Cleanroom facilities are essential in the production of semiconductor wafers because structures are being created that are sub-micron in size. Any airborne contamination could ruin the products and so these are filtered to give ultra-clean operating conditions. The power discrete devices made at Philips Semiconductors' Hazel Grove PowerFab2 facility are tiny, bearing components typically 400 times smaller than a pinhead: a single dust particle can contaminate the end-product and make it useless.
For this reason, great care was taken in designing and refurbishing an older bipolar fab building. “We say refurbishment, but in fact the only item retained was the sub wafer and steel frame that had to be considerably reinforced to withstand the additional loads imposed on it,” says Geoff Dicken, project manager, PowerFab2. “For PowerFab2, the steel frame structure had to support a new ceiling grid structure, itself holding the fan filter units, lighting systems, electrical supplies and infill panels. Also supported by the steel frame was the ductwork distribution system for fresh air to be transferred to the plenum above the cleanroom, the pipework to the cooling coils, and the extract ductwork from the ion implantation units. A floor was constructed when faults in the old building were discovered. This was necessary to meet the vibration criteria established.”
The construction and start up of PowerFab2 followed a team approach by Philips Semiconductors (Hazel Grove) and (Meissner + Wurst)Pearce Ltd.
Work started in May 1997 and was completed in February 1998 – on time and within the $21.8 million budget (excluding process tools). Only 67 days after the first equipment was delivered, the first wafers were produced. Indeed, realizing this construction feat, without delays, and during such an uncertain period in semiconductor history gave the achievement even more significance.
PowerFab2 cleanroom showing planets/ garmented workers.
Record hook-up time was achieved through detailed planning and through the involvement of all concerned parties. Facilities, equipment and process engineers, equipment buyers and suppliers, equipment handling contractors, the mechanical and electrical contractors, and specialist gases contractors were all involved in the planning, ensuring the sufficient allocation of space, the availability of services, and the timely purchasing and delivery of equipment. Heavy emphasis was placed on the importance of each individual's role and their cooperation with the other involved parties.
The 2,000 m2 cleanroom is a “ballroom” concept using FFUs to produce the Class 10 and Class 100 conditions at 21 degrees Celsius (+or- 1 degree C), 45 +or- 3 percent rH. Major elements of the cleanroom have all been previously proven in IC fabs. In particular the M+W fan filter units and ceiling grid system, Ritterwand partitioning, and the Mahle floor system were used to give the quality of finish and flexibility of layout always required by the semiconductor industry.
Particular attention was given to the services layout in the sub wafer area due to the limited headroom available – only 2 meters compared with the more usual 10 to 14 meters Not only the designs of today's PowerFab2, but possible equipment layout plans of the future had to be predicted to ensure optimum use of the initial layout design. This was achieved with the outstanding team effort of the design crew, which included not only M+W Pearce but also Philips Semiconductors' on-site facilities, equipment and process engineers.
Looking to the future
Sub floor services received the same attention to detail in the planning and layout as the sub wafer in order not only to realize the 67-day hook-up time but also to allow for additional facilities in other areas of the fab to be incorporated at a later date. An equipment installation program was established, which focused heavily on future requirements. The sub floor design enabled installation of future equipment without causing fab downtimes during connection. Sufficient additional connections were included in the design to allow services to be extended, with additional areas quarantined for use by other services at a later date. All of these features followed the frame sequence wherever possible to maximize space. Those services not used by a particular piece of equipment were not closed off altogether, but rather a gap was left – the next generation of equipment may require this service. In addition, pipe sizes, extract routes, electrical distribution and IT infrastructures and systems were all carefully considered to satisfy future requirements.
Safety is paramount
Semiconductor cleanrooms require a highly sophisticated alarm system not only to detect smoke, fire and gas/chemical leaks, but also to avoid unwanted alarms. The Cerberus DMS 7000 AlgoRex Interactive System provides a high degree of central management forming part of a complete danger management system.
A fully integrated building management system with approximately 1,000 sensors controls the services and environment to ensure a safe and controlled process wafer fab. The system provides wide capabilities in terms of routing high sensitivity smoke detection, extract system monitoring, air sampling, and gas detection to the hub of the danger management system, which is housed in a central control room. In an emergency the equipment in the central control room provides the location of the incident and indicates what substances the alarm response team should be aware of in that area. This ensures that the most efficient and accurate corrective action is taken.
The danger management system is highly sensitive in that it differentiates between various types of particles (e.g. smoke vs. dust) and will recognize the need to raise the alarm for even a minor incident, preventing it from turning into a disaster. In this way, unwanted alarms are avoided, which are costly both in terms of the re-laundering of protective clothing and in terms of product waste, while in cases of genuine emergency employees, equipment and facilities receive the highest level of protection possible.
From construction to completion
Employees working in the cleanroom are required to wear the industry-standard semiconductor cleanroom garments (with snoods, overshoes, and gloves) to ensure conformance to the anti-contamination rules.
The temperature at 21 degrees Celsius
(? 1), humidity at rH 45 percent (? 3) and positively re-circulated airflow are all carefully monitored to ensure a constantly maintained production environment.
Advances in cleanroom technology also play an important role in realizing environmental goals such as the ISO14001 standard, which specifies requirements for the development, implementation and maintenance of environmental management systems to ensure compliance with stated environmental policy and objectives.
Philips Semiconductors has written environmental policies and objectives and has been audited by a third party (SGS Yarsley) who have confirmed that Philips has an environmental management system that meets the requirements of the ISO14001 standard. The accreditation audit took place in June 1997.
The continued adherence to the ISO14001 standard is monitored by regular follow-up audits by the third party assessors. The new PowerFab2 facility improves Philips' position in adhering to these standards and in meeting the standards set by other world-wide quality and environmental awards.
The main production from PowerFab2 uses Philips Semiconductors' TrenchMOS technology. Launched three years ago, it has proved tremendously successful. Since then, the company has been refining the TrenchMOS process to shrink the geometries and improve the manufacturability of the products. The new production facilities of PowerFab2 enable the cell pitch (or repeat pattern distance) to be shrunk from 11 micron to 9 micron, enabling the cell packing density to be increased from 6.2 million to 9 million cells per square inch. This gives a 20 percent reduction in the RDS(ON) so that the devices made using this refined TrenchMOS technology offer designers a choice of lower heat dissipation for the same size chip, or a smaller chip with the same dissipation. These options are particularly useful when designing mobile electronic equipment. TrenchMOS products are now being used in almost every part of the electronics industry, including automotive, mobile communications, computers and electronic data processing.
In the near future, Philips Semiconductors will also start producing TOPFET2 in PowerFab2, which is a new process for producing protected power devices for automotive applications and further extends the company's comprehensive range of advanced power handling discretes.
“With the opening of PowerFab2, Philips Semiconductors' Discrete Power Business Line sees the completion of a large investment program, which has put in place an industrial infrastructure capable of supporting aggressive growth plans in several key power markets,” says Jan-Willem Reynaerts, marketing manager for the Power Business Line. “In these new fabs, Philips is producing a very wide range of both Bipolar (PowerFab1) and MOS (PowerFab2) products aimed at providing customers with all their power requirements, thus supporting Philips' one-stop-shop approach.”
This article was contributed by Philips Semiconductors' Power Discretes Business Line, which currently ranks 7th world-wide. It has been compiled by Sarah Ward [BA(Hons)], marketing communications manager for the Power Discretes Business Line of Philips Semiconductors, and is based on the contribution from Geoff Dicken, Philips Semiconductors' project manager responsible for the construction of PowerFab2.
About Philips Semiconductors
Philips Semiconductors, a division of Royal Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the eigth largest semiconductor supplier in the world.
Philips has been involved with discrete semiconductors almost since they were first developed in 1947, with the production of the first discrete semiconductors starting in 1953. The Hazel Grove facility, home to the power discretes business line, was started in 1967 and has been refurbished several times over the years. The latest investment in PowerFab2 was preceded by a $47 million investment two years ago in its Bipolar facility, which also set new standards by using 5-inch wafers for bipolar.