Hole Sidewall Research Articles

Effect of substrate temperature on sidewall erosion in high-aspect-ratio Si hole etching employing HBr/SF6/O2 plasma

A Si deep-trench etching process using HBr/SF6/O2 plasma was studied. It was found that when the hole trench width was decreased from 190 to 140 nm, erosions at the topmost part of the Si hole sidewall were observed at an incidence of 10 ppm, which was checked from top-down views of 928 million hole shapes per wafer. It was confirmed that when the cathode temperature was increased to 140 °C, no Si erosion occurred. It was found that etching at a higher temperature reduced the halogen content in the film deposited on the sidewall, making the film more protective, and suppressed Si erosion.

A Study on the Etching Residue of Nano-Scale Patterns in C4F8/CH2F2/O2/Ar Plasma

The demand for miniaturization and high integration of semiconductor devices has ever been increasing. In order to achieve the requirements of the semiconductor industry, plasma etching processes using fluorocarbon-based gases are being designed to have higher selectivity and ion energy. Generally, to have a higher selectivity to the mask material, a more polymerizing gas (i.e. low F/C ratio gas) is used [1, 2], and therefore the removal of etching residues formed inside the pattern after the etching process has a crucial effect on the performance of the semiconductor devices. As the pattern size becomes smaller, there is an area that cannot be cleaned by the conventional wet cleaning method. Recently, various dry-cleaning techniques using plasma radicals and ions have been proposed [3, 4]. However, for precise control and understanding of residue removal, a detailed compositional analysis of the etching residue must be performed. These studies are also very important in evaluating the effectiveness of dry-cleaning. However, little research has been done to investigate the characteristics of etching residues formed inside the nano-scale patterns (i.e. sidewall and bottom) in much detail. In this work, we conducted a study on the characteristics of the etching residues formed inside the nano-scale patterns. A C4F8/CH2F2/O2/Ar mixture gas plasma was used to form a high-aspect-ratio silicon dioxide contacts (HARCs) on a silicon wafer. The chemical compositions and binding states of etching residues inside the patterns were examined by an x-ray photoelectron spectroscopy (XPS) with angle changes in detail. To investigate the formation of etching residues, the plasma characteristics (i.e. radicals, ions and electrons) were examined in parallel using an optical emission spectroscopy (OES) and a Langmuir probe (LP) system. As a result of the analysis, it was observed that the etching residues formed on the sidewalls of the line and hole patterns changed to the same tendency. At the same time, it was confirmed that depending the etched depth, the composition of the residue on the sidewall of holes and lines changed. [1] Takahashi, Kunimasa, Masaru Hori, and Toshio Goto. "Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 14.4 (1996): 2004-2010. [2] Kwon, B. S., et al. "Ultrahigh selective etching of SiO2 using an amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas." Journal of The Electrochemical Society 157.3 (2010): D135-D141. [3] Koh, Kyongbeom, et al. "Quasi atomic layer etching of SiO2 using plasma fluorination for surface cleaning." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36.1 (2018): 01B106. [4] Cagomoc, Charisse Marie D., et al. "RF plasma cleaning of silicon substrates with high-density polyethylene contamination." Japanese Journal of Applied Physics 57.1S (2017): 01AB04.

Analysis for effects of ultrasonic power on ultrasonic vibration-assisted single-pulse laser drilling

An investigation of water-based ultrasonic-assisted single-pulse laser drilling is reported for drilling thin section super-alloy sheets to show the influence of ultrasonic power on both blind-hole drilling quality and through-hole drilling quality using different single laser pulses. The effects of ultrasonic power on drilling quality (e.g., hole geometry, hole sidewall surface morphology, and hole wall recast layer, etc.) were experimentally investigated for ultrasonic-assisted millisecond single-pulse Nd:YAG laser drilling. It was found that the ultrasonic vibration incorporated into the single-pulse Nd:YAG laser drilling process could obviously improve the inner hole wall surface morphology/quality in terms of relatively clean and better-profiled hole wall surface with less defects/spattering, better uniformity, and smaller surface roughness. It was indicated that the alteration of the molten material flowing/spattering/expelling due to the contribution of ultrasonic vibration was the main reason of improving the drilling quality for ultrasonic vibration-assisted single-pulse laser drilling. It was also shown that the influencing trends of ultrasonic power on hole circularity deviation, hole sidewall surface morphology, and hole sidewall surface roughness for through holes were similar to those for corresponding blind holes. Except the sample sheet thickness difference, under the same other drilling conditions, hole cross sections and recast layers contributed to the main differences between the drilled through holes and blind holes, which was mainly caused by their difference of the flow and expelling of the molten material.

Modeling of cavitating flow induced by an ultrasonic horn above a solid target with a microhole

Ultrasonic cavitation may be involved in many manufacturing-related applications, such as ultrasonic cleaning, ultrasonic cavitation peening, and ultrasound-assisted water-confined laser micromachining (UWLM). However, the previous physics-based modeling work has been very limited for cavitating flow induced by an ultrasonic horn near a solid target with a microhole. Such modeling work is reported in this paper, where two-dimensional compressible fluid mechanics equations, together with an equation governing the vapor-volume fraction evolution, are solved numerically. The model prediction shows reasonable consistency with experimental results in the literature for cavitating flow induced by an ultrasonic horn in water relatively far from a solid wall. Then the model is used to study the cavitating flow induced by a horn placed near a solid wall with a microhole. Under the studied conditions, the model calculations show that the horn-induced peak pressure magnitude at the microhole center decreases as the hole becomes deeper. On the other hand, the horn-induced temporal peak pressure at the hole bottom surface is spatially relatively uniform in the r (radial) direction, while the peak pressure on a solid surface without the hole decreases quickly with r. However, the peak pressure induced on the hole sidewall is not spatially uniform, and the largest peak pressure on the sidewall occurs at the hole bottom. The model may help future fundamental research work on ultrasonic horn-induced cavitating flow near a solid wall with a microhole, and may also provide a useful guiding tool for related manufacturing applications.

Micro-drilling in ceramic-coated Ni-superalloy by electrochemical discharge machining

Thermal barrier coating has been applied in turbine blades and vanes to improve the combustion temperature and thus the thermal efficiency. However, the fabrication of film cooling hole in the components with thermal barrier coating is challenging because the physical and chemical properties of each layer are quite different. Electrochemical discharge machining (ECDM) is a promising machining method for the fabrication of film cooling hole in these multi-layer materials. The gas film formed around the electrode, which acts as the dielectric during the machining, makes it possible for the ECDM to machine both electrical conductive and non-conductive materials. In this study, the current waveforms for the machining of both the coating and the superalloy substrate were investigated. It showed that only the electrochemical discharge exists during the machining of the coating. However, when machining the superalloy substrate, both the electrochemical discharge and the electrical discharge take place. Analysis of the experimental results revealed that the electrical discharge is the main factor to make the material on the superalloy substrate remove, while the electrochemical discharge results in a small secondary material removal on the machined surface. The surface roughness on the hole sidewall for the coating and the superalloy substrate were measured to be Ra 10.2 μm and Ra 5.6 μm, respectively. The thickness of recast layer on the machined surface of the superalloy substrate is 15 μm.

The Cutting Parameter Optimization in Helical Milling of Ti Alloys with Small Diameter Tools and the Study of their Cutting Performance

Titanium alloys are widely used in modern aircraft manufacturing. The hole-making technology with high quality becomes a crucial aspect of aircraft assembly. Helical milling process has drawn much attention due to its high machining quality and efficiency. In this work, the cutting performance of small diameter tools (3mm) in helical milling Ti alloy is studied. The parameters of spindle speed, tangential feed speed and pitch (axial feed per revolution) are optimized to reduce cutting force and processing time. The evolutions of the cutting force, burr size, hole side wall roughness and diameter with increasing hole number are investigated. Results show that burr size and hole side wall roughness are much lower than the requirement of aircraft assembly under the optimized parameters of 7000r/min (spindle speeds), 0.1mm (pitch), 0.02mm/tooth (tangential feed). Due to the poor stiffness and large deflection of small diameter tools, excessive hole diameter error is the most prominent problem to be concerned in helical milling process.

Amplification of Plasma at Different Initial Temperatures inside a Microhole by a Short Laser Pulse and the Effect on the Hole Sidewall

Microholes with diameters varying with the hole depth have promising applications in important applications, but their manufacturing is difficult when the diameter of the hole is very small and/or varies complicatedly with the depth. In the authors’ previous work (Dabir-Moghaddam et al., 2016), physics-based modeling study has been carried out on the interaction of a short laser pulse with a plasma plume that pre-exists in a microhole and the resulted effect on the sidewall of the hole. The model calculations have implied that a novel dual-pulse laser ablation and plasma amplification (LAPA) technique is potentially feasible for drilling microholes with diameters that are different at different hole depths. In this paper, further model calculations have been performed to study the effect of different initial plasma temperatures. Under the studied conditions, it has been found that laser amplification of a plasma plume with a higher initial temperature can lead to a larger heat flux to the hole sidewall surface and a larger surface vaporization depth in the sidewall, which indicates that more significant material removal will be expected. On the other hand, a lower initial plasma temperature can lead to more non-uniform vaporization depths at different sidewall locations, indicating that a spatially more selective material removal will be expected.

Modeling of picosecond laser-induced plasma amplification inside a microhole and an implied novel technology to drill microholes with varying diameters with depth

Microholes with varying diameters at different depths are very desirable in various important applications. However, it is very challenging to produce microholes with varying diameters when the variation is in a complicated way and/or when the hole diameter is very small. This paper presents physics-based modeling work on the interactions among a picosecond (ps) laser pulse, a pre-existing plasma plume inside a microhole, and the hole sidewall. The modeling work implies the potential feasibility of a novel dual-pulse laser ablation and plasma amplification (LAPA) process for drilling microholes with varying diameters at different depths.

The Effect of EDM Die-Sinking Parameters on Non-Conductive Materials

The machining ability of electrical discharge machining (EDM) die-sinking on acrylic as non-conductive material was studied. The objective of the study is to establish a new setup to machine a non-conductive material by using EDM die-sinking. Acrylic plastic material was selected as to represent the other groups of non-conductive materials. The experiment was conducted using a discharge sinking machine with copper as the tool electrode. Metal insert as conductive material was plug-in into acrylic workpiece. Polarity of the setup was set to positive at the copper electrode and negative at the plug-in metal insert. The variable input parameters such as electric discharge current, voltage, pulse on time and pulse off time had been observed to review machinibility of die-sinking EDM by taking the overcut and taper of sidewall of holes produced. It was found that the highest current supply during machining, the deepest hole occurred on the acrylic workpiece. Thus, the new method purposed on this study proved that non-conductive material can be machined using the EDM die-sinking.

Advanced microhole arrays for light trapping in thin film silicon solar cells

We present a comprehensive theoretical analysis accompanying our experimental development of micro-structured thin film polycrystalline silicon solar cell absorbers. Our focus is on 2D-periodic arrays of holes which do not act as a superficial scattering grating but pierce the entire silicon absorber layer. We deviate from the commonly used model of vertical hole sidewalls by employing conical frustum shaped holes with a range of opening angles. Additionally, an experimentally motivated front texture is applied to the simulated solar cell absorbers and varied in texture aspect. Based on this parametric absorber model, for a single domain period of 2μm, we discuss light trapping and optical losses in thin film cells with absorptive front and back contacts and a perfectly transparent glass encapsulation layer. Implications from this study are that light trapping in square periodic arrays with periods larger than the wavelength of light can be enhanced by microholes but that it cannot replace a front texture which provides both antireflection and scattering.

Effect of Perforation Structure of Cathode GDL on Liquid Water Removal in PEFC

In order to alleviate water flooding in cathode electrode of polymer electrolyte fuel cell (PEFC), it is essential to understand the liquid water bahavior across porous media and design the optimum electrode structure for enhancing water drainage on cathode side. In this study, the liquid water transport in the cathode of an operating PEFC was visualized macro- and microscopically using optical techniques, and the effect of perforation structure of cathode gas diffusion layer (GDL) on the water removal and performance improvement was discussed. The perforated GDL was fabricated by electric discharge machining (EDM) and manual micro-drilling technique. It was found that the perforation holes machined by the micro-drilling promotes the liquid water discharge from the GDL and effectively reduces water accumulation in the cathode electrode, because the hydrophobic PTFE coating at the hole sidewall is not damaged.

Nanosecond laser pulse interactions with breakdown plasma in gas medium confined in a microhole

The previous investigations on nanosecond laser pulse interactions with breakdown plasma in a gas medium confined in a microhole have been limited. This kind of plasma has been studied in this paper. Due to the significant measurement difficulty resulted from the very small spatial and temporal scales involved, a physics-based computational model has been employed as the investigation tool. The model is developed by solving gas dynamic equations numerically using the finite difference method based on an essentially non-oscillatory scheme. The gas dynamic equations are coupled with suitable equation of state, where the electron number density for plasma region is calculated through the Saha equation. Using the model, the spatial confinement effects of the microhole sidewall on the plasma evolution under laser radiation have been investigated. It has been found that under the studied conditions the hole sidewall confinement can greatly enhance the plasma temperature, pressure, and thrust (over the same surface area). The enhancement should be due to the sidewall’s restriction on the plasma lateral expansion and the sidewall’s reflection of the pressure wave induced by plasma. This study implies potential advantages of the breakdown plasma confined in a microhole in many relevant applications, such as laser propulsion and laser-induced breakdown spectroscopy. The developed model also provides a useful guiding tool for future fundamental research and practical applications in many areas related to laser interactions with gas breakdown plasma.

파우더와 솔더를 이용한 저비용 비아홀 채움 공정

Abstract This study proposed a noble process to fabricate TSV (Through Silicon Via) structure which has lower cost, shorter production time,and more simple fabrication process than plating method. In order to produce the via holes, the Si wafer was etched by a DRIE (DeepReactive Ion Etching) process. The via hole was 100
um in diameter and 400
um in depth. A dielectric layer of SiO 2 was formed bythermal oxidation on the front side wafer and via hole side wall. An adhesion layer of Ti and a seed layer of Au were deposited. Solderingprocess was applied to fill the via holes with solder paste and metal powder. When the solder paste was used as via hole metal line,sintering state and electrical properties were excellent. However, electrical connection was poor due to occurrence of many voids. In thecase of metal powder, voids were reduced but sintering state and electrical properties were bad. We tried the via hole filling process byusing mixing solder paste and metal powder. As a consequence, it was confirmed that mixing rate of solder paste (4) : metal powder (3)was excellent electrical characteristics.

Dry Etching Solutions to Contact Hole Profile Optimization for Advanced Logic Technologies

As CMOS technology has been continuously scaling down and the dual-stress liner scheme is introduced for simultaneous stress enhancement of both n-MOS and p-MOS, contact etch has started to act as a critical role for the robust performance of integrated circuit. In this work, we investigated the impact of dry etching process on contact hole profile. Results demonstrate the overall contact hole profile can be rigorously controlled if the radio frequency (rf) powers and etching chemistries in inter layer dielectric (ILD) etch step are well balanced. Free local pull-back at contact hole sidewall has to leverage the optimization of etch selectivity of silicon nitride over silicon oxide in liner removal step. Besides, the post etch treatment (PET) is also proven to be imperative for the process window enhancement for such pull-back reduction.

The Interactions of Microhole Sidewall With Plasma induced by Femtosecond Laser Ablation in High-Aspect-Ratio Microholes

High-aspect-ratio microholes have many important applications, but their drilling is very challenging. Femtosecond (fs) laser ablation provides a potential solution, but involves many complicated physical processes that have not been well understood, which have hindered its practical application. One of these is that the plasma induced by laser ablation at the hole bottom will transfer some of its energy to the hole sidewall as it expands in the microhole. The plasma–sidewall interaction has been rarely studied in literature, and it is still not clear if or not the energy transferred from the plasma is sufficient to cause significant material removal from the sidewall. Direct time-resolved observations are extremely difficult due to the small temporal/spatial scales and the spatial constraint inside the hole, while the sidewall characterization after laser ablation is difficult to distinguish between the possible material removal due to plasma energy transfer and that due to direct laser energy absorption by the sidewall. In this paper, a physics-based model is applied as the investigation tool to study the plasma–sidewall interaction in fs laser drilling of high-aspect-ratio microholes. It has been found that for the studied conditions the energy transferred from the plasma is not sufficient to cause significant material removal from the sidewall through any thermally induced phase change process.

Seebeck effect of as‐grown and micro‐structured metallic (Zn,Al)O

AbstractWe studied the Seebeck coefficient S of sputtered Zn0.98Al0.02O samples with free carrier concentrations varying from 1018 to 1021 cm–3. The temperature dependence of the Seebeck coefficient at low carrier concentrations exhibits typical semiconductor behavior (S < 0 and pronounced phonon drag below 80K) whereas the metallic as‐grown Zn0.98Al0.02O shows a sign reversal of the Seebeck coefficient with decreasing temperature which is related to the not square‐root‐like density of states of this degenerately doped metallic material. Furthermore, metallic specimens were microstructured by photolithography and wet‐chemical etching with a pattern based on a square grid with a unit cell consisting of a centered square‐hole. The Seebeck coefficient changed systematically with decreasing size of the unit cell. The change of S is caused by a shift of the Fermi energy due to the creation of additional surface traps at the sidewalls of the micro holes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and luminescence characterization of two-dimensional GaAs-based photonic crystal nanocavities

This paper describes the design and fabrication process of a two-dimensional GaAs-based photonic crystal nanocavity with InAs quantum dots (QDs) emitters and analyzes the optical characteristics of cavity modes at room temperature. The micro-luminescence spectrum recorded from the nanocavities exhibits a narrow optical transition at the lowest order resonance wavelength of about 1137 nm with about 1 nm emission linewidth. In addition,the spectra of photonic crystal nanocavities processed under different etching conditions show that the verticality of air hole sidewall is an important factor determing the luminescence characteristics of photonic crystal nanocaivties. Finally,the variance of resonant modes is also discussed as a function of r/a ratio and will be used in techniques aimed at improving the probability of achieving spectral coupling of a single QD to a cavity mode.

Inductively coupled plasma etching of GaAs suspended photonic crystal cavities

The authors studied the dry-etching process by chlorine-based inductively coupled plasma for fabricating GaAs suspended photonic crystal cavities. To achieve low optical loss in such resonators, the photonic crystal holes must demonstrate simultaneously smooth sidewalls and good verticality. The influence of various parameters of the inductively coupled plasma process was investigated: a systematic analysis is provided on the dependency of hole sidewall roughness and shape on the process parameters such as gas mixture, etching power, pressure, and rf bias. The authors show that a combination of high pressure, high bias, and high etching power in an inductively coupled plasma with a Cl2/N2 chemistry is beneficial for achieving straight and smooth sidewalls, and wall tilt of less than 4° was obtained.

Accumulated sidewall damage in dry etched photonic crystals

Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800to70ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6×103to1.2×105cms−1 as the etching time increases from 3to50min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.

Focused ion beam milling of photonic crystals in silicon on insulator

A photonic crystal slab, consisting of an array of circular sub-micron diameter holes in Silicon on Insulator (SOI), has been fabricated using focused ion beam (FIB) milling. This application requires the sidewalls of the holes to be very smooth and as nearly perpendicular to the slab as possible. The shape of holes is adversely affected by redeposition of milled material. The effects on the sidewall shape due to different FIB parameters, such as beam current, dwell time, and scanning pattern have been researched. It is shown that a spiral-shaped scanning pattern performs much better than the conventional rater scan. A combination of dwell time, beam current and number of scanning loops, optimising the geometry of holes, has been determined.