Anisotropic Etching Process Research Articles

Investigation of the Process of Plasma Through Etching of HkMG Stack of Nanotransistor with a 32-nm Critical Dimension

The processes of plasma etching of stack layers to form a structure of a metal gate of a nanoscale transistor with a dielectric with a high level of dielectric permittivity (HkMG) are investigated. A resist mask formed by fine-resolution electron-beam lithography is used in the etching. The plasma etching of the stack’s layers is carried out in one technological etching cycle without a vacuum break. The sequential anisotropic etching process of the stack of polysilicon, tantalum nitride, and hafnium nitride, as well as the etching process of the gate insulator based on hafnium oxide with a high degree of selectivity in relation to the underlying crystalline silicon, which guarantees the complete removal of the layer of hafnium oxide and the minimal loss of the silicon layer (not more than 0.5 nm), is investigated.

Investigation of the Process of Plasma Through Etching of HkMG Stack of Nanotransistor with a 32-nm Critical Dimension

The processes of plasma etching of stack layers to form a structure of a metal gate of a nanoscale transistor with a dielectric with a high level of dielectric permittivity (HkMG) are investigated. A resist mask formed by fine-resolution electron-beam lithography is used in the etching. The plasma etching of the stack’s layers is carried out in one technological etching cycle without a vacuum break. The sequential anisotropic etching process of the stack of polysilicon, tantalum nitride, and hafnium nitride, as well as the etching process of the gate insulator based on hafnium oxide with a high degree of selectivity in relation to the underlying crystalline silicon, which guarantees the complete removal of the layer of hafnium oxide and the minimal loss of the silicon layer (not more than 0.5 nm), is investigated.

Iso-height lines of multifractal etched silicon rough surfaces

Morphology of etched silicon wafers during anisotropic etching process is investigated utilizing the geometrical exponents of iso-height contour lines. The images obtained from field emission scanning electron microscopy show pyramidal microstructures which disappear in large time scales and porous silicon structures are formed. The morphology of these microstructures is investigated utilizing the data obtained from atomic force microscopy and contour loop analysis. The results show that the anisotropic etching breaks the up-down symmetry in the height fluctuations of etched silicon surfaces. Area of the contour loops increases by enhancement of pyramids sizes. Fractal dimensions of the loops decrease at the beginning of etching process. Distributions of loops and geometrical exponents of iso-height lines in different etching times are determined. The results indicate that in spite of asymmetry in the height fluctuations, the hyperscaling relation and Zipf's law are verified for the multi-affine silicon surfaces during etching process.

The effect of increasing interfacial strength in micro fluidic system for heat detection with micro-sandglass shaped interlocks

We present a useful method to increase interfacial strength for micro fluidic system of calorimetry biosensor. The micro-sandglass shaped posts were fabricated by deep silicon reactive ion etching and Tetramethyl ammonium hydroxide (25 wt% TMAH) anisotropic etching processes, sequentially. The interfacial strength can be controlled by structure of interlock which dependents on the TMAH etching time and diameter of micro pillar. The fabricated micro-standglass shaped interlocks were applied in micro fluidic structure to increase interfacial strength of micro fluidic structure. The detection result of reactive heat using calorimetry biosensor demonstrates that the interfacial strength can be increased by micro-standglass shaped interlocks to avoid leakage in micro fluidic system.

A Partially Etched Structure of Light‐Addressable Potentiometric Sensor for High‐Spatial‐Resolution and High‐Speed Chemical Imaging

In this study, a partially etched structure of a light‐addressable potentiometric sensor (LAPS) is fabricated for high‐spatial‐resolution and high‐speed imaging of chemical species. An anisotropic etching process based on tetramethylammonium hydroxide (TMAH) is optimized to fabricate the structure, which strikes a balance between the imaging performance and the mechanical strength of the sensor plate. The etched region of the sensor plate with a thickness of 47 µm yields a 12‐fold enhancement of the photocurrent signal at a high frequency of 120 kHz and a 10‐fold frequency bandwidth in comparison with the frame region with a thickness of 150 µm due to the reduced traveling distance of charge carriers inside the semiconductor. This result represents a new approach for high signal‐to‐noise ratio, high‐spatial‐resolution, and high‐speed measurement.

Difference in anisotropic etching characteristics of alkaline and copper based acid solutions for single-crystalline Si

The so called inverted pyramid arrays, outperforming conventional upright pyramid textures, have been successfully achieved by one-step Cu assisted chemical etching (CACE) for light reflection minimization in silicon solar cells. Due to the lower reduction potential of Cu2+/Cu and different electronic properties of different Si planes, the etching of Si substrate shows orientation-dependent. Different from the upright pyramid obtained by alkaline solutions, the formation of inverted pyramid results from the coexistence of anisotropic etching and localized etching process. The obtained structure is bounded by Si {111} planes which have the lowest etching rate, no matter what orientation of Si substrate is. The Si etching rate and (100)/(111) etching ratio are quantitatively analyzed. The different behaviors of anisotropic etching of Si by alkaline and Cu based acid etchant have been systematically investigated.

Deterministic Nanopatterning of Diamond Using Electron Beams.

Diamond is an ideal material for a broad range of current and emerging applications in tribology, quantum photonics, high-power electronics, and sensing. However, top-down processing is very challenging due to its extreme chemical and physical properties. Gas-mediated electron beam-induced etching (EBIE) has recently emerged as a minimally invasive, facile means to dry etch and pattern diamond at the nanoscale using oxidizing precursor gases such as O2 and H2O. Here we explain the roles of oxygen and hydrogen in the etch process and show that oxygen gives rise to rapid, isotropic etching, while the addition of hydrogen gives rise to anisotropic etching and the formation of topographic surface patterns. We identify the etch reaction pathways and show that the anisotropy is caused by preferential passivation of specific crystal planes. The anisotropy can be controlled by the partial pressure of hydrogen and by using a remote RF plasma source to radicalize the precursor gas. It can be used to manipulate the geometries of topographic surface patterns as well as nano- and microstructures fabricated by EBIE. Our findings constitute a comprehensive explanation of the anisotropic etch process and advance present understanding of electron-surface interactions.

Comparison of the Etch Mask Selectivity of Nickel and Copper for a Deep, Anisotropic Plasma Etching Process of Silicon Carbide (SiC)

This paper reports research performed on comparing the etch mask selectivity of two different hard mask material layers, specifically nickel and copper, used for deep, anisotropic plasma etching of Silicon Carbide (SiC) substrates. Hard masks are required when performing deep etches into SiC given the extreme inertness of SiC combined with the high ion energies needed for the plasma etching of this material. Using a recently developed deep, highly-anisotropic inductively-coupled plasma process, we performed etches of SiC substrates with patterned hard masks composed of different types of materials to measure and compare their mask selectivity. The mask selectivity is important since it relates to how thick the hard mask layers must be in order to survive the required etch time to obtain a desired etch depth, and the thickness of the patterned hard mask layer has a direct impact on the resultant dimensional tolerances that can be obtained from the etch process. Using a deep, highly-anisotropic etch process we measured that the mask selectivity of nickel to be approximately 25 and that of copper to be 163. The capability to etch highly-anisotropic deep features into SiC using hard mask material layers has important implications for a number of applications in MEMS and microelectronics.

Selective Pattern Transfer of Nano-Scale Features Generated by FE-SPL in 10 nm Thick Resist Layers

High performance single nanometer lithography is an enabling technology for beyond CMOS devices. In this terms a novel mask- and development-less patterning scheme by using electric field, current controlled Scanning Probe Lithography (FE-SPL) in order to pattern structures on different samples was developed. This work aims to manufacture nanostructures into different resist by using FE-SPL, whereas plasma etching at cryogenic temperatures is applied for an efficient pattern transfer into the bottom Si substrate. The challenge for future quantum devices, generated by SPL and cryogenic etching, is finding a resist that is at most 10 nm in thickness and has a plasma durability high enough for pattern transfer into silicon. As a first step towards future quantum devices the silicon-to-resist selectivity of calixarene, AZ Barli, poly (3-hexylthiophen-2, 5-diyl) and polymethylmethacrylat for the anisotropic cryogenic dry etching process was estimated. A silicon-to-resist selectivity of about 4:1 for each of these resists was found. With these results, nano-scale, highly parallel double line features in silicon for future double patterning were generated.

Electrical field-induced faceting of etched features using plasma etching of fused silica

This paper reports a previously unreported anomaly that occurs when attempting to perform deep, highly anisotropic etches into fused silica using an Inductively-Coupled Plasma (ICP) etch process. Specifically, it was observed that the top portion of the etched features exhibited a substantially different angle compared to the vertical sidewalls that would be expected in a typical highly anisotropic etch process. This anomaly has been termed as “faceting.” A possible explanation of the mechanism that causes this effect and a method to eradicate it has been developed. Additionally, the method to eliminate the faceting is demonstrated. It is theorized that this faceting is a result of the interaction of the electro-potential electrical fields that surround the patterned nickel layers used as a hard mask and the electrical fields directing the high-energy ions from the plasma to the substrate surface. Based on this theory, an equation for calculating the minimum hard mask thickness required for a desired etch depth into fused silica to avoid faceting was derived. As validation, test samples were fabricated employing hard masks of thicknesses calculated based on the derived equation, and it was found that no faceting was observed on these samples, thereby demonstrating that the solution performed as predicted. Deep highly anisotropic etching of fused silica, as well as other forms of silicon dioxide, including crystalline quartz, using plasma etching, has an important application in the fabrication of several MEMS, NEMS, microelectronic, and photonic devices. Therefore, a method to eliminate faceting is an important development for the accurate control of the dimensions of deep and anisotropic etched features of these devices using ICP etch technology.

Ultrafast laser based hybrid methodology of silicon microstructure fabrication for optoelectronic applications

As an alternative approach to conventional lithography based fabrication, simple methodology of ultrafast laser writing followed by chemical processing for fabrication of silicon microstructures is studied and presented. Laser fluence and number of pulses dependent laser-matter interaction study reveals several concurrent extreme nonlinearities that influence the structural morphology in both longitudinal and transverse directions. High intensity femtosecond pulse propagation produces inevitable structural features, such as quasi aperiodic surface textures, V-shaped craters, re-casted melt and debris. To minimize such undesired effects, isotropic and anisotropic chemical etching processes have been systematically optimized. Such hybrid protocols resulted into definite microstructures, with surface quality comparable to those obtained from other lithographic fabrication methods. The proposed methodology is expected to provide control over desired feature sizes, for large-scale and cost-effective fabrication of microstructures for many optoelectronics applications.

Fabrication of a Si lever structure made by double-angled etching with reactive gas cluster injection

The reactive gas cluster injection process is an etching method that uses a neutral cluster beam without plasma. Low-damage Si etching can be realized with this method because of the very low irradiation energy; the product is free of charge-up problems and vacuum UV light damage. The ClF3–Ar neutral cluster injection system for angled etching was constructed with a nozzle that was placed at 45° from the sample normal. The angled anisotropic Si etching is demonstrated with a high aspect ratio. The lever structure, which is often used in microelectromechanical systems (MEMSs), was fabricated by double-angled etching with reactive gas cluster injection. A simple fabrication process for the lever structure was achieved by double-angled etching with reactive gas cluster injection. These results show that various three-dimensional (3D) structures can be fabricated by repeated anisotropic etching with varying angles and directions. It is expected that the angled anisotropic etching process will enable the creation of unprecedented structures for use in MEMSs or photonic crystals.

Experimental investigation of SF6–O2 plasma for advancement of the anisotropic Si etch process

This study examines the impact of varying the internal process parameters, such as the concentrations of oxygen and fluorine in a SF6–O2 plasma, in two capacitively coupled plasma etch chambers with different geometries. Silicon wafers were used to investigate the anisotropic nature of etch profiles. The oxygen and fluorine concentrations were measured via optical emission spectroscopy using the actinometry technique, which requires the electron energy distribution function to remain unchanged under the different plasma conditions employed in this work. A Langmuir probe was used to investigate the electron energy distribution function, where the chamber pressure, power, and process duration were kept constant and the oxygen concentration was varied from 0 to 60 vol. %. The results showed that in both the chambers, the atomic concentrations of oxygen and fluorine increased rapidly when the fraction of oxygen in the SF6 plasma was increased to 20 vol. % and decreased with further addition of oxygen. Scanning electron microscopy showed an etch feature with a minimal lateral run-out at an O2 concentration of 20 vol. % in both the chambers. The distribution of electron energy and the concentrations of oxygen and fluorine exhibited similar patterns as functions of the oxygen concentration in the SF6 plasma in the two chambers, but the values were different because of the different chamber geometries, which also affected the silicon etch rate and lateral run-out.

Redesigned t-PFF-v device fabricated with one-step anisotropic chemical wet etching process: enhanced separation efficiency for colloidal particles in continuous-mode

A pinched flow fractionation device with trapezoid-shaped pinched segment and cross-flow side channels (t-PFF-v) was redesigned and fabricated with a one-stop anisotropic chemical wet etching process and its enhanced separation capability was demonstrated for spherical polystyrene (PS) particles with diameter ranges of 2–8 µm. The tilted sidewalls and vertical focusing channels of the t-PFF-v device led to an improved separation resolution (Rm,n) via enhanced separation distance of PS particles at the pinched segment (Δxm,n) and reduced effluent particle distribution width (sn). Using this t-PFF-v device with Wp (pinched segment width) of 25 µm, PS particles with diameters of 4, 6, and 8 µm were simultaneously separated with good separation resolution (R4,6 = 3.2 and R6,8 = 3.4). Moreover, by adapting even smaller pinched segment width (Wp = 15 µm), PS particles with diameters of 2 and 4 µm, not well separated in the previous studies, were clearly separated with 9.5-fold improvement in R2,4 compared with the normal PFF device (n-PFF). The effects of inlet flow rate ratio (Q2/Q1) on the separation efficiency were also carefully investigated and provided additional insight on the separation processes within the pinched segment of t-PFF-v device. The drain flow through the cross-flow v-channels helps better alignment of particles at the sidewall of pinched segment and resulted in significantly reduced distribution of effluent particles, even under the operating conditions with low Q2/Q1 values.

Исследование процесса анизотропного плазменного травления пассивирующих слоев Si3N4–SiO2 в условиях низкой полимеризации

Исследование процесса анизотропного плазменного травления пассивирующих слоев Si3N4–SiO2 в условиях низкой полимеризации

Anisotropic etching for laser texturing of multicrystalline silicon wafer

ABSTRACTFor texturing of multicrystalline silicon wafers for solar cells, a HF-free texturing process was proposed by employing alkali cleaning (anisotropic etching) process after laser texturing. KOH/isopropyl alcohol (IPA) was more effective than KOH because the cleaning rate was rather slow but the shape of textured surface could be kept during the cleaning. After laser texturing with 5 min KOH/IPA cleaning at 80°C, the solar cell efficiency was increased from 4.6% to 12.6% because of the removing droplets of laser induced defects and the formation of microscopic textures by anisotropic etching.

Periodic Upright Nanopyramids for Light Management Applications in Ultrathin Crystalline Silicon Solar Cells

Motivated by the primary benefit of reduced material cost, the thickness of crystalline silicon solar cells has been continuously reduced. Laboratory and industrial studies have explored ultrathin crystalline silicon solar cells below 50 μ m with ambitious endeavors toward thicknesses of only a few micrometers. Ultrathin crystalline silicon solar cells require compatible small-scale surface textures to enhance the optical absorption. For this purpose, a novel submicron periodic nanostructure—periodic upright nanopyramids (PuNPs)—is fabricated by an integrated process of laser interference lithography and anisotropic etching of silicon in an alkaline solution. By simulation and measurements, we demonstrate that PuNPs are able to reduce front surface reflectance more effectively than conventional micron-scale pyramid textures and previously investigated periodic inverted nanopyramids (PiNPs). With a silicon nitride antireflection coating, we predict that PuNPs reduce the front surface reflectance to below 1% at an angle of incidence of 8°, which is comparable to black silicon. The superior antireflective property of PuNPs contributes to an absorbed photocurrent density of 40.8 mA/cm2 for a 40 μ m silicon absorber layer, which is 0.7 mA/cm2 higher than PiNPs, 0.8 mA/cm2 higher than inverted pyramids and 1 mA/cm2 higher than upright pyramids.

Effects of etching conditions on surface morphology of periodic inverted trapezoidal patterned Si(100) substrate

In this paper, the anisotropic etching process of Si(100) wafers in tetramethyl ammonium hydroxide (TMAH) solution with isopropyl alcohol (IPA) is investigated in detail. An inverted trapezoidal pattern is developed. A series of experiments are performed by changing TMAH concentration, IPA concentration, etching temperature and etching time. The structure of inverted trapezoidal patterns and roughness of the bottom surface are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that with TMAH concentration increases, the roughness of bottom surface will decrease. The addition of IPA into TMAH solution improves the morphology of the bottom surface significantly. Low temperature is beneficial to get a smooth bottom surface. Furthermore, etching time can change the bottom surface roughness. A model is proposed to explain the etching processes. The hillock area ratio of the bottom surface has the same tendency as the etching area ratio. Finally, smooth silicon inverted trapezoidal patterns are obtained for epitaxial growth of GaN-based light emitting diode (LED) devices.

Effect of NH2OH on Etching Characteristics of Si{100} in KOH Solution

Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most extensively used etchants for wet anisotropic etching process. Amongst these two etchants, KOH is a low cost etchant and provides high etch rate anisotropy between Si{111} and Si{100} planes. Increasing the etch rate is an important research problem for both academic and industrial applications. In this research, we study the effect of hydroxylamine (NH2OH) in 20 wt% KOH on the etching characteristics of Si{100}. This type of wafer orientation (i.e. Si{100}) is selected owing to its popularity in fabricating planar semiconductor devices (e.g. diode, transistor, complementary metal oxide semiconductor (CMOS), etc.) and MEMS components (e.g. cantilever, diaphragm, etc.). A systematic parametric analysis of various concentrations of hydroxylamine (from 0 to 20% in step of 5%) added 20 wt% KOH is carried out and its effect on the etching characteristics is discussed. We have found that the etch rate of Si{100} is increased threefold when 15% NH2OH is added to 20 wt% KOH solution. Additionally, this concentration also exhibits improved etching characteristics including undercutting rate, etch selectivity, and surface morphology. We have obtained improved etching characteristics when NH2OH is added to 20 wt% KOH. Due to an improvement in etching characteristics, present research is very useful to pave the path toward application in microfabrication industries as well as academic research laboratories.

Anisotropic etching of graphene in inert and oxygen atmospheres

We study the selective preparation of graphene zigzag edges by crystallographically anisotropic etching processes. Exfoliated graphene on a set of substrates is heated at various temperatures in argon atmospheres with different oxygen concentrations in the ppm range. The removal of carbon atoms from armchair sites at predefined antidots is studied by scanning electron and force microscopy. The anisotropy of etching is determined by the choice of the substrate, graphene's layer thickness and sample conditioning. We show that under all experimental conditions, gaseous oxygen at low concentrations is responsible for graphene etching. SEM image of anisotropically etched antidots in graphene and dependence of etch rate on added oxygen concentration.