THE APPLICATION OF LASER ANNEALING TO DOPANT PROFILING FOR SEMICONDUCTOR DEVICES

Abstract
For many device structures there is a requirement for an annealing technique which has the facility to tailor junction dopant profiles ; bipolar transistors and IMPATT diodes are example, where the need is for uniformly doped planar junctions. Conventionally, techniques such as vapour phase epitaxial growth of doped silicon layers, or the concentration dependent diffusion coefficients of certain dopants have been used to approximate to this type of profile. However, as ever finer device geometries are sought, the junction gradients produced using these techniques become significant, and the concomitant degradation in operating performance unacceptable. As an alternative lasers, either pulsed or scanned cw, in conjunction with ion-implantation may be used. Rectangular doping profiles are readily attainable by pulsed laser annealing. This has immediate application to high frequency microwave devices and it has been shown that this may be readily used. The application to high efficiency bipolar transistors however depends on the ability to incorporate the technique into a bipolar fabrication process.