Testing liquid-handling system components to ensure purity and reliability
Donald C. Grant, Dennis Chilcote, Wayne Kelly, Mark R. Litchy – CT Associates, Inc.
Allen Rodemeyer, Dave Henderson, Kenji Kingsford – Saint-Gobain Performance Plastics
Because the processes used to produce state-of-the-art microcircuits are extremely sensitive to contamination, the cleanliness of the systems that supply process chemicals and other fluids is a critical concern to semiconductor manufacturers. Contaminants from equipment subsystems and components can and do lead to process defects and lower-yielding wafers. For example, particulate contamination can cause open or short circuits, structural defects, altered electrical properties, and unreliable photolithographic reproduction. Metallic contaminants on the wafer surface can diffuse into the substrate during subsequent heat treatments, causing drifts in surface potential, current leakage, structural defects in vapor-grown epitaxial layers, and reduced breakdown voltage of gate oxides.
While the need for ultraclean equipment has long been clear, cleanliness guidelines for the manufacturers who produce such systems have been slow in coming. SEMI has recently released specifications for particulate and metallic contamination in components. Not included, however, are specifications for particle release, while requirements for metallic extractables are based on extraction into water. Section 3.7 states that the relative leach-out performance of polymer components in actual use with other chemicals, (e.g., acids and bases) cannot be directly derived by using the ultrapure water (UPW) data. Hence, companies must set their own specification for their products and components used to transport process chemicals. The chemical-management division of BOC Edwards (Santa Clara, CA), for example has adopted specifications for particle release and metal extraction from components used in its chemical delivery systems.
Another major concern for semiconductor manufacturers is component reliability, since equipment failure results in costly fab downtime. Often a component’s resistance to damage is dependent on the chemical it contacts. For example, diaphragm valves have two main modes of failure. Internal metal components such as springs usually fail because of metal corrosion caused by exposure to acids that permeate the diaphragm. Hydrochloric acid (HCl) is thought to be the greatest contributor to this type of failure. The other major failure mode is diaphragm fatigue, possible exacerbated by environmental stress cracking (ESC). In ESC, crack propagation through plastics subjected to stress is accelerated by a weak plastic-chemical interaction. Hydrofluoric acid (HF) is believed to be the chemical most responsible for fatigue failure of fluoropolymer diaphragms.
In response to these industry concerns, component supplier Saint-Gobain Performance Plastics (Garden Grove, CA) has adopted a testing program for its components used in high-purity semiconductor applications. This article describes the testing program that was conducted by CT Associates (Bloomington, MN), the program’s goals, the experimental and analytical procedures used and examples of the test results.
CTA publication #45: MICRO, 19(5):41-51, 2001