Extraction of the Trench Sidewall Capacitances in an n-Type 4H-SiC Trench Metal– Oxide–Semiconductor Structure

In this work, a method was investigated to extract trench sidewall and trench bottom capacitances of a SiC trench metal-oxide-semiconductor (MOS) structure. Five groups of 4H-SiC trench MOS capacitors were designed and fabricated, with various trench bottom widths and trench mesa widths. High-frequency capacitance-voltage (HFCV) measurements at 100 kHz were performed on these trench MOS structures. The relationships between trench MOS capacitances and the widths of trench bottom as well as trench mesa were studied. As expected, under the same bias voltage, the measured trench MOS capacitances were proportional to the trench bottom widths and trench mesa widths. Based on this, the contributions of capacitances from the bottom, mesa, and sidewall of trench in trench MOS structure were studied systematically. The oxide thicknesses at different locations in trench were extracted. The C-V characteristics of the MOS capacitors from trench sidewall and trench bottom could also be deduced, from which the flat-band voltage and the charges in oxide of these two MOS capacitors could be subsequently calculated and analyzed. This method provides a convenient and precise technology to monitor process control in SiC trench MOSFETs manufacturing.