White Oak: Top Fab of 1999

John Baliga, Associate Editor -- Semiconductor International, 5/1/1999

Going from first concrete to full production within two years, this facility went straight to 250 nm technology.

The 800,000 sq.ft. site integrates wafer fab with probe, assembly and test. This reduces the time to produce the final packaged product, as well as the probability of yield loss associated with shipping wafers to a packaging facility, and it allows White Oak to ship product straight to its customers.

Every aspect of the facility's ramp up schedule was aggressive. It went straight to 250 nm technology to stay competitive with other 64 Mb DRAM facilities that had started a year or so earlier. The company essentially built two factories, front- and back-ends concurrently, rather than one at a time. The fab is still ramping up on technology shrinks. It currently runs 240 and 200 nm CMOS processes and is developing sub 200 nm process. The company plans to implement technology shrinks every six months.

White Oak is a joint venture company of Motorola Semiconductor Products Sector (Austin, Texas) and Infineon Technologies, formerly Siemens Semiconductor Group (Munich, Germany). Though the company operates as an independent entity, it borrowed the knowledge and experience from the two parent companies to achieve its aggressive schedule. The two companies have another joint venture fab, Semiconductor300, in Dresden, Germany.

Safety and quality

Fig. 1. The White Oak facility in Sandston, Va. was producing 250 nm technology DRAMs within two years of its groundbreaking.

In spite of the fast schedule of construction, base construction of the facility had a very good safety record. The four million man-hour construction effort surpassed the one million man-hour mark on two occasions without time lost to injury. The average recordable and lost time injury rates were only 25% of the industry rate.

This safety performance carried over into the facility's first year of manufacturing. Recordable and time lost rates remained less than half the industry average. The company expects to receive OSHA STAR certification from the Virginia Occupational Safety and Health Administration this year, a rarity for any company less than three years old. It would be the fifth fab in the United States to receive that certification.

In addition, the facility received its ISO 9002 certification in December 1998. The facility could not have achieved it so quickly unless its quality systems and processes were 'built in' from the beginning at a high level. If any shortcuts had been taken in achieving first silicon or qualification, the certification would not have been possible.

With this quality minded approach, the facility was able to achieve first silicon just 100 days after receiving its first tool. Three days later, first silicon had been converted into first components, achieving fully functional front- and back-end manufacturing areas. According to the company, its first silicon yields exceeded those of the reference site from which they transferred the technology.

Facility and process

Fig. 2. White Oak's lithography area has a ballroom configuration. A bright light inspection step is pictured.

The manufacturing area has a bay and chase layout, with a class M1 clean area (<1@0.1µm). Table 1 lists the cleanroom area in the facility by class. The lithography and wet areas are in a ballroom layout (Fig. 2).

In an effort to reduce costs, but not sacrifice manufacturing flow or functionality, the CMP and implant areas were constructed without a subfab and are contiguous with the rest of the manufacturing areas.

White Oak's most complex process uses 21 masking levels. It uses DUV (248 nm) lithography on features below 0.25 µm. Shallow trench isolation (STI) is used to isolate word and bit lines, while deep silicon trench (DT) is used to make the storage capacitors. CMP with endpoint capability is performed on polysilicon, oxide and tungsten films. Borderless contact and tungsten CMP are a part of the interconnect process.

Defect reduction strategy

The company's philosophy for contamination control was to start clean, build clean and stay clean. Everyone involved in the construction of the facility received classroom training on build clean protocols. From the time groundbreaking started, general area cleaning was required at least three times a shift.

After building dry-in, shoe covers, head covers, beard covers and gloves were required for all construction work in the facility. The requirements kept going up as the facility progressed towards its final configuration of clean manufacturing areas.

The yield management approach includes defect inspections in the process flow, a cross-functional particle improvement team to address random defect and related problems, daily yield meetings and full availability of information and data from all points in the process. A monitor system correlates electrical data at wafer test to the defect data collected during processing, using on-the-fly automatic defect classification (ADC). This provides engineers immediate feedback on yield impact from defects.

The facility has a fully integrated computer integrated manufacturing (CIM) system in place, which allows full availability of all necessary data for yield analysis. All data from the start of wafer processing to the end of the packaging process is available to yield enhancement engineers for their daily evaluation of systematic process problems and weekly electrical parameter monitoring (Fig. 3).

CIM and automation

Fig. 3. Inspection and yield data from all phases of manufacturing are available to yield enhancement engineers.

White Oak's CIM and automation systems are a combination of commercially available systems and proprietary systems from both parent companies. The main CIM system has an integrated MES with specialized applications for statistical process control (SPC), equipment warranty tracking, engineering data analysis (EDAS) and automated material handling (AMHS). A universal graphical user interface (GUI) simplifies the use of the system for all users.

The system performs automatic lot verification at each process step and paperless material routings for product and test wafer flows. All specifications are on-line, with web-based viewing and electronic sign-off.

Equipment integration is a part of the CIM system. All metrology tools had full data upload capability before first silicon was achieved. The company used SECS simulation tools to develop the equipment integration interfaces before the tools were even delivered. Over 500 process tools in the fab have recipe select and download capability along with data collection capabilities on-line and fully functional.

Wafers are moved from bay to bay using stockers and track systems. A unique feature in the diffusion area is a BOCS opener inside the stocker and deliver-open cassettes only, which is part of the work methods within the area.

More than 80% of the assembly equipment in the back-end part of the facility is automated. Fully automatic magazine tracking and throughput optimization is performed while maintaining full lot integrity. Back-end automation is fully integrated with the facility's CIM system.

The CIM system is also fully integrated with the enterprise system. Turning orders into lot starts and lot completions into fulfillments are all done in the enterprise system, and it is seamlessly linked with production control to closely match production to demand.

Environmental responsibility

The Environmental Safety and Industrial Hygiene group (ESIH) at White Oak developed its hazardous waste management program by defining a series of best management practices that exceed state regulations. The team also created a series of quality documents that comply with White Oak's ISO 9002 documentation format.

The ESIH group enforces a hazardous waste program built around these best management practices including bulk waste storage systems, secondarily-contained transfer lines, an aggressive waste minimization and pollution prevention program, and a fully trained emergency response team.

Commitment to people

Even with all of the technology made available to White Oak by its two parent companies, the management emphasizes that it is the employees that have made their success possible. Group decision making, team goal setting, and cooperative leadership are underscored in every area of the company.   

(http://www.whiteoaksemi.com)