Digital`s New Fab 6 Weighs in at Sub-Class 1
By Susan English
Hudson, MA–On a 165-acre site off Interstate 495 sits, a semiconductor manufacturing plant constructed to accommodate three successive generations of CMOS technology, from 0.35 to 0.18 micron on 8-in. wafers. Possibly making it the first U.S. company to build-in such advanced technology, Digital Semiconductor`s new Fab 6, a $435 million semiconductor wafer fabrication facility boasts 526,000 ft2 of space, including a sub-Class 1 (0.1µm) cleanroom. The expandable 34,000-ft2 sub-Class 1 area is 35 times cleaner than Class 1 in real-time operating mode and is rated at less than one particle per cubic foot (measured at 0.1µm).
According to Fab 6 manager Scott Sieber: “Our existing fabs basically were not capable of moving beyond half a micron in terms of process feature size. The investment decision was made based on the need to drive three new process generations over the next number of years into a new fab area consistent with 8-in. wafer processing, which is the `state of the art` right now.” Currently, just under 10 million transistors are being placed on one die, and by the year 2,000, Digital expects one of its devices to hold 100 million transistors.
Fab 6 was built by Digital Semiconductor, a new business unit formed last June by Digital Equipment Corp. (Maynard, MA) to design, develop, manufacture and market semiconductors and semiconductor products such as microprocessors and PCI-based peripheral chips. The company has developed semiconductor products since 1975, but only recently became a merchant vendor in response to what a company spokeswoman cited as the “rapidly growing needs of a spectrum of worldwide markets.” Construction of Fab 6 not only introduces Digital as a potentially large merchant market competitor in the lucrative semiconductor industry, but heralds its focus on contamination-free manufacturing. Construction on the fab was begun in May 1992 and completed in June 1994. Equipment installation began in June and was completed by September, when test production of its wafers was initiated. Revenue production is slated to begin in early 1996.
A lot of pre-planning went into the design and construction of Fab 6. The “advance group” mentioned by Sieber was a cross-functional group of six to eight employees from different aspects of semiconductor processing–development, process engineering, industrial engineering and equipment engineering. The group got together a year-and-a-half to two years before the fab even started construction, Sieber says, to do some benchmarking at 10 to 12 different fab operations around the world. As a result, Fab 6 is essentially a composite of what they considered to be the best design-build techniques.
Marshall Contractors (Rumford, RI) and Industrial Design Corp., (IDC; Portland, OR), were hired as construction manager and architectural engineer, respectively. A contamination-free group was created within Sieber`s Fab 6 organization to bring product and procedural specifications to the planned fab. Not only did most of the equipment for the fab undergo special cleaning and packaging; once on site, installation was subject to a whole set of special procedures for unwrapping and cleaning before being physically installed. During the construction phase, a strict five-phase construction protocol was instituted to ensure that particles were not introduced into the cleanroom envelope.
Flexibility for future expansion was a primary design consideration. As a full down-flow fab rather than a bay-and-chase style, its walls can be moved wherever needed, because the entire fab space runs at the sub-Class 1 spec. ULPA filters located throughout the ceiling system filter 5 million ft3 of air per minute before blowing it through the fab area, moving it through the whole building to keep it at sub-Class 1. Other support cleanroom space includes a 5,000-ft2 Class 100; a 2,000-ft2 Class 1,000; and 75,000-ft2 at Class 10,000, although cleanroom areas vary according to production needs at any given time. Minienvironments are used specifically to control the environment within the company`s track system and steppers and around wet benches. Control of air around the wet benches also acts as an operator safety precaution as protection from acid splashes and other chemical hazards.
Fab 6 comes equipped with 8 miles of stainless steel, high purity piping, 4.7 miles of chemical distribution piping and 3 miles of DI water piping; 4.1 miles of exhaust duct and four underground tunnels totaling 1/6 miles. All materials throughout the fab are ultrapure, adding to the upfront cost of the fab, but “we had to make an investment upfront in the best materials we could possibly specify at this point, because we can`t reconstruct the fab at a later point in time. We intentionally made some relatively expensive investments in state-of-the-art technology right now, knowing it probably wouldn`t be necessary at 0.35 µm, but certainly by the time we get down to quarter-micron or 0.18 µm, we will absolutely have to have this level of cleanliness-controlled fab space,” says Sieber.
Before entering the fab, employees must replace their street clothes with a “building suit,” a two-piece polyester garment consisting of a long-sleeved top and a pair of pants put on over the undergarments. If entering the Class D1 cleanroom or support areas, they are then required to wear appropriate cleanroom garments over the building suit. n
CleanRooms incorrectly identified an artist`s rendition of a building in the article “Customer Demand for Cleaner Supplier Products/ Processes Drives Facilities Upgrades,” May 1995, p. 9. The building is Fluoroware, Inc.`s proposed new state-of-the-art manufacturing facility to be built on the present 155,000 ft2 site.