Strain relaxation of SiGe islands on compliant oxide

Abstract

The relaxation of patterned, compressively strained, epitaxial Si0.7Ge0.3 films transferred to borophosphorosilicate (BPSG) glass by a wafer-bonding and etch-back technique was studied as an approach for fabricating defect-free Si1−xGex relaxed films. Both the desired in-plane expansion and undesired buckling of the films concurrently contribute to the relaxation. Their relative role in the relaxation process was examined experimentally and by modeling. Using x-ray diffraction, Raman scattering and atomic force microscopy, the dynamics of in-plane expansion and buckling of Si0.7Ge0.3 islands for island sizes ranging from 10 μm×10 μm to 200 μm×200 μm for anneal temperatures between 750 and 800 °C was investigated. Lateral relaxation is favored in small and thick islands, and buckling is initially dominant in large and thin islands. Raising the temperature to lower viscosity of the oxide enhances the rate of both processes equally. For very long annealing times, however, the buckling disappeared, allowing larger, flat, and relaxed islands to be achieved. Cross-sectional transmission electron microscopy observation on a relaxed Si0.70Ge0.30 island revealed no dislocations, confirming that SiGe relaxation on BPSG is a good approach to achieve high quality relaxed SiGe.

Local bending of thin film on viscous layer

“…The stress/strain at the bimaterial interface induced by the lattice mismatch can also cause wrinkling, or variably called corrugation, undulation, convolution and ripples of a thin film [7][8][9][10][11] . Liu et al [11] reported that germanium (Ge) deposition dots on the compliant thin silicon film of Silicon-on-Insulator (SOI) substrates cause the local bending mode of a compliant film as shown in Fig.1.…”

Mechanics of relaxing SiGe islands on a viscous glass

“…Figure 7 plots the experimental data for 30 nm and 60 nm thick SiGe films [33] . The predictions of the linear perturbation analysis correspond to the straight lines in Fig.7.…”

“…The shear lag model has also been formulated in two dimensions [39], and solved numerically for the expansion of a square island [27]. Figure 5 plots the strain scaled by the initial mismatch strain, against the time scaled by the square of the island size [33] . With such scaling, the shear lag model predicts one single curve in each plot for all island sizes.…”

“…Islands of various sizes are annealed above the glass transition temperature of BPSG [33]. Small islands (L < 30 #m) expand, but large islands wrinkle, After a long time of annealing, the wrinkles disappear for mid:sized islands (30#m < L < 80#m), but cause fracture for large islands, Figure 2 shows a part of a 100/zm island annealed for 90rain at 790~ At the corner, the island expands in both inplane directions, and remains flat.…”

Novel Adhesion Test for Environmentally Assisted Fracture in Thin Films

“…There are many different stress relief mechanisms observed in thin films. The residual stress can be partially relieved by plastic deformation and surface reconstruction [6], or simply by mechanical film failure, especially if the stress levels are high, and, in addition, externally applied mechanical and thermal stresses are present combined with environmental effects. In some cases, films and protective coatings fail due to environmental effects and long-term moisture exposure, causing corrosion of the substrate, or the film, or both.…”