A Novel Deep Hole Etching in NLD Plasma Low GWP Gases
As for etching of quartz or glass, CF<sub>4</sub> and C<sub>3</sub>F<sub>8</sub> and C<sub>4</sub>F<sub>8</sub> are mainly used. And, much SF<sub>6</sub> gas is used for etching of silicon. The case that uses together a C<sub>4</sub>F<sub>8</sub>-CVD method is also in sidewall protection film formation. However, these gases have a very large GWP. Since a MEMS market becomes larger in the future, the gas used by DRIE needs the reduction in GWP. This research is developing quartz etching technology, and succeeded in etching of the GWP free etching of Pyrex glass via using C<sub>3</sub>F<sub>7</sub>I. Furthermore, the method of performing anisotropic deep silicon etching by introducing a sputtering system into DRIE technology was invented, and C<sub>4</sub>F<sub>8</sub> free etching anisotropic etching was also successful. Therefore, the NLD etching in the MEMS field is very useful equipment, which can realize drastic GWP reduction and can propose highly efficient etching technology.
Deep dry etching of borosilicate glass using fluorine-based high-density plasmas for microelectromechanical system fabrication
For the fabrication of microelectromechanical system devices, deep trench etching of borosilicate glass (Corning 7740) has been investigated using SF6/Ar inductively coupled plasma. Since borosilicate glass contains metal elements which produce nonvolatile fluorides, dry etching of its smooth surface is a difficult issue. In this article, requisite conditions for etching glass with a smooth surface and high mask selectivity have been discussed on the basis of the results of a comprehensive experimental study of the effects of substrate bias power and Ar addition on the removal of involatile fluoride residues deposited via the backscattering of etch products in the vicinity of the substrate surface. Under optimized etching conditions, deep trench etching of borosilicate glass to 32 μm depth and 15 μm width has been accomplished using 3-μm-thick chrome metal masks.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.