Harris Semiconductor`s Fab 8 takes innovative approach to cleanrooms
The world`s first 8-in. power semiconductor facility maintains a Class 1 environment aided by SMIF technology.
By Susan English-Seaton
Harris Semiconductor (Mountaintop, PA) announced in January the opening of its newly constructed 8-in. power MOS wafer fabrication facility, touted as the world`s first 8-in. power semiconductor facility. By combining a Class 1,000 ballroom environment with Class 1 and sub-Class 1 SMIF integration, Fab 8 can maintain a Class 1 environment during manufacturing operations, tool installations and service — anticipating manufacturing technology requirements for the next several years.
Prompted by a 40 percent CAGR from 1994 to 1997, the expansion is expected to more than double Harris` power MOS product output — the company was the first manufacturer of logic level output metal-oxide semiconductor field effect transistors (MOSFETS) and insulated gate bipolar transistors (IGBTs). In the next 12 to 18 months, 200 new products are projected to go into Fab 8. The 150,000-sq. ft. fab offers an 8-in. discrete power pipeline with onsite capabilities encompassing all phases from design through delivery.
Adjacent to Harris` present facility on the 84-acre tract that houses its 4-in., 5-in. and 6-in. wafer fabs, Phase One of the new ISO 9002-certified facility was completed at a cost of approximately $140 million out of a total project cost of $250 million. Additional tooling will be segued into the remaining phases. The second phase is scheduled for January 1998; the third phase will be completed by mid-1999. Symmes, Maini and McKee (Cambridge, MA) and Marshall Contractors (Providence, RI) were retained to do the design/build. The cleanroom clean support area is located in a 104,000-sq. ft. building. The 24,500-sq. ft. cleanroom features Class 1 ULPA-filtered laminar flow minienvironments for tools with submicron feature size capability.
Project Raptor ramps up
With a timetable that included ramp to 90 percent capacity in four months and 100 percent of product qualifications completed in the first six months, “Project Raptor” — named after the speedy, voracious Velociraptor which appeared in the Steven Spielberg movie “Jurassic Park” — lived up to its name. Fab 8 was up and running in a record 13 months. But that cinematic horror paled in comparison to the obstacles presented by the weather — the heaviest snowfall in 100 years. Says Bill Burrell, 8-in. wafer fab project leader-engineering: “It was December 6 when we started working on the parking lot outside. Then we got hit with the `winter from hell.` We spent more time plowing snow than shoveling dirt. But we continued and got the footers in place. The first piece of steel was raised the first week of February 1996.”
Because speed and innovation were key to the project, tasks were started simultaneously. Even as the outer shell was being built, construction on the inner cleanroom had begun. SMIF technology, which kept the wafers protected in a Class 1 environment, enabled tools to be changed and set up without stopping the manufacturing process. Parts were completed so tools could be installed in the sequence they were needed to make the first wafers go through the line.
Harris` Semiconductor Products Division manufactures a range of standard analog, logic and discrete power semiconductors, as well as military and aerospace, automotive and telecom-specific semiconductors. Puneet Saxena, lead engineer/ manufacturing analyst at Harris` Semiconductor Products Division, says: “For us, this was a new and very different project. We had had no prior experience with 8-in. wafers. In fact, this is the world`s first 8-in. power MOSFET fab, so nobody had any prior experience with 8-in. wafers or the equipment that went with it–like the SMIF, for instance. There were a lot of technological firsts for us. Right from the beginning, I think we challenged all the assumptions that go into constructing a building of this magnitude. We tried to figure out how we could make things go faster using a “whatever it takes” kind of philosophy. The industry standard for projects similar to this is in the neighborhood of 28 to 36 months. We had first silicon out in 13 months starting from scratch.”
A common sense approach to tooling
“There are two kinds of companies,” says Harris` Burrell, `the quick and the dead!` Our motto has been and remains `Whatever it takes.` We`ve broken a lot of paradigms during this construction. We`ve done things with a common sense approach: Put the tools in the sequence you use them. Don`t put in 20 diffusion furnaces, one right after the other, `cause you only need one to do the first diffusion!”
David Hollock, 8-in. wafer fab project leader-manufacturing, agrees: “The SMIF environment allows you to be that flexible. You can be running a tool and be running product and installing another tool right next to that tool because of the way the isolation has worked. Contamination can`t get into that piece of tool whether you`re installing a piece of equipment right next to it or cutting pipe. Aside from the flexibility, you are also able to run with lower operational costs. If the fab were a Class 1 ballroom, it would require three to four times the amount of air-handling equipment we`re using. Those are two big savings factors in this fab.”
Mike Wieder, president of Air Filtration Management, Inc. (Bethlehem, PA), acted as a pre-building consultant to Harris on the Raptor Project. In fact, his firm performed Fab 8`s cleanroom certification. “This fab subscribes to total isolation technology. They maximized the benefit of that. They realized that the environment around needs to be clean — to be controlled– but we do not need to overdesign and compensate for the Class 1 environment. They took those attributes and were, in turn, able to capitalize on the downsizing of the other parts of the environment and look to the efficiencies.” Wieder also points out that Harris departed from the total Class 1 approach in its other fabs, designing a full Class 1 room and integrating minienvironments into it on a sequential basis.
Fab 8 combines innovation/aesthetics
Fab 8`s 24,500-sq. ft. cleanroom was designed at Class 1,000 with minienvironments certified at Class 1 or sub-Class 1, certified at better than Class 100. Seventy percent of the tools are SMIF integrated, while the remaining 30 percent are enclosed in adaptive SMIFs and minienvironments. An innovation is the attached maintenance area of about 5,500 sq. ft., which also operates at Class 1,000. This allows fab technicians to go back and forth between the fab and the cleaning environment without having to degown. Hollock says, “We built Class 1,000 maintenance rooms for the technicians and operators so that they can go directly from the fab into these rooms. If they take a part off the machine that needs to be cleaned, or soldered or etched, they don`t have to put it in a pass-through, get degowned, take that part, bring it back, wipe it down, put it in the pass-through, get gowned up, go back into the fab, and then put it back on the machine.” Unlike the fab, which is built on a 34-in. raised floor, the parts cleaning area is built on a solid floor.
The fab boasts windows and generous expanses of glass throughout the facility, affording fab personnel views of the surrounding mountain. The site itself includes an additional 40 acres of woods for the next expansion. A building automation system monitors 3,000 points throughout the fab, automatically paging the appropriate maintenance mechanic. Quality is a hallmark of operations throughout, including the technology for the environmental systems, says Hollock. A new wastewater treatment plant and a planned reclamation system are also part of the project. A fluoride wastewater recycling program takes fluoride rinse water, runs it through an RO unit, concentrates the fluorides, and sends them to the treatment plant. The water is then returned to the DI water system, which generates 500,000 gallons of water per day, 250 gallons per minute.
Attached to the three-story main fab building is the central utilities plant. On the lower level are the gas bunkers and chemical distribution systems. Both chemicals and gases are distributed from single sources on the second level through the valve manifold boxes, then delivered to the tool. The top floor of the plant is on the same level as the wafer fab itself and houses the Class 1,000 parts cleaning and maintenance rooms attached to the fab`s cleanroom. Above the wafer fab on the third level is the fan deck. Air exchange in the cleanroom is 200 to 300 air changes per hour, 1.5 times that for the minienvironments. Air speed is roughly 20 to 25 ft./min. in the room. In the minis, it`s about 80 ft./min. Air handlers located in four areas in the fab are coupled into a common plenum, then run through an individual duct to an individual filter. Each filter is serviced specifically through a flex duct running down through the room, through the floor, and up through the walls. Above the ceiling, it is returned to the recirculation units.
On the roof are recirculation and makeup air units, a pipe for ammonia exhaust, acid-bearing exhaust, and a volatile organic incinerator. Says Burrell, “Some of our photo materials have some organics, and they`re accumulated and burnt off before anything is released into the atmosphere.”
The ballroom-type diffusion area, with its BTI furnaces, has an ULPA-filtered ceiling over 50 percent of it, with full-filter coverage above the minis. Harris is currently working with Asyst software on a tool integration project, which will probably take another 9 to 12 months and is about 30 percent complete.
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The SMIF environment means that the fab can maintain a Class 1 environment during manufacturing operations, tool installations and service.
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The Harris fab`s Class 1,000 gowning room.
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In the central utilities plant, gas bunkers and chemical distribution systems supply gas and chemicals from single sources through valve manifold
boxes to the tool.