In the manufacturing process of float glass often atmospheric pressure chemical vapourdeposition (APCVD) reactors are integrated on-line for the deposition of functional thinsolid films. Such functional films have applications in architectural glass, flat panel displaysand solar cells. As glass moves downstream in the process, the thin film is deposited attemperatures between 500 to 700°C. The high temperatures make it difficult to monitor thedeposition process and thin film quality control is commonly done at the end of the line or atlower temperatures. A time delay therefore exists between the point of thin film depositionand subsequent quality control, which can lead to large quantities of defective product beingproduced before faults are detected.It is therefore desirable to monitor in the APCVD reactor for rapid feedback of unexpecteddeviations from desired process conditions, reaction progress and fault detection.High uniformity of film properties across the substrate are important, but APCVD reactorsare often empirically designed and the detailed chemical reaction mechanism is unknown.This leads to inefficient gas flow patterns and precursor utilization as well as difficulties inthe design of new reactors.The APCVD deposition of tin oxide from the mono-butyl-tin tri-chloride (MBTC) is anexample of such a process.Optical monitoring instruments in-situ and in-line on the APCVD reactor provided rapidfeedback about process stability and progress non-invasively. Near infrared diode laserabsorption spectroscopy (NIR-LAS) monitored the concentration of the reaction specieshydrogen chloride (HCl) in-situ and spatially in the coating zone. A mid-infrared gratingabsorption spectrometer (IR-GAS) with novel pyro-electric array detector monitored theconcentration of precursor entering the coating system simultaneously. In combination theseinstruments provide the means for rapid process feedback.Fourier transform infrared absorption spectroscopy (FTIR) was used to investigate theunknown decomposition pathway of the precursor to find the yet unknown key tin radical thatinitiates film growth. Stable species forming during MBTC decomposition over a temperaturerange of 170 to 760°C were investigated but the tin intermediate remains unknown.Computational fluid dynamics (CFD) is routinely employed in research and industry for thenumerical simulation of CVD processes in order to predict reactor flow patterns, depositionrates, chemical species distribution or temperature profiles. Two and three dimensionalmodels with complex geometries and detailed reaction models exist.A three dimensional computational fluid dynamics (CFD) model of the used APCVD reactorwas built using the Fluent CFD software. The numerical simulation included a chemicalmodel that predicted qualitatively the chemical species distribution of hydrogen chloridein the gas phase. This was confirmed through comparison with NIR-LAS results. Designshortcomings due to inefficient flow patterns were also identified.In combination the optical tools developed provide the means for safe and efficient manufacturing of thin films in APCVD reactors. CFD simulations can be used to increase precursorutilization and film uniformity in the development of new reactor designs.
|Date of Award||1 Aug 2014|
- The University of Manchester
|Supervisor||Philip Martin (Supervisor)|
- Tin oxide
- Process monitoring
- Near-infrared diode laser absorption spectroscopy
- Fourier transform infrared spectroscopy