Characterization of 10 μm thick porous silicon dioxide obtained by complex oxidation process for RF application

This paper proposes a 10 μm thick oxide layer structure, which can be used as a substrate for RF circuits. The structure has been fabricated by anodic reaction and complex oxidation, which is a combined process of low temperature thermal oxidation (500 °C, for 1 h at H2O/O2) and a rapid thermal oxidation (RTO) process (1050 °C, for 1 min). The electrical characteristics of oxidized porous silicon layer (OPSL) were almost the same as those of standard thermal silicon dioxide. The leakage current through the OPSL of 10 μm was about 100–500 pA in the range of 0–50 V. The average value of breakdown field was about 3.9 MV cm−1. From the X-ray photo-electron spectroscopy (XPS) analysis, surface and internal oxide films of OPSL, prepared by complex process were confirmed to be completely oxidized and also the role of RTO process was important for the densification of porous silicon layer (PSL) oxidized at a lower temperature. For the RF-test of Si substrate with thick silicon dioxide layer, we have fabricated high performance passive devices such as coplanar waveguide (CPW) on OPSL substrate. The insertion loss of CPW on OPSL prepared by complex oxidation process was −0.39 dB at 4 GHz and similar to that of CPW on OPSL prepared by a temperature of 1050 °C (1 h at H2O/O2). Also the return loss of CPW on OPSL prepared by complex oxidation process was −23 dB at 10 GHz, which is similar to that of CPW on OPSL prepared by high temperature.