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 S 11 signal is expected to vary monotonically with the doping concentration. S 11 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 S 11 data with the differential dS 11 /dV data commonly used for dopant profiling. In standard SMM operating conditions, the S 11 data are monotonic over the full frequency range of 1-20 GHz, while the dS 11 /dV data show a monotonic dependence on the doping concentration between 1014 and 1020 atoms/cm 3 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 dS 11 /dV for dopant profiling applications. We also show S 11 based calibrated capacitance measurements and capacitance-voltage curves of differently doped sample regions and of p-n junction interfaces.