Academic literature on the topic 'Method of section etching by HF solution'

Silicon dioxide (SiO2) and silicon nitride (Si3N4) are widely used as an insulating layer to separate interconnection, due to the characteristic of their wide band gap. As the feature size of semiconductors has been continuously decreasing and their structures have become more complex recent years, SiO2 as an insulating layer is reaching its limit. One of the ways to overcome this limitation, next generation 3D structure semiconductors are developed. In order to manufacture these kinds of devices, a removal of SiO2 is required, however, as both SiO2 and Si3N4 layers are revealed, the highly selective SiO2 etching process over Si3N4 is needed. If the Si3N4 layers were etched during the SiO2 layer etching process, the Si3N4 layer could not be function as an insulating layer and an etch stop layer. As an etchant for the SiO2 layer, hydrofluoric acid (HF) and ammonium fluoride (NH4F) combining solution is mainly used. However, it is known that HF solution also causes the material loss of the Si3N4 layers. Therefore, the study of etching behaviors of SiO2 and Si3N4 in HF solution is needed. In HF solutions, main etching species of SiO2 and Si3N4 exists as fluorine species. The concentration of these fluorine species depends on various conditions, such as pH of the solution or the composition of HF and NH4F. Therefore, the dependence of SiO2 and Si3N4 etching rates on the conditions of HF solutions were investigated. To investigate the etching rates of SiO2 and Si3N4, the blanket SiO2 and Si3N4 wafer in which deposited on Si wafer by the low-pressured chemical vapor deposition method were used, respectively. A patterned SiO2/Si3N4 multi-stack structures were fabricated by plasma-enhanced chemical vapor deposition, to verify whether SiO2 was selectively etched over Si3N4 in HF solution. The HF solutions were prepared by adding various concentrations of HF to deionized water and NH4F was added in some cases. The pH of the HF solution was controlled by adding hydrochloric acid or ammonium hydroxide. The temperature maintained at 25 °C during the etching processes using a water bath. The blanket SiO2 and Si3N4 wafers were immersed in these solutions for 3 and 60 mins, respectively. The etching depth of the SiO2 and Si3N4 films was measured by spectroscopic ellipsometry. The morphology of patterned SiO2/Si3N4 multi-stack structures after etching process was observed using field-emission scanning electron microscopy (FE-SEM). The pH and the concentrations of each fluorine species of the prepared HF solutions were calculated based on the equilibrium constants, molar balance, and charge balance. To obtain the HF solution with the high SiO2 etching selectivity over Si3N4, blanket SiO2 and Si3N4 wafers were etched under various pH and initial concentrations of HF solution. As the pH of the HF solution was increased, at the same initial HF concentration, the SiO2/Si3N4 etching selectivity was increased. Meanwhile, the etching selectivity of SiO2 over Si3N4 was increased with the initial concentrations of HF increased, at a fixed pH of the solution. To investigate the reason for the dependencies of the SiO2 and Si3N4 etching rates on pH and initial concentrations of HF, the concentrations of each fluorine species were calculated. As a result, the etching mechanisms and the etching behaviors of SiO2 and Si3N4 in the HF solutions were suggested. Based on the etching kinetics of SiO2 and Si3N4, a patterned SiO2/Si3N4 multi-stack structure etching conditions were controlled to investigate the SiO2/Si3N4 selective etching ability of the HF solution. The cross-sectional FE-SEM images visually showed that high SiO2 etching selectivity compared to Si3N4 was achieved. As a result, highly selective SiO2 etching without loss of Si3N4 was obtained by adjusting only the concentrations of HF and NH4F, without any special additives through the suggested SiO2 and Si3N4 etching kinetics.

Ion implantation is a well established technique to dope selectively prespecified regions of silicon substrates. It has the drawback that a thermal treatment is required to activate the dopant and to reconstruct the crystal lattice. This leads to dopant diffusion in depth and also laterally, when the implantation has been preformed through a patterned mask.In this paper two different approaches to determine the doping profile using chemical etching and TEM are presented. Cross-section specimens are prepared using a technique described elsewhere, followed by preferential etching.The first approach is well established and is based on the combined action of HF and HNO3.Low concentrations of HF are used to keep the etching rate low enough. Figure 1 shows a cross-section of a boron implanted and annealed sample which has been etched using the solution HF(40%):HNO3(65%)= 1:300 at 5°C for 80 seconds. The etching rate is proportional to the doping level, as shown in figure 2 and it can be observed that the lowest level which one can delineate with this solution is of the order of 1017cm−3, which is in agreement with the delineated level of figure 1, namely 6·1017 cm−3.

We propose and demonstrate an unconventional method suitable for releasing microelectromechanical systems devices containing an Al layer by wet etching using SiO2 as a sacrificial layer. We used 48% HF solution in combination with 20% oleum to keep the HF solution water-free and thus to prevent attack of the Al layer, achieving an outstanding etch rate of thermally grown SiO2 of ≈1 µm·min−1. We also verified that this etching solution only minimally affected the Al layer, as the chip immersion for ≈9 min increased the Al layer sheet resistance by only ≈7.6%. The proposed etching method was performed in an ordinary fume hood in a polytetrafluorethylene beaker at elevated temperature of ≈70 °C using water bath on a hotplate. It allowed removal of the SiO2 sacrificial layer in the presence of Al without the necessity of handling highly toxic HF gas.

Classical photoelectrodes for Dye Sensitized Solar Cells (DSSCs) were fabricated by using the electrochemical method on the titanium (Ti) template, for that the fabrication process would influence the characteristics of the DSSCs. In this study, at first three different methods were used to etch Ti templates from 10 to 17 min, (1) polishing-chemical etching: Ti template was annealed at 450°C for 1 h, abraded using number 80 to 1500 SiC sheet, and then etched in a solution of 5% HF + 95% H2O; (2) electrochemical polishing-chemical etching: Ti template was annealed at 450°C for 1 h, electrolytic polishing with 42% CH3OH + 5% HClO4 + 53% HOCH2CH2OC4H9solution, and the chemical-etching in a solution of 5% HF + 95% H2O; (3) chemical etching: Ti template was etched in a solution of 5% HF + 95% H2O and annealed at 450°C for 1 h. When the etching time was changed from 10 to 17 min, the thicknesses of Ti templates decreased from 75.3 μm to 14.8 μm, depending on the etching method. After etching process, the TiO2nanotube arrays were fabricated as the photoelectrode of DSSCs by electrochemical process, in which the Ti as anode and platinum (Pt) as cathode. The electrolyte solution included C2H4(OH)2, NH4F, and deionized water. After annealing the grown TiO2nanotube arrays at 450°C for 3 h, we would show that the etching process had large effect on the structure and transmittance ratio of the TiO2nanotube arrays.