[en] The use of selective epitaxial growth for the implementation of SiGe to improve device performance has several advantages compared to non-selective growth. However, some issues such as thickness non-uniformity (micro-loading on μm scale and gas depletion on wafer scale) and facet formation have to be solved. We give an overview of our selective epitaxial SiGe growth process in a standard production Chemical Vapor Deposition (CVD) reactor, and for Ge contents between 0 and 32%. Our process allows to deposit layers with no pattern dependence on growth rate and Ge content (no micro-loading) and with very high cross-wafer uniformity (standard deviation <2%). Facet formation is avoided by choosing the correct growth conditions, and by preventing lateral growth over the mask material. The combination of excellent layer quality, facet-free growth, and the proven layer uniformities permit a successful implementation of SiGe in device technologies as demonstrated by the performance of SiGe BiCMOS (0.25 and 0.35 μm), and p-type hetero-MOS devices (L_poly down to 50 nm)

[en] We describe a new technique for the fabrication of a thin strain relaxed buffer (TSRB). This method is based on the incorporation of carbon during the epitaxial growth of a thin constant composition Si_0.78Ge_0.22 layer. An annealing step is carried out after growth in order to increase the relaxation and therefore the stability of the buffer. This method allows to prepare smooth and defect free TSRBs with 91% relaxation. First Hall mobility measurements at 77 K of strained silicon on top of the TSRB (single side modulation doped structure) show promising electron mobility value of 18,500 cm²/(V s)

[en] Tin disulfide (SnS₂) is a n-type semiconductor with a hexagonally layered crystal structure and has promising applications in nanoelectronics, optoelectronics and sensors. Such applications require the deposition of SnS₂ with controlled crystallinity and thickness control at monolayer level on large area substrate. Here, we investigate the nucleation and growth mechanism of two-dimensional (2D) SnS₂ by chemical vapor deposition (CVD) using SnCl₄ and H₂S as precursors. We find that the growth mechanism of 2D SnS₂ is different from the classical layer-by-layer growth mode, by which monolayer-thin 2D transition metal dichalcogenides can be formed. In the initial nucleation stage, isolated 2D SnS₂ domains of several monolayers high are formed. Next, 2D SnS₂ crystals grow laterally while keeping a nearly constant height until layer closure is achieved, due to the higher reactivity of SnS₂ crystal edges than basal planes. We infer that the thickness of the 2D SnS₂ crystals is determined by the height of initial SnS₂ islands. After layer closure, SnS₂ grows on grain boundaries and results in 3D growth mode, accompanied by spiral growth. Our findings suggest an approach to prepare 2D SnS₂ with a controlled thickness of several monolayers and add more knowledge on the nucleation and growth mechanism of 2D materials. (paper)

[en] In this contribution we describe the chemical changes at the surface of GaAs upon adsorption of tri-methyl-aluminum (TMA). TMA is used to grow Al₂O₃ with atomic layer deposition (ALD) usually using H₂O as oxygen source. Recently, it was pointed out that the adsorption of TMA on various III-V surfaces reduces the native oxide, allowing the growth of an abrupt III-V/High-K interface with reduced density of defects. Synchrotron radiation photoemission spectroscopy (SR-PES) is a powerful method to characterize surfaces and interfaces of many materials, as it is capable to determine their chemical composition as well as the electronic properties. We performed in-situ SR-PES measurements after exposing a GaAs surface to TMA pulses at about 250°C. Upon using the possibility of tuning the incident photon energy we compared the Ga3d spectra at 41 eV, 71 eV, 91 eV and 121 eV, as well as the As3d at 71 eV and 91 eV. Finally, we show that using SR-PES allows a further understanding of the surface composition, which is usually not accessible with other techniques.

[en] The rapid cadence of MOSFET scaling is stimulating the development of new technologies and accelerating the introduction of new semiconducting materials as silicon alternative. In this context, 2D materials with a unique layered structure have attracted tremendous interest in recent years, mainly motivated by their ultra-thin body nature and unique optoelectronic and mechanical properties. The development of scalable synthesis techniques is obviously a fundamental step towards the development of a manufacturable technology. Metal-organic chemical vapor deposition has recently been used for the synthesis of large area TMDs, however, an important milestone still needs to be achieved: the ability to precisely control the number of layers and surface uniformity at the nano-to micro-length scale to obtain an atomically flat, self-passivated surface. In this work, we explore various fundamental aspects involved in the chemical vapor deposition process and we provide important insights on the layer-dependence of epitaxial MoS₂ film’s structural properties. Based on these observations, we propose an original method to achieve a layer-controlled epitaxy of wafer-scale TMDs. (paper)

[en] We present a method for area selective deposition of 2D WS₂ nanoribbons with tunable thickness on a dielectric substrate. The process is based on a complete conversion of a pre-patterned, H-terminated Si layer to metallic W by WF₆, followed by in situ sulfidation by H₂S. The reaction process, performed at 450 °C, yields nanoribbons with lateral dimension down to 20 nm and with random basal plane orientation. The thickness of the nanoribbons is accurately controlled by the thickness of the pre-deposited Si layer. Upon rapid thermal annealing at 900 °C under inert gas, the WS₂ basal planes align parallel to the substrate. (letter)

[en] High resolution X-ray diffraction (HRXRD) measurements were performed using a commercially-available X-ray metrology tool, the BedeMetrix-L, on small test pads containing arrays of SiGe line structures selectively deposited in Si recesses with various window dimensions. Reciprocal space maps (RSMs) were performed in two orthogonal <110> directions in order to determine the lattice parameter parallel and perpendicular to the lines. With narrow lines, asymmetric relaxation effects were seen: the SiGe was fully strained along the long dimension of the lines while there was significant relaxation along the short dimension of the lines. The magnitude of the relaxation increased significantly for lines with short dimension below about 1 μm. We show how to determine the lattice parameters, and hence the strain of the SiGe in the [110] and [-110] directions, the Ge composition and the relaxation initially using RSMs, but with an extension to measurements more suitable for in-fab metrology

[en] Due to its high intrinsic mobility, germanium (Ge) is a promising candidate as a channel material (offering a mobility gain of approximately ×2 for electrons and ×4 for holes when compared to conventional Si channels). However, many issues still need to be addressed before Ge can be implemented in high-performance field-effect-transistor (FET) devices. One of the key issues is to provide a high-quality interfacial layer, which does not lead to substantial drive current degradation in both low equivalent oxide thickness and short channel regime. In recent years, a wide range of materials and processes have been investigated to obtain proper interfacial properties, including different methods for Ge surface passivation, various high-k dielectrics and metal gate materials and deposition methods, and different post-deposition annealing treatments. It is observed that each process step can significantly affect the overall metal–oxide–semiconductor (MOS)-FET device performance. In this review, we describe and compare combinations of the most commonly used Ge surface passivation methods (e.g. epi-Si passivation, surface oxidation and/or nitridation, and S-passivation) with various high-k dielectrics. In particular, plasma-based processes for surface passivation in combination with plasma-enhanced atomic layer deposition for high-k depositions are shown to result in high-quality MOS structures. To further improve properties, the gate stack can be annealed after deposition. The effects of annealing temperature and ambient on the electrical properties of the MOS structure are also discussed. (paper)

[en] We have investigated the three-dimensional configuration of lattice distortions, including lattice plane tilt and twist, in a high-Ge-content constant-composition Si_0.3Ge_0.7 (CC-SG)/compositionally graded SiGe strain-relaxed buffer (graded SRB)/Si(001) stacked structure. Position-dependent ω–2θ–φ mapping (or three-dimensional reciprocal space mapping) by synchrotron-based nanobeam x-ray diffraction revealed the in-plane distributions of both local tilt and twist within an area of 10 × 10 μm on the sample surface. Depth-resolved crystal information was extracted analytically on the basis of structural features in the graded SRB layer. As a result, a series of tomographic maps that show the three-dimensional distributions of tilt and twist around the CC-SG/graded SRB interface were obtained. Tomographic analysis indicates that the orientation of lattice planes in the graded SRB abruptly changes at a specific depth and at a specific interval. The misfit dislocation distribution observed using transmission electron microscopy is not homogeneous but concentrated at a specific depth, which accounts for the abrupt changes of lattice plane tilt and twist. Our tomographic results clearly verify the dislocation morphology in the SiGe stacked structure, which demonstrates that this analysis method can be a powerful tool for quantitative and non-destructive elucidation of a three-dimensional lattice structure with high spatial resolution. (paper)

[en] Highlights: • Atomic layer is deposited by O₃ chemisorption reaction on H-terminated Si(100). • O-content has critical impact on the epitaxial thickness of the above-deposited Si. • Oxygen atoms at dimer/back bond configurations enable epitaxial Si on O atomic layer. • Oxygen atoms at hydroxyl and more back bonds, disable epitaxial Si on O atomic layer. - Abstract: Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic layers of oxygen (O) with interesting electronic and optical properties. To understand the fundamentals of Si epitaxy on O atomic layers, we investigate the O surface species that can allow epitaxial Si chemical vapor deposition using silane. The surface reaction of ozone on H-terminated Si(100) is used for the O deposition. The oxygen content is controlled precisely at and near the atomic layer level and has a critical impact on the subsequent Si deposition. There exists only a small window of O-contents, i.e. 0.7–0.9 atomic layers, for which the epitaxial deposition of Si can be realized. At these low O-contents, the O atoms are incorporated in the Si-Si dimers or back bonds (-OSiH), with the surface Si atoms mainly in the 1+ oxidation state, as indicated by infrared spectroscopy. This surface enables epitaxial seeding of Si. For O-contents higher than one atomic layer, the additional O atoms are incorporated in the Si-Si back bonds as well as in the Si-H bonds, where hydroxyl groups (-Si-OH) are created. In this case, the Si deposition thereon becomes completely amorphous