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Single-crystal silicon carbide (4H-SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for fabrication of next-generation semiconductor devices. In this work, we report a hybrid polishing process combining thermal oxidation pretreatment and soft abrasive polishing to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. By thermal oxidation pretreatment, the hardness of the carbon face has been reduced from 4.6 GPa to 1.7 GPa, which enables highly efficient polishing using CeO 2 slurry. For conventional CeO 2 slurry polishing without pretreatment, scratches still existed after a long polishing duration for 16 h. The probable scratch removal mechanism in CeO 2 slurry polishing has been proposed based on surface morphology changes during polishing. Whereas a scratch-free surface with well-ordered SiC atomic steps was obtained within a short polishing duration of only 3 h when polishing was conducted on a thermally oxidized surface. Our results demonstrate that hybrid polishing combining surface pretreatment and soft abrasive polishing is a promising approach to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. [ABSTRACT FROM AUTHOR]

Tungsten alloy is a crucial engineering material for electrical and optical applications. However, damage-free and highly efficient polishing of tungsten has not been realized yet. We report the abrasive-free polishing of tungsten alloy using electrochemical polishing (ECP), which is an etching process. To achieve balance between polishing efficiency and surface quality, a two-step ECP process has been proposed. Current-driven ECP lasting for 3 min, as the first step, quickly removed the surface grinding marks and subsurface damage while the following potential-driven ECP lasted for 20 min, as the second step, improved the surface roughness and an ultra-smooth surface with an Ra roughness of 17.6 nm was finally obtained. [ABSTRACT FROM AUTHOR]

To realize the damage-free finishing of CVD-SiC substrates, which are used as materials for space telescope mirrors and glass lens molds, plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP) were combined. In this study, the properties of such CVD-SiC substrates, including their surface morphology, composition and crystalline orientation, were investigated. Lapping using diamond abrasives and conventional chemical mechanical polishing (CMP) using CeO 2 slurry were conducted for comparison with the proposed atmospheric-pressure-plasma-based finishing process. Many scratches and a subsurface damage (SSD) layer were formed by the diamond lapping of CVD-SiC. Conventional CMP using CeO 2 slurry was conducted for the damage-free finishing of CVD-SiC. However, the polishing efficiency was very low. In the proposed process, PCVM, which is a noncontact dry etching process, was performed to remove the SSD layer while PAP, which combines plasma modification and soft abrasive polishing, was performed for damage-free surface finishing. PCVM was conducted on a diamond-lapped CVD-SiC surface. After PCVM for a short duration of 5 min, the scratches and SSD layer formed by lapping were completely removed, although the surface roughness was slightly increased. PAP using a resin-bonded CeO 2 grindstone was conducted to decrease the surface roughness of CVD-SiC processed by diamond lapping and PCVM for 5 min, for which a loose-held-type grindstone was demonstrated to be very useful. A flat and scratch-free surface with an rms roughness of 0.6 nm was obtained after PAP finishing. [ABSTRACT FROM AUTHOR]

Electro-chemical mechanical polishing (ECMP), which combines anodic oxidation and soft abrasive polishing, was applied to single-crystal SiC. Ceria (CeO 2 ) slurry was used as an electrolyte for anodic oxidation as well as a polishing medium to remove the oxide layer. As a result of anodic oxidation, the surface hardness decreased from 34.5 GPa to 1.9 GPa, which made it possible to polish the oxidized SiC surface using a very soft abrasive such as CeO 2 . It was found that the material removal rate (MRR) of ECMP for a diamond-abrasive-polished surface was 3.62 μm/h. ECMP using CeO 2 slurry was conducted for 30 min on a diamond-abrasive-polished surface. All the scratches were completely removed and a smooth surface with a root mean square (RMS) roughness of 0.23 nm was obtained. [ABSTRACT FROM AUTHOR]

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO. CeO was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced. [ABSTRACT FROM AUTHOR]

Thermal oxidation (TO) and abrasive polishing were combined for atomic-scale planarization of 4H-SiC. It was found that the oxide/SiC interface was atomically flat regardless of the thickness of the oxide. The specimen prepared by TO was dipped in HF solution to remove the oxide. However, owing to the residual silicon oxycarbide (Si-C-O), the step/terrace structure of 4H-SiC could not be observed. Nanoindentation tests revealed that the hardness of Si-C-O was much lower than that of SiC. A thermally oxidized SiC surface was polished using CeO2 abrasives, which resulted in an atomically flat surface with a well-ordered two-bilayer step/terrace structure. [ABSTRACT FROM AUTHOR]

Even though anodizing has been proved to be a highly efficient oxidation approach of single crystal SiC, the oxidation mechanism is still unrevealed. In this work, the initiation and development of the local oxidation phenomenon during anodizing of SiC have been experimentally studied. Local oxidation occurred on the charge carrier-rich areas like damaged areas and doping sites. The oxidation of the damaged areas has a higher priority compared with that of doping sites during anodizing of SiC. For anodizing of damaged areas, the protrusions generated by local oxidation gathered around the damaged areas. In contrast, protrusions were randomly distributed for anodizing of doping sites. [ABSTRACT FROM AUTHOR]

Abstract: We proposed a novel polishing technique named plasma assisted polishing (PAP) for the finishing of some difficult-to-machine materials, such as diamond, silicon carbide, sapphire and so on. In this work, PAP was applied to the smoothing of reaction sintered silicon carbide (RS-SiC) surface. Experimental results indicated that a higher oxidation rate led to a smoother surface. The smoothing mechanism was discussed based on the relationship between oxidation rate of RS-SiC and polishing rate of oxide layer. Through increase in the oxidation rate and decrease in the polishing rate, a smooth surface with 11.42 nm p–v and 0.91 nm rms was obtained. The amount and depth of scratches also decreased after PAP using ceria abrasives compared with the surface polished by diamond abrasives. [Copyright &y& Elsevier]

Structural phase transition is often expected when crystalline substrates with high mechanical strength are processed by diamond abrasion at nanoscale. The structural evolution and formation of 3 C-SiC substrates abraded by diamond were explored using molecular dynamics simulation. The evoluted structures were derived by analyzing bond length, bond angle and coordination changes of SiC and diamond abrasives before and after nano-abrasion. Our simulation results explicitly elucidate the stable, graphene-like two-dimensional (2D) structural evolution and formation from SiC and diamond crystalline. This generolized finding of 2D structural formation from three-dimensional (3D) materials in nano-abrasion may shed light on developing new preparation options to make graphene-like 2D-SiC, which is predicted to be a chemically and mechanically stable semicondcuting material with oustanding opto-electro properties. [ABSTRACT FROM AUTHOR]

To reveal dislocations in SiC wafers, conventionally, molten KOH etching method has been widely used. However, when highly doped sites exist on the wafer, the molten KOH etching method is not applicable owing to the enhanced isotropic electrochemical etching phenomenon. In this study, plasma etching is first applied to reveal dislocations in a 4H-SiC wafer with both highly doped and lightly doped areas. The mechanisms of dislocation revelation by dry etching have been theoretically analyzed and it has been revealed that the dislocation revelation ability of dry etching is highly related to the temperature of the etching process. The results demonstrate that inductively coupled plasma (ICP) etching can maintain its effectiveness for dislocation revelation of SiC wafers regardless of the doping concentrations. This work offers an alternative approach to indiscriminately and accurately reveal dislocations in SiC wafers. [ABSTRACT FROM AUTHOR]