Recently, along with the miniaturization of a semiconductor device, there has been a demand; or a technique which forms a shallow pn junction.
As a method for forming such a pn junction, ion implantation has been used conventionally. For example, a p-type impurity such as boron is introduced into an n-type silicon substrate by ion implantation and, thereafter, p-type impurity is electrically activated using a halogen lamp or the like thus forming the pn junction, and various devices are formed using such a pn junction.
Various attempts have been made to form the shallow junction using the ion implantation. Although the shallow junction may be formed by electrically activating the impurity which is injected by various annealing methods such as a flash lamp method, a laser annealing method and the like, a depth of the pn junction formed by the ion implantation is limited. For example, the shallow introduction of boron impurity is difficult. That is, it is difficult to set acceleration energy of B ions or BF2 ions to low energy of several keV and hence, in she ion implantation, the depth of the ion introduced region is limited to approximately 10 nm from a surface of a substrate.
Accordingly, recently, as a technique which can efficiently form the shallower junction, various doping methods have been proposed and a plasma doping technique has been attracting an attention as a technique which is suitable for practical use among these doping methods. The plasma doping is a technique in which a reaction gas containing impurity to be introduced is excited in plasma and the plasma is radiated to a surface of the substrate thus introducing the impurity into the substrate. According to this technique, even when the impurity is boron, it is possible to form the shallow junction having a depth of 7 nm (see non-patent documents 1, 2, for example).    Non-patent document 1: Plasma Doping Technique: written by Bunji Mizuno (vol. 70, No. 12, p. 1458-1462 (2001)    Non-patent document 2: Reliable and enhanced performances of sub-0.1 μm pMOSFETs doped by low biased Plasma Doping, Damian Lenoble et al, VLSI Symposium, sponsored by IEEE and Japan Society of Applied Physics, p. 110, 2000.