TABLE OF CONTENTS One of the first problems to plague the infant microchip fabrication efforts was contamination. The industry started with a cleanroom technology developed by the space industry. However, these techniques proved inadequate for large-scale manufacturing of chips. Cleanroom technology has had to keep pace with chip design and density evolution. The ability of the industry to grow has been dependent on keeping up solving contamination problems presented by each generation of chips. Yesterday's minor problems become the killer defects of today's chips.
Semiconductor devices are very vulnerable to many types of contaminants. They fall into five major classes.
Particles
Metallic ions
Chemicals
Bacteria
Airborne molecular contaminants (AMCs)
Particles. Semiconductor devices, especially dense integrated circuits, are vulnerable to all kinds of contamination. The sensitivity is due to the small feature sizes and the thinness of deposited layers on the wafer surface. These dimensions are down to the submicron range. A micron or micrometer ( m) is very small. A centimeter contains 10,000 m. Another way to envision a micron is that a human hair is about 100 m in diameter (Fig. 5.1). The small physical dimensions of the devices make them very vulnerable to particulate contamination in the air coming from workers, generated by the equipment, and present in processing chemicals (Fig. 5.2). As the feature size and films become smaller (Fig. 5.3), the allowable particle size must be controlled to smaller dimensions.
