ON THE DETERMINATION OF 2-DIMENSIONAL CARRIER DISTRIBUTIONS

The shrinkage of semiconductor devices to submicron levels has led to an increasing demand to characterise dopant and carrier profiles with very high precision and resolution. Whereas for one-dimensional profiling the development of characterisation tools has more or less kept up with the improvements in processing technology leading to established performance levels for techniques like secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP), the situation is less favourable with respect to two-dimensional profiling. The main reason being that the requirements placed in terms of sensitivity and spatial resolution are such that no direct application of SIMS or SRP is possible. In the present paper we review the recent progress made in this field using 2D-SRP, the development of nano-SRP and the visualisation of the carrier distribution using chemical delineation and atomic force microscope imaging. We will discuss not only the technical concepts of the tools involved but illustrate their capabilities using a number of examples such as high energy channelled implantation, B-implantation and lateral diffusion from B-doped epilayers. The comparison of these results with those of simulation programs shows that although a global agreement in lateral profile shape can be found there are at the same time fine details which point out discrepancies with existing theoretical predictions.