Silicon-on-Diamond — An engineered substrate for electronic applications

Silicon on Diamond (SOD) is a substrate engineered to address the major challenges of silicon-based ULSI technology, in particular, to provide for enhanced thermal management and charge confinement. The SOD concept is achieved by joining a thin, single crystalline Si device layer to a highly oriented diamond (HOD) layer that serves as an electrical insulator, heat spreader and supporting substrate. Therefore, SOD represents an alternative SOI concept, where the thermally insulating SiO 2 has been replaced by highly thermally conductive diamond. Initial experiments and theoretical assessments have been aimed at demonstrating the improved thermal management properties of fabricated SOD wafers and comparing them to Si and SOI [A. Aleksov, X. Li, N. Govindaraju, J.M. Gobien, S.D. Wolter, J.T. Prater, Z. Sitar, Silicon on Diamond: an advanced Silicon on Insulator technology, Diamond and Related Materials, 14, 308–313 (2005).], [A. Aleksov, S.D. Wolter, J.T. Prater, Z. Sitar, Fabrication and Thermal Evaluation of Silicon on Diamond Wafers, Journal of Electronic Materials, 34 (2005) 1089.]. The experimental results are in good agreement with the values obtained by finite element modeling (FEM). The results show that for a 1.5 μm thick Si device layer, SOD can sustain more than 10 times higher power than SOI. This in turn will permit a more than 3-fold greater integration density of circuits fabricated on SOD as compared to SOI. Having validated the superior thermal management properties of SOD, the second task has been to compare device operation on SOD and SOI to identify whether the Si layer degrades during the SOD fabrication process. In addition, the analysis of the interface properties between the Si device layer and diamond is important in order to better understand the operation of devices on SOD and identify their limitations. For this reason, Schottky and pn-junction diodes were fabricated on the Si device layer of SOD and SOI wafers. The first results of the electrical analyses indicated that there are no additional leakage currents in SOD devices compared to devices on SOI. In addition, CV measurements indicated no differences in the device behavior i.e. no additional charge trapping with respect to SOI in the frequency range of 1 kHz–10 MHz.