Comparison of APCVD to LPCVD Processes in the Manufacturing of ZnO TCO for Solar Applications

A FirstNano EasyTube 3000 CVD system with a 3” diameter horizontal tube furnace was used to investigate the optimization of both APCVD (Atmospheric Pressure Chemical Vapor Deposition) and LPCVD (Low Pressure Chemical Vapor Deposition) processes to grow both boron and fluorine doped ZnO films with a sheet resistance, slice resistance and haze suitable for their potential utilizations as TCO (Transparent Conductive Oxide) layers for photovoltaic applications. Growth rates as high as 100 nm per minute have been obtained in some parameter regions for both processes. In both cases the resulting material property parameters were the same or better than reported in the literature. Although the horizontal hot wall CVD R&D reactor is not optimum for uniform TCO thin film deposition it allowed us to investigate the interrelationship of the most critical parameters with the resulting material properties. The driving force for this work is the ultimate goal of demonstrating a process parameter solution suggesting that ZnO films (usable for either display system manufacturing and/or photovoltaic applications) can be deposited with optimized material properties that are comparable to LPCVD or sputtering processes, but that the APCVD solution could be more economical for large scale thin film ZnO coating implementation. Ultimately our desire is to transfer such a ZnO deposition process to our proprietary, APCVD CVDgCoat™ platform, which has the ability to coat up to 4 meter wide glass sheets and metal foils.