The transformation of silicon into semiconductors is a uniquely complex and a potentially hazardous process; one where the pace of technological change is fast and furious. The safety professional working in the semiconductor industry is challenged to find practical engineering-based strategies and to safely manage ever-changing technologies. This paper outlines one phase of the semiconductor manufacturing process called "wafer fabrication"; identifies potential chemical, physical and health hazards associated with this process; and discusses the management of process-related changes.
Semiconductors are the backbone of the telecommunications and computer industries, and all things electronic. Thanks to semiconductors, today's automobiles have more electronic capabilities than the space shuttle! Semiconductors can be discrete devices or integrated circuits (ICs); thousands of tiny electronic components integrated into one small device referred to as die or chip. Each electronic component or feature (transistors, resistors, capacitors, and diodes) is fabricated one layer at a time, in and on circular platens of pure silicon (sil/i-ken) called wafers. In 1980, features were 2.0 microns(µ) fabricated on 75mm (3-inch) wafers. In 2003, the feature size is 0.13µ on 300mm (12-inch) wafers (Jansen 114). According to International Technology Roadmap for Semiconductors (ITRS 97), by 2006, feature size will be 0.09µ or 90 nanometers (nm) (Table 1). By contrast, a single strand of human hair is about 50µ wide. With feature sizes this small, submicroscopic dust contamination has the potential to scrap an entire wafer. As a result, wafer fabrication must be created in a very unique manufacturing environment called a cleanroom or fab.
Cleanrooms are 1,000 to 100,000 times cleaner than a hospital operating room. A class number is assigned to the cleanroom technology necessary to protect the product. This class number equals the number of particles per cubic foot of air that is allowed in a cleanroom; all other particles are filtered out by High Efficiency Particulate Air (HEPA) filters. Where specific process operations require a higher-class cleanroom than currently employed, mini-environments are installed within the cleanroom. Nanotechnology requires an inert gas (nitrogen) mini-environment. Generally, air flows from ceiling to floor. In some cleanrooms, return air travels through plenums located in the fab walls to recirculation / pressurization fans above and outside the cleanroom; other cleanrooms utilize grated flooring for the return air. A certain percentage of the air is recirculated. Makeup air from outside the building replaces what air is exhausted through local exhaust systems on equipment. The rate of room air exchange varies with a room's static pressure requirements. A positive pressure is maintained to ensure cleanroom integrity. Air is conditioned for temperature and humidity since static from low humidity would destroy the chips' delicate circuitry and tight temperature control is critical for most fab chemistries.
Cleanroom apparel helps to control the particles generated by human bodies and clothing. Humans generate up to one million particles per minute, even when sitting still. Humans who work in the cleanrooms never hold or touch a wafer directly.
