Characterization of strained Si/Si1−xGex/Si heterostructures annealed in oxygen or argon

Liu

Electrochem. Solid-State Lett.

et al. 2006

We have recently developed a novel reverse-graded ͑RG͒ buffer system, in which the Ge content decreases with distance from the Si interface. These thin ͑90 nm͒ RG layers are capable of supporting the growth of relaxed SiGe layers ͑85% relaxed͒ with defect densities as low as 10 5 /cm 2 . Good quality strained Si has also been successfully grown on these substrates. However, the thermal stability of this novel heterostructure has not been explored. In this paper, we establish, by high-resolution X-ray diffraction, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy, that the heterostructure is stable up to 1000°C with no further strain relaxation in both the RG layer and strained Si layer. Hence, it is clear that this thin RG heterostructure is highly suitable as a buffer system for the growth of high-mobility strained Si or Ge devices.The execution of Moore's law beyond the 45 nm node has become possible with the recent innovation of strained channel technology. It has been reported that effective mobility of electrons and holes increased by up to three times in strained Si channels and eight times in strained Ge channels, respectively. 1-3 The integration of strained channels into Si wafer processing is critically dependent on the success of heteroepitaxy technology, which remains a challenging proposition. The 4.2% lattice constant mismatch between pure Si ͑a = 0.543 nm͒ and Ge ͑a = 0.569 nm͒ must be accommodated with minimum threading dislocation density ͑TDD͒ in the strained Si channel, so far achieved by the use of various buffer layers. The most widely accepted buffer approach is via continuous forward grading of SiGe on Si, followed by a relaxed SiGe layer with constant concentration, topped by a thin strained Si or Ge channel layer. 4 This approach can reduce the TDD to 10 5 /cm 2 ; however, up to a 5-m-thick buffer layer is needed to grow the high quality SiGe layer. Earlier studies have found that the self-heating effect of a device on a relaxed SiGe buffer is proportional to the square root of the buffer thickness. 5,6 Thus, investigations on a high-quality thin buffer layer are relevant and necessary in order to improve device performance.Recently, we proposed a novel reverse-graded ͑RG͒ buffer grading system, where the Ge concentration decreases gradually from the Si substrate towards the relaxed SiGe layer. 7 We have demonstrated that the defect density of this heteroepitaxy system is comparable to, if not better than, the current state of the art, with a thickness only 10% of the forward graded buffer system. 7 We believe that the success of this method depends on the residual strain in the RG layer, which exerts force on the misfit dislocations and prevents them from propagating upwards and terminating on the top SiGe layer as threading dislocations. Nevertheless, it has been reported that, during high-temperature anneals encountered in a typical semiconductor fabrication, strain relaxation of strained SiGe, 8 strained Si, 9 and diffusion of Ge into the strained Si la...

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confidence: 98%

Thermal Stability of a Reverse-Graded SiGe Buffer Layer for Growth of Relaxed SiGe Epitaxy

Liu

Electrochem. Solid-State Lett.

et al. 2006

“…While pure-spin-current transport with a long spin lifetime has been reported for the strained SiGe(111) channel layer [10]. However, the quality of the epitaxial layer strongly depends on the various types of defects generated in the epilayer during the growth process, and the presence of the defects can severely reduce device performances [11,12]. Very common defects such as misfit dislocations and stacking faults are generated through the strain relaxation of the strained epilayer [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

(Digital Presentation) Strain Engineering of Heteroepitaxial SiGe/Ge on Si with Various Crystal Orientations

Alam¹,

Wagatsuma²,

Okada³

et al. 2022

ECS Trans.

Strained SiGe layers with high Ge concentrations are grown on the Ge and Ge-on-Si substrates with various crystal orientations, and structural properties are studied. Particularly, initial stages of defect formation and related surface morphology are investigated. It is found that cracks are generated in the tensile-strained layer and surface ridge roughness is formed around the cracks although the total relaxation ratio of the SiGe layer is almost 0 %. Due to annealing the tensile strain is partially relaxed by creating additional trench-like roughness with the initially formed ridge roughness left unchanged. This comparative investigation of strain relieving defect formation provides quite useful information toward applications to strained SiGe-based optoelectronic and spintronic devices with enhanced performances.

“…Such a high dislocation density degrades the device performance by decreasing the carrier mobility and increasing the leakage current. 4,5) Various techniques have been proposed to obtain high-quality strain-relaxed SiGe layers, such as the use of compositionally graded buffer layers, 6) Ge condensation, 7) and growth on low-temperature Si or Ge buffer layers. 8) However, for most of the growth techniques, the relaxation degree is insufficient, even if the SiGe layer thickness is much larger than the critical thickness for strain relaxation.…”

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confidence: 99%

Strain relaxation of Si_0.75Ge_0.25in hydrogen-implanted Si_0.75Ge_0.25/B-doped Si_0.70Ge_0.30/Si heterostructure

Chen

Xue

Wang

et al. 2014

Appl. Phys. Express

An approach used to obtain a high-quality strain-relaxed SiGe layer by investigating the preferential aggregation and homogenization of nanometric bubbles along the B-doped Si 0.70 Ge 0.30 interlayer in the H-implanted Si 0.75 Ge 0.25 /B-doped Si 0.70 Ge 0.30 /Si heterostructure has been proposed. The formation of nanometric bubbles is found to be closely correlated to the B atoms doped in the buried Si 0.70 Ge 0.30 layer. Moreover, with the B-doped ultrathin Si 0.70 Ge 0.30 interlayer, the formed nanometric bubbles can interact with dislocation loops and eject them by gliding to the Si 0.70 Ge 0.30 /Si interface. The threading dislocation density is 3.3 ' 10 5 cm %2 , which is superior to that of the sample grown with a graded buffer layer.