Direct comparison of cross-sectional scanning capacitance microscope dopant profile and vertical secondary ion-mass spectroscopy profile

Abstract

The scanning capacitance microscope (SCM) has been shown to be useful for quantitative 2D dopant profiling near the surface of silicon. An atomic force microscope is used to position a nanometer scale tip at a silicon surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been recently demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. The applied ac bias voltage as a function of position is then input into an inversion algorithm to extract the dopant density profile. The new feedback approach allows for the use of a quasi-1D model in the inversion algorithm. Since there are no alternative 2D dopant profiling techniques which are well established at present, evaluation of the quantitative character of 2D SCM measured profiles has been a challenge. To avoid this obstacle, we have developed sample preparation methods which allow direct comparison of lateral SCM measured profiles on cleaved wafers (cross-sectional plane) with vertical secondary ion-mass spectroscopy (SIMS) profiles. The direct comparison of inverted SCM data and SIMS profiles indicates that quantitative 2D dopant profiling can be achieved by the SCM on a nanometer scale.