2D carrier profiling of InP-based structures using scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM)

Scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM) are powerful techniques originally developed for measuring two-dimensional carrier distribution in Si device structures with nanometer spatial resolution. Both methods are based upon an atomic force microscope (AFM) equipped with a conducting tip that is biased relative to the sample. In SSRM, the spreading resistance value derived from the measured electrical current is a function of the local carrier concentration at the surface region surrounding the probe´s tip. SCM provides two-dimensional information on carrier concentration through measurement of the dC/dV signal of the MOS capacitor formed by the probe and the semiconductor sample. In this paper, we report the successful application of SSRM and SCM to the analysis of various InP semiconductor device structures. Results are presented for cross-sectioned multi-layer epi test structures. Comparison of the SCM and SSRM profiles with one-dimensional secondary ion mass spectrometry (SIMS) depth profiles shows good qualitative agreement. Spatial resolution (<20 nm), dynamic range (10¹⁵-10²⁰ atoms/cm³), and reproducibility are discussed for both methods