Research On MOCVD On-Line Monitoring Instrument

MOCVD (Metal Organic Chemical Vapor Deposition) is one of the key technologies inmanufacturing optoelectronic devices based on the nitride semiconductor and ZnO etc. Manyconditions and parameters involved in the epitaxial growth process of MOCVD have effectson the quality and performance of the devices directly. On-line monitoring instrument is theimportant part of MOCVD with the on-line measurement of temperature, film thickness,material and warpage during the process. This dissertation focuses on the demand for theparameter measurement of MOCVD. An on-line monitoring instrument wih temperature, filmthickness and warpage measurement was carried out.(1)The installation of the on-line instrument in the chamber of MOCVD and themultiplexing structure of temperature, film thickness and warpage measurement weredicussed, guaranting the uniformity of the flow and the temperature field.(2)Based on the infrared measurement theory, a dual-wavelength measurement theory withinnovative structure and correction algorithm was proposed. Four-stage amplifier circuitof weak signal, constant temperature control circuit with thermoelectric cooler, ADcapture circuit, precise capture position circuit of the modulation susceptor and the issuesin the Printed Circuit Board layout, all of them were designed. Experiment illustrates thatthe technical feature of the on-line instrument reach the requirement: temperature rangefrom750℃to1150℃; repeatability within1℃; the accuracy within1℃upon1000℃,noise within0.2℃, the accuracy within5℃from750℃to1000℃, noise within0.8℃;insentive to changes in height within2mm. Finally, the temperature field distribution wasanalyzed by the on-line monitoring instrument.(3)Baed on the principle of optical interference, the film thickness was measured bydetecting the reflected light of the laser. The epitaxial material and the roughness were alsodiscussed by analyzing the interference curves. Constant power drive circuit of laser,modulation circuit with direct digital sythesizer and lock-in amplifier circuit of weaksignal were designed. The process of the epitaxial growth, the growth rate and the filmthickness were analyzed from the interference curves in experiment.(4)Four major effects contributing to the wafer warpage during epitaxial growth werediscussed. The theory and the optical structure of the warpage measurement were stydied,as well as the measurement circuit based on the Position Sensitive Detector. Besides, the calculation algorithm, the error analysis and the solution were carried out.(5)The modular design was proposed based on the functional requirement of the on-lineinstrument. The software structure was builded with uC/OS-II operating system. Thefunctional designs were completed, improving the expansion and the compatibility of theinstrument.The temperature and the film thickness measurement were completed in the on-linemonitoring instrument of this paper, and the design of the warpage measurement wascarried out. The system test verified that the design was right and could be developed formore applications, such as flow monitor and gas pressure control etc, which giveimportant guidances to the design of the on-line monitoring instrument on MOCVD.