Characterization Techniques for Ion-Implanted Layers in Silicon

In this work, we review some techniques used for the characterization of ion implanted layers, with the aim to identify the best approach in various experimental conditions. With regard to dopant profiles, Secondary Ion Mass Spectrometry (SIMS) or Time-of-Flight (ToF)-SIMS are discussed. In the case of very thin layers (of the order of 10 nm) and for specific elements, ToF-SIMS is the best choice. For some devices, it is also necessary to analyse rather thick layers with low dopant concentration, and in this case dynamic SIMS gives better performances. Mass spectroscopy cannot provide information about the electrical activity of dopants. The profile of electrically active dopants can be obtained by the Differential Sheet Resistance (DSR) and Hall Resistance (HR) technique. This technique has the advantage that the carrier density and mobility are independently measured, thus providing information about the crystal quality in the layer, in addition to the dopant distribution. In the Spreading Resistance (SR) technique, a resistance profile is measured and turned into a carrier concentration profile with the aid of literature mobility data or by comparison with data from reference samples with known doping concentration. This approach may lead to wrong concentration data if the carrier mobility is degraded, for instance because of unrecovered damage. Various microscopy techniques are commonly used for the analysis of residual crystal defects, for instance the Transmission Electron Microscopy (TEM) and the Scanning Electron Microscopy (SEM) associated with selective etching. Recently, a new technique based upon microphotoluminescence (mu-PL) measurements (so-called "EnVision") proved to be a valid alternative to selective etching. A study about the residual damage after silicon implantation and annealing is reported. The conclusions reached by selective etching and conventional microscopy and by micro-photoluminescence are consistent with each other, but micro-photoluminescence has the advantage of providing a non-destructive analysis of large silicon areas. The best approach for monitoring metal contamination depends on the specific contaminant and hence of the contamination mechanism. Minority carrier lifetime measurements are suitable for fast diffusing contaminants (e.g. iron), whereas DLTS provides better sensitivity for slow diffusers such as molybdenum and tungsten.