Dislocation Motion in SOI Observed with LEEM

Future Si-based microelectronic devices will combine many recent innovations, such as the use of strained thin films, and silicon-on-insulator substrates. Consequently, the effects of interfaces on strain relaxation and dislocation motion have become increasingly important. Strain relaxation in reduced-dimensionality structures is difficult to study using standard techniques. Transmission electron microscopy (TEM) is destructive and requires extensive sample preparation. X-ray diffraction is not suited to studying the dynamics of individual dislocations. Low-energy electron microscopy (LEEM) is a non-destructive technique that requires only a clean surface. By virtue of the strain field surrounding a dislocation, LEEM can be used to observe buried dislocations underneath a Si (001) cap layer. As shown in Fig. 1, we have demonstrated the use of low-energy electron microscopy to view dislocation motion in thin films on silicon-on-insulator (SOI). Motion of a single dislocation in a strained Si0.89Ge0.11 film on SOI is activated by raising the sample temperature to 950oC.

Figure 1. Dark-field LEEM images of dislocation motion on a SiGe film on SOI, during an anneal at 950oC. Images show the progress of a single dislocation (a) before the new dislocation has appeared, (b),(c) as the dislocation is blocked by two different, perpendicular dislocations, and (d) after it has traversed through the field of view. Arrows in (b) and (c) indicate the blockage points of the dislocation, and in (d) the dark region indicates that the dislocation has traversed the left-most vertical dislocation. The bar in (a) indicates a distance of 1mm.

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