Gas-phase FT-IR characterization of ion implant process effluents

Ion implant processes utilize materials that are potentially toxic to humans and damaging to the environment. Consequently, a number of preventive measures have been implemented to address environmental control and to minimize worker exposure risks. Safer dopant handling and delivery can be achieved by using reduced pressure gas sources. Materials not implanted onto wafers are instantly exhausted from the tool through roughing pumps or accumulated and later discharged using cryo pumps. Up until now, there has been limited knowledge about the nature and volume of gaseous emissions released by ion implant tools. Such information can be used to assess post-pump environmental and safety hazards, provide indirect measures of dopant utilization efficiencies, and offer crucial details necessary to customize pollution control solutions. This paper summarizes the analyses performed at the exhaust of selected roughing and cryo pumps of an Axcelis GSD-VHE ion implanter. Analyses were performed during standard implant processes using arsine (AsH₃), phosphine (PH₃), and boron trifluoride (BF₃) sources. The characterization study was performed in a quantitative, continuous, in-line mode using a Fourier transform infrared (FT-IR) spectrophotometer. The analytical tool was calibrated in-situ to attain accurate measurements. Continuous monitoring provided time dependent concentrations of selected species during tuning and implant stages. In addition, characterization studies during cryo regeneration identified the temperature dependent release of a number of parent dopant and process by-product species.