CHARACTERIZATION OF NI ON SI WAFERS - COMPARISON OF SURFACE-ANALYSIS TECHNIQUES

The need for improved characterization of materials used in the fabric ation of semiconductor devices has been driven by the semiconductor in dustry's desire to increase device densities on substrate. This need i s reflected in the analytical surface science community by efforts to develop methods for detection of trace impurities on semiconductor sub strates at extremely low levels. With improvements in standard techniq ues continually occurring, and with new methods of trace analysis alwa ys being developed, it is important to assess the relative abilities o f the suite of surface analysis techniques available for materials cha racterization and to develop well-characterized standard samples for t hese comparisons. This paper reports on a collaborative effort to revi ew the capabilities of several approaches to trace surface analysis. A s a test case, Ni contamination of Si wafers in the dose range 10(14)- 10(10) cm-2 has been chosen. The emphasis of this paper will be on the capabilities of SARISA (surface analysis by resonant ionization of sp uttered atoms) as an example of laser post-ionization secondary neutra l mass spectrometry for the detection of contaminants in the near-surf ace region. Results on analyses of the same standard samples by other techniques will also be presented. These techniques include total refl ection x-ray fluorescence and heavy ion backscattering spectrometry. T he results of this comparison show that there are several techniques t hat can accurately determine metal contaminations on Si wafers in this concentration range and that the method of choice depends on other co nsiderations, such as speed or accuracy of analysis.