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Analysis of trace impurities in semiconductor-grade metal alkyl compounds by inductively -coupled plasma spectrometry
Group III Metal alkyl compounds, such as trimethylindium (TMI), trimethylaluminum (TMA), and trimethylgallium (TMG) are used in metal organic chemical vapor deposition (MOCVD) process to grow semiconductor layers. The analysis of these metal alkyls that are used for growing semiconductor layers is important to ensure product quality. In addition to determining the impurity concentration, its speciation is equally important. This is because volatile impurities are more harmful to the product than the non-volatile ones because they get easily incorporated in the final product. Attempts were made to analyze the samples by inductively coupled plasma-atomic emission spectrometry (ICP-AES) by dissolving them in xylene and kerosene. Different types of calibrations were performed and it was determined that a positive bias exists if non-volatile standards are used for quantification of analytes. This bias is mainly because the impurity analytes are volatile in nature hence more sensitive in nature. A chemometric scheme was developed to remove this calibration bias by analyzing samples at two different spray chamber temperatures. This scheme results in data that are consistent with decomposition experiments where the sample was converted to inorganic form prior to analysis. As verification experiments, exponential dilution results were obtained and they agree with decomposition and chemometric schemes. A graphite furnace was used for the quantification of volatile analytes. Chemical modifiers (ethers with heavy alkyl groups) were used to achieve a temporal separation between the matrix and the analyte. This solved the matrix suppression effect on analytes due to simultaneous vaporization of the matrix and analyte. The concentrations of analytes from different techniques were found to be consistent with each other.
Gupta, Rajesh Kumar, "Analysis of trace impurities in semiconductor-grade metal alkyl compounds by inductively -coupled plasma spectrometry" (2000). Doctoral Dissertations Available from Proquest. AAI9978504.