Characterization of an Oxidized Porous Silicon Layer by Complex Process Using RTO and the Fabrication of CPW-Type Stubs on an OPSL for RF Application

Abstract

This paper proposes a 10-µm thick oxide layer structure that can be used as a substrate for RF circuits. The structure has been fabricated using an anodic reaction and complex oxidation, which is a combined process of low-temperature thermal oxidation (500 °C, for 1 hr at H2O/O2) and a rapid thermal oxidation (RTO) process (1050 °C, for 1 min). The electrical characteristics of the oxidized porous silicon layer (OPSL) were almost the same as those of standard thermal silicon dioxide. The leakage current density through the OPSL of 10 µm was about 10 to 50 nA/cm 2 in the range of 0 to 50 V. The average value of the breakdown field was about 3.9 MV/cm. From the X-ray photo-electron spectroscopy (XPS) analysis, surface and internal oxide films of OPSL prepared by a complex process were confirmed to be completely oxidized. The role of the RTO process was also important for the densification of the porous silicon layer (PSL) oxidized at a lower temperature. The measured working frequency of the coplanar waveguide (CPW) type short stub on an OPSL prepared by the complex oxidation process was 27.5 GHz, and the return loss was 4.2 dB, similar to that of the CPW-type short stub on an OPSL prepared at a temperature of 1050 °C (1 hr at H2O/O2). Also, the measured working frequency of the CPW-type open stub on an OPSL prepared by the complex oxidation process was 30.5 GHz, and the return was 15 dB at midband, similar to that of the CPW-type open stub on an OPSL prepared at a temperature of 1050 °C (1 hr at H2O/O2).