Reactive Ion Etching System Research Articles

Fabrication of Nanometer-scale Pillar Structures by Using Nanosphere Lithography

In this work, we have successfully fabricated a periodic array of nanostructures on the GaN, sapphire and silicon substrates by using a nanosphere lithography. First, a polystyrene nanosphere monolayer with a diameter of 500 nm was spin-coated on the substrates; then, an oxygen plasma was applied to the monolayer using a reactive ion etching system to make spacings among the nanospheres so that one could control the on/off ratio of the pitch and the shape of the nanoscale pillar structures. Next, evenly-spaced polystyrene nanospheres were used as a mask for inductivelycoupled plasma reactive ion etching to make nanoscale pillar structures of different shapes and depths on the substrates. These experimental results are expected to offer a milestone for the application of nanostructures to various semiconductor devices.

Dual etch processes of via and metal paste filling for through silicon via process

We investigated the etched slope control of silicon via and the filling of the through silicon via (TSV) with nano-scale Ag paste. Patterns for a 10 μm-diameter hole and line were etched using the Bosch process in a deep reactive ion etching system (the first etching process). The diameter of via (Top) and the depth of the via were about 10.6 μm and 80 μm, respectively, with a nearly vertical profile. In sequence, the tapered via and the removal of the scallops were obtained using an inductively-coupled etching system (the second etching process). We investigated the effects of gas pressure and input power on the slope of the TSV during the second etching process. In the second etching process, as the process pressure increased from 10 to 80 mTorr, the diameter of via (Top) decreased from 13 to 12.2 μm. Meanwhile, the expansion of via (Top) increased with increasing source power from 200 to 600 W. We found that the expansions of the via (Top) size were related to the desorption of by-product and the arrival of ion flux. We achieved a smooth surface and a slope angle of about 86° using the dual etch process. Finally, the depth of the 80 μm via was filled with nano-scale Ag paste using a vacuum-assisted filling method.

Correlation of plasma characteristics to etch rate and via sidewall angle in a deep reactive ion etch system using Langmuir probe and optical emission spectroscopy

A Langmuir probe and optical emission spectroscopy were used in a deep reactive ion etch system to correlate plasma parameters (atomic fluorine and argon emission, electron density, ion density, and electron average energy) with the etch rate and via sidewall angle. All data were obtained for coil powers ranging from 200 to 800 W, platen powers ranging from 7 to 16 W, and pressure ranging from 3.8 to 62 mTorr with constant SF6 and Ar flow rates of 112 and 18 SCCM (SCCM denotes cubic centimeter per minute at STP), respectively. Results indicate that there is a correlation with etch rate for all plasma parameters except for argon emission. For argon emission, the etch rate exhibits a double-valued relation where the etch rate can either increase or decrease with increasing argon emission intensity due to changes in pressure which affect the energy coupling efficiency. As expected, the etch rate increases for measured increases in fluorine emission, electron density, and ion density. The etch rate, however, decreases with increasing average electron energy due to collision processes. In contrast, no correlation is observed between any of the measured plasma parameters with sidewall angle. The last result is consistent with the idea that sidewall angle is primarily controlled by the passivation cycle as opposed to the etching cycle, where all the authors’ data were obtained.

Minimizing permeability of PET substrates using Oxygen plasma treatment

Surface plasma treatment in a reactive ion etching system is used to observe a considerable decrease in permeability of polyethylene terephthalate to gases. The effects of oxygen plasma on the surface properties and morphology of PET polymers are investigated by scanning electron microscopy (SEM), x-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). In addition, the optical transmission properties of the treated samples have been investigated corroborating the findings of SEM and AFM analyses. Moreover, the penetration of air through the treated substrates was investigated using a vacuum test. The treated PET substrates can be used to realize flexible plasma display panels.

Improved impermeability of PET substrates using oxygen and hydrogen plasma

A considerable decrease in permeability of polyethylene terephthalate (PET) films by means of surface plasma treatment in a reactive ion etching system is reported. The effects of oxygen and hydrogen radio frequency plasma on the surface properties of PET polymers are investigated by infrared spectroscopy, scanning electron microscopy (SEM), and X-ray photon spectroscopy (XPS). The surface morphology of the samples has been investigated using SEM and atomic force microscopy (AFM). The optical transmission spectroscopy has been studied further confirming the significant effect of O-plasma. Also the penetration of air through the treated substrates was investigated using a vacuum test. It is found that oxygen and hydrogen plasmas lead to about four-fold reduction in the penetration of air through the PET films, while the effect of hydrogen plasma has been more significant. In addition, oxygen plasma results in a rougher surface as observed both by AFM and SEM analyses. The formation of nanostructures on PET surfaces has been observed at plasma powers of 0.3 W/cm 2.

Plasma texturing for silicon solar cells: From pyramids to inverted pyramids-like structures

We have studied systematically a dry and free mask texturing process of crystalline silicon wafers using SF 6/O 2 plasmas in a reactive ion etching (RIE) system, with special attention on the effect of the RF plasma power and the SF 6/O 2 ratio on the texture of the silicon surface. In particular, we have found that by increasing the RF power, with an optimized SF 6/O 2 ratio and pressure it is possible to switch from a random texture, to a pyramid-like texture and finally to an inverted pyramid-like texture. This resulted in average reflectance values as low as 6%, which open an exciting opportunity for crystalline silicon solar cells applications.

Effects of Ar and O 2 additives on photopatternable sol–gel etching in an SF 6-based plasma for planar lightwave circuit fabrication

We present a novel study of the interaction of SF 6-based plasmas with sol–gel materials in a parallel plate reactive ion etching (RIE) system. The purpose of these experiments was to obtain quantitative measures and optimisation of the RIE parameters, which can be used in the microfabrication of planar lightwave circuit (PLC) devices. The sulfur hexafluoride chemistry is chosen due to its excellent etching properties of SiO 2, which is one of the components of the photopatternable sol–gel materials and is not present in typical photoresist materials. Fast process etching rate and good selectivity is achieved by varying SF 6 flow and power delivered to the electrodes. The study also reveals a marginal influence of oxygen and argon flow on the character of the sol–gel etching. The experimental data obtained can be used as a reference for any sol–gel devices fabricated using widely available RIE reactors.

High Rate Deep Si Etching using Capacitively Coupled Plasma

High rate deep Si etching using SF6/O2 gas chemistry by Magnetically-Enhanced Reactive Ion Etch (MERIE) system using a Dipole-Ring Magnet (DRM) is studied. It is capable of etching holes 40 μm in diameter in a Si substrate at etch rates as high as 50 μm/min. It was found that the Si etch reaction is dominated by the density of fluorine radicals, which is realized at high frequency and pressure. In holes with higher aspect ratios, it was found that the Si etch rate at the bottom of holes is determined not only by the supply of fluorine radicals, but is also influenced by an etch-inhibiting effect related to the sidewall of the hole. Using an 8 μm square mask, holes with straight sidewalls were etched to a depth of 60 μm at an etch rate of 24 μm/min.

Dry Etching of Nanosized Si2Sb2Te5 Patterns using TiN Hard Mask for High Density Phase-change Memory

Compared to Dram and flash memory, CRAM (chalcogenide random access memory), which is a non-volatile memory using a reversible phase change between amorphous and crystalline state, has many advantages such as high speed, high sensing margin, low operating voltage, and is being pursed as a next generation memory. Being able to pattern and etch chalcogenide in nanoscale is essential for the integration of CRAM. We investigated the etching characteristics of Si2Sb2Te5 in a CHF3/O2 gas mixture using a reactive ion etching system. The nanosized Si2Sb2Te5 patterns were defined by electron-beam lithography, and a hard mask TiN was chosen for Si2Sb2Te5 etching. Using these optimized etching parameters and patterning conditions, 500nm Si2Sb2Te5 square could be successfully obtained with good profiles and uniformity.

Dry Etching of Nanosized Ge<SUB>1</SUB>Sb<SUB>2</SUB>Te<SUB>4</SUB> Patterns Using TiN Hard Mask for High Density Phase-Change Memory

Being able to pattern and etch chalcogenide materials in nanometer scale is essential for the integration of high density chalcogenide random access memory. We investigated dry etching methods for the patterning of Ge1Sb2Te4 films in CHF3/O2 gas mixture using reactive-ion etching system. The gas species CHF3/O2 can reach good etched features with smooth sidewall and a taper angle of 86 degrees. The nanosized Ge1Sb2Te4 patterns were defined by electron-beam lithography using hydrogen silsesquioxane as negative type e-beam resist. A hard mask of TiN, to which the selectivity of Ge1Sb2Te4 is as high as 12, was chosen for employing a CHF3/O2 gas mixture for Ge1Sb2Te4 etching. The Ge1Sb2Te4 line with width of 170 nm could be successfully obtained with good profiles and uniformity using these optimized patterning conditions, which could be very helpful for fabricating high density chalcogenide random access memory based on Ge1Sb2Te4.

Time-multiplexed, inductively coupled plasma process with separate SiCl[sub 4] and O[sub 2] steps for etching of GaAs with high selectivity

The authors present the results and the optimization procedure for a time-multiplexed dry etching process to etch GaAs in an inductively coupled plasma reactive ion etching system. The gas feed chopping sequence employed a SiCl4 etch phase and an O2 passivation phase. Care is taken not to intermix O2 with SiCl4. The investigated structures consist of pillars, trenches, stripes, and holes, all with lateral structure size of 1 μm or less. This feature size is interesting for diffractive elements and cavities in integrated mid-IR optoelectronics. They achieve an aspect ratio of 10 for holes, 17 for trenches, and 30 for stripes with a selectivity of 200:1 on open areas. The improvements in the sidewall morphology are related to the O2 passivation step investigated by optical emission spectroscopy and energy dispersive x-ray analysis that reveals a Si-rich SiOX sidewall.

Etching Characteristics of Polycrystalline 3C-SiC Films Using Enhanced RIE

This paper describes magnetron reactive ion etching (RIE) characteristics of polycrystalline (poly) 3C-SiC thin films grown on thermally oxidized Si substrates by atmospheric pressure chemical vapor deposition (APCVD). The best vertical structures were obtained by the addition of 40 % O2, 16 % Ar, and 44 % CHF3 reactive gas at 40 mTorr of chamber pressure. Stable etching was achieved at 70 W and the poly 3C-SiC was undamaged. These results show that in a magnetron RIE system, it is possible to etch SiC with lower power than that of the commercial RIE system. Therefore, poly 3C-SiC etched by magnetron RIE has the potential to be applied to micro/nano electro mechanical systems (M/NEMS).

Etching Characteristics and Surface Morphology of Nitrogen-Doped a-SiC Films Prepared by RF Magnetron Sputtering

Amorphous nitrogen-doped silicon carbide (a-SiCxNy) thin films were deposited on Si substrates by RF magnetron sputtering of a SiC target in a N2+Ar atmosphere. The N2/Ar flow ratio was adjusted by varying the N2 flow rate and maintaining constant the Ar flow rate. In order to investigate the influence of N2/Ar flow ratio on composition, bonding structure, morphology and surface roughness of the deposited films, the following techniques were used: Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and atomic force microscopy (AFM). Moreover, using a reactive ion etching (RIE) system the a-SiCxNy samples were etched in SF6+O2 gases mixtures. To better understand the variation of the etching rate as a function of the nitrogen content in the film, temporal mass spectrometry analysis of main effluents generated during etching process was performed.

Deep level characteristics in n-GaN with inductively coupled plasma damage

The effects of energetic ion-induced damage on deep traps in n-GaN have been investigated using deep level transient spectroscopy. The energetic ions were produced in an inductively coupled plasma reactive ion etching (ICP-RIE) system. The electrons captured at the trap levels E1 (0.25 eV) and E2 (0.62 eV), in a control sample, were found to depend logarithmically on the duration of the filling pulse, indicating a relationship to dislocations. The dramatic increase in the concentration of deep level E1 traps, as a function of etching-bias voltage, is thought to indicate the introduction of a VN-related complex. On the other hand, the concentration of deep level E2 traps shows an initial increase at an etching-bias of −50 V, followed by a decrease at higher etching-bias voltages. This trend was also observed in the room-temperature yellow luminescence spectra and x-ray photoelectron spectroscopy, which suggests that the deep level E2 is associated with point defects in the form of VGa-impurity complexes.

Effect of gas residence time on the morphology of silicon surface etched in SF 6 plasmas

This paper describes the effect of the SF 6 gas residence time on the morphology of silicon (1 0 0) samples etched in a reactive ion etching system. Profilometry and atomic force microscopy techniques were used to characterize the etching process focusing attention on the evolution of the surface morphology. Under the condition of variable pressure and gas flow rate, the decrease of the residence time leads to an increase of the silicon etch rate concomitantly with an increase of the surface roughness. Contrary fact is observed when the gas flow is fixed and the pressure is varied. Here, the increasing of residence time leads to a constant increase of silicon etch rate with small variations in final surface roughness. To better understanding this resident time effect, mass spectrometry analyses were realized during the discharge for both gas flow conditions.

Prediction of plasma etch process by using actinometry-based optical emission spectroscopy data and neural network

Optical emission spectroscopy (OES) data were used to construct neural network models of plasma etch process. According to a statistical experiment, actinomeric OES data were collected from the etching of oxide thin films in a CHF 3–CF 4 magnetically enhanced reactive ion etching system. The etch responses modeled include an etch rate, a profile angle, and an etch rate-nonuniformity. Principal component analysis was applied to reduce the dimensionality of OES data. Three data variances adopted are 98, 99, and 100%. For each data variance, backpropagation neural network models were constructed. The training factors optimized by genetic algorithm include the training tolerance, magnitude of initial weight distribution, number of hidden neurons, and two gradients of activation functions in the hidden and output layers. The presented models demonstrated much improved predictions over the previous ones. The improvements were 43, 61, and 17% for the etch rate, profile angle, and etch rate-nonuniformity models, respectively.

Two-beam-current method for e-beam writing gray-scale masks and its application to high-resolution microstructures

A two-beam-current method is introduced for e-beam writing in the fabrication of gray-scale masks. Compared with the simpler single-current method, the two-beam-current method offers two important advantages: (a) it can achieve a much larger dynamic range for e-beam exposure; (b) the writing time for a gray-scale mask can be reduced when a large pattern is to be written. Here, the new method is first described in detail and its application to the fabrication of our new gray-scale mask is demonstrated. Then, the improved gray-scale masks were employed to fabricate large dynamic range, high-resolution micro-optical elements of less than a couple of micrometers depth, using deep ultraviolet lithography at 248 nm wavelength and an inductively coupled plasma reactive ion etching system.

Reactive-ion etching of Ge 2Sb 2Te 5 in CF 4/Ar plasma for non-volatile phase-change memories

Etching of Ge 2Sb 2Te 5 (GST) is a critical step in the fabrication of chalcogenide random access memories. In this paper, the etch characteristics of GST films were studied with a CF 4/Ar gas mixture using a reactive-ion etching system. We observed a monotonic decrease in etch rate with decreasing CF 4 concentration indicating its importance in defining the material removal rate. Argon, on the other hand, plays an important role in defining the smoothness of the etched surface and sidewall edge acuity. We have studied the importance of gas mixture and RF power on the quality of the etched film. The smoothest surfaces and most vertical sidewalls were achieved using a CF 4/Ar gas mixture ratio of 10/40, a background pressure of 80 mTorr, and power of 200 W.

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1 0-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH 4/O 2/NH 3 was employed. The L1 0-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness ( R a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1 0-FePt was successfully realized in the present study.

Plasma etching of As2S3 films for optical waveguides

Chalcogenide glasses are good candidate materials for ultra-fast non-linear optic devices. In this work, we present the photolithographic process and the plasma etching of arsenic tri-sulphide (As2S3) film. The films were deposited on thermally oxidized silicon substrates by ultra-fast pulsed laser deposition. To protect As2S3 film from photo-resist developer, thin resist layer ∼100–200nm was remained on the UV exposed area by controlling resist development time. After removing the protective layer in oxygen plasma, As2S3 waveguides were patterned in inductively coupled plasma reactive ion etching (ICP-RIE) system using CF4–O2 gas mixture. We investigated the etch rate and the etch selectivity to photo-resist of As2S3 as a function of bias power, induction power, operating pressure, and gas flow rate ratio of CF4 and O2. The film is mainly etched by the chemical reaction with fluorine radicals. The content of oxygen in the plasma determines the etched sidewall profiles and nearly vertical profile was obtained at high oxygen content plasma.