Current efforts in the Process Analytical Chemistry and Control Technology group at Bell Laboratories, Lucent Technologies, have focused on the development of an online method for real-time characterization of organiccontaining effluents (principally trimethyamine (TMA) and methanol) produced during a high-temperature processing. On-line analysis of the gas streams was performed by combining FT-IR spectrometry with partial least squares (PLS) to obtain quantitative information for process control. The gas-phase infrared spectra were measured at a resolution of 16 cm -1 under atmospheric conditions. The correlation coefficients for all the components including water were larger than 0.999, and the standard errors of prediction were much less than 1% by weight. The effect of CO 2 on the predictability of other components is discussed. Results of our experiment showed that the predicted errors for TMA and methanol increased by as much as 10 and 15%, respectively, as the amount of CO 2 increased to 100% of the most intense absorption peak in the spectra.
An uitrasonic timsof-flight method Is described for continuous concentration monitoring of in situ electrochemically generated arsine. The method is based on accurate measurements of the speed of sound, which is a sensitive function of the composition of a binary gas mixture, particularly with gases of disparate molecular weights, i.e. arsine and hydrogen. Speed of sound measurements made on flowing streams of argon-helium and arsine-hydrogen at ambient temperature and pressure are in excellent agreement with values predicted by using an acoustic model based on Meal gas theory. Highly repeatable calibration curves are obtained for each binary gas mixture analyzed over the entire range (0-100%) of compositions. The callbration was found to be independent of the volumetric flow rate of the gas mixture over the range of pressures 0-30 psig. The ultrasonic method offers a practical solution to accurate and reliable concentration monitoring of a wide range of gas-phase reagents used in the fabrication of devices.
The use, transportation, and storage of the hazardous gas, arsine, raise serious safety issues. Consequently, there is considerable interest in the generation of arsine on demand from less hazardous substances. We report the first use of in situ generated arsine for III-V epitaxy. The gas has been generated electrochemically at an arsenic cathode in an aqueous electrolyte and used to supply a hydride vapor phase epitaxy reactor. InGaAs/InP test structures were grown on InP substrates and were similar to comparison structures grown using tank arsine. Recessed-gate enhanced Schottky metal-semiconductor field-effect transistors were fabricated and exhibited well-behaved current-voltage characteristics.
An experimental investigation was conducted on the electrochemical generation of arsine from high purity (99.9999%), vapor‐deposited arsenic metal in alkaline solutions. A novel method using high‐sensitivity mass spectrometry (MS) coupled to an electrochemical hydrogen calibration (MS‐HC) cell was employed for quantitative analysis of gaseous products. Applications of this method showed the current efficiency for arsine formation to be 95–97% over two orders of magnitude change in the current density. An independent chemical method involving direct oxidation of arsine by silver nitrate confirmed the current efficiency values obtained with MS‐HC. MS experiments conducted up to 200 atomic mass units reveal that arsine and hydrogen are the only gaseous species produced in the electrochemical reduction of arsenic. A scheme is presented for an on‐demand electrochemical generator system that can provide high‐purity arsine over a wide range of concentrations and flow rates to meet the requirements for practical electronic processing applications.
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