1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and in particular to a method of fabricating a semiconductor device with extremely shallow-junctioned source/drain structures.
2. Description of the Related Art
As the integration level of semiconductor devices increases, the junction depth of the source/drain structures of MOS transistor is reduced more and more, and extremely shallow source/drain junctions are becoming more important.
Referring to FIG. 1, a conventional method of fabricating a P-type semiconductor device with shallow junctions will be described. In FIG. 1, an N-type well 22 is formed in the semiconductor silicon substrate 21, and then a device isolation layer 23 is formed in the field area of the silicon substrate 21 by LOCOS process. A gate oxide layer 24, gate electrode 25, and insulator spacer 26 are then formed on the silicon substrate 21 and BF.sub.2 ion implantation is performed onto the active area of silicon substrate 21 defined by the field area at the dose of 2E15/cm.sup.2 to 5E15/cm.sup.2 and the energy of 15 keV to 40 keV in order to form P.sup.+ source/drain 27 of the transistor.
Thereafter, an interlayer insulator film 29, e.g. tetraethylorthosilicate glass (TEOS) layer is deposited on the entire surface of the silicon substrate 21 and then a planarizing insulator film 29 is deposited thereon.
However, when the BF.sub.2 ion implantation is performed in order to create the P.sup.+ source/drain 27, the surface layer of the silicon substrate 21 is damaged due to the implanted ion impact so that it becomes an amorphous silicon layer, and some point defects occur under the interface between the amorphous layer and the crystalline layer. Further, during the subsequent thermal process, the diffusivity of boron is increased due to the point defects and therefore the junction depth of the source/drain 27 is increased. In addition, some secondary defects or extended defects occur, and since the electrical activity of the boron is thus decreased, the leakage current in the junction is significantly increased. Therefore, the conventional technique is unsuitable to form an extremely shallow junction with excellent electrical characteristics.