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3 The Nanofab Program OVERVIEW The NIST Nanofab is an integral part of the mission of the Center for Nanoscale Science and Technology―to develop and maintain a national shared-use facility, the Nanofab, with state-of-the-art, nanoscale fabrication and measurement capabilities―and it is an integral part of the CNST vision to be recognized as a world leader in each of its research areas and for providing ready access to unexcelled nanoscale measurement and fabrication facilities. The group leader has been at NIST for only a short period of time. The Nanofab facility contains a modern set of commercially available fabrication and metrology tools that exceed or match capabilities at university nanofabrication facilities. A small subset of this tooling is on a par with equipment at industrial nano- facilities. The Nanofab is supported by seven process engineers and three process technicians. This high level of staffing in the Nanofab differs from that in university facilities, where such support is minimal. For reference, typical industrial processing support operates with a 1:1 ratio of process engineers and technicians. The Nanofab model for meeting the needs of the fabrication projects required by its users provides two options: hands-on processing by the user or processing by Nanofab staff. With either strategy, the Nanofab staff provides consultation services to define both process development requirements and a process flow for the project. PHYSICAL PLANT AND TOOLS The Nanofab is housed in a newly constructed, 19,000 ft² clean-room facility incorporating the necessary requisites for safe, contamination-free operation in Class 100 and Class 1000 environments―that is, temperature control, humidity control, deionized (DI) water, air volume handling, and laminar airflow. At present, 25 percent of the clean- room space is unused and available for future tooling and wafer processing needs. The Nanofab tooling is a mixture of inherited equipment from the NIST complementary metal oxide semiconductor facility (deposition, RIE, film thickness measurement, diffusion, contact print lithography, and SEM applications), new RIE and characterization tooling and FIB tooling, and new nanofabrication-specific tooling (electron-beam [or e-beam], nanoimprint, and mask-making applications). The Nanofab tool set can nominally accommodate 150 mm diameter wafers and has the flexibility to process small-dimension (20 mm) substrates. In the second quarter of 2009, significant new tooling (a second e- beam lithography system, an atomic layer deposition [ALD] unit, and two additional RIE units) will be added to the Nanofab. Reports from the CNST director, the Nanofab manager, and process staff indicate that the facility has reached limits in air-handling capacity, and yet at least five new tools are planned for delivery. Other utility deficiencies (DI water and heating, ventilating, and air conditioning [HVAC]) were also described. 12
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PROCESSING ACTIVITIES The Nanofab tour, the presentations by group leaders and project leaders, the posters, and the presentation by the Nanofab manager did not provide sufficient information for the panel to be able to gauge the process activity level and the process capabilities of the Nanofab facility. Process integration capabilities, workloads, and tool utilizations for the facility were not adequately described. A general impression of the panel is that the facility is large, almost lavish. The Nanofab is underused at this stage. It is currently completing its initial tool-up, and the tools being turned on this year will result in greater overall utilization of the facility. Staffing and utilities are being stressed by the addition of new tools, even with the modest level of use in the facility. The process activities described during the review are summarized in Appendix A. The process examples explicitly described during the review imply that the Nanofab program has as its major focus the fabrication of MEMS structures and as its secondary focus, the fabrication of a single layer of nano features using one photolithography step―that is, a combination of an e-beam exposure, a metal deposition, and a subtractive or additive removal of material. The CNST is a relatively new entity, so such a focus is not unexpected. Two of the five examples presented highlighted individual process steps in multilevel nanostructures. As the center’s projects mature, it can be assumed that Nanofab activities will transition to creating more nanoscale structures. TOOLING ISSUES The Nanofab facility is tool-rich and yet is expanding in the next 6 months by increasing its capabilities in deposition (ALD), RIE, and e-beam lithography. These tool additions are significant in terms of capitalization, complexity, and engineering support requirements. The justifications for these tool additions, in view of the fact that the present tool set is underused, were not described. Future Nanofab tooling additions would benefit from a long-term planning strategy for tools, staffing, and process needs to ensure efficiencies in tool utilizations. The centerpiece tool for the Nanofab is the Vistec 300 E-beam writer. Commentary on tool utilization and e-beam-specific projects was lacking, even though a second e-beam tool has been acquired. Tooling inconsistencies were observed during the panel’s visit, including the following: Justification for six RIE-specific tools (two arriving in the second quarter of 2009), Justification for a second state-of-the-art e-beam tool and justification for locating this sophisticated tooling outside the clean-room area, Lack of state-of-the-art metal lift-off tooling (spray heated solvent) and CO2 snow cleaning, Lack of sputter deposition tooling, and No ion milling capability. 13
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OPERATIONAL STRATEGY The goal of the Nanofab program is to serve researchers from NIST, other government laboratories, academic institutions, and commercial enterprises. Operational strategies to reach the broader commercial user base are not well defined. Much of the operation and the suite of equipment seem to have been modeled after academic nanofabrication facilities. While this emulation of existing facilities increases the chances of quickly creating a functional entity, for the development of this new facility the significant and rarely possible investment in new capability should be done in a way that would not duplicate but rather create entirely new capability for the U.S. research and development (R&D) community. Coupling and exploiting the unique strengths of the CNST and NIST, in metrology, for example, and making these available to the R&D community would be a significant contribution to the U.S. research base and a tremendous asset in the United States. Also useful to guide direction and operation would be an analysis of the user community and identification of currently unmet needs. CONCLUSIONS AND RECOMMENDATIONS The Nanofab facility contains a remarkable set of the most modern commercially available fabrication and metrology tools. This major investment in capital equipment and staff resources should be a tremendous asset for the CNST researchers and could be extremely valuable for commercial enterprises. The Nanofab facility is a new entity. It requires time to mature and to demonstrate its full potential as an asset to NIST and to academic and industrial users. The CNST and the Nanofab program must analyze the unmet needs in the growing nanoscale research community and determine how strengths of the CNST and NIST can address these needs, taking care not simply to duplicate existing capabilities. The Nanofab facility requires oversight in several areas: Chart e-beam activity in the laboratory, thereby justifying a two e-beam facility; Document tool utilization; Chart processing experiments in the facility to create a process history and an activity history for the facility; Develop a tool plan and a complementary staffing plan to support the tooling plan; Develop for the outside user a set of charging and access methods that is based on clear criteria for allocating resources; Develop a plan to remedy HVAC, air handling, and DI water deficiencies in the laboratory; and Develop a set of process capabilities complemented with process modules for the facility. The Nanofab program should be reviewed again during the 2010 calendar year to gauge progress in meeting the Nanofab goal of state-of-the-art nanoscale processing. 14
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The panel’s evaluation yielded the following conclusions: The technical merit relative to the state of the art is low in terms of impact to date; the potential, with appropriate continued development, is high. The capital infrastructure is outstanding in many cases, although some highly useful tools seem to be missing. Some essential facility capabilities such as air handling are reported to be inadequate. Staffing levels seem low. The achievement of desired objectives and impact will be examined when more information is available in future reviews. 15