Plasma Reactive Ion Etching Research Articles

Techniques of cryogenic reactive ion etching in silicon for fabrication of sensors

Cryogenic etching of silicon, using an inductively coupled plasma reactive ion etcher (ICP-RIE), has extraordinary properties which can lead to unique structures difficult to achieve using other etching methods. In this work, the authors demonstrate the application of ICP-RIE techniques which capitalize on the cryogenic properties to create different sensors geometries: optical, electrical, magnetic, and mechanical. The three techniques demonstrated are (1) single step deep etches with controllable sidewall profiles. Demonstrating this, silicon pillars with over 70μm depth and less than 250nm sidewall roughness were etched using only 1.6μm of photoresist for use as solar cells. (2) Using the cryogenic etch for thick metallization and liftoff with a thin photoresist mask. Demonstrating this second technique, a magnetic shim was created by deposition of 6.5μm of iron into 20μm deep etched trenches, using the remaining 1.5μm photoresist etch mask as the liftoff mask. Using the same technique, 15μm of copper was lifted off leaving a 20μm deep plasma enhanced chemical vapor deposition silicon oxide coated, silicon channel with copper. (3) Use of a two step cryogenic etch for deep etching with reduced sidewall undercutting. This was demonstrated by fabrication of deep and anisotropic microelectromechanical systems structures; a mechanical resonator was etched 183μm deep into silicon with less than 3μm of undercutting. This work also describes the etch parameters and etch controls for each of these sensors.

Size-Dependent Strain Relaxation and Optical Characteristics of InGaN/GaN Nanorod LEDs

In this paper, InGaN/GaN nanorod LEDs with various sizes are fabricated using self-assembled Ni nanomasks and inductively coupled plasma-reactive ion etching. Photoluminescence (PL) characteristics exhibit size-dependent, wavelength blue shifts of the emission spectra from the nanorod LEDs. Numerical analyses using a valence force field model and a self-consistent Poisson, Schrodinger, and drift-diffusion solver quantitatively describe the correlation between the wavelength blue shifts and the strain relaxation of multiple quantum wells embedded in nanorods with different averaged sizes. Time-resolved PL studies confirm that the array with a smaller size exhibits a shorter carrier lifetime at low temperature, giving rise to a stronger PL intensity. However, the PL intensity deteriorates at room temperature, compared to that of a larger size, possibly due to an increased number of surface states, which decreases the nonradiative lifetime, and hence reduces the internal quantum efficiency.

Fabricating gratings on nitrides grown by MOVPE for DFB lasers

AbstractIn an achievement we believe marks a first, we succeeded in fabricating corrugation gratings in indium‐nitride (InN) films grown by metal organic vapor phase epitaxy (MOVPE) for distributed feedback lasers. The resulting temperature‐independent devices are suitable for wavelength demultiplexing and modulation in optical communications systems. The grating periods are in the first‐order wavelength region of 1.55 μm. We also formed gratings in gallium nitride epitaxial layers, applying electron‐beam (EB) lithography to form grating patterns in nitride substrates and inductively‐coupled plasma reactive ion etching (ICP‐RIE) to transfer EB resist patterns to nitrides. The depth of the grating grooves can be controlled by adjusting ICP‐RIE etching times to attain suitable coupling coefficients for forward and backward propagating waves in DFB lasers. We also introduce UV imprinting, a new grating fabrication technique that offers significant promise. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Width and temperature dependence of hysteretic current–voltage character in long Niobium microbridges

We report a study of the switching behavior in the current–voltage characteristics of long (∼8 μm) Nb microbridges in the hysteretic regime. Microbridges of various widths, ranging from . 71 μ m to 3.7 μ m , were prepared via standard optical lithography and reactive plasma etching techniques and the switching behavior was studied in a temperature range of 0.8 T c ⩽ T ⩽ T c . The current driven switching from superconducting to normal state of the bridge was analyzed in the Ginzburg–Landau formalism while the resistive-to-superconducting switching was analyzed using the hotspot model.

Evolution of metal-compound residues on the walls of plasma etching reactor and their effect on critical dimensions of high-k/metal gate

It was found that critical dimensions of high-k/metal gates obey the multivariate linear approximation with the precision of 3σ=±0.86nm, whose explanatory variables are amounts of metal compounds remaining on the plasma reactor walls. To measure their amounts, the authors assumed they are proportional to amounts of atoms sputtered out by Ar plasma and falling onto a Si wafers placed on a wafer stage. In this study, effects of metal compounds of W, Ti, Ta, and Hf, which are used to construct full-metal/high-k gates, were measured. It was found that Ti and Ta compounds dominate the fluctuation of critical dimensions and the dependency of their amount on wafer numbers being etched obeys a simple difference equation. From these results, they can estimate and minimize the fluctuations of critical dimensions in mass fabrications.

4H-SiC Trench Metal Oxide Semiconductor Field Effect Transistors with Low On-Resistance

The fabrication and characteristics of high-performance 4H-SiC trench metal oxide semiconductor field effect transistors (MOSFETs) are presented. Vertical trench etching of SiC without sub trenches was performed by inductive coupled plasma-reactive ion etching (ICP-RIE) with SF6, O2, and HBr. It was found that the drain–source current (Ids) of a single channel plane was strongly dependent on the crystallographic planes, but that of unit cells was almost independent of the crystallographic planes. Specific on-resistance (Ron,sp) at gate–source voltage (Vgs)=20 V, drain–source voltage (Vds)=1 V is estimated to be 2.9 mΩ cm2, and the blocking voltage is 900 V. Moreover, Ids at Vds=5 V is over 100 A. The chip is 3.0×3.0 mm2. The lowest on-resistance in the fabricated trench MOSFETs is 1.7 mΩ cm2 and the blocking voltage is 790 V. The chip is 0.5×0.5 mm2.

GaN MOS Capacitors and FETs on Plasma-Etched GaN Surfaces

The electrical characteristics of gallium nitride (GaN) metal-oxide-semiconductor (MOS) capacitors and field-effect transistors (FETs) made on as-grown surfaces, dry-etched surfaces using reactive-ion etching (RIE), and wet-etch treated surfaces after the dry etch were measured. Capacitance and conductance techniques were used to obtain the MOS properties for capacitors. Devices with only an RIE plasma dry-etch process have poor yield and noisy capacitance in the low-frequency accumulation region. Those on dry/wet-etch treated samples have more negative ultraviolet (UV) assistant capacitance-voltage (CV) shift, and higher interface-state densities than those on as-grown samples, but have similar surface potential fluctuation. Threshold voltages of 2 V for an as-grown GaN MOSFET and 1 V for a dry/wet-etched MOSFET were measured. Maximum field-effect mobility for long-channel (Lch = 100 μm) MOSFETs on the as-grown GaN wafer and the dry/wet-etched GaN wafer were obtained as 167 cm2 V−1 s−1 and 119 cm2 V−1 s−1, respectively. The higher interface trap density and lower field-effect mobility indicate that post-plasma-etch wet etching can only partially remove the damages from RIE.

Mechanism of reducing line edge roughness in ArF photoresist by using CF[sub 3]I plasma

The roughening mechanism of ArF photoresist during etching was investigated to find out why CF3I gas reduces the line edge roughness (LER) in the photoresist pattern better than CF4 gas. Since the plasma of reactive ion etching (RIE) consists of ultraviolet (UV) photons, radicals, and ions, the authors used a UV lamp and a neutral beam source for evaluating the effect of different plasma compositions on the photoresist roughness. The roughness was found not to increase only by UV photons or F radicals, but increase under the CF4 RIE plasma which has both UV photons and F radicals. A C–F modified layer was generated on the resist surface because the UV damaged CO bonds reacted with F radicals and the resist surface became softer and shrank. Since CF3I plasma has a lower UV intensity and fewer F radicals compared with CF4 plasma, the shrinkage on the sidewall of the photoresist was suppressed and resulted in a smaller LER when this plasma was used.

High resolution, high sensitivity inorganic resists

New inorganic electron-beam resists have been developed on the basis of the aqueous chemistries of Zr and Hf. With a 30-keV electron-beam, resist sensitivities as low as 8 μC/cm 2 have been realized. At higher exposure doses, 15-nm lines and 36-nm dense features have been written with line-width roughness near 2 nm. In reactive-plasma etching, the resists exhibit etch resistance >7× that of thermal SiO 2.

X-ray diffraction study of gold nitride films: Observation of a solid solution phase

The structure of nitride containing gold films produced by reactive ion sputtering and nitrogen plasma etching is investigated using x-ray photoelectron spectroscopy and x-ray diffraction. It is found that gold nitride is a solid solution of nitrogen atoms dissolved in a fcc gold matrix. Differences between the strain and lattice parameters of gold and gold nitride films were observed and are explained by interstitial nitrogen present in the latter.

Generation and Assembly of Spheroid-like Particles

This paper reports a straightforward approach in generating spheroid-like particles and also the orientational orders observed in the self-assembly of these particles. Nonspherical particles, such as spheroid-like particles, are useful in both fundamental studies and industrial applications due to the geometry impact that they bring to the bulk properties of various material systems. Developing processes to generate nonspherical particles is an ongoing quest to meet the need of using such particles in different applications. The approach reported here takes advantage of a controlled chemical etching process. Exposing the spherical silica particles partially to carbon tetrafluoride in a reactive ion plasma-etching chamber transformed the particles from spherical shape into spheroid-like shape. A simple model is proposed to predict the geometry of the resulting nonspherical particles. The shape and dimension of the nonspherical particles generated through such a process matched well with the prediction of the model. The assembly of these spheroid-like particles showed a unique orientational order associated with the alignment of their axes. This approach will help further studies on the fundamental properties of the nonspherical particles, such as packing, rheology, and optical interaction.

Light Output Power Enhancement of GaN-based Vertical Light Emitting Diodes via Fabricating Surface Nanorod Arrays

In this research, we demonstrated two approaches to fabricate nanorod arrays on the surface of GaN-based vertical light emitting diodes (VLEDs). The first approach was via synthesizing single-crystal ZnO nanorod arrays in aqueous solution at room temperature. The light output intensity and wall-plug efficiency of the GaN-based VLEDs with the ZnO nanorod arrays shows 38.9 and 41.2% increases, respectively, at 200 mA current injections compared to that of a VLED without ZnO nanorod arrays. The second approach was formed by spinning nano silica spheres and inductively coupled plasma-reactive ion etching. The light output power of the VLEDs with the dry etched nanorod arrays showed about 40% enhancement than that without the nanorod arrays. The large enhancement of VLED with both ZnO or GaN nanorod arrays was mainly due to the total internal reflection destruction, and the gradually changed refractive index from the nanorod arrays layer.

MWIR HgCdTe Photodiodes based on high-density plasma-induced type conversion

A novel fabrication process for planar n-on-p junction HgCdTe infrared photodiodes has previously been demonstrated based on H2/CH4 plasma-induced type conversion in a parallel-plate reactive ion etching (RIE) tool. In this work, it is demonstrated that high-performance photodiodes can also be fabricated based on H2/CH4/Ar plasma-induced type conversion in an inductively coupled plasma (ICP) RIE plasma tool. This tool has significantly greater control over the plasma condition, and the plasma condition for the type conversion process is significantly different to that associated with the junction formation process that has previously been demonstrated based on the parallel-plate RIE reactor. Photodiodes have been fabricated based on different ICPRIE plasma process conditions, and characterized by current–voltage and noise measurements. The performance characteristics of these photodiodes are comparable to those reported for diodes, based on established fabrication processes based on ion implantation or ion beam milling. The effects of the ICPRIE process parameters used for junction formation on the respective photodiode performance characteristics are investigated in terms of the plasma-induced type conversion mechanisms.

Three-dimensional discharge simulation of inductively coupled plasma (ICP) etching reactor

More and more importance has been attached to inductively coupled plasma (ICP) in semiconductor manufacture. For a deep understanding of the plasma discharge process in the etching reactor, this study made a three-dimensional simulation on the Ar plasma discharge process with the commercial software CFD-ACE, which is according to the real experiment conditions and data supplied by North Microelectronic Corporation. The error of the simulation results is in the range of ±20% with credibility. The numerical results show that the three-dimentional spatial distribution of electron density is reduced from the chamber center to the wall. The distribution of electron density, electron temperature and power deposition is related to the shape and placement of the coil.

Seasoning of plasma etching reactors: Ion energy distributions to walls and real-time and run-to-run control strategies

Wafer-to-wafer process reproducibility during plasma etching often depends on the conditioning of the inside surfaces of the reactor. Passivation of reactor surfaces by plasma generated species, often called seasoning, can change the reactive sticking coefficients of radicals, thereby changing the composition of the radical and ion fluxes to the wafer. Ion bombardment of the walls may influence these processes through activation of surface sites or sputtering, and so the spatial variation of ion energies on the walls is important. These seasoning processes may occur during a single etching process or on a wafer-to-wafer basis. The seasoning of plasma etching reactors will be discussed using results from a computational investigation of p-Si etching in chlorine plasmas. The transport of etch products, passivation of walls, and sputtered products from walls are accounted for, as well as differentiating the ion energy distributions to different surfaces. A real-time, closed-loop control of etch rate to counter the effects of seasoning was achieved using the bias voltage as an actuator.

Ion-radical synergy in HfO2 etching studied with a XeF2/Ar+ beam setup

To gain more insight into fundamental aspects of the etching behavior of Hf-based high-k materials in plasma etch reactors, HfO2 films were etched in a multiple-beam setup consisting of a low energy Ar+ ion beam and a XeF2 radical beam. The etch rate and etch products were monitored by real-time ellipsometry and mass spectrometry, respectively. Although etching of HfO2 in XeF2/Ar+ chemistry is mainly a physical effect, an unambiguous proof of the ion-radical synergistic effect for the etching of HfO2 is presented. The etch yield for 400 eV Ar+ ions at a substrate temperature of 300 °C was 0.3 atoms/ion for Ar+ sputtering and increased to 2 atoms/ion when XeF2 was also supplied. The etch yield proved to follow the common square root of ion energy dependence both for pure sputtering and radical enhanced etching, with a threshold energy at room temperature of 69±17 eV for Ar+ ions and 54±14 eV for Ar+ ions with XeF2.

Void-Free Room-Temperature Silicon Wafer Direct Bonding Using Sequential Plasma Activation

Room-temperature Si/Si wafer direct bonding has been performed by an optimized sequential plasma activated bonding process. A shorter O2 reactive ion etching (RIE) plasma (∼10 s) treatment followed by treatment with N2 radicals for 60 s is used for surface activation. The activated wafers are brought into contact in ambient air. After storage at room temperature for 24 h, high bonding strength (∼2.25 J/m2) is achieved without requiring any annealing process. This value is close to the bulk-fracture strength of silicon. Furthermore, no annealing voids are observed at Si/Si interfaces even if the bonded wafer pairs are heated from 200 to 800 °C in subsequent processes. The bonding interfaces and their optical transmittances are also investigated. This void-free, room-temperature bonding technique based on sequential plasma activation is inexpensive and suitable for the microelectromechanical system manufacturing process and wafer-scale packaging.

Superconducting MgB2 nanobridges and meanders obtained by an electron beam lithography-based technique ondifferent substrates

In this work, we report on the fabrication and characterization ofMgB2 nanostructures on different substrates, namely silicon nitride and sapphire.Magnesium diboride films are fabricated by an all-in situ method consistingof the co-evaporation of B and Mg followed by in situ annealing at highertemperature. Samples thus obtained are characterized at low temperature and show aTc of about 34–38 K. The nanostructures are then defined by electron beam lithographycombined with physical etching (reactive plasma etching and ion milling).In this way, MgB2 nanostructures and meanders have been obtained with rather good electrical andtransport properties both on SiN and sapphire. The fabrication of superconductingMgB2 nanobridges on sapphire with a thickness of the order of a few tens of nanometersrepresents a step forward in the field of nanodevices, such as single-photon detectors, basedon this mid-temperature superconducting material.

NF<sub>3</sub>ガス系プラズマRIEを用いたLiNbO<sub>3</sub>単結晶のマスク非使用による微細表面加工

Possibility of the deep etching using plasma reactive ion etching (RIE) without an etching-mask (mask-less) for -Z and +Z parts formed on the same surface by partially polarization reversing LiNbO3 single crystal polarized in the direction of c-axis is investigated. NF3/H2 mixture gas was used. The etching rates, depths and the profiles of etched surfaces were evaluated by atomic force microscopy (AFM) and optical microscope. The etching rate for -Z surface was larger than that for +Z surface. The extension of +Z domain by the partially polarization-reversing was observed. Applying the high voltage quickly for the partially polarization-reversing, the area of +Z domain was extended compared with applying voltage slowly. Apparent step at the boundary between -Z and +Z parts formed on the same surface was observed. Using NF3/H2 mixture gas, segments are removed efficiently. It is concluded that RIE etching using NF3/H2 mixture gas is suitable for processing of LiNbO3 crystal surface without a etching-mask compared with CF4/H2 mixture gas.

Fabrication of InGaN/GaN nanorod light-emitting diodes with self-assembled Ni metalislands

We report the fabrication of InGaN/GaN nanorod light-emitting diodes (LEDs) usinginductively coupled plasma reactive-ion etching (ICP-RIE) and a photo-enhanced chemical(PEC) wet oxidation process via self-assembled Ni nanomasks. An enhancement by a factorof six times in photoluminescence (PL) intensities of nanorods made with the PEC processwas achieved in comparison to that of the as-grown structure. The peak wavelengthobserved from PL measurement showed a blue shift of 3.8 nm for the nanorods madewithout the PEC oxidation process and 8.6 nm for the nanorods made with the PECoxidation process from that of the as-grown LED sample. In addition, we havedemonstrated electrically pumped nanorod LEDs with the electroluminescence spectrumshowing more efficiency and a 10.5 nm blue-shifted peak with respect to the as-grown LEDsample.