Regular maintenance of the cleanroom is essential. The cleaning personnel must wear the same garments as the operators. Cleanroom cleaners and applicators, including mops, must be carefully specified. Normal household cleaners are far too dirty for use in cleanrooms. Special care must be taken when using vacuum cleaners. Special cleanroom vacuums with HEPA filtered exhausts are available. Many cleanrooms will have built-in vacuum systems to minimize dirt generation during cleaning.

The wipe-down of process stations is done with special wipes made from non-shedding polyester or nylon, prewashed to reduce contamination. Some are prewetted with an isopropyl alcohol and DI water solution, which provides convenience and eliminates secondary contamination from spraying cleaners in the cleanroom.27

The wiping procedure is critical. Wall surfaces should be wiped from top to bottom and deck surfaces from back to front. Cleaning chemicals in spray bottle, if used, should be sprayed into wipes, not onto the surfaces. This prevents overspray onto the wafers and equipment. Cleanroom cleaning has, itself, become a critical supporting operation. Many fabs use outside certification services24 to identify and document cleanliness levels, practices, documentation, and control procedures. Certification standards for cleanroom maintenance schedules is identified in the ISO Global Cleanroon Standards (ISO 14644-2).

Copper metallization has become the metal of choice for advanced ULSI devices. While the copper has many advantages (see Chapter 13), there is a serious downside. Copper contamination inside a silicon wafer raises havoc with the electrical operation of the component devices. Isolating the copper processing areas...