Building Vibration-free Environment–Key Issue for Sicilian Volcano Fab
By Alfred Vollmer
Catania, Sicily–SGS-Thomson Microelectronics (ST) of St. Genis, France is now in the process of ramping up its new 0.35-micron, 8-inch fab in Catania, Sicily (Italy). By the end of the year, the semiconductor company expects to be producing 4-Mbit and 16-Mbit flash memories at the rate of 1,000 wafers/week, despite the M5 fab`s location at the base of an active volcano.
The project is only one of several new fabs and fab expansions under way at the France-based company, which is moving assertively to maintain its fabrication expertise as it sees rising revenues and profits.
Major challenges
Catania is located just at the base of Mount Etna, one of the few remaining active volcanoes in Europe. The mountain has had several eruptions within the last few years, and smoke issues constantly from its summit crater. Thus, the entire area is prone to seismic disturbances, and building the fab posed a major challenge.
To ensure a vibration-free environment, the site of the new fab was the subject of extensive geological surveys before the building foundations were laid. The building`s entire supporting structure is provided by 520 concrete pillars, tested with loads in excess of 2,000 tons and driven 32 meters into the ground. The new building is made up of three separate parts. The first part is a four-story building dedicated entirely to services for its Class 1 laboratory. The second and largest block complies with stringent specifications for minimum vibrations, which are required for submicron production.
The fab is completely isolated from adjacent buildings by flexible couplings. The floors and the walls of the underground areas are separated from the pillars supporting the laboratory by means of flexible couplings. Furthermore, all rotary motors are mounted on anti-vibration springs and the fluid speed in the facility`s pipes is low in order to reduce vibrations. These measures were intended to result in a level of vibration less than 3.15 microns/sec at a frequency between 4 and 100 Hz, complying with Class E specifications; early results indicate that even these tight numbers were exceeded.
Cleanroom equipment
The first floor houses the air-conditioning equipment, while the second floor contains the services for the equipment installed in the cleanroom. Meissner & Wurst of Stuttgart, Germany, was responsible for delivering and installing the cleanroom equipment. The air is changed 450 times/hour and 4,240,000 m3 of air are recycled every hour while 202,000 m3 of air is newly introduced. Air speed is 0.45m/s, while temperature is 21+/-0.25°C with a relative humidity of 40 +/-1.5 percent. The maximum noise is 60 dBa and the power consumption is 22 MVA, which is about the same as an Italian town with 25,000 inhabitants.
The Class 1 laboratory is situated on the third floor. It is in this area that the sophisticated equipment will be installed. And the fab might even be ready for 300-mm equipment. “For us, 300 mm is more an equipment problem than a building problem,” says Pasquale Pistorio, president and CEO of ST.
The third and tallest building is separated from the second building by flexible couplings. In the underground basement are the cloakrooms and services. The ground floor contains the reception, where the personnel must change into special shoes. On the first floor there is a Class 10 changing room of about 500 m2. Above this there is the EWS department with a 600 m2 Class 10 area. The fifth floor is dedicated to CAD/CAM, data processing and design, while the top floor is occupied by offices. In total, the working area will be 15,950 m2. Of this, 3,500 m2 is Class 1 cleanroom areas and 1,800 square meters are reserved for CAD, design and offices.
The first steppers were installed in January. Up to now, three Canon 3000i4 steppers are installed, however, 20 steppers of this type are on order. The first 8-inch wafer handling took place in February and plans called for production of about 50 developmental wafers/week by the end of August. In Autumn, ST`s schedule calls for 100 wafers/week with a first output of 40 wafers/week. Target production for October, November, and December is 400, 800, and 1000 wafers/week, respectively, with 90, 340, and 680 wafers leaving the fab per week.
The building capacity is for 25,000 to 30,000 wafers/month, which might be reached in about three years, says Pistorio. He added that the Catania fab is extendible to 0.18-micron geometries.
ST will not rest on its laurels when the Catania fab is completed. The firm is engaged in heavy capacity expansion, and making long-range plans for two additional fabs to come on-line late in the decade.
“One will be in Europe and one outside Europe,” says Pistorio. “These plants will come on-line 1999 or later,” he explains, saying that they will use 8-inch wafers. Capacity has not been determined.
“Our objective is to be ready. And then we can accelerate or delay our plans to build a new fab. We have the concept of a modular capacity growth,” said Pistorio. He added, “We try to optimize three parameters of the decision: Access to the market, existence of know-how, and competitiveness, which includes cost of labor and cost of energy.” Another important aspect might be government funding.
In 1994, ST`s 8-inch fab in Crolles, France, went into operation and in 1995 the company`s Phoenix, AZ, fab started to ramp up. In addition to the M5 plant in Catania, expansion work is under way at the Agrate, Italy, fab, which is expected to be ready for operation in 1997. The new Agrate line will process 5000, 8-inch wafer starts/week.
In late summer, ground-breaking ceremonies for an 8-inch fab took place. Heavy construction machinery is already on site in Rousset, France (close to Nice and Marseilles), where an 8-inch fab is being built for production in 1998. n
Editor`s Note: Alfred Vollmer is a European Correspondent for Solid State Technology, CleanRooms` sister magazine.