Chemical And Mechanical Polishing Research Articles

A Systematic Study of the Factors Affecting the Surface Quality of Chemically Vapor-Deposited Diamond during Chemical and Mechanical Polishing.

Diamond surfaces must be of high quality for potential use in semiconductors, optical windows, and heat conductivity applications. However, due to the material's exceptional hardness and chemical stability, it can be difficult to obtain a smooth surface on diamond. This study examines the parameters that can potentially influence the surface quality of chemically vapor-deposited (CVD) diamonds during the chemical and mechanical polishing (CMP) process. Analysis and experimental findings show that the surface quality of polished CVD diamonds is significantly influenced by the crystal structure and the growth quality of the diamond. In particular, when the surface roughness is below Ra 20 nm, the pores and grain boundaries on CVD diamond obstruct surface roughness reduction during mechanical polishing. To obtain a smooth polished surface, careful consideration of the size of diamond abrasives and polishing methods is also a prerequisite. Chemical mechanical polishing is a novel method to achieve a surface quality with roughness below Ra 3 nm, as in this method, the anisotropy of the CVD diamond allows the uneven steps to be efficiently erased. However, the chemical actions of polishing slurry should be controlled to prevent the formation of chemical etching pits.

Treatment of industrial effluent to reclaim copper using adsorption technique

ABSTRACT Effluent generated during metal finishing in industries contains large amount of heavy metals, which get discharged into water bodies and creates environmental pollution as well as loss of metal values. Present studies report the adsorption of copper (Cu) from the effluent using Tulsion T-42 resin. Experiments were carried out for the adsorption of Cu from the effluent of Chemical and Mechanical Polishing (CMP) industries using cationic resin Tulsion T-42 (adsorbent). To get the optimized adsorption condition for copper the studies were carried out with varying process parameters i.e., contact time, adsorbent dose, pH, etc. Result of the batch experiments shows that 95% copper was adsorbed from the effluent containing 100 ppm copper using 0.1 g Tulsion T-42 in 50 mL feed solution at pH 4.0 in contact time of 30 min. The obtained data from Cu adsorption studies fitted well with Freundlich adsorption isotherm and followed second-order rate reaction. The 99% copper was found to be eluted from loaded adsorbent using 10% sulfuric acid in 60 min contact time. FT-IR result confirmed that complex with active sulphonic group of Tulsion T-42 was formed. The findings of the studies will be useful for the reclamation of copper from the waste water of metal finishing industries.

A Flexible Piezoelectric Strain Sensor Array With Laser-Patterned Serpentine Interconnects

In consideration of its high electromechanical coupling coefficient, thinned piezoelectric thick film from the bulk materials by chemical and mechanical polishing (CMP) process is used for high-performance piezoelectric harvesters and flexible sensors. Here, the flexible strain sensor 3 × 3 array based on CMP fabrication method is presented for the first time, and the laser-patterned flexible stainless steel serpentine wires as interconnects signal. The testing results show that the output voltages of the strain sensor array exhibit good linearity towards the corresponding strains, and also increase with the applied frequency. The maximum sensitivity of strain sensor array is 1.88 mV/μe. Moreover, this sensor array is demonstrated to monitor the surface strain of a complex structure such as the contraction and expansion of irregular balloon, which indicates its great promising in monitoring vital signs for heart healthcare.

Adsorption of Arsenic Ions Transforms Surface Reactivity of Engineered Cerium Oxide Nanoparticles.

Cerium oxide (CeO2) nanoparticles (NPs) are massively used as abrasives in the chemical and mechanical polishing (CMP), an essential process to manufacture semiconductor wafers. The CMP process for arsenide-based semiconductor materials produces wastewater with co-occurring arsenic (As) ions and CeO2 NPs. We found that CeO2 NPs adsorbed both arsenite (As(III)) and arsenate (As(V)) ions and the adsorption isotherms suggested different adsorption energies and capacities of the two species. Applying the ferric reducing ability for nanoparticle assay, we revealed that the adsorbed As(III) and As(V) each reduced CeO2 NP surface reactivity but followed different mechanisms. The adsorbed As(III) ions below a critical coverage (110 mmol/kg) increased occupation of Ce 4f orbitals and thus reduced electron mobility of the original CeO2 NPs. The adsorbed As(V) ions withdrew electrons from Ce 4f orbitals and likely became oxidizing agents that greatly inhibited the original surface reducing ability. Electron paramagnetic resonance analysis further revealed that adsorbed As(III) and As(V) ions decreased the propensity of CeO2 NPs to produce reactive oxygen species. This work highlights the importance of examining NPs in their post-use phases in which surface reactivity and hazard potential can be greatly altered by chemical exposure history and NP surface transformations.

Characterization of high-quality relaxed flat InGaN template fabricated by combination of epitaxial lateral overgrowth and chemical mechanical polishing

We report the characterization of thick completely relaxed InGaN layers grown using epitaxial lateral overgrowth (ELO) with a facet structure. ELO-InGaN layers were successfully grown on a stripe-patterned GaN template. The full width at half maximum of the X-ray rocking curve of ELO-InGaN on the InGaN templates was smaller than that of non-ELO InGaN. Because of the difficulty in improving the morphology of ELO-InGaN layers grown on patterned GaN templates, chemical and mechanical polishing (CMP) was performed to obtain a flat c-plane surface. The photoluminescence intensity of InGaN/GaN multiple quantum wells (MQWs) on the CMP-ELO-InGaN template was approximately two times stronger than that of MQWs on the GaN template. Furthermore, the peak wavelength of the MQWs on the CMP-ELO-InGaN template was longer than that on the GaN template because of the high In pulling effect.

A new processing technique for fabrication of ultra-thin wafer

Ultra-thin wafer with high quality was obtained by a new processing technique, which combined ultrasonic wet etching, temporary bonding, and chemical and mechanical polishing (CMP). In order to obtain a warp-free thin wafer, the pristine silicon wafer was subjected to initial thinning by ultrasonic wet etching. The temporary bonding was then conducted to anchor the wafer and ensure a stress-free de-bonding of the polished ultra-thin wafer from the supporting wafer. The subsequent CMP was applied to further reduce the thickness and roughness of the wafer. Measurements showed the as-fabricated ultra-thin wafer had an average thickness of 76 ± 2 μm, an average surface roughness of 0.32 nm, and a compressive stress of 101.4 MPa. The as-fabricated ultra-thin wafer showed improved overall appearance, with no obvious breakage, deformation, or damages on the surface.

Retreatment of silicon slurry by membrane processes

The purpose of the present study is to develop a process to regenerate the polish liquid used in Chemical and Mechanical Polishing (CMP), called “slurry”, and more specifically Silicon CMP slurry. Physico-chemical analyses show a considerable dilution of slurry through washing waters used in polishing. Thus, this effluent has been characterised for a better identification of the deviations from the slurry of reference (Point Of Use). Hence, the principle is to regenerate this effluent by membrane processes. The ultrafiltration results obtained at laboratory scale have led to the development of an industrial prototype. An optimal utilisation of this treatment allows completing a two-step process: the reconcentration by ultrafiltration and a chemical adjustment by addition of concentrated slurry. A stable behaviour of the slurry at the different steps of the process has been observed. Polishing results are similar with retreated and POU slurries. Furthermore, the functioning at industrial scale permits to maintain the performances obtained on the laboratory pilot.

High Topography Polyimide CMP Process

This paper reports a process of filling and planarization of microstructures for MEMS and wafer level packaging application. In this work, cavities of 5-10mm depth and 20-100mm in length/width are filled using multiple coatings of polyimide with kinematic viscosities in the range of 20-130St. Such filling results in overfilling of polyimide in the range of 2 to 10mm due to variation in density and geometry of microstructure. A chemical and mechanical polishing (CMP) based planarization process, to achieve polyimide thickness variation <0.2mm in varied structures is presented.

Copper recovery from low concentration waste solution using Dowex G-26 resin

Huge amounts of effluent of low copper content are generated in electrical and electronic parts manufacturing industries. Here we report an adsorption process using strongly acidic exchanger Dowex G-26 for copper recovery from dilute sulfate solution containing 0.5–0.7 g/L copper, which is similar to the chemical and mechanical polishing (CMP) waste generated in electronic industries. The structures of activated and copper-loaded resins were compared by FT-IR spectroscopic characterization to confirm the adsorption phenomena. Various process parameters viz. contact time, solution pH, resin dose were investigated for copper recovery from the waste effluent. Copper adsorption from the solution was complete within a contact time of 14 min for an aqueous/resin (A/R) ratio of 100 mL/g and equilibrium pH of 2.5. The mechanism for copper adsorption by Dowex G-26 resin was found to follow a Langmuir isotherm and second-order reaction rate. 99.7% of the copper was eluted effectively from the loaded resin by 10% sulfuric acid at an A/R ratio of 25 in a contact time of 20 min to produce a copper-enriched solution. After copper recovery, the raffinate generated could be disposed safely without affecting the environment.

The impact of wafer nanotopography on threshold voltage variation in NAND flash memory cells fabricated with poly-silicon chemical mechanical polishing

Based on simulation, the threshold voltage (VT) variation for NAND flash memory cells fabricated with the self-alignment of the poly-silicon floating gate is expected to be related to the peak-to-valley value (PV) of wafer nanotopography. After chemical and mechanical polishing (CMP) of the poly-silicon floating gate, the PV of the remaining height of the poly-silicon floating gate linearly increased with the PV of wafer nanotopography. As a result, the VT variation linearly increased with the PV of the remaining height of the poly-silicon floating gate after CMP. These simulation results show, in particular, that the VT variation of NAND flash memory cells induced by wafer nanotopography becomes larger and larger as the device size becomes smaller and smaller.

Hydrated α-Fe 2O 3[formula omitted] surface structure: Role of surface preparation

The surface structure of α- Fe 2 O 3 ( 1 1 ¯ 0 2 ) was studied under two different surface preparation conditions using crystal truncation rod (CTR) diffraction. Wet chemical and mechanical polishing (CMP) at 298 K results in a crystalline surface termination in which the top layer of iron atoms is absent compared to the stoichiometric bulk termination. Annealing in air at 773 K resulted in a transformation of the surface to a structure consistent with hydroxylation of the stoichiometric termination. These results agree with theoretical predictions of Lo et al. [C.S. Lo, K.S. Tanwar, A.M. Chaka, T.P. Trainor, Phys. Rev. B 75 (2007) 075425] and clearly show an ambient pressure surface preparation path leading to a stoichiometric hydroxylated surface, which is apparently a meta-stable configuration at room temperature.

A Computational Study on Slurry Flow Between a Wafer and Pad in CMP (Cases without Groove, with Circular Grooves and Radial Grooves)

In recent years, CMP (Chemical and Mechanical Polishing) greatly has taken its role as technology of planarizations to produce multi-level inter-connections. While slurry is flowing on a polishing pad in CMP, the polishing pad is in contact with the wafer to polish the wafer surface. Grooves are expected to supply slurry evenly, and to remove wasted particles. Our study aims at developing the design of the best patterns of grooves. By predicting slurry flows between wafers and polishing pads in CMP using CFD, the influence of the slurry flow by the grooved pad can be analyzed. In this paper simulations were carried out for cases without groove, with circular grooves and radial grooves. With analysis of the flow field, how grooves affect the velocity distributions are studied. We also simulated the replacement of old slurry to new slurry, and the roles of the grooves are discussed.

High temperature processing of poly-SiC substrates from the vapor phase for wafer-bonding

The transfer by wafer-bonding of single-crystalline SiC thin films to a polycrystalline SiC substrate to obtain a “quasi-wafer” requires high quality polycrystalline substrates with controlled bulk properties (thermal conductivity, electrical resistivity) as well as with very low surface roughness (RMS < 5 nm) and bowing (< 10 μm). Currently, available polycrystalline SiC wafers are processed by sintering or by Chemical Vapor Deposition (CVD). Sintered ceramic wafers are very heterogeneous (mixture of 3C, 6H, 4H and silicon), while CVD ones are of better quality (homogeneous and textured 3C). The aim of this paper is to investigate the fabrication and the properties (bulk and surface) of SiC substrates with large (0.1 to a few mm) grains. To meet these requirements, two high temperature processes (around 2000 °C) for single crystal growth were used: Physical Vapor Transport (PVT) and the recently developed CVD Feed Physical Vapor Transport (CF-PVT). Structural investigations performed on large grain wafers sliced and polished from the grown ingots showed an important influence of the initial seed on the grain size, polytype and crystallographic texture. Chemical and Mechanical Polishing (CMP) of such structures was studied and optimized to obtain low surface roughness. The intra-grain roughness is very low (RMS < 0.5 nm) but a few nanometer of height steps were observed between grains. The relations between bulk properties, surface functionalization and process conditions are discussed. This first seeding step with commercial substrates is necessary for the creation of original substrates which can be used for the fabrication of new substrates.

Surface diffraction study of the hydrated hematite [formula omitted] surface

The structure of the hydroxylated α-Fe 2O 3 ( 1 1 ¯ 0 2 ) surface prepared via a wet chemical and mechanical polishing (CMP) procedure was determined using X-ray crystal truncation rod diffraction. The experimentally determined surface model was compared with theoretical structures developed from density functional theory (DFT) calculations to identify the most likely protonation states of the surface (hydr)oxo moieties. The results show that the hydroxylated CMP-prepared surface differs from an ideal stoichiometric termination due to vacancies of the near surface bulk Fe sites. This result differs from previous ultra high vacuum studies where two stable terminations were observed: a stoichiometric (1 × 1) termination and a partially reduced (2 × 1) reconstructed surface. The complementary DFT studies suggest that hydroxylated surfaces are thermodynamically more stable than dehydroxylated surfaces in the presence of water. The results illustrate that the best fit surface model has predominantly three types of (hydr)oxo functional groups exposed at the surface at circumneutral pH: Fe–OH 2, Fe 2–OH, and Fe 3–O and provide a structural basis for interpreting the reactivity of model iron-(hydr)oxide surfaces under aqueous conditions.

AFM study of SrTiO3 and YBa2Cu3O7-δ multilayer surface treated with chemical mechanical polishing process

We have studied the surface morphology of SrTiO3 (STO) and YBa2Cu3O7-δ (YBCO) thin films fabricated by pulsed laser deposition technique in a multilayer structure. Study was focused on the surface morphology of an STO thin film deposited on an YBCO layer that received chemical and mechanical polishing (CMP) treatment. The CMP process could remove the presence of the outgrowth on the STO thin film, improve its smoothness and facilitate a good epitaxial growth of the next deposited YBCO film. As a result, we could fabricate a high quality YBCO thin film on the YBCO/STO structure with Tc = 91 K and Jc = 4 × 106 A/cm2.

Optimum physical-chemical pre-treatment of copper damascene wastewater

Chemical and mechanical polishing (CMP) of copper damascene circuits will typically produce copper levels in excess of regulatory limits in wastewater with a unique process chemistry, including high solids. Physical-chemical methods were investigated to determine the optimum treatment depending upon pre-treatment and/or water reuse requirements. Jar test studies revealed that an alum dose of 150-200 mg/L together with anionic polymer aid provided a good removal of turbidity. If the treatment objective is simply solids and copper reduction for discharge to a sewer system, then solids removal can combined with precipitation of copper hydroxide for relatively inexpensive pre-treatment. The presence of peroxide from the process solution, however, may make it difficult to achieve copper values below 5 mg/L, depending on the associated process conditions. If the objective is to remove solids and recover copper, which may also allow recovery of water for reuse, then solids removal by alum and polymer can be followed by ion exchange by a strong acid cation resin. As with precipitation, however, effective copper removal by ion exchange requires pre-treatment of peroxide by chemical reduction. The exchange of dissolved aluminum also reduces the capacity of the resin for copper.