DIELECTRICALLY ISOLATED SUBSTRATE AND FABRICATION THEREOF

PURPOSE: To obtain a highly reliable dielectrically isolated substrate, and fabrication method thereof, in which warping and delamination are eliminated by surely preventing generation of void in glass layer. CONSTITUTION: After making an isolation trench 12 in one surface of a silicon substrate 11 and depositing an isolation oxide 13, a polysilicon layer 14 is formed. The polysilicon layer 14 is then subjected to spin etching and planarized except the trench 12. Subsequently, a soot layer 15 is formed and a supporting substrate, i.e., a silicon substrate 17, is superposed thereon before being heat treated to bond the silicon substrates 11, 17. Finally, the silicon substrate 11 is abraded on the rear side thereof thus forming a plurality of insular silicon layers 11a, 11b,... isolated through the trench 12.