Category Archives: Microscopy

The IEEE Photonics Conference 2014 (IPC-2014) has announced a Call for Papers seeking original technical presentations in lasers, optoelectronics, optical fiber networks and related topics for the industry’s premier fall photonics conference. Scheduled for October 12-16, 2014 at the Hyatt Regency La Jolla in San Diego, CA, the conference was previously known as the IEEE LEOS Annual Meeting.

As the premier autumn gathering for scientists and engineers in photonics and light-related technologies involving quantum electronic devices, as well as other laser and lightwave applications, the IEEE Photonics Conference is anticipated to include more than 500 technical papers, invited plenary talks on important industry issues, weekend events for young photonics professionals and students, as well as a manufacturers’ exhibition.

The short course, Introduction to Silicon Photonics Device Design & Fabrication, is designed to teach students how to design passive silicon photonic devices using analytic and advanced numerical techniques. Student designs will be fabricated by a state-of-the-art rapid-prototyping 100keV electron-beam lithography facility.  All designs will be tested using an automated optical probe station and the data provided to the students.  Students will then analyze their experimental data.

The paper submission deadline is May 9, 2014 and papers will be accepted immediately. Authors will be notified in late June of the acceptance status of their paper. The complete Call for Papers can be found at http://www.ipc-ieee.org/call-for-papers.

Papers are invited in the following areas:

  • Biophotonics
  • Displays & Lighting
  • High Power/Intensity Sources
  • Microwave Photonics
  • Nanophotonics
  • Non-Linear and Ultrafast Optics
  • Optical Communications
  • Optical Fiber Technology
  • Optical Interconnects
  • Optical Micro/Nano Resonators & Devices
  • Optical Networks & Systems
  • Photonic Integration and Packaging
  • Photonic Materials & Metamaterials
  • Photodetectors, Sensors, Systems & Imaging
  • Semiconductor Lasers

Four Special Symposia Topics Announced

Supplementing the regular conference program will be four special symposia featuring invited speakers:
–    Optoelectronic Devices for Solar Energy Harvesting — covering photovoltaics, solar fuel devices, solar desalination, solar water purification, and photocatalysis
–    High Power Diode Lasers & Systems – covering advances along the entire laser technology chain: diode laser sources, beam-combining, optical systems, packaging, reliability, and manufacturing of laser systems
–    Hollow Core Fiber Space Division Multiplexing – covering the state of the art in hollow core space division multiplexing (SDM) for optical communications.
–    Optomechanics – covering developments at the intersection of two previously distinct subjects:  Optical (micro-)cavities and micro (nano) mechanical resonators.

For registration and other information about IPC-2014, visit http://www.ipc-ieee.org/ or contact:

Ingrid L. Donnelly, CMP
Senior Conference Planner
IEEE Photonics Society (formerly LEOS)
445 Hoes Lane
Piscataway, NJ 08854
Tel: +1 732.562.5597
[email protected]

ON Semiconductor today signed a definitive agreement to acquire Truesense Imaging, Inc., a provider of high-performance image sensor devices addressing a wide range of industrial end-markets including machine vision, surveillance, traffic monitoring, medical and scientific imaging, and photography. Under the terms of the agreement, ON Semiconductor will pay approximately $92 million in cash to acquire Truesense Imaging.

“The pending acquisition of Truesense Imaging is a step towards our stated strategic goal of expanding our presence in select segments of the industrial end-market,” said Keith Jackson, president and CEO of ON Semiconductor. “With the acquisition of Truesense, we will augment our abilities to deliver a broad range of high-performance image sensors to the industrial end-market and at the same time significantly expand our customer footprint. I am excited about the growth opportunities the combination of the two companies presents in the high-performance imaging market.”

“ON Semiconductor is an ideal strategic fit for Truesense as we share a common vision for expanding the capabilities of high-performance sensors used in the world’s most demanding imaging applications,” said Chris McNiffe, CEO of Truesense Imaging, Inc. “This combination enables us to leverage our technology base and four decades of imaging expertise with ON Semiconductor’s R&D, manufacturing and global logistics infrastructure. We are very excited to join the ON Semiconductor organization and to enable new growth opportunities for both our customers and our employees.”

Truesense Imaging’s revenue for 2013 was approximately $79 million with gross and operating margins of approximately 44 percent and 23 percent, respectively. Truesense Imaging will be incorporated in ON Semiconductor’s Application Products Group (APG) business group. The transaction has been approved by ON Semiconductor’s and Truesense Imaging’s boards of directors (or authorized committees thereof) and is anticipated to close before the end of the second quarter of 2014, subject to required regulatory approvals and customary closing conditions.

By Dan Tracy, Industry Research and Statistics, SEMI

Semiconductor industry revenues reported by the World Semiconductor Trade Statistics (WSTS) reached a record high in 2013 with global revenues totaling over $305 million. In addition, the WSTS report showed that total unit shipments for integrated circuit devices (ICs) increased by over 9 percent last year; thus, 2013 proved to be a strong year for unit shipments. The IC shipment growth ties to the continuing strong consumer demand for mobile electronics. ICs consumed in mobile products are fabricated using device technologies based on 32nm, 28nm, and below technologies, that require leading-edge materials, such as 300mm wafers and advanced photoresists, to fabricate.

Given the strong unit trends, some year-end materials data collected by SEMI registered growth rates significantly lower than the 9 percent observed in unit shipments. As commented on in last month’s article on reclaim wafers, wafer shipments for prime electronic grade (excluding reclaim) grew just 0.4 percent for the year. The article explained factors around this low area shipment growth.  In addition to shipments, silicon wafer revenues declined by almost -13 percent in 2013, marking the second consecutive year of double-digit revenue declines in the silicon wafer market (semiconductor applications only). Aggregate average selling prices are declined for silicon and a significant factor contributing to the decline in 2013 was the weakened yen.

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he average yen-to-US dollar exchange rate was 80¥/US$ in 2012. In 2013, it weakened to 98¥/US$. Given the strong market position Japanese material suppliers have in the industry, including silicon wafers, this trend dampened the revenues reported in U.S. dollars.  Another material segment where the exchange conversion impacted the revenues was the photoresist market. Again, a number of Japanese companies are key industry suppliers in this segment, and photoresist revenues declined in 2013 — even for the advanced resist materials and despite the strong IC unit growth.

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Finally, the impact of the weaker yen played out in the SEAJ book-to-bill equipment trends as well (SEAJ: Semiconductor Equipment Association of Japan).  Total billings for fab, test, assembly & packaging, and other semiconductor equipment reported by the SEAJ declined by almost -30 percent when reported in U.S. dollars.  That same data set when reported in Yen, posts a year-over-year decline of -14 percent.

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Source: SEAJ, March 2014

2013 was a strong year for IC unit shipment growth. Downward price pressures and a weakened Yen, however, contributed to a challenging year for semiconductor materials and equipment suppliers alike as far as revenue growth. These factors are important in comparing year-over-year trends.

SEAJ-BB

For more information on SEMI Market Research, visit www.semi.org/en/MarketInfo. For information on SEMI, visit: www.semi.org

Honeywell announced today that it has introduced new RadLo low alpha plating anodes based on proprietary technology to help reduce alpha particle radiation that can lead to data errors in semiconductors.

The new plating anodes for semiconductor packaging wafer bumping applications expand Honeywell’s RadLo offerings and employ proprietary Honeywell metrology and refining techniques.

“Our new low alpha plating anodes are already in high volume manufacturing at leading sub-contractors and have been qualified with OEM tool manufacturers,” said Chris Lee, product line director for Honeywell’s Advanced Metals and Polymers business. “The qualifications and rapid adoption demonstrate that we are serving an important need and helping our customers meet their challenges.”

Alpha particle radiation emanating from semiconductor packaging materials can cause data errors in memory cells, creating soft errors that can ultimately cause mobile phones, tablets, servers, gaming consoles, and other end use devices to malfunction. As semiconductors shrink and functional demands increase, chips are more sensitive to soft errors. Designers of packaging materials for semiconductors are now turning to low alpha materials such as Honeywell’s RadLo line to address the issue effectively.

At such extremely low alpha emission levels, accurate measurement of alpha flux is difficult due to the effects of contaminants and background radiation such as cosmic rays. To address this issue, Honeywell employs robust metrology and process controls.

The introduction of the RadLo anodes also supports the semiconductor industry’s move toward flip chip packaging and the increased adoption of electroplating for wafer bumping applications. Honeywell is uniquely positioned to manufacture plating anodes for use in wafer bumping with very high-purity (>99.99% pure) metal offerings, including low alpha lead (Pb), low alpha tin (Sn) and copper (Cu). Low alpha Sn anodes are available in several low alpha grades, including <0.002 counts per hour/cm2.

A new microscopy method could enable scientists to generate snapshots of dozens of different biomolecules at once in a single human cell, a team from the Wyss Institute of Biologically Inspired Engineering at Harvard University reported Sunday in Nature Methods.

Such images could shed light on complex cellular pathways and potentially lead to new ways to diagnose disease, track its prognosis, or monitor the effectiveness of therapies at a cellular level.

Cells often employ dozens or even hundreds of different proteins and RNA molecules to get a complex job done. As a result, cellular job sites can resemble a busy construction site, with many different types of these tiny cellular workers coming and going. Today’s methods typically only spot at most three or four types of these tiny workers simultaneously. But to truly understand complex cellular functions, it’s important to be able to visualize most or all of those workers at once, said Peng Yin, Ph.D., a Core Faculty member at the Wyss Institute and Assistant Professor of Systems Biology at Harvard Medical School.

“If you can see only a few things at a time, you are missing the big picture,” Yin said.

Yin’s team sought a way to take aerial views of job sites that could spot up to dozens of types of biomolecules that make up large cellular work crews.

To capture ultrasharp images of biomolecules, they had to overcome laws of physics that stymied microscopists for most of the last century. When two objects are closer than about 200 nanometers apart — about one five-hundredth the width of a human hair — they cannot be distinguished using a traditional light microscope: the viewer sees one blurry blob where in reality there are two objects.

Since the mid-1990s, scientists have developed several ways to overcome this problem using combinations of specialized optics, special fluorescent proteins or dyes that tag cellular components.

Ralf Jungmann, Ph.D., now a postdoctoral fellow working with Yin at the Wyss Institute and Harvard Medical School, helped develop one of those super-resolution methods, called DNA-PAINT, as a graduate student. DNA-PAINT can create ultrasharp snapshots of up to three cellular workers at once by labeling them with different colored dyes.

To visualize cellular job sites with crews of dozens of cellular workers, Yin’s team, including Jungmann, Maier Avendano, M.S., a graduate student at Harvard Medical School, and Johannes Woehrstein, a postgraduate research fellow at the Wyss Institute, modified DNA-PAINT to create a new method called Exchange-PAINT.

Exchange-PAINT relies on the fact that DNA strands with the correct sequence of letters, or nucleotides, bind specifically to partner strands with complementary sequences. The researchers label a biomolecule they want to visualize with a short DNA tag, then add to the solution a partner strand carrying a fluorescent dye that lights up only when the two strands pair up. When that partner strand binds the tagged biomolecule, it lights up, then lets go, causing the biomolecule to “blink” at a precise rate the researchers can control. The researchers use this blinking to obtain ultrasharp images.

They then repeat the process to visualize a second target, a third, and so on. Then they overlay the resulting images to create a composite image in which each biomolecule – each cellular worker — is assigned a different color. This allows them to create false-color images that simultaneously show many types of biomolecules — far more than they could simultaneously visualize by labeling them with different colored dyes. And these false-color images allow them to spot enough cellular workers at once to capture the entire scene.

To test Exchange-PAINT, the researchers created 10 unique pieces of folded DNA, or DNA origami, that resembled the numerals 0 through 9. These numerals could be resolved with less than 10 nanometers resolution, or one-twentieth of the diffraction limit.

The team was able to use Exchange-PAINT to capture clear images of the 10 different types of miniscule DNA origami structures in one image. They also used the method to capture detailed, ultrasharp images of fixed human cells, with each color tagging an important cellular component – microtubules, mitochondria, Golgi apparatus, or peroxisomes.

Yin expects the method, with further development, to be able to visualize dozens of cellular components at once.

“Peng’s exciting new imaging work gives biologists an important new tool to understand how multiple cellular components work together in complex pathways,” said Wyss Institute Founding Director Don Ingber, M.D., Ph.D. “I expect insights from those experiments to lead to new ways to diagnose and monitor disease.” Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Boston Children’s Hospital and Professor of Bioengineering at Harvard School of Engineering & Applied Sciences.

In support of Governor Andrew Cuomo’s nanotechnology-based education and economic development strategy, the SUNY College of Nanoscale Science and Engineering (CNSE) and Albany Law School (Albany Law) today announced the launch of a joint educational program, “Ecosystem for Nanotechnology, Entrepreneurship and Law,” (eNTEL) which will integrate the strengths of each institution to uniquely prepare student entrepreneurs to launch startup companies and attract business investment as a means of further driving New York’s fast-growing innovation economy.

“This partnership is a testament to Governor Andrew Cuomo’s visionary blueprint for economic growth, including the groundbreaking ‘Start-up NY’ initiative, which is laying the foundation for New York to expand its global leadership in nanotechnology research, development, commercialization and manufacturing,” said Dr. Pradeep Haldar, CNSE Vice President of Entrepreneurship Innovation and Clean Energy Programs and Head of CNSE’s Nanoeconomics Constellation. “We are excited to embark on this partnership with the prestigious Albany Law School to create a one-of-a-kind program that will further enhance New York’s ecosystem for nanotechnology-based entrepreneurship and set the stage for retaining top talent and attracting business and investment growth that will benefit our region and state.”

“Albany Law School is excited to partner with the globally recognized SUNY College of Nanoscale Science and Engineering to create the cutting-edge eNTEL program, which will draw business investment and the resultant jobs to the region, and attract and retain top-tier students who are interested in the exciting area at the intersection of law, science, technology, engineering, and entrepreneurship,” said Penelope Andrews, Albany Law School President and Dean. “We look forward to this collaboration and to playing a defining role as New York leads the world in 21st century entrepreneurial opportunities.”

Through the eNTEL program, both CNSE and Albany Law will foster a culture of interdisciplinary collaboration that will assemble the experience, knowledge, and expertise of each institution’s faculty and staff, as well as practitioners and experts in the Capital Region, to create training opportunities, joint classes and collaborative projects, all intersecting with technology, entrepreneurship, and the law which will be issued jointly by CNSE and Albany Law.

Students will work in teams to explore ways to develop products from idea to commercialization; create a “Tech Transfer Practicum” in which students from both CNSE and Albany Law will bring business ideas generated by CNSE student researchers to market; provide Albany Law students with vital real-world experience through placement in an externship with the CNSE Office of Technology Innovation and Commercialization; and, in collaboration with Albany Law’s Government Law Center, the school’s Tax and Transactions Clinic will provide free start-up legal assistance to selected very early stage businesses and nonprofit organizations, including those founded by CNSE students that have educationally appropriate legal needs.  These initiatives will give students from both institutions opportunities to bring ideas to market and grow them into successful businesses to create economic development opportunities in the region, and to provide opportunities for area attorneys to service the businesses after the initial stage.

Portions of the program will be implemented over the next five years, with more than 200 students expected to be trained in the scientific, commercial, and legal aspects of nanoentrepreneurship, simultaneously strengthening the network of alumni, faculty, engineers, entrepreneurs, and practicing attorneys involved with the nanoscale industry in the Capital Region and throughout New York State. Additionally, the program aims to attract top engineering, business, and law students to the region to enhance enrollment at both institutions.

CNSE is a critical enabling resource in catalyzing new research, development, and business investments from the various sectors of the nanotechnology industry across New York State, fostering vital partnerships to produce and commercialize nanotechnology innovations, leading to economic development and job creation. Albany Law is America’s oldest independent school of law and is a nationally recognized center of learning and teaching as it provides opportunities to develop habits of critical analysis, understanding of theory, and the acquisition of professional skills. Through this agreement, each institution offers an affiliation with a distinguished cadre of faculty, researchers, students, experts, and leaders who are notable in their respective fields of study.

Columbia Engineering researchers have experimentally demonstrated for the first time that it is possible to electrically contact an atomically thin two-dimensional (2D) material only along its one-dimensional (1D) edge, rather than contacting it from the top, which has been the conventional approach. With this new contact architecture, they have developed a new assembly technique for layered materials that prevents contamination at the interfaces, and, using graphene as the model 2D material, show that these two methods in combination result in the cleanest graphene yet realized. The study is published in Science on November 1, 2013.

“This is an exciting new paradigm in materials engineering where instead of the conventional approach of layer by layer growth, hybrid materials can now be fabricated by mechanical assembly of constituent 2D crystals,” says Electrical Engineering Professor Ken Shepard, co-author of the paper. “No other group has been able to successfully achieve a pure edge-contact geometry to 2D materials such as graphene.”

He adds that earlier efforts have looked at how to improve ‘top contacts’ by additional engineering such as adding dopants: “Our novel edge-contact geometry provides more efficient contact than the conventional geometry without the need for further complex processing. There are now many more possibilities in the pursuit of both device applications and fundamental physics explorations.”

First isolated in 2004, graphene is the best-studied 2D material and has been the subject of thousands of papers studying its electrical behavior and device applications. “But in nearly all of this work, the performance of graphene is degraded by exposure to contamination,” notes Mechanical Engineering Professor James Hone who is also a co-author of the study. “It turns out that the problems of contamination and electrical contact are linked. Any high-performance electronic material must be encapsulated in an insulator to protect it from the environment. Graphene lacks the ability to make out-of-plane bonds, which makes electrical contact through its surface difficult, but also prevents bonding to conventional 3D insulators such as oxides. Instead, the best results are obtained by using a 2D insulator, which does not need to make bonds at its surface. However, there has been no way to electrically access a fully-encapsulated graphene sheet until now.”

In this work, says Cory Dean, who led the research as a postdoc at Columbia and is now an assistant professor at The City College of New York, the team solved both the contact and contamination problems at once. “One of the greatest assets of 2D materials such as graphene is that being only one atom thick, we have direct access to its electronic properties. At the same time, this can be one of its worst features since this makes the material extremely sensitive to its environment. Any external contamination quickly degrades performance. The need to protect graphene from unwanted disorder, while still allowing electrical access, has been the most significant roadblock preventing development of graphene-based technologies. By making contact only to the 1D edge of graphene, we have developed a fundamentally new way to bridge our 3D world to this fascinating 2D world, without disturbing its inherent properties. This virtually eliminates external contamination and finally allows graphene to show its true potential in electronic devices”

The researchers fully encapsulated the 2D graphene layer in a sandwich of thin insulating boron nitride crystals, employing a new technique in which crystal layers are stacked one-by-one. “Our approach for assembling these heterostructures completely eliminates any contamination between layers,” Dean explains, “which we confirmed by cross-sectioning the devices and imaging them in a transmission electron microscope with atomic resolution.”

Once they created the stack, they etched it to expose the edge of the graphene layer, and then evaporated metal onto the edge to create the electrical contact. By making contact along the edge, the team realized a 1D interface between the 2D active layer and 3D metal electrode. And, even though electrons entered only at the 1D atomic edge of the graphene sheet, the contact resistance was remarkably low, reaching 100 Ohms per micron of contact width—a value smaller than what can be achieved for contacts at the graphene top surface.

With the two new techniques—the contact architecture through the 1D edge and the stacking assembly method that prevents contamination at the interfaces—the team was able to produce what they say is the “cleanest graphene yet realized.” At room temperature, these devices exhibit previously unachievable performance, including electron mobility at least twice as large as any conventional 2D electron system, and sheet resistivity less than 40 Ohms when sufficient charges are added to the sheet by electrostatic “gating.” Amazingly, this 2D sheet resistance corresponds to a “bulk” 3D resistivity smaller than that of any metal at room temperature. At low temperature, electrons travel through the team’s samples without scattering, a phenomenon known as ballistic transport. Ballistic transport, had previously been observed in samples close to one micrometer in size, but this work demonstrates the same behavior in samples as large as 20 micrometers. “So far this is limited purely by device size,” says Dean, “indicating that the true ‘intrinsic’ behavior is even better.

The team is now working on applying these techniques to develop new hybrid materials by mechanical assembly and edge contact of hybrid materials drawing from the full suite of available 2D layered materials, including graphene, boron nitride, transition metal dichlcogenides (TMDCs), transition metal oxides (TMOs), and topological insulators (TIs). “We are taking advantage of the unprecedented performance we now routinely achieve in graphene-based devices to explore effects and applications related to ballistic electron transport over fantastically large length scales,” Dean adds. “With so much current research focused on developing new devices by integrating layered 2D systems, potential applications are incredible, from vertically structured transistors, tunneling based devices and sensors, photoactive hybrid materials, to flexible and transparent electronics.”

“This work results from a wide collaboration of researchers interested in both pure and applied science,” says Hone. “The unique environment at Columbia provides an unparalleled opportunity for these two communities to interact and build off one another.”

The Columbia team demonstrated the first technique to mechanically layer 2D materials in 2010. These two new techniques, which are critical advancements in the field, are the result of interdisciplinary efforts by Lei Wang (PhD student, Electrical Engineering, Hone group) and Inanc Meric (Postdoc, Electrical Engineering, Shepard group), co-lead authors on this project who worked with the groups of Philip Kim (Physics and Applied Physics and Applied Mathematics, Columbia), James Hone (Mechanical Engineering, Columbia), Ken Shepard (Electrical Engineering, Columbia) and Cory Dean (Physics, City College of New York).

KEIBOCK LEE, Park Systems, Santa Clara, CA.

3D atomic force microscopes can measure critical dimensions, line edge roughness and sidewall roughness in a way that is highly accurate, non-destructive and cost-effective.

One of the most challenging features in the semiconductor industry is the continuous research and the subsequent fabrication of integrated circuits with enduringly smaller critical dimensions (CDs). As shown in FIGURE 1, CDs must be measured at the top, middle and bottom of features, as well as various parameters such as line edge roughness (LER), the line width roughness (LWR) and the sidewall roughness (SWR).

The characterization of such factors that determine the shape and the roughness of the device patterns for device manufacturers is of utmost importance due to the fact that they directly affect the device performance. Optical measurement techniques, which are limited in terms of resolution. Therefore, the existing prevalent method for measuring these factors prior was primarily the scanning electron microscopy (SEM) with its image analysis software. Despite the fact that this technique offers substantial advantages such as automation and compatibility with standard critical dimension SEM tools, it cannot provide the user with high resolution LER data due to the fact that SEM resolution is reaching its limits, therefore 3D AFM offers a highly desirable solution. Leading manufacturers have implemented AFM that can measure resist profile, LER and SWR in a way that is highly accurate, non-destructive and cost-effective. The precise and full characterization of such features is extremely essential during the pattern transfer process as it offers the possibility of imaging all surfaces of the pattern.

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FIGURE 1. LER, LWR and SWR are the limiting factors of resolution in optical lithography.

What is non–contact 3D AFM?
The basic principle of non-contact 3D-AFM is that a cantilevered beam rapidly oscillates just above the surface of the imaging sample. This offers several advantages, as compared to the traditional contact and intermittent modes. One of the advantages is that there is no physical contact between the tip and the surface of the sample. Moreover, as depicted in FIGURE 2, the Z-scanner, which moves the tip, is decoupled from the XY scanner, which solely moves the sample, thus, offering flat scanning and an additional benefit of improved Z-scan bandwidth. Furthermore, by tilting the Z-scanner, the sidewall of the nanostructures can be accessed and roughness measurements performed along the sidewall of photoresist lines. At the same time, measurements of the critical dimensions of top, middle, and bottom lines can be made.

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FIGURE 2. The independent tilted Z-scanner enables measurements of the sidewalls of features.
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FIGURE 3. Combination of the three acquired images for 3D AFM pattern reconstruction.

Data acquisition is performed by a conical tip in predefined tilted angles, typically 0º, a, and -aº. Consequently, and by combining these three scans (a method called image stitching), the 3D pattern can be constructed, as shown in FIGURE 3. This provides an excellent and extremely accurate method that takes advantage of the interference pattern of the standing waves in order to measure features such as the total height, the top, middle, and bottom width. 3D AFM is capable of advanced three-dimensional imaging of both isolated, and dense line profiles. It is less costly than the alternative techniques (CD-SEM and focused ion beam (FIB)) for imaging and measuring parameters of line profiles since the preparation of the sample is by far simpler.

Noise levels in 3D-AFM
A critical requirement when dealing with metrology tools is associated with constraining the level of noise in the manufacturing environment. A study of noise levels on a 300 mm wafer (FIGURE 4) shows the overall 3D AFM system noise at levels are lower than 0.05 nm (0.5 angstrom).

Roughness measurements
Roughness can be transferred into the final etched profile, thus, roughness measurements can describe and determine the quality of the patterns. The tilted Z scanner in combination with the low noise levels that are prevalent during the AFM process can provide accurate results in terms of sidewall roughness measurements. FIGURE 5 depicts the 3D AFM imaging of a photoresist semi-dense line pattern and the respective grainy structure of its sidewall. The precision with which the SWR was measured is validated by the high repeatability (0.08nm 1 sigma for 5 sites wafer mean) for the sidewall roughness of about 6.0 nm.

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FIGURE 4. 3D AFM noise levels on a 300 mm wafer. The system noise level is less than 0.05 nm at every position and typically 0.02~0.03 nm RMS.
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FIGURE 5. 3D AFM image of a photoresist semi-dense line pattern imaged with Z-scanner tilt. The bottom figure clearly depicts the grainy structure of the sidewall.

It needs to be noted that roughness depends, amongst others, on the aerial image contrast (AIC) or in other words the physics of exposure. AIC is determined as the quotient between the subtraction and the addition of the maximum and minimum image intensities.

Several consequent series of images with variable exposure reveal that LER significantly increases when the AIC is decreased, a fact that underlines that AIC is a controlling factor for LER. Moreover, and as depicted in FIGURE 6, reduced levels of AIC produced line profile images of the resist that were more blunted, and also smaller sidewall angles (SWA).

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FIGURE 6. Park 3D AFM line profiles at different AIC levels reveal the proportionate relationship between SWA and AIC.
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FIGURE 7. A 3D AFM image of a 300 nm photoresist line pattern yields full information regarding the morphology of the sidewall (top) Side-wall Roughness is different at different AIC levels, a fact that indicates the connection between LER and SWR (bottom).

FIGURE 7 illustrates the capability of Park 3D AFM to image all surfaces of the pattern, in contrast to the conventional AFM or the SEM, which cannot fully characterize the surface data, and obtain information such as base, top and both sidewall roughness from sidewall characterization. A 300 nm photoresist line pattern was imaged and the respective line profiles were obtained that clearly showed a substantial difference in terms of SWR between 97% and 40% AIC. More specifically, the lower the value of AIC, the more increased was the measured roughness. This intense decrease of roughness is underlying the fact that LER and the measured sidewall roughness are clearly correlated.

Finally, it needs to be emphasized the role of non-contact 3D AFM in terms of preserving the tip sharpness of the cantilever. In an independent study, researchers performed 150 consecutive measurements using the same tip and the tip wearing proved to be minimal. This is a prominent feature of AFM that prevents the continuous costly replacement of the tip but also ensures that the sample will be viable and not damaged by the AFM cantilever. The preservation of the tip sharpness allows for continual measurements of high resolution roughness data.

Conclusions
The potentialities of the innovative, non-destructive imaging technique of 3D AFM has several advantages compared to conventional SEM systems. An independent and tilted Z-scanner overcomes the disadvantages of alternative metrology tools and measure parameters such as detailed sidewall morphology and roughness, and sidewall angle characterization that render the optimization and evaluation process easier and far more detailed. •


KEIBOCK LEE is president and general manager of Park Systems, Santa Clara, CA.

Abingdon, EnglandOxford Instruments (OXIG:LSE) has acquired Asylum Research (Santa Barbara, CA), a maker of scanning probe microscopes (SPM) with subsidiaries in the UK, Germany, and Taiwan. Its products are used by academic and industrial customers across the world for a wide range of materials and bioscience applications.

Asylum Research is being acquired from its management for an initial debt free, cash free consideration of $32 million with a deferred element of up to $48 million payable over three years depending on performance. Asylum Research generated Earnings Before Interest and Taxation (EBIT) of $1.1 million in 2011 from revenue of $19.6 million, and had gross assets of $6.2 million. The acquisition will be funded from existing facilities and is expected to be completed before the end of December 2012.

The acquisition of Asylum Research is in line with Oxford Instruments’ 14 Cubed objectives, to achieve a 14% average compound annual growth rate in revenues and a 14% return on sales by the year ending March 2014.  This acquisition contributes to the planned acquisition element of the revenue growth objective. While Asylum Research is expected to deliver less than the 14% targeted margin in this and the next financial year, following the acquisition the 14 Cubed margin target for the Group remains unchanged.

Approximately 60% of Asylum Research turnover comes from customers working in the materials science area where the customer base and routes to market are shared with Oxford Instruments. This opens opportunities for market synergies and the development of new integrated products. The remainder of Asylum Research’s turnover is in the bio-nano area where SPM instruments are used for research into soft materials such as DNA. This market provides a new growth opportunity for Oxford Instruments.

Jonathan Flint, Chief Executive of Oxford Instruments, noted, "The acquisition of Asylum Research significantly increases our footprint in the nanotechnology space and complements our strong position in electron microscopes with a presence in another fundamental nanotechnology measurement technique. The acquisition also gives us access to the rapidly growing bio-nano market as it allows customers to perform analysis of organic samples in their natural liquid environments, something which cannot readily be done using electron microscopes.