Search

A laterally diffused metal oxide semiconductor (LDMOS) has been fabricated on a 12.2 μm buried oxide (BOX) silicon-on-insulator (SOI) substrate, successfully achieving a breakdown voltage of over 2000 V. This paper describes the proposed drift structure for SOI LDMOS. The proposed LDMOS drift structure adopts SOI reduced surface electric field (SOI RESURF) technology, which uses the BOX layer to establish the breakdown voltage. SOI RESURF technology achieves a high breakdown voltage by enhancing the critical electric field of the SOI layer. The proposed drift structure is characterized by the formation of an N-type buried diffusion layer with a concentration gradient at the SOI layer/BOX layer interface that consists of eight levels from the source to the drain. This structure increases the critical electric field of the SOI layer to 0.55 MV/cm compared to the normal critical electric field of silicon (Si), which is typically 0.3 MV/cm. As a result, a breakdown voltage of over 2000 V was achieved with a 12.2 μm BOX layer.

The etching characteristics of SiO 2 films, which were irradiated with Si 2+ focused ion beams, in a buffered HF solution were comprehensively investigated. Dependence of the etching rate on the dose was investigated. The rate increased with increasing dose (8 × 10 13 –1 × 10 15 cm −2 ), however it decreased for doses exceeding a critical value (1 × 10 15 cm −2 ). The TRIM simulation indicated that irradiation with this critical value resulted in the concentration of vacancies at the Si site equal to that of Si atoms in SiO 2 . These results can be explained by considering the enhancement of etching by vacancies and the retardation by implanted Si atoms. The retardation was confirmed experimentally.

The dose-dependent etching characteristics of SiO2 films irradiated with 40 keV Si2+ focused ion beams (FIBs) were comprehensively investigated. The etching rate in a buffered HF increased with increasing dose (8 ×1013–1 ×1015 cm-2), however it decreased for doses exceeding a critical value (1 ×1015 cm-2). The maximum selectivity of the etching rate of the irradiated region to the nonirradiated region was about 14, which was obtained for irradiation with the critical dose. The numerical simulation indicated that all of the Si atoms in SiO2 were displaced by irradiation with this critical dose. A simple model for the etching characteristics was proposed, in which the enhancement of etching by vacancies and the retardation of etching by implanted Si atoms were considered. The etching characteristics obtained by the experiments were quantitatively explained by the model.

This paper describes a new wide-voltage SOI-BiCDMOS technology for high-temperature automotive applications. This technology is capable of integrating 35V, 60V, and 80V Nch and Pch LDMOS, 35V BJT, and 6V CMOS devices on a single chip. The devices are completely isolated dielectrically using both deep trench isolation (DTI) and a buried oxide (BOX) layer in a silicon-on-insulator (SOI) wafer for stable operation at high temperatures up to 175°C. The devices were developed using a 0.35μm process. In particular, the LDMOS devices have achieved competitive levels of low Ron∗ A and good SOA.

In the automotive IC using thick-film silicon on insulator (SOI) semiconductor device, if the gettering capability of a SOI wafer is inadequate, electrical characteristics degradation by metal contamination arises and the yield falls. At this time, an automotive IC was made experimentally for evaluation of the gettering capability as one of the purposes. In this IC, one of the output characteristics varied from the standard, therefore failure analysis was performed, which found trace metal elements as one of the causes. By making full use of 3D perspective, it is possible to fabricate a site-specific sample into 0.1 micrometre in thickness without missing a failure point that has very minute quantities of contaminant in a semiconductor device. Using energy dispersive X-ray, it is possible to detect trace metal contamination at levels 1E12 atoms per sq cm. that are conventionally detected only by trace element analysis.

The dose-dependent etching characteristics of SiO2 films irradiated with 40 keV Si2+ focused ion beams (FIBs) were comprehensively investigated. The etching rate in a buffered HF increased with increasing dose (8 ×1013–1 ×1015 cm-2), however it decreased for doses exceeding a critical value (1 ×1015 cm-2). The maximum selectivity of the etching rate of the irradiated region to the nonirradiated region was about 14, which was obtained for irradiation with the critical dose. The numerical simulation indicated that all of the Si atoms in SiO2 were displaced by irradiation with this critical dose. A simple model for the etching characteristics was proposed, in which the enhancement of etching by vacancies and the retardation of etching by implanted Si atoms were considered. The etching characteristics obtained by the experiments were quantitatively explained by the model.