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

Broadband dS(11)/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 aremonotonic over the full frequency range of 1-20 GHz, while the dS(11)/dV data show a monotonic dependence on the doping concentration between 10(14) and 10(20) 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.