Lookup NU author(s): Dr Enrique Escobedo-Cousin,
Dr Sarah Olsen,
Dr Piotr Dobrosz,
Professor Steve Bull,
Professor Anthony O'Neill
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The structural reaction of sub- and supercritical thickness-strained Si layers on novel thin SiGe strain-relaxed buffers (SRBs) during high-temperature annealing used in device fabrication is investigated. Atomic force microscopy, chemical defect etching, scanning electron microscopy, optical profilometry, optical microscopy, and Raman spectroscopy are used to study defect formation and morphology on thin and thick Si0.82 Ge0.18 SRBs grown using a C-induced relaxation technique. For subcritical thickness layers, the defect density was found to be similar in both thin and thick SRBs and both structures responded similarly to annealing, indicating good thermal stability of thin SRB technology. The root-mean-square surface roughness of strained Si grown on thin SRBs was ∼50% lower than on similarly grown thick SRBs and conventional step-graded thick SRBs, and was robust during annealing. The impact of strained Si layer thickness on surface morphology is also analyzed. Using detailed filtering techniques, macro- and microroughness are distinguishable. For the first time, we show that exceeding the critical thickness has a greater impact on microroughness than on macroroughness. Whereas macroroughness is similar for sub- and supercritical thickness-strained Si layers, the microroughness is ∼2× larger in supercritical layers than in subcritical thickness layers. Prominent surface defects were detected on supercritical strained Si layers. The defects align with the cross-hatch morphology and double in density following annealing. It is proposed that the defects originate from localized threading dislocations assisted by further strain relaxation in the metastable strained Si layers. This is substantiated through the observation of stacking faults in the strained Si. In contrast, surfaces of subcritical thickness-strained Si layers on thin SRBs are defect-free. © 2007 American Institute of Physics.
Author(s): Escobedo-Cousin E, Olsen SH, Dobrosz P, Bull SJ, O'Neill AG, Coulson H, Claeys C, Loo R, Delhougne R, Caymax M
Publication type: Article
Publication status: Published
Journal: Journal of Applied Physics
ISSN (print): 0021-8979
Publisher: American Institute of Physics
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