Papers by Keyword: Electrochemical Etching

Abstract: In this work, nanostructure porous silicon surface was prepared using electrochemical etching under different current densities. I have studied the surface morphology and photoluminsense of four samples prepared at current densities 5 , 10 , 15 and 20 mA/cm²at fixed etching time 10 min.photoluminsense study showed that the energy gap of the porous silicon samples are is 3.1eV,and it was higher than the energy gap of bulk silicon which was 1.08 eV. A scanning electron microscope (SEM) micrographs were used to estimate the surface area. The surface area of the porous layer is strongly dependent on the porous layer geometry and its depth. The optical reflectance measurements were obtained by using an optical reflectometer (UV) which is equipped with an integrating sphere in the (200-1100) nm wavelength range, which reveals that the textured cells with PS layer sources have lower reflectivity value compared to the textured cell without PS structure.

Abstract: . Electrochemical etching is widely used to process refractory metals such as tungsten and molybdenum. Flow field is one of the crucial factors that influence the surface quality in electrochemical etching. In this paper, the electrochemical etching flow field was analyzed via FLUENT, the characteristics of flow field in electrochemical etching are studied, furthermore, the effects of four different outlet forms of electrolyte on flow field uniformity, electrolyte velocity and pressure distribution are investigated. Under the same electrolyte flow rate, the flow field characteristics of different outlet forms are analyzed by velocity vector diagram, pressure distribution nephogram, velocity and pressure curve diagram. The simulation results indicate that stable electrolyte velocity and uniform pressure distribution of flow field are obtained when the outlet form of electrolyte adopts the optimized flat. Finally, the fixture for this outlet form is designed and fabricated, and experimental verification is carried out, which shown that the flow field is uniform and the crystal plane of the workpiece is well-distributed which according with the process requirements.

Abstract: In this study, Zinc Oxide (ZnO) microstructures were grown on porous silicon (PS) using chemical bath deposition (CBD) method by varying the growth time. The field emission scanning electron microscopy (FESEM) revealed the morphology and sized of ZnO. The X-ray diffraction (XRD) spectra indicate the high quality growth of ZnO on PS surface. Raman analyses revealed the peaks shift of E₂(High), characterized wurtzite lattice and indicates good crystallinity of ZnO.

Abstract: Anodization of silicon carbide (SiC) in hydrofluoric acid (HF) solutions is a promising way to etch this material which is very resistant against traditional chemical etching methods. Moreover, it has been shown that several reproducible porous SiC morphologies can be performed varying anodization conditions (current density, electrolyte composition, UV lighting) and/or substrate properties (doping type and level). This paper proposes a state of the art of porous SiC etching in GREMAN and a presentation of the morphologies achievable using anodization in HF based electrolytes.

Abstract: In this work, we have developed a selective wet etching technique for n+-SiC substrate using electrochemical etch process. A mixture of hydrofluoric acid and hydrogen peroxide was used as an electrolyte and the etch rates exceeding 200 μm per hour at the current density of 50 mAcm^-2 was achieved. This process is highly selective and the etching process stops at the interface of n+ SiC substrate and n-SiC epi layer. Using this process, we have successfully fabricated 180 to 250 μm thick 4’’ n-SiC epitaxial free standing wafers by separating them from a 350 μm thick n+ SiC substrate. After the substrate is completely removed, free standing wafer is characterized for wafer bow and minority carrier lifetime, using both Si-face and C-face. The wafer bow was reduced from 40 μm to 20 μm after the substrate removal. It was found that the process of removing the substrate does not introduce any extra damage to the wafer as far as the lifetime is concerned. The hole lifetime measured by microwave photoconductivity decay technique was unchanged at around 2 μsec, measured from both Si-face and C-face. These results are very promising and open up many avenues for many device applications where lightly doped free standing epitaxial semiconductor thin film is needed.

Abstract: A typical metallographic preparation (i.e. mechanical grinding and chemical etching) and electrochemical etch-polishing was carried out to observe the microstructure of pure silver and two silver-copper alloys (Sterling silver Ag 925 and Ag 333) in circular blanks used for coin production. The obtained micrographs revealed cold working effects on the coin rim caused by the rimming process. These rim effects are the reason for local differences in the mechanical properties of circular blanks, posing a challenge to tool lifetime. To quantify these effects, a micro hardness-mapping was performed and analysed.

Abstract: In this work, seeded porous silicon (PSi) was used as a substrate in the growth of ZnO nanostructures. PSi was prepared by electrochemical etching method. ZnO thin films as seeded were deposited via sol-gel spin coating method. ZnO nanostructures were grown on seeded PSi using hydrothermal immersion method. In order to study the effect of post-heat treatment on the substrate, post annealing temperature were varied in the range of 300 to 700 °C. The FESEM results shows ZnO thin film composed of nanoparticles were distributed over the PSi surface. Based on AFM characterization, the smoothest surface was produced at post annealing temperature of 500 °C. There are two different peaks appeared in PL characterization. The peak in near-UV range is belonging to ZnO thin films while a broad peak in visible range can be attributed to ZnO defects and PSi surface. In addition, FESEM, XRD and PL were used to characterize the ZnO nanostructures. The FESEM results revealed ZnO nano-flower were successfully grown on seeded PSi. Hexagonal wurtzite of ZnO with dominated by the plane (100), (002), and (101) was found by XRD characterization. Two different peaks in UV range and visible range can be attributed to ZnO nano-flower and various defects of ZnO, respectively.

Abstract: In this study the possibility to apply electrochemical impedance spectroscopy as an alternative method for the characterisation of the intermetallic microstructures of Sn-3.5Ag lead free solder samples was investigated. The aim of the study is to compare the electrochemical impedance spectra of solder samples, reflowed with different heat profiles. A quenching technique was applied in order to solidify the solder samples in cylindrical crucibles. Differences in the microstructures of the solidified alloys were achieved by changing the temperature of the quenching media. The molded and cross sectioned specimens were observed using both optical microscopy and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). The microstructure of the ingots was revealed by selective electrochemical etching. The electrochemical impedance spectrum (EIS) was measured before and also after the selective etching process. The complex impedance spectra contain information regarding the characterized microstructure. Our aim is to determine quantitative parameters which are identical to the characteristics of the microstructure.

Abstract: Uniformity is an important index of the template electrochemical etching. Due to the uneven current distribution between the two electrodes, the etching depth of the workpiece center and edge are significantly different,and the deviation of which is up to 15% or more. In this study, the causes of edge effect is analyzed. A compensation method is proposed and proved by experiments.The results show that: this method is simple, and the uniformity can be reduced to about 3%. It is suitable for the processing of high uniformity requirements in microstructure machining.

Abstract: The anodic current-potential behaviors of PS fabrication by doubled-cell electrochemical etching method have been studied. There are three reaction regions: porous silicon formation region, a transition region and electropolishing region in I-V curves. Polishing current and the HF acid concentration has a directly proportional relationship, the electropolishing current of silicon increased with the increase of the concentration of HF, in a certain concentration range. The electropolishing current of silicon increased with increasing the sweep rate on the condition of the same HF concentration.