Crystalline quality of silicon layer formed by FIPOS technology

Abstract

The crystalline quality and electrical characteristics of isolated silicon layers fabricated by the FIPOS (Full Isolation by Porous Oxidized Silicon) technology have been studied. Transmission electron microscopy (TEM) was used to evaluate the crystalline quality and CMOS devices were used to determine the electrical characteristics of the isolated layers. Dislocations are generated in the isolated layers. These dislocations are caused by the thermal stresses present in the thick porous silicon layer during the oxidation process. Lowering the porous silicon density is effective in reducing the density of dislocations. The density of dislocations is two or three orders of magnitude lower than that in the silicon-on-sapphire (SOS) or in the epitaxial layer of the oxygen implanted silicon. The field effect mobility of n- and p-channel MOSFETs in the isolated silicon layer is the same as that in bulk silicon. The drain leakage currents of n- and p-channel MOSFETs are on the order of 10 -13-10 -14 A per 6.5 μm channel width. These results show that the dislocations do not degrade the electrical characteristics and that the isolated silicon layer is of high quality.