Average Etch Rate Research Articles

A novel ultra-violet assisted anisotropic etching of plastic to realize micro-gears

An ultraviolet assisted chemical etching of plastic is reported in which the etching of PET substrates is anisotropic in the direction of light illumination. A strong solvent as di-methyl-formamide (DMF) is exploited to perform the chemical etching process and patterning of the desired structures is feasible using a Ge/Cu bi-layer as the masking film. Etch rate depends strongly on the intensity of the ultra-violet light and temperature of the solution during this etching process. An average etch rate of 15 μm/h is achieved with little mask undercut in the presence of 6–8 mW/cm 2 of 365 nm UV at a temperature of 120 °C. The highest achieved etch rate in this technique is 40 μm/h using an intensity of 16 mW/cm 2 for the UV illumination. The effects of solution temperature during etching, the intensity of light, and the amount of the solvent above the sample have been studied. This technique has been applied to etch 80 μm of PET substrates and to make 40 μm thick square membranes with an area of 500 μm×500 μm. Also 120 μm thick micro-gears have been realized with a diameter of 900 μm. The gears have been freed and installed on their corresponding axels with a diameter of 100 μm.

Ultraviolet light treatment of thin high‐density polyethylene films monitored with a quartz crystal microbalance

AbstractUltraviolet (UV) treatment is an effective method for modification of the surface properties of polymeric materials. In this study, the effects of the ozone‐generating UV light treatment of thin high‐density polyethylene (HDPE) films were monitored with the quartz crystal microbalance (QCM) technique both in the presence of ozone and without it. The films were further characterized by X‐ray photoelectron spectroscopy, optical microscopy, and atomic force microscopy. We found that the ozone not only modified the surface properties of the HDPE films but also etched away the polymer layer. An average etching rate of 0.48 nm/min was determined. UV light exposure of the polymer film in an argon atmosphere resulted only in minor degradation of the films; the presence of ozone was needed to cause the destruction and loss of material. The QCM technique was a straightforward method for the monitoring of the kinetics of the ablation induced by the UV–ozone treatment process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2833–2839, 2004

Plastic micromachining assisted by ultraviolet illumination

A novel ultra-violet assisted micro-machining technique is presented in which the etching of Poly-Ethylene-Terephthalate substrates is anisotropic in the direction of light illumination in a Di-Methyl-Formamide solution. The effects of solution temperature and light intensity have been studied. An average etch rate of 10 /spl mu/m/hr is achieved with insignificant mask undercut.

Anisotropic Etching of GaAs Using CCl2 F 2 / CCl4 Gases to Fabricate 200 μm Deep Via Holes for Grounding MMICs

In this study we have investigated the reactive ion etching of 60 μm diam, 200 μm deep holes in 3 in. diam semi-insulating GaAs wafer using a combination of and gases for fabrication of through substrate via holes for grounding in monolithic microwave integrated circuits (MMICs). The effect of process parameters viz. pressure, ratio, and power on GaAs etch rate and resultant etch profile was investigated. Two kind of masks, photoresist and Ni, were used to etch GaAs and their performance was compared by investigating effect on etch rate, etch depth, etch profile, and surface morphology. The etch profile, etch depth, and surface morphology of as-etched samples were characterized by scanning electron microscopy. The desired 200 μm deep strawberry profile, with a top μm and bottom μm, was obtained at 40 mTorr process pressure with an average etch rate μm/min using Ni mask. The vias were then metallized by depositing a thin seed layer of Ti/Au (1000 Å) using radio frequency sputtering and Au (5 μm) electroplated to connect the front side pad and back side ground plane. The parasitic inductance offered by these vias was pH. The developed process was then integrated into the MMIC process line and a 16-18 GHz amplifier was fabricated using grounding vias with yield >90%. © 2003 The Electrochemical Society. All rights reserved.

In situ measurements of sensor film dynamics by spectroscopic ellipsometry. Demonstration of back-side measurements and the etching of indium tin oxide

A new liquid flow cell design for in situ ellipsometric measurements on transparent multilayer samples using variable angle spectroscopic ellipsometry is presented. In this cell, films made on transparent substrates are in direct contact with liquid solution. Ellipsometry measurements are made through the transparent substrate, that is, from the back-side relative to the incident light so that films are in continuous contact with the liquid. This cell is not limited to just one angle of incidence of light allowing the films to be characterized at several angles before, during and after liquid contact. The spectral range of measurements is limited only by absorption of light in the underlying transparent substrate and not by the liquid solution that the film is in contact with. As a demonstration, we have measured and analyzed the dynamics of an indium tin oxide film on glass undergoing acid etching. Data from this in situ experiment were successfully modeled and the ITO layer thickness decreased uniformly during the etching process with an average etch rate of 0.23 nm/min.

Macrodistribution of anodic dissolution rate at a rotating disk electrode with partially insulated surface

Macrodistribution of etching rates of a macroscopically nonuniform, partially “dipped,” rotating disk electrode of low-carbon steel in 1 M NaCl at pH 1 with photoresist insulation and the density of active rectangular holes being ∼1.6 holes/mm2 is studied at dimensionless etching rates i0avg/il = 0.2–1.1, where i0avg is the average current density per active surface and il the limiting anodic current density determined by the ionic transport rate. The distribution of the average etching rates in the normal direction is determined by the primary current distribution and is insensitive towards the type of the dissolution rate distribution in a cavity.

Characteristics of He/O 2 atmospheric pressure glow discharge and its dry etching properties of organic materials

In this study, the characteristics of atmospheric low temperature plasmas generated by capillary electrodes with capillary dielectrics were investigated for the application of microelectronic cleaning processes. The characteristics of the plasmas were studied as a function of capillary aspect ratios, input power, electrode distance, He/O 2 gas flow rate, etc., using a high voltage probe, current probe, and optical emission spectroscopy (OES). The voltage between the electrodes increased with the increase of input power, the increase of electrode distance, the decrease of He flow rate, and the increase of O 2 flow rate. The increase of the voltage has led to unstable filamentary discharge from the stable capillary discharge. The use of electrodes with capillary dielectrics instead of a conventional dielectric barrier electrode (the electrode covered with non-capillary dielectric) not only decreased the electrode voltage, therefore, increased the stability of the plasma but also increased the discharge current and, therefore, the intensity of the plasma. Increased ionization and dissociation of the plasma species could be observed by OES with the increase of input power in He/O 2 mixtures. However, with the increase of O 2 flow rate in a constant He flow rate, the emission peaks from He decreased due to the increased electron consumption by oxygen while the emission peaks from O 2 + and O increased due to the increased ionization and dissociation rates with the increase of oxygen concentration in the He/O 2 gas mixtures. Also, using a He/O 2 gas mixture, organic materials such as photoresist could be successfully removed with the average etch rates higher than 200 nm/min.

Comparison of Dry and Wet Etch Processes for Patterning SiO2 / TiO2 Distributed Bragg Reflectors for Vertical-Cavity Surface-Emitting Lasers

A dry etch process for patterning distributed Bragg reflectors (DBRs) for vertical-cavity surface-emitting lasers was demonstrated. The etching was conducted using an inductively coupled plasma (ICP) system. Both and based etching chemistries were investigated. Very slow etch rates were obtained for when using a chemistry due to the low volatility of the etch products, Using an based chemistry, similar etch rates for and were obtained, which is desired for etching through the alternating and layers of the DBR. An average etch rate of 1200 Å/min was achieved at ICP and radio frequency (rf) powers of 500 and 250W, respectively. Wet chemical etch processing was also explored using a buffered oxide etchant (BOE) and diluted HF. Etch rates of ∼2050Å/min and ∼2.7 μm/min were obtained for BOE and (1:3), respectively. However, a significant etch-undercut of the DBR structure and delamination at the interfaces, due to internal stress created between these layers, were observed when these wet etchants were used. © 2001 The Electrochemical Society. All rights reserved.

Application of Radio-Frequency Plasma Glow Discharge to Removal of Uranium Dioxide from Metal Surfaces

Recent experiments have shown that radio-frequency (rf) plasma glow discharge using NF3 gas is an effective technique for the removal of uranium oxide from metal surfaces. The results of these experiments are analyzed to explain the measured dependence of the UO2 removal or etch rate on the NF3 gas pressure and the absorbed power in the plasma. The NF3 gas pressure in the experiments was varied from 10.8 to 40 Pa, and the deposited power in the plasma was varied from 25 to 210 W. The UO2 etch rate was strongly dependent on the absorbed power and, to a lesser extent, on the NF3 pressure and decreased exponentially with immersion time. At 210 W and 17 Pa, all detectable UO2 in the samples (~10.6 mg each) was removed at the endpoint, whereas the initial etch rate was ~3.11 μm/min. When the absorbed power was ≤50 W, however, the etch rate was initially ~0.5 μg/min and almost zero at the endpoint, with UO2 only partially etched. This self-limiting etching of UO2 at low power is attributed to the formation of nonvolatile intermediates UF2, UF3, UF4, UF5, UO2F, and UO2F2 on the surface. Analysis indicated that the accumulation of UF6 and, to a lesser extent, O2 near the surface partially contributed to the exponential decrease in the UO2 etch rate with immersion time. Unlike fluorination with F2 gas, etching of UO2 using rf glow discharge is possible below 663 K. The average etch rates of the amorphous UO2 in the NF3 experiments are comparable to the peak values reported in other studies for crystalline UO2 using CF4/O2 glow discharge performed at ~150 to 250 K higher sample temperatures.

Comparison of Cl2 and F-based dry etching for high aspect ratio Si microstructures etched with an inductively coupled plasma source

The differences between Cl2 and F-based dry etching are compared in this article. Inductively coupled plasma sources have been used to generate plasmas using both Cl2 and SF6/C4F8 chemistries. Trenches etched using Cl2 suffered less aspect ratio dependent etching effects because the trenches can be etched at a much lower pressure than with F-based gases. A 1.4 μm wide, 65 μm deep trench can be obtained with an aspect ratio of 46 in 12 h. The average Si etch rate was 90 nm/min and the selectivity to electroplated Ni was 23. The sidewall was vertical and smooth and the trench openings were nearly the same width before and after etching. Adjacent trenches with 0.14 μm mask opening and 2 μm line width were etched using these two etching technologies. With Cl2 etching, a wider 0.25 μm trench opening, due to the mask erosion effect, with a depth of 5.6 μm was obtained in 50 min. However, the 0.33 μm undercut increased the trench opening to 0.8 μm for 10.7 μm deep trenches after the F-based etching for 55 min. The Si etch rate in a large open area using F-based etching was 1818 nm/min, which is much faster than 201 nm/min when Cl2 etching was used. However, the Si etch rate, 112 nm/min for Cl2 and 195 nm/min for F-based gases, was similar when the trench opening was decreased to submicrometer dimensions. This shows that the Cl2 etching provides better dimension and profile control with comparable Si etch rate to F-based etching when etching submicrometer trenches. The loading effect using Cl2 chemistry is less than with F-based etching. The Si etch rate was 1.74 μm/min for ∼100% Si exposed area and 3.68 μm/min when the exposed Si area was ∼0% in F-based etching. Scalloping, which is a periodic undercut near the top of the sidewalls, disappeared when using an electroplated Ni mask. The size and period of the scalloped features decreased as the Si exposed area and etch time increased.

Cryogenic etching of deep narrow trenches in silicon

Deep and narrow anisotropic etching of silicon structures has been investigated in a low-pressure high density plasma reactor working with a cryogenic chuck. We have previously demonstrated the feasibility of this technique on such structures. Improvement of etch rate and profiles has been studied and new results show 2 μm wide trenches etched to a depth of 50 μm at an average etch rate of 5 μm/min with highly anisotropic profiles and very high selectivity (>500:1) toward the SiO2 mask. An evaluation of a commercially available reactor from Alcatel has been carried out and similar results are obtained. A phosphosilicate glass mask has been used to study the effect on profiles. It is shown that undercut is reduced while bowing is independent of the mask material. Since surface temperature strongly affects the profiles, wafer deformations in our cryogenic chuck have been measured and temperature evolution across the wafer has been estimated. A significant temperature difference of 10 °C between the chuck and the wafer is expected for thin wafers (210 μm).

Surface Kinetics of Polyphenylene Oxide Etching in a CF 4 / O 2 / Ar Downstream Microwave Plasma

A downstream microwave plasma etcher with in situ diagnostics has been constructed to elucidate the chemical mechanisms in plasma etching of polyphenylene oxide (PPO). reactant gases are used. Stable reaction products are investigated with mass spectrometry while reactive‐free radical information is obtained using optical emission spectroscopy. Additionally, the weight loss of PPO is measured to determine average etch rate. A linear correlation between weight loss measurements of PPO laminates and integration of CO and formation measured by mass spectrometry suggests that real‐time monitoring of polymer etching can be achieved. Etching dynamics are studied with gas compositions of varied from 6.6 to 30%. The etch process exhibits a dynamic reduction in rate with . spectra of X‐ray photoelectron spectroscopy show an increase in fluorination of the etched surface with . A kinetic model based on the dynamic change of the number of carbon sites that are fluorinated is proposed. © 2000 The Electrochemical Society. All rights reserved.

Deep anisotropic etching of silicon

We are interested in etching very deep anisotropic trenches (∼100 μm) with high aspect ratios (depth/width) (∼20–50) and high etch rates (∼5 μm/min). A high density plasma helicon reactor using SF6/O2 chemistry and a cryogenic chuck has been used for etching very narrow trenches from 1.2 to 10 μm wide on n-type Si wafers with a SiO2 mask. The first results show significant features that demonstrate the feasibility of this method. Two-micron-wide trenches have been etched to a depth of 80 μm at an average etch rate of 2.7 μm/min. The resulting profiles are highly anisotropic and selectivity of Si/SiO2 is remarkably high (>500).

Contact hole model for etch depth dependence

The dependence of the etch depth of a contact hole or circular via on the diameter of the hole opening is derived for a simple model which includes the effect of the bombarding ions and the neutral radicals on the etching. The ion etch rate at the center of the contact hole is proportional to the ion energy flux and the neutral etch rate is proportional to the neutral flux expression for molecular flow in a pipe. The total etch rate expression is found by Langmuir kinetics. The linear experimental relation for the etch depth versus the inverse diameter holds in this model for etching in the near ion flux-limited regime. The dependence of the etch depth and average etch rate on the etch time is given for this model.

Model for etch depth dependence on GaAs via hole diameter

Reactive ion etching of via holes for grounding of monolithic microwave integrated circuits has become the industry standard. It is well known that the via etch rate decreases as a function of decreasing via mask diameter as well as increasing etch depth. A model has been developed which relates the experimental etch rates in Cl2/BCl3/Ar plasmas to the ion and neutral fluxes incident on the wafer. This model provides a useful tool for designers and process engineers to predict etch depths and average etch rates as functions of via diameter and total etch time.

On ion track geometry in the etching process

The geometry of the etched tracks in polyethylene terephthalate has been analyzed during the chemical etching in 5 mole/l LiOH at 40°C after several etching times (90, 180, 270, 360 min) by the alpha-particle transmission method. The evolution of the etched track geometry was found to emerge from two separate opposite funnels via two interconnected cones combined with a cylindrical tube, up to two double-cone shapes combined with a central cylnder. The process of ion track etching was found to be rather erratic with an average track etching rate being about 30 times higher than bulk etching rate. The doublecone entrance shape of the pores points at slightly different structure of the near-surface area of the foil which might be due to the special thin foil production technology.

Smooth and anisotropic reactive ion etching of GaAs slot via holes for monolithic microwave integrated circuits using Cl2/BCl3/Ar plasmas

A process to produce very smooth and highly anisotropic through-the-wafer slot via holes using reactive ion etching in Cl2/BCl3/Ar mixtures has been developed. In this study, we have extensively investigated the GaAs etch rate and resultant etch profiles as functions of bias voltage, gas ratio, flow rate, chamber pressure, aspect ratio, and etch time. An optimum via hole etching process using a Plasma Therm 790 reactive ion etching system was determined to be 300 V bias voltage, gas flow ratio of Cl2:BCl3:Ar=4:3:10, and chamber pressure of 15 mTorr. The average etch time for 20 μm wide ×60 μm long vias on a 50 μm thick 3 in. diam wafer is 180 min using a total flow rate of 50 sccm, which corresponds to an average etch rate of 0.3 μm/min. This process has been successfully implemented on two-stage Ka-band monolithic microwave integrated circuit driver amplifiers fabricated by TRW. Under a pulsed bias with Vds=5.0 V and an input power of 15 dBm, the average power added efficiency was greater than 40% with a 13–14 dB gain between 32 and 36 GHz. A peak power added efficiency of 44% was achieved at 35 GHz.

Trends in aluminum etch rate uniformity in a commercial inductively coupled plasma etch system

The effects of process conditions and chamber geometry on the uniformity of Al etched by Cl2 were measured in a Lam TCP™ 9600 SE etch reactor. A computer simulation accurately predicted etch uniformity and aided in the explanation of uniformity trends. Parameters used in the experimental matrix included pressures between 6 and 24 mT, flow between 25 and 100 sccm, power supplied to the plasma between 0 and 350 W, and chamber heights ranging from 6 to 12 cm. The distinctive features of this study include the large number of input parameters studied in a commercial reactor and the accurate predictions obtained from a self-consistent simulation without free parameters. Reducing residence time in the experiments by adjusting chamber height or flow rate produces a more center-fast etch, as expected. The flow simulations were useful in corroborating intuitive arguments and in explaining anomalous results such as the effect of pressure on etch uniformity. More specifically, comparison of simulations and measurements demonstrated the quantitative connection between the Peclet number, the residence time, and the edge uniformity over a large range of process conditions. In addition to explaining general trends with residence time, Peclet number considerations also clarify the differing effects of pressure, flow rate, and chamber height change on uniformity. No attempt was made to impose plasma effects in the flow simulation because measurements of the neutral temperature and dissociation fraction were not available. Plasma power was observed experimentally to slightly improve uniformity without changing the average etch rate.

Plasma Etching of Hydrogen-Silsesquioxane

ABSTRACTCF4 plasma etching of hydrogen-silsesquioxane films on bare silicon substrates was conducted. An increase in average etching rate and a decrease in dielectric constant from 2.9 to 2.7 were observed after a top layer was removed from the surface of the film, indicating that a negative density depth gradient in the film was developed during the cure processing, A small part of the reduction in dielectric constant may be attributed to structural change resulting from the plasma interaction with the films since a small amount of Si-F bonds were identified in the surface layer of the film after plasma etching. There are indications in the x-ray photoelectron spectroscopy (XPS) spectra that traces of fluorocarbon polymer residue have been generated during the plasma etching. The results of this study also indicate a possibility of obtaining a lower dielectric constant HSQ film by plasma etching.

Atomic scale etching processes of n-Si(111) in NH4F solutions: In situ scanning tunneling microscopy

In situ scanning tunneling microscopy (STM) was employed to examine the electrochemical etching process of an n-Si(111) electrode in dilute NH4F solutions under potential control. Time-dependent STM images have revealed prominent effects of microscopic structures of Si on the rate of its dissolution. Multiple hydrogen-terminated Si atoms at the kink and step sites were eroded more rapidly than the monohydride Si step. This presumably resulted from the difference in reactivity of these hydrogen-terminated Si species. It is demonstrated that the density of kinks plays a main role in controlling the etching rate of Si. In the absence of kinks, not only the monohydride but also the dihydride steps were found to be stable. The etching rate of the monohydride step is substantially increased from a negligible value to 15 nm/min by the introduction of kink sites. The average etching rate for a dihydride step was 32 nm/min. Overall, the difference in the reactivity guides the dissolution of Si in a layer-by-layer fashion.