Control of Impurities in the Epitaxial Growth of High Quality GaAs. Response of the Molecular Beam-Mass Spectrometer Analysis and Calibration.

摘要

A molecular beam-mass spectrometer (MBMS) has been developed to sample ambient gas atmosphere in epitaxial growth systems at high temperatures and at atmospheric pressure. At present the MBMS is capable of analyzing ppm quantities of gaseous species that result from chemical transport reactions between the ambient H2 atmosphere and the growth system components (e.g., fused quartz and graphite). The MBMS consists of three differentially pumped stages separated by a nozzle and a skimmer orifice and a detector aperture. The gas is expanded through the nozzle to establish a supersonic flow region (Mach disc) which is sampled by the skimmer to develop a well-collimated molecular beam. The molecular beam is then ionized and detected by a quadrapole mass analyser. The response and interpretation of the data from the MBMS are analyzed and discussed to obtain an overall calibration of the system. The sensitivity for most gaseous species in H2 at atmospheric pressure and at 800 C is better than 1 ppm without chopping the beam. Initial results indicate that there are ppm levels of Ar, CO and H2O in palladium purified H2. In addition, the formation of SiO and H2O by chemical transport reactions between H2 and fused quartz at 700 C and above are in good agreement with existing high temperature thermodynamic data. (Author)