Etching Quality Research Articles

Temporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath

The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time through the sheath to the RF period is τion/τRF = 0.3). The position of the presheath/sheath edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath region. The characteristic bimodal structure of the time-averaged ion distributions found in previous experiments is observed to arise from the time-dependent ion dynamics, in accord with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and etching quality.

Rapid prototyping of silicon microstructures by means of a new masking process and crystal orientation dependent etching

Silicon micromachining for MEMS components requires deep etching processes in combination with etch-resistant masks. The usual masking and lithographic procedures are expensive and unsuitable for fast layout changes. We developed a machining possibility, which combines the flexibility of laser direct writing with the shape quality of crystal orientation dependent etching of silicon. The main step is substituting SiO 2 or Si 3N 4 mask layers by etch-resistant metal films. These films can be directly patterned with a laser marking system followed by a well-known etch process in KOH.

Micromachining Processing of 3D Micro Tensile Specimens Based on Inductively Coupled Plasma Etching

Based on the mechanism of inductively coupled plasma (ICP) etching,the micromachining processing of 3D micro tensile beams is researched in the light of the structure characteristics of the thermal silicon dioxide micro-tensile beams and with the purpose of solving the main problems in the processing. The influences of ICP etching process parameters on etching quality,including micro loading effect and aspect ratio effect in existence,are presented. The micromachining processing of the beams is introduced in detail. The pivotal procedure is double-masks-twice-ICP etching to form stair-opening structures and to obtain the free-standing thermal silicon dioxide beams on the surface of silicon. Using the high selectivity of single crystal silicon in ICP etching,the processing method is applicable in the fabrication of micro tensile beams with various films.

Formation of atomically clean silicon surfaces in a low-energy low-pressure microwave plasma

The influence of the regimes and chemical composition of the low-energy highly ionized ECR plasma of a low-pressure microwave gas discharge on the etch rate and nanomorphology of differently oriented single-crystal silicon surfaces is studied. Model mechanisms of the processes controlling the etch rate and etch quality of atomically clean silicon surfaces with a desired orientation are considered.

Electromagnetic Modeling of Plasma Etch Chamber for Semiconductor Microchip Fabrication

In the plasma etch chamber used to fabricate semiconductor microchips, maintain- ing the symmetry and uniformity of the electric fleld in the plasma discharge region is critical. Very-high-frequency (VHF) RF sources are attractive for such applications as they improve the e-ciency of plasma generation. Electromagnetic efiects become important at these frequencies, and etch chamber design requires careful investigation of the electromagnetic fleld spatial struc- ture in the chamber. In this paper, we apply the flnite-difierence time-domain (FDTD) method to examine various electromagnetic efiects in the plasma etch chamber and investigate strategies for improved chamber design. These efiects include the standing wave efiects and asymmetric fleld distributions that can be caused by asymmetric RF power feed conflgurations. The FDTD method is formulated in both cylindrical and Cartesian coordinate systems to facilitate modeling of rotationally symmetric chamber and asymmetric RF feed structures. The electric fleld dis- tribution generated by various RF feed conflgurations is studied at difierent VHF frequencies. Based on the FDTD simulations, we have been able to identify a variety of design approaches for ensuring electric fleld symmetry and uniformity. When the electromagnetic efiects become signiflcant, it is indispensable to fully understand the electrodynamic behavior of the RF flelds in the etch chambers because any nonuniformity of the electric flelds in the plasma region would directly have an impact on the etch uniformity and quality. In this paper, we apply the FDTD technique (2) to model the RF wave behavior in the chamber. We particularly pay attention to the electric fleld distribution at the wafer level and the corresponding electromagnetic efiects at very high frequency. The FDTD method is formulated in both cylindrical and Cartesian coordinate systems to facilitate modeling of rotationally symmetric chamber and asymmetric RF feed structures. We couple the FDTD formulation with the CPML (2) absorbing boundary conditions to accurately simulate the RF power delivery via a coaxial line. 2. COMPUTATIONAL METHOD DESCRIPTION To make the computational model conformal to the geometrical features in the cylindrical etching chamber, we formulate the FDTD method in the cylindrical coordinate system. In the cylindrical coordinate system, the Maxwell's curl equations for linear, isotropic, nondispersive materials can

Analysis of mechanism of carbon removal from GaAs(1 0 0) surface by atomic hydrogen

Etching of carbon contaminations from the GaAs(1 0 0) surface by irradiating with atomic hydrogen, which is one of the key reactions to promote high-quality thin films growth by molecular beam epitaxy (MBE), has been investigated by mass spectrometry (MS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It is shown that during the cleaning process at room temperature a total reduction of the Auger carbon signal, accompanied by desorption of methane as major reaction product, can be observed. The reaction pathways as well as the processes responsible for the observed carbon removal are discussed in detail to give a support for etching and growth quality enhancement not only in thin films epitaxy but in all atomic hydrogen promoted gas-phase III–V semiconductor processes.

”Dry-Etching System” with Q-switched DPSS Laser for Flat Panel Displays

Laser-dry-etching method has attracted a great deal of interest in industry because of the many potential benefits such as enormous cost reduction and chemical-free manufacturing environment. The authors have been developing various laser-dry-etching systems for large-scale Flat panel displays (FPDs). All these systems try to balance between etching speed and etching quality. It is crucial to have high-quality processes in the mass production lines, which operate 7 days per week, 24 hours per day. In this paper, the etching qualities of liquid crystal displays (LCDs) that are the representative of FPDs are outlined. Especially in laser-dry-etching for color filter (CF) substrate of LCD, the selective removal of indium tin oxide (ITO) films at black matrix (BM) position is much more difficult than at other positions. The authors have developed a new etching method so called “grazing incidence method with laser-dry-etching (GI-LDE)”. The selective removal of ITO films at black matrix position has become possible by using this method.

Ultrafast laser micromachining of 3C-SiC thin films for MEMS device fabrication

Femtosecond pulsed laser (800 nm, 120 fs) micromachining of thin films of 3C-SiC (β-SiC) semiconductor deposited on silicon substrate was investigated as a function of pulse energy (0.5 μJ to 750 μJ). The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, Coulomb explosion and photomechanical fragmentation, were correlated with the effects of pulse energy. The results show that the etch rate is higher and the ablation threshold is lower than those obtained with nanosecond pulsed excimer laser ablation, suggesting femtosecond laser’s potential for rapid manufacturing. In addition, the etch rates were substantially higher than those achievable in various reactive ion and electrochemical etching methods. Excellent quality of machined features with little collateral thermal damage was obtained in the pulse energy range (1–10 μJ). The leading material removal mechanisms under these conditions were photomechanical fragmentation, ultrafast melting and vaporization. At very low pulse energies (<1 μJ), nanoscale material removal has occurred with the formation of nanoparticles that is attributed to Coulomb explosion mechanism. The effect of assist gas on the process performance at low and high energy fluences is also presented.

Thermal transient characterisation of the etching quality of micro electro mechanical systems

The paper presents a non-destructive thermal transient measurement methodology that can reveal micron-sized differences among etched layers of MEMS structures. MEMS resonator devices and bridge structures made of polycrystalline silicon differing in etching times were investigated by simulations and measurements as well. Simulations showed that tiny differences in etching times of the sacrificial layers can cause significant changes in heat distribution. In the measurement process the voltage transients of the devices were captured. The results were transformed into temperature transients. Utilising temperature transients, small differences could be detected among the structures. The paper demonstrated simulation and measurement experiments by the applicability of thermal transient methodology for non-destructive testing of the etching quality in MEMS structures.

Femtosecond pulsed laser microfabrication of SiC MEMS microgripper

We report the capability of an ultrafast laser to pattern an electrostatic-comb-drive microgripper in the chemically difficult-to-etch 3C-SiC thin films. A microgripper with overall dimensions 1.2 mm×0.35 mm and a gap of 20 μm was designed and fabricated for the purpose of grasping and transporting microscale objects in hostile and harsh environments. Atmospheric pressure chemical vapor deposition was used to deposit thin films (∼2 μm) of 3C-SiC on 〈100〉 silicon substrates. A Ti:sapphire laser with 120 fs pulse width, 800 nm wavelength, and 1 kHz repetition rate was then used to perform “nonthermal” micromachining of thin films. Subsequent KOH anisotropic etching was used to dissolve the silicon substrate and release the gripper structures. The influence of laser pulse energy on the etch rate and quality of microfabricated grippers was examined and illustrated.

Cryogenic etch process development for profile control of high aspect-ratio submicron silicon trenches

A cryogenic etch process using low temperature (T⩽−100°C) and SF6 and O2 gases is presented for fabricating high aspect ratio silicon microstructures, including photonic devices and micro- and nanoelectromechanical systems. The process requires only a single electron beam resist mask and results in open area etch rates of 4μm∕min. Various etch process parameters, including O2 flow, rf forward power, substrate temperature, and chamber pressure were studied, and the resulting effect on the etch quality was evaluated in terms of sidewall verticality and surface roughness. The optimized process uses low temperature (T=−110°C) and low chamber pressure (P=7mTorr) and enables sidewall verticality greater than 89.5° with roughness of 1–10nm. A silicon etch selectivity of 26:1 was obtained for 380nm thick electron beam resist. Using the optimized process, a silicon-on-insulator Fabry-Pérot optical cavity with integrated rib waveguides and deeply etched silicon/air distributed Bragg reflector mirrors was fabricated and tested. The device exhibits sharp resonance peaks with full width at half maximum Δλ=0.45nm, free-spectral range of 26 nm, finesse F=58, and quality factor Q=3400 (at λ0=1531.6nm). The optical measurements and extracted mirror reflectance (R≈95%) confirm the high quality of our optimized etch process.

Parameter optimization for an ICP deep silicon etching system

The paper aims at investigating the parameter optimization of silicon micro- and nano-sized etching by an inductive coupled plasma-reactive ion etching system. The source power and the SF6 gas pressure are two main parameters that dominate etching. A pre-test is conducted to estimate the process window of the SF6 gas pressure at some given source powers. The process window is a parameter range in which the etching result is acceptable but may not be the best. In order to achieve excellent etching quality, the Taguchi experimental method is applied to evaluate parameters and find their optimum conditions. With the source power and SF6 gas pressure being set into the process window, four parameters, which are the substrate temperature, the bias power, the gas cycle time and the C4F8 gas flow rate, are evaluated and optimized for micro- and nano-sized etching. An impressive result, 200-nm-diameter pillar array with the pitch of 400 nm, is realized.

Fabrication and structural characterization of interdigitated thin film La1 − xSrxCoO3(LSCO) electrodes

For the prospective use as micro-Solid Oxide Fuel Cell (μ-SOFC) cathodes and for the investigation of reaction kinetics, La1 − xSr x CoO3 (LSCO) mixed ionic electronic conducting thin films were deposited by DC and RF sputtering onto a number of different substrate materials and characterized. Standard photolithographic and wet chemical etching methods were utilized to microstructure the LSCO films and XRD, SEM, AFM, WDS, and RBS were used to characterize their structure, topography, and chemistry. Sputtering resulted in very homogeneous and smooth thin crystalline films with Sr deficiency and submicron sized grains. Hydrochloric acid was found to readily etch LSCO with the etching quality strongly dependent on substrate material. LSCO films were most easily etched when deposited directly on silicon substrates, etched at intermediate rates when deposited on Gd:CeO2 films, and most resistant to etching after deposition onto single crystal yttria stabilized zirconia (YSZ) substrates. Imperfect etching was attributed to interface formation and the presence of impurities.

Reactive ion etching of glass for biochip applications: Composition effects and surface damages

Due to its insulating properties, transparency, and well known surface chemistry, glass represents an interesting alternative to silicon or polymers for biochip processing. However, high aspect-ratio posts for DNA electrophoresis have only been reported in expensive quartz substrates. Therefore, we investigate here metal mask transfer by fluorocarbon plasma etching in nine silica or glasses of different grades. With increasing amounts of non-SiO 2/non-B 2O 3 oxides in the material, the etch rate decreases and, in some cases, strong surface roughening appears. Furthermore, even for fused silica, surface damages such as cone-like defects were observed. Consequently, soda-lime slides coated with silica by plasma enhanced chemical vapor deposition (PECVD) were used as a good compromise between etching quality and cost. Electrophoresis chips with features down to 100 nm and aspect-ratio up to 10 could then be fabricated.

Deep etching of epitaxial gallium nitride film by multiwavelength excitation process using F2 and KrF excimer lasers

The deep etching of GaN(0001) thin films epitaxially grown on Al2O3(0001) has been investigated by laser ablation using F2 and KrF excimer lasers. The simultaneous irradiation with F2 and KrF excimer lasers markedly improves etching quality compared with single-KrF excimer laser ablation and provides almost the same quality as that in the case of single-F2 laser ablation with a high etching rate. Additionally, the present method achieves the deep etching of a GaN film of more than 5 μm in depth with steep side walls at an angle of 87° by changing the laser incidence angle.

Impact on Diffraction Efficiency of Binary Optical Elements for Spot Exposure Superposing Ratio

In fabrication of free form optical surfaces, spot exposure is a typical mode in laser photolithography. Proper selection of spot exposure superposing ratio is the key to optimize etching quality and writing speed. In this paper, a new composite diffractive grating structure is modeled for the influence on diffraction efficiency of binary optical elements caused by spot exposure superposing ratio. Composite grating can be transformed into one simple rectangular grating and two triangular gratings. Angular spectrum theory is used to describe the mathematical expression of the composite diffractive grating. Through simulation analysis, the relationships between diffraction efficiency and the other three items as grating depth, spot radius, and blaze wavelength, has been shown. Simulation results indicate that shape error caused by spot exposure ratio impact the diffraction efficiency greatly in deep etching, and the transmittance will reach maximal point approximately while spot exposure ratio is over 60%. This conclusion can be taken as the theoretical foundation for exposure frequency selection in laser photolithography figure generation.

Effects of mechanical agitation and surfactant additive on silicon anisotropic etching in alkaline KOH solution

Agitation is a key method that significantly affects silicon wet anisotropic etching quality including the etching rate and surface roughness. This study introduced the ultrasonic agitation to improve the roughness quality of etched (1 0 0) silicon plane in 30 wt.% KOH solution. These etching characteristics have been compared with those using magnetic stirring and no agitation. In ultrasonic agitation condition, the etching rate increases linearly with agitating power, but the surface roughness worsens. Although the etching rate always exceeds 1.2 μm/min and the average roughness, R a is below 15 nm, the membrane microstructures are damaged easily by ultrasonic agitation. Moreover, the KOH solution with added anionic surfactant, dihexyl ester of sodium sulfosuccinic acid, is also used to evaluate the etching properties of (1 0 0) silicon under without agitation. Owing to increasing hydrophilic ability between the hydrogen bubble and silicon surface and the effect of silicon wettability, the etching properties are promoted drastically. Experimental results show that the average roughness, R a can be reduced to 7.5 nm in aqueous KOH with anionic surfactant, which is about eight times better than achieved by the pure KOH solution without agitation for etching temperature of 100 °C. Meanwhile, the etching rate can be enhanced to 4.9 μm/min, which is 1.44 times better than that is obtainable in a pure KOH solution with ultrasonic agitation. The etching rate of the KOH solution with added surfactant is about twice that in the KOH solution with isopropyl alcohol (IPA) for etching temperature of 80 °C. Furthermore, this study also illustrates the reflectivity of etched surface for visible wavelength and the fabrication of thin film microstructures.

Stress control in masking layers for deep wet micromachining of Pyrex glass

In this paper, we report three etching masking technologies of Cr/Au, Cr/Cu and PECVD amorphous silicon developed for Pyrex glass micromachining in hydrofluoric acid solution. Our study reveals that the residual stress, especially the tensile stress, in the mask layers is responsible for the pinholes on the glass surface and notch defects on the edge formed at the etch edges of glass due to the breakage of highly stressed mask layers during the etching process. The Cr/Au metal mask can achieve a glass etch depth up to 100 μm, along with a number of pinholes and notch defects on the edge due to the high tensile residual stress in the Cr/Au layer. The Cr/Cu metal masking layer improves the glass etch quality by the reduced residual stress. Detailed studies have been done using the amorphous silicon film as a glass etch mask. The PECVD process and the subsequent annealing process have been optimized to reduce the compressive residual stress in the amorphous silicon layer. The maximum etch depth in the glass can be as high as 200 μm and almost without pinholes and notch defects on the edge. To our knowledge, this is the best result reported in the literature so far.

식각액에 따른 용융실리카의 레이저 습식 식각 특성 비교 연구

식각액에 따른 용융실리카의 레이저 습식 식각 특성 비교 연구

Low-loss photonic crystal defect waveguides in InP

We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material. Using Fourier analysis of the Fabry-Pérot fringes obtained in transmission, we derive the propagation losses. Values as small as 1.8 dB/mm for waveguides consisting of three rows of missing holes (W3) were measured. We believe that the reduction in losses is due to the high quality of etching carried out using a high beam voltage–current ratio regime of chemically assisted ion-beam etching.