Abstract: A trap filter chamber (16) removes chemical by-products created during the manufacturing process of semiconductor wafers in a low pressure chemical vapor deposition reactor (12). A vapor containing the process by-products is discharged from the reactor to the trap chamber (16) by way of connecting pipe (14). The vapors are drawn through the trap chamber by a vacuum pump (20). The connecting pipe at the inlet of the trap chamber has a tapered diameter section (28, 30) such that its outlet is larger in diameter than its inlet. The tapered section gradually and linearly reduces the pressure from the reactor to the inlet of the trap filter chamber thereby substantially reducing particulate by-product build-up at the inlet to the trap filter caused by temperature-pressure related precipitation.