E SC 412 Nanotechnology: Materials, Infrastructure, and Safety Wook Jun Nam © 2013 The Pennsylvania State University Unit 2 Infrastructure Lecture 2 Facilities © 2013 The Pennsylvania State University Unit Outline • Infrastructure * What is it ? * Why do we need it in nanotechnology ? • Facilities • Equipment Systems * Vacuum Based Systems * Non-vacuum Based Systems © 2013 The Pennsylvania State University Lecture Outline • Introduction • Facilities − Why do we need special facilities ? − Types * Clean work stations * Tunnel/Bay structures * Cleanrooms * Mini-environments © 2013 The Pennsylvania State University Why do we need special facilities ? • • • • • Place for manufacturing Safety Contamination control Protection of workers and environment Process control © 2013 The Pennsylvania State University What are some examples of the facilities used ? • Clean Work Stations • Tunnel/ Bay Structures • Cleanrooms • Mini-environments − SMIF boxes http://techon.nikkeibp.co.jp/NEA/archive/200205/183172/ © 2013 The Pennsylvania State University Clean Work Stations • One approach in nanofabrication and synthesis is to create individual work stations, such as chemical hoods with air filters and non-shedding materials. • A large room with the work stations (or hoods) arranged in rows, so products under fabrication can be moved to each station, without coming in contact with “dirty” air. © 2013 The Pennsylvania State University Clean Work Stations • Filters in the clean hoods are known as High Efficiency Particle Attenuation (HEPA) filters. • HEPA filters consist of large, porous fibers folded into a filter holder in an accordion design. • HEPA filters allow a large volume of air to pass at a low velocity (90-100 ft/min.) and have a filtering efficiency of 99.99%. © 2013 The Pennsylvania State University The HEPA Filter Design Dirty Air Clean Air Public Domain: Image Generated by CNEU Staff for free use © 2013 The Pennsylvania State University Clean Work Stations • A typical clean hood has a HEPA filter mounted in the top. • “Dirty” air is pushed through the filter and exits in a laminar pattern. • A shield directs the exiting air over the work area in the hood. • These type of hoods are known as vertical laminar flow (VLF) hoods. © 2013 The Pennsylvania State University VLF Hood Cross Section Perfilter Blower Air Flow HEPA Filter Clean Air Work surface Public Domain: Image Generated by CNEU Staff for free use © 2013 The Pennsylvania State University Glove box • Glove box is an enclosed workstation which provides inert atmosphere. • The gas (argon, nitrogen or helium) continuously circulates between the glove box and the gas purification system. The gas is purified to a value of < 1 ppm in relation to moisture and Oxygen. © 2013 The Pennsylvania State University Basic Components of Glove box Glove Box Vacuum-tight stainless steel working space. Glove Ports / Gloves Butyl gloves for comfortable working. Antechamber : For material transfer. http://home2.btconnect.com/MBRAUN-UK/technical-guide.htm Vacuum Pump - to evacuate the system - To pump antechamber - for final cleaning of the purifiers at the end of the regeneration cycle © 2013 The Pennsylvania State University Basic Components of Glove box Gas Purification System Usually attains < 1 ppm Oxygen Usually attains < 1 ppm moisture Purifier can be regenerated using hydrogen/nitrogen mixed gas Control Panel For central controlling and monitoring of the system http://home2.btconnect.com/MBRAUN-UK/technical-guide.htm © 2013 The Pennsylvania State University Basic Operation of Glove box G : Gas flow Circulation between box and purifier F : Exhaust filter Inlet/outlet of the circulation tubes are protected by aerosol filters. The filters supply particle-free atmosphere and separate the box from the purifier(s) and tubes V : Valves Usually electropneumatic valves http://home2.btconnect.com/MBRAUN-UK/technical-guide.htm C : Cooling (heat exchanger) Electric heat as well as compression heat increase the gas temperature © 2013 The Pennsylvania State University Basic Operation of Glove box P : Purifier Unit (regenerable) Oxygen: Removed by chemical binding at polydispersed copper Moisture (water vapor): Removed by adsorption in microporous molecular sieve Other gases: Removes all gases that react with Cu or CuO. Traps gases that fit into the 1.3 nm holes of the molecular sieve B : Blower (circulation unit) Causes the circulation of gas flow. It is encapsulated in a vacuum-tight container http://home2.btconnect.com/MBRAUN-UK/technical-guide.htm © 2013 The Pennsylvania State University Glove Box Applications • • • • • • Allows work with anaerobic organisms or anaerobes. (living organisms that do not require oxygen for survival and could possibly react negatively, and even die, if oxygen is present) Allows use of oxygen/moisture sensitive materials Allows inert welding Allows battery production; e.g., lithium batteries need a moisture free production environment Allows deposition of relatively contamination-free thin films; e.g., Al, Cu, P3HT/PCBM Can be used to allow work with hazardous materials such as high-biosafety level pathogens and radio active material © 2013 The Pennsylvania State University Tunnel/Bay Concept • For more stringent particulate control clean hoods are less popular because of the potential for personnel induced contamination • This contamination issue can be solved by dividing the fabrication/synthesis area into clean regions called “bays” or “tunnels” • Work stations are then located in these bays/tunnels © 2013 The Pennsylvania State University Tunnel/Bay Concept • In this design, clean air enters into a bay or tunnel from above by HEPA filters built into the ceiling • Materials are less vulnerable to personnelgenerated contamination because there are fewer workers in the immediate area • On the downside, tunnel/bay designs are more expensive to construct than hoods and are less versatile than cleanrooms, when it comes to process changes © 2013 The Pennsylvania State University Tunnel/Bay Design HEPA Filters Clean Air Public Domain: Image Generated by CNEU Staff for free use © 2013 The Pennsylvania State University The Cleanroom Approach • Simply stated, a cleanroom is a volume (a room) where contamination is reduced and controlled • A cleanroom is designed to minimize contaminants © 2013 The Pennsylvania State University © 2013 The Pennsylvania State University Cleanroom Contamination • Humans are the biggest source of cleanroom contamination. – A cleanroom operator, even after air showering, can give off between 100,000 and 1,000,000 particles per minute-this number increases when a person is in motion • At two miles per hour, a human gives off up to 5 million particles per minute! • Processing equipment is the second biggest source of cleanroom contamination. – Often processing support equipment is placed in the chase area of a cleanroom © 2013 The Pennsylvania State University Cleanroom Personnel • Humans must be isolated as much as possible from the delicate materials and equipment found in a cleanroom • Personnel must be covered in special cleanroom garments (“bunny suit”) consisting of a hood, facemask, coveralls, boots, and gloves © 2013 The Pennsylvania State University Gowning • Many cleanroom gowning procedures do not protect a user from hazards of the cleanroom. They only protect the cleanroom from particles generated from the users • Additional protective equipment is required for certain processes © 2013 The Pennsylvania State University Gowning Protocol • With the exception of shoe covers, gowning for the cleanroom occurs in a top down fashion: – This is done to reduce particulate shedding • Gowning for the cleanroom occurs in the following order: – – – – – – – Shoe covers Facemask and hair net Hood Bunny suit Boots Gloves Goggles © 2013 The Pennsylvania State University Air Shower http://www.clearsphere.ie/products-equipment-accessories.htm#3 http://encyclopedia2.thefreedictionary.com/clean+room © 2013 The Pennsylvania State University Total Cleanroom Strategy • This strategy employs an open fabrication/synthesis area • Air filtering is accomplished by HEPA filters in the ceiling with returns in the floor, to give a continuous flow of clean air • The continuous flow of clean air allows for a faster recovery, which is the amount of time it takes for the filters to return the area to an acceptable condition after a disturbance • A class 1 facility turns over air every 6 seconds! © 2013 The Pennsylvania State University A Cleanroom Van Aznt, Peter. Microchip Fabrication 4th Edition. McGraw Hill. New York. 2007 © 2013 The Pennsylvania State University The Modern Cleanroom • The traditional cleanroom layout is the ballroom design, where individual process tunnels open into a central hallway • Every cleanroom is a trade-off between cleanliness and cost, but all are built from a primary design – – – – A sealed room that is supplied with clean air Building materials that are non-contaminating Systems to prevent accidental contamination Vibration control, for sensitive equipment © 2013 The Pennsylvania State University Cleanroom Elements Cleanrooms utilize a series of techniques to keep contamination from adversely affecting the fabrication/synthesis process: – – – – Adhesive floor mats Static control Gowning Area Double-door pass-throughs – – – – – Air pressure Shoe cleaners Air showers Glove cleaners Service bays © 2013 The Pennsylvania State University The Mini-environment Approach • Rising cleanroom costs with diminishing returns on effectiveness have resulted in another concept of isolating materials in as small an environment as possible • The problem of how to string together a number of mini-environments, such that a product is never exposed to room air is solved by transporting the samples in a clean environment • One example of the industrial application of this approach is Hewlett-Packard’s Standard Mechanical Interface (SMIF) © 2013 The Pennsylvania State University The SMIF System • SMIF systems have three main parts: – The pod, or box ,for transportation of materials – The isolated mini-environment at the next process station – A mechanism for extracting and unloading materials at each successive processing station © 2013 The Pennsylvania State University The SMIF System Isolated pod w/ vacuum or inert atmosphere Load lock Robotic loading arm Internal seal to main chamber Wafers in a cassette Process Chambers Standard Mechanical Interface (SMIF) Public Domain: Image Generated by CNEU Staff for free use © 2013 The Pennsylvania State University The SMIF System • SMIFs have the advantage of: – Better temperature and humidity control – Reduced yield losses due to contamination • However, pods can be too heavy and expensive • Robots can be used to handle SMIF boxes, which drives up cost and complexity © 2013 The Pennsylvania State University Unit 2 Infrastructure Lecture 2 Facilities © 2013 The Pennsylvania State University SUMMARY Facilities • Introduction • Facilities − Why do we need special facilities ? − Types * Clean work stations * Tunnel/Bay structures * Cleanrooms * Mini-environments © 2013 The Pennsylvania State University
