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Did You Know?: Scifres Nanofabrication Laboratory at Birck Nanotechnology Center

January 7, 2011

A researcher or student entering the Scifres Nanofabrication Laboratory might look like something from a science-fiction film, but in this university cleanroom, wearing jumpsuits, gloves, boots and face masks is necessary to keep it the cleanest in the country.

A 2010 study published in the proceedings of an IEEE conference found that no other university cleanroom is as clean as this cleanroom, which is part of Birck Nanotechnology Center.

Cleanrooms control the amount of particles in the air, along with temperature, humidity, vibration and electromagnetic interference, to allow extremely small-scale research to be conducted without the interference of contamination.

Types of fabrication processes used in this cleanroom research:

* Lithography -- three-dimensional imaging, similar to photography, that creates the very small patterns used in fabrication.
* Etching -- the transfer of patterns generated with the lithography process into three-dimensional structures.
* Deposition -- depositing films of various materials on surfaces to use in the creation of structures.
* Thermal -- the use of heat energy to diffuse chemicals into the base materials in the creation of devices.

Most of this research involves devices that measure between 10 and 1,000 nanometers. (60,000 10-nanometer lines can be placed across the diameter of one human hair.) This type of research would not be possible with particles floating in the air.

The average home or office has about 300,000 particles per cubic foot of air. This cleanroom has less than 1 particle per cubic foot of air.

The International Organization for Standardization set criterion for cleanrooms between ISO Class 9 (the loosest) and ISO Class 1 (the cleanest). Birck's cleanroom is 45 percent ISO Class 3, 40 percent ISO Class 4 and 15 percent ISO Class 5.

Although ISO Class 9 is the loosest cleanroom, it is about 100 times cleaner than an office or home. The cleanest hospital surgical room is usually ISO Class 8, meaning there are 10,000 times more particles in each cubic foot of air than in the BNC cleanroom.

The factors below combine to ensure that the cleanroom maintains ISO standards.

* Three-level facility structure:

 - The bottom subfab level provides support space and houses cleanroom support equipment to keep vibrations and contaminants from the cleanroom itself.
-  An air handling level allows for constant clean air circulation and filtration.
- The 25,000-square-foot cleanroom laboratory has 13 bays and 15 chases.

* Construction materials:

- Waffle slab flooring, which resembles a Belgian waffle, provides strength and stability against vibration better than a solid pour of concrete.
- Walls were built from Plascore™ -- nonshedding, baked enamel aluminum panels with a honeycomb structure on the inside-- for stability and cleanliness.
- Glass, another nonshedding material, allows for natural sunlight and aids in energy conservation.
* Air circulation:

- An Ultra Low Penetration, Air (ULPA) filter is 99.999 percent effective on 100-nanometer particles.
- Cleanroom air is changed 9.5 times per minute. Air in an average home is changed six times per hour.
- A perforated and raised floor allows for continual air circulation. Ninety percent of cleanroom air is circulated in a closed loop; the remaining 10 percent comes from the outside.
* Constant cleaning:

- Specially trained crews clean eight hours per day, every day.
- Large pieces of equipment, before entering the cleanroom, are wiped down twice, then filtered air is blown down on them for 12 hours.

* Gowning:

- Before people enter the gowning area, they put on shoe covers and walk on a permanently tacky floor to remove particles. A bouffant cap is used to cover hair. 
- Next, an air shower removes particles from street clothes.
- Top-down gowning takes place in the gowning room. Everyone entering the cleanroom must wear a jumpsuit made of Gore-Tex, a waterproof, breathable fabric that acts as a filter. A hood, goggles, face veil, boots, gloves and safety glasses also must be worn.
- A second air shower removes particles from the jumpsuit, allowing entrance into the cleanroom.

The feat of maintaining a cleanroom is not an easy one, but through careful planning, construction and cooperation between its users and staff members, Purdue's Scifres Nanofabrication Laboratory provides a clean atmosphere for conducting small-scale research.

Source: John Weaver, facility manager for Birck Nanotechnology Center

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