A novel TEM technique for junction delineation in integrated circuits

Abstract

Ion implantation is a well established technique to dope selectively prespecified regions of silicon substrates. It has the drawback that a thermal treatment is required to activate the dopant and to reconstruct the crystal lattice. This leads to dopant diffusion in depth and also laterally, when the implantation has been preformed through a patterned mask.In this paper two different approaches to determine the doping profile using chemical etching and TEM are presented. Cross-section specimens are prepared using a technique described elsewhere, followed by preferential etching.The first approach is well established and is based on the combined action of HF and HNO3.Low concentrations of HF are used to keep the etching rate low enough. Figure 1 shows a cross-section of a boron implanted and annealed sample which has been etched using the solution HF(40%):HNO3(65%)= 1:300 at 5°C for 80 seconds. The etching rate is proportional to the doping level, as shown in figure 2 and it can be observed that the lowest level which one can delineate with this solution is of the order of 1017cm−3, which is in agreement with the delineated level of figure 1, namely 6·1017 cm−3.