Mechanical Polishing Technology Research Articles

Fabrication of on-chip single-crystal lithium niobate waveguide microstructures based on mask-chemical mechanical polishing technology

Single-crystal thin-film lithium niobate (TFLN) photonic devices have become a highly popular research area in recent years. The mask-chemical mechanical polishing (CMP) etching technique for TFLN photonic devices has garnered significant attention due to its potential for the efficient and large-scale fabrication of integrated photonic device microstructures. This paper focuses on the physical processes involved in etching TFLN waveguide microstructures using mask-CMP technology. Innovatively, the pressure distribution function of a superelastic polishing pad is combined with the Preston equation to establish a finite element theoretical model. Based on this model, systematic theoretical calculations and analyses were conducted on factors affecting etching efficiency and waveguide structure, such as load magnitude, contact pressure, and mask dimensions. The simulation results were compared with experimental data. This research provides a theoretical reference for advancing the large-scale, high-efficiency fabrication of TFLN photonic chips using mask-CMP etching technology.

Polycrystalline Diamond Film Growth on Gallium Nitride with Low Boundary Thermal Resistance

As the demand for high-frequency and high-power electronic devices has increased, gallium nitride (GaN), particularly in the context of high-electron mobility transistors (HEMTs), has attracted considerable attention. However, the ‘self-heating effect’ of GaN HEMTs represents a significant limitation regarding both performance and reliability. Diamond, renowned for its exceptional thermal conductivity, represents an optimal material for thermal management in HEMTs. This paper proposes a novel method for directly depositing diamond films onto N-polar GaN (NP-GaN) epitaxial layers. This eliminates the complexities of the traditional diamond growth process and the need for temporary substrate steps. Given the relative lag in the development of N-polar material growth technologies, which are marked by surface roughness issues, and the recognition that the thermal boundary resistance (TBRGaN/diamond) represents a critical factor constraining efficient heat transfer, our study has introduced a series of optimizations to enhance the quality of the diamond nucleation layer while ensuring that the integrity of the GaN buffer layer remains intact. Moreover, chemical mechanical polishing (CMP) technology was employed to effectively reduce the surface roughness of the NP-GaN base, thereby providing a more favorable foundation for diamond growth. The optimization trends observed in the thermal performance test results are encouraging. Integrating diamond films onto highly smooth NP-GaN epitaxial layers demonstrates a reduction in TBRGaN/diamond compared to that of diamond layers deposited onto NP-GaN with higher surface roughness that had undergone no prior process treatment.

Nano-CeO2 for the Photocatalytic Degradation of the Complexing Agent Citric Acid in Cu Chemical Mechanical Polishing

Cu interconnect chemical mechanical polishing (CMP) technology has been continuously evolving, leading to increasingly stringent post-CMP cleaning requirements. To address the environmental pollution caused by traditional post-CMP cleaning solutions, we have explored the use of photocatalytic processes to remove citric acid, which is a commonly used complexing agent for CMP. In this study, CeO2 abrasives, characterized by a hardness of 5.5, are extensively employed in CMP. Importantly, CeO2 also exhibits a suitable band structure with a band gap of 2.27 eV, enabling it to photocatalytically remove citric acid, a commonly used complexing agent in Cu CMP. Additionally, the integration of H2O2, an essential oxidant in Cu CMP, enhances the photocatalytic degradation efficiency. The research indicates that the removal rate of single-phase CeO2 was 1.78 mmol/g/h and the degradation efficiency increased by 40% with the addition of H2O2, attributed to the hydroxyl radicals generated from a Fenton-like reaction between H2O2 and CeO2. These findings highlight the potential of photocatalytic processes to improve organic contaminant removal in post-CMP cleaning, offering a more sustainable alternative to conventional practices.

Photocatalytic assisted chemical mechanical polishing for silicon carbide using developed ceria coated diamond core-shell abrasives

The practical application of current photocatalytic-assisted chemical mechanical polishing (PCMP) technology still faces some challenges and difficulties, such as complex preparation process of abrasives, chemical failure, and the use of toxic chemicals. Herein, novel CeO2-coated diamond core/shell structure abrasives were successfully synthesized using a chemical precipitation method and applied in SiC-PCMP. After coating CeO2 on the surface of the diamond, the materials removal rate (MRR) was 56 % higher than that of the diamond abrasives. With ultraviolet (UV) irradiation, the MRR of CeO2/diamond abrasives (11.5 nm/min) increased by about 195 % compared with CeO2/diamond composite abrasives without UV. High surface quality (Ra: 0.4 nm) of the SiC substrate was obtained under UV light irradiation. The materials removal mechanism of SiC-PCMP was proposed.

Electrolyte Effect on Photoetching of Gallium Nitride

The limited material removal rate of conventional chemical mechanical polishing (CMP) significantly hinders the fabrication efficiency and surface quality, thereby preventing the development of gallium nitride (GaN)-based devices. Moreover, the incorporation of photoelectrochemistry in CMP has garnered increasing attention because of its potential to enhance the quality and efficiency of the GaN process. However, a considerable gap still exists in the comprehensive understanding of the specific photoelectrochemical (PEC) behavior of GaN. Here, we report the influence of the electrolyte on the PEC etching of GaN. Various acids and bases were tested, with their pH being carefully adjusted. The concentrations of the cations and anions were also examined. The results showed that photocorrosion/photoetching was more pronounced in sulfuric acid, phosphoric acid, and nitric acid environments than in alkaline environments, but it was less pronounced in hydrochloric acid. Furthermore, the effects of pH and anion concentration on photoetching were investigated, and the results revealed that photoetching in acidic environments weakened with increasing pH levels and diminished with increasing sulfate concentration. The underlying reasons contributing to this observation were explored. These findings provide ideas for improving the photoetching efficiency of GaN, thereby enriching the photoelectrochemical mechanical polishing (PECMP) technology of GaN.

Enhancing the electric charge output in LiNbO3-based piezoelectric pressure sensors.

Lithium niobate (LiNbO3) single crystals are a kind of ferroelectric material with a high piezoelectric coefficient and Curie temperature, which is suitable for the preparation of piezoelectric pressure sensors. However, there is little research reporting on the use of LiNbO3 single crystals to prepare piezoelectric pressure sensors. Therefore, in this paper, LiNbO3 was used to prepare piezoelectric pressure sensors to study the feasibility of using LiNbO3 single crystals as a sensitive material for piezoelectric pressure sensors. In addition, chemical mechanical polishing (CMP) technology was used to prepare LiNbO3 crystals with different thicknesses to study the influence of these LiNbO3 crystals on the electric charge output of the sensors. The results showed that the sensitivity of a 300 μm sample (0.218 mV kPa-1) was about 1.23 times that of a 500 μm sample (0.160 mV kPa-1). Low-temperature polymer heterogeneous integration and oxygen plasma activation technologies were used to realize the heterogeneous integration of LiNbO3 and silicon to prepare piezoelectric pressure sensors, which could significantly improve the sensitivity of the sensor by approximately 16.06 times (2.569 mV kPa-1) that of the original sample (0.160 mV kPa-1) due to an appropriate residual stress that did not shatter LiNbO3 or silicon, thus providing a possible method for integrating piezoelectric pressure sensors and integrated circuits.

An experimental investigation of sapphire grinding by porous and vitrified M0.5/1.5 diamond grinding wheel

Monocrystalline sapphire is known to be difficult to machine. Sapphire generally is machined with chemical mechanical polishing technology. However, low material removal rate (MRR) in machining gives rise to several limitations on mass manufacture of sapphire. Fixed ultrafine abrasive grinding is a promising technology for precision grinding of sapphire substrate and offers the possibility of improving manufacture efficiency. In this study, a novel porous and vitrified M0.5/1.5 diamond grinding wheel and preparation equipment are fabricated in an innovative way to precisely grinding sapphire. The experimental results demonstrate the recommended technological parameters for the grinding wheel, speed for which is below 1200 rpm, pressure below 15 N, and sapphire spindle speed lower than 30 rpm. Meanwhile, the removal mechanism of sapphire under the recommended technological parameters is in ductile grinding mode. Besides, in this study, the MRR of sapphire is 10.2 µm / h when the recommended technological parameters are adopted, the Sa of the sapphire after grinding is 0.03 µm and no depth of subface damage layer is observed.

Abrasion behavior of TiO2 catalyzing H2O2 to synergistically remove single crystal 6H-SiC under ultraviolet irradiation

Ultraviolet photocatalytic-assisted chemical mechanical polishing technology can effectively improve the processing efficiency and surface quality of single crystal SiC. In this paper, the chemical mechanical synergy (CMS) effects of TiO2 catalyzing H2O2 to synergistically remove single crystal 6H-SiC under ultraviolet irradiation were investigated by means of friction and wear. The ball-on-disk friction and wear test was carried out under two conditions M-Ⅰ (UV light for 20 min) and M-Ⅱ (UV light only in the last 10 min). The results showed that under UV light irradiation, anatase TiO2 exhibited photocatalytic and abrasive effects (including mending effect, rolling effect, ploughing effect, polishing effect and protective film effect) during the friction process. The longer the irradiation time, the stronger the chemical reaction on the oxidation of SiC by TiO2 catalyzing H2O2; the higher the TiO2 concentration, the greater the material removal of SiC. At last, the material removal model of single crystal SiC under the condition of ultraviolet light on TiO2 catalyzing H2O2 was established, and the synergistic effect of mechanics and chemistry was analyzed intuitively.

Research on Chemical Mechanical Polishing Technology for Zirconium-Based Amorphous Alloys

Crystallization often occurs in the processing of amorphous alloys, causing the materials lose their excellent properties. The study adopts chemical mechanical polishing of amorphous alloys, presenting the effect of the rotational speed of the polishing turntable, size of abrasive, polishing pressure, and oxidant concentration. The Taguchi method is used to find the best processing parameters, and AFM is used to characterize the machined material surface. At the same time, XPS is used to detect the change of oxide film composition with the addition of oxidant. The results indicate the optimum process parameters: rotational speed of the polishing turntable is 75 r/min, polishing pressure is 28.3 kPa, the size of abrasive is 0.5 μm, and the size of abrasive is a significant factor affecting surface roughness Sa. In addition, as the size of abrasive increases, the material removal rate increases while the surface roughness Sa increases. At pH 10, with an abrasive particle size of 0.5 μm, as the H2O2 concentration increases, the MRR first rapidly decreases at 0.21 wt.% H2O2, and then gradually increases, while the Sa decreases. Furthermore, with the addition of oxidant, the main composition of the surface oxide film changes from oxide to hydroxide, and the contents of Zr4+ and Cu0/Cu1+ elements increase. The findings can provide a feasible chemical mechanical polishing process for zirconium-based amorphous alloys to obtain a satisfactory polishing effect.

Application of an optimized alkaline cleaning solution for inhibitor removal during the post-CMP process: Performance evaluation and mechanism analysis

With the continuous miniaturization of the feature size of semiconductor integrated circuits, the development of chemical mechanical polishing (CMP) technology for copper interconnection has been promoted, and at the same time, more stringent requirements and challenges have been put forward for post-CMP cleaning technology. Benzotriazole (BTA), which has been used as an inhibitor to decrease metal corrosion especially in copper CMP process, is the main object to be removed after the CMP process due to its highly hydrophobic nature. However, the current post-CMP cleaning method cannot achieve an effective balance between high removal efficiency of BTA and excellent surface quality after CMP cleaning. Therefore, a novel and efficient alkaline cleaning solution for post-CMP cleaning of copper is proposed, which is based on tetraethylammonium hydroxide (TEAOH), l-glutamate (Glu) and polyvinylpyrrolidone (PVP). The cleaning effect of copper surface was characterized by contact angle measurement, electrochemical system, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The ion exchange of TEAOH and Glu promotes desorption of BTA molecules from the copper surface. The presence of PVP plays a key role in improving the surface quality after cleaning. This cleaning solution was proved to be effective for BTA removal and achieving a nearly defect-free clean surface.

Study on the Preparation and Performance of Self-Regressive Fixed Abrasive Chemical Mechanical Polishing Pad

Chemical mechanical polishing (CMP) technology is one of the key technologies to realize the global planarization of semiconductor wafer surfaces. With the increasing popularity and universality of its application, more and higher requirements are put forward for ultra-precision machining. As an important part of the CMP system, polishing pads occupy a dominant position. In this paper, a self-regressive fixed abrasive polishing pad (SR-FAPP) was prepared by photo-curing. The physical and mechanical properties of the SR-FAPP and the retreat threshold of the abrasive particles on the SR-FAPP were studied. After the CMP of the SiC wafer with a polyurethane polishing pad and the SR-FAPP, it was found that the material removal rate of the former was 75% higher than that of the latter, and the surface roughness of the latter was 75% higher than that of the former. In the micro-morphology, the scratches on the surface of the latter’s polished SiC wafer were obviously reduced, which effectively improved the unevenness of the scratches on the surface of the SiC wafer after polishing, thus providing a reference for the preparation and performance research of the polishing pad.

Effect of Particle Size Distribution, pH, and Na+ Concentration on the Chemical Mechanical Polishing of Sapphire and 4H-SiC (0001)

As two typical representatives of super-hard materials, sapphire and silicon carbide, their processing has always been a hot spot. Chemical mechanical polishing (CMP) technology is the only way to achieve global planarization, and it has also become one of the most important processes for precision machining of sapphire and silicon carbide. This paper introduced the relationship between the removal rate and surface roughness of sapphire and 4H-SiC (0001) and the size distribution and pH of alumina slurry. More importantly, this paper explored the negative effect of Na+ on the removal rate of alumina-based sapphire polishing slurry, and the more negative effect of Na+ on the removal rate of alumina-based silicon carbide polishing slurry and the surface state of SiC(0001). At the end of the article, the polishing mechanism of sapphire with alumina as a brasive was given.

Friction and wear mechanisms for single crystal GaN based on an electro-Fenton enhanced chemical reaction

Electro-Fenton polishing is a chemical mechanical polishing (CMP) technology with enhanced chemical reaction, which hydroxyl radicals (•OH) can be efficiently and controllably generated by using an electric Fenton method. The oxidation and corrosion of single crystal gallium nitride (GaN), and the synergistic mechanism of chemical and mechanical effects in the electro-Fenton polishing process are key to the electro-Fenton polishing of GaN. This article evaluated the effects of different media (electrolyte, H2O2, Fenton, and electro-Fenton) and different conditions (H2O2 mass fraction, means of H2O2 addition, cathode potential, Fe–C catalyst mass fraction, and pH) through ball-disk friction and wear tests. The results showed that electro-Fenton media demonstrated the best oxidation and corrosion effects on the GaN surface among the four media. In the electro-Fenton slurries, the oxidation was very sensitive to the H2O2 mass fraction which showed that 5 wt % H2O2 was the optimal mass fraction; the oxidation efficiency was greatly improved by regularly supplementing H2O2. The friction and wear behavior of GaN exhibited a good response to the cathode potential with the optimal cathode potential being −0.5 V. Meanwhile, the best Fe–C catalyst mass fraction was 3 wt % and the optimal pH was 2. In addition, the friction and wear behavior were investigated, and the energy spectrum tests was carried out to verify the effect of the chemical reaction. The synergistic mechanism of chemical action and mechanical removal in the friction and wear process was revealed. This research provides theoretical support for on-line electro-Fenton polishing technology.

Novel photoelectrochemically combined mechanical polishing technology for scratch-free 4H-SiC surface by using CeO2-TiO2 composite photocatalysts and PS/CeO2 core/shell abrasives

4H-SiC is a promising next-generation semiconductor. To obtain a scratch-free SiC surface with less/no residual oxide layer at an ideal material removal rate (MRR), a novel photoelectrochemically combined mechanical polishing (PECMP) technique was proposed. Polystyrene (PS)/CeO2 core/shell abrasives and CeO2-TiO2 composite photocatalysts immobilized on a titanium mesh were synthesized and characterized. The results of hydroxyl radical trapping tests present that the strongest photocatalytic activity is achieved by CeO2-TiO2 when UV-light and anodic bias are applied simultaneously (the optimal conditions). SiC-PECMP comparison tests were conducted in water containing 6.5 wt% PS/CeO2 on a home-made polisher, and after polishing, surface morphologies, surface roughness values (Ra) and MRRs were compared. The best polishing results (Ra: 0.738 nm, MRR: 1.109 μm/h) are realized under the optimal conditions. This was further demonstrated by another verification test, and a scratch-free surface (Ra: 0.113 nm) with less residual oxide layer was obtained. The scratch-free surface is attributed to the elastic core/shell abrasives and to the mild photocatalytic reaction. The ideal MRR is ascribed to the enhanced photocatalytic activity of the composite photocatalysts. Therefore, the feasibility of the proposed method is demonstrated, and this technique may be utilized to manufacture other semiconductors.

Non-spherical abrasives with ordered mesoporous structures for chemical mechanical polishing

The chemical mechanical polishing (CMP) technology has been widely used for surface modification of critical materials and components with high quality and efficiency. In a typical CMP process, the mechanical properties of abrasives play a vital role in obtaining the ultra-precision and damage-free surface of wafers for improvement of their performances. In this work, a series of fine structured rod-shaped silica (RmSiO2)-based abrasives with controllable sizes and diverse ordered mesoporous structures were synthesized via a soft template approach, and successfully applied in the sustainable polishing slurry for improving the surface quality of cadmium zinc telluride (CZT) wafers. Compared with commercial silica gel, solid and mesoporous silica spheres, the RmSiO2 abrasives present superior elastic deformation capacity and surface precision machinability on account of their mesoporous structures and rod shapes. Especially, ultra-precision surface roughness and relatively effective material removal speed were achieved by the CMP process using the RmSiO2 abrasives with a length/diameter (L/d) ratio of 1. In addition, a potential CMP mechanism of the developed polishing slurry to CZT wafer was elucidated by analyzing X-ray photoelectron spectra and other characterizations. The proposed interfacial chemical and mechanical effects will provide a new strategy for improving abrasives’ machinability and precision manufacture of hard-to-machine materials.

Study on the Influence of Sapphire Crystal Orientation on Its Chemical Mechanical Polishing

Sapphire has been the most widely used substrate material in LEDs, and the demand for non-C-planes crystal is increasing. In this paper, four crystal planes of the A-, C-, M- and R-plane were selected as the research objects. Nanoindentation technology and chemical mechanical polishing technology were used to study the effect of anisotropy on material properties and processing results. The consequence showed that the C-plane was the easiest crystal plane to process with the material removal rate of 5.93 nm/min, while the R-plane was the most difficult with the material removal rate of 2.47 nm/min. Moreover, the research results have great guiding significance for the processing of sapphire with different crystal orientations.

Selection of Abrasive for Chemical Mechanical Polishing of the 304 Stainless Steel

Chemical mechanical polishing (CMP) technology is widely used in ultra-precision machining of various materials, and the abrasive are an important component of CMP slurry. In this paper, the effects of the abrasive type, the abrasive size and its concentration on material removal rate (MRR) and surface quality in CMP 304 stainless steel were studied through a series of experiments. The results show that the MRR in CMP 304 stainless steel using slurry with the white corundum abrasive is the highest, and the MRR in CMP 304 stainless steel using slurry with the silica abrasive is the lowest, but the surface quality in CMP 304 stainless steel using slurry with the silica abrasive is the best. The MRR and surface roughness increase with the increase of abrasive size, but the surface roughness increases slowly with the increase of abrasive size. With the increase of abrasive concentration, the MRR first increases and then decreases, while the surface roughness value changes slightly, indicating that the abrasive concentration in polishing slurry has little effect on the surface quality. These research results can provide a reference for the design of CMP slurry.

Selection on Surfactant in Polishing Slurry for Chemical Mechanical Polishing 304 Stainless Steel

Stainless steel will become one of the main substrate materials for flexible large-scale displays. As the substrate of the flexible displays, the biggest problem of stainless steel is that the surface roughness is too large. It is necessary to polish the surface of stainless steel with ultra-precision. Chemical mechanical polishing (CMP) technology will be one of the most practical processing technologies to make the surface of stainless steel ultra-smooth and damage-free. In this paper, the material removal rate (MRR) and surface roughness were studied based on the hydrogen peroxide oxidant and ferric chloride oxidant with different surfactants in chemical mechanical polishing (CMP) slurry by experiments. The results show that it can obtain the maximum of the MRR and the optimal surface quality when using 0.04 wt% sodium hexadecyl sulfate as the surfactant of the hydrogen peroxide-oxalic acid based polishing slurry and when using 0.2 wt% nonylphenol ethoxylate or 0.8 wt% OP-10 emulsifier as the surfactant of the of ferric chloride-oxalic acid based polishing slurry. The results of this study can provide a reference for further research on the chemical mechanical polishing of stainless steel.

Study on Dispersant of Hydrogen Peroxide-Oxalic Acid Polishing Slurry in Chemical Mechanical Polishing of 304 Stainless Steel

Flexible display has become a research hotspot for next-generation display technology. Stainless steel materials will become one of the main materials for flexible large-size display substrates, and chemical mechanical polishing (CMP) technology will be one of the most practical processing technologies to achieve super-smooth, non-destructive surface of stainless steel material. In this paper, through a series of experiments, the material removal rate and surface roughness of hydrogen peroxide oxidizer under different dispersants and different dispersant contents were studied. The results shown that when the content of dispersant sodium hexametaphosphate is 1.2% wt, the material removal was the largest, which was 146nm / min. the surface roughness after CMP was relatively low, Ra = 10nm. Sodium hexametaphosphate was selected as the dispersant of the solution. The research results provided a reference for further study of 304 stainless steel chemical mechanical polishing fluid.

Surface polished of bulk methylammonium lead tribromide single crystal

Organic-inorganic halide perovskite materials have been demonstrated with wide applications in optoelectronics and ionization radiation detection. For bulk as-grown crystals, the existence of surface cracks and defects can significantly increase charges recombination and reduce the performance of the device. Herein, we polished the crystal surfaces with both mechanical and chemical mechanical methods at room temperature. After been chemical-mechanical polished, the crystal surface with root mean square roughness about 0.5 nm was obtained. Optical transmission and photoluminescence spectra indicate that chemical mechanical polishing technology can effectively reduce the density of crystal surface defects. The achieved low leakage current density on the surface and bulk crystal is 0.05 nA mm−2 and 0.07 nA mm−2, respectively. Furthermore, the current-voltage curve under visible photons and X-ray photons reveals that surface polishing treatment can suppress the charges recombination and increase the charges transportation.