Reactive Ion Beam Etching Research Articles

Electrical damage induced by reactive ion-beam etching of lead-zirconate-titanate thin films

Ion-beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) thin films with x equal to 0.54 grown on Pt∕TiOx∕SiO2∕Si substrates has been performed using pure Ar gas and a varying CHF3∕Ar gas mixing ratio. The etch rate dependence on the process parameters (gas composition, current density, and acceleration voltage) has been investigated. PZT etch rate under 40% CHF3 in Ar can reach 100nm∕min with an acceleration voltage of 900 V and a current density of 0.7mA∕cm2 (in comparison to 35nm∕min in pure Ar). A selectivity ratio of 8 has been obtained between PZT and photoresist (1.3 in pure Ar). We have evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases less under a gas mixture than under a pure argon beam, and that the preferential etching observed at the grain boundaries under a pure argon beam disappears when we increase the proportion of CHF3 in the gas mixture. For some etching parameters (current density, acceleration voltage, and gas mixing ratio), we have observed electrical damage. C(V) and hysteresis loops P(E) measurements before and after etching have demonstrated these degradations. We have noted a large decrease of the permittivity after the etching process, independently of the current density and the acceleration voltage. The ferroelectric damage was illustrated by a large increase of the average coercive field after etching in pure argon. The presence of CHF3 in the plasma partially reduces the damage.

Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN (0 0 0 1) substrates

This paper attempts to form AlGaN/GaN quantum wire (QWR) network structures on patterned GaN (0 0 0 1) substrates by selective molecular beam epitaxy (MBE) growth. Substrate patterns were prepared along 〈 1 1 2 ¯ 0 〉 - and 〈 1 1 ¯ 0 0 〉 -directions by electron cyclotron resonance assisted reactive-ion beam etching (ECR-RIBE) process. Selective growth was possible for both directions in the case of GaN growth, but only in the 〈 1 1 2 ¯ 0 〉 -direction in the case of AlGaN growth. A hexagonal QWR network was successfully grown on a hexagonal mesa pattern by combining the 〈 1 1 2 ¯ 0 〉 -direction and two other equivalent directions. AFM observation confirmed excellent surface morphology of the grown network. A clear cathodoluminescence (CL) peak coming from the embedded AlGaN/GaN QWR structure was clearly identified.

High temperature resistant antireflective moth-eye structures for infrared radiation sensors

The Fresnel reflections occurring at the interfaces of a silicon wafer shall be drastically reduced by reactive ion beam etching of so called moth-eye structures into both surfaces of the wafer. This kind of impedance matching is advantageous to a multilayer interference system when the silicon wafer shall be used as an entrance window for high temperature thermopile infrared radiation sensors and emitters. The transmission was measured to be increased by more then 60%, compared to a polished silicon wafer.

Dry Etching of PZT Thin Films for Bilayer Actuator Realization

Reactive Ion Beam Etching (RIBE) of Pb(Zr,Ti)O3 thin film is performed for the via formation on a bilayer actuator. This actuator has been developed in the frame of health monitoring system for aircraft composite structures. The bilayer realization requires bore vias to connect the different conductive layers. It represents a 4 μ m thick PZT layer to etch. The etching conditions have been optimized to obtain high PZT etch rate and high selectivity ratio. The use of Ar/CHF3 gas mixture allows to reach a PZT etch rate of 950 Å/min, and a PZT/photoresist selectivity of the order of 7. Such a result makes possible the etching of high PZT thickness (several μ m). We have demonstrated that RIBE was an appropriate technique to perform PZT vias.

Reactive Ion Etching and Ion Beam Etching for Ferroelectric Memories

The fabrication of the FeRAM requires the development of etching processes for ferroelectric thin films and electrodes as well as deposition processes. But different etching methods have different impacts such as resolution and process-induced damages. In this paper, reactive ion etching (RIE) and ion beam etching (IBE) for ferroelectric thin films and Pt electrodes have been studied in details. Different silicon-based ferroelectric thin films and their corresponding electrodes have been etched successfully. To compensate the possible oxygen loss caused by the etching process, the samples should be annealed in O2 at 550°C for 30 min after RIE and IBE etching.

A novel copper damascene technique for power loaded SAW structures

ABSTRACTThe damage of finger electrodes of surface acoustic wave (SAW) structures due to material transport (acoustomigration) forming voids and hillocks is strongly associated with the SAW stress field, the temperature and properties of the fingers material and their configuration. By application of Cu thin films a significant higher performance of SAW structures with respect to power durability, reliability and lifetime is obtained. In the present paper Cu finger electrodes of a special power SAW test structure were fabricated in trenches of STX quartz substrates using the copper damascene technique. In comparison with conventional finger electrodes located on the substrate surface, such an embedded structure enables some new features regarding their acoustical and acoustomigration behavior. So high power SAW load cannot cause fatal failures by shorts between adjacent fingers. This fact is specially important for SAW devices in the GHz range. The trench structuring into the substrate was carried out by reactive ion (RIE) or ion beam etching (IBE) technique using a metallic hard mask. Etched trenches were filled with a conductive Ta-Si-N / Cu-layer system by magnetron sputtering in a cluster tool, and structured by a chemical-mechanical polishing (CMP) process. Subsequently, after cleaning an insulating Ta-based barrier (system Ta-Si-O / Ta-Si-N) layer was deposited on the wafer surface. This covering layer also acts as a protective coating. Such a metallization system enables sufficient bonding properties using Al-wires. First results of electrical measurements show that travelling SAW could be excited in quartz substrates.

Silver Patterning by Reactive Ion Beam Etching for Microelectronics Application

AbstractDry etching of silver for the metallization in microelectronics is investigated. Etching is performed using an electron-cyclotron-resonance reactive-ion-beam-etching system (ECR-RIBE) in an Ar/CF4 or Ar/CF4/O2 mixture. The etch characteristics are strongly affected by ion energy (beam voltage and microwave energy); the O2 concentration in the reactive mixture has only a small effect. An anisotropic, smooth etch profile and clean surface are obtained. Focused ion beam (FIB) and atomic force microscopy (AFM) have been used to study the etched profile and the roughness, respectively.

XPS studies on damage evaluation of single-crystal diamond chips processed with ion beam etching and reactive ion beam assisted chemical etching

A number of ion beam techniques were examined for their ability to etch single-crystal diamond. Both etching ability and the amount of resulting surface damage were examined. The techniques evaluated included ion beam etching (IBE), reactive ion beam etching (RIBE), ion beam assisted chemical etching (IBAE) and reactive ion beam assisted chemical etching (RIBAE). Etching rate of RIBAE processing of diamond is higher than other processing methods and it is 1.98 μm/h. When using the oxygen ion beam methods (RIBE and RIBAE processing), adsorption of oxygen occurs on the sample surface, and subsequent annealing treatment desorbs the oxygen that was previously adsorbed on surface of the diamond. Moreover, when the annealing treatment was carried out on the diamond with RIBE processing, damage of the diamond surface was observed using X-ray photoelectron spectroscopy (XPS). As a result, with all of the ion beam processes studied, the diamond crystal structure is changed into graphite or amorphous structures. Among the four processing methods, the RIBAE processing method exhibits the least amount of damage on the diamond crystal structure. Previously in this type of research, ion beam damage was seldom investigated. We also show that XPS measurement is an effective means for the evaluation of ion beam damage.

Deposition of SiO 2 films by low-energy ion-beam induced chemical vapor deposition using hexamethyldisiloxane

Room-temperature preparation of silicon dioxide films with smooth surfaces and small carbon was achieved by low-energy ion beam induced chemical vapor deposition (IBICVD) with a bubbling system for hexamethyldisiloxane (HMDSO). When prepared using bubbled HMDSO and assisted O 2 gas under irradiation of 150 eV Ar ions, the film contained carbon of 0.2% and the root mean square of the surface roughness of the film was 2.0 nm. However, when prepared using the bubbled HMDSO under irradiation of 150 eV oxygen ions, the film contained carbon less than 0.1%, and the surface roughness was 0.25 nm. It is considered that low-energy oxygen ion bombardment promotes not only chemical reaction and dissociation of HMDSO but also reactive ion beam etching on the film surface.

Fabrication of Four-Probe Fine Electrodes Using Scanning-Probe Nanofabrication

We have fabricated four-probe Pt electrodes on a sapphire substrate by scanning-probe nanofabrication and reactive ion beam etching. Surface roughness, gap width and height of the fabricated electrodes were 0.3 nm, 150 nm and 4 to 5 nm, respectively. In order to test the quality of the fine electrodes, we evaluated the current through a multi-walled carbon nanotube (MWNT) placed on the electrodes. The measured two-probe resistance of the MWNT was 130 kΩ which included the contact resistance, while the leakage resistance was larger than 1 TΩ.

Fabrication of AlGaN/GaN Quantum Nanostructures by Methane-Based Dry Etching and Characterization of Their Electrical Properties

Attempts were made to fabricate AlGaN/GaN quantum nanostructures by dry etching, and to assess etching damage through characterization of their electrical properties. An electron-cyclotron-resonance-assisted reactive ion beam etching (ECR-RIBE) process using a CH4-based gas mixture was applied to AlGaN/GaN heterostructure wafers, and the process was characterized and optimized using in situ X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements. Addition of nitrogen gas to the standard gas mixture of CH4/H2/Ar was found to be extremely effective in improving the etching characteristics, etched surface morphology and surface stoichiometry, and in preventing accumulation of Ga and Al metallic clusters. After testing the fabrication feasibility of various nanostructures, AlGaN/GaN quantum wire (QWR) structures of various widths were fabricated, and their electrical characteristics were investigated to detect etching damage. Clear Shubnikov-de Haas (SdH) oscillations were observed at 1.6 K in the QWR structures under strong magnetic fields. A nonlinear Landau plot indicated the presence of a one-dimensional confinement potential with a subband energy spacing of 1.4 meV. The measured wire conductance can be well explained by a simple theory, taking account of the sidewall depletion of 23 nm due to Fermi level pinning. No clear changes in sheet carrier concentration and mobility due to plasma damage were detected.

Comparison of surface morphologies of SiO 2 films prepared by ion-beam induced chemical vapor deposition and ion-beam assisted deposition

The surface topographies of silicon dioxide films prepared by low-energy ion-beam induced chemical vapor deposition (IBICVD) and ion-beam assisted deposition (IBAD) were studied using an atomic force microscopy (AFM). In the case of IBICVD, when prepared using bubbled hexamethyldisiloxane (HMDSO) and assisted O 2 gas under irradiation of 150 eV Ar ions, the root mean square (RMS) of the surface roughness of the film was 2.0 nm. However, when prepared using the bubbled HMDSO under irradiation of 150 eV oxygen ions, the RMS deduced to 0.25 nm. In the case of IBAD, when deposited using evaporated silicon monoxide under irradiation of 150 eV oxygen ions, the RMS was 0.20 nm. As a reference, the RMS of fused silica was changed from original 0.70–0.40 nm after irradiated of 150 eV oxygen ions. It is concluded that low-energy oxygen ion bombardment not only promotes chemical reaction and dissociation of precursor but also leads to a smooth surface due to reactive ion beam etching on the film surface.

Reactive Ion Beam Etching of In-Containing Compound Semiconductors in an Inductively Coupled Cl2/Ar Plasma

Reactive ion beam etching (RIBE) of InP, InGaAs, InGaAsP, InAs, InAlAs and InSb was performed in a Cl2/Ar mixture using an inductively coupled plasma source. The etch rate and etch yield for InP showed the most significant variation with substrate temperature, while all the material etch rates were strongly dependent on ion energy. The etching was dominated by ion-assisted mechanisms up to ion energies of ∼600 eV and by physical sputtering at higher energies. The high density plasma accelerates etch rates predominantly by ion-neutral synergism and not by subverting the usual etch reactions.

Reactive Ion Beam Etching of PZT Thin Films

Lead titano-zirconate ferroelectric thin films have developed a great interest for their applications in memory devices, and more recently in microelectromechanical systems because of their interesting piezoelectric properties. The patterning has become an essential element for PZT integration in devices. Reactive ion beam etching of sputtered PZT(54/46) thin films has been performed using Ar/CHF 3 gas. The dependence of etch rate and selectivity with the etching parameters has been investigated. PZT etch rate and selectivity reaches 900 Å/min and 7.5 respectively. We have evaluated the PZT surface damage by contact mode AFM. It appears that the roughness increases after ion bombardment. We have observed electrical damaged. These degradations are underlined by carrying out C(V) and hysteresis loops before and after etching.

Nanofabrication Using Atomic Force Microscopy Lithography for Molecular Devices

We have fabricated fine metal electrodes on a smooth insulating substrate for measurement of molecular devices properties. Nanometer-scale four-term electrodes resist patterns were fabricated using a system based on atomic force microscopy (AFM) and transferred to metal by reactive ion beam etching (RIBE). We obtained Pt, Au, and Ti four-term electrodes having linewidths of less than 100 nm on a smooth surface, whose roughness was less than 1 nm.

Etching behaviour of pure and metal containing amorphous carbon films prepared using filtered cathodic vacuum arc technique

A preliminary study on the etching behaviour of pure and metal containing amorphous carbon (a-C) films has been studied using reactive ion etching (RIE) as well as reactive ion beam etching (RIBE). The RIE etching of a-C films, prepared from pure and 1 at.% Al containing carbon cathodes, displays a significant increase in etching rate with increase in discharge power. The inclusion of even a small percentage of metal causes a drastic reduction in the etching rate. The films that contain higher percentages of metal become more difficult to etch using RIE with oxygen plasma. Therefore, etching of the samples by RIBE technique using a plasma mixture of oxygen and argon has been carried out. A significant reduction in the etching rate with increasing metal content was observed for both Al and Ti containing a-C films. This led us to try etching of Ti containing a-C films by RIE technique using a plasma mixture of CF 4 and oxygen. The result shows that the etching rate increases with increasing Ti content. The analysis of the etched surfaces measured by visible Raman indicates that all the surfaces remain almost the same regardless of the processes undergone. However, the morphology measured using Atomic Force Microscopy (AFM) shows that the surface roughness increases significantly after etching, especially for the pure carbon films.

Patterning of wave guides in LiNbO3 using ion beam etching and reactive ion beam etching

A number of current and future optoelectronic components require the creation of waveguides in LiNbO3. In order to accomplish this, trenches between one and ten microns deep must be patterned into the LiNbO3 substrate. We have demonstrated the formation of near-vertical, smooth-walled trenches up to ten microns deep using Ar ion beam etching (IBE) and Ar/CHF3 reactive ion beam etching (RIBE) processes. Both Ar IBE and Ar/CHF3 RIBE processes can achieve etching rates of up to 100 nm/minute. Our patented RIBE process [K. E. Williams, et al. U.S. Patent No. 6,238,582 (29 May 2001)] has the additional advantage of providing up to a 5:1 selectivity for etching the LiNbO3 over a photoresist mask. The collimated beam available with IBE and RIBE allows control over feature profiles and redeposition removal. Using a combination of RIBE and a multiangle process, the sidewall angle and smoothness of the mask have been transferred into LiNbO3 substrates to depths between one and ten microns. This depth range can be expanded in either direction if an appropriate mask can be fabricated.

Corrugated neat thin-film conjugated polymer distributed-feedback lasers

Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The spectral width of the DFB laser (down to ΔλDFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (ΔλTWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy densities.

Reactive Ion Beam Etching of GaN and AlGaN/GaN for Nanostructure Fabrication Using Methane-Based Gas Mixtures

The basic etching characteristics of electron cyclotron resonance reactive ion beam etching (ECR-RIBE) of GaN and AlGaN/GaN using methane-based mixtures have been studied in view of application to nanostructure fabrication. GaN could be etched by using a gas mixture of CH4/H2/Ar at a rate of about 10 nm/min, which is suitable for nanostructure fabrication. The etching process was also applicable to the standard AlGaN/GaN heterostructure. Etching along <1100> and <2110> stripe patterns revealed {0111} and {1121} sidewall facets, respectively, indicating that the etching is a facet-revealing process, being dominated by chemical reactions with low physical damage. However, the etching depth showed anomalous saturation at 400–500 nm, and the roughness of the surface increased with time. An in situ X-ray photoelectron spectroscopy (XPS) study detected the formation of Ga droplets. By adding N2 into the gas mixture, Ga droplet formation was suppressed, etch depth saturation disappeared and a smooth etched surface was obtained. Using the optimized etching conditions with N2 addition, an AlGaN/GaN nanowire structure with a wire width of 110 nm has been successfully fabricated.

An InGaAsP/InP Twin-Guide Laser Diode with Rectangular Ring Cavity

A twin-guide laser diode, which consists of an active waveguide with rectangular ring cavity and a transparent output waveguide coupled to each other as a directional coupler, has been fabricated and its performance has been investigated. Four straight waveguides and total internal reflection (TIR) mirrors conceptually construct the ring cavity, which enhances the traveling wave characteristics such as mode purity. Lasing light is coupled to the transparent passive output waveguide by vertical evanescent coupling. The cavity mirrors were fabricated by Ar/Cl2/H2 reactive ion beam etching (RIBE) at the elevated process temperature to enhance the desorption rate of InClx for a smooth etching surface. The threshold current was measured to be 230 mA, corresponding to a threshold current density of 4 kA/cm2. The emission peak wavelength is approximately 1.56 µm. The fabricated device shows single mode operation at current levels up to 1.4 times the threshold current.