Practical Electron Microscopy and Database

In semiconductor fabrication, silicide stringers are a critical defect observed under the spacer regions, as highlighted in Figure 183. These stringers arise due to two main factors. First, over-etching of the oxide liner during spacer formation can leave behind metal under the spacer. This metal reacts with silicon during the silicidation process, forming silicide, which can extend along the sidewalls from source to drain. This unintentional formation of silicide can create metallic shorts, leading to functional failure of the transistor. Second, silicon may be inadvertently deposited on the sidewalls of the spacer during the reactive ion sputter cleaning process. This deposited silicon can similarly react with the metal during the silicidation process, resulting in silicide formation along the sidewalls, leading to electrical shorts.

The TEM images in Figure 183 provide both cross-sectional and plan views of these silicide stringers, clearly illustrating their formation beneath the spacer. These defects are of particular concern in failure analysis, as they can cause unintended electrical pathways that degrade device performance. Mitigating the formation of silicide stringers requires process optimization, such as refining the wet-clean process or adjusting the sputter clean procedure, to prevent metallic shorting and ensure device reliability.

[1] Raghaw S. Rai and Swaminathan Subramanian, Role of transmission electron microscopy in the semiconductor industry for process development and failure analysis, Progress in Crystal Growth and Characterization of Materials, 55, pp.63-97, 2009.