Single Crystal Si Films Research Articles

In-situ deposited HfO2 and Y2O3 on epi-Si/p-Ge—a comparative study of the interfacial properties and reliability

Single-crystal Si films six-monolayers in thickness were epitaxially grown on Ge(001) surface to minimize the formation of undesirable GeO x with subsequent deposition of HfO2 and Y2O3. The interfacial properties and reliability of the in-situ deposited high-κ oxides on epi-Si/p-Ge(001) were compared. We have achieved interface trap density (D it) values of (1–3) × 1011 eV−1cm−2 in the Y2O3/epi-Si/p-Ge(001), which are two times lower than those of the HfO2/epi-Si/p-Ge(001). The capacitance-equivalent-thicknesses under different annealing conditions were extracted to analyze the interdiffusion in the gate stacks under various thermal treatments. Y2O3/epi-Si/Ge exhibited higher thermal stability than HfO2/epi-Si/Ge. In both high-κ’s gate stacks, the effective charge sheet densities (ΔN eff) are lower than the targeted value of 3 × 1010 cm−2. Compared to the Y2O3 gate stacks, attainment of a high acceleration factor of 11 in the HfO2 gate stacks suggested an improved defect-carrier decoupling in the latter stacks.

Evaluation of uncertainty in measuring thin crystal thickness and extinction distance by Kossel-Möllenstedt pattern analysis

In this paper, the local thickness of single crystal Si film sample and the extinction distance <inline-formula><tex-math id="M11">\begin{document}$ {\xi }_{400} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M11.png"/></alternatives></inline-formula> of the (400) plane of Si crystal are obtained by analyzing the double-beam converging beam diffraction (CBED) pattern of single crystal Si film sample under the 200 kV of accelerated voltage. The factors affecting the measurement uncertainty are analyzed, and the influence coefficients of each factor on the measurement uncertainty are discussed by using the concept of first-order partial derivative. The measurement uncertainty of thin crystal thickness and extinction distance are evaluated and expressed according to national standards GB/T 27418-2017. The conclusions are as follows. The local thickness of the measured Si crystal is estimated at 239 nm, the combined standard uncertainty is 5 nm, and the relative standard uncertainty is 2.2%. With the inclusion probability being 0.95, the coverage factor is 2.07 and the expanded uncertainty is 11 nm. With the accelerated voltage being 200 kV, the extinction distance of Si crystal (400) plane is estimated at 194 nm, the combined standard uncertainty of the extinction distance is 20 nm, and the relative standard uncertainty of the extinction distance is 10%. With the inclusion probability being 0.85, the coverage factor is 1.49 and the expanded uncertainty is 30 nm. The main factors that can affect the combined standard uncertainty of sample thickness <i>t</i><sub>0</sub> are camera constant, accelerating voltage and sample thickness, while the factors that influence the combined standard uncertainty of extinction distance are camera constant, accelerating voltage and extinction distance. The influence of the uncertainties of the measurement data of the Kossel-Möllenstedt pattern on the uncertainty of the extinction distance is <inline-formula><tex-math id="M12">\begin{document}${n}_{i}{\left( {\xi }/{t}\right)}^{3}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M12.png"/></alternatives></inline-formula> times that on the sample thickness, and their influence on the slope of the fitting line is about <inline-formula><tex-math id="M13">\begin{document}$ {n}_{i} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M13.png"/></alternatives></inline-formula> times that on the intercept of the line, where <inline-formula><tex-math id="M14">\begin{document}$ {n}_{i} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M14.png"/></alternatives></inline-formula> is a positive integer and greater than or equal to 1. If the sample is not too thin, that is, <inline-formula><tex-math id="M15">\begin{document}$ {n}_{i} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212271_M15.png"/></alternatives></inline-formula> is greater than 1, then the uncertainty of crystal thickness will be smaller than the uncertainty of extinction distance.

A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited.

Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light.

Observation of Superheating of Si at the Si/SiO2 Interface in Pulsed-laser irradiated Si Thin Films

ABSTRACTSubstantial superheating of single-crystal Si films at and near the bottom Si/SiO2 interface was observed. This was accomplished via back-side irradiation of a (100) single-crystal Si film on a quartz substrate using an excimer-laser pulse. The spatiotemporal details of the melting transition were tracked in situ using surface-side and substrate-side transient reflectance measurements, and the one-dimensional thermal profile evolution within the solid film during the heating period was numerically computed using the experimentally extracted temporal profile of the incident beam and temperature-dependent optical and thermal parameters of the materials. A simple lower-bound estimation identifies that superheating in excess of 100 K was attained within Si along the bottom (100)-Si/SiO2 interface even at moderate beam energy densities.

Low temperature liquid phase epitaxy with Sn‐based solvent

AbstractSilicon thin film is an attractive option for solar cell applications because of their low cost potential. Liquid Phase Epitaxy (LPE) is an interesting technique because it allows growth of single crystal Si film even at low temperature (<800 °C). Main difficulties are the low solubility of silicon in usual solvent and the presence of a native silicon oxide. In this study, we developed a technique using two successive different Sn‐based melts, one to remove native oxide, second one to grow the active layer under argon or hydrogen flow. This technique leads to smooth and homogeneous Si layer presenting a p/p+ structure. Solar cells were fabricated using standard technology. The photo‐generated current density is in the 16‐19 mA/cm2 range after of Si3N4 coating deposition. To improve active layer thickness and to enlarge the Si solubility, we proposed to use metallic alloys as Si‐Sn‐Cu‐Al. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Tensile-Strained Single-Crystal Si Film on Insulator by Epitaxially Seeded and Laser-Induced Lateral Crystallization

Tensile-strained single-crystal silicon films on insulator islands have been grown from Si wafer substrates by a process combining selective epitaxial growth (SEG) and pulsed laser crystallization. An amorphous Si film on an insulator island is completely melted by a single excimer laser pulse, leading to the solidification of the molten Si seeded from epitaxially grown single-crystal Si regions. Analyses of the resulting microstructures reveal that the laterally crystallized film is single-crystalline. A tensile strain of up to 8.8×10-3 within the crystallized region was measured by Raman spectroscopy. The tensile-strained Si film has potential applications in high-performance devices for three-dimensionally stacked integrated circuits.

Characterization & Analysis of Sub-Grain Boundaries in Sequential Lateral Solidification Processed SOI Films

AbstractThe nature of the formation of sub-grain boundaries within sequential lateral solidification (SLS) processed thin silicon films has been examined using single crystal Si films as a pre- cursor material. Experimental details include the use of an excimer laser projection system and straight-slit beamlets to produce directionally solidified microstructures. Within the SLS processed silicon-on-insulator (SOI) films, three microstructurally distinct regions are identi-fied: (1) an initial planar defect-free area (the extent of which can depend on laser fluence and orientation); (2) a transitional area within which the sub-grain boundaries appear and propagate in a well-defined direction relative to the crystallographic orientation; and (3) a final area characterized by sub-grain boundaries aligning approximately to the scan direction, and the in-plane texture becoming more random. We discuss the results within the context of a plastic deformation model of sub-grain boundary formation.

An Origin of KL Absorption Edge in Si·K-XAFS

A small jump of X-ray absorption is observed at about 130eV above the a-Si:H K edge. The jump was explained as a multielectron excitation, which is identified as a Is2p→3p'ε'p transition. The jump is called as KL absorption edge. XAFS spectra of a-Si, a-Si:H thin films and single crystal Si films are observed using synchrotron radiation. The energy of the jump is measured and determined as 136eV above the K edge. The observed energy suggests that the small jump of X-ray absorption indicates the existence of microcrystalline Si in the a-Si and a-Si:H thin films.

Surface Cleaning for Silicon Epitaxy Using Photoexcited Fluorine Gas

ABSTRACTWe studied surface cleaning using photoexcited fluorine gas diluted with hydrogen (UV/F2/H2). We found that UV/F2/H2 cleaning selectively removes native Si oxides from thermal oxides without etching the bulk Si. After UV/F2/H2 cleaning, hydrogen atoms terminate almost all the dangling bonds on the Si surface, and fluorine atoms terminate the few remaining bonds. UV/F2/H2 cleaning also flattens the Si surface. We applied UV/F2/H2 cleaning to Si epitaxy and obtained single-crystal Si films with preannealing and growth temperatures as low as 600°C, 150°C lower than for conventional methods. UV/F2/H2 cleaning is a good dry precleaning method for various processes that include Si epitaxy.

Removing native oxide from Si(001) surfaces using photoexcited fluorine gas

This letter discusses the reaction between (001) oriented Si surfaces and photoexcited fluorine gas resulting in the removal of the native Si oxide. For an F2/Ar gas system, the bulk Si was etched in areas where the native Si oxide had been completely removed. However, by using an F2/H2 gas system, only the native Si oxide was removed. We used this method to remove the native Si oxide in Si epitaxial growth. A high-quality single-crystal Si film surface was obtained up to a maximum temperature of 600 °C through this Si growth process. We also characterized the etching of a thermal oxide, silicon nitride, and silicon carbide.

Mechanisms and kinetics of Si atomic-layer epitaxy on Si(001)2×1 from Si2H6

Single-crystal Si films have been grown on Si(001)2×1 substrates by ultraviolet (UV) photostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML), 1 ML=6.8×1014 cm−2, over a wide range of deposition parameters: growth temperature (Ts=180 –400 °C), Si2H6 exposure (peak pressure during gas pulse=0.1–5 mTorr), UV laser energy density (ℰ=250–450 mJ cm−2 where ℰmax is determined by Ts ), and number of UV laser pulses per cycle. A film growth model, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, is used to describe the reaction pathway for the process. Si2H6 is dissociatively adsorbed on Si surface dimers as two SiH3 radicals which subsequently dissociate to SiH2 and H. Site blocking during the adsorption and surface dissociation steps limits the surface coverage to 2.9×1014 SiH2 cm−2 (hence, R=0.43 ML per cycle). The H terminated silylene-saturated surface is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≊20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts<180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≊0.5 eV. At Ts>400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Plan-view and cross-sectional transmission electron micrographs together with selected-area and convergent-beam electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.

XPS and AES analysis of Si/Ge heterostructure interface

In this paper a Si/Ge (111) heterostructure grown by rapid lamp heating and very low pressure chemical vapor deposition (RLH/VLP-CVD) has been studied. X-ray diffraction and Raman scattering spectra have shown that the epilayer is a single crystal Si film with good structure. The results of XPS and AES analysis indicate that there is a broad transition region composed of GexSi1−x (0 ⩽ x ⩽ 1) alloy material between the epilayer and the substrate, so that a Si-GexSi1−x-Ge multilayer heterostructure has been obtained. In the transition region the oxygen concentration is very low, which is perhaps caused by Ge atoms in the layer. In the Si epilayer oxygen atoms are found in the interstitial sites in the Si lattice.

Recrystallization of silicon film on insulating layers using a laser beam split by a birefringent plate

20-μm-wide, 1-mm-long, single-crystal Si films on SiO2 have been produced using a cw Ar laser beam split by a birefringent quartz plate. The single-scan recrystallized region width has been widened by multiple beam splitting. The resultant single-crystal region obtained by multiple scan from the seed is a 90-μm-wide and 100-μm-long area with rare grain boundaries. This split beam method uses the stable and highly efficient TEM00 mode and needs no prepatterned antireflection layers.

Growth of Si on insulators using electron beams

The use of electron beams for melting and recrystallizing polycrystalline silicon layers in silicon-on-insulator structures is described. The formation of single crystal Si films with low angle grain boundaries or of large parallel grains has been achieved, similar to results for other beam and radiant heat source techniques. However, the electron beam approach has been much less thoroughly investigated than other heating sources. The advantages and disadvantages of electron beams, relative to other heat sources, are discussed, as well as the current state of application.

Epitaxial film transfer technique for producing single crystal Si film on an insulating substrate

Epitaxial film transfer, a new technique for producing a single crystal Si film with both large size and high quality on an insulating substrate, is demonstrated. The technique in which an epitaxial Si film is transferred to a secondary substrate by using three fundamental processes of epitaxial growth, bonding of two wafers, and substrate elimination, can produce a 2-in. single crystal Si film as thin as 1.5 μm on a insulating substrate. Thickness variation can be controlled to ±0.06 μm across a 2-in. wafer. An epitaxial Si film is transferred without significant degradation in quality although a fine film waving exists.

PROPERTIES OF EPITAXIAL Si FILMS GROWN ON YTTRIA-STABILIZED CUBIC ZIRCONIA SUBSTRATES BY CHEMICAL VAPOR DEPOSITI ON

Epitaxial growth of single-crystal Si films on monocrystalline yttria-stabilized cubic zirconia, (Y₂O₃)_m (ZrO₂)_(1-m) substrates with m=0.09 - 0.33 has been realized for the first time by the pyrolysis of SiH₄ in H₂ carrier gas. Films and substrates were characterized by means of Nomarski optical and scanning electron microscopies, reflection electron diffraction, MeV₄He₊ Rutherford backscattering and channeling, X-ray diffraction, transmission electron microscopy (TEM), secondary ion mass spectrometry, and electrical measurements. Single-crystal film growth was achieved on the three principal substrate cubic planes (100), (110), and (111) in the temperature range 975-1077°C at deposition rates of 0.08 - 1.2µm/ min. The orientations of the Si films were found to be the same as those of the substrates. The nearsurface crystal quality of several 0.4µm thick, (100) oriented Si films on yttria - stabilized zirconia was found by MeV He⁺ channeling and TEM to be superior to that of commercial (100) Si on sapphire films of similar thickness. The electrical properties of nominally undoped films were found to depend critically on the pre-deposition, in-situ substrate preparation. The effect of the ionic superconduction properties of the substrate material on the structure of the deposited Si films will also be discussed.

Lateral seeding epitaxy by cw Ar laser irradiation and by high temperature chemical vapor deposition technique

A single crystal Si film of [111] orientation has been obtained over patterned amorphous insulating layer stripes for lateral seeding recrystallization. High-temperature, vapor-phase-epitaxial (VPE) growth technique has been utilized to form single and polycrystalline Si films on (111) Si substrate with the insulator stripes. The single crystal film on the exposed Si substrate and polycrystalline film on insulator were recrystallized with a scanning cw Ar laser. Topographical features and crystalline perfection associated with the laser-induced recrystallization were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and TED (transmission electron diffraction). At high power laser irradiation, the resulting recrystallization of polycrystalline Si seeded by single crystal Si deposited on substrate has been observed.

Electron mobility enhancement in epitaxial multilayer Si-Si1−xGex alloy films on (100) Si

Enhanced Hall-effect mobilities have been measured in epitaxial (100)-oriented multilayer n-type Si/Si1−xGex films grown on single-crystal Si substrates by chemical vapor deposition. Mobilities from ∼20 to 40% higher than that of epitaxial Si layers and ∼100% higher than that of epitaxial SiGe layers on Si were measured for the doping range ∼8×1015–∼1017 cm−3. The mobilities of multilayer Si/SiGe films approach that of single-crystal Si films at ∼2×1017 cm−3. No mobility enhancement was observed in multilayer p-type (100) films and n-type (111)-oriented films. Experimental studies included the effects upon film properties of layer composition, total film thickness, doping concentrations, layer thicknesses, and growth temperature.

Recrystallization of Si on amorphous substrates by doughnut-shaped cw Ar laser beam

Continuous single-crystal Si films longer than 600 μm over SiO2 have been produced with or without lateral epitaxial growth from bulk silicon seed by changing the mode structure of the cw Ar laser beam. The thermal profile of the laser spot is controlled by using a doughnut-shaped beam instead of usual Gaussian one to suppress competitive nucleation from side edges of the molten zone. The result indicates that the liquid-solid interface line profile is the most essential limiting parameter on the mechanism of regrowth.

Oriented Crystal Growth of Si on SiO2 Patterns by Pulse Ruby Laser Annealing

Poly-Si films 200–600 nm thick deposited on (100) Si substrates having SiO2 stripe patterns have been transformed by Q-switched pulse ruby laser irradiation with energy densities between 1.0 and 2.0 J/cm2 into single crystals on the SiO2 patterns as well as on the Si. The regrowth of poly-Si on SiO2 starts laterally from regrown poly-Si on Si just after or during the vertical growth of poly-Si on Si by liquid phase epitaxy. Such lateral growth of poly-Si on SiO2 makes single crystal Si film formation possible on entire SiO2 patterns up to 4 µm wide under appropriate laser power and poly-Si thickness conditions. However, straight stacking faults in the <311> direction remain in Si films grown on SiO2, although dislocations generated in the Si regrown on Si escape to the sample surface along the inclined plane of the SiO2 window edges.