INTRODUCTION
The mission of the Engineering Physics Division (EPD) is to promote U.S. industrial innovation through the development of a high-quality physical measurement infrastructure that is specifically relevant to realizing length traceability and that will underpin future electronics. The division has 79 research staff (including 1 NIST fellow), 95 guest researchers, and 20 students. It is responsible for dimensional, nanometer-scale, and surface metrology, accelerometry, acoustic-pressure metrology and standards, and advanced electronics manufacturing, testing, and standards. The division is divided into five groups: CMOS and Novel Devices, Dimensional Metrology, Nanoelectronics, and Nanoscale Metrology, and Surface and Nanostructure Metrology.
ASSESSMENT OF TECHNICAL PROGRAMS
CMOS and Novel Devices
The CMOS and Novel Devices Group has 10 staff scientists, 10 guest researchers, and 6 other affiliated staff. The group advances measurement science to accelerate the commercialization and manufacture of high-performance and reliable electron devices for the electronics industry by developing new characterization techniques, physics-based models, and data analysis methods. The group develops the advanced metrology tools to enable quantitative and mechanistic assessment of reliability issues in emerging electronic devices.
Another thrust is to develop new measurements, physical models, and data analysis techniques to accelerate the development and commercialization of nanoelectronic-device-based medical technology for life sciences and personalized health care. The CMOS and Novel Devices Group has three technical programs—reliability for present and future CMOS; back-end-of-line (BEOL) reliability and metrology; and nanobiotechnology and bioelectronics. The first two programs are closely coupled with the semiconductor industry and are important to this multi-trillion-dollar industry.
CMOS reliability has become more challenging to quantify as dimensions have shrunk. Reliability is an important issue for both consumer and military electronics technology. This PML team has made several major technical achievements that address the reliability issue. They include a probe station that has been modified to make massively parallel current voltage measurement—this tool allows for rapid acquisition of data from which reliability models can be produced; the refinement of a technique for measuring low-level defect concentrations produced in the CMOS device during operation; and the development of a unique high-definition spin resonance tool that allows exploration of the structure of the defects that are being measured electronically. The three projects represent important contributions to the semiconductor industry, where NIST will continue to play an important role. The challenge is that as CMOS scaling comes to its end, the metrology will have to continue to adapt. An exciting application of the spin resonant tool will be in biotechnology. An exemplary contribution of the team is that a tool originally developed to address semiconductor problems will find its main applications in biotechnology.
A second team has focused on BEOL. This team is addressing many of the issues related to 3D integration in semiconductor chips. The semiconductor industry is using more chip volume, which results in expanding the chip vertically. The CMOS and Novel Devices Group has developed several scanning probe and RF techniques for measuring subsurface interfaces and defects and has developed techniques for determining the thermal stress in Cu vias. Stress determination is important because 65 percent of microelectronic failures are stress-related. Three-dimensional (3D) integration will become ubiquitous as the industry pursues multifunctionality in its chip development.
Interaction with the semiconductor industry continues to be important. There may be emerging needs for reliability studies and standards in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) technology. NIST needs to continue to track developments in this constantly changing environment. A third team addressing bioelectronics is relatively small, with four staff members and two guest researchers. However, the technical results are exciting and lay out a promising biochip development pathway. The researchers have demonstrated biological nanopores on a chip that can distinguish the size of proteins electronically. This is an important research direction that is being followed worldwide. The biggest challenges in the technology will be developing artificial nanopores that can replace the organic pores.
The impressive nanopore work can be used for protein sizing and ultimately could be integrated with a CMOS-based field-effect transistor (FET). The tip-based electron spin resonance equipment was also impressive. This is a unique instrument originally developed for semiconductor characterization, with exciting possibilities in PML’s new initiative in physical measurements on living things. The division’s effort to create a strategic plan to integrate its biological work into this new initiative is commendable.
Nanoelectronics
The Nanoelectronics Group is composed of 11 research staff members and 25 guest researchers. The group conducts basic research to advance the optical and electrical measurement science infrastructure necessary for innovation in nanoelectronic and thin-film devices and their component materials. Within the group are three subgroups that address optical spectroscopy of nanostructures, thin-film electronics, and nanoelectronic device metrology.
The optical spectroscopy of nanostructures subgroup focuses on Raman spectroscopy to access the optoelectronic properties of novel nanomaterials. The focus has been on carbon nanotubes. The emphasis is shifting to graphene and to dichalcogenides. This subgroup has been instrumental in assessing the health and environmental risks of nanomaterials.
The thin-film electronics subgroup develops rigorous measurements and methodology needed for continued U.S. leadership in manufacturing and innovation of emerging electronic devices. An example of the interdisciplinary work done by the Nanoelectronics Group was the development of a standard cleaning technique for graphene. Graphene is particularly difficult to clean because the plasma cleaning normally used to remove photoresist and other polymers will destroy graphene films. The thin-film electronics subgroup is developing metrology for flexible electronic, high-performance heterojunction devices and Li battery technology. An example is the development of internal photoemission spectroscopy to quantify band offsets for gate stacks on alternate-channel FETs. These measurements utilized a NIST-unique test structure incorporating graphene as an electrically and optically transparent electrode.
The nanoelectronic device metrology subgroup seeks to develop measurements that quantify physical processes and electronic properties and to manipulate such processes and properties to enable innovation through entirely new functionality. An example is the projects in is click chemistry, which expands molecular electronics to molecules that do not self-assemble, allowing the build-up of complex molecular layers and electrode variety and adding new functionality at well-designed nanometer distances and concentrations. Another example is the development of eutectic gallium indium electronic junctions, which address the difficult problem of contacts to molecular layers.
Research in nontraditional materials for the purpose of developing the next generation of measurement technologies is a solid rationale for the team’s planned direction. However, it will be important that PML avoid duplication of effort conducted by better-funded teams investigating the science or technology of these speculative materials systems.
Surface and Nanostructure Metrology
The Surface and Nanostructure Metrology Group consists of 14 research staff and 12 guest researchers. The group project teams focus on optical methods for 3D nanostructure metrology; nanostructured optics and optical surface metrology; forensic topography and surface metrology; traceable scanning probe nanocharacterization; atom-based metrology; and atomically precise electronic devices.
The team investigating optical methods for 3D nanostructure metrology focuses on resolving critical issues in deep subwavelength line width and defect metrology for the U.S. semiconductor industry. Combining light scattering with algorithms, they are able to extract information from subwavelength line widths. They are reporting the world’s smallest multidimensional measurements of objects using optical imaging, providing quantitative information from scattered light images at resolutions previously thought impossible.
The nanostructured optics and optical surface metrology subgroup is developing innovative methods for measurements of ultraprecise flat, spherical, free-form, and nanostructured surfaces and is also developing novel nanostructured optics.
The forensic topography and surface metrology subgroup is developing rigorous metrics and algorithms for forensic firearm and tool mark identification. This work has produced calibration bullets and cartridge cases that serve as laboratory standards. This impressive work illustrates the impact of metrology in non-traditional areas.
The subgroup on traceable scanning probe nano characterization provides fundamental nanoscale length metrology for such applications as semiconductor manufacturing, optics, photonics, and data storage. This group is seeking to understand and characterize tip sample interactions. This is important work; it will be interesting to see how the new efforts on atom-based metrology develop. The subgroup on atom-based metrology is developing the intrinsic metrology needed to enable atomically precise devices at the ultimate scaling limit, applicable to the emerging class of quantum devices.
Dimensional Metrology
The Dimensional Metrology Group realizes and disseminates the SI unit of length, concentrating on dimensional measurements ranging from micrometers to kilometers. The group of 18 full-time staff and 2 guest researchers develops and deliver cutting-edge dimensional metrology technologies, including critical measurement services and standards for industrial manufacturing such as the precise measurement of aircraft and automotive parts to ensure proper mating of parts. The group also collaborates on dimensional metrology tasks relating to NIST research on measuring discrepancies of the value of the universal gravitation constant, G, and evaluation of hip replacement artifacts.
The group has developed the world’s best Fabry-Perot refractometer, which will enable a portable, low-cost, and accurate length standard under ambient conditions. The length standard (which, since 1983, has been referenced to the speed of light) is currently limited by the accuracy of the air wavelength, which in this device is known to 5 in 10−9 due to the water vapor contribution to the refractive index of air. Further improvement in this accuracy is anticipated when this contribution is corrected for. Because the refractive index in gases depends on pressure, the Fabry-Perot reflectometer can also be used to realize a portable primary standard for pressure. An open question remains: How well can one maintain long-term stability of the mirror reflectivities under ambient conditions? It might be
worthwhile to consider whether it is possible to scale this down to make a NIST-on–a-Chip device. NIST-on-a-Chip is an integrated program to develop and deploy NIST-treaceable measurements and physical standards that are deployed in the customer laboratories, factories, devices, and systems; are easily used and integrated; provide a wide range of measurements and standards relevant to the particular customer needs and applications; and are manufacturable.
The group needs to play an important role in the advanced manufacturing initiative for both long-range and short-range metrology. This would draw the group closer to the other groups in the PML. If not currently being done, the group’s researchers could benefit from sabbaticals at customer industries. This is particularly relevant for the fast-changing technologies addressed by the group.
Nanoscale Metrology
The Nanoscale Metrology Group provides advanced measurement science, standards, and calibration services for acceleration, shock, and acoustics. The group is an active participant in standards committees in the Institute of Electrical and Electronics Engineers (IEEE), International Organization for Standardization (ISO), and Semiconductor Equipment and Materials International (SEMI) and also provides services for shock measurements for military and sports applications.
The group has revitalized its vibration calibration services activity by opening a state-of- the-art primary calibration system to support U.S. calibration laboratories. They have also refocused their metrology service efforts on developing primary calibration devices aimed at the rapidly growing, multibillion-dollar MEMS industry for microphones and inertial sensors.
Hearing loss is a major medical issue for millions of Americans and for veterans who have suffered hearing losses as a consequence of combat. The group has created a state-of-the-art capability to measure and calibrate the performance of hearing aids with incorporated adaptive filters. They have also developed test methods to perform the uncertainty analysis of manikin instrumentation during underwater blast testing.
PORTFOLIO OF SCIENTIFIC EXPERTISE
The CMOS and Novel Devices Group is a combination of physicists, biophysicists, and engineers. Many of the investigators have industrial experience and are sensitive to the needs and limitations of the semiconductor industry; this is especially true for the team doing the reliability work. The group expertise strongly supports the responsibilities of the group. Considering the new emphasis on the measurement of living things, it would be useful for the group to add a protein chemist to work with the nanopore team.
The Nanolectronics Group has two Department of Commerce (DOC) silver medal winners and has taken on leadership roles in their respective scientific communities.
The Surface and Nanostructure Metrology Group has received several prestigious awards, including the 2013 research and development (R&D) 100 Award and the 2013 Intel Outstanding Researcher in Metrology Award. In addition, the group has been extremely successful in obtaining both internal and external funding.
ADEQUACY OF FACILITIES, EQUIPMENT, AND HUMAN RESOURCES
The facilities are more than adequate for the technical program described in the CMOS and novel devices area. Some of the equipment developed by the reliability team is unique. The biotechnology team collaborates across NIST and with the National Institutes of Health (NIH) for access to biospecific facilities.
The facilities are adequate to support the work of the Nanolectronics Group and the Surface and Nanostructure Metrology Group. Some of the equipment used by the latter group (particularly for dimensional calibrations) is unique and located inside carefully controlled environments.
DISSEMINATION OF OUTPUTS
The Nanolectronics Group has a solid publication record. In addition to publications the Surface and Nanostructure Metrology Group provides dimensional calibrations in the range from micrometers to 0.1 meter.
