Point of Use Particle Removal – Keeping the Ductwork Clear

Point of Use Particle Removal – Keeping the Ductwork Clear
Joe Van Gompel and Jago Snook; BOC Edwards

The manufacture of semiconductors requires deposition of layers of silicon, silicon dioxide, tungsten, or other materials. The deposition is typically done through thermal or plasmaenhanced chemical vapor deposition (CVD) reactions with gases such as silane (SiH4) or tungsten hexafluoride (WF6). Some semiconductor deposition processes generate significant quantities of solids in the form of nonvolatile particulate. Finer particulate (<1 micron) behaves more like a gas and less like a solid in the exhaust stream. This fine particulate is very difficult to remove using conventional abatement devices such as wet scrubbers, ultimately leading to a clay-like buildup in the ductwork and in the rooftop scrubber. This problem is exacerbated with higher flows of silane and other deposition gases in 300-mm fabs. Conversely, fine particulate responds well to electrostatic removal. A point of use (POU) wet electrostatic precipitator (WESP) has been developed and was shown to remove fine particulate very effectively. The WESP is downstream of the existing abatement device to intercept residual solids before they enter the ductwork. Customer tests on a high-silane poly deposition process have shown solids removal levels of > 99% by weight based on solids entering the electrostatic precipitator after the POU scrubber.