Delta-doping of boron by photo-excited CVD

From the past years, doping of impurity atoms has been one of the crucial issues in semiconductor technologies. Recent development in metal-oxide-semiconductor (MOS) transistors that are densely integrated on a wafer surface in ULSI urges doping in a very confined region, which is currently investigated as shallow doping. The representative process tools include plasma and cluster ion beam doping. Although the concept of delta doping, where a high-density doped layer is embedded in a Si crystal, was proposed 20 years ago, research activities have been limited. However, delta doping is certainly a key element for three-dimensional integration of MOS transistor units. Also, advanced electron devices based on vertical transport between delta-doped layers may be realized in the future.