The present invention disclosed herein relates to a semiconductor device, and more particularly, to a semiconductor device having a local silicon-on-insulator (SOI) structure and a method of forming the same.
The present invention has been derived from research undertaken as a part of IT R & D program of the Ministry of Information and Communication and Institution of Information Technology Association (MIC/IITA) [2006-S-004-02], integrated development of silicon-based high-speed optical interconnection IC.
A semiconductor device formed on a silicon-on-insulator (SOI) substrate may have high radiation tolerance and latch-up immunity, restrain the short channel effect, and operate with low power consumption, by means of a buried oxide (BOX) layer buried in a substrate under the device. Furthermore, the semiconductor device can operate at a high speed because an operating region of the semiconductor device is capacitively insulated from the substrate.
There are mainly two types of methods for forming a typical SOI substrate. One is a wafer bonding method that bonds two wafers with an oxide layer therebetween. The other is a separation by implanted oxygen (SIMOX) method. In the SIMOX method, a high concentration oxygen ion implanted layer is formed at a predetermined depth of a silicon wafer by implanting oxygen ions from the surface of the silicon wafer. Subsequently, the silicon wafer is thermally treated to form a BOX layer.
In the wafer bonding method, a SOI substrate can be obtained by bonding two silicon wafers with an oxide layer having a thickness of more than 1 micrometer. In this case, the broader the surface area of the wafer is, the more difficult it is to ensure proper bonding and uniformity of wafer thickness.
Also, a BOX layer must be formed with a thickness of more than 1 micrometer in order to integrate an optical element and an electrical element onto the SOI substrate. Accordingly, a high concentration (of greater than 5×1018 atom/cm2) ion implantation is required to form a BOX layer having a thickness of 1 mm in the SIMOX method. However, a high concentration ion implantation may increase the threading dislocation density, the oxide precipitate density and the lattice defects of silicon, and cause silicon inclusions and pinholes in the BOX layer. Subsequently, the reliability and the operating characteristics of a semiconductor device may be deteriorated.