Reactive Ion Etching System Research Articles

Polymer surface morphology control by reactive ion etching for microfluidic devices

Abstract This paper presents the novel method to control polymer surface morphology using reactive ion etching (RIE) technique and its application to microfluidic devices. By using this method, polymer surface morphology could be controlled in the wide range between smooth surface and grassy surface with a newly developed electron cyclotron resonance (ECR)-RIE system. It was found that the polymer surface morphology is closely related to metal micromask concentration on the surface. Our system could easily control the micromask concentration only by changing the total pressure in the chamber. The etching characteristics of 75 mol% O 2 –CF 4 gas mixture were systematically investigated as a function of total pressure. The smoothest surface with the arithmetic mean roughness value ( R a ) less than 10 nm was achieved at 0.1 Pa. On the other hand, the grassy surface with high aspect ratio of 80 was uniformly formed on the polymer surface under the higher-pressure range from 1.0 Pa to 1.5 Pa. Furthermore, the proposed method was applied to microfluidic channels with multiple pillars, and a hybrid structure with smooth and grassy surfaces.

ICP etching of polycrystalline diamonds: Fabrication of diamond nano-tips for AFM cantilevers

Diamond nano-tips for measurements of living-cell activities have been fabricated from polycrystalline diamond/Si substrates using an inductively coupled plasma reactive ion etching (ICP-RIE) system. Mixtures of O 2 and CF 4 gas in a plasma was used as etching atmosphere. The etching properties of polycrystalline diamond film have been characterized. During etching of polycrystalline diamond, unintentional nano whiskers were formed due to the inhomogeneity of chemical bonds at grain boundaries. Finally, nano-tips longer than 10 μm and with an apex radius below 50 nm without nano whiskers have been realized.

O2/N2 Plasma Etching of Acrylic in a Multi-layers Electrode RIE System

We investigated dry etching of acrylic (PMMA) in O2/N2 plasmas using a multi-layers electrode reactive ion etching (RIE) system. The multi-layers electrode RIE system had an electrode (or a chuck) consisted of 4 individual layers in a series. The diameter of the electrodes was 150 mm. The etch process parameters we studied were both applied RIE chuck power on the electrodes and % O2 composition in the N2/ O2 plasma mixtures. In details, the RIE chuck power was changed from 75 to 200 W.% O2 in the plasmas was varied from 0 to 100% at the fixed total gas flow rates of 20 sccm. The etch results of acrylic in the multi- layers electrode RIE system were characterized in terms of negatively induced dc bias on the electrode, etch rates and RMS surface roughness. Etch rate of acrylic was increased more than twice from about 0.2 µm/min to over 0.4 µm/min when RIE chuck power was changed from 75 to 200 W. 1 sigma uniformity of etch rate variation of acrylic on the 4 layers electrode was slightly increased from 2.3 to 3.2% when RIE chuck power was changed from 75 to 200 W at the fixed etch condition of 16 sccm O2/4 sccm N2 gas flow and 100 mTorr chamber pressure. Surface morphology was also investigated using both a surface profilometry and scanning electron microscopy (SEM). The RMS roughness of etched acrylic surface was strongly affected by % O2 composition in the O2/N2 plasmas. However, RIE chuck power changes hardly affected the roughness results in the range of 75-200 W. During etching experiment, Optical Emission Spectroscopy (OES) data was taken and we found both N2 peak (354.27 nm) and O2 peak (777.54 nm). The preliminarily overall results showed that the multi-layers electrode concept could be successfully utilized for high volume reactive ion etching of acrylic in the future.

SU‐8 as a structural material for labs‐on‐chips and microelectromechanical systems

Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented.

Chemical gases sensing properties of diamond nanocone arrays formed by plasma etching

A uniform diamond nanocone array was formed by plasma etching of diamond film in a hot filament chemical vapor deposition (HFCVD) system. A surface amorphous carbon coating layer, which is formed during CH4/H2 plasma-etching process, was removed by Ar plasma in a reactive ion etching system. The hydrogenation of diamond nanocones was performed in H2 ambience by using the same HFCVD system. The air-diluted NH3 and NO2 gases sensing properties of the diamond cone arrays had been studied by using electric current versus measurement time characteristics at room temperature. The repeatable chemical sensing properties of the hydrogenated diamond cone array sensor are enhanced, in comparison with as-formed diamond film. Surface two-dimensional hole gas structure and greatly increased surface-to-volume ratio both play a key role for the excellent detection performance. As-formed diamond nanocone arrays show a promising prospect for applications as chemical sensor for both reducing (NH3) and oxidizing (NO2) gases.

Magnetron Reactive Ion Etching of Polycrystalline 3C-SiC Thin Films

This paper describes the magnetron reactive ion etching (RIE) characteristics of polycrystalline (poly) 3C-SiC thin films grown on thermally oxidized Si substrates by using atmospheric pressure chemical vapor deposition (APCVD). The etch rate of the poly 3C-SiC thin films was varied from 20 ˚ to 400 ˚ depending on conditions, such as the gas flow rates, the chamber pressure, the RF power, and the electrode gap. The best vertical structures were obtained by the addition of 40 % O2, 16 % Ar and 44 % CHF3 reactive gas at a 40-mTorr 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 a commercial RIE system. Therefore, poly 3C-SiC etched by magnetron RIE has a potential for applications to be applied to micro/nano electromechanical systems (M/NEMS).

Study of fluorine bombardment on the electrical properties of AlGaN∕GaN heterostructures

The effects of fluorine ion bombardment on the channel transport properties of AlGaN∕GaN heterostructures have been investigated. Ion bombardment of the heterostructure was carried out within a CF4 plasma in a reactive ion etching system at various self-bias voltages. Hall mobility and sheet electron concentration for the two-dimensional electron gas showed strong dependence on bombardment duration and postbombardment annealing. A systematic study of the behavior of implanted fluorine ions in the annealed heterostructure reveals diffusion followed by accumulation of the ions at the heterointerface. Implications of such behavior on the performance of high electron mobility transistors are briefly discussed.

Fabrication of low-loss channel waveguides in Al2O3 and Y2O3 layers by inductively coupled plasma reactive ion etching

Etching of amorphous Al2O3 and polycrystalline Y2O3 films has been investigated using an inductively coupled reactive ion etch system. The etch behaviour has been studied by applying various common process gases and combinations of these gases, including CF4/O2, BCl3, BCl3/HBr, Cl2, Cl2/Ar and Ar. The observed etch rates of Al2O3 films were much higher than Y2O3 for all process gases except for Ar, indicating a much stronger chemical etching component for the Al2O3 layers. Based on analysis of the film etch rates and an investigation of the selectivity and patterning feasibility of possible mask materials, optimized optical channel-waveguide structures were fabricated in both materials. In Al2O3, channel waveguides were fabricated with BCl3/HBr plasma and using a standard resist mask, while in Y2O3, channel waveguides were fabricated with Ar and using either a resist or a sputter deposited Al2O3 mask layer. The etched structures in both materials exhibit straight sidewalls with minimal roughness and sufficient etch depths (up to 530 nm for Al2O3 and 250 nm for Y2O3) for defining waveguides with strong optical confinement. Using the developed etch processes, low additional optical propagation losses (on the order of 0.1 dB/cm) were demonstrated in single-mode ridge waveguides in both Al2O3 and Y2O3 layers at 1550 nm.

High etch rates of poly-crystalline 3C-SiC films in magnetron enhanced CHF 3 plasmas

Magnetron enhanced reactive ion etching (RIE) of poly-crystalline 3C-SiC thin films grown on thermally oxidised Si substrates has been investigated in CHF 3 plasmas. The magnetron enhanced RIE can stably etch the poly-crystalline 3C-SiC thin film at a lower ion energy (70 W) without any damage than can the commercial RIE system. The best vertical structure was improved by the addition of 40% O 2 and 16% Ar with the CHF 3 reactive gas.

Etching Studies of Post-Annealed SiC Films Deposited by PECVD: Influence of the Oxygen Concentration

Amorphous silicon carbide thin films (SiC) were produced by PECVD technique at room temperature. Post-annealing was used to crystallize the SiC films. These films were etched in reactive ion etching system using SF6 + O2 gas mixtures. The influence of O2 concentration in process was investigated by mass spectrometry technique. Using this technique, it was possible to estimate the better conditions where the etching rates are optimal and also to verify the contributions of etchant species like F and O on the production of the main volatile products SiF4, CO and CO2.

Inductively coupled plasma reactive ion etching of ZnO films in HBr/Ar plasma

The etching characteristics of ZnO thin films were examined in an HBr/Ar gas mix using an inductively coupled plasma reactive ion etching system. The etch rate and etch profile were systematically investigated as a function of gas concentration. In addition, the effects of etch parameters such as coil rf power, dc-bias voltage, and gas pressure were studied. As the HBr concentration increased, the etch rate of the ZnO films gradually decreased while the etch profile was improved. Surface analyses including X-ray photoelectron spectroscopy and atomic force microscopy were employed to elucidate the etch mechanism of ZnO in an HBr/Ar chemistry.

마그네트론 RIE을 이용한 M/NEMS용 다결정 3C-SiC 식각 연구

The magnetron reactive ion etching (RIE) characteristics of polycrystalline (poly) 3C-SiC grown on /Si substrate by APCVD were investigated. Poly 3C-SiC was etched by gas, which can form a polymer as a function of side wall protective layers, with additive and Ar gases. Especially, it was performed in magnetron RIE, which can etch SiC at a lower ion energy than a commercial RIE system. Stable etching was achieved at 70 W and the poly 3C-SiC was undamaged. The etch rate could be controlled from to by the manipulation of gas flow rates, chamber pressure, RF power, and electrode gap. The best vertical structure was improved by the addition of 40 % and 16 % Ar with the reactive gas. Therefore, poly 3C-SiC etched by magnetron RIE can expect to be applied to M/NEMS applications.

Surface micromachined capacitive ultrasonic transducer for underwater imaging

This study presents the primary design, fabrication process and device measurement of a Capacitive Micromachined Ultrasonic Transducer (CMUT) for underwater acoustic imaging. Theoretical analysis and computer simulations of the CMUT are performed. The CMUT fabrication uses the full surface micromachining techniques of the Micro Electro Mechanical System (MEMS). These techniques are Low Pressure Chemical Vapor Deposition (LPCVD), photolithography, Reactive Ion Etching System (RIE) dry etching, sacrificial layer wet etching, metal thermal evaporation coating and Plasma‐Enhanced Chemical Vapor Deposition (PECVD). Several important issues regarding fabrication are discussed. The measured input impedance of the CMUT is in agreement with the theoretical prediction. The received signal has a 35 dB signal‐to‐noise ratio indicating that practical applications of the immersion CMUT are feasible and that the radiation pattern measurement of the CMUT array has good beamforming characteristics for underwater imaging.

Detailed analysis of the influence of an inductively coupled plasma reactive-ion etching process on the hole depth and shape of photonic crystals in InP∕InGaAsP

The authors report on the fabrication of photonic crystals in the InP∕InGaAsP∕InP material system for applications at telecommunication wavelengths. To achieve low optical loss, the photonic crystal holes must demonstrate smooth sidewalls and should be simultaneously deep and cylindrical. The authors present the etching process of these structures based on a Cl2∕Ar∕N2 chemistry with an inductively coupled plasma reactive-ion etching system. A systematic analysis is provided on the dependency of the hole sidewall roughness, depth, and shape on the process parameters such as etching power, pressure, and chemical composition of the plasma. They found that a low plasma excitation power and a low physical etching are beneficial for achieving deep holes, whereas for the nitrogen content in the plasma, a delicate balance needs to be found. Nitrogen has a negative impact on the hole shape and surface roughness but is capable of preventing underetching below the mask by passivation of the sidewalls. With the authors’ process more than 4μm deep holes with low conicity have been demonstrated.

Nanolithographic patterning of transparent, conductive single-walled carbon nanotube films by inductively coupled plasma reactive ion etching

The authors report successful patterning of transparent, conductive single-walled carbon nanotube films down to 100nm lateral dimensions by photolithography or e-beam lithography and subsequent O2 plasma etching using an inductively coupled plasma reactive ion etching (ICP-RIE) system. They systematically study the effect of ICP-RIE etch parameters, such as substrate bias power, chamber pressure, and substrate cooling, on the nanotube film etch rate and etch selectivity. They also characterize the effect of the linewidth etched on the nanotube film etch rate for widths ranging from 50μm down to 100nm. Furthermore, by fabricating standard four point probe structures using the patterning capability developed, the authors investigate the effect of different resist processes on the resistivity of patterned single-walled carbon nanotube films and the effect of ICP reactive ion etching on the resistivity of partially etched nanotube films. In addition, they demonstrate that using an ICP-RIE system provides significant advantages, such as faster etch rates and better etch selectivity, over conventional parallel plate RIE plasma systems, making it possible to pattern lateral features as small as 100nm in nanotube films. The simple and efficient “top-down” patterning capability developed in this article could open up many opportunities for integrating single-walled nanotube films into a wide range of electronic and optoelectronic devices.

Reactive Ion Etching of Ge[sub 2]Sb[sub 2]Te[sub 5] in CHF[sub 3]∕O[sub 2] Plasma for Nonvolatile Phase-Change Memory Device

The etching characteristics of (GST) films were studied with a gas mixture using a reactive ion etching system. The variations of etch rates and etch profiles caused by changes in the gas-mixing ratio were investigated under constant pressure and applying power. Then the etching parameters were optimized. The etch rate is up to , and the selectivity of GST to is as high as 3 times. The smooth surface was achieved using optimized etching parameters of oxygen concentration of 4% in the gas mixture, pressure of , and power of .

Reactive ion etching technique for via-hole applications in thick GaAs wafers

The dry etching technique has been developed to etch via holes through a 5-mil-thick GaAs wafer by rf power and reactive gas pressures in a reactive ion etching system. The etching parameters are optimized for a slope profile suitable for power field effect transistors and monolithic microwave integrated circuit applications. The selectivity between GaAs and photoresist and the average etching rate can be higher than 30 and 1.1μm∕min, respectively. Furthermore, the slope angle measured from the vertical is larger than 11°, which is well suited for a thick GaAs via-hole etching process. Before the metal for the via-hole substrate is sputtered, the wet chemical etching solution based on HCl–H2O2∕H2O at room temperature is used to smooth the sidewall for a better connection. To probe these source pads, the via-hole resistances of the pseudomorphic high electron mobility transistors (PHEMTs) are measured to be less than 0.5Ω with more than 97.2% yield in a 4in. diameter GaAs wafer. It is found that the rf performance for low-noise and power PHEMTs can be further improved.

The reactive ion etching characteristics of AlGaN/GaN SLs and etch-induced damage study of n-GaN using Cl 2/SiCl 4/Ar plasma

In this study, the etching characteristics of Al x Ga 1 − x N/GaN superlattices with x=0.11 and 0.21 of Al and n-GaN with Cl 2/SiCl 4/Ar plasma using reactive ion etching (RIE) system were investigated. By varying gas ratio and rf power, it was found that SiCl 4 is an effective getter to remove residual oxygen in the chamber and has a strong physical sputtering effect to remove the oxide layer during the etching, and a nearly nonselective smooth etching of Al x Ga 1− x N/GaN SLs with the high etch rate of 220 nm/min could be obtained. X-ray photoelectron spectroscopy (XPS) and Hall measurements were employed together to reveal the correlation between stoichiometry and electrical changes of n-GaN induced by plasma etching. Combining with N 2O plasma post-etch treatments to restore etched surfaces, those results suggested that oxygen not only influences morphology of the Al-containing samples, but also electrical properties of n-GaN by changing the status of oxygen-related defects, which may play crucial roles in determining the nature of the damage.

Study of plasma charging-induced white pixel defect increase in CMOS active pixel sensor

Plasma process-induced “white pixel defect” (WPD) of CMOS active pixel sensor (APS) is studied for Si3N4 spacer etch back process by using a magnetically enhanced reactive ion etching (MERIE) system. WPD preferably takes place at the wafer edge region when the magnetized plasma is applied to Si3N4 etch. Plasma charging analysis reveals that the plasma charge-up characteristic is well matching the edge-intensive WPD generation, rather than the UV radiation. Plasma charging on APS transfer gate might lead to a gate leakage, which could play a role in generation of signal noise or WPD. In this article the WPD generation mechanism will be discussed from plasma charging point of view.

Transmission properties of dual-band cross-dipole fractal slit arrays for near- and mid-infrared wavelengths

The periodic arrays of two-stage cross-dipole fractal slits etched on a $200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick gold film exhibit two resonance pass bands in the near- and mid-infrared region. The sample was fabricated by electron beam lithography and reactive ion etching system, and the width of the fractal slits is about $120\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The transmission coefficient exceeds 1 at the peak wavelength if normalized to the area of the fractal slits. The measured transmission spectrum in the frequency domain around the short wavelength pass band agrees well with the simulation results obtained via the transfer-matrix method. The existence of two resonance bands and their relative positions can be well explained by the geometric self-similarity of the fractal structure. Both transmission spectrum and electric field distribution analysis show that the two resonance bands result from the interaction of the incident light with the individual primary and secondary elements of the two-stage fractal structure.