Application of small pulsed ion beams for depth profiling on beveled semiconductor structures

Depth profiling using line scans at beveled structures is an alternative to conventional sputter depth profiling. The method is particularly attractive for analysis techniques like scanning Auger microanalysis (SAM) and time of flight secondary ion mass spectrometry (ToF-SiMS) where focused electron and ion beams are available. It is found to be useful in semiconductor device applications and is specially advantageous in cases where layers with thickness in the nanometer range are buried under thick overlayers. We demonstrate that the preparation of smooth and very flat bevels (0.01 degrees - 0.1 degrees) for heteroepitaxial multilayer structures in combination with ToF-SIMS line scan analysis enables the possibility of depth profiling with high depth resolution. In a comparison of measured and calculated line scans in SiGe quantum wells, SiGe hetero-bipolar transistor (HBT) structures, and delta-doping layers (B, Sb, Ge in Si), different contributions to the depth resolution, such as interfacial and surface roughness, beam diameter, and information depth of the used signals, are evaluated. For buried delta dopings ToF - SIMS easily measured FWHM thickness values below 2.5 nm and decay length of 0.75 nm at the line scans. For SiGe HBT s and SiGe quantum wells, the Ge decay length in the line scan analysis was found to be 0.8 nm.