硅空间电荷区金属污染物的监测
摘要: Metal surface contaminantscanbe successfully monitored oversilicon processing steps using theSCP/SPVtechnique, and applying recombination lifetime and depletion widthasqualification parameters.
The carrier-recombination lifetime measurement is a recognized technique to provide metal contamination control in silicon wafers. However, commonly used surface photo voltage (SPV) techniques are designed to measure metal dissolved in the silicon bulk . This restricts their capability because surface contamination is as important, if not more important. The exact magnitude of metal concentration cannot be reliably estimated because metals-iron in particular-exhibit enormous complexing activity, and the diffusion length/lifetime considerably differs for different complexes, metal states (atomic, precipitated or gettered), and charge state of the diffusing metal that lead to an underestimation of the total metal concentration. Also, the single lifetime measurement does not distinguish between different metal contaminants.
The surface charge profiler (SCP) is an alternative technique that allows measuring recombination lifetime within the subsurface space charge region (SCR) that is a considerable part of the silicon device area. The metals might be distinctive while using a reassociation kinetics approach.1 Since impurities are always introduced into silicon through the surface, properprocess conditions allow the metal traces to remain on the surface and be evaluated. If an accurate metal content is not needed, this competing method is attractive to evaluate metal present in different device fabrication processes including oxidation/diffusion steps.
SCP utilization
The SCP supplied by QC Solutions Inc. (Billerica, Mass.) performs process-monitoring functions withouttouching the wafer surface, or in any other way affecting the surface''s condition. The tool enables the measurement of the near-surface doping type, the SCR''s width, doping concentration/resistivity, and the minority-carrier recombination lifetime. It also maps these parameters.
