The relaxation process of ion-implanted strained silicon films and strained Si_1-xGe_x alloys was studied to determine the magnitude of critical strain necessary for the breakdown of solid phase epitaxial regrowth in both biaxial tension and compression. Tensile strained silicon layers 50 nm thick were grown via Molecular Beam Epitaxy on relaxed Si_1-xGe _x virtual substrates. Substrate alloy compositions ranged from 10 to 30% Ge. Compressively strained 50 nm Si_1-xGe_x layers were grown on Si substrate via Chemical Vapor Deposition with Ge compositions ranging from 16 to 26%. All samples underwent a 5, 12, or 18 keV Si ⁺ implant at a fluence of 1x10¹⁵ atoms/cm² to generate amorphous layers ∼15, 30, or 40 nm thick, confining them within the strained layers. The regrowth process, defect morphology, and the effect of implant damage proximity to the Si/SiGe interface was then studied between 500 and 800°C.

Strain relaxation of the layers post processing was quantified by High-Resolution X-Ray Diffraction rocking curves and reciprocal space maps. Upon annealing, the solid phase epitaxial regrowth (SPER) process broke down for the highest level of tensile strain and for all levels of compressive strain. Additionally, regrowth related defects were observed in the relaxed samples using cross-section and plan-view Transmission Electron Microscopy (TEM). In tension, regrowth related defects were nucleated as the amorphous-crystalline front advanced to the surface. Once regrowth was complete, the regrowth related defects propagated down to the strained interface and formed stacking faults which promoted further relaxation. In compression, the advancing amorphous-crystalline front roughened and nucleated an extended dislocation network. The density of these dislocations were stable and did not depend on temperature or duration of anneals.

The results from this study conclude that the SPER process can be achieved without strain loss or defect nucleation for moderate strain values in tension. However, in compression all strain levels in this study nucleated defects and exhibited strain relaxation.