Strain and defects depth distributions in undoped and boron-doped Si1−xGex layers grown by solid phase epitaxy

Abstract

Strain-conserving doping of a pseudomorphic metastable Ge0.06Si0.94 layer on Si(100) by low-dose BF2 + implantation A detailed characterization of undoped and heavily boron-doped Si 1Ϫx Ge x layers with xϭ0.21, 0.26, and 0.34 grown on ͑001͒ Si wafers by solid phase epitaxy is presented. The starting material for solid phase epitaxial growth was prepared by amorphization of epitaxial SiGe-Si heterostructures by ion implantation. In order to obtain doped layers, boron was also implanted into some of the amorphous samples. After regrowth, the strain depth distributions of the SiGe layers were measured using axial channeling angular scans and the defect distributions were observed by high-resolution electron microscopy. A defect-free region ranging from 0 nm ͑undoped layer of x ϭ0.34) to 30 nm ͑doped layer of xϭ0.21) in thickness was observed next to the layer-substrate interface. In the upper region of the layers, strain-relieving defects, identified as planar faults, were observed. Some isolated defects were also present at the layer-substrate interfaces of most of the samples. The measured strain depth profiles show that ͑i͒ the defect-free regions are not always fully strained; the defects located at the interfaces being responsible for this partial relaxation; ͑ii͒ the strain is almost constant throughout the defect-free layers because it cannot be relieved due to the absence of defects; and ͑iii͒ the strain progressively decreases towards the sample surfaces in the region of the layer where the strain-relieving defects are located. Comparison between the undoped and boron-doped layers show the consequences of the strain compensation effect due to the incorporation of boron atoms into the lattice. The defect-free regions of the doped layers are thicker and closer to coherency than those in the undoped layers of the same composition and the defect density in the upper region of the layers is significantly reduced. As a result of the strain compensation effect, a 30-nm-thick heavily doped layer with xϭ0.21 is found to be defect free and fully strained throughout its whole thickness although the corresponding undoped layer was partially relaxed and showed strain-relieving defects.

Strain relaxation mechanisms in Si1−xGex layers grown by solid-phase epitaxy: Influence of the layer composition and growth temperature

“…8 The parameters used to characterize the strain in the layers are the lattice misfit (f) between the bulk lattice constants of layer and substrate, which depends on the Ge content of the layers, and the normalized strain of each slice (∑), which gives the fraction of the strain for coherency on the silicon substrate. This experimental procedure is described elsewhere in detail.…”

“…11 Knowledge of the values of the phonon frequencies allows the inversion of Eq. 4,5,8,9 Figure 1b shows the HREM image of the sample with x = 0.26 grown at 800°C. (2) and thus the determination of the Ge fraction and a value of the normalized strain representative of the whole epitaxial layer.…”

Design and fabrication of 50-nm thin-body p-MOSFETs with a SiGe heterostructure channel

“…This is believed to be due to the lower effective mass of holes in Si Ge which could account for a 20% enhancement and probably the existence of biaxial compressive strain in the channel which lifts the degeneracy of the light-hole (LH) and heavy-hole (HH) bands at the point, leading to an even lower in-plane effective mass of the topmost HH band [4], [5]. The strain and defects depth profile of SPE grown SiGe layers on (100) Si has been studied in [21]. In that work, it was found that a fully-strained defect-free 30-nm thick Si Ge layer can be grown by SPE if it is heavily boron-doped.…”

“…In that work, it was found that a fully-strained defect-free 30-nm thick Si Ge layer can be grown by SPE if it is heavily boron-doped. Undoped samples are 80% strained, i.e., partially relaxed, for the same Ge composition [21]. In our SiGe-channel device considered here, the SPE first proceeds vertically from the heavily doped source region, in which full compressive strain is believed to exist in the graded SiGe layer.…”

Growth of misfit dislocation-free p/p+ thick epitaxial silicon wafers on Ge–B-codoped substrates

“…In the previous reports, great efforts have been expended on the elimination of MDs in p + /p and p/p + epiwafers. Masazara [2], Herzog [3], Lee [4], Tillack [5], Rodriguez [6] presented Ge-B codoping in epi-layers to reduce the mismatch strain in the p + /p epi-wafers. Lin [7] pointed out that mismatch strain in the p/p + epi-wafers could be reduced by Ge-B codoping in the heavily borondoped substrates, thereby, the warpage and bow of epiwafers could be reduced.…”