Cyclotron Resonance Reactive Ion Etching Research Articles

Negative differential resistance characteristics of nanoscale in‐plane gate devices

AbstractNanoscale in‐plane gate devices are fabricated by electron beam lithography followed by electron cyclotron resonance reactive ion etching. We investigate the negative differential resistance (NDR) of the InGaAs/InAlAs in‐plane gate devices. In our nanoscale devices, the NDR phenomenon is most likely caused by a real space transfer of electrons from the high mobility channel to the low mobility layer. The NDR characteristics are related to the effective channel width of in‐plane gate devices and get more pronounced when the channel conductance is enhanced by applying the gate voltages. In addition, the NDR effect depends on the channel geometry. The NDR onset voltage shifts toward lower drain‐source voltages when the channel length or width is decreased. Furthermore, high drain‐source voltage characteristics are found to be affected considerably by the channel shape. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Negative Differential Resistance in InGaAs/InAlAs Nanoscale In-Plane Structures

Nanoscale in-plane structure devices are fabricated by electron beam lithography followed by electron cyclotron resonance reactive ion etching. We investigate the negative differential resistance (NDR) of InGaAs/InAlAs in-plane structure devices. The NDR appears in the current–voltage (I–V) characteristics of simple two-terminal in-plane short-channel devices. NDR characteristics depend on the effective channel width of in-plane gate transistors and become more pronounced when the channel conductance is increased by applying gate voltages. In a short-channel in-plane gate transistor, a more prominent NDR is observed and the NDR appears even at room temperature. In addition, the NDR onset voltage shifts to lower voltages when the channel length decreases. The NDR phenomenon is most likely caused by the real-space transfer of electrons from a high mobility channel to a low mobility layer.

High Q whispering gallery modes in GaAs/AlAs pillar microcavities

We report the observation of whispering gallery modes (WGM) in high quality GaAs/AlAs pillar microcavities defined by electron-beam lithography and electron cyclotron resonance reactive ion etching. Photoluminescence experiments, conducted using InAs quantum dots as an internal probe, reveal a remarkably simple WGM spectrum, consisting of a single series of TE modes. For diameters ranging from 3 to 4 mum, Q-factors in excess of 15 000 were measured, allowing for WGM lasing. Noticeably, sub-micron diameter micropillars also display high Qs (~ 1000), close to the limit set by intrinsic radiative losses. These results open the way to the development of original microlasers and improved quantum-dot single photon sources.

Raman scattering study of GaN nanostructures obtained by bottom-up and top-downapproaches

GaN nanocolumnar structures were grown by plasma-assisted molecular beam epitaxy(PAMBE) and also fabricated by electron cyclotron resonance reactive ion etching(ECR-RIE) of a compact GaN film parallel to the [111] direction of the Si(111) substrates.Scanning electron microscopy shows that the nanocolumns fabricated by PAMBE havea length of about 300–500 nm with diameters ranging from 20 to 150 nm whilenanowhiskers formed by RIE have diameters of 40–80 nm and a height between 1.4 and1.7 µm. A comparative study of the vibrational spectrum (including optical and interfacephonons) of the nanostructures using conventional macro-Raman and micro-Ramanscattering as well as surface-enhanced Raman scattering is presented.

Improved Etched Surface Morphology in Electron Cyclotron Resonance-Reactive Ion Etching of GaN by Cyclic Injection of CH4/H2/Ar and O2 with Constant Ar Flow

Electron cyclotron resonance reactive ion etching (ECR-RIE) conditions for GaN using CH4/H2/Ar are investigated. GaN can be etched even with continuous etching using CH4/H2/Ar when Ar gas of a higher flow rate is introduced, but only rough etched surfaces are obtained. A cyclic injection method using CH4/H2/Ar etching gas and O2 ashing with constant Ar flow is introduced for GaN etching for the first time, and a rather high etch rate and very smooth etched surfaces are successfully obtained. The cyclic injection of CH4/H2 and O2 prevents deposition of carbon polymers by oxygen plasma, and constant Ar flow removes the surface oxidized layer formed during the O2 ashing by Ar+ ion etching. Under the optimized etching condition, an etch rate of 34 nm/min and a good morphology of etched surfaces (rms of less than 1.0 nm) are obtained.

Photonic crystal waveguides with propagation losses in the 1dB∕mm range

High-quality photonic crystal waveguides have been fabricated in the InGaAsP∕InP and GaAs∕AlGaAs material systems aimed at the communication wavelengths of 1.55 and 1.31 μm. The waveguides consist of omitted rows of holes in a triangular lattice of air holes etched into the semiconductor heterostructures by electron cyclotron resonance reactive ion etching. Efficient waveguiding has been observed in optical transmission measurements, with waveguide losses ranging from 1.5dB∕mm for a waveguide with three missing row of holes (W3) to 0.2dB∕mm for seven missing rows (W7).

CH 4 -based dry etching of high Q InP microdisks

CH 4 -based InP dry etching techniques have been investigated by using electron cyclotron resonance etching and reactive ion etching (RIE) methods to obtain microdisk and ring structures having smooth, vertical sidewalls, and specular etched surfaces. The RIE method is chosen for the device etch process owing to the higher perfection of the surfaces generated by this process. Excess CH4 introduced in the InP RIE process was found to generate excessive polymers and resulted in sloped, rough sidewalls. A multistep RIE process involving a high-pressure (75 mTorr) condition, followed by a lower pressure (15 mTorr) etching to the completion of the structure was developed that leads to very smooth sidewalls. This process was successfully utilized in the fabrication of vertically coupled microdisk resonators.

Reactive ion etching of deeply etched DBR-structures with reduced air-gaps for highly reflective monolithically integrated laser mirrors

An electron cyclotron resonance reactive ion etching process is investigated for the fabrication of third order deeply etched distributed Bragg reflectors suitable for monolithically integrated laser mirrors. At a period of 550-nm, air-gaps as small as 150 nm down to a depth of 4.5 μm were realized in AlGaAs/GaAs heterostructures. The reflectivity of the deeply etched DBRs was tested by the device properties of microlasers with a cleaved facet on one side and a DBR on the other side. From the light output characteristic of the lasers a systematic improvement of the mirror reflectivity is observed by reducing the air-gap.

Technology and realization of metallic curved waveguide mirrors in polymer film waveguides based on anisotropic plasma etching

Curved waveguide mirrors acting in the same way as cylindrical lenses are fabricated in a polymer film waveguide. The waveguide material used is Cyclotene 3022™ (bisbenzocyclobutene) developed by the Dow Chemical Company. The waveguide mirror structure is dry etched into the film waveguide employing electron cyclotron resonance reactive ion etching. To enhance their reflectivity the vertical dry-etched sidewalls are metallized. Curved polymer film waveguide mirrors showing a reflectivity of 75% are realized.

Zn-vapor diffused Er:Yb:LiNbO 3 channel waveguides fabricated by means of SiO 2 electron cyclotron resonance plasma deposition

We report here the fabrication method and operation of Zinc-vapor diffused channel waveguides on Erbium/Ytterbium (Er/Yb)-doped Lithium Niobate (LiNbO 3). electron cyclotron resonance (ECR) plasma deposition technique, UV photolithography and Reactive Ion Etching (RIE) are used to define an SiO 2 mask for pattern transfer. The whole process is performed at low temperatures eliminating typical LiO 2 out-diffusion problems and achieving low surface damage. The flexibility of the fabrication technology has been shown to be potentially applicable to integrated optics. EDAX measurements reveal good confinement and homogeneity of the diffused regions. Atomic Force Microscopy (AFM) surface characterization shows the swelling of the diffused areas, consistent with the topoepitaxial growth of a Zn x Li y Nb z O w layer.

Electron cyclotron resonance reactive ion etching of GaAs in chlorine-methane

Highly anisotropic ECR etching of sub-half-micron features in GaAs and AlGaAs using a Cl 2CH 4 mixture is reported. Etch depths greater than 1 μm with aspect ratios nearing 5:1 were achieved while maintaining vertical sidewalls, sharp transitions and smooth etched surface.

Effect of N2 Addition on Aluminum Alloy Etching by Electron Cyclotron Resonance Reactive Ion Etching and Magnetically Enhanced Reactive Ion Etching

Aluminum alloy etching is an important process in ultra-large-scale integration (ULSI) fabrication. We investigated the effect of N2 addition to Cl2+BCl3 gas mixture on aluminum-copper alloy etching by electron cyclotron resonance reactive ion etching (ECR-RIE) and magnetically enhanced reactive ion etching (MERIE). In ECR-RIE, N2 addition was effective in suppressing residues and post-etch corrosion of aluminum alloy interconnects; on the other hand, in MERIE, N2 addition promoted the formation of residues and post-etch corrosion. This difference is probably caused by BClX+ in plasma, because it was found by mass spectral analysis that N2 addition increased the amount of BClX+ in plasma of ECR-RIE, but it decreased that in plasma of MERIE.

Computer Simulation and Measurement of Capacitance-Voltage Characteristics in Quantum Wire Devices of Trench-Oxide MOS Structure

We have proposed the trench-oxide metal-oxide-semiconductor (MOS) structure as a novel quantum wire device. In this paper we present results of computer simulation based on a self-consistent system and calculated quantized electron distribution and capacitance-voltage (C-V) characteristics. We have also fabricated the quantum wire MOS structure using electron beam lithography and electron cyclotron resonance reactive ion etching method and carried out measurements of C-V characteristics at 0.55 K. Possible evidence of one-dimensional quantum effect is obtained for the first time from C-V measurements using the 28 nm-wide trench-oxide structure.

Magnetically confined plasma reactive ion etching of GaAs/AlGaAs/AlAs quantum nanostructures

An electron cyclotron resonance reactive ion etching machine has been successfully run under low magnetic field conditions. We call this the magnetically confined plasma condition. Under this condition, a new process using SiCl4 with a small amount of O2 has been developed for etching nanometer scale structures on GaAs, AlGaAs, and AlAs multilayer materials. The effects of the percentage of O2, the rf power, the microwave power, and the flow rate are described. 100 nm quantum dots have been etched on multiple quantum well materials to a depth of about 1 μm. Vertical and smooth sidewalls were obtained on these nanostructures. Poly-methylmethacrylate (PMMA) electron beam resist can be used directly as a dry etch mask, and the selectivity between GaAs and PMMA can be as high as 28:1. Raman spectroscopic studies showed that the process induced no detectable damage to the surface for an etch depth of 130 nm and only very little damage for deeper etching.

Effects of etch chemistry on SF6-based tungsten etching by electron cyclotron resonance reactive ion etching

Studies of etch chemistry effects on SF6-based tungsten etching have been performed in an electron cyclotron resonance microwave reactive ion etching system. The etch chemistry and, therefore, reactive species concentrations were varied in several ways and the effect of these variations on etch rate and anisotropy of etched features were evaluated. Reactive species concentrations were altered by varying the residence time in a pure SF6 plasma or by introducing argon or nitrogen in the SF6 plasma under constant residence time. For pure SF6 and under conditions similar to those in a parallel plate radio frequency system, the tungsten etch rate was more than three times greater—presumably the results of higher dissociation efficiencies. As residence time was increased from 1 to 30 s the etch rate was decreased by greater than a factor of 2 and linewidth loss was reduced from better than 50 to 5%. Addition of argon to the plasma reduced the etch rate while maintaining short residence times. The addition of nitrogen to SF6 resulted in a complex behavior that provided optimum etch rate with minimum linewidth loss for a 50/50 mixture. In evaluating the behavior, sidewall passivation processes and competitive reactions in the gas phase are discussed.

Proposal of Trench-Oxide Metal-Oxide-Semiconductor Structure and Computer Simulation of Silicon Quantum-Wire Characteristics

We propose “trench-oxide metal-oxide-semiconductor (MOS)” structures as a novel formation method of silicon-based low-dimensional quantum structures, which are considered to be basic elements of future ultrahigh-speed and ultralarge-scale integrated devices. In this method, the applied gate voltage forms the potential well confined in an additional direction defined by ultrafine “trenches” on the oxide layer of the MOS structure. We characterize “trench-oxide MOS” quantum wire structures by two-dimensional numerical calculation of the shape of the potential well, the subband energy levels and the electron density, and investigate the possibility of the experimental observation of quantized density of states peculiar to quantum wires, by measuring capacitance-gate voltage (C-V) characteristics of “trench-oxide MOS capacitors.” We also have successfully fabricated “trench-oxide MOS” quantum wires with the width of 16 nm using electron beam (EB) lithography and electron cyclotron resonance reactive ion etching (ECR-RIE).

Identification of volatile products in low pressure hydrocarbon electron cyclotron resonance reactive ion etching of InP and GaAs

Volatile species produced during CH4/H2 and CH4/H2/Ar electron cyclotron resonance (ECR) reactive ion etching (RIE) of InP and GaAs at pressures of 2 mTorr have been investigated with secondary ion mass spectrometry diagnostics. A CH4/H2 ECR plasma with −120 V rf bias on the sample stage is found to etch InP but not GaAs. However, etching of GaAs does occur at this bias if the CH4/H2 mixture is diluted with Ar, showing the importance of physical bombardment to ‘‘activate’’ the GaAs surface. Group V hydrides are usually considered the most dominant volatile products in hydrocarbon RIE. In this work, it is shown that Ar dilution of a CH4/H2 mixture significantly increases the proportion of group V organometallic to hydride species in both GaAs and InP etching. More important, the main group III volatile ions from this etching process have been positively identified for the first time as In(CH3)+2 and Ga(CH3)+2 ions in InP and GaAs etching, respectively. Finally, the application of volatile product identification to end-point detection is demonstrated with a depth resolution better than 50 Å.

Optical properties of modulation-doped quantum wires fabricated by electron cyclotron resonance reactive ion etching

Modulation-doped GaAs/AlGaAs quantum wires have been fabricated using electron-beam lithography followed by electron-cyclotron resonance reactive ion etching to selectively deplete the electron gas. This technique has the advantages of low damage to the quantum well, strongly anisotropic etching, and reproducible control over the etch depth. The quantum wires exhibit high photoluminescence efficiencies when etched as close as 200 Å to the electron gas. The fundamental gaps show the large optical red shifts associated with strongly spatially indirect transitions. The spacings between one-dimensional subbands determined from inelastic light scattering measurements are larger than 2 meV.

A Comparison Between Dry Etching with an Electron Cyclotron Resonance Source and Reactive Ion Etching for GaAs and InP

ABSTRACTEtching with an electron cyclotron resonance (ECR) source provides several advantages over conventional reactive ion etching (RIE). In this work, the results of GaAs and InP etching using a multipolar ECR source are presented and compared to RIE. The effects of microwave and rf power, gas composition, pressure, and source to sample distance on the etch characteristics of GaAs and InP were evaluated. Three different etch gases were used including CCl2F2, BCl3, and Cl2. The influence of microwave power on etch characteristics is compared to conventional parallel plate system using rf power alone.

Sidewall damage in n+-GaAs quantum wires from reactive ion etching

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+-GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room-temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low-temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.