FTIR based process control for industrial reactors

Aiming to process control of industrial high yield / high volume CVD reactors, the potential of Fourier transform infrared spectroscopy (FTIR) has been checked as a monitoring tool. Tin oxide deposition on glass by oxidation of dimethyl tin dichlorid in a cold-wall thermal CVD reactor was selected as test case. Four different FTIR monitoring modes have been evaluated and found feasible : transmission, (gas) emission, reflection and surface emission. The most detailed information of the composition of the gas atmosphere in the deposition zone is derived from the transmission and (gas) emission measurements. The emission mode is best suited for high temperature CVD reactors, needs only low effort for optical adaptation of the monitoring system but higher effort in data treatment for process control. Information on both gas composition and surface layer are derived from the reflection and the surface emission modes. Depending on the polarization state of the surface emission, spectra contain information either on the sample surface only or on the reacting gas phase, too

Infrasorb: Optical detection of the heat of adsorption for high throughput adsorption screening of porous solids

The demand for fast screening methods in modern materials chemistry led to the development of a room temperature operated high-throughput tool for adsorption screening. Within five minutes a porosity screening of a large sample pool can be realized. Using a variety of different porous materials (activated carbons, porous polymers, metal-organic frameworks, zeolites) and the test gas n-butane, the reliability of the new instrument is shown. Furthermore, possible applications in the determination of n-butane capacities and BET surface areas are given as well as the application in synthesis or product control. The presented data exhibit high quality factors for the correlation of integrated signal intensity (heat of adsorption) and specific surface areas (above 0.97). As an example for the applicability of other gases that can be used with this tool, screening measurements using cyclohexane as test gas are also presented. The developed automated screening tool is an important step to overcome the bottle-neck between high-throughput syntheses technologies developed in the last decades and measurement of adsorption properties

FTIR monitoring of industrial scale CVD processes

Chemical vapour deposition (CVD) as well as infiltration (CVI) processes are key technologies in many industrial sectors, including extensive use in micro electronics, surface protection of components, for energy efficient optical coatings on glass for buildings and for manufacturing fibre reinforced ceramic composite materials. Gaseous precursors containing the elements to be deposited are pyrolysed at the heated substrate or, alternatively, by exciting the molecules with laser photons or by a plasma. Although the techniques are used on a technological scale, the underlying chemistry is not completely understood. The goal of the presentation is to improve CVD process control by a multipurpose, knowledge based feedback system for monitoring the CVD/CVI process with in-situ FTIR spectroscopic data as input information. In the presentation, three commonly used, and distinctly different, types of industrial CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch p rocess for manufacturing carbon fibre reinforced SiC composites for high temperature applications, (ii) a continuously driven CVD thermal process for coating float glass for energy protection, and (iii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibres (i) The CVI process operates near 1000oC, in the low pressure region and with CH3SiCl3 (MTS) as a SiC precursor. Using FTIR emission spectroscopy, several gaseous species have been detected including MTS, SiCl2, (SiCl3)n=1,2, SiCl4, HSiCl3, CH4, CH3Cl and HCl which, consequently, can be monitored simultaneously. (ii) The CVD process operates at atmospheric pressure. A model reactor has been developed for studying the concentration dependence of FTIR emission spectra. The measured spectra are compared with calculated spectra which have been derived by optical modelling of a multilayer based optical model. (iii) Based on an industrial 6kW cw-CO2- laser, a laser driven process currently runs in a prototy pe coater. Layers of graphitisised carbon and several ceramic materials (SiC, TiCxNy, TiB2, BN, etc.) have been deposited on carbon fibres and on SiC fibres. Depending on the selected precursor, the chemistry of the laser driven CVD process is characterised by photothermal reaction paths, typically in the temperature region 1300oC -2500oC and photolytical paths. The FTIR measurements have been carried out by rapid extraction of the gaseous reaction products and measurements in an optimised volume gas cell. As an example, the deposition of SiC layers from MTS results in the detection of HCl, HSiCl3, H2SiCl2, SiCl2, CH4, CO and C2H2

NIR diode laser based process control for industrial CVD reactors

The proposed new technical approach for CVD process control is characterised by a "chemistry based" feedback system with in-situ optical data as input information. The selected optical sensors continuously analyse the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties, which in turn establish a data basis for process control. Diode laser spectroscopy in the near infra red (NIR-DLS) has been successfully applied for monitoring industrial CVD reactors. This technology has some notable potential advantages for production process applications. For example, the technology is robust and simple to operate, interference between species detection can be reduced, and simultaneous multi-point monitoring is readily achieved. The new process control approach is currently being verified on different industrialised CVD coaters. The paper will present some results of recent process monitoring studies on deposition of SnO2 layers on glass, based on the oxidation of (CH3)2SnCl2, which is used in high volume production for low-E glazings. Kinetic investigations support the empirically determined stiff correlation between gas phase composition and deposition rate

NIR Diode Laser Based Process Control for Industrial CVD Reactors

The proposed new technical approach for CVD process control is characterised by a chemistry based feedback system with in-situ optical data as input information. The selected optical sensors continuously analyse the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties, which in turn establish a data basis for process control. Diode laser spectroscopy in the near infra red (NIR-DLS) has been successfully applied for monitoring industrial CVD reactors. This technology has some notable potential advantages for production process applications. For example, the technology is robust and simple to operate, interference between species detection can be reduced, and simultaneous multi-point monitoring is readily achieved . The new process control approach is currently being verified on different industrialised CVD coaters. The paper will present some results of recent process monitoring studies on dep osition of SnO2 layers on glass, based on the oxidation of (CH3)2SnCl2, which is used in high volume production for low-E glazings. Kinetic investigations support the empirically determined stiff correlation between gas phase composition and deposition rate

NIR diode laser based process control for industrial CVD reactors

The proposed new technical approach for CVD process control is characterised by a "chemistry based" feedback system with in-situ optical data as input information. The selected optical sensors continuously analyse the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties, which in turn establish a data basis for process control. Diode laser spectroscopy in the near infra red (NIR-DLS) has been successfully applied for monitoring industrial CVD reactors. This technology has some notable potential advantages for production process applications. For example, the technology is robust and simple to operate, interference between species detection can be reduced, and simultaneous multi-point monitoring is readily achieved. The new process control approach is currently being verified on different industrialised CVD coaters. The paper will present some results of recent process monitoring studies on deposition of SnO2 layers on glass, based on the oxidation of (CH3)2SnCl2, which is used in high volume production for low-E glazings. Kinetic investigations support the empirically determined stiff correlation between gas phase composition and deposition rate