Frequency Analysis of Dopant Profiling and Capacitance Spectroscopy Using Scanning Microwave Microscopy

Broadband dS11 /dV dopant profiling at gigahertz frequencies and in situ calibrated capacitance-voltage spectroscopy of silicon p-n junctions using scanning microwave microscopy (SMM) are reported. Using a 3-D finite element model to obtain the E-field distribution at the tip/sample interface, we show that the reflected S₁₁ signal is expected to vary monotonically with the doping concentration. S₁₁ imaging performed on two doped silicon samples confirms the simulation results for the full SMM operating frequency range of 1-20 GHz. In this frequency range, we compare the S₁₁ data with the differential dS₁₁ /dV data commonly used for dopant profiling. In standard SMM operating conditions, the S₁₁ data are monotonic over the full frequency range of 1-20 GHz, while the dS₁₁/dV data show a monotonic dependence on the doping concentration between 1014 and 1020 atoms/cm³ only at lower frequencies. A nonmonotonic behavior is typically observed at higher frequencies and an interpretation based on charged carriers dynamic is given. This is important for routine and robust frequency selection workflows of dS₁₁/dV for dopant profiling applications. We also show S₁₁ based calibrated capacitance measurements and capacitance-voltage curves of differently doped sample regions and of p-n junction interfaces.