Minority carrier lifetime measurements for contactless oxidation process characterization and furnace profiling
Contactless minority carrier lifetime (lifetime) measurements by means of microwave detected photoconductivity are employed for oxidation process characterization and furnace profiling. Characterization is performed on oxidized float zone substrates with high resistivity and outstanding bulk quality, suggesting that the measured effective lifetime is strongly dominated by interface recombination and therefore reflects the oxide quality. The applied approach requires neither test structures nor time consuming measurements and is therefore of particular interest if high throughput is required. The method is used to investigate the impact of oxidation furnace leakage as well as to analyze the oxidation homogeneity across a horizontal oxidation furnace. For comparison, capacitance-voltage measurements are conducted to characterize the oxide properties. It is found that any type of furnace leakage, which induces fixed oxide charges as well as interface states, has a heavy impact on the measured effective lifetime, especially on the shape of generation rate dependent lifetime curves. Furthermore, a distinct lifetime decrease towards the tube door of the oxidation furnace could be observed. The latter is even detectable in an ideal oxidation process, generating high quality oxides. Besides plain equipment characterization, the presented approach is suitable to optimize the oxidation process itself regarding different parameters like temperature, gas flow, pressure, or process time.
Engst, Christian R.