Surface analysis, depth profiling, and evaluation of Si cleaning procedures by postionization sputtered neutral mass spectrometry

The characterization of metallic impurities and dopant profiles near or on wafer surfaces is increasingly important as Si device features shrink. Conventional methods of surface analysis are ineffective in the near‐surface region. We have used laser postionization sputtered neutral mass spectrometry to determine the efficacy of dry cleaning methods of silicon surfaces and perform shallow doping depth profiling. Unlike secondary ion mass spectrometry, postionization is free of matrix effects in the near‐surface region (<100 Å), and permits quantitative analysis. The ability of this technique to track the cleaning of contaminated wafers is demonstrated. Hydrocarbon contamination on the surface limits the determination of Ca. The importance of the ubiquitous hydrocarbon contamination on wafers is also seen in interpreting very shallow depth profiles. Preliminary results demonstrate that ultrahigh intensity (10¹⁴ W/cm²) postionization shows promise as a nonselective, but effective means for surface analysis and shallow depth profiling.