Advances in experimental technique for quantitative two-dimensional dopantprofiling by scanning capacitance microscopy

Several advances have been made toward the achievement of quantitative two- dimensional dopant and carrier profiling. To improve the dielectric and cha rge properties of the oxide-silicon interface, a method of low temperature heat treatment has been developed which produces an insulating layer with c onsistent quality and reproducibility. After a standard polishing procedure is applied to cross-sectional samples, the samples are heated to 300 degre es C for 30 min under ultraviolet illumination. This additional surface tre atment dramatically improves dielectric layer uniformity, scanning capacita nce microscopy (SCM) signal to noise ratio, and C-V curve flat band offset. Examples of the improvement in the surface quality and comparisons of conv erted SCM data with secondary ion mass spectrometry (SIMS) data are shown. A SCM tip study has also been performed that indicates significant tip depl etion problems can occur. It is shown that doped silicon tips are often dep leted by the applied SCM bias voltage causing errors in the SCM measured pr ofile. Worn metal coated and silicided silicon tips also can cause similar problems. When these effects are tested for and eliminated, excellent agree ment can be achieved between quantitative SCM profiles and SIMS data over a five-decade range of dopant density using a proper physical model. The imp act of the tip size and shape on SCM spatial accuracy is simulated. A flat tip model gives a good agreement with experimental data. It is found that t he dc offset used to compensate the C-V curve flat band shift has a consist ently opposite sign on p- and n-type substrates. This corresponds to a posi tive surface on p- type silicon and to a negative surface on n-type silicon . Rectification of the large capacitance probing voltage is considered as a mechanism responsible for the apparent flat band shift of (0.4-1) V measur ed on the samples after heating under UV irradiation. To explain the larger flat band shift of (1-5) V, tip induced charging of water-related traps is proposed and discussed. (C) 1999 American Institute of Physics. [S0034-674 8(99)03001-4].