A mathematical model for the rate of CuCl vaporization was developed based on the laws of mass and energy conservation and constitutive relationships describing low pressure gas flows. This model was needed for the design of a unit operations scale system to be used in solar cell fabrication. This system continuously produces a Cu2S film on a moving CdS substrate by a solid state reaction. Experimental verification of the model was carried out using laboratory scale experiments. Over a range in vaporization rates that are useful for unit operations scale experimentation 0.225 to 5.66×10−6 kg CuCl/s, model behavior is in good agreement with experimental observation. Over the major portion of this range calculated and observed rates agree within 10%. Agreement is no worse than 18.5% over the entire range. Aspects of the model relevant to commercial scale design are discussed.
A contamination control study of a Silicon Valley Group Thermco Systems Vertical Thermal Reactor(VTR) is presented. Trace elements of contaminants such as water vapor and oxygen have been shown to significantly affect the integrity of the silicon nitride film deposited by the low pressure chemical vapor deposition (LPCVD) process. This study documented the effects of process parameters on gaseous contamination levels, i.e., O2 and H2O vapor. Starting with a baseline process, the effects of an excursion of pre-deposition temperature ramp-up and stabilization condition, wafer load/unload and various post deposition conditions were explored. An axial profile of moisture and oxygen levels along the wafer load was obtained using Linde's Low Pressure Reactor Analysis(LPRAS) methodology. In addition, other process parameters such as gas flow rates during load and unload of wafers, pre-deposition N2 purge and process tube exposure time to ambient environment were- investigated. The wafers were analyzed for contaminants on the wafer surface or in the deposited silicon nitride film using FTIR and Auger spectroscopy techniques. They showed low levels of Si-O and no measurable Si-H or N-H bonds.
The study of the wafer atmosphere during processing has become a key practice in understanding interactions of the process gases with the wafer, internal chamber surfaces and other process gases. For today's ULSI fabrication, Low Pressure Chemical Vapor Deposition (LPCVD) of tungsten has become common for sub-micron contact and via filling and was the chosen process for this investigation. The wafer atmosphere during key process steps of the tungsten LPCVD process has been characterized by mass spectrometry. During the tungsten LPCVD process studied, the TiN surface was first conditioned for tungsten deposition by generating active nucleation sites. This is followed by the actual deposition. After the deposition, wafer backside etch with NF3 plasma, wafer removal and an in situ chamber clean with NF3 and H2 plasmas performed. This paper discusses the mass spectral analysis of the tungsten LPCVD process during the nucleation, backside etch and in situ chamber clean process steps. Additionally, this paper describes benefits of in situ gas analysis.
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