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Refractive Index Variation of Magnetron-Sputtered a-Si1?xGex by “One-Sample Concept” Combinatory
摘要： Gradient a-Si1?xGex layers have been deposited by "one-sample concept" combinatorial direct current (DC) magnetron sputtering onto one-inch-long Si slabs. Characterizations by electron microscopy, ion beam analysis and ellipsometry show that the layers are amorphous with a uniform thickness, small roughness and compositions from x = 0 to x = 1 changing linearly with the lateral position. By focused-beam mapping ellipsometry, we show that the optical constants also vary linearly with the lateral position, implying that the optical constants are linear functions of the composition. Both the refractive index and the extinction coefficient can be varied in a broad range for a large spectral region. The precise control and the knowledge of layer properties as a function of composition is of primary importance in many applications from solar cells to sensors.
关键词： SiGe,optical properties,spectroscopic ellipsometry
更新于2025-09-10 09:29:36
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Layer-Dependent Dielectric Function of Wafer-Scale 2D MoS <sub/>2</sub>
摘要： Wafer-scale, high-quality, and layer-controlled 2D MoS2 films on c-sapphire are synthesized by an innovative two-step method. The dielectric functions of MoS2 ranging from the monolayer to the bulk are investigated by spectroscopic ellipsometry over an ultra-broadband (0.73–6.42 eV). Up to five critical points (CPs) in the dielectric function spectra are precisely distinguished by CP analysis, and their physical origins are identified in the band structures with the help of first-principles calculations. Results demonstrate that the center energies of these CPs exhibit intriguing layer dependency, which are interpreted by the intrinsic layer-dependent transitions in MoS2. Specially, the change in the imaginary part of the dielectric functions versus the thickness exhibits a “W” like curve, and the two valley bottoms appear at about four-layer and 10-layer respectively. These complex fluctuations are attributed to the alternating domination of the decreasing excitonic effect, the increasing joint density of states, and the mass density increase in relative thick MoS2 samples.
关键词： layer-dependent dielectric function,two-step method,spectroscopic ellipsometry,wafer-scale 2D MoS2
更新于2025-09-10 09:29:36
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Charge transient behaviour and spectroscopic ellipsometry characteristics of TiN/HfSiO MOS capacitors
摘要： A combination of two powerful techniques, namely, charge Deep level transient spectroscopy and spectroscopic ellipsometry is employed on atomic layer deposited Si-metal oxide semiconductor capacitors (MOSCAPs) to investigate the energy ef?ciency of the physical process. Ultra-thin TiN/HfSiO acted as gate-dielectric stack on Si substrate was carefully subjected to rapid thermal processing and subsequent spectroscopic measurements to determine the transient behaviour of charges and electro-optical characteristics. Some key parameters such as trap concentration, activation energy required to surmount the traps, capture cross section, refractive index and extinction coef?cient are found to play an important role in order to assess the energy ef?ciency of the devices both in terms of post-process quality of the retained surface and residual ef?ciency of the process by virtue of dynamics at atomistic scales. The results may provide a useful insight to the Si manufacturing protocols at ever decreasing nodes with desirable energy ef?ciency.
关键词： energy efficiency,charge Deep level transient spectroscopy,MOSCAPs,spectroscopic ellipsometry,TiN/HfSiO
更新于2025-09-10 09:29:36
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(TiO <sub/>2</sub> ) <sub/>1?x</sub> (TaON) <sub/>x</sub> Solid Solution for Band Engineering of Anatase TiO <sub/>2</sub>
摘要： Band engineering of anatase TiO2 was achieved by means of an anatase (TiO2)1?x(TaON)x (TTON) solid solution. Epitaxial thin films of TTON (0.1 ≤ x ≤ 0.9) were synthesized by nitrogen plasma-assisted pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. Epitaxial growth of anatase TTON was confirmed by X-ray diffraction. The lattice constants of the TTON thin films increased with TaON content in accordance with Vegard’s law, indicating formation of a complete solid solution. The bandgaps, band alignment, and refractive indices of the TTON thin films were investigated by combination of spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The bandgap of the anatase TTON systematically decreased with increasing x, mainly because of an upward shift in the valence band maximum caused by broadening of the valence band as a result of hybridization of the shallow N 2p orbital. The position of the conduction band minimum was rather insensitive to chemical composition, which makes the band alignment of anatase TTON suitable for photocatalytic water splitting with visible light. The refractive index of anatase TTON monotonically increased with an increase in x.
关键词： Epitaxial thin films,Vegard’s law,X-ray photoelectron spectroscopy,TTON solid solution,Band engineering,Photocatalytic water splitting,Spectroscopic ellipsometry,Nitrogen plasma-assisted pulsed laser deposition,Anatase TiO2
更新于2025-09-10 09:29:36
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Thermal Atomic Layer Etching of Silicon Using O2, HF and Al(CH3)3 as the Reactants
摘要： The thermal atomic layer etching (ALE) of silicon was performed using O2, HF and Al(CH3)3 as the reactants at temperatures from 225-290°C. This thermal etching process is based on Si oxidation using O2 and conversion of SiO2 to Al2O3 using trimethylaluminum (TMA). Al2O3 is then fluorinated by HF to produce AlF3 prior to removal of AlF3 by a ligand-exchange reaction with TMA. Thermal Si ALE was studied using silicon-on-insulator (SOI) wafers. In situ spectroscopic ellipsometry was employed to monitor simultaneously both the thickness of the top SiO2 layer and the underlying silicon film during Si ALE. These studies observed that the silicon film thickness decreased linearly with the number of reaction cycles while the thickness of the SiO2 layer remained constant. Using an O2-HF-TMA exposure sequence, the Si ALE etch rate was 0.4 ?/cycle at 290°C. This etch rate was obtained using static reactant pressures of 250, 1.0 and 1.0 Torr, and exposure times of 10, 5 and 5 s, for O2, HF and TMA, respectively. The SiO2 thickness was 10-11 ? under these reaction conditions at 290°C. The Si ALE etch rate increased with O2 and TMA pressure before reaching a limiting etch rate at higher O2 and TMA pressures. The order of the reactants affected the Si etch rate. Changing the exposure sequence from O2-HF-TMA to O2-TMA-HF reduced the etch rate from 0.4 to 0.2 ?/cycle at 290°C. Lowering the etch temperature below 290oC also resulted in the reduction of the Si etch rate. Atomic force microscopy (AFM) measurements determined that the root-mean-squared (RMS) roughness of the surface was 2.0 ± 0.2 ? before and after the Si ALE using the optimum reaction conditions. Lowering the static O2 pressures below 250 Torr reduced the etch rate and also increased the RMS surface roughness. There was no evidence for any change in the Si ALE process for ultrathin Si films with thicknesses <100 ? in the quantum confinement regime. Thermal Si ALE should be useful for silicon applications in many areas including electronics, optoelectronics, thermoelectrics and photonics.
关键词： silicon,HF,thermal atomic layer etching,spectroscopic ellipsometry,Al(CH3)3,O2,atomic force microscopy
更新于2025-09-10 09:29:36
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Effect of deposition rate on the growth mechanism of microcrystalline silicon thin films using very high frequency PECVD
摘要： The intrinsic microcrystalline silicon thin films were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Two series of films with different deposition rate 0.30 nm/s and 1.94 nm/s were prepared. The film surface and gas phase reaction growth processes were monitored with real-time spectroscopic ellipsometry and optical emission spectroscopy. The effect of deposition rate on the microcrystalline silicon thin film growth mechanism has been studied. The microcrystalline silicon surface growth was analyzed with KPZ model. The results show that the growth exponent of β is 0.448 for the films with low deposition rate, and the growth exponent of β is 0.302 for the films with high deposition rate. The growth exponent does not increase with deposition rate, but declines. And the reasons for this phenomenon were explained.
关键词： Real time spectroscopic ellipsometry,Microcrystalline silicon,High rate deposition,Optical emission spectrum,Growth mechanism
更新于2025-09-09 09:28:46
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Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation
摘要： The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2×10-4, 3.5×10-4 and 5×10-4 mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr2N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN2 = 2×10-4 mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr2N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr2N phase and semiconducting behaviour of CrN.
关键词： spectroscopic ellipsometry,thin films,chromium nitrides,electrical properties,microstructure
更新于2025-09-09 09:28:46
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Dynamic SIMS, spectroscopic ellipsometry and x-ray diffractometry analysis of SiGe HBTs with Ge grading
摘要： In this paper, SiGe heterojunction bipolar transistors (HBTs) with Ge concentrations up to 40 atomic percent (at%) and different slopes of Ge gradients are characterized by comparing dynamic secondary ion mass spectrometry (D-SIMS) and multi-angle spectroscopic ellipsometry (SE). X-ray diffractometry (XRD) was used as reference. D-SIMS results show that sputter rate and Ge content calibration have major impact on depth pro?le measurements of HBTs with graded SiGe. Strained and relaxed SiGe show differences in Ge content calibration and no difference in sputter rate calibration. Jiang’s protocol was used for Ge content calibration and proven to be valid up to ～50 at% Ge. SE with a combination of 3 angles of incidence (AOIs) (59, 65, 71°) in comparison with the single AOI (71°) realized in industrial setup for semiconductor manufacturing environment was analyzed to ?nd a more stable solution for revealing the thickness of plateau and gradient parts of SiGe base. SE with 71° AOI and rotating compensator is the best choice for in-line HBT with Ge grading characterization. The determination of gradient shape continues to be a challenging task for SE, due to high parameter correlations and the need to use some ?xed parameters within the ?tting procedure. D-SIMS remains the favorite for graded pro?le determination. Results of D-SIMS and SE with ?xed parameters are in good agreement with XRD for HBTs with Ge grading.
关键词： SiGe,XRD,spectroscopic ellipsometry,SIMS,HBT
更新于2025-09-09 09:28:46
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Anisotropic optical properties of highly doped rutile SnO <sub/>2</sub> : Valence band contributions to the Burstein-Moss shift
摘要： The interband absorption of the transparent conducting semiconductor rutile stannic oxide (SnO2) is investigated as a function of increasing free electron concentration. The anisotropic dielectric functions of SnO2:Sb are determined by spectroscopic ellipsometry. The onsets of strong interband absorption found at different positions shift to higher photon energies with increasing free carrier concentration. For the electric field vector parallel to the optic axis, a low energy shoulder increases in prominence with increasing free electron concentration. We analyze the influence of different many-body effects and can model the behavior by taking into account bandgap renormalization and the Burstein-Moss effect. The latter consists of contributions from the conduction and the valence bands which can be distinguished because the nonparabolic conduction band dispersion of SnO2 is known already with high accuracy. The possible origins of the shoulder are discussed. The most likely mechanism is identified to be interband transitions at |k| > 0 from a dipole forbidden valence band.
关键词： interband absorption,spectroscopic ellipsometry,Burstein-Moss shift,SnO2,bandgap renormalization
更新于2025-09-04 15:30:14