New devices, materials compound ESH concerns for chip industry

If you're not quite sure what a compound semiconductor is, don't feel too bad. You're not alone, as Brett Davis discovered when he began organizing a technical session for next month's Semiconductor Safety Association (SSA) symposium on the ESH challenges of making the devices.

Davis, a principal staff engineer in the environmental, health, and safety department at Motorola Semiconductor Products Sector, remembers the reaction to his call for papers after SSA responded enthusiastically to his proposal. "Just to give you an idea of how much learning [about the devices] is going on, I immediately received about a half dozen phone calls from people asking, 'What the heck is a compound semiconductor?'"

Davis's experience is an extreme example of an industry adjusting to the introduction of new materials, new device structures, and new processes. Mike Zimmerman, a member of SSA's board of directors and symposium cochairman, wanted to see the ESH aspects of those issues addressed in this year's event, scheduled for April 11–13 in New Orleans. The symposium's three tracks cover "boot camp" basics, safety and industrial hygiene, and environmental issues, and Zimmerman says he challenged the cochairs of the tracks to "go look at some of the leading-edge technology issues" when recruiting papers for this year's conference. "I wanted to open it up as ESH professionals so we can see how we fit into the big picture."

Some of these issues include 157-nm lithography, interconnect technology, low- and high-k dielectric materials, and copper processes as well as compound semiconductors, says Zimmerman, a former ESH operations manager for TI who now oversees the chipmaker's account at International Sematech.

Zimmerman says he asked himself the question, "As an ESH professional how can we support the industry?" In terms of 157-nm lithography, "we're dealing with new equipment designs. We want to make sure we have the safety and health people and the environmental people in the early design phase to make sure we minimize the amount of energy consumption, minimize emissions, and make sure the equipment complies with SEMI Standard S2 or CE marking standards. We want to minimize operator exposure to the laser system or whatever ends up being the heart of what makes 157-nm lithography successful."

The concerns don't stop there, though. "Then you get into the photomask and chemical issues," Zimmerman points out. "You've got a whole new set of chemical properties [to deal with]. We want to make sure the health and environmental people are looking at the health risk to workers; how we manage that so that we bring in the chemicals that do the job with minimal risk to the workers." Additional ESH concerns include waste disposal.

Zimmerman emphasizes what must be an axiom for experts in his field: "It's much easier for an ESH professional to fix problems in the conceptual and design phase than when [a tool or process] is already in the factory."

That principle assumes extra importance in any discussion of compound semiconductors, notes Zimmerman, particularly because of the prevalent use of gallium arsenide (GaAs) wafers in the manufacturing process. "Right now it seems there are a handful of companies really dealing with it. My understanding is that in the past [gallium arsenide] applied mainly to government and military applications. To be honest with you, when I worked at TI I didn't see much of that. I know that Brett [Davis] is very passionate about it."

Davis's involvement with the new devices came about after a Motorola compound semiconductor fab in Tempe, AZ, called him to consult. The GaAs facility needed help managing the hazards of working with highly toxic materials, but Davis soon realized his extensive ESH background had done little to prepare him for what he found at the plant. "They're kind of on an island," he notes.

Davis drew on his network of contacts at Motorola, International Sematech, SEMI, SIA, and SSA. The notoriously competitive industry is "pretty comfortable sharing ESH practices," he points out, adding wryly, "and all are aware that by using best practices we have a fighting chance to stay out of the news." He discovered, however, that expert ESH knowledge in the compound semiconductor area, and specifically in GaAs processes, is limited because production is so small and isolated.

Manufacturing "tends to be in little factories," Davis says. "There were solutions I thought were state of the art and some I thought were back of the envelope. Those people I did contact didn't have contacts themselves within the industry. I'm kind of a team guy, so I said to myself, 'Let's see if we can build something here,' and it looked like the best avenue to take was SSA," he recalls. He found a sympathetic audience when he suggested the session. "I was preaching to the choir. They were looking for a reason to hold a session that kind of crosses the environmental and safety areas. They jumped at the opportunity."

Davis hopes that the session at the SSA symposium is a first step toward a much better understanding of the environmental and safety issues raised by growing production of compound semiconductors. "There are some significant challenges in the safety and environmental arena that are unique to compound semiconductors, particularly to those using arsine."

Steve Van Tassell, safety and security manager for Conexant Systems in Newport Beach, CA, points out that more GaAs fabs have come on-line in the last few years because of the proliferation of cellular phones, personal digital assistants, and related wireless communications products.

"Arsenide is probably the biggest issue," says Van Tassel, who is cochair of the symposium's safety and industrial hygiene track. He notes that the "more traditional" CMOS processes use arsenic as a dopant, for example. He calls the element's use in these individual processes "pretty well managed and very mature. But in GaAs processing, your actual wafer is essentially half arsenic. This raises a lot of different concerns in etch and CMP. And if you're doing backside grinding, GaAs wafers tend to be brittle." Metallorganic CVD processes are closely related to GaAs as is molecular beam epitaxy, he adds.

Indeed, backgrinding is just one area of concern, Davis agrees. Backgrinding of a GaAs substrate can cause particulates to put dissolved arsenic into a fab's wastewater, the Motorola ESH expert points out. Around the beginning of the year EPA published a new regulation reducing the amount of arsenic permitted in drinking water to 10 µg/L.

Publicly owned treatment works generally copy the drinking water standard in determining the allowable amount of arsenic in the public's supply of potable water, Davis stresses. "That's going to be a real problem," he says. "Somewhere around 20 µg/L it really starts getting hard. It'll require much more attention and more cost."

Other challenges loom. Fab processes using large quantities of both arsine and phosphine gases raise "delivery and handling safety issues, storage issues, fire code requirements that you be able to treat for catastrophic releases. That's not so easy when you're talking about highly flammable toxic materials," Davis says.

Further problems arise "when you start talking about exhaust gases and their treatment," he continues. Metallorganics using hydrogen as a carrier gas lead to "an exhaust stream that is possibly pyrophoric and certainly toxic. How do you treat for that before you release it to the environment? It's certainly a more complicated situation than silicon oxide processing."

Other new concerns that the symposium will address include ergonomics and the long-term health effects of materials handling, notes Van Tassell. A new federal ergonomics standard in the United States draws attention to the semiconductor industry's transition to 300-mm wafer processing and related issues, he points out. "There are tremendous human factors issues that that introduces." The use of reticle pods and the role of the people in an automated fab are also on the industry's radar.

In terms of materials and health effects, two presentations in the safety and industrial hygiene track are "on the fringe of the sort of concern you see in the more popular press," Van Tassell says. One paper set for the afternoon April 11 session on advances in industrial hygiene concerns teratogenicity of DUV photoresist. Teratology is the study of malformations or serious deviations from the normal type in organisms.

SSA members have had a hand in several successes in the ESH area, Zimmerman asserts. He notes the "significant impact" the organization has made in equipment design with the implementation of SEMI's S2 standard. "A lot of discussion that happened through SSA helped to make that into a standard, and even at SSA there are still discussions on how to implement it to make it successful."

As noted by Davis, a key reason for the successes has been the free flow of information in the industry among experts from different companies. Reduction in PFC emissions began with "a lot of initial research work at SSA," which has developed as "a fairly close group working together over the years," says the organization's president.

This working relationship has yet to solve a problem in at least one area, Zimmerman acknowledges. "The one area that we continually need to work on is integration, where ESH has to be an element and integrated into a process involving not just environmental, safety, and health professionals but process people and equipment designers as well."

Davis expects a lively exchange when he moderates the session on compound semiconductors. He and SSA have also organized a lunchtime roundtable discussion in order to encourage a greater flow of information on the topic and, perhaps, demystify it. Defining a compound semiconductor should be high on the list of topics. "I'm sure somebody will say, 'No, it's the 3-5 metals and all the various combinations of those.' And somebody else will say, 'Oh yeah? Have you ever tried to deal with indium?'"

More information on the SSA's annual symposium can be found at http://www. semiconductorsafety.org.