In Situ Stress Measurements via Wafer Curvature Detection Technology

Rachel S. Goldman


2094 H.H. Dow Building

T: (734) 647-6821




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During heteroepitaxial growth of films and heterostructures, misfit strain may be relaxed elastically and/or plastically. Although the mechanisms of these strain relaxation processes have been studied for decades, the interplay between elastic and plastic relaxation, as well as the effects of diffusion and segregation on both processes, are not well understood. For example, in highly-mismatched epitaxial systems, stress relaxation is generally driven by elastic relaxation of strain via island nucleation, a so-called "Stranski-Krastanow"(SK) growth mode transition, resulting in the formation of self-assembled quantum dots. We have been examining this transition in real-time, using simultaneous in-situ wafer curvature and reflection high-energy electron diffraction measurements. Our studies of InAs/GaAs reveal an onset of stress relaxation following the SK growth mode transition, suggesting that the islands formed during the SK growth mode transition do not relax strain immediately. In addition, we find that In surface segregation plays a substantial role in the stress relaxation of capped and stacked quantum dot structures, often influencing the subsequent island nucleation. Finally, we find evidence for diffusion-enhanced suppression of plastic relaxation in stacked quantum dot structures. We are currently in the process of investigating the transition from elastic to plastic relaxation using real-time measurements of the stress evolution during growth. We are also in the process of developing a generic model for these effects, through investigations in a variety of semiconductor systems.