Horizontal Etching Research Articles

Influence of electrolytic plasma spatial distribution on nanoporous structure etching on 4H-SiC surface

Single-crystal SiC nanoporous structure has important applications in the field of micro electromechanical systems, chemical sensors and biomedical devices. However, SiC exhibits a strong chemical inertness due to the short interatomic distance and high binding energy, making it significantly challenging to fabricate nanoporous structure. Electrolytic plasma-assisted chemical etching (EPACE) based on electrochemical anodic oxidation and high-activity electrolytic plasma etching is an ideal method for SiC nanoporous structure etching. In which, the spatial distribution of electrolytic plasma has an important impact on EPACE performance, such as etching efficiency and stability. In order to analyze the impact mechanism, this paper studies EPACE in tool electrode mounting posture of vertical and horizontal types by visual observation, real-time recording of voltage-current waveforms during processing, and the morphology analysis of SiC nanoporous structure after etching. It can be found that in the vertical etching type, EPACE can proceed stably because the workpiece immersion depth is greater than the bubble accumulation thickness. However, in the horizontal etching type, bubbles accumulate seriously between the workpiece and the liquid surface, which may cause bubble cavitation and abnormal discharge, leading to damage to the etching surface. The etching current in the vertical etching type is about 1.3 times that of the horizontal etching type, indicating that the bubble mass transfer in the vertical etching type is faster and the etching impedance is smaller, which is beneficial to improve the etching efficiency and obtain a uniform nanoporous structure. Finally, a SiC nanoporous layer with a thickness of 10.6 μm was prepared at etching time t = 50 min in vertical etching type, and the etching efficiency was 212 nm/min. In addition, the prepared nanoporous structure (nanofiber) was connected to the SiC substrate, indicating that it has a good bonding strength.

Exploring oxide-nitride-oxide scalloping behavior with small gap structure and chemical analysis after fluorocarbon or hydrofluorocarbon plasma processing

The scalloping of oxide-nitride-oxide (ONO) stacked layers on vertical sidewalls during high-aspect-ratio contact etch is commonly seen and characterized by the horizontal etching of oxide and nitride layers at different etch rates. To understand the mechanisms of ONO scalloping in complex plasma chemistry, it is crucial to examine the surface chemistry of silicon dioxide and silicon nitride processed with single fluorocarbon (FC) or hydrofluorocarbon (HFC) gases. To simulate the isotropic etching of SiO2 and Si3N4 sidewalls, we use a horizontal trench structure to study the effect of neutral radicals produced by FC (Ar/C4F8), HFC (Ar/CH3F, CH2F2, or CH3F), FC/HFC (Ar/C4F8/CH2F2), or FC/H2 (Ar/C4F8/H2), plasma for aspect-ratio (AR) up to 25. To eliminate the effect of ions, oxide and nitride trench structures were treated by inductively coupled plasma. The changes in the film thickness as a function of AR were probed by ellipsometry. Additionally, x-ray photoelectron spectroscopy (XPS) measurements on oxide and nitride substrates processed by Ar/C4F8 and Ar/CH2F2 plasma were performed at various locations: outside of the trench structure, near the trench entrance (AR = 4.3), and deeper in the trench (AR = 12.9). We find a variety of responses of the trench sidewalls including both FC deposition and spontaneous etching which reflect (1) the nature of the FC and HFC gases, (2) the nature of the surfaces being exposed, and (3) the position relative to the trench entrance. Overall, both the etching and deposition patterns varied systematically depending on the precursor gas. We found that the ONO scalloping at different ARs is plasma chemistry dependent. Oxide showed a binary sidewall profile, with either all deposition inside of the trench (with FC and FC/H2 processing) or etching (HFC and FC/HFC). Both profiles showed a steady attenuation of either the deposition or etching at higher AR. On the nitride substrate, etching was observed near the entrance for HFC precursors, and maximum net etching occurred at higher AR for high F:C ratio HFC precursors like CHF3. XPS measurements performed with Ar/C4F8 and Ar/CH2F2 treated surfaces showed that Ar/C4F8 overall deposited a fluorine-rich film outside and inside of the trench, while Ar/CH2F2 mostly deposited a cross-linked film (except near the trench entrance) with an especially thin graphitic-like film deep inside the trench.

Investigation of a Macromolecular Additive on the Decrease of the Aluminum Horizontal Etching Rate in the Wet Etching Process

The effect of a macromolecular additive on the etching rate of aluminum (Al) horizontal etching in the wet process was investigated in this work. The horizontal etching in the Al wet etching process became more evident as the film Al becomes thicker. The proposed macromolecule additive, including polyethylene-polypropylene glycol, was added into the Al etchant solution to reduce the Al horizontal etching rate (ER). The undercut problem during metal patterning can then be improved. By using this method, the Al horizontal ER was reduced from 2.0 to 0.9 μm per minute and the selection ratio between the horizontal and vertical ER was effectively improved from 3 to 1.3 times. As well, a hypothesis of physical mechanism for the improvement was proposed. The dispersed particles from the additive emulsion inhibited the transport and exchange of liquid in a horizontal direction. This work provides an alternative reference to improve the selection ratio performance in the metal wet etching process compared with that when using traditional method.

Control of etch profiles in high aspect ratio holes via precise reactant dosing in thermal atomic layer etching

Thermal atomic layer etching (ALE) was studied in HfO2-based 3D NAND test structures with an aspect ratio of more than 50:1. Etching was performed via ligand exchange with dimethyl-aluminum chloride (DMAC) after surfaces had been fluorinated with hydrogen fluoride (HF). In these 3D NAND structures, we found that the horizontal etch rate of HfO2 as a function of depth (depth loading) depended on the DMAC dosing but was nearly independent of the HF dose. The HF dose and the process pressure were keys to increasing the overall etch amount per cycle. With the highest tested HF dose of 192 Torr s and a total process pressure of 8 Torr, we achieved a uniform etch amount of 0.6 nm per cycle. In addition, we investigated the impact of film quality and film coating conformality in these structures on the depth loading in the succeeding ALE processes. The type of precursor, precursor dosing, deposition rate, and substrate temperature played a fundamental role in controlling the film quality and conformality of the deposited HfO2 layers inside high aspect ratio holes. Fluorination studies on blanket films revealed that fluorination efficiency is improving for pressures in the Torr range compared to previous milliTorr experiments and that only temperatures above 250 °C increased the fluorine concentration in HfO2 significantly, whereas fluorine levels were unchanged between 150 and 250 °C.

Risk Assessment of Horizontal Wet Etching Equipment System in Manufacturing Plant Industry

Maintenance is one of the important roles in the high technology manufacturing industry. It is related to the key performance factors of the company such as quality, productivity, and cost. To achieve these factors, a reliability plan should be implemented which helps to maximise production value by implementing successful asset maintenance. This research project aims to focus on the critical process equipment known as Horizontal Wet Etching Equipment (HWEE) used in the wet etching process. The components in the HWEE system were identified by referring to the process and instrumentation diagram (PID) of the equipment and were categorised in different modes. Data on mean time to repair (MTTR) and mean time between repairs (MTBF) were collected based on previous company records. The data were analysed using MAROS software. Failure Mode and Effect Analysis (FMEA) was done to understand the risk of each of the components. The result shows that piping and gearbox have the highest RPN with 126 and 105, respectively. This study helps to identify critical components and is able to help the company to improve equipment reliability and reduce maintenance cost. Corrective action can be implemented to reduce the RPN for both components. Thus, it would help the industry to increase the key performance and become more competitive in the business environment.

Causes of anisotropy in thermal atomic layer etching of nanostructures

In this work, the authors have investigated the dependence of the anisotropy level in an atomic layer etching (ALE) process of Al2O3 on form factor constraints when the ALE process involves etching in non-line-of-sight locations beneath a silicon nitride mask. In the experiments described here, thermal etching of Al2O3 without the use of any direction-inducing plasma components was explored utilizing the well characterized hydrogen fluoride/dimethyl-aluminum-chloride atomic layer etching process. The degree of anisotropy was quantified by measuring the ratio of lateral etch rate of this process in comparison to the vertical etch rate as a function of process step time inside 60 nm holes of aluminum oxide. Inside these holes, the authors determined that the horizontal etch rates slowed to an amount of 19% compared to the vertical rate when short process times were used. For process times operating in the saturation mode of the ALE process, horizontal etch rates per cycle could be sped up to 71% of the vertical rate but never reached parity with the latter. The authors propose a simple mechanism for explaining the anisotropy dependence on process step time and applied a reduced-order algorithm to model it. In this model, the authors introduced fitting parameters for surface modification depths and reaction times to match the experimentally found etch results. Conclusions could be drawn regarding topological hindrance or tortuosity for reactants to reach surfaces in shaded areas under the mask and for reaction by-products to escape from these locations and the impact on etch rate. In addition, the authors recognize that this mechanism could explain the unwanted depth dependence of the etch rate per cycle in high aspect ratio structures.

(Invited) Characterization of Isotropic Thermal ALE of Oxide Films in Nanometer-Size Structures

Isotropic atomic layer etching (ALE) is increasingly becoming an option and even a necessity for modern chip manufacturing. Especially for application such as 3D-NAND memory, the ability to perform isotropic etches will be a critical addition to the established suite of reactive ion etching. In this work, we have characterized the reaction of aluminum oxide (Al2O3) via the vapor-based DMAC ligand exchange mechanism in nanometer-size structures in which the oxide is buried below a silicon nitride mask. In the oxide, we measured vertical and horizontal etch rates and found that the etch showed some residual anisotropy even though all elements of the etch itself (flow, no plasma) were none-directional. We applied a simple Monte-Carlo simulation to show that anisotropy is caused by a delay in the onset of the horizontal etch beneath the mask and by molecular scattering effects in the vapor phase above the nano-structures. We are contrasting these results with experimental findings in structures without an anisotropy of the etch.

Hydrogen Atom Desorption Induced By Electron Bombardment on Si Surface

1. Introduction Developments of nano-scale quantum device have been expected to open new approaches for information-processing. Among the various quantum devices proposed so far, a solid state qubit is one of the potential candidate devices to bring further progress to the modern computer technology. The nuclear spin qubit proposed by Kane, which is a phosphorus donor atom embedded in a Si lattice, has advantages such as longer relaxation time and higher process compatibility with Si LSI technology [1]. To manipulate a single dopant precisely on a Si substrate, a method employing electron bombardment from an STM tip on hydrogen-terminated Si surface has been proposed [2], [3]. Though successful experimental results including desorption of hydrogen atoms and adsorption of phosphorus atoms with atomic resolution have been reported, the relation between the number of desorbed hydrogen atoms and the number of bombarded electrons, which is one of fundamental issues for fabrication, has not been given in details. In this research, we study hydrogen atom desorption on Si(111) surface quantitatively for aiming at the development of atomic lithography. 2. Method First, a Si(111) wafer is chemically etched in aqueous NH4F solution (40%) in order to obtain hydrogen-terminated smooth surface for single atom desorption [4]. To exclude generation of etch pits, N2 bubbling has been employed prior to the etching to remove dissolved O2 in the solution. Next, the wafer is put into a vacuum chamber, and electrons are injected from an STM tip to the surface during STM image scanning. Tunneling electrons with appropriate energy can break Si-H bonds resulting in desorption of hydrogen atoms. 3. Experimental Results 3.1 Flattening of Si Surface Because the horizontal etching rate of Si(111) is larger than that of vertical one in the aqueous NH4F solution, flatter surface has been obtained. Our results show that the optimum etching time is about 15 minutes. Moreover, FT-IR result indicates that the surface is terminated by hydrogen atoms successfully. 3.2 Hydrogen Desorption Fig. 1 shows STM scan images of Si(111) before and after of hydrogen desorption. For this case, hydrogen desorption was done by STM scanning with +3.5 [V] and 4 [nA] sample bias, and all the hydrogen atoms in the scanned area were desorbed. On the other hand, surface images were obtained by STM scanning with -2. 5 [V] and 0.5 [nA] sample bias. Brighter region in the surface image (Fig. 1 (b)) corresponds to the hydrogen desorption area because dangling bonds increase electrical conductivity. Fig. 2 shows the ratio of hydrogen desorption area to the scanning area as functions of the tunneling current and the bias voltage. It can be seen that bias voltage lager than 3.1 [V] is required for desorption and desorption area increases approximately in proportion to the tunneling current. We also carried out electron bombardment without scanning. By applying a voltage pulse to the tip at the center position of an STM image and controlling the applied voltage, tunneling current, and pulse duration time, we can obtained suitable experimental parameters for minimizing the area of hydrogen desorption. The results show that a voltage pulse with 3.6 [V] amplitude and 70 [ms] duration desorbs hydrogens on about 30 sites. 4. Conclusion We have studied about the desorption of hydrogen atoms on Si(111) surface caused by electron bombardment, and confirmed by utilizing STM scanning that the desorption area is proportional to the tunneling current. Also, we demonstrated that the number of desorption sites can be minimized by applying a voltage pulse and controlling its duration time precisely. By extending the results obtained in this research, it could be possible to develop atomic lithography technique using STM.

The densities and dimensions of recoil-track etch pits in mica

Measurements of alpha-recoil-track densities in mica as a basis for geological dating depend on an etch model relating the number of tracks per unit volume (NRT) to the counted number of etched tracks per unit area (ρRT). The model of Gögen and Wagner (2000) implies that ρRT increases linearly with etch time (tE), so that NRT can be calculated from the slopes or intercepts of step-etch functions ρRT(tE). This model rests on the assumption that the etch rate of the mica surface (vV) and the horizontal etch pit growth rate (vH) are both constant, in contradiction with experimental results and computer simulations of mineral dissolution. We present results of four different experiments aimed at relating etch pit densities to volumetric track densities. Step-etch data are vulnerable to observation-related artefacts at increasing tE and lack the resolution to confirm or refute the supposed linear increase of ρRT with tE. The intercepts of regression lines fitted to step-etch data are imprecise and perhaps inaccurate. Intercept estimates based on mirror-image counts and (etch)–anneal–etch experiments indicate that vV increases during the initial etching stages. The (etch)–anneal–etch results show that no pre-etch is in fact required, implying that surface tracks are more resistant to annealing than tracks in the bulk of the mineral. Track-size measurements confirm that vH is also not constant but decreases with increasing etch-pit size. The results show that no recoil-track etch pit in phlogopite etched in 40% HF grows larger than ca. 7μm and that the track-size distribution becomes quasi-invariant at >6min etching. This signifies that there exist accessible etching conditions at which the etch-pit size distribution becomes a fixed, distorted reflection of the size distribution of latent recoil tracks. It is not improbable that track addition and loss also cancel each other out in this equilibrium state, in which case both the etch-pit size distributions and densities ρRT become independent of etch time.

Reduction of Reactive-Ion Etching-Induced Ge Surface Roughness by SF6/CF4 Cyclic Etching for Ge Fin Fabrication**Supported by the National Basic Research Program of China under Grant No 2011CBA00607, the National Natural Science Foundation of China under Grant No 61376097, the Zhejiang Provincial Natural Science Foundation of China under Grant No LR14F040001, and Specialized Research Fund for the Doctoral Program of Higher

An SF6/CF4 cyclic reactive-ion etching (RIE) method is proposed to suppress the surface roughness and to optimize the morphology of Ge fin, aiming at the fabrication of superior Ge FinFETs for future CMOS technologies. The surface roughness of the Ge after RIE can be sufficiently reduced by introducing SF6-O2 etching steps into the CF4-O2 etching process, while maintaining a relatively large ratio of vertical etching over horizontal etching of the Ge. As a result, an optimized rms roughness of 0.9nm is achieved for Ge surfaces after the SF6/CF4 cyclic etching with a ratio of greater than four for vertical etching over horizontal etching of the Ge, by using a proportion of 60% for SF6-O2 etching steps.

The texturization process during horizontal acidic etching of multi-crystalline silicon wafers

Horizontal wet-chemical etching of silicon wafers in an HF/HNO3/H2SiF6 mixture is the most widely-used technique to texturize multi-crystalline silicon wafers for solar cell production. For the first time, the etch rates were determined separately for the upper and lower side during the horizontal texturization and the their different morphologies. The dependency of the surface morphology from the etch rate and etch depth is proven. Furthermore, the influence of the temperature and stirring rates on the morphological development for the upper and lower side of the wafer were examined. From temperature-dependent measurements, activation energies in the range from 17kJ/mol to 40kJ/mol on the upper side and from 23kJ/mol to 40kJ/mol on the lower side dependent from the etching time were determined. The observed results reveal a connection between the etch depth, the agitation of the etch solution, the morphology and the reflectivity of the separate wafer sides.

Reduction of RIE Induced Ge Surface Roughness by SF6-CF4 Cyclic Etching Method

The SF6-CF4 cyclic RIE etching method is proposed in this work to effectively control the surface roughness and morphology of Ge Fins, aiming at the fabrication of superior Ge FinFETs for future CMOS applications. It is found that the surface roughness of Ge after RIE etching can be sufficiently suppressed by introducing SF6-O2 etching steps into CF4-O2 etching, with remaining a relatively large selectivity of vertical etching to horizontal etching of Ge. As a result, with a SF6-O2 proportion of 60%, an optimized RMS roughness of 0.9 nm has been revealed for Ge surfaces after etching with a selectivity of over 4 for vertical etching to horizontal etching of Ge.

Reduction of RIE Induced Ge Surface Roughness by SF6-CF4 Cyclic Etching Method

Introduction Ge is one of the most promising channel materials to further improve the performance of Si CMOS due to its high hole and electron mobility [1-3]. In order to overcome the current Si FinFET technology, 3D channel structure is mandatory for Ge MOSFETs. To fabricate Ge Fins, CF4- or SF6-based RIE etching is usually employed for Ge etching [Ref. needed]. However, both CF4 and SF6 RIE etching results in large surface roughness which strongly degrades the performance of Ge FinFETs. On the other hand, it is necessary to realize high selectivity of anisotropic etching of Ge which is important to obtain superior static electrical control of Fin channel. In this research, we developed a SF6-CF4 cyclic RIE etching method for Ge Fin formation with suppressed surface roughness. The impact of inserting SF6-O2 etching steps into CF4-O2 etching process on the surface roughness of Ge was systematically investigated, as well as the ratio of vertical etching to horizontal etching of Ge. It is found that with a time proportion of 60% for SF6-O2etching steps, a minimum RMS of 1.1 nm is obtained for Ge Fin etching. Experiments The CF4-O2 and SF6-O2 RIE cyclic etching were carried out for (100) Ge surfaces with the same pressure, plasma power and total gas flow. Different time proportions of 0%, 20%, 40%, 60%, 80% and 100%, were used for SF6-O2 etching steps during the CF4-O2etching, with a total etching time of each cycle for 20 s. The selectivity of vertical and horizontal etching of Ge was examined using SEM, and the surface roughness of Ge after etching was evaluated using AFM. Results and discussion Figure 1 shows the etching rate of CF4-O2 and SF6-O2 cyclic etching with different time proportion of SF6-O2 step. It is observed that the etching rate significantly increases with increase of SF6-O2 etching proportion, due to the high reactivity of SF6 with Ge [4]. The RMS of Ge surfaces after CF4-O2 and SF6-O2 cyclic etching for 20 s is evaluated by AFM (Figure 2). It is confirmed that large amount of surface roughness is generated for Ge surface after both CF4-O2 and SF6-O2 etching. With introducing SF6-O2 etching steps into CF4-O2 etching, the surface roughness of Ge is obviously reduced. The RMS values of Ge surface after CF4-O2 and SF6-O2 cyclic etching are summarized in Figure 3 as a function of the time proportion of SF6-O2 etching. It is found that with a time proportion of 60% for the SF6-O2 step, a minimum RMS of 1.1 nm is obtained for the Ge surface. The impact of SF6-O2 proportion to the ratio of vertical and horizontal etching for Ge is also examined, as shown in Figure 3. It is found that the selectivity of vertical etching decreases with increasing the SF6-O2 proportion. However, a relatively high selectivity of vertical etching of over 4 is still maintained with a time proportion of 60% for SF6-O2etching, resulting in Ge Fins with superior morphology (Figure 4). Conclusion A CF4-O2 and SF6-O2 cyclic etching method is proposed for Ge Fin formation. It is found that with a time proportion of 60% for SF6-O2etching step, superior morphology is achieved for Ge Fins with sufficiently suppressed surface roughness of 1.1 nm.

Liquid-Phase Capillary Etching of Poly(Dimethylsiloxane) Microchannels With Tetra-n-Butylammonium Fluoride

Easy fabricability, along with other unique properties, has made poly(dimethylsiloxane) (PDMS) one of the most commonly used materials for microfluidics-based microdevices. However, unlike other polymer materials commonly used for microdevices, the PDMS cannot be easily etched or further changed upon polymerization, and therefore, fabrication method has been rather limited to replication molding. Here, we demonstrated liquid-phase capillary etching of the PDMS microchannels with tetra-n-butylammonium fluoride (TBAF) and characterized its etching profiles depending on the initial microchannel widths, TBAF flow rates, TBAF concentrations, and substrates used for the microfluidic channel sealing. The characterization showed that the microchannel circumference etch rate was linearly proportional to the TBAF flow rate and was faster at higher TBAF concentration. On the other hand, influence of the TBAF concentration on the horizontal and vertical etch rates was vastly different, with the vertical etch rate being much more affected by the concentration change. Potential applications of the liquid-phase capillary etching method were demonstrated by fabricating the PDMS microchannels with round-shaped cross sections, a microdevice with embedded 3-D metal electrodes with the electrodes directly exposed to the microfluidic channel, and a glass-PDMS-glass sandwich microchannel for high-clarity optical detection. We believe that the characterization of the liquid-phase capillary etching along with the applications demonstrated here will provide new capabilities for fabricating the PDMS-based microdevices that could not be easily fabricated by conventional replication molding processes.

多晶Si酸制绒刻蚀稳定性的研究

多晶Si酸制绒刻蚀稳定性对制绒工艺有重要的影响。本文主要研究酸刻蚀量在横向和纵向的不同，结合槽体内部分析液体流向分布对刻蚀稳定性的影响，强调设备结构设计对工艺稳定性影响的重要性。 The stability of etch depth of multi-crystalline silicon plays an important role in acid texturing process. In this paper, differences of horizontal and vertical etch depths were discussed. Combing with the analysis of the chemical flow direction’s influence on acid texturing etching stability, this paper emphasized the importance of the equipment structure’s design to the process stability.

Application of Confocal Microscopy to Evaluate the Morphology of Acidic Etched Mc-silicon

The acidic texturization using HF/HNO3/H2SiF6 mixtures is the standard treatment of as-cut multicrystalline silicon (mc-Si) wafers to remove the saw damage and to reveal the undisturbed bulk material. Furthermore, by the texturization a certain surface morphology at the bulk silicon should be generated that leads to an enhanced light trapping by multi-reflection of the incident light within the surface. The present paper work is focused on the development of the surface morphology formed during the horizontal etching of an as-cut multicrystalline silicon wafer in a common HF/HNO3/H2SiF6 etch mixture. In a procedure of stepwise etching about 1μm silicon was removed per etching step. After each step the same spot of the silicon surface, one on the upper side and one on the lower side, was measured by confocal microscopy. The obtained micrographs were treated with image analytical methods and line profiles and other relevant morphology sensitive parameters were extracted. It can be shown, that the resulting morphology depends on the blueprint of the microcracks under the as cut structure, and that the first microns of saw damage removal are the important steps to generate an effective texture. Furthermore, a statistically significant relationship between the reflectivity of the wafer surface and a morphology parameter was derived.

Textural development of SiC and diamond wire sawed sc-silicon wafer

The present work compares the time-dependent evolution of the surface morphology during the horizontal acidic etching of diamond wire (DW) and SiC slurry (SP) sawn single-crystalline wafer by means of scanning electron microscopy (SEM), confocal microscopy, reflectivity measurements, and the measurement of the etch rates. Both sawing processes lead to different as cut structures which have a significant impact on the evolution of the wafer surface morphology during the acidic etching. This initial structure controls the sites where the chemical attack preferentially occurs and affects therefore to a considerable extent the morphology of the etched surface as well as the rate of which this morphology is formed. Based on the experimental results is discussed why the texturization of DW sawn wafers remains incomplete if acidic etch mixtures and etch parameters are used that were optimized for the etching of SP wafers. To create homogeneously texturized DW sawn wafers of low reflectivity the development of new etchants and new etch conditions for is necessary.

A Comparative Study of the Morphologies of Etch Pits in Semi-Insulating Silicon Carbide Single Crystals

Contactless resistivity mapping, scanning electron microscope (SEM) and confocal laser microscope have been used to study the relationship of the resistivity and the etching behavior of the semi-insulating 6H-SiC wafer. Evidence is presented that the morphologies of the etch pits vary significantly with the impurity concentrations. The V impurity strongly affects the etch rates of edge, screw and mixed dislocations. For the dislocation containing the Burgers vector component of <0001>, its vertical etch rate is enhanced distinctly. In contrast, the horizontal etch rate becomes larger for the dislocation containing the Burgers vector component of < >. The shape of the etch pits reflects the Fermi level of the semi-insulating wafer and the net shallow impurity concentration.

Fabrication of tapered waveguide by ashed photoresist

It is necessary to interconnect various optical components with different input or output sizes in hybrid integrated optics. Integration of optical devices on an optical printed circuit board sometimes requires a tapered waveguide to match a backbone waveguide to a smaller optical device in order to minimize optical loss. In this work a backbone waveguide of 20×25μm2 cross-section is tapered to a 3×5μm2 cross-section. The tapered waveguide is fabricated by soft lithography, which imprints an optical polymer using a polydimethlysiloxane mold. A master of the tapered waveguide structure used to make the mold is prepared by plasma ashing of patterned photoresist. The ratio of the stripping rate (vertical etching) to the trimming rate (horizontal etching) can be changed as a result of the line-width-dependent stripping rate. Thus narrower portions of a line become thinner (vertically) than the wider portions of the line during a single ashing step. Fabricated tapered waveguide shows higher optical transmission than that of an abruptly matched waveguide.

Experimental analysis of the surface roughness evolution of etched glass for micro/nanofluidic devices

Roughness of channel surfaces, both deterministic and random, is known to affect the fluid flow behavior in micro/nanoscale fluidic devices. This has relevance particularly for applications involving non-Newtonian fluids, such as in biomedical lab-on-chip devices. While several studies have investigated effects of relative large, deterministic surface structures on fluid flow, the effect of random roughness on microfluidic flow remains relatively unexplored. In this study, the effects of processing conditions for wet etching of glass including etching time and etching orientation on centre-line average (Ra) and the autocorrelation length (ACL) were investigated. Statistical distribution of the roughness was also studied. Results indicated that ACL can be tailored in the range of 1–4 µm by changing etching time in horizontal etching while Ra was found to increase weakly with etching time in all three etching orientations. Analysis of the experimental data using the Kolmogorov–Smirnov goodness-of-fit hypothesis test shows that the glass surface roughness does not follow a Gaussian distribution, as is typically assumed in the literature. Instead, the T location-scale distribution fits the roughness data with 1.11% error. These results provide promising insights into tailoring surface roughness for improving microfluidic devices.