Trace gas analysis by diode laser cavity ring-down spectroscopy

Abstract

Semiconductor manufacturers and UHP gas suppliers focus great attention and resources on monitoring trace moisture in semiconductor gases. Laser infrared technique is considered to be one of the only methods available that has the sensitivity for moisture contamination monitoring in corrosive gases. By adsorptive forces, moisture strongly adheres to any surface with which it comes in contact. As wafer features approach 0.10 /spl mu/m, there is an ongoing need to monitor for and control moisture. Trace moisture in ambient bulk gases must be measured currently to less than 1000 PPT, and by 2008, to less than 100 PPT. For moisture in corrosive gases, less than 500 PPB is required today, a level that is difficult to detect using existing analytical technologies. Thus trace moisture analyzers must have ultralow sensitivity and be extremely responsive to avoid losses of silicon wafer batches in semiconductor processing that are worth more than several hundred thousand dollars. In this work, trace moisture monitoring was done by diode laser cavity ring-down spectroscopy incorporated in the MTO-1000-H/sub 2/O analyzer.