Influence of sample parameters on TXRF analysis of semiconductor surfaces

Due to its outstanding properties TXRF is widely used in semiconductor industry for the analysis of silicon wafer surfaces. The presence of metal contamination on the wafer surface is a serious limiting factor to process yields for the production of integrated circuits.

In general TXRF is known to allow for linear calibration typically using an internal standard for quantification. For small sample amounts (low ng region) the thin film approximation is valid neglecting absorption effects of the exciting and the detected radiation. However, for higher total amounts of samples deviations from the linear relation between fluorescence intensity and sample amount have been observed (saturation effect - figure 1).

 

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Fig.1 Linearity test

Aim of the project is an investigation of TXRF sample parameters (e.g. shape, density) and their influence on absorption effects and hence the fluorescence intensity to improve the statistical quality of TXRF quantification. Sample shapes on different reflector materials, as a result of drying, different preparation techniques and reflector materials will be investigated by micro-XRF and confocal white light microscopy (figure 2).

 

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Fig. 2 Image of a 500 ng As sample on a Si reflector

A mathematical model will be developed to simulate fluorescence intensities and absorption effects with respect to the sample parameters. The results of the measurements and the simulations will be used to characterize the ideal TXRF sample and to improve the sample preparation techniques.