Superior Large-Scale Relaxation and Defectivity in SiGe Layers Grown on Pre-Threaded Si Substrates
M Erdtmann, M T. Currie, Joseph Woicik, David R. Black
State-of-the-art applications involving relaxed SiGe virtual substrates have a low tolerance for defectivity, i.e., threading dislocation density (TDD) and dislocation pile-up density (DPD). Yet in order for virtual substrates to achieve relaxation, it is necessary for copious densities of dislocations to be introduced during the growth process. How well-controlled dislocations nucleate and glide in the SiGe layer during growth predominately determines the final TDD and DPD. When growth is performed on prime Si substrates, which contain few threading dislocations, dislocations must initially nucleate from heterogeneous sources. If unintentionally introduced, these sources are uncontrollable in both their distribution and activation, which leads to non-uniform relaxation, increased dislocation interactions, and higher DPD and TDD. If intentionally introduced, previous experimental work suggests that very high source densities are required to achieve relaxation, which leads to short dislocation glide lengths and hence higher TDD. Moreover, when the growth is performed on large-diameter substrates, the probability of a dislocation gliding to a free edge is diminished, which forces dislocations to remain entrenched in the wafer interior and thus contribute to dislocation interactions. We demonstrate that greater control of SiGe/Si relaxation can be obtained by growing on large-diameter pre-threaded substrates with an elevated TDD. This unique approach facilitates initial dislocation nucleation from the threading dislocations of the substrate rather than from heterogeneous sources. Because the substrate threading dislocations have a spatially uniform distribution and a balanced distribution of Burgers vectors, the initial relaxation is uniform and well-controlled. Compared to layers grown on 200 mm-diameter prime Si substrates, a drastic reduction in the DPD of Si0.90Ge0.10 layers is observed over the entire wafer area when grown on 200 mm-diameter pre-threaded Si substrates. Likewise, a final TDD of less than 2.5x105 cm-2 over the entire wafer area is realized. This approach is not specific to SiGe single layers and can readily be extended to other structures, such as compositionally graded buffers, and other materials systems, such as the III-V semiconductors.
Journal of Applied Physics
dislocation pile up density (DPD), relaxed SiGe, Si substrates, threading dislocation density (TDD)
, Currie, M.
, Woicik, J.
and Black, D.
Superior Large-Scale Relaxation and Defectivity in SiGe Layers Grown on Pre-Threaded Si Substrates, Journal of Applied Physics
(Accessed November 28, 2023)