Diode laser absorption spectroscopy for process control - Sensor system design methodology

[摘要] A laser absorption spectroscopy (LAS)system has been developed at Lawrence Livermore National Laboratory for process control. LAS has proven itself to be an accurate and reliable method to monitor both density and composition. In this paper the important features and components of an industrial LAS diagnostic are described. Application of this approach to vaporization processes requires careful selection of the species and transitions to be monitored. The relative vapor pressure, hyperfine structure, isotopic frequency shifts, and electronic temperature all effect the selection of a particular transition. In this paper we describe the methodology for choosing the optimal transition or transitions. Coevaporation of a titanium-niobium alloy is used to illustrate the methodology. In a related paper, T.M. Anklam et al.,'Evaporation rate and composition monitoring of electron beam PVD processes' (Surface and Coatings Technology, 76/77 (1995) 681-686), describe the application of this diagnostic to monitoring and controlling composition in a physical vapor deposition process of industrial interest.

[发布日期] 1995-12-01

[效力级别]  Proceedings Paper

[关键词] process control;laser absorption spectroscopy