Composition and Growth Mechanisms of a Boron Layer Formed Using the Molecular Layer Doping Process

A new doping process, molecular layer doping (MLD), allows for formation of extremely shallow junctions. We have studied the composition and growth mechanisms of boron layers formed on a Si substrate through the MLD process using diborane as the boron feed gas. At temperatures below 600°C, a pure boron layer is formed through the deposit of boron generated through thermal decomposition of diborane. At temperatures over 700°C, the boron layer contained silicon. At 800°C, a boron silicide layer is formed through reaction of boron with the silicon in the substrate. The growth rate of a boron silicide layer depends on the orientation of the Si substrate. However, that of a pure boron layer does not depend on the orientation. The composition of the layer after annealing at 900°C was analyzed using the RBS method and was found to be SiB6. Results of MLD processes on several kinds of underlying layers (e.g., SiO2, Si3N4, poly-Si) are also presented.