3C-SiC Surface Research Articles

Heteroepitaxy of 3C-SiC on different on-axis oriented silicon substrates

The heteroepitaxial growth of 3C-SiC films on on-axis (100), (110), and (111) Si oriented substrates has been investigated. A multistep growth process using low-pressure chemical vapor deposition with trichlorosilane as the silicon precursor was conducted at a growth temperature of 1350 °C. X-ray diffraction analysis (θ-2θ and polar figure) and numerical simulation have been shown to be a suitable method to investigate and understand the SiC film structural properties for each substrate orientation. Epitaxial SiC films with first order twins, at least for growth on (100) and (111) Si, were obtained. SiC growth on (110) Si, on the other hand, showed a change in the growth direction by the observation of first and second order twins from the ⟨110⟩ to ⟨111⟩ direction. This is due to the high growth rate of (110) 3C-SiC/(110) Si heteroepitaxial system which encourages the SiC film to grow in a direction with a higher packing density. It was observed that the 3C-SiC surface morphology and average residual stress depends strongly on the silicon substrate orientation, as confirmed by atomic force microscopy analysis and radius of curvature measurements.

Elaboration of (1 1 1) oriented 3C–SiC/Si layers for template application in nitride epitaxy

Various aspects of the elaboration of (1 1 1) oriented 3C–SiC films on silicon are discussed within a comparative study of different layer characteristics for (1 1 1) and (1 0 0) orientations. The dissimilarities between both orientations are pointed out. This includes the growth mode during the nucleation, the efficacy of defect healing during the growth, the dopant incorporation and the warping of the epiwafer. The results of 3C–SiC surface preparation by chemical mechanical polishing are also demonstrated. All the characteristics of (1 1 1) oriented layers are discussed from the point of view of the application of 3C–SiC/Si epiwafers as templates for nitride growth. The characteristics of AlGaN/GaN based high electron mobility transistor elaborated on 3C–SiC/Si template are presented to validate the template's concept.

Adsorption of atomic and molecular oxygen on 3C-SiC(111) and(1¯1¯1¯)surfaces: A first-principles study

Density-functional theory calculations were performed to investigate the adsorption of oxygen on 3C-SiC(111) and $(\overline{1}\overline{1}\overline{1})$ surfaces, including single O atom, double O atoms, and variable oxygen coverage adsorptions. We find that the bridge (BR) and on-top (OT) sites are the most stable adsorption sites for the (111) and $(\overline{1}\overline{1}\overline{1})$ surfaces, respectively. According to the two-dimensional potential energy surface achieved, the lowest continuous oxygen diffusion path over the whole surface seems to be $\text{BR}\ensuremath{\rightarrow}\text{H}3\ensuremath{\rightarrow}\text{BR}\ensuremath{\rightarrow}\text{BR}(\text{neighbor})\ensuremath{\rightarrow}\text{etc}\text{.}$ By studying the double O atoms adsorption on 3C-SiC(111) surface, we find that 2-BR is the most favorable configuration. By comparing adsorption energies and O-O distances with reference values, we get that there is an electronic induction effect, which helps to get a more stable adsorption structure, between neighboring O adatoms with small amount of negative charge, which favors a medium O-O distance. Spin-unrestricted first-principles molecular-dynamics calculations have been carried out to achieve more dynamic information and comprehensive understanding of the molecular oxygen adsorption on a 3C-SiC(111) surface. The results confirm our determined diffusion path and one of the preferred double atoms configuration. By studying the adsorption of oxygen at 3C-SiC(111) and $(\overline{1}\overline{1}\overline{1})$ surfaces as a function of oxygen coverage, we find that the adsorption energy initially increases [1/9--3/9 monolayer (ML)] then significantly decreases (3/9--6/9 ML) with increasing oxygen coverage and finally reaches a stable value (7/9--1.0 ML) for 3C-SiC(111) surface. For $3\text{C-SiC}(\overline{1}\overline{1}\overline{1})$ surface, the trend is similar to the (111) surface case; however the variation is small when the oxygen coverage is above 3/9 ML and the adsorption energy at 1/9 ML coverage is lower. By combining the results of adsorption energy, structure evolution, and electronic-density difference calculations, we get that the total adsorption energy is determined by the interaction between adatoms and surface reconstructions: attractive (respectively, repulsive) interactions between adatoms make the adsorption structure more (respectively, less) stable, i.e., it gets a larger (respectively, smaller) adsorption energy; however, surface reconstructions can eliminate the stress caused by repulsive interactions between adatoms and make the adsorption structure to be stable.

Structural Properties of 3C-SiC Grown by Sublimation Epitaxy

The present paper deals with morphological and structural investigation of 3C-SiC layers grown by sublimation epitaxy on on axis 6H-SiC(0001) at source temperature 2000 °C, under vacuum conditions (<10-5 mbar) and different temperature gradients in the range of 5-8 °C/mm. The layer grown at a temperature gradient 6 °C/mm has the largest average domain size of 0.4 mm2 assessed by optical microscope in transmission mode. The rocking curve full width at half maximum (FWHM) of (111) reflection is 43 arcsec which suggests good crystalline quality. The AFM image of the same layer shows steps with height 0.25 nm and 0.75 nm which are characteristic of a stacking fault free 3C-SiC surface and c-axis repeat height, respectively.

Characteristics of Polycrystalline 3C-SiC Thin Films Grown on AlN Buffer Layer by CVD

This paper describes the characteristics of poly (Polycrystalline) 3C-SiC grown on SiO2 and AlN buffers, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each buffer layer were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (Full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was 1100 °C. The surface chemical composition and the electron mobility of poly 3C-SiC grown on each buffer layer were investigated by XPS and Hall Effect. The chemical compositions of surface of poly 3C-SiC grown on SiO2 and AlN were not different. However, their electron mobilities were 7.65 ㎝2/V.s and 14.8 ㎝2/V.s, respectively. Therefore, since the electron mobility of 3C-SiC/AlN was two times higher than that of 3C-SiC/SiO2, AlN is a suitable material, as buffer layer, for SiC growth with excellent crystalline quality.

Molecular dynamics simulations of nanoscratching of 3C SiC

We have carried out molecular dynamics simulations of nanoindentation followed by scratching at constant depth on the Si-terminated (0 0 1) surface of 3C SiC. The dependence of the friction coefficient, scratch hardness, and wear on scratching depth, velocity, direction, and indenter size and shape are investigated. In general, both the scratch hardness and friction coefficient increase with indentation depth but decrease with increasing scratching speed. We also find that the scratch hardness and friction coefficient are anisotropic, i.e. they are larger when scratching in the [1 1 0] direction than in the [1 0 0] direction. The friction coefficient also depends on the rake angle of the tool and is larger for a pyramidal indenter, due to the presence of a large negative rake angle in this case. While the primary mode of wear observed for scratching is ploughing in good agreement with experimental studies, there is significantly more pile-up and chip formation in the [1 1 0] direction. We have also used the shortest path ring distribution, pair-correlation function, bond-angle distribution and bond number analysis to investigate the nature of the plastic deformation due to nanoscratching. We find that scratching leads to a partial amorphization of the material along the scratching trajectory. The size of the amorphization region increases with scratching velocity, thus explaining the decrease in scratch hardness and friction coefficient for higher scratching velocities.

Ohmic contacts to polycrystalline 3C–SiC films for extreme environment microdevices

Ohmic contact characteristics were studied under the surface treatments of poly 3C–SiC films heteroepitaxially grown on SiO 2/Si wafers by APCVD. The poly 3C–SiC surface was polished to remove submicron-sized roughness and to get flat and smooth surface using chemical–mechanical polishing (CMP) process. However, some scratching marks on the poly 3C–SiC have remained surface due to the mechanical defect of CMP process. To remove a part of subsurface damage and scratching marks, the polished surface was oxidized by wet-oxidation furnace and it has been etched by diluted HF solution. Titanium tungsten (TiW) thin film was deposited on the surface treated poly 3C–SiC using circular transmission line model as a metallization process and it was annealed through the rapid temperature annealing (RTA) process to improve interfacial adhesion. The contact resistivity of the treated 3C–SiC surface was measured as the lowest 1.2 × 10 −5 Ω cm 3 at 900 °C for 45 s.

Atomic Crack Defects Developing at Silicon Carbide Surfaces Studied by STM, Synchrotron Radiation-Based μ-spot XPS and LEEM

Atomic structure and morphology of 6H-SiC(0001) and 3C-SiC(100) surfaces are studied by scanning tunneling microscopy (STM), synchrotron radiation-based !-spot x-ray photoemission spectroscopy (!-spot XPS) and low energy electron microscopy (LEEM). STM shows very high quality Si-rich 6H-SiC(0001) 3x3 surfaces with less than 2% of atomic defects. Si removal upon annealing leads to atomic crack defects formation with a novel 2"3x2"3-R30° reconstruction coexisting with few 3x3 domains having no crack, suggesting important stress relief during the phase transition. LEEM also shows cracks formation on cubic 3C-SiC(100) surfaces and gives insights about surface morphology with large faceting and mesa (!m) formation. These defect fractures developing upon Si removal are likely to be also generated during initial oxidation since the initial oxygen interaction tends to relieve surface strain on SiC in contrast to Si surfaces. These atomic crack defects could be related to the interface electronic states recurrent at SiO2/SiC interfaces.

Multimillion-atom nanoindentation simulation of crystalline silicon carbide: Orientation dependence and anisotropic pileup

We have performed multimillion-atom molecular dynamics simulations of nanoindentation on cubic silicon carbide (3C-SiC) surfaces corresponding to three different crystallographic directions, (110), (001), and (111), using pyramidal-shaped Vickers indenter with 90° edge angle. Load-displacement (P-h) curves show major and minor pop-in events during loading. Detailed analysis of the (110) indentation shows that the first minor discontinuity in the P-h curve is related to the nucleation of dislocations, whereas the subsequent major load drops are related to the dissipation of accumulated energy by expansion of dislocation loops and changes of slip planes. Motion of dislocation lines in the indented films involves a kink mechanism as well as mutually repelling glide-set Shockley partial dislocations with associated extension of stacking faults during the expansion of dislocation loops. Our simulations provide a quantitative insight into the stress distribution on slip planes and stress concentration at kinks and dislocation cores. The estimated Peierls stress is 7.5GPa≈3.9×10−2G, where G is the shear modulus. We find that similar deformation mechanisms operate during nanoindentation of the three surfaces but the calculated hardness values are different, the highest being 27.5GPa for the (111) plane. Anisotropic pileup patterns are observed after the indenter is unloaded and they all reside on (111) and (1¯1¯1) slip planes. These patterns are closely related to dislocation activities on the two slip planes. The anisotropy is a consequence of the asymmetry of the 3C-SiC crystal in which only (111) and (1¯1¯1) slip planes are active out of the {111} family.

Surface studies of hydrogen etched 3C-SiC(001) on Si(001)

The morphology and structure of 3C-SiC(001) surfaces, grown on Si(001) and prepared via hydrogen etching, are studied using atomic force microscopy (AFM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). On the etched samples, flat surfaces with large terraces and atomic steps are revealed by AFM. In ultrahigh vacuum a sharp LEED pattern with an approximate (5×1) periodicity is observed. AES studies reveal a “bulklike” composition up to the near surface region and indicate that an overlayer consisting of a weakly bound silicon oxide monolayer is present.

Molecular dynamics simulations of reactive etching of SiC by energetic fluorine

Molecular dynamics simulations were performed to investigate F continuously bombarding Si-terminated 3C-SiC(001) surfaces with incident energies of 10, 100 and 200 eV at normal incidence and room temperature. For an energy of 10 eV, deposition only occurs on the surface. For energies larger than 10 eV, accompanying the saturation of F uptake, a balance between F deposition from the incident atoms and F removal from the fluorinated substrate is established, while the steady-state etching is reached. The simulated results demonstrate that Si atoms in SiC are preferentially etched, which is in good agreement with experiments. The preferential etching of Si results in formation of a C-rich interfacial layer whose thickness increases with increasing incident energy. The analysis shows that Si-containing etch products are dominant.

극한 환경 MEMS용 옴익 접촉을 위한 다결정 3C-SiC 박막의 표면 처리 효과

This paper describes the TiW ohmic contact characteristics under the surface treatment of the polycrystalline 3C-SiC thin film grown on wafers by APCVD. The poly 3C-SiC surface was polished by using CMP(chemical mechanical polishing) process and then oxidized by wet-oxidation process, and finally removed SiC oxide layers. A TiW thin film as a metalization process was deposited on the surface treated poly 3C-SiC layer and was annealed through a RTA(rapid thermal annealing) process. TiW/poly 3C-SiC was investigated to get mechanical, physical, and electrical characteristics using SEM, XRD, XPS, AFM, optical microscope, I-V characteristic, and four-point probe, respectively. Contact resistivity of the surface treated 3C-SiC was measured as the lowest at for 45 sec. Therefore, the surface treatments of poly 3C-SiC are necessary to get better contact resistance for extreme environment MEMS applications.

In situ study of the initial stages of diamond deposition on 3C–SiC (100) surfaces: Towards the mechanisms of diamond nucleation

The mechanisms involved in the diamond nucleation on 3C–SiC surfaces have been investigated using a sequential in situ approach using electron spectroscopies (XPS, XAES and ELS). Moreover, diamond crystals have been studied by HRSEM. The in situ nucleation treatment allows a high diamond nucleation density close to 4 × 10 10 cm − 2. During the in situ enhanced nucleation treatment under plasma, a negative bias was applied to the sample. The formation of an amorphous carbon phase and the roughening of the 3C–SiC surface have been observed. The part of these competing mechanisms in diamond nucleation is discussed.

Stability of 3C-SiC surfaces under diamond growth conditions

The present study deals with the interaction of C-terminated c(2×2) and Si-rich 3×2 3C-SiC (100) reconstructed surfaces with a microwave plasma chemical vapor deposition used for diamond growth. Pure hydrogen and hydrogen/methane exposures have been carried out. Their effects on the atomic ordering and the stoichiometry within the first planes have been studied in situ using low energy electron diffraction and electron spectroscopies: x-ray photoelectron spectroscopy, x-ray Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy. 5min plasma exposures result in a lost of the initial reconstructions, a postplasma oxygen contamination, and strong modifications of the stoichiometry within the first planes. Indeed, the stability of well defined 3C-SiC surfaces depends strongly on their termination: C-terminated surface exhibits a high inertia while the Si-rich surface undergoes partial etching. The three first silicon atomic planes involved in the 3×2 reconstruction are removed upon pure hydrogen plasma while a monolayer is preserved after hydrogen/methane exposure.

Evaluation of Schottky Barrier Height of Al, Ti, Au ,and Ni Contacts to 3C-SiC

The Schottky barrier height (SBH) of Al, Ti, Au, and Ni contacts to n- and p-type 3C-SiC is investigated by means of I-V and C-V measurements. All metal contacts to n- (net donor concentration: 1.0 x 1016 /cm3) and p-type (net acceptor concentration: 4 x 1016 /cm3) 3C-SiC show the rectifying I-V characteristics except for Al contact to n-type 3C-SiC. Only Al contact to n-type 3C-SiC shows the ohmic characteristics. As the work function of metal is increased from 4.3 (Ti) to 5.2 (Ni) eV, SBH for n-type 3C-SiC is increased from 0.4 to 0.7 eV and SBH for p-type 3C-SiC is decreased from 2.2 to 1.8 eV. The small change of SBH for 3C-SiC may be correlated to the crystal orientation and the defects on the surface of 3C-SiC.

‘Switch-Back Epitaxy’ as a Novel Technique for Reducing Stacking Faults in 3C-SiC

A new technique that reduces stacking fault (SF) density in 3C-SiC, termed switch-back epitaxy (SBE), is demonstrated regarding its effects on morphological and electrical properties. SBE is a homoepitaxial growth process on backside of 3C-SiC grown on undulant-Si. The key feature of SBE, the surface polarity of residual SFs in 3C-SiC, which cannot be erased by heteroepitaxial growth on undulant-Si, is converted from the Si-face to the C-face. The SF density on the surface of 3C-SiC grown by SBE shows a remarkable decrease to one-seventh lower than that on undulant- Si. The leakage current of pn-diode epitaxially fabricated on the 3C-SiC substrate grown by SBE decreases to as low as one-thirtieth that on 3C-SiC substrate grown without SBE. These results suggest that SBE eliminates the SFs on the surface of 3C-SiC and subsequently reduces the leakage current at pn-junction thus fabricated.

Low Energy Ion Modification of 3C-SiC Surfaces

The effects of argon and nitrogen bombardment of 3C-SiC surfaces at acceleration voltages below 2 keV were studied by stylus profilometry, reflectometry, reflection high energy electron diffraction and Auger electron spectroscopy (AES). The erosion rate of the SiC surface was determined. It was found that the sputtering rate for argon was three times higher compared to nitrogen. AES measurements revealed argon and nitrogen incorporation at a depth of a few nanometers as well as stoichiometric changes at the same depth scale independent of the acceleration voltage. In the case of the interaction of nitrogen ions with the 3C-SiC surface the formation of a SiCNalloy was detected.

The structural models for the reconstructions of 3C-SiC(111) and 6H-SiC(0001) surfaces

We propose a double-trimer model and a single-trimer model for reconstructions observed on the surface of the 3C-SiC(111) island and the 6H-SiC(0001)surface, respectively. We study their atomic and electronic structures by using firstprinciples calculations within density-functional theory. The total energy calculationsindicate that the double-trimer model and the single-trimer model are energetically morefavourable than the previously reported DV model and Tri-Ad model, respectively. Thesimulated scanning tunnelling microscopic images for these two models agree fairly wellwith the experimental observations. The surface energy band structures of thesingle-trimer model and the Tri-Ad model were compared, which might providea criterion for the further discrimination of the exact models by experimentalevaluation.

Strong dispersion of the surface optical phonon of silicon carbide in the near vicinity of the surface Brillouin zone center

The surface optical or Fuchs–Kliewer phonons of the (0 0 1) surface of 3C-SiC and the Si-terminated (0 0 0 1) surfaces of 4H- and 6H-SiC have been investigated with high resolution electron energy loss spectroscopy (HREELS). For each of the SiC polytypes the frequency of the surface optical phonon changes with surface reconstruction, indicating subtle differences in the static polarization at differently reconstructed surfaces. Due to their anisotropy, hexagonal surfaces exhibit a second, much weaker Fuchs–Kliewer mode. For all surfaces under examination, a linear dispersion of the Fuchs–Kliewer mode frequency has been found for wave vectors close to the Γ ¯ -point. This dispersion can be explained by dynamical dipole coupling between atomic oscillators at the surface of the highly polar silicon carbide.

Surface morphology and structure of hydrogen etched 3C-SiC(001) on Si(001)

AbstractThe surface of 3C-SiC(001) single-crystal epilayers grown on Si(001) substrates is well known to be inhomogeneous and defective. Therefore, the control and understanding at the atomic scale of 3C-SiC surfaces is a key issue. We study the effect of hydrogen etching at different temperatures on the morphology of 3C-SiC(001) surfaces by using Nomarksi optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). As-grown 3C-SiC(001) samples have been hydrogen etched in a horizontal hot-wall chemical vapor deposition (CVD) reactor at atmospheric pressure for different times and temperatures. Flat, high-quality surfaces presenting defined atomic terraces were observed within the 3C-SiC grain boundaries after etching at 1200°C for 30 minutes. Higher etching temperatures resulted in surfaces with step bunching and enlarged surface defects. Samples etched under the best conditions have been studied using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES).