The continued downscaling of semiconductor transistors, both laterally and in depth, results in acute characterization challenges. Metrology tools must ensure lateral resolution of a few nanometers as well as high depth resolution while retaining high sensitivity.
Dynamic Secondary Ion Mass Spectrometry (SIMS) enables access to high depth resolution at low primary impact energies (≤500 eV). However, it still utilizes a micron sized beam to probe nanometer sized structures. In order to overcome the beam size limitation when analyzing small features, one can seek to localize (laterally and in depth) the signal emitted by the device by specifically tracking the molecular secondary ions emitted from the 3D area of interest. This novel method is referred to as Self-Focusing SIMS.
Four test samples produced by the same SiGe growth recipe were employed to both investigate a micro-loading growth effect and validate a new quantification model. The samples used were a SiGe blanket wafer, a SIMS pad in the scribe line (50x60 μm2) which is larger than the beam size, an equally spaced uniformly boron doped vertical SiGe FIN structure with evenly spaced SiGe and Si3N4, and an SRAM device with SiGe structure occupying 11% of the total analysis area.
The Self-Focusing SIMS approach to analyzing small features proved about ten times faster than a direct study of the feature with say TEM or APT. In addition, as SIMS is averaging over many such structures, the signal-to-noise is high, resulting in more statistically reliable results compared to TEM or APT. On the other hand, no compositional variation within the confined area can be determined using this technique.
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Compositional Measurement of Confined SiGe Devices with Self-Focusing SIMS to learn more!
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