While progressive chip makers were installing bulk delivery systems of specialty gases in the late 1990s, the real boom is happening now
By Chris Anderson
In today’s atch-every-penny world of semiconductor fab construction, is it any wonder that bulk specialty gas distribution systems are replacing multiple gas cabinets as the workhorse of gas delivery?
Built to feed the ever increasing gas appetite of the 300-mm wafer process, bulk delivery has other benefits, such as lower cost of ownership, lower raw materials costs, as well as increased worker safety and purity due to fewer cylinder changeouts.
“It is difficult to come up with a raw number of what the savings are for companies who use bulk supply for specialty gases, since each situation is different,” says Kevin Albaugh, director of research and development for Tonawanda, N.Y.-based Praxair Electronics. “But in applications where the demand is there, it is safe to say they will see tens of percentage cost reduction.”
But this is not the only development on the gas distribution front. Companies looking to add value as suppliers are bringing more robust diagnostic tools to market to not only monitor but intelligently control gas distribution within the fab.
The use of fluorine in the chemical vapor deposition (CVD) process is spiking and, for some manufacturers, the volume of fluorine gases used for chamber cleaning has gas suppliers scrambling to develop and bring on-site fluorine generators to market. In addition, these same distributors are heavily researching and testing what could become the next ìhotî gas: Supercritical CO2. This compoundís low surface tension could make it a key compound at the 65-micron (µm) or 45-µm nodes in the near future.
Moving the gas
While some companies were installing bulk delivery systems of specialty gases in the late 1990s, the real boom is happening now. Tools at newer fabs are larger to accommodate the larger wafers, and the result is these tools require more gas, and at higher pressures to function properly.
Bulk specialty gas delivery provides the new generation of chip producers the best of both worlds—a high volume of gas delivered to multiple tools from a single source, with resultant lower costs of both the capital equipment for the gas delivery system and of volume pricing on the raw materials.
For the largest of the new fabs, the decision to switch from gas cabinets as a means of gas supply and distribution is often a no-brainer. This, however, is not so easy for smaller semiconductor manufacturers. “I'd say that a good rule of thumb is that up to about 50 standard liters a minute is as far as a gas cabinet is efficient,” says Mike Marmaro, global product manager for special gases and equipment for BOC Edwards (Wilmington, Mass). “Anything above that and you need to either add multiple gas cabinets or a special bulk gas system.”
If indicated by need, the bulk systems replace multiple gas cabinets and, as Marmaro points out, one bulk system that replaces six gas cabinets is not six times as expensive. “Plus, there is the ongoing economic benefit of price of the product itself, which is less expensive the higher the volume purchased,” he says.
But these benefits donít mean that existing fabs are necessarily going to switch over from their current gas delivery methods. “Customers will change to the 300-mm fab whenever they have reached a point that it is cheaper for them to be making the 300-mm wafers than it is to continue making the 8-inch wafers,” says Isabelle Lauzon, sales and marketing director for Air Liquide Electronics U.S. (Dallas). “It is when companies are building a new fab that they are going to take advantage of the opportunity for the newest processes, and that is why we are seeing more and more bulk distribution systems for gases and chemicals.”
The backroom inner workings of an Air Liquide bulk delivery system.
Another benefit of bulk gas systems is the greatly decreased need to change out cylinders. The benefits are two-fold. First, the fewer connections and re-connections made, the lower the likelihood the process gases will become contaminated—an issue that can directly affect yield. Second, less frequent change-outs greatly reduce the potential that employees will be exposed to these often hazardous materials.
Still, even with these benefits there are challenges and safeguards needed with bulk specialty gas distribution systems. The switch from a gas cabinet supplying a single tool to the bulk systems that supply multiple tools mean systems reliability is more important than ever.
“The days of one gas cabinet, one tool are gone,” says Bill Tucker, technical manager for BOC Edwardsí Huntsville, Ala., office. “What we are seeing are more customers who want equipment to provide redundancy, so if they lose a particular source, they maintain process safely,” he says. “We have at least half a dozen redundancy systems that we offer, but they are very specific to our customers and they want them because they donít want any tool to stop for any circumstance.”
While tool downtime has always been a focus, the newer gas delivery systems are causing some suppliers in the industry to beef up their on-site gas handling services to manage logistics as well as head off potential problems. In the past year, for example, Air Liquide introduced a service product offering called FabGenius. Not only is the system collecting data, but itís learning what is normal for the operation of that particular system and what isn't. “Its purpose is to differentiate between real alarms and false alarms or to know what constitutes a problem that will evolve and get worse,” says Lauzon. “Sometimes, monitoring systems will send an alarm based on a deviation. FabGenius will be able to determine which are normal deviations and which ones need attention. This will cause fewer alarms and can even help alert [managers] about evolving problems that will need attention.”
As Lauzon points out, the control room, where data is received about the gas distribution systems, are often static areas of data collection. Data is routed to the control room and alarms sound at predetermined thresholds. “Normally, customers will have some kind of centralized monitoring system where some of the key parameters of the distribution center in their fab are being sent back to the control room,” Lauzon says. “But that is just monitoring-the system is monitoring and has an alarm but it doesn't think. It just beeps when there is something going wrong.”
With FabGenius, Air Liquide says it's taking the next step.
On-site generation evolution
On-site generation units are the ultimate in high-use equipment to supply gas needs. Nitrogen-generating plants have been commonplace for years at many semiconductor makers.
But today, as cost-consciousness pervades the industry, and new gases and chemicals are adopted by semiconductor manufacturers, the movement is toward producing next-generation systems. When it comes to traditional on-site gas generators, Marmaro says the push from BOC Edwards over the years has been to increase the energy efficiency of its units to keep them attractive to customers. “Reducing the kilowatt hours needed to produce each ton of gas can produce significant savings over the life of the unit and we continue to work to make the most energy-efficient generation plants we can,” he says.
Today, specialty gases are also getting attention for on-site generation plants. Fluorine, in particular, is getting the attention of gas companies that are looking to provide an alternative to supplying customers who are increasingly using nitrogen tri-fluoride (NF3) in their manufacturing processes.
BOC Edwards has developed large-scale on-site fluorine-generating products, such as this F400, geared to both high- and lower-volume users.
“People have been looking for new chamber cleaning gases because they are trying to get gases that have lower global warming potential, and get better efficiencies and utilization rates,” says Nancy Irwin, commercial manager, fluorine, for BOC Edwards. “These days, NF3 is becoming the chamber cleaning gas of choice for many companies.”
This spike in the use of NF3, combined with the need for greater volumes of gas in new fabs, has gas suppliers working to develop fluorine generation units as an alternative to NF3. “It is basically the fluorine that is doing the work within the chamber,” says Irwin. “You don't need the nitrogen, but if manufacturers wanted to use just fluorine the only way to get it was in cylinders—and that was not a very attractive option because of cost, safety and handling concerns.”
Both BOC Edwards and Air Liquide are investing heavily in R&D activities for bringing large-scale fluorine generation units to the market. “We have really cranked up the process in the past year and a half,” says Lauzon. “Now we have some of our generators approved by process tool makers, and we are in the process of setting up beta sites.”
BOC Edwards already has developed two fluorine generation products geared to both high- and lower-volume users. For now, though, itís not the semiconductor market leading the way. “We are finding that the liquid crystal display, flat panel display market is ahead of the semiconductor market in its interest level of on-site fluorine,” says Irwin. “But that's because those processes will use as much as three to four times the amount of fluorine as a semiconductor fab would use.”
A supercritical future?
As suppliers bring new products to market to meet the needs of the development cycle, the R&D divisions are peering years into the future to be ready for the next technological process leap. One compound receiving intense scrutiny is supercritical CO2.
In its supercritical state, CO2 has a number of desirable characteristics that could make it an effective solvent for the cleaning of post-etch residue, low-k material drying and copper removal. Its combination of high density, low viscosity and low surface tension have some targeting it for use in wafer processing below 65 nanometers (nm).
“With supercritical CO2, you can tailor its solvent properties to mimic a lot of the conventional materials,” says Praxair's Albaugh. “But you don't have the surface tensions forces, so you can flow it into very small openings. That technology is probably a couple of years out from a broad acceptance in the marketplace, but it is definitely something we are working on, and we have demonstration systems running in the field today.”
While Air Liquide is also investing in supercritical CO2, Lauzon thinks adoption may be a bit farther in the future. ìMost people were saying that they would need supercritical CO2 at the 65 (nm) node,” she says. “But now, many are saying that they wonít need it until 45. This is because there is such pressure on cost, these plans were supposed to change to have a different process at the next node; instead, they are really trying to make the existing process work at the smaller nodes in order to avoid costs.”
While more process compounds and chemicals may be used in the liquid phase, Albaugh says the state of the products of the future is a moot point. “I think the customers are always looking for new molecules to improve their performance or reduce the cost of their devices,” he says. “Some of the molecules will end up being gases, but I donít think the customers really care what the phase is. What they really care about is the performance.”
CHRIS ANDERSON is a special correspondent for CleanRooms. He can be contacted at [email protected]