Damage-free Polishing Research Articles

Towards atomic-scale smooth surface manufacturing of β-Ga2O3 via highly efficient atmospheric plasma etching

Abstract The highly efficient manufacturing of atomic-scale smooth β-Ga2O3 surface is fairly challenging because β-Ga2O3 is a typical difficult-to-machine material. In this study, a novel plasma dry etching method named plasma-based atom-selective etching (PASE) is proposed to achieve the highly efficient, atomic-scale, and damage-free polishing of β-Ga2O3. The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga2O3. The core of PASE polishing of β-Ga2O3 is the remarkable lateral etching effect, which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition. As revealed by density functional theory-based calculations, the intrinsic difference in the etching energy barrier of atoms at the step edge (2.36 eV) and in the terrace plane (4.37 eV) determines their difference in the etching rate, and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature. The polishing of β-Ga2O3 based on the lateral etching effect is further verified in the etching experiments. The Sa roughness of β-Ga2O3 (001) substrate is decreased from 14.8 to 0.057 nm within 120 s, and the corresponding material removal rate reaches up to 20.96 μm/min. The polished β-Ga2O3 displays significantly improved crystalline quality and photoluminescence intensity, and the polishing effect of PASE is independent of the crystal faces of β-Ga2O3. In addition, the competition between chemical etching and physical reconstruction, which is determined by temperature and greatly affects the surface state of β-Ga2O3, is deeply studied for the first time. These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga2O3 via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga2O3.

Study of damage mechanism on single crystal 4H-SiC surface layer by picosecond laser modification (PLM)

The stable structure, high hardness, and brittleness of single-crystal 4H-SiC present challenges in achieving efficient and damage-free polishing processing. Ultra-short pulsed laser-induced surface modification provides a new solution to enhance the manufacturability of 4H-SiC. This paper aims to investigate the underlying mechanism of the picosecond laser-induced surface structural changes in 4H-SiC and the process of material removal from solid to vapour, elucidating the interaction mechanism between picosecond laser and 4H-SiC. A temperature gradient distribution model for picosecond laser irradiation on 4H-SiC was built to reveal the formation mechanism of subsurface crack damage. The results show that a combination of phase explosion and thermal effects controlled picosecond laser-modified 4H-SiC surfaces deposited spherical SiO2 particles and the process. The study demonstrates that the cracking behaviour in the subsurface of picosecond laser-modified SiC predominantly occurs in the recast region. The fundamental cause of cracking is attributed to the tensile stresses generated by thermal effects and the volumetric changes in the molten material resulting from the overlapping of neighbouring spots in alternating hot–cold cycles. The nanoindentation demonstrated that laser modification can effectively enhance the machinability of SiC. The findings of this study can provide a theoretical basis for efficient non-destructive machining of hard and brittle materials.

Damage-free polishing of SiC by Slurryless Electrochemical Mechanical Polishing

Damage-free polishing of SiC by Slurryless Electrochemical Mechanical Polishing

Development of High-Efficiency Damage-Free Polishing Technology for Large-Sized Single Crystal Diamond Substrates by Plasma-Assisted Polishing

Development of High-Efficiency Damage-Free Polishing Technology for Large-Sized Single Crystal Diamond Substrates by Plasma-Assisted Polishing

Atomic-scale and damage-free polishing of single crystal diamond enhanced by atmospheric pressure inductively coupled plasma

Diamond is an imperative material for fabricating functional components used in ultra-hard cutting tools, infrared optical windows, high-performance heat dissipations, and other fields. However, high surface roughness caused by competitive crystal growth in diamonds is troublesome. Besides, diamond polishing is challenging due to extreme hardness and chemical inertness. This work is focused on highly efficient and damage-free diamond polishing enhanced by atmospheric pressure inductively coupled plasma (ICP) modified silicon plate. A rapid decrease in the surface roughness from Sa 308 nm–0.86 nm over 300 μm2 in 120 min proclaims ICP enhanced polishing a highly efficient technique. Simultaneously, an atomically smooth, high-quality diamond surface is obtained with a surface roughness of Ra 0.26 nm over 20 μm2. The polishing mechanism based on the OH∗ modification of silicon plate and diamond surface, dehydration condensation reaction occurring at the interface of OH∗ terminated surfaces, and subsequent mechanical shearing of carbon, is proposed. The optical emission spectra of ICP, and XPS of the polished diamond surface endorse the material removal mechanism. The TEM and Raman analysis of the ICP enhanced polished surfaces promote the damage-free removal of the mechanically induced damaged layer. The ICP enhanced polishing with modified silicon plate shows great potential in damage-free atomic processing and a promising future as a commercial diamond polishing technique.

Dominant factors and their action mechanisms on material removal rate in electrochemical mechanical polishing of 4H-SiC (0001) surface

Slurryless electrochemical mechanical polishing (ECMP) has been confirmed as a highly efficient damage-free polishing technique for SiC wafers. To increase the material removal rate of ECMP, it is essential to have a better understanding of the anodic oxidation mechanism of SiC to obtain a much higher anodic oxidation rate. In this study, we investigated the effects of electrolyte temperature, surface damage, doping concentration, and strain on the anodic oxidation rate of SiC. All these factors were found have a promotional effect on the anodic oxidation of SiC. The promotional effects of processing-induced damage and doping on SiC anodic oxidation were attributed to the processing-induced residual strain and doping-induced strain on the SiC surface, which were observed by Raman spectroscopy. The relationship between anodic oxidation rate and strain on the SiC surface was quantitatively investigated by applying a strain-controllable anodic oxidation device. Both compressive and tensile strains were found to increase the anodic oxidation rate of SiC. The promotion mechanism of the strain on the anodic oxidation of SiC was studied by conductive atomic force microscopy observations. This study is expected to be an important guide for improving the efficiency of ECMP and will contribute to the practical application of ECMP.

Electrostatic self-assembly design of core@shell structured Al2O3@C nanospheres towards high-efficiency and damage-free polishing sapphire wafer

A novel core@shell structured nanocomposite particles with carbon as soft shell and nanoAl2O3 as hard core were prepared by electrostatic self-assembly, and the subsequent hydrothermal and high temperature treatment. By adjusting concentration of nanoAl2O3, the average size of the composite particles vary from 750 nm to 150 nm, the corresponding to the thickness of the carbon shell in the range of 355–55 nm. On the basic of the TEM and Raman results, the shell materials were composed of the amorphous carbon. As confirmed by XPS, the Al2O3 @C composite particles had a stable structure, owing to the formation of the interfacial bonding between carbon shell and nanoAl2O3 after the carbonization process. Moreover, the nanoAl2O3 @carbon composite abrasive could lead to a decrease in the surface damage and roughness of the sapphire wafer compared with the nanoalumina abrasive, owing to the elastic effect coming from the amorphous carbon shell.

Highly efficient and damage-free polishing of GaN (0 0 0 1) by electrochemical etching-enhanced CMP process

An electrochemical etching-enhanced CMP process was proposed to realize the highly efficient and damage-free finishing of GaN. In this process, electrochemical etching was first used to remove the damaged layer induced by grinding or lapping, and CMP was then conducted to flatten the etched surface. The etching rate could reach 1.46 μm/min using NaOH solution as the electrolyte which was highly efficient. It was found that the etching rate and surface roughness can be balanced by adjusting the applied potential. CMP was carried out on an etched GaN sample and the surface roughness was reduced from 69.8 nm to 0.64 nm, and its surface quality was also confirmed to be desirable through photoluminescence. These results demonstrate that the proposed electrochemical etching-enhanced CMP process is highly effective and efficient to obtain a crack-free, damage-free and smooth GaN surface.

High-Efficiency Planarization of SiC Wafers by Water-CARE (Catalyst-Referred Etching) Employing Photoelectrochemical Oxidation

Catalyst-referred etching (CARE) is an abrasive-free and damage-free polishing method that involves applying a catalytic reaction at the contact point of the catalyst surface and workpiece in a chemical solution. An atomically flat silicon carbide (SiC) wafer surface can be obtained by the CARE process. Recently, it was found that water can be used as a chemical solution, even in the case of SiC polishing. However, its current removal rate of 4H-SiC (0001) 4°off-axis substrate is only 2 nm/h and is expected to increase. In this study, the use of photoelectrochemical oxidation in combination with the CARE process using water was investigated, successfully increasing the removal rate up to approximately 100 nm/h.

Novel polyelectrolyte–Al2O3/SiO2 composite nanoabrasives for improved chemical mechanical polishing (CMP) of sapphire

Abstract

電気化学機械研磨による単結晶SiC基板の高能率・ダメージフリー研磨（第1報）

電気化学機械研磨による単結晶SiC基板の高能率・ダメージフリー研磨（第1報）

Core/Shell Structured Solid-Silica/Mesoporous-Silica Microspheres as Novel Abrasives for Chemical Mechanical Polishing

The allotropic silica microsphere as a novel abrasive, which consisted of a solid-silica ( S SiO2) core and a mesoporous-silica shell ( M SiO2), was introduced into chemical mechanical polishing (CMP) process. The shell thickness of the core/shell structured S SiO2/ M SiO2 microspheres was tailored by adjusting the amount of cetyltrimethylammonium bromide (mesoporous template) and tetraethylorthosilicate (silica source). The obtained S SiO2/ M SiO2 samples were structurally confirmed by small-angle X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy and nitrogen adsorption–desorption technique. The results of oxide CMP experiments revealed that the S SiO2/ M SiO2 abrasives exhibited higher material removal rate (=269 nm/min), lower root-mean-square (=0.203 nm) surface roughness as well as lower topographical variations than those of conventional solid-silica abrasives (137 nm/min, 0.343 nm). The enhanced CMP performance might be attributed to the optimization of the real contact environments between abrasives and substrates based on the synergetic aspects of chemical corrosion and mechanical abrasion. These results suggested that the core/shell structured S SiO2/ M SiO2 abrasives presented an important potential application in efficient and damage-free polishing. This work will provide experimental and theoretical basis for the design and application of porous abrasives or core/shell structured composites with porous shells in CMP.

Achieving a Damage-Free Polishing of Mono-Crystalline Silicon

This paper experimentally investigates the micro-structural changes in mono-crystalline silicon induced by abrasive polishing with abrasive grain size and applied pressure. It was found that while the large abrasives of about 15 μm and 300 nm in diameter induce both residual amorphous phase and various residual crystalline structures and dislocations, the finer abrasives of about 50 nm in diameter only produce residual amorphous phase in the top subsurface of polished silicon. With the fine abrasives, reducing applied pressure reduces the amorphous layer thickness, and a damage-free polishing can be achieved at the pressure of 20 kPa.

Damage-free polishing of monocrystalline silicon wafers without chemical additives

This investigation explores the possibility and identifies the mechanism of damage-free polishing of monocrystalline silicon without chemical additives. Using high resolution electron microscopy and contact mechanics, the study concludes that a damage-free polishing process without chemicals is feasible. All forms of damages, such as amorphous Si, dislocations and plane shifting, can be eliminated by avoiding the initiation of the β-tin phase of silicon during polishing. When using 50 nm abrasives, the nominal pressure to achieve damage-free polishing is 20 kPa.

Surface Properties of Polished Stainless Steel

This paper deals with a method of polishing AISI304 stainless steel to obtain a high degree of smoothness, and also deals with geometrical, optical and chemical properties of stainless steel surfaces polished by various methods. Flat specimens are polished supersmoothly to a surface roughness of 20 angstromes Rz by terminating the damage-free polishing of the damaged surface layer to a point prior to the appearance of the grain boundary due to crystallographic anisotropy. The near normal reflectances of variously polished specimens are measured by a monochrometer as a function of wavelength in the range of 0.3-0. 8μm and 2.5-20μm. The reflectance is strongly effected by the wavelength and surface roughness and the infrared reflectance is affected by Surface integrity a swell as surface roughness. Surface composition profiles are measured by IMMA and AES, which show that chromium is depleted at the very topmost oxidized layer on the ultrafinely polished surface.