Evaluating Gas/Gas Handling Suppliers
Choosing the right gas and/or gas handling supplier can save a fab money, time and gas delivery headaches.
By LISA A. COLEMAN
Since gases are one of the few things that come into contact with the wafer surface, understanding how they are delivered, maintained and how the equipment is serviced is critical to semiconductor manufacturers. Some fabs need hundreds of gases for wafer manufacturing, while others only need a handful of bulk and specialty gases. Depending on what your facility produces will determine the kind of gas and/or gas handling service you need.
When picking a gas supplier, semiconductor fab managers list the following as some of the important criteria: company experience, reliability record, cost, safety record, whether or not they provide on-site management and purification for bulk gases. In addition, if a gas company also provides the gas delivery system for your plant, you may need to evaluate even more criteria such as what materials are used to manufacture components.
The partnering option
Fabs go through a lengthy gas vendor selection. Some fabs choose to receive regular gas deliveries via trucks and they are responsible for the gas handling into the fab (depending on what the fab is manufacturing), while others hire on-site management. Obviously, if your firm has been successfully using a particular gas supplier in one of its other fabs, chances are this same company will be a good choice for your new facility. For example, at Motorola`s MOS-12 die manufacturing fab (Chandler, AZ), an on-site gas manager has run the fab`s gas operations–both bulk and specialty gases–incident-free in the three years since the plant has been on-line. The big advantage to having on-site gas management is, “the people are definitely experts not only in gases but in gas handling,” says Jeff Martin, facility support manager for MOS-12. “So that allows us to let our experts focus on the semiconductor manufacturing process.”
Martin`s advice for any companystarting from the drawing board to find a gas company is to benchmark gas companies against each other. Take note of the company`s capabilities at procuring the gases your company needs, make sure it has an adequate engineering staff or R&D group that can test gases, and check out its components for gas handling and the purification system. Says Martin, “See if they can provide on-site gas management services. Also, they need to have consultants available that can help in the design and construction of the facility. And, of course, they have to be cost competitive.”
Martin is an advocate of the “build clean” philosophy, that is, gas suppliers who have gas handling capabilities should be manufacturing their gas handling equipment in cleanrooms. “Today`s technology requires that,” he says. His gas company made the investment to build a cleanroom and use analytical equipment in their cleanroom to monitor the fabrication and welding process. “You build it clean, it comes on-line much faster. It saves us a lot of time to get a process up and running and get the product out the door.”
Because MOS-12 has on-site management, there are a number of purification systems onsite, too. Bulk gases, such as argon, nitrogen and oxygen are purified on-site. The large purification systems were installed and operated by their gas manager. Most of the newer semiconductor fabs that are manufacturing at a submicron level do need large purification systems for the bulk gases to reach the necessary purity levels of below 1 ppb.
Not all fabs are manufacturing silicon at submicron levels; the gallium-arsenide fab at Raytheon (Andover, MA) is at 3 microns although its gate levels are submicron. Raytheon`s gas needs are quite different than Motorola`s. Although Raytheon doesn`t need ppt gas, it does benefit from the decreased particle counts. “The pressures that the memory fabs put on the gas suppliers to reduce defect densities allow us to receive the benefits of their hard work,” says Jerry Gedaly, engineering manager in Raytheon`s GaAs fab. “Since we`re not necessarily driving the technology, we look for somebody that can give us technical support and make us cognizant of some of the improvements that they offer that we may only have read about,” he adds.
In choosing its gas suppliers, IBM Microelectronics (Essex Junction, VT) uses a competitive evaluation rating technical expertise, quality, service and supply capacity. But, most importantly it looks for a gas supplier`s willingness to work on total cost management. “How willing is the gas company to work with its customers on their manufacturing costs from start to finish,” says Robert M. Halverson, advisory engineer in IBM Microelectronics Materials Science Lab.
Doing in-depth analysis of the supplier is worth the effort, says Halverson. “It`s worth making the supplier visits, going out to manufacturing facilities and viewing processes and looking at SQC [Statistical Quality Control] data and talking to customer references,” says Halverson. “Our advice is to look to the experts and do a competitive evaluation whenever possible as opposed to going with one source.”
Texas Instruments is also an advocate of third-party gas management. Says Larry Dilda, chemical coordinator at Texas Instruments Chemical Operations Division (Dallas, TX), “In a perfect world, point of use (gas handling) would be sufficient. But, you need a third party to operate your chemicals and gases to be able to respond to new developments and every day events that would take your time away from the job of making more and better chips.” Like other fabs, TI looks for a gas company that has a proven ability to respond effectively to its needs and a comprehensive quality assurance program to ensure the purity and consistency of the fab`s requirements.
TI ranks its possible gas vendors by product quality, certification, safety, service,availability, material SQC, and continuous quality improvement, says Dilda. “Also, ask for data from the company and compare it to others. But, remember, the cheapest or the most expensive is not always the best. You have to consider your needs now and in the future. Do not pick a supplier and think you are going to change them,” he says.
Can they deliver?
Delivery is an important issue with many fabs, for example, Raytheon receives nitrogen deliveries every second day. Because there is no nitrogen pipeline in its area, Raytheon wanted to find a gas supplier that was super-reliable and could meet its constant gas needs. Reliability also means delivering in winter weather conditions. Raytheon`s Gedaly says his gas supplier fills the nitrogen tank even in the worst weather, such as the recent blizzard. Gedaly also likes to make sure a gas supplier will be able to provide technical help for other severe weather conditions such as frigid temperatures that require adding evaporators to the tank to keep it from freezing over.
Because Raytheon has such frequent deliveries it does check several delivery details. Gedaly recommends asking the following questions of your gas vendor:
1. How is the delivery truck cleaned?
2. How is the truck purged and what cleaning solutions are used that can actually be removed from the truck?
3. What capabilities do they have of cleaning big distribution tanks and how are those cleaning chemicals removed without a trace?
Nitrogen pipelines
Of course, in many parts of the country snow and ice are not an issue and delivery of bulk process gases comes via pipeline. Over 35 miles of pipeline lie beneath Santa Clara and San Jose, CA, while 25 miles of pipeline lie underneath Arizona to bring nitrogen to businesses that need it. Air Products and Chemicals, Inc. (Allentown, PA) owns and operates both pipelines as well as one in Korea. Because there are several semiconductor fabs clustered in these areas, the pipeline delivers nitrogen to most of them and Air Products manages the delivery.
In Santa Clara and San Jose, over 60 customers use the pipeline. To ensure that there are no problems on the line, an Air Products technician drives the pipeline every day checking for disturbances or digging. Each customer site is checked.
Air Products does have a system of services called Megasys, which they also call “on-site service” where it manages the customer`s gas use, pipeline usage, on-site purifiers and specialty gases and equipment. In addition, Praxair (Danbury, CT) has a smaller pipeline in California and most recently it has just formed a joint venture with Shanghai Meishan Group Corp. Ltd. in the People`s Republic of China. Under the terms of the agreement, Praxair will own 70 percent of the joint venture company and Shanghai Meishan will own 30 percent. The joint venture will build a 550 tons-per-day air separation plant to supply oxygen, nitrogen and argon by pipeline to Shanghai Meishan Metallurgical Corp. The plant will also supply liquid oxygen, nitrogen and argon to the glass, metals, chemicals, electronics and other industries in the Nanjing region.
Specialty gases
“Although existing technology is sufficient to provide efficient and economical bulk gas delivery,” says Dr. Sowmya Krishnan, manager of technology and applications development at Ultra Clean Technology (Menlo Park, CA), “it falls short in the case of specialty gases.” Ultra Clean Technology is a manufacturer of optimally designed high-quality gas delivery systems for the semiconductor industry. According to Krishnan, specialty gases remain “the major contributor of contamination to semiconductor processes because of their tendency to react with the surfaces they contact as well as with atmospheric impurities.” Because specialty gas delivery systems are beset with problems–decreased component lifetimes, increases in maintenance requirements and system downtime–processing costs for the semiconductor manufacturer increase, notes Krishnan.
Obviously, these are major considerations for evaluating a gas supplier. Raytheon`s Gedaly suggests looking at safety issues as well as the cylinder materials and gas purity. First, what type of emergency response can the gas supplier provide if, for example, there`s a leaky cylinder. “We feel that if they are going to sell toxics and corrosives, they need to have set up contingency training to deal with those situations,” says Gedaly.
In addition, Raytheon looks at the type of cylinder design being used, the type of material the cylinder is made of, how the cylinder is cleaned, how it is valved, and whether or not the cylinder valve can be purged. “So far we haven`t been able to find anyone that makes a cylinder valve that you can purge,” says Gedaly.
Texas Instruments looks for equipment that is leak-proof and non-contaminating including heat tracing tubing lines between the gas bottle and the fab to prevent condensation in the line. Or, double wall tubing can be used for pyrophoric gases to keep employees and the plant protected. IBM Microelectronics, considers gas handling equipment to be a main source of contamination.
Bruce Technologies International (BTI; North Billerica, MA), a supplier of vertical reactors, horizontal furnaces and state-of-the-art process management software systems is a user of bulk and specialty gases. Two things that Michael Schroth, manager of BTI`s process technology group, looks for are the specialty gas purity at the cylinder and the integrity of the gas at the point of use. “I want the quality of the gas to be better or at least equivalent when entering the process chamber,” he says.
While BTI is a “user” of gas supplies in its Class 10 Process Technology Lab, it is primarily a supplier of semiconductor process equipment. BTI manufactures vertical reactors and horizontal furnaces–which can process as many as 300 wafers at one time. During the chip making process, wafers are repeatedly transported in and out of furnaces that use gases and to deposit films onto each wafer. Different gas recipes for each manufacturing process step are compiled. Each furnace contains software controls, automation and gas delivery cabinets. The BTI furnaces use its APEX process management software to manage the manufacturing process and the equipment, performance history database. The system monitors equipment, allows recipe editing, and provides details on gas flows, pressure and flat zones. This is also one way BTI handles the question of safety at the process equipment level.
Contamination-free gas delivery
Besides software and other monitoring measures to ensure contamination-free gas delivery, there are four issues that users must evaluate: 1) base material selection; 2) component selection; 3) gas panel design; and 4) delivery system manufacturing techniques.1 These are factors that must be confronted for ultra clean gas delivery because as device densities and complexity increase, contamination-free gases will be even more of a necessity. n
References
1. Kobayashi, H. “How Gas Panels Affect Contamination,” p. 81-86. Semiconductor International, Sept. 1994.
2. Krishnan, Sowmya. “Specialty Gas Delivery Requires Our Attention,” p. S3, Gas Handling and Delivery Supplement to CleanRooms magazine, Oct. 1995.
 |
Bulk gas supply systems like BOC Gases` tube trailer provide specialty gases such as silane, arsine, diburane and phosphine, eliminating cylinders and changeouts and ensuring consistent purity from pad to site.
 |
 |
Praxair illustrates the different methods of gas delivery to a semiconductor fab. From the left, for example, an on-site nitrogen plant draws in atmospheric gases to produce nitrogen, or bulk delivery of gas is made via trucks. From the right, specialty gases arrive in cylinders or tube trailers prior to entering either the gas cabinet or the ultrahigh purity delivery system. From the lower right, recycling systems recycle exhaust from semiconductor process tools.
 |
A view of the subfab at Motorola`s MOS 12 wafer fabrication facility. A gas handling system is being installed.
 |
Air Products and Chemicals, Inc. has developed the world`s largest nitrogen purifier for use in several electronics applications. The system can purify over 400,000 standard-ft3/hour of nitrogen while maintaining impurity levels of less than 1 ppb of moisture.
 |
An Apogee vertical process reactor installed at Bruce Technologies International. The reactor sits in a Class 10 process technology lab. The reactor is used for batch thermal process of 150- and 200-mm wafers. Users have precise control on gas flow among other things.