The feasibility of using EDX in a FEG TEM to measure the arsenic dopant concentration in a modern semiconductor device was examined and the results obtained were compared with those from traditional SIMS dopant concentration profiling techniques. Using a FEG TEM it is possible to measure arsenic concentrations down to 0.01 at %(0.025 wt. %) with a lateral resolution of a few nanometers.

A schematic view of a trench cell structure is shown at left, with a FIB/TEM image of the cells superimposed.

Fig. 1. FIB-TEM section of a pair of trench capacitors.
Fig. 2. DF STEM image illustrating a series of analyses adjacent to a trench in a plain-view specimen (1000s each).
Fig. 3. Typical EDX spectrum obtained near the interface with the dielectric. Ar peak from ion milling.
Fig. 4. Plot showing the variation in concentration of As dopant in Si with distance from the dielectric.
Fig. 5. Comparative SIMS profile for the average As concentration around the trenches, derived from an average of hundreds of trenches.

This work was performed on a Philips CM20 FEG TEM/STEM.