Particles: keeping the killer out; firms plan class 1 offensive against fine particles

Electronic News, June 8, 1992 by Jeff Dorsch

Firms Plan Class I (Costly) Offensive Against Fine Particles

The "killer particle" has probably been floating around in your fab for years. Semiconductor manufacturers and their vendors of equipment and materials have been striving for years to make conditions in wafer fabrication plants as clean as possible. Despite their best efforts, fine particles left over from construction years ago or from other sources may not be intercepted by older air filters, particles which could do in a 16-megabit dynamic random access memory (DRAM) or an advanced microprocessor.

In the submicron era of device manufacturing, smaller and smaller particles can do damage. Many companies are looking to establish class 1 conditions wherever wafers are stored or moved, which can be an expensive proposition. "When you start to jump to class 1 and submicron, the (construction) cost jumps up, and it's not linear," noted Richard Shepherd, who recently served as special projects manager for Du Pont Photomasks during that company's construction of a class 1 clean room for pellicle manufacturing in Danbury, Conn.

As critical as fab construction is becoming in preventing particulate contamination, even more important are the interiors of fabrication equipment, "where wafers spend most of their life," observed Michele Klein, general manager and vice president of marketing for High Yield Technology Inc., a supplier of in-situ particle monitoring equipment in Sunnyvale, Calif. Water vapor is process chambers is a common problem.

"We have a very conscious effort to drive particle levels down," said Karl Heiman, product marketing manager for polysilicon etching at Lam Research Corp., Fremont, Calif. "We have a lot of engineers dedicated to doing this." One factor Lam has found is that turbulence can be created if a loadlock is not completely at atmosphere when opened, he noted.

Frank Shinneman, vice president of sales and marketing for Materials Research Corp., Orangeburg, N.Y., said "We have had people assigned to a particle reduction team. We excessively eliminate sources of particles in the equipment." Edward Erny, MRC's director of marketing for thin-film process equipment, said the company has taken a number of measures to reduce potential sources of micro-contamination, including eliminating or minimizing any moving part that could create particles, eliminating the need to handle wafers in a vacuum and eliminating the need to remove the wafer clip ring or clamps.

"The sputtering target itself can be a source of (contaminating) materials," Mr. Shinneman said. "Titanium tungsten has a very high film stress. The target is made by the compression of powders; you can't melt titanium and tungsten at the same time. That can affect the number of particles."

Ms. Klein of High Yield Technology credited Sematech for getting device makers to understand the economic value of in-situ particle monitoring as part of a cost-of-ownership model. "The economic perspective they took was very helpful," she said. "It planted a seed. They got a big company like Intel and a little company like HYT to talk." She claimed "Almost every major U.S. semiconductor manufacturer is a significant user" of in-situ particle monitoring now, along with a number of semiconductor equipment vendors.

HYT has signed Eaton to an original equipment manufacturer (OEM) deal for its high-current ion implanters, and is looking to establish OEM relationships with other equipment vendors, Ms. Klein said.

As wafers are transported around a fab line, they are subject to atmospheric contamination. One answer is the standard mechanical interface (SMIF) approach developed by Hewlett-Packard and commercialized by Asyst Technologies Inc., Milpitas, Calif., which involves the use of enclosures, sealed "boxes," around wafer cassettes as they are moved from one piece of equipment to another, maintaining class 1 conditions around the wafers at all times.

Anthony C. Bonora, Asyst's senior vice president of engineering and technology, sees two kinds of customers for the SMIF technology: the advanced fabs using 200mm wafers and working with device dimensions of a half-micron or less, and the volume producers with 150mm fab lines who need "greater flexibility."

SMIF is gaining wider acceptance because it "provides isolation (from contaminants) and is a gateway to automation," he added.

Susan P. Billat, president of Benchmark Strategies, a consulting firm in Palo Alto, Calif., sees an adherence to "ultraclean" semiconductor manufacturing starting to make a difference in both competition and profits. "Ultraclean leaders" in the industry include Texas Instruments, Micron Technology, Cypress Semiconductor and Motorola, she said.

"A lot of these ultraclean manufacturing programs are paying off," Ms. Billat commented. "Ultraclean manufacturing does pay for itself, many times over. But even with ultraclean, the 'crashes' still come along."

SMIF technology "chugs along" in industry accpetance, according to Ms. Billat. "Taiwan Semiconductor Manufacturing Co. seems very vocal in their pleasure." She also sees "a pent-up demand for in-situ (particle) monitoring. More and more will be clustered onto individual tools."