Relaxation of strained silicon on virtual substrates

Doctoral thesis English OPEN
Parsons, Jonathan
  • Subject: QC | TK

The relaxation of variable thickness strained silicon layers on 20% and 50% germanium composition virtual substrates have been quantified using two independent methods. High resolution X-ray diffraction offers a means to measure relaxation directly, and a defect etching technique has been developed from which relaxation can be determined by the measurement of dislocation densities. Comparisons between the relaxation of tensile strained silicon in this work and compressively strained Si1−xGex in other works, suggest that strained silicon is unusually stable to relaxation. Observation of dislocation structures with defect etching and transmission electron microscopy have shown that the additional stability arises from the interaction of dislocations which inhibits glide. Extended stacking faults, which only form when the strain is tensile (and are therefore absent in compressively strained Si1−xGex), are more effective at impeding dislocation glide and it is their increased density in thicker layers which yield enhanced stability, even after high temperature annealing.
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    50 references, page 1 of 5

    2.14 Cross-sectional diagram showing the forces acting on a nucleated halfloop dislocation, as used in the People and Bean critical thickness model. Adapted from People and Bean [1985]. . . . . . . . . . . . . . . . . . .

    2.15 Graph showing the critical thickness regimes of Matthews and Blakelee (equation 2.13), and People and Bean (equation 2.15). . . . . . . . . .

    2.16 Cross sectional view showing a threading dislocation (a) gliding towards an orthogonal misfit dislocation, marked by the cross with surrounding strain field in grey, (b) being forced to glide in a smaller channel region, h∗. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    2.17 Graph showing the Freund dislocation pinning regime (equation 2.16), together with the critical thickness of Matthews and Blakeslee (equation 2.13). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    2.18 Schematic representation of the modified Frank-Read process showning (a) a splitting reaction, (b) the Frank-Read mechanism closing a halfloop, (c) expanding half-loop to reach the surface, and (d) a pile-up formed by the expansion of dislocation half-loops along two glide-planes. Adapted from LeGoues et al. [1992] . . . . . . . . . . . . . . . . . . .

    2.19 Schematic representation of a step graded virtual substrate, with misfit interfaces is arrowed. . . . . . . . . . . . . . . . . . . . . . . . . . . .

    2.22 Simplified hard sphere representations of a face-centred cubic lattice showing (a) stacking of the {111} planes, and (b) a top-down view of the stacking sequence. Taken from Cottrell [1964]. . . . . . . . . . .

    2.23 Simplified hard sphere representation of a cross section through a stacking fault (in grey) caused by one partial dislocation at point P, running into the plane of the page. Adapted from Kosevich [1979]. . . . . . . .

    2.24 Schematic diagram of the formation of an extended stacking fault in a tensile strained layer. Adapted from Mar´ee et al. [1987]. . . . . . . . .

    2.25 Cross-sectional view of a microtwin formed by the successive nucleation of 90◦ partial dislocations on adjacent glide-planes, which forms a step on the surface along its length. Adapted from Wegscheider and Cerva [1993]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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