A portable instrument has been developed for measuring silicon-containing aerosols in near real-time using laser-induced breakdown spectroscopy (LIBS). The instrument uses a vacuum system to collect and deposit airborne particulate matter onto a translatable reel of filter tape. LIBS is used to analyze the deposited material, determining the amount of silicon-containing compounds present. In laboratory testing with pure silica (SiO2), the correlation between LIBS intensity for a characteristic silicon emission and the concentration of silica in a model aerosol was determined for a range of concentrations, demonstrating the instrument’s plausibility for identifying hazardous levels of silicon-containing compounds.
Two-side Surface Photovoltage (TS-SPV) based on measuring SPV from both wafer sides is proposed as novel approach for silicon surface contamination monitoring. TS-SPV is applied to investigate the process of diffusion of implanted iron in lightly doped p-type silicon during Rapid Thermal Anneal (RTA). Good correlation was found for iron distribution vs. RTA conditions in the temperature range from 375 to 1100oC. The portion of electrically active interstitial iron measured by TS-SPV was studied as function of RTA time and temperature conditions. Low thermal budget RTA combined with TS-SPV is proven to be effective to monitor iron contamination and to identify the contamination sources character and location.
Although N-type CZ material exhibits a high initial lifetime ideally suited to the fabrication of high efficiency solar cells, degradation of wafer lifetime during processing leading to a decrease in cell efficiency can occur due to the growth of pre-existing small oxygen clusters. The mechanism for lifetime degradation associated with oxygen defects is discussed. Lifetime degradation can be avoided and high cell efficiencies achieved by using wafers with a lower initial oxygen concentration.
One major source of metals contamination during high temperature processing are metals pre-deposited on the wafers surface before thermal treatment and metals cross-contamination from other wafers and/or furnace components. This study investigates the mechanism of metals transfer via gas phase vs. temperature and oxygen gas flow conditions. We also investigated the crosscontamination from Silicon Carbide (SiC) components at elevated temperatures. Cross-contamination from SiC can be explained as (a) metal diffusion from the direct contact area between silicon wafer and SiC (MDD -Metals Direct Diffusion) and (b) metal desorption from the SiC surface and re-adsorption on the silicon wafer surface from the gas phase (MAG -Metals Adsorption from Gas Phase). Both MDD and MAG contamination components are driven by SiC surface metal contamination. Using high resolution Surface Photo-Voltage (SPV) iron mapping we investigated the character of iron cross-contamination. Iron diffusion and desorption activation energies were experimentally determined.
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