MONITORING OF GAS-PHASE SPECIES IN METALORGANIC VAPOR-PHASE EPITAXY BY FIBEROPTICS BASED FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

Fiber-optics based Fourier transform infrared (FTIR) spectroscopy is demonstrated as a technique for remote in-situ monitoring of concentration levels of organometallic species in gas delivery lines to metalorganic vapor phase epitaxy (MOVPE) systems. The concentration measurements are based on infrared absorption at 2800-3000 cm(-1) corresponding to C-H stretching vibrations in alkyl ligands. Trimethylgallium (TMG), trimethylindium (TMI), tertiary butyl phosphine (TBP), and tris-dimethylaminophosphine (DMAP) are used in sample monitoring studies. The detection limit varies with the number of C-H bonds from 0.05 Torr at room temperature for TMG and TMI, to 0.006 Torr for DMAP. The ability of the technique to detect chemical species, as well as to monitor concentration levels, is illustrated by the appearance of methane in turn-on transients of TMG and TMI bubblers that have been stored for a length of time. A mathematical analysis of turning on and off flow from a bubbler containing an organometallic precursor is presented and used to identify wall condensation and chemical interactions for TMI and DMAP in gas delivery lines.