As ultralarge-scale integration (ULSI) patterns are refined, the electrical charge of the signal decreases and is more sensitive to noise, such as dark and leakage currents. The effects of minute quantities of contaminants, not previously a problem, must be suppressed. This requires high-performance process technology that satisfies the following three principles [1]:

Ultraclean process environment

Ultraclean wafer surface

Process parameters: perfectly controlled equipment