Successful implementation methods of atmospheric CVD on a glass manufacturing line

Abstract

Large area thin film coating of glass substrates adds value and performance to the glass that is often unachievable by conventional tinting of the glass composition. Far infra red coatings, applicable for low emittance window glass, have been commercially successful due to their ease of manufacture and enhanced performance compared to uncoated glass. By producing the coated glass by chemical vapor deposition (CVD) directly on a float glass manufacturing line, economies of scale and production simplicity are achievable that escape off-line deposition technologies. The critical success factors that make on-line coatings commercially successful, such as float bath compatible, high deposition rate chemistry and flexible reactor design will be discussed. Manufacturing difficulties arise with on-line coatings, however, due to the speed of glass production along with the lack of atmosphere control inherent to the glass making process. Due to the highly thermally activated chemistry of CVD, stable substrate temperatures as well as insensitive thin film designs are necessary for high product yields and quality control. By utilizing novel multilayer structures, normal and off angle color can be controlled such that typical production thickness nonuniformities are masked thereby yielding an aesthetically pleasing product. Material and design constraints for on-line low emittance glass, mirror coatings and architectural solar control coated glass produced using these techniques will be described. CVD deposition chemistry also is an important factor which is critical to efficient on-line coating processes. Individual thin film growth rates need to be typically greater than 200 Å/s for commercial on-line coatings. High material loading, with gas phase precursor concentrations up to 3–4%, are often necessary to achieve such growth rates. The CVD chemistry must be stable and compatible with the high loading and temperature such that high deposition efficiencies can be achieved without excessive particulate production or gas phase ignition. CVD precursor design and vaporization techniques will be described which can satisfy these constraints. With proper choice of precursor and additive chemistry, high deposition efficiency, long runtime and low cost deposition processes can be achieved. When combined with thickness insensitive thin film designs, these chemistries have successfully produced a wide variety of cost-effective on-line coated products.