Chemical Polishing Research Articles

Investigation on the surface treatments of CdMnTe single crystals

The surface quality of CdMnTe crystal plays an important role in the performance of CdMnTe nuclear radiation detectors. In this paper, the surfaces of CdMnTe samples treated by Mechanical Polishing (MP), Chemical Polishing (CP), Chemical–Mechanical Polishing (CMP), and CMP followed by CP treatment (CMP+CP) were investigated. The structural properties of CdMnTe surfaces were characterized by a High Resolution Scanning Electron Microscope (HRSEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The Circular Transmission Line Model (CTLM) was adopted to reveal the specific contact resistivity (ρc) of Au/CdMnTe contacts after various surface treatments. The AFM measurements shown an ultra-smooth surface was achieved after the CMP+CP treatment with the roughness value of 0.84nm, and the surfaces by MP, CP and CMP were with the roughness of 8.2nm, 5.1nm and 1.4nm, respectively. The XPS analysis indicated that the (Te+Te4+)/(Cd+Mn) ratios of the CdMnTe samples after the CMP+CP and MP treatment were 1.1 and 1.07 which are close to stoichiometric composition, while after the CP and CMP treatment were 2.00 and 1.40 which are enriched with Te. The CMP+CP treatment decreased the Te4+/(Te+Te4+) ratio from 7% in CMP to 1%, which reveals the surface with few Te oxides. The specific contact resistivity (ρc) was used to determine the ohmic characteristic of Au/CdMnTe contacts by the CTLM. The calculated ρc values of Au/CdMnTe contacts on the CP, CMP and CMP+CP treated surfaces are 383, 112 and 15Ωcm2, respectively.

The Research of Reactivity between Nano-abrasives and Sapphire during Polishing Process

Reactivity between nano-sized abrasives and sapphire wafer has been studied by interfacial solid state reaction during polishing process, and the abrasive with the highest reactivity has been selected from magnesium oxide, silicon dioxide and ferric oxide. Using the Sol-Gel polishing films, sapphire wafers were polished in the form of wet and dry mechanical chemical polishing respectively. The Raman spectra and Grazing incidence X-ray diffraction records show that aluminum silicate with the composition mullite was formed on the polished wafer surface, and silicon dioxide has the highest reactivity than other oxide abrasives under the same conditions during polishing the sapphire substrates.

Micropatterned freestanding magnetron sputtered Mg-alloy scaffolds

AbstractFreestanding scaffolds were fabricated of Mg5W (wt.% yttrium) alloy using magnetron sputtering technology. Appropriate method was found to produce scaffolds with high reproducibility, spatial resolution of 1 μm and good mechanical properties. Two different techniques were used for surface finishing, microblasting and chemical polishing. SEM investigation showed high surface quality after chemical polishing while microblasting influenced mechanical properties of the Mg5W alloy. Magnetron sputtering offers a high potential for the production of microstructured scaffolds.

Fabrication of Si and Ge vertical nanowire for transistor applications

One–dimensional nanostructures, such as nanowhisker, nanorod, nanowire, nanopillar, nanocone, nanotip, nanoneedle, have attracted significant attentions in the past decades owing to their numerous applications in electronics, photonics, energy conversion and storage, and interfacing with biomolecules and living cells. Such one–dimensional nanostructures are potential alternatives to planar metal–oxide–semiconductor field–effect transistors (MOSFETs) owing, for example, to their unique electronic structure and reduced carrier scattering caused by one–dimensional quantum confinement effects. Yet whether nanowire field effect transistors (NWFETs) can indeed outperform their planar counterparts is still unclear [1]. Three–dimensional integration and the combination of different material systems are central themes of electronics research. The manufacturing of nanostructured devices relies on either bottom–up approaches such as synthesis or growth process or top–down approaches such as lithography or etching process. Here, vertical Si nanowire and hetero–structure integration of Ge nanowire will be firstly fabricated for the first time to demonstrate the top–down etching process, which is applicable to fabricate vertical transistors. The key step in fabricating 3D vertical devices is the construction of the insulating layer between the contact electrodes. An isolation process without chemical or mechanical polishing steps was also developed to control layer engineering at this length scale.

Polishing of PbTe and Pb1 − x Sn x Te surfaces with H2O2-HBr-C2H2O4 solutions

We have studied the chemical polishing of the surface of single crystals of PbTe and Pb1 − xSnxTe solid solutions by H2O2-HBr-C2H2O4 bromine-releasing etchants. The dissolution rate of the crystals has been determined as a function of etchant composition, solution stirring rate, and temperature. The polished surfaces have been examined by microstructural analysis and scanning electron microscopy. We have located the composition boundaries of solutions for the dynamic chemical polishing of the semiconductor materials studied.

Influence of Fabrication Parameter on the Nanostructure of SiNWs under HF/AgNO<sub>3</sub>/Fe(NO<sub>3</sub>)<sub>3</sub> Etching System

Large-area SiNWs has been successfully fabricated through one-step metal-assisted chemical etching process at room temperature. The effects of key fabrication parameters (AgNO3 concentration, Fe (NO3)3 concentration, and etching time) on the nanostructure SiNWs were carefully investigated by SEM, TEM, respectively. The results show that AgNO3 concentration and Fe (NO3)3 concentration play important roles to the lengths and arrangements of SiNWs arrays in one-step MACE. The morphological transition of Si surfaces from solid nanowires to porous nanowires can be found with increasing AgNO3 concentration and Fe (NO3)3 concentration, which indicates that the re-dissolved Ag+ would work as the main oxidative species for oxidizing the silicon substrate and forming SiNWs in the HF/ AgNO3/ Fe (NO3)3 etching system. The length of SiNWs is increased with increasing AgNO3 concentration from 0.005 mol/L to 0.02 mol/L and etching time, the chemical polish phoenomenon can be observed when the Fe (NO3)3 concentration increases to 0.5 mol/L. A novel mechanism is proposed to explain the formation of SiNWs in HF/ AgNO3/ Fe (NO3)3 solution.

Fabrication of low cost soft tissue prostheses with the desktop 3D printer.

Soft tissue prostheses such as artificial ear, eye and nose are widely used in the maxillofacial rehabilitation. In this report we demonstrate how to fabricate soft prostheses mold with a low cost desktop 3D printer. The fabrication method used is referred to as Scanning Printing Polishing Casting (SPPC). Firstly the anatomy is scanned with a 3D scanner, then a tissue casting mold is designed on computer and printed with a desktop 3D printer. Subsequently, a chemical polishing method is used to polish the casting mold by removing the staircase effect and acquiring a smooth surface. Finally, the last step is to cast medical grade silicone into the mold. After the silicone is cured, the fine soft prostheses can be removed from the mold. Utilizing the SPPC method, soft prostheses with smooth surface and complicated structure can be fabricated at a low cost. Accordingly, the total cost of fabricating ear prosthesis is about $30, which is much lower than the current soft prostheses fabrication methods.

A Chemism Analysis of Alkali in the Chemical Mechnical Polishing Process of SiC Substrate

In this study, according to physic-chemical characteristic of the SiC crystals, we analyzed and researched the role of pH modifier in SiC crystal substrate chemical mechanical polishing and the surface after polishing. We used different polish agents which was made up with inorganic and organic bases to experiment, and then analyzed the results. The parameters of the polishing specimen, such as the removal rate of material, surface scanning and the roughness, were analyzed and used to determine the different pH modifiers played different roles in the stability of polish agents and surface quality of the specimen.

The effect of chemical treatment on the strength and transmittance of soda-lime cover glass for mobile

Most cracks in sheet glasses originate in edges and are a major cause of decreasing strength. Glass covers are being adopted in more mobile devices, especially smart phones, and are required to enhance reliability. In this study, micro-cracks in the chamfered edge of soda-lime cover glasses were eliminated by chemical polishing process with several etchants, and their mechanical properties and transmittance were measured. After ammonium fluoride and organic acid solution treatment, the transmittance of glass was not degraded and the strength was increased up to 20%. However, in the case of HF-based solutions, the strength of soda lime glasses increased but its transmittance decreased.

Laser polishing of niobium for superconducting radio-frequency accelerator applications

Interior surfaces of niobium cavities used in superconducting radio frequency accelerators are now obtained by buffered chemical polish and/or electropolish. Laser polishing is a potential alternative, having advantages of speed, freedom from noxious chemistry and availability of in-process inspection. We studied the influence of the laser power density and laser beam raster rate on the surface topography. These two factors need to be combined carefully to smooth the surface without damage. Computational modeling was used to estimate the surface temperature and gain insight into the mechanism of laser polishing. Power spectral density analysis of surface topography measurements shows that laser polishing can produce smooth topography similar to that obtained by electropolish. This is a necessary first step toward introducing laser polishing as an alternative to the currently practiced chemical polishing.

Smoothing single-crystalline SiC surfaces by reactive ion etching using pure NF3 and NF3/Ar mixture gas plasmas

In pure NF3 plasma, the etching rates of four kinds of single-crystalline SiC wafer etched at NF3 pressure of 2 Pa were the highest and it decreased with an increase in NF3 pressure. On the other hand, they increased with an increase in radio frequency (RF) power and were the highest at RF power of 200 W. A smooth surface was obtained on the single-crystalline 4H-SiC after reactive ion etching at NF3/Ar gas pressure of 2 Pa and addition of Ar to NF3 plasma increased the smoothness of SiC surface. Scanning electron microscopy observation revealed that the number of pillars decreased with an increase in the Ar-concentration in the NF3/Ar mixture gas. The roughness factor (Ra) values were decreased from 51.5 nm to 25.5 nm for the As-cut SiC, from 0.25 nm to 0.20 nm for the Epi-SiC, from 5.0 nm to 0.7 nm for the Si-face mirror-polished SiC, and from 0.20 nm to 0.16 nm for the C-face mirror-polished SiC by adding 60% Ar to the NF3 gas. Both the Ra values of the Epi- and the C-face mirror-polished wafer surfaces etched using the NF3/Ar (40:60) plasma were similar to that treated with mirror polishing, so-called the Catalyst-Referred Etching (CARE) method, with which the lowest roughness of surface was obtained among the chemical mirror polishing methods. Etching duration for smoothing the single-crystalline SiC surface using its treatment was one third of that with the CARE method.

Electrogenerated chemical polishing of copper

Stress free polishing method is preferred for a damage free surface of copper with ultra-flatness and ultra-smoothness. Such a surface offers a perfect substrate for integrated circuits and micro-electromechanical systems fabrication. A new polishing method, called electrogenerated chemical polishing (EGCP), is proposed based on the principle of the scanning electrochemical microscope (SECM) and the diffusion controlled chemical reaction. Roughness of a Cu surface is reduced from 100.5nm to 3.6nm by the proposed method. To demonstrate the planarization capability of this new method, a patterned Cu surface with an array of micro-columns is planarized with a peak-valley (PV) value from 4.7μm to 0.059μm.

Voiding Phenomena in Copper-Copper Bonded Structures: Role of Creep

For its good resistivity and reliability, copper remains the most widely used material for metal interconnections since the early 1990s [1]. Concerning the 3D-integration technological transition for next generation integrated circuits, copper still remains interesting as a bonding material. In this specific configuration, this metal allows wafer or die level assembly of active component strata with high bonding strength and it also ensures interlayer electrical conduction, reducing interconnection delays and increasing overall performances [2-3]. In the process temperature range from 300°C to 400°C, the voiding mechanism that drives the structure failure [4-5] shows similar characteristics to stress-induced voiding previously reported in basic encapsulated copper interconnections [6]. However, regardless of the bonding technique, void density, shape and location exhibit variations which cannot be explained by the mechanisms previously established. In this paper, we investigate several factors, including copper surfaces roughness, copper layer microstructure and bonding processing parameters to weight their impact on the voiding phenomenon. Better understanding of void formation has enabled the achievement of wafer assemblies exhibiting much higher reliability and bonding quality.200mm thermally oxidized silicon substrates are used in this study. 500nm-thick copper layer are then deposited on a 20nm-thick titanium nitride layer which is used to prevent copper diffusion into silicon substrate. Copper-copper bonding is studied through two different bonding techniques: direct bonding at room temperature under atmospheric pressure after surface activation by chemical and mechanical polishing (CMP activated bonding) and thermocompression bonding (TC bonding) using a combination of a thermal budget and compressive stress. In both cases, additional post-bonding annealing is accomplished under nitrogen atmosphere.In our bonded copper layers configuration, voiding phenomenon is supposed to have different origins:- Residues of the copper surface roughness which is brought into contact during bonding process and trap some volume- Presence of metal oxide on sample surfaces and its subsequent degradation by annealing- Nucleation and growth of cavities due to standard metallurgical creep mechanisms of copper layers during its thermomechanical loadingIn order to evaluate roughness impact on the voiding phenomenon, bonding was performed thanks the two different techniques on copper surfaces exhibiting identical surface topology properties (post CMP treatments) (Fig. 1a). In order to aggravate void creation, TC bonding was also performed with extreme parameters in terms of pressure values and copper surface roughness (Fig. 1b). Void densities and volumes were estimated by high resolution Secondary Electron Microscopy (SEM) cross-sections observations (Fig. 2). A special attention was paid to imaging conditions and analysis. Indeed we operated data collection over large sections of about 40µm. In the context of this study we were able to appreciate significant differences between bonded samples. More specifically we focused on volume variations and size distributions which enabled us for instance to highlight the role of roughness in voiding phenomenon.Other possible causes for void generation were also investigated using dedicated experiments:- Gold-gold TC bonding was performed as a bonding reference system involving oxide free metallic layers- Bonding of copper layers carefully deposited on copper bulk substrates to highlight the influence of thermomechanical stress (Fig. 3)In the light of these results, the impact of the different factors will be discussed and the main source of voiding due to creep deformation will be demonstrated. FIGURES CAPTIONS Fig 1 : 20 x 20 µm² AFM scans of copper surface. a- In CMP bonding configuration: RMS roughness is 0.2 nm. b- In TC bonding configuration: RMS roughness is 22 nm. Fig 2 : SEM cross section. a – On CMP activated bonding after a post bonding annealing at 400°C. b – On TC bonding performed at 400°C under a pressure of 2.9 MPa on high-roughness surfaces. Voids are arrowed. Fig 3 : SEM cross section of TC bonding involving copper layers deposited directly on copper bulk substrate. Voids are arrowed. ACKNOWLEDGEMENTS The authors would like to thanks the French Direction Générale de l’Armement (DGA), the French Direction Générale de la Compétitivité de l’Industrie et des Services (DGCIS) and SOITECSA for its financial support. REFERENCES [1] P. C. Andricacos, et al., IBM J. Res. Dev., vol. 42, no. 5, pp. 567–574, Sep. 1998.[2] N. Sillon, et al., pp. 1 –4., IEDM 2008. [3] R. Taibi, et al., pp. 219–225, ECTC 2010.[4] C. S. Tan, et al., Appl. Phys. Lett., vol. 87, no. 20, pp. 201909, 2005.[5] P. Gondcharton, et al., MRS Online Proc. Libr., vol. 1559, 2013, doi : 10.1557/opl.2013.718.[6] H. Okabayashi, Mater. Sci. Eng. R Rep., vol. 11, no. 5, pp. 191–241, 1993.

Microstructural Characterization of Mg–0.3Al–0.2Ca Alloy Using Ion Milling Surface Preparation Technique

The Vickers microindentation and spherical nanoindentation tests were carried out on a polycrystalline Mg–0.3Al–0.2Ca alloy specimen. Specimens were prepared with chemical polishing and ion milling techniques. The electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) were used to study the plastic deformation inside and around the indents with a cold-field emission scanning electron microscope. The distribution of strain fields, slip lines, and twins was imaged on an indented surface. A crystallographic orientation mapping was performed to map the local crystallographic misorientation associated with channeling contrast variations. The chemical polishing technique was used to remove the material from the surface and allow the study of deformed microstructure at a maximum depth of the indent. The combination of ECCI and EBSD with chemical polishing and ion milling surface preparation techniques proved to be beneficial to study the indentation-induced plastic deformation in a polycrystalline Mg–0.3Al–0.2Ca alloy specimen.

Winery wastewater treatment by combination of Cryptococcus laurentii and Fenton’s reagent

Winery wastewaters (WW) have high levels of organic matter, resulting in high COD and BOD and suspended solids. This paper studies the combination of biological and chemical processes in WW treatment. Among 10 yeast isolates, Filobasidium sp. (AGG 577) and Cryptococcus laurentii (AGG 726) were selected due to their superior performance in COD removal. During WW degradation, COD and total polyphenols (TPP) content removal of 89–90% for Filobasidium sp. and 90–93% for C. laurentii were obtained. However, despite similar degradation efficiency for both yeasts, COD kinetics and pH evolution during treatment reveals that C. laurentii presents a faster response than Filobasidium sp. The toxicity (inhibition of Vibrio fischeri luminescence) of C. laurentii treated WW decreases to an inhibition value below 2.5%. However, treated WW exceeds the legal limits, making necessary an additional treatment. In this case, the selection of Fenton’s reagent as a chemical final polish step process is a good compromise between efficiency and lower practical complexity. The best results for both COD and TPP removal were obtained with H2O2 initial concentration of 39.2mM and a H2O2:Fe2+ molar ratio of 15:1. The combined C. laurentii – Fenton’s reagent treatment of WW achieved a total reduction of 98% and 96%, for COD and TPP, respectively.

Etching behavior of PbTe and Pb1 − x Sn x Te crystal surfaces in aqueous H2O2-HBr-tartaric acid solutions

The chemical polishing of the surface of single crystals of PbTe and Pb1 − x Sn x Te solid solutions by H2O2-HBr-tartaric acid bromine-releasing etchants has been studied for the first time under reproducible hydrodynamic conditions. The dissolution rate of the crystals has been determined as a function of etchant composition, solution stirring rate, and temperature. The polished surfaces have been examined by microstructural analysis and electron microscopy. We have located the composition boundaries of solutions for the dynamic chemical polishing of the semiconductor materials studied.

Structural and Electronic Properties of Gold Contacts on CdZnTe with Different Surface Finishes for Radiation Detector Applications

State-of-the-art room-temperature, high-resolution x-ray and gamma-ray semiconductor detectors can be fabricated from CdZnTe (CZT) crystals. The structural and electronic properties of the CZT surface, especially the contact interfaces, can have a substantial effect on radiation detector performance, for example leakage current, signal-to-noise ratio, and energy resolution, especially for soft x-rays and large pixilated arrays. Atomically smooth and defect-free surfaces are desirable for high-performance CZT-based detectors; chemo-mechanical polishing (CMP) is typically performed to produce such surfaces. The electrical behavior of the metal/CZT interface varies substantially with surface preparation before contact deposition, and with choice of metal and deposition technique. We report a systematic study of the structural and electronic properties of gold (Au) contacts on CZT prepared with different surface finishes. We observed subsurface damage under Au contacts on CMP-finished CZT and abrupt interfaces for Au on chemically-polished (CP) CZT. Schottky barrier formation was observed for Au contacts, irrespective of surface finish, and less charge trapping and low surface resistance were observed for CP-finished surfaces. Pre-deposition surface treatment produced interfaces free from oxide layers.

Abrasive-Free Chemical Polishing of Hard Disk Substrate with Benzoyl Peroxide-H<sub>2</sub>O<sub>2</sub> Slurry

The effect of benzoyl peroxide (BPO) as an initiator in H2O2slurry for abrasive-free chemical polishing of hard disk substrate was investigated. The results of abrasive-free polishing tests show that the introduction of BPO increases material removal rate (MRR) and decreases the value of Roughness (Ra). To further investigate the mechanism of abrasive-free polishing, electron spin-resonance spectroscopy (EPR) tests, auger electron spectrometer (AES) and electrochemical tests were conducted. Electron spin-resonance spectroscopy (EPR) tests show the concentration of radicals increase and promote the reaction on the surface of hard disk substrate. Auger electron spectrometer (AES) and electrochemical tests indicate chemical changes happen on the surface of hard disk substrate, and the formed oxide film may be sparse or porous. The results imply that the introduction of BPO can effectively improve the effect of abrasive-free polishing.

Correlation of fundamental photoreflectance spectra with surface quality of bulk ZnTe semiconductor grown from Te solution

Large size ZnTe single crystals were grown from Te‐solution with the vertical Bridgman method. The fundamental photoreflectance (PR) spectra of bulk ZnTe crystal subjected to a successive sequence of surface treatments, i.e., mechanical and chemical polishing, and passivation, have been measured over the wavelength range 200–600 nm at room temperature (RT) for the first time. The shape, relative intensity and evolution of the distinct E0, E1, E1+∆1 and E2 transitions during each stage of wafer processing were investigated. It was found that, those distinct transitions vary with varying crystal surface quality. The intensity of the reflectance peaks is large with sharp peak profile when the surface has good crystalline quality. However, E0 peak can be easily eliminated by a small amount of structural damages on the wafer surface. The dispersion tendency of the E1 and E1+∆1 peaks suggesting the wafer surface is widespread covered by structural damages. The reflection peaks’ intensity were all reduced after passivated with H2O2 solution. E2 peak intensity is more easily to be reduced during passivation.

Adhesion Assessment of BNT Films on Titanium Substrates Using a Scratch Test

Lead-free piezoelectric (Bi1/2Na1/2)TiO3 (BNT) films were deposited on 0.2 mm thick pure titanium (Ti) substrates by a hydrothermal method. Scratch tests were performed to quantitatively assess the adhesion strength between BNT films and Ti substrates. Ti substrates were pretreated by chemical polish and mechanical polish respectively prior to BNT film deposition with a view of investigating the effects of substrate surface pretreatments on the adhesion of BNT film. In the scratch test, the behaviour of BNT film exfoliation was investigated by SEM observation. The scratch test results revealed that the chemical polish pretreatment effectively improved the adhesion of BNT films.