previous blog articles I've had the opportunity to interview Henry Berg, CEO of Zplasma, and discuss his company's Xenon based Discharge Produced Plasma EUV source.  Zplasma's Stable DPP source is quite different from the generic DPP description above.  Zplasma's stable pinch operation results from a patented, proprietary technique called Sheared Flow Stabilization (SFS)® which stabilizes the plasma and eliminates explosive pinch terminations. The stable pinch operation of an SFS design DPP source is required to produce the high power levels required for HVM lithography. As described by Henry Berg, there are six critical advantages to Zplasma's SFS source technology:

a) Longer Light Pulse: SFS pulses are 10 to 100 times longer due to their stable nature, allowing for more light collection.

b) High Power without High CE: Long SFS pulses and side-on optical collection access increase throughput and lower required CE, enabling HVM operation with xenon and eliminating the need for molten tin.

c) No Debris: SFS ends the plasma pinch without explosive termination, eliminating high-energy debris.

d) Low Instantaneous Power: SFS pulses allow for EUV light production without the high instantaneous power levels that cause electrode thermal stress and ablation.

e) Dose Uniformity: SFS allows the length of each EUV pulse to be adjusted under control of the power supply, allowing for extremely accurate dose uniformity.

f) Adjustable Geometry: SFS makes pinch geometry adjustable for optical matching to the stepper IF.
  
Given Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP) design concepts, how might we improve EUV power output and system performance?


Minimizing Source Plasma Opacity
Maximizing EUV light Output

EUV light emitted from a tin or xenon plasma discharge is partially absorbed by the opacity of source plasma.  More specifically, the 13.5nm light is readily absorbed by many gases and solid materials, inclusive of the low pressure vapor state of the tin or xenon utilized to create the plasma. This means that the intensity of the emitted EUV light diminishes as it is partially absorbed and diffused during its transit through the plasma cloud and transport to the stepper's intermediate focus (where the EUV light is collected).  A reduction in the rate of absorption and diffusion by the plasma can sometimes be achieved by reducing the pressure of the gas comprising the plasma. This has the effect of reducing the density of the plasma, lessening its opacity, and potentially increasing power output by increasing the transmission efficiency of the emitted EUV light.  This pressure adjustment is critical as the plasma will be extinguished if the pressure is too low (insufficient gas density/pressure to sustain the plasma) and will similarly cease to ionize if the pressure is too high. Experimentation is required to determine the optimal pressure and plasma density for maximum production and transmission of EUV light.  I suspect ASML has optimized this parameter on their Sn/LPP EUV source.  This technique is discussed in a 2005 paper:  Comparison of experimental and simulated extreme ultraviolet spectra of xenon and tin discharges by E.R. Keift, K. Garloff, J.J.A.M. van der Mullen and V. Banine.  


Maximizing the Transmission Efficiency
 of EUV Light to the Wafer Stage

To carry the EUV transmission efficiency discussion further, in some EUV system designs the wafer stage chamber is maintained at the same vacuum pressure (approximately 5x10-4 Torr), as the plasma source chamber and share the vacuum environment sustained by the pressure controllers and vacuum pumps supporting the EUV plasma. The pressure inside the wafer stage area is also critical as additional absorption and diffusion of the EUV light can occur there during transit from the intermediate focus coupling (IF) to the wafer stage.  Reductions of EUV energy propagation efficiency in the wafer stage chamber can be pressure related and contribute to path loss concerns exemplified in the source plasma opacity discussion above.  It is probable that higher levels of EUV dosing can be obtained by maintaining the wafer stage chamber under high vacuum pressure at <1x10-7 Torr. 

An excellent example of increased energy transfer efficiency under high vacuum conditions and the resulting effects on lithography are illustrated in a 2006 Nano Letters paper by Benjamin D. Myers and Vinayak P. Dravid, Variable Pressure Electron Beam Lithography (VP-eBL): A New Tool For Direct Patterning of Nanometer Scale Features on Substrates With Low Electrical Conductivity.  I found this paper quite interesting in that it addresses concerns common to both EUV and eBeam technologies.  The primary purpose of this paper was to illustrate a methodology for mitigating surface charging effects on electrically insulated wafer substrates patterned with eBeam lithography while simultaneously optimizing the resolution of the patterned images.  The paper also illustrates how differences in vacuum pressure effect eBeam (energy) propagation.  In the experiment, a differentially pumped vacuum system maintained an electron beam column under high vacuum while enabling operation of the wafer stage within pressures ranging from high vacuum to 3 Torr.  It was determined that a decrease in beam-gas path length (BGPL) and resulting electron beam scattering occurring at higher pressures mitigated surface charging and secondary electron proximity effects while enhancing image resolution.  However, the beam scattering also reduced the number of electrons available to dose the patterned resist requiring longer write times.  Longer write times or specialized dose requirements can now be optimized with computational lithography techniques inclusive of shot tasking and dose modulation.  To follow the discussion of exhibits in this paper, click on the link above. In Figure 1, exhibit (A) illustrates the insulated substrate surface charge induced displacement and distortion of eBeam imaging at high vacuum pressure.  Subsequent improvement in image resolution and accuracy are illustrated in exhibit (B) at .4 Torr, and in exhibit (C) at 1 Torr.  In Figure 2, Exhibits (A) through (D) and similarly Figure 3, Exhibits (A) through (C), illustrate eBeam induced surface trenching in the resist which decreases when the pressure is increased.  These examples illustrate the increase in energy transfer efficiency under high vacuum conditions and resulting decrease at higher pressures.  Figure 4, illustrates how electron beam dose requirements increase at higher gas pressures along with the interactive effect on minimum line width.  While there have been studies and process gas specific absorption coefficients established for electron beams and spectral light across a range of pressure regimes, it is well recognized that both forms of energy propagate most efficiently in a high vacuum environment, hence the term “vacuum EUV”. 

It follows that an EUV source and wafer stage chamber maintained at separate optimal pressure levels, approximately 5x10-4 Torr for the source (plasma opacity optimized),  and <10-7 Torr for the wafer stage chamber, more efficient transfer of EUV light can likely be obtained. This scenario requires a means of isolating the two vacuum chambers, perhaps by differential pumping, and transferring the EUV light through a transparent window or aperture at the intermediate focus (IF).  There are candidates for low loss EUV window material which could facilitate such a design.  In addition, there is a patented EUV source design featuring a differentially pumped source and wafer stage chamber coupled by a gas flow/conduction limiting optical aperture which efficiently conducts the EUV light across the two pressure regimes. http://www.google.com/patents/US6576912


Dueling Etendue – A Hybrid Dual DPP Source Design
 to Double Power Output

The search for high power EUV production techniques has been primarily focused on identification of energy conversion efficient source materials (solid and gaseous) and the most efficient means of ionizing them.  Recent research has determined that the best two ionization techniques are Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP).  As I point out in this article, the two techniques seem to be tied at maximum EUV power levels of 62 watts for DPP and 55 watts for LPP.  An approach to achieving higher power levels might be to operate two DPP sources simultaneously within one vacuum system, theoretically generating twice the power output.  The challenge would be optically coupling two sources to the stepper IF to truly double the power.  This might not be easily achieved.   Simultaneously capturing the maximum brilliance of two plasma sources could be challenging as the hardware interface to the IF must accommodate the optimal plasma profile angles for two discrete light sources to effect the most efficient etendue.  It's possible Bragg Cell EUV mirrors could be utilized to assist in effecting dual source DPP etendue.  Any concerns with absorptive losses from the Bragg Cell mirrors would be negated by the additional power afforded by the dual source design.

In my opinion a good candidate design technology for a hybrid EUV source resides with Zplasma.  The original system built by Zplasma utilized Xe as its source gas feed which produced a 2% bandwidth energy conversion efficiency (CE) of 0.5% which is low, however the efficiency will increase to 1.5% with a power supply optimized for the source.  By substituting Xe with SnH4, the energy conversion efficiency could be increased further to become competitive with Sn Laser Produced Plasma efforts to date. In addition to the increase in CE, higher EUV output power levels might be obtained if Zplasma's patented Sheared Flow Stabilization Z-pinch performs as well with SnH4 as it does with Xe.  Zplasma's system design might also accommodate the concept of Dual DPP sources as etendue match concerns might be minimized by its z-pinch source characteristics affording side on collection of light from the plasma.  In addition, the DPP configuration could accommodate an optional H2 plasma clean maintenance regimen.  A successful technique utilized by Gigaphoton in its source development program minimizes tin (Sn) particulate contamination by optimal positioning of a superconducting magnet in the source which deflects tin particles away from critical wafer stage and optical components.  Assuming a viable hybrid EUV source design is identified, how might further R&D funding be obtained given the current economic climate?


A Proposal for a New National Photonics Initiative Agenda Funding High Priority Challenges
 to Manufacturing

An important SPIE co-sponsored initiative took place on February 28, 2013 in Washington, DC, titled, “Optics and Photonics: Lighting a Path to the Future.”  Other organizations co-sponsoring the event included the IEEE Photonics Society, Optical Society of America (OSA), IEEE Photonics Society,  American Physical Society, and the Laser Institute of America.  The event was attended by many government agencies who traditionally sponsor research. The goal of the conference was to foster better government collaboration with American optics and photonics industries and forge a National Photonics Initiative (NPI).  The value of this proposed initiative is best exemplified by recent (non-government) semiconductor industry manufacturers' investments in ASML and Cymer.  The collaboration of industry and government in key photonic and optical science endeavors could distribute R&D expenditures among participants and reduce costs across many disciplines. While I was researching and writing this blog article, the benefits of a coordinated NPI program became more apparent.  After reviewing the many technical papers written on the subject of EUV and related technologies, I believe it is accurate to say that the level of participation by private industry, universities and government sponsored funding is probably unprecedented, and has created a reciprocally proportionate wealth of intellectual property and patent filings spanning many entities and corporations.  While we all support the concept of independent research, competitive concerns with ownership of applicable intellectual property may have slowed investment in the development of the EUV program. It is my opinion that a hybrid EUV source with superior power output and HVM performance might be assembled from the assortment of promising technologies and IP developed thus far.  Should a hybrid EUV concept be successfully proven, ensuing IP cross licensing concerns could potentially inhibit cooperation and progress.  This concern has been addressed previously by SEMATECH and other groups cooperatively sponsoring other past and present research programs.  The current pause in the pace of EUV development should foment renewed enthusiasm for jointly developed technology, intellectual property and reduction of R&D costs outside the domain of the foundries in order to prevent further stratification and/or dissolution of the traditional semiconductor equipment vendor base.  

On July 25, 2013 I received the following communication from NIST from which I have excerpted the following:

MEMORANDUM FOR Advanced Manufacturing Distribution 
From: The NIST Advanced Manufacturing Technology Consortia (AMTech) Program Team

“It is my pleasure to inform you that the National Institute of Standards and Technology (NIST) has released a Federal Funding Opportunity (FFO) for the Advanced Manufacturing Technology Consortia (AMTech) Program.  This is a new competition for awards to establish new or strengthen existing industry-led consortia in planning research that addresses high-priority challenges impeding the growth of advanced manufacturing in the United States.  NIST anticipates awarding $4 million in early 2014 as a result of this AMTech announcement.  Awards are expected to be up to two-years in duration and range between about $250,000 and $500,000.  As a leading voice in advanced manufacturing, we believe your members or constituents may have interest in AMTech and this newly announced funding opportunity.  AMTech-supported consortia will identify and prioritize long-term, pre-competitive industrial research needs; enable technology development; and create the infrastructure necessary for more efficient transfer of technology.  Teaming and partnerships are strongly encouraged including participation by the full value chain, including small-and mid-sized firms.  By convening key players across the entire innovation life cycle, the objectives of the AMTech Program are to eliminate critical barriers to innovation; increase the efficiency of domestic innovation efforts; and collapse the time scale to deliver new products and services based on scientific and technological advances. The end goal will be a growth of advanced manufacturing in the U.S. and an increase in the global competitiveness of U.S. Companies.  The AMTech Program will host two webinars on August 15, 2013, and August 20, 2013, at 2:00 p.m. Eastern time.  Participants are required to register in advance.  The events will offer guidance on the AMTech Program and preparing proposals, and will provide an opportunity to answer questions from the public about the program.  Participation in the free event is not required to submit an application.  Information on and registration for the event is available at www.nist.gov/ampo.  To assist in identifying potential collaborators for a consortium, the AMTech Program is creating a LinkedIn group where individuals can provide their area(s) of interest and communicate with each other.  Visit www.nist.gov/ampo for more information about joining.”

In considering this proactive initiative by NIST, I believe it is accurate to state that timely availability of EUV lithography technology is one of the high-priority challenges impeding the growth of more advanced manufacturing in the United States.

I propose that SPIE and the industry groups comprising the National Photonics Initiative consider establishing an additional agenda coordinated with SEMATECH to pursue government funding of advanced research in EUV development.  Further, there should be emphasis on directing available grant funding to the many promising start up companies whose entrepreneurial potential for technological contribution have been precluded by the prevailing economic climate in Silicon Valley, Wall Street and the larger U.S. economy.  We all applaud the cooperation of major players such as Intel, Samsung, and TSMC as they collectively support the efforts of ASML, but we must also ensure proactive support for promising, small business based entrepreneurial start up companies that have traditionally made the best and brightest contributions to Silicon Valley and the semiconductor industry.

Thomas D. Jay
Semiconductor Industry Consultant
Thomas.Dale.Jay@gmail.com
ThomasDaleJay.blogspot.com
Thomas D. Jay  Investment Commentary
Thomas D. Jay  YouTube Channel








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Corporate or private entities mentioned in this article are the respective owners of their logos, trademarks, service marks 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.

Correction:  A previous reference in this article was made crediting Ushio for a technique utilizing a superconducting magnetic field to mitigate tin particulate debris.  This statement was made in error and corrected on August 8, 2013.  Gigaphoton developed the superconducting magnet particulate mitigation technique as reported by Business Wire on July 1, 2013.  My apologies to Gigaphoton and Ushio for this unintentional error.  
Thomas D. Jay, August 8, 2013

Acknowledgments and Links

ASML News Release Source: Seeking Alpha.com 7/17/2013

Intel's Quad Core i7 Microprocessor
Intel Corporation, You Tube

ASML/Cymer's current technique for production of EUV light, ASML, You Tube

The challenges in the design and implementation of EUV technology for high volume manufacturing are formidable,
Jos Benschop, ASML, You Tube

Z-Pinch DPP Source Reference, Wikipedia.org

Development of Sn-fueled high-power DPP EUV Source Enabling HVM, Yusuke Teramoto, Zenzo Narihiro, Daiki Yamatani, Takuma Yokoyama, Kazunori Bessho,
Yuki Joshima, Takahiro Shirai, Shinsuke Mouri, Takahiro Inoue, Hiroshi Mizokoshi, Gohta Niimi*, Tomonao Hosokai*, Hironobu Yabuta, Kohkan C. Paul, Tetsu Takemura, Toshio Yokota, Kiyoyuki Kabuki, Koji Miyauchi, Kazuaki Hotta, and Hiroto Sato Gotenba Branch, Hiratsuka Research and Development Center, Extreme Ultraviolet Lithography System Development Association  *Ushio Inc.

www.zplasma.com, Henry Berg, CEO, Zplasma, Inc.

Comparison of experimental and simulated extreme ultraviolet spectra of xenon and tin discharges by E.R. Keift, K. Garloff, J.J.A.M. van der Mullen and V. Banine

Variable Pressure Electron Beam Lithography (VP-eBL): A New Tool For Direct Patterning of Nanometer Scale Features on Substrates With Low Electrical Conductivity, Benjamin D. Myers and Vinayak P. Dravid

http://www.google.com/patents/US6576912

www.nist.gov/ampo

National Photonics Initiative

NPI Agenda

SEMATECH





Monday, February 18, 2013

Zplasma to Attend SPIE Advanced Lithography 2013 Seeking Xenon Z-pinch EUV Source Funding


In the previous weeks I've written two blog articles which speak to the engineering complexities and capital intensity associated with the current development of EUVL (Extreme Ultra Violet Lithography) technology. An intensive effort is under way to provide a next generation 13.5 nanometer EUV light source required to print ever smaller nanoscale transistors and computer chips. Moore's law is marching on to again double the number of transistors on a chip and is being fueled by massive investments by major players in the semiconductor industry. Recently Intel, TSMC and Samsung invested over $6 Billion in ASML, a large well capitalized lithography equipment industry leader based in the Netherlands. ASML in turn purchased Cymer a critical supplier of laser technology providing key components in ASML's product line. The major investment in ASML was to ensure timely development and availability of HVM (High Volume Manufacturing) certified EUV lithography systems for shipment in late 2013 and projected 450 mm HVM production two or three years hence. EUV source development has been problematic and presents many challenges. Xtreme Technologies/Ushio and Gigaphoton and others are competing in the EUV source market with well funded programs. These efforts are being coordinated with imec, a major research and development center in Belgium. While billions are being spent on developing laser based, Sn plasma source technologies, innovative and cost effective engineering solutions are being researched with out the capital infusion and celebrity afforded some of the world's largest semiconductor equipment manufacturers.

Enter Zplasma. Funded by the U.S. Department of Energy in 1998, the University of Washington in Seattle, U.S.A., began construction of a ZaP Flow Z-Pinch Experiment. Henry Berg, an entrepreneur-in-residence at the university, started working with Nelson and Shumlak in 2011 to design and create a 200 watt commercial light source based on Sheared Flow Stabilization (SFS) technology, and then designed a proof of concept prototype to prove that the physics worked at the reduced size necessary for optical compatibility with steppers. Realizing that with xenon gas SFS produces a long pulse of EUV light at a wavelength of 13.5 nanometers, and that the semiconductor industry needed light sources of this type, the university filed for and was granted two patents on the invention. Zplasma was formed with Henry Berg as its CEO. The university and Zplasma executed an exclusive license agreement covering the two patents and the transfer of the commercial source prototype to Zplasma. More information on Zplasma may be found here at the company's web site.

During my most recent visit to the Zplasma website I sent a request to info@Zplasma.com for more detailed information on the company and its Z-pinch EUV source technology. Expecting a response from a MARCOM staffer I received a reply directly from Henry Berg, Zplasma's CEO. Having many questions about Zplasma and its Xe based EUV source technology, Henry and I exchanged questions and answers via email which allowed me to gain additional insight into Zplasma's feature/benefits and their significance given current concerns with impediments to HVM (High Volume Manufacturing) EUV source development. Much of the content of this blog entry is verbatim response to my questions from Henry Berg discussing the salient points of Zplasma technology and its differentiation from competitive EUV source technology. After discussion with Henry I thought this format might be the best way to convey a thorough discussion on a variation of Z-pinch ion source design in advance of SPIE Extreme EUV Lithography IV later this month.

I should point out that during the course of my blogging activities I have never held any financial interest in any of the companies or organizations I have mentioned. I've ceased my market trading activities over a year ago and currently do not hold positions in any stock or security (this disclosure does not preclude possible future investment or interest activities). My immediate interest is in rejoining active participation in the semiconductor industry which has been my career, and contributing meaningful discussion to critical issues facing our industry. In my opinion, Zplasma's patented technology could be of great interest to the EUV lithography community and the larger semiconductor industry. SPIE Advanced Lithography 2013 is an excellent opportunity for the EUV lithography community to initiate a thorough evaluation of Zplasma.  What follows below is a brief introductory description of Zplasma's current research and development effort as conveyed by Henry Berg. The questions related to the following discussion are mine followed by Henry's well articulated answers.



Henry Berg, CEO Zplasma, Inc.
“When we started the commercialization effort two years ago, I did not anticipate that it would be so incredibly difficult to get industry support to develop this technology. The primary barrier has been that since nobody has ever stabilized an EUV-emitting plasma before, the industry has no understanding of the benefits of a stable plasma. Every previous source of EUV light has been based on unstable plasma, where you have a very brief time to produce as much EUV light as possible, hence the focus on CE, the switch to molten tin and industrial lasers, and all of the problems with debris damaging the collector optics.We are very excited about the potential our source has to enable high volume EUV lithography. Our source technology is so much simpler than LPP or LDP that it will not only be much less costly to build and to operate, but it will also be durable and reliable. We need financial and development support to take the prototype we have and develop it into the HVM source it needs to become.”



Discussion

Zplasma's Xenon Plasma EUV Source Technology

Questions by
Thomas D. Jay, Semiconductor Industry Consultant

Answers provided by
Henry Berg, CEO Zplasma, Inc.



Could you explain Zplasma's Z-pinch function, its vacuum pressure regime, and plasma formation process?
"The vacuum chamber is pumped down to a few microtorr. A small amount of xenon gas is then injected. Power is applied to ionize the gas into plasma. The plasma is accelerated. The Z-pinch forms from the flowing plasma, pinches down and the central portion of the pinch emits a pulse of EUV light. The available plasma is consumed, the pinch dims, and the plasma exhaust exits through a small hole in the endwall of the outer electrode. There is a long time between pulses, our target operation at 7 kHz means there is a pulse every 143 microseconds. Since pulses last on the order of 10 microseconds, there is plenty of time for the gas plenum to recharge the acceleration region with gas for the next pulse."



In addition to the Z-pinch phenomenon are external magnets utilized to confine and/or control the plasma?
"No. Gas is injected into the annular space between an inner electrode and an outer electrode. The gas is ionized into plasma and accelerated axially. The inner electrode then has a rounded tip that allows the Z-pinch to form between the tip of the inner electrode and the outer electrode end wall. The outer electrode has openings to allow side-on optical collection of the light. The outer electrode also has a small hole at the end that allows the plasma exhaust to exit and be collected away from the optics."



What differentiates Zplasma's Z-pinch technology from competing systems?
"There are two things going on here. All DPP sources, including ours, use a Z-pinch. Gas is injected between two electrodes, ionized into plasma, and a pinch forms. Cymer and Xtreme both built DPP sources that worked this way. The problem was that the pinch that formed was highly unstable, so it blew apart. This meant that they couldn’t get meaningful high power levels without melting their electrodes, and even at low power levels debris was produced and they couldn’t collect enough light. Our core innovation is Sheared Flow Stabilization (SFS). With SFS, you inject the gas upstream of the pinch assembly point. The gas is ionized into plasma, and the plasma is accelerated axially and only then allowed to come together. The result is a Z-pinch which is stabilized by the moving plasma. The duration of the pinch can be adjusted by changing the amount of gas injected or adjusting the input power waveform."


Is there a specific plasma pressure regime which optimizes the Sheared Flow Stabilization effect?

"Sheared Flow Stabilization requires the gas to be injected into the acceleration region in a certain way and with a certain uniformity to create the proper sheared flows in the plasma. Unlike unstable discharges, our input waveform can significantly affect the duration of the pulse, we will optimize our output pulses in this manner for maximum EUV output. We have deliberately not factored in any such optimizations that we are not sure about. We do not have a power supply capable of outputting an adjustable waveform."



Your literature comments, “The duration of the pinch lasts ten to a hundred times longer than other Z-pinches (quoted at 100 nanoseconds), then has a controlled end.” Please describe all of the parameters acting on a “controlled end” to the pinch.
"The length of the pinch can be stretched by adding more gas and stretching the input power waveform. The pinch has a natural end because the available gas is consumed, but it fades quietly rather than ending explosively like the other DPP sources. You can also end the pinch early by ramping down your input power waveform. There are six critical advantages to SFS:

a) Longer Light Pulse: SFS pulses are 10 to 100 times longer due to their stable nature, allowing for more light collection.

b) High Power without High CE: Long SFS pulses and side-on optical collection access increase throughput and lower required CE, enabling HVM operation with xenon and eliminating the need for molten tin.

c) No Debris: SFS ends the plasma pinch without explosive termination, eliminating high-energy debris.

d) Low Instantaneous Power: SFS pulses allow for EUV light production without the high instantaneous power levels that cause electrode thermal stress and ablation.

e) Dose Uniformity: SFS allows the length of each EUV pulse to be adjusted under control of the power supply, allowing for extremely accurate dose uniformity.

f) Adjustable Geometry: SFS makes pinch geometry adjustable for optical matching to stepper IF."



What is the current Xe Z-pinch EUV source CE (energy Conversion Efficiency)?
"Our prototype CE is limited because we are powering it with a capacitor bank that rings. A proper pulsed power supply that can shape the output waveform will solve that problem. We have 2% BW CE of 0.5% in the lab now, that will go to 1.5% with the right power supply."



Given sufficient funding, what is the projected CE on a larger, scaled for power Z-pinch EUV source?
"Stable plasma means we do not need to focus on improving CE. Our 200W target assumes we never get more than 1.5%. Of course, we will be optimizing CE as well to increase beyond that. The theoretical CE limit with xenon is 2-4%."



Does the Zplasma ion source provide increased Xe CE when compared to competing Xe EUV source designs? If so what is the percentage in CE gain?
"All discharge-produced-plasma sources (Cymer DPF, Xtreme DPP, Zplasma Stable DPP) use a Z-pinch as the core EUV-producing mechanism. SFS is what has driven our current CE so high despite the ringing capacitor bank, we are already where Cymer and Xtreme were with optimized power supplies. Our HVM 200W target assumes we only get to 1.5% CE, but we will optimize for higher CE as part of the development process, and I would love to see us exceed 2%. But we didn’t assume ANY new inventions or innovations to hit 200W, so improvements would just drive us over 200W."


What components must be scaled to achieve desired HVM power levels?

"We need a high voltage pulsed power supply that can run at 7 kHz and we need to couple the electrodes to a forced-flow chiller system for cooling."


Can you describe an optimal 7kHz power supply design specification or is there a commercially available model you've selected?

"We cannot identify a commercially available model, though I would love to use something off the shelf if possible. Other discharge sources have all used custom-built magnetically switched supplies, and our source would work with any of those supplies. 7 kHz was chosen so as not to push the limits of previously developed pulsed power supplies. Our plan is to build an IGBT-switched supply that is fully adjustable so we can stretch our pulses out even further and produce more EUV light. We have identified a partner who can produce the power supply we need."


What variable parameters must this source power supply provide (example: pulse width, amplitude, wave form shape, pulse rise time ramp)?

"The supply we would have made would allow all of these to be adjusted. There is a lot of exciting work still to be done extending SFS Z-pinches and increasing the amount of EUV light that is produced from each pinch."


Would a new “scaled for power” HVM design be price and performance competitive with other EUV systems of similar HVM performance?
"Our source technology is much cheaper and simpler than other ways of generating EUV light. There are no other systems of similar HVM performance, but I estimate that our source will be about 10x cheaper to make and 5x cheaper to operate than the present HVM EUV sources."



What is the peak resolution at 13.5 nm for Xe EUV spectra? Is there comparable (or better) spectral resolution and out of band performance for Xe Z-pinch as compared to a Sn source?
"EUV source power is measured in a 2% bandwidth around 13.5 nm, thus 2% BW EUV. Radiation outside of this region is called out-of-band (OOB) radiation. So our goal is to deliver 200 W of 2% BW EUV to the stepper intermediate focus (IF). We produce the same light as previous DPP sources, but do it from a much smaller EUV emission volume and in a stable manner. I haven’t talked about it much, but our OOB results should be outstanding. We do not have the OOB light from a laser to contend with. Our source will need to be coupled with an ellipsoidal multilayer mirror to couple the light to the IF. One cool thing about how that works is Bragg layer reflection will reduce the transmission of any OOB light that is present. But it is not having to worry about light from a laser pulse that is the main OOB differentiator."



Given SFS and your comments on dose error, does Zplasma's Z-pinch produce fewer neutrals than Sn based plasma systems?
"One key advantage of SFS is that you can shorten or lengthen the duration of the pinch under control of the power supply. So the source can adjust based on light being delivered to the IF to keep the EUV light energy dose within very tight bounds. There will be no significant debris from the source, as the root cause of high-energy debris is the violent instabilities in the plasma. Present LPP and LDP sources have an exploding Sn plasma droplet, so high energy ions and fast neutrals are both produced. Previous DPP sources all had the xenon Z-pinch that blew apart, also showering out debris. Our core focus has been eliminating the root cause of the DPP debris. Once we have our source operating, we will place optical collector coupon material in the right places and conduct durability tests. In theory, fast neutrals are produced by collisions with fast ions, so the dramatic reduction in fast ions should reduce fast neutrals. Our plasma is also moving orthogonally to the collector optics, so no debris mitigation is needed."



With a reduced debris profile utilizing Xe instead of Sn source feed material, will the system accommodate an H2 plasma cycle for mitigation of residual Xe induced particulates or surface contamination of the source/optics?
"Our system would indeed accommodate an H2 plasma cycle if needed. We have done a whole bunch of runs with hydrogen as part of our lab work testing the prototype. Our goal is to operate without generating any high-energy debris that hits the optics."



Given the reduction in high energy ions and fast neutrals is it possible to minimize or eliminate shot noise by ramping and shaping the power supply output and resulting EUV pulse characteristics?
"We do not know the answer to this question. It is possible that there will be shot noise variation compared to LPP/LDP based on how our source produces the photons, but we do not expect any differences, and I am not sure I see a mechanism that could result in differences. This is something that we will look at when we have the ability to do so."


If sufficiently funded, could an HVM, high power, Zplasma Z-pinch EUV source be delivered on time and in quantity to accommodate requirements at ASML and other stepper vendors?

"Yes, if ASML and/or Nikon fully supported the stepper integration process. Our focus is on the core technology to produce the light. We would need Carl Zeiss or Media Lario to make the mirror and Fraunhofer to make the mirror coating. Development of this technology with the right funding and support could be very rapid – no new innovations are required."


What is the estimated cost to scale components to desired HVM power levels?

"$6-8M to get to a fully functional 200W HVM prototype. This is for the core EUV-producing unit only. Stepper integration will require adding an ellipsoidal multilayer mirror."


Recent major R&D investments have been made in EUV source technology by Intel, TSMC and Samsung. Zplasma's EUV source design with all its potential features and benefits seems worthy of major funding in the “best of breed” competition currently in progress. With the approach of SPIE Extreme EUV Lithography IV in February 25 – 28, have you attracted new interest in funding?

“We are talking to several companies about financial backing and partnering with us to develop our source. Recently, we have been talking to IMEC, and are hoping to have further discussions with Global Foundries, Intel, TSMC, SK Hynix and Samsung at the upcoming SPIE conference in San Jose.”

If Zplasma's Xe Z-pinch EUV source can be scaled to power levels required for HVM at existing or further optimized CE levels, significant improvements in MTBF and debris mitigation might be achieved. A more simplified EUV source design with stable plasma operation could enhance dose uniformity and device product yields offsetting further diversification of investment in the search for optimal EUVL for HVM.

I'd like to thank Henry Berg for his personal response to my inquiries concerning Zplasma and his enthusiastic assistance in providing engineering data affording an insightful overview of his company. 

Henry Berg, CEO of Zplasma will be attending SPIE Advanced Lithography, February 24 - 28, 2013 in San Jose, CA.

Thomas D. Jay
Semiconductor Industry Consultant
Thomas.Dale.Jay@gmail.com
For more information on Zplasma visit www.Zplasma.com

For information on the SPIE Advanced Lithography 2013 Extreme Ultraviolet Lithography IV program click on the link below:
http://spie.org/app/program/index.cfm?fuseaction=conferencedetail&export_id=x12540&ID=x10947&redir=x10947.xml&conference_id=1039349&event_id=996835