Chemical Mechanical Polishing Method Research Articles

Surface roughness evolution law in full-aperture chemical mechanical polishing

Ultra-high precision revolution surfaces are crucial to mechanical components like bearings but are difficult to achieve using conventional machining. Meanwhile, it is challenging to predict the surface roughness evolution law during processing. Accordingly, this study proposed an ultra-precision full-aperture chemical mechanical polishing (CMP) method for processing revolution surfaces. More importantly, a theoretical surface roughness Ra model was established by assuming that the three-dimensional surface morphology can be simplified to two-dimensional identical triangles, each peak can be uniformly removed, and the material removal at the valleys can be neglected compared to that at the peaks. The model provides an intuitive understanding of the Ra evolution law during the full-aperture CMP. Interestingly, Ra first decreases parabolically, determined by the initial surface roughness Ra0, the material volume removal rate MRRV, and the polishing time t. Then, it stabilizes. In addition, the theoretical MRRV model was summarized. The cylindrical guiding surface of a bearing was polished with the developed full-aperture CMP method. In 6 min, Ra can be significantly reduced from the initial 201.09 nm to 1.50 nm almost parabolically and stabilizes. Experimental results basically validate the theoretical Ra model, except that a slow decreasing stage appears intermediately because the real surface cannot be perfectly uniform. Additionally, the roundness error RONt is reduced by 34 %. Furthermore, the full-aperture CMP method and Ra model are successfully applied to other revolution surfaces. This study provides mechanistic insight into Ra evolution modelling pertaining to the manufacturing process.

Investigation on the effect of chemical mechanical polishing sapphire substrate on chemical vapor deposition growth of two-dimensional MoS2

Two-dimensional molybdenum disulfide (2D MoS2), with atomic-level thickness, whose crystal crystallinity and size are easily influenced by the surface morphology of the substrate during growth. This work systematically investigates the impact of chemical mechanical polishing (CMP) sapphire substrate on chemical vapor deposition (CVD) growth of 2D MoS2. A green and highly efficient CMP method for the sapphire substrate is first proposed, whose maximum material removal rate (MRR) of 4.27 µm/h with surface roughness (Ra) of 0.10 nm (AFM, scanning area of 5 × 5 μm2) can be attained. The size and thickness statistics of 2D MoS2 domains grown on different substrates indicate that the CMP sapphire substrate in this work can promote the size and monolayer uniformity of 2D MoS2 during CVD growth. Meanwhile, Raman and photoluminescence (PL) spectra of monolayer MoS2 grown on different substrates also indicates the monolayer MoS2 grown on the CMP sapphire substrate in this work has superior crystalline quality and optical properties. The above findings have provided new insights into the mechanisms underlying 2D MoS2 growth on surfaces in various states and are expected to accelerate the development of large size large-size and high-quality growth of two-dimensional material for further device applications.

A new magnetic enhanced chemical mechanical polishing method for quartz glass slender holes

Due to the limitations of tool size, field assisted polishing methods are often employed for polishing the internal surfaces of slender holes with large aspect ratios. However, in existing polishing methods, fields are often applied in isolation, which limits the ability to obtain high surface quality. Furthermore, it is rare for polishing method studies to fully leverage the advantages of multiple fields to create a synergistic effect. Therefore, developing a polishing method that harnesses the synergistic interaction of multiple fields, and revealing the polishing mechanism, is crucial for achieving high-quality internal surfaces of quartz slender holes. To address this problem, a novel magnetic enhanced chemical mechanical polishing method was proposed in this paper and a systematic process study was carried out to analyze the synergistic effects of magnetic and chemical fields. To evaluate the effects of process parameters on material removal and forecast MRR, the material removal process was modeled and validated based on the consistency between experimental and theoretical values. Suitable process parameters are determined through experiments and analysis on magnetic field distribution and process parameters. By conducting EDS mapping and XPS analyses on the reaction product, the enhancement mechanism of magnetic field on material removal in the chemical mechanical polishing process was identified. Under the assistance of a magnetic field, the magnetic abrasive particles encircle the CeO2 particles to fully contact the workpiece surface. The contact force between the polishing tool and the workpiece surface increase. Both of the effects promote the chemical reaction and enable the reaction layer on the surface to be removed in time to obtain higher surface quality. As a result, this method achieves high-efficiency and high-quality polishing, significantly reducing the surface roughness Sa of slender holes from 0.3 μm to 77 nm, with a material removal rate of 141 μm/h.

Chemical Mechanical Polishing for Monocrystal SiC Assisted by the Heterogeneous Sono-Fenton Oxidation

The efficient chemical mechanical polishing (CMP) ability of monocrystal SiC determines the development of advanced semiconductor device. In order to improve the ultra-precision polishing efficiency for SiC, a CMP method based on the heterogeneous sono-Fenton oxidation was proposed. The effects of heterogeneous sono-Fenton on SiC surface softening and polishing based on hydroxyl radical oxidation were studied by means of the corrosion and CMP experiments. Utilizing the indentation tester, the ultra depth of field microscope and optical profilometer, the synergistic effects of heterogeneous sono-Fenton method on the improvement of SiC surface softening and polishing performance were revealed. The research results showed that the change rates of SiC hardness and elastic modulus after heterogeneous sono-Fenton corrosion were the highest, which were 0.12 and 0.6, respectively. The depth variation of indentation on SiC after heterogeneous sono-Fenton corrosion was the highest, which was 1.741 μm. Correspondingly, the improvement degree of SiC surface quality after polishing based on the heterogeneous sono-Fenton corrosion was the greatest and the material removal rate was the highest, which were Sa2.94 nm and 0.469 μm h−1, respectively.

Synergistic effect of abrasive friction and glycine on improving chemical mechanical polishing performance of single-crystal GaN substrate

With the rapid development of the third-generation semiconductor materials, the chemical mechanical polishing rate and surface quality of single-crystal gallium nitride (GaN) substrates have been a research hot-spot. In this work, the synergistic effect of abrasive friction and glycine (Gly) on improving the chemical mechanical polishing (CMP) performance of single-crystal GaN substrate is proposed and studied systematically. The results indicated that the polishing solutions with Gly have a 2.3-fold improvement in material removal rate (MRR) as well as scratch-free surface than that without Gly. The maximum MRR of the single-crystal GaN substrate is 129.4 nm/h with surface roughness (Ra) of 0.64 nm attained by using the polishing solutions containing only 3 wt% potassium persulfate (K2S2O8). In contrast, when Gly is added as a reaction reagent, which can be activated by abrasive friction, the maximum MRR is increased to 304.2 nm/h with Ra of 0.42 nm. Meanwhile, the epitaxial evaluation indicates that two-dimensional (2D) MoS2 grown on processed single-crystal GaN substrate has superior crystalline quality and optical properties. Finally, the polishing mechanism of the single-crystal GaN substrate using the mixed solutions of K2S2O8 and Gly is discussed. The proposed CMP method has potential applications in the semiconductor and microelectronics industries.

Nanoscale Surface Refinement of CoCrMo Alloy for Artificial Knee Joints via Chemical Mechanical Polishing.

In this study, we address the challenge of surface roughness in CoCrMo alloys, typically used in artificial knee joints, which can initiate a cascade of biological responses causing inflammation, osteolysis, joint instability, and increased susceptibility to infection. We propose the application of a chemical mechanical polishing (CMP) technique, using an ecologically responsible slurry composed of 4 wt% SiO2, 0.3 wt% H2O2, 1.0 wt% glycine, and 0.05 wt% benzotriazole. Our innovative approach demonstrated significant improvements, achieving a material removal rate of 30.9 nm/min and reducing the arithmetic mean roughness from 20.76 nm to 0.25 nm, thereby enhancing the nanoscale surface quality of the artificial knee joint alloy. The smoother surface is attributed to a decrease in corrosion potential to 0.18 V and a reduction in corrosion current density from 9.55 µA/cm2 to 4.49 µA/cm2 with the addition of BTA, evidenced by electrochemical tests. Furthermore, the preservation of the phase structure of the CoCrMo alloy, as confirmed by XRD analysis and elemental mapping, ensures the structural integrity of the treated surfaces. These outcomes and our simulation results demonstrate the effectiveness of our CMP method in engineering surface treatments for artificial knee joints to optimize friction behavior and potentially extend their lifespans.

A New Environmentally Friendly Chemical Mechanical Polishing Method Applied for Surface Finishing Ti-6Al-4V Alloy

A New Environmentally Friendly Chemical Mechanical Polishing Method Applied for Surface Finishing Ti-6Al-4V Alloy

Tribological Study on Photocatalysis-Assisted Chemical Mechanical Polishing of SiC

Silicon carbide (SiC) is widely used as a power semiconductor substrate material, even if it takes a large amount of processing time to secure an appropriate surface as a wafer for devices after chemical mechanical polishing (CMP). Therefore, studies on SiC CMP have focused on shortening the processing time by increasing material removal efficiency. Among the methods of SiC CMP that have been widely studied recently, the photocatalysis-assisted CMP (PCMP) method is known to efficiently increase the material removal rate (MRR) of SiC under UV light and photocatalysts. However, a limited number of comparative studies have been conducted on PCMP from a tribology perspective. In this article, a comparative study was conducted from a tribology perspective on CMP, mixed abrasive slurry CMP (MAS CMP), and PCMP. The experimental results demonstrated that SiC PCMP has higher friction and processing temperature than MAS CMP and general CMP, which may be caused by photocatalytic oxidation and the TiO2 particles used as photocatalysts.

Highly efficient and atomic scale polishing of GaN via plasma-based atom-selective etching

Plasma-based atom-selective etching (PASE) of GaN is conducted to realize the highly efficient planarization of the GaN surface. Inductively coupled plasma with high temperature and high concentration of radicals is used as the source of PASE. The non-toxic carbon tetrafluoride is chosen over chlorine as the reaction gas, and the volatility of the etching products will be improved at high temperatures in the PASE of GaN. After 2 min of PASE, the GaN surface roughness is reduced from Sa 135.8 nm to Sa 0.527 nm. The material removal rate of PASE of GaN is measured to be 93.01 μm/min, thousands of times higher than that of the conventional chemical mechanical polishing method. The crystal structure of the GaN subsurface is well-ordered without any damage or defects. PASE is thus proven to be a non-destructive etching method. In this study, the effects of radio frequency power and reaction gas flow rate on PASE are also investigated. Surface temperature and concentration of radicals are found to be the critical factors in the PASE of GaN.

Study of the humidity-controlled CeO2 fixed-abrasive chemical mechanical polishing of a single crystal silicon wafer

To address the problem of low polishing efficiency in traditional loose-abrasive chemical mechanical polishing, a humidity-controlled fixed-abrasive chemical mechanical polishing method is proposed, which uses a CeO2 pellet to perform polishing at a specific humidity level. The results of both the nano-scratch tests and the fixed-abrasive polishing experiments demonstrate that the water molecules have an irreplaceable role in the material removal of silicon and that a higher ambient humidity results in better material removal. Fixed-abrasive polishing experiments under saturated humidity can yield a surface roughness less than Ra 2 nm at an efficiency of 0.9 µm/h, and the minimum stress on the polished surface is only a few tens of megapascals. The method is validated to be effective for the stress relief process after grinding.

Optimized chemical mechanical polishing of Parylene C for high-density wiring in flexible electronics

With the rapid development of flexible electronics, an increasing number of microfabrication strategies originating from the Si-based integrated circuits field have been explored on organic materials. Parylene C, a polymer, has been widely used in the microelectromechanical systems field because of its outstanding fabrication merits, such as room-temperature processability, conformal coating, and precise thin film deposition capability with the thickness tunable from 1 nm to 100 μm. As a good dielectric material, the Parylene C is also suitable for interlayer dielectrics in flexible electronics. This study develops an optimized chemical mechanical polishing (CMP) technique of Parylene C for high-density redistribution wiring in high-performance flexible electronics. The roughness of the Parylene C surface after CMP was as low as 14.3 ± 1.5 Å. The problems of slurry pollution and mechanical failure of the Parylene film that degrade the dielectric performance of the Parylene C could be avoided by taking the optimized CMP method. The multi-material structure constructed by Parylene C, Silicon and electroplated Copper was prepared and polished using the optimized CMP process. Additionally, a flexible wiring sample has been successfully patterned by the Damascene process through the optimized CMP process. In this sample, both the distance between each wire and the wire width were as small as 5 μm. The optimized Parylene C CMP process is easy-to-realize, highly efficient, low cost, and with minor defects; it provides a promising way to achieve high-density interconnection in high-performance flexible electronic devices.

Picosecond Laser-Assisted Chemical Mechanical Polishing (CMP): Aiming at the Si-Face of Single-Crystal 6H-SiC Wafer

Silicon carbide (SiC) presents huge application potential in semiconductor devices. However, attributed to its high hardness and stability, there always appears an urgent problem about how to improve the efficiency of chemical mechanical polishing (CMP) of the SiC Si-face. In this study, an effective picosecond laser-assisted CMP method is proposed, which first preprocesses the Si-face with picosecond laser and then carries out CMP. Scanning electron microscopy (SEM), nano scratch tester (NST), and X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface alteration of SiC Si-face by picosecond laser pretreatment (PLP). The results demonstrate that the ripples and polycrystalline layer produced by PLP improve the surface machinability, and the C–O, Si–C–O, and Si–O bonds oxidized by PLP lead to easier removal by CMP. Hence compared with the no laser pretreated (NLP) samples, the material removal rate (MRR) of PLP samples is much higher in the first 45 min of CMP and the surface roughness (Rq) is lower after CMP. The proposed method has certain scientific significance and industrial production guidance for SiC semiconductor device manufacture.

Highly efficient chemical mechanical polishing method for SiC substrates using enhanced slurry containing bubbles of ozone gas

In this study, a highly efficient method for chemical mechanical polishing (CMP) of silicon carbide (SiC) substrates using enhanced slurry was proposed and developed. The enhanced slurry contains bubbles of ozone gas generated by ozone gas generator in pure water mixed with a conventional commercially available slurry. Therefore, the enhanced slurry has an oxidizing effect on the Si-face of SiC substrates. To confirm the effectiveness of bubbles enclosing ozone gas, both nano-indentation test and X-ray photoelectron spectroscopy (XPS) analysis were conducted. As a result, the hardness decrease of the Si-face of the SiC substrate was confirmed through the nano-indentation test, and the generation of reaction products was confirmed on Si-face of SiC substrate in the XPS analysis. According to a series of experimental results of our proposed highly efficient CMP method for SiC substrates, the removal rate can be increased when the enhanced slurry was applied, comparing with that for the not only conventional commercially available slurry but also commercially available dedicated slurry.

An Efficient and High Quality Chemical Mechanical Polishing Method for Copper Surface in 3D TSV Integration

The goal of chemical mechanical polishing (CMP) is to achieve a flat and smooth surface for through silicon via (TSV) application. In order to obtain high efficiency and high quality copper CMP process, we have developed copper CMP slurry with optimal component ratio of peroxide, citric acid, benzotriazole, and silica particle. A high-resolution surface profile measuring instrument combined with other measurements is used to analyze the CMP performance of TSV. In addition, the chemical reaction mechanism in slurry for removal copper has been discussed considering surface adsorption. It is revealed that the polishing time increases with decreasing content of oxidizing agent peroxide. The polishing speed for silica particle mixed slurry is accelerated comparing with the conventional slurry. The polishing time becomes longer with increasing value of pH owing to declining sharply of free hydrogen ion in slurry solution. Further, the high quality of polishing appears on the wafer with smooth and glossy surface of copper by applying fast and slow slurry, which is contributed to reduction of the chemical polishing and enhancement of the mechanical polishing. The optimized polishing slurry prepared in this paper and the proposed two-stage polishing technique can achieve high quality copper surface polishing while greatly improving polishing efficiency.

Effect of Sr(OH)2 as a pH Regulator on Different Plane Sapphire Substrate Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) process is widely used on GLSI multilayer metallization planarization which requires the highest precision atomic surface. In order to improve the removal rate and surface quality of sapphire substrate, CMP method was used and a novel pH regulator Sr(OH)2 was investigated. According to c/a/r-plane sapphire CMP experimental results good surface quality and higher material removal rate (MRR) were obtained by using the Sr(OH)2 solution as pH regulator comparing with traditional KOH as pH regulator. Meanwhile, it indicated Sr(OH)2 cannot only replace the traditional pH regulators, but also not introduce other metal ions contamination for sapphire CMP. According to the chemical thermodynamics basic principles, the trend and products of chemical reaction between sapphire and traditional water-based SiO2 slurry and between sapphire and Sr(OH)2 was analyzed by using HSC software. In addition, the action mechanism of Sr(OH)2 on sapphire substrate CMP was investigated. According to the results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), it was found there were solid-chemical reactions between Sr(OH)2 and sapphire and Al2Si2O7·2H2O, Al2SiO5, SrAl2Si2O8 and SrAl2O4 were generated on the sapphire surface, which improved chemical action effectively and material removal rate. This CMP method of improving chemical action has important significance to actual production.

Photo-Assisted Chemical Mechanical Polishing of Si Wafer Using Phosphorescent Particles as a Luminescent Agent

Chemical mechanical polishing (CMP) is used for fabricating semiconductor wafer surfaces because it produces smooth and damage-free surfaces. Polishing efficiency is a key factor to decrease fabrication costs. Photo-assisted CMP—a promising method to improve polishing efficiency—requires a special setup allowing the material surface to be directly illuminated by the excitation light, which increases initial setup costs. Thus, a photo-assisted method that improves polishing efficiency without a special setup is strongly desired. We report a photo-assisted CMP method that employs phosphorescent particles (PhPs). X-ray analysis demonstrates that the Si surface is oxidized by photo-chemical treatment using PhPs. Further, photo-assisted CMP using PhPs added into a polishing slurry improves the material removal rate for Si under UV irradiation on the polishing pad; however, large and blocky PhPs generate defects on the polished surface. A double-layered polishing pad (abrasive layer partly stacked on the phosphorescent layer) is proposed to obtain smooth and defect-free surfaces. Compared with conventional CMP, photo-assisted CMP using the double-layered pad achieves higher polishing efficiency and smoother (0.19 nm Ra) surfaces without generating defects under optimal polishing conditions; thus, this method has potential applications to achieve semiconductor wafer fabrication with a simple polishing setup.

Study on high efficient sapphire wafer processing by coupling SG-mechanical polishing and GLA-CMP

Abstract A novel surface finish process sequence has been developed with a sequential process employing sol-gel (SG) semi-fixed abrasive polishing tool and gas-liquid assisted chemical mechanical polishing (GLA-CMP) instead of general copper-resin lap or plate (CP) and chemical mechanical polishing (CMP) to enhance the surface finishing efficiency for sapphire wafer. The surface and subsurface quality of sapphire wafer after the SG and GLA-CMP process have been compared with those by CP and CMP, respectively. Results show that the SG polishing can offer a better surface quality in terms of both surface roughness and sub-surface damage for the next fine polishing step. Based on the contact mechanics models, yielding effects of the SG polishing pad are found to be effective to scratch mitigation. This trend is consistent with experimental results. Furthermore, oxygen is applied as catalyst to improve the removal material rate (MRR) of sapphire by GLA-CMP. It is found that oxygen concentration can improve MRR of sapphire polishing. Among four combinations of CP, SG, CMP, and GLA-CMP, the machining by coupling SG and GLA-CMP shows the maximum MRR approximately as high as 77.6 nm/min, more than 10.23% larger than that of CP-machined wafer and traditional CMP. Ultra-smooth wafer surface with damage-free can be achieved by this new process sequence and the sapphire wafer with qualified surface can be obtained within 50 min by GLA-CMP, which is 90 min shorter than the original 140 min polished by the conventional CMP method. Compared to the conventional surface finish process sequence, the proposed sequence shows superior processing efficiency and quality for sapphire wafers.

Planetary motion-assisted chemical mechanical polishing method of difficult-to-process substrate

Planetary motion-assisted chemical mechanical polishing method of difficult-to-process substrate

超音波振動を援用した高効率CMPの研究

超音波振動を援用した高効率CMPの研究

Electrical Characteristics of Top-Gated Graphene Field Effect Transistors Fabricated on Stainless Steel (STS) Substrate.

Top-gated Graphene transistors with Al2O3 gate-dielectric on the flexible stainless steel substrate have been demonstrated. Graphene was synthesized on copper foil using a chemical vapor deposition method and transferred onto the stainless steel substrate by wet transfer technique. The stainless steel substrate was polished by chemical mechanical polishing method and the spin-on-glass layer was coated on the surface to improve the surface roughness. The average surface roughness R(a) was as low as 5.9 nm from the AFM measurement. The measured hole and electron mobilities from the current-voltage characteristics at room temperature were calculated as high as 310 and 45 cm2/Vs, respectively. In addition, the effect of surrounding temperature up to 355 K on the electrical variations was investigated. The mobility was inversely proportional to the temperature with negligible hysteresis where the temperature coefficient was calculated as low as -0.65 %/K.