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A nanotechnology facility designed to accommodate the research of today and prepared for advances of tomorrow

NOTE: This is the first in a series of articles on the state-of-the art Birck Nanotechnology Research Facility at Purdue University. Throughout this year and into 2007, we will be featuring exclusive coverage of some of the leading nanotechnology facilities in the U.S.

The Birck Nanotechnology Center at Purdue University provides both an appealing façade and a high level of functionality. The open architectural style supports the collaborative, interdisciplinary nature of the research being performed in the building.

“The Birck Nanotechnology Center (BNC) building at Purdue University is itself a scientific instrument,” states Research Development Manager George Adams. “All elements of the facility work together to the same end, enabling nanoscale research.” The building includes the largest and cleanest university cleanroom in the United States, a separate biological cleanroom, a uniquely designed link between the two clean-room types for materials transfer, and highly sophisticated general laboratories optimized for nanoscale research. These cleanrooms and laboratories in turn support an advanced equipment set. This entire facility is supported by a highly experienced technical staff. The infrastructure of building, equipment, and staff is the foundation for and the partner with Purdue’s researchers in their quest to push the limits in nanoscience, nanoengineering, and nanotechnology and to create novel materials, structures, and devices that are life-changing. The opportunities appear limitless.

Beginning with the nanofabrication clean-room equipment set, the capability for lithography has been pushed to six nanometers (0.006 micrometers) with a newly purchased Leica Vec-torBeam lithography system, additional e-beam and optical lithography systems, including double-side alignment tools, round out the lithography area of the BNC. To achieve this capability, Building Manager Mark Voorhis tuned the cleanroom control system to maintain less than two-tenths of a degree temperature variation in this portion of the cleanroom. This, coupled with ISO Class 3 (Class 1) particle control, a NIST-A vibration rating on the cleanroom waffle slab, and low EMI levels, allow the VectorBeam to achieve its full capability.

Advanced etching capability allows the patterns obtained in the lithography area to be replicated in various films on the wafers. Two STS deep reactive-ion etchers, a soon-to-be-delivered etcher from Panasonic, and several other reactive-ion etch systems provide the ability to etch a wide variety of materials with high aspect ratios.

The Scifres Nanofabrication Laboratory, a semiconductor-style cleanroom specially designed for nanotechnology research, provides clean zones ranging from ISO Class 3 to ISO Class 5 zones with exceptional vibration and temperature control. (Photo courtesy HDR Architecture; Steve Hall, and Hedrich Blessing.)

The nanofabrication cleanroom uses a three-floor approach, with utilities supplied from the subfab below the cleanroom and air handling provided from the floor above the cleanroom. The use of a subfab reduces equipment installation time and cost, critical for a research facility where equipment changes will be ongoing.

Deposition has long been a strength at Purdue, and the capabilities of twelve evaporators and sputterers, as well as several chemical vaporization deposition (CVD) and plasma-enhanced CVD (PECVD) systems have been supplemented with the acquisition of two atomic layer deposition (ALD) systems. This wide variety of systems allows both common and exotic films to be deposited while minimizing concerns of cross-contamination.

Ion implantation, diffusion and oxidation, and wet-chemical processing round out the cleanroom tool set. This equipment is located in the 25,000 square foot Scifres Nanofabrication Laboratory, a cleanroom containing six bays at ISO Class 3 (Class 1), five bays at ISO Class 4 (Class 10), and two bays at ISO Class 5 (Class 100) clean zones. A bay-chase design with large chases and smaller bays was used for two principal reasons. First, this approach minimizes first cost and operating cost by reducing the amount of the cleanroom under filter. Second, a physical barrier is placed between the “operations” portion of the equipment and the “maintenance” portion of the equipment. The mass of the equipment is recessed in the chase where the ultimate in cleanliness is not needed and where most of the maintenance functions are performed.

The cleanroom is the typical semiconductor-style three-floor cleanroom with a subfab level, cleanroom level, and air-handling level. The subfab is not part of the airflow path, and contains support equipment for the cleanroom tools. For example, the vacuum pumps of a reactive-ion etcher are located in the subfab where the contamination they generate is isolated from the clean-air path. Inert gases are also located in the subfab, while hazardous gases are located in one of three gas rooms—toxic, flammable, or pyrophoric. The subfab also serves as a utility distribution level. Electrical power, exhaust, and piping systems are distributed on this level, with connections to both sub-fab equipment and to cleanroom equipment.

The subfab level is on grade, with a high column density to provide the vibration control desired for the clean-room waffle slab. Dividing the subfab from the cleanroom is a high-aspect-ratio waffle slab. The beams are 36” deep on 24” centers, with a 4 1/2” thick pan between the beams. This pan is penetrated at regular intervals with utility sleeves to provide a path for the distribution of utilities from the subfab to the cleanroom.

The cleanroom level is further subdivided into the air-distribution space above the terminal (ULPA) filters, the cleanroom itself, and the underfloor area for air return and utility distribution. The air-distribution system is a duct-ed supply with a plenum return. Balancing boxes supply air through flexible ducts, “elephant trunks,” to the filter modules. The filter modules supply a gasket seal between the module and the T-bar ceiling system— the non-critical seal. A gel seal is used between the filter and the module because it is the pressurized and, therefore, critical seal.

The cleanroom bays and chases are separated by demountable wall panels attached to a support system that allows the mounting of utilities and Unistrut brackets directly to the mullion. Glass panels are utilized frequently to achieve an open feel to the cleanroom.

The cleanroom floor is a standard perforated panel, but the chase floor is a grated panel. The grating allows below-floor piping to be traced without removing panels and provides a lower pressure drop in the airflow path. The cleanroom floor stands two feet above the epoxy-coated waffle slab, allowing ample space to maximize airflow uni-directionality and to ease installation and servicing in underfloor areas.

The upper level of the cleanroom building contains both make-up and recirculation air handlers. Multiple-fan units, each with six man-liftable, independent fans, handle the recirculation airflow through the cleanroom, providing nine air changes per minute. Fan independence means that no fan is a single point of failure for air circulation; the other five fans provide “instant backup” should a fan fail. By using small, identical fans, an in-house stock of a few relatively inexpensive spare fans allows for timely replacement of a failed fan-motor assembly.

Entry to the nanofabrication cleanroom follows standard protocols for a cleanroom of this classification. A pre-gowning area provides step-over benches where shoe covers are donned, and an open area where bouffant caps are added. Following the swipe of an ID badge and check against a database to ensure that the user’s cleanroom training is current, an air shower provides access to the gowning room. A standard top-down gowning protocol is used for donning hoods, GORE-TEX jumpsuits, boots, and gloves. Finally, a second air shower provides access to the cleanroom.

The cleanroom of the Birck Nanotechnology Center in Discovery Park at Purdue University is enabling nan-otechnology research in many areas. A cleanroom portion of this comprehensive facility is a driving force in nanoscience and the development of new nanoscale devices.

John R. Weaver II serves as the Facility Manager for the Birck Nanotechnology Center at Purdue Uni-versity.He is responsible for the facility infrastruc-ture,safety and training activities,and cleanroom and laboratory operations.John received his BS degree in Chemistry at Adrian College in 1972,and joined RCA Solid State Division in process engineering in the world’s first production CMOS fabrication facility.In 1975 he moved to Hughes Aircraft Company’s Solid State Products Division in Newport Beach,California, where he continued his role in high-volume manufacturing-support engineering.In 1977 he moved to what is now Delphi Corporation in Kokomo,Indiana.During his career,John has been involved in a variety of roles in semiconductor process support,process development, and processing facilities development.He can be reached at 765-494-5494 or jrweaver@purdue.edu