Papers by Keyword: Chemical Mechanical Polishing

Abstract: Shallow trench isolation via chemical mechanical polishing (CMP-STI) tests of Si wafers using CeO₂ slurry were studied. The impact of CeO₂ slurry's solid concentration on the SiO₂ removal rate and the selectivity ratio The effects of the solid concentration of CeO₂ slurry on the removal rate of SiO₂ and selectivity (SiO₂/Si₃N₄) were investigated. The CeO₂ abrasive was well matched to the XRD standard pattern, confirming that it had a cubic phase and the absence of any impurities. The SEM image showed that CeO₂ primary particles had a spherical-like shape with a size within 30-60 nm. Additionally, the prepared CeO₂ slurry showed a relatively high dispersion level. The wettability degree of the CeO₂ slurry on top of the Si wafer surface was also sufficient. Furthermore, results from polishing tests indicated that both the SiO₂ removal rate and the selectivity increased linearly with a rise in CeO₂ solid concentration.

Abstract: The development of non-destructive quantitative evaluation techniques for the in-plane depth distribution of sub-surface damage (SSD) layer induced by mechanical processing of chemical mechanical polishing (CMP) finished SiC wafers is essential to reduce the occurrence of crystal defects during epitaxial growth. Until now, no wafer inspection method has been able to nondestructively and quantitatively assess the in-plane depth distribution of the SSD. This study investigates the correlation between the scattered light intensity measured nondestructively by the Laser light scattering (LLS) method and the SSD depth estimated by destructive inspection using the Dynamic AGE-ing^® method, a sublimation-controlled etching and growth process, to develop a novel non-destructive SSD inspection method. As a result, it was found that there is an exponential relationship between the scattered light intensity by the LLS method on the bare wafer surface and the depth of the SSD layer that contributes to the formation of in-grown stacking faults (IGSF) during subsequent epitaxial growth. The results show that SiC wafer inspection using the novel LLS method, which introduces this relational equation, enables non-destructive and quantitative evaluation of SSD depth and in-plane distribution.

Abstract: Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.

Abstract: 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.

Abstract: In this paper, a series of chemical mechanical polishing (CMP) experiments for magnesia alumina (Mg-Al) spinel were carried out with different abrasives, and the materials removal rate (MRR) and surface quality was evaluated to explore their different effects. The scanning electron microscope (SEM) and laser particle size analyzer were also employed to test the micro-shape and size distribution of abrasives. Then, the mechanism of different effects with different abrasives was analyzed in CMP for Mg-Al spinel. Those experimental results suggest that different subjecting pressure ratios of abrasives to polishing pad with different abrasive are the key factors leading to difference polishing performances in CMP.

Abstract: Polishing of Silicon Carbide (SiC) seed crystals and substrates to achieve an extremely smooth, level surface, and an optically clear finish takes many surface finishing steps with very long processing times producing a significant amount of slurry waste and utilizing numerous lapping and polishing machines. This paper presents a newly developed cost-efficient SiC polishing process which reduces these operations to two surface finishing steps for achieving an optically clear finish on monocrystalline SiC material where the same size of diamond abrasives for lapping and polishing steps allows to carry out stock removal lapping and polishing processes on a single platform (machine) without concern of cross-contamination and making it as a very cost-efficient and high-throughput polishing process for SiC seed crystals and substrates.

Abstract: Processing silicon carbide (SiC) wafers to achieve an epi-ready quality finish typically requires many lapping and a very long chemical mechanical polishing (CMP) steps. In this paper, we report the thinning down of 6” SiC wafers to sub-nanometer surface finish in less than two hours. Three process steps (rough grinding, nanogrinding and CMP) are involved. Rough grinding thins down the wafer with fast feed rate and maintain excellent flatness. Nanogrinding allows the surface finish to improve down to a few nanometers. The last CMP step provides high planarization efficiency. Overall the throughput of SiC processing is substantially increased over current market solutions.

Abstract: The study mainly explores the surface profile of sapphire wafer after polishing by the method of chemical mechanical polishing (CMP). Pattern-free polishing slurry with SiO₂ abrasive particle is used to polish the sapphire wafer. This paper observes the phenomena of surface profile and surface scratches of sapphire wafer under different pressures and different rotational velocities during CMP. The study uses atomic force microscope (AFM) to scan the surface of sapphire wafer focusing on three axial lines of 0∘, 45∘and 90∘from the position of near edge passing the center of sapphire wafer. The study also selects five positions on a specific area to draw the surface profiles on the axial lines of 0∘, 45∘and 90∘. It can be observed that the central area of sapphire wafer has lower depression than other areas because the central area is polished more polishing times. Besides, the depression on the central area of sapphire wafer has a greater depression value and it has more and larger surface scratches when it is polished under a greater down force and at a faster rotational velocity.

Abstract: The ultra-thin stainless steel sheet will be used in flexible displays for substrate material. The application of the substrate requires its surface very smooth, no defects and damage free. Chemical mechanical polishing (CMP) has been considered as a practical and irreplaceable planarization technology in the ultra precision machining of the flexible display substrate. In chemical mechanical polishing of ultra-thin stainless steel, the oxidant of polishing slurry has an important influence on the material removal rate (MRR). In this paper, the influences of oxidant in slurry on MRR and surface roughness had been studied in CMP of ultra-thin 304 stainless steel based on alumina (Al₂O₃) abrasive. The research results show that the oxidant of the hydrogen peroxide and the oxalic acid have the interaction in CMP 304 stainless steel and when using the only one oxidant in polishing slurry, the hydrogen peroxide or oxalic acid, the MRR is less than the maximum. The oxalic acid can provide a strong acidic environment to ensure the stability of the hydrogen peroxide in polishing slurry and to improve the MRR in CMP 304 stainless steel. The research results can provide the reference for studying the slurry in CMP of ultra-thin stainless steel.

Abstract: In order to avoid the environmental pollution and the harm to body of traditional polishing slurries, an environment-friendly chemical mechanical polishing technology is proposed for SiC wafer in this study. With this method, SiC material is removed by utilizing the strong oxidability of nanotitanium dioxide particles in chemical mechanical slurry in the existence of ultraviolet. While, the oxidbillity will recede in absence of ultraviolet when the polishing process finishes. On the basis of investigating in the reaction mechanism between SiC and nanotitanium dioxide, the slurries are prepared for the environment-friendly chemical mechanical polishing technology. The results show that the ultraviolet-assisted CMP slurry has strong oxidation for SiC material. This method is high-efficient for polishing SiC wafer. The surface roughness is reduced to about Ra 0.1μm from Ra 0.818μm after polishing for one hour.