Perfluoroelastomer Seals Are Compatible With Industry Gases
Brian Dance, Contributing Editor -- Semiconductor International, 9/1/2001
Corrosive fluorine-based gas mixtures used in semiconductor production can rapidly degrade the performance of many types of gas sealing ring used in plasma etching, chemical vapor deposition and similar processes. Degradation is especially likely if the temperature is high, and can result in early failure through material contamination and costly equipment downtime.
Precision Polymer Engineering (Blackburn, England) has developed a "Perlast" perfluoroelastomer material that contains a perfluoropolymer filler. One of the most chemically inert materials available, it is said to be the first totally fluorine-compatible material for seals that are suitable for use with fluorine-based ClF3 and NF3 chemistries, as well as with conventional wet and dry processes.
Perfluoroelastomers are co-polymers usually made of tetrafluoroethylene and perfluoromethylvinylether. They offer exceptional resistance to attack by many highly reactive materials, including strong oxidizing agents. Elemental carbon has been used as a filler, but the resulting material does not satisfy the needs of the industry. Without a filler, perfluoroelastomers do not provide the required mechanical performance. If silicon dioxide is used as a filler, the resulting material has inadequate chemical resistance. Semi-crystalline perfluoroelastomers have been tried as fillers, but do not have the required mechanical properties.
The new Perlast material is a perfluoroelastomer in which a semi-crystalline fluorinated filler is dispersed in the form of a microscopic powder with particle diameters of <100 nm. Seals of this material are translucent because the particle size is less than the wavelengths of visible light. The extremely high surface interaction between the filler and perfluoroelastomer results in good sealing. Various semi-crystalline perfluoropolymers can be used as fillers.
The finely dispersed filler can be made in a high-purity aqueous medium to produce a metal-free product of extreme purity. The amount of filler should be in the 10-30% range to achieve a product with the desired characteristics.
