Steep Sidewalls Research Articles

Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etching

Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.

Microfabrication of Magnetic Tunnel Junctions Using CH$_{3}$OH Etching

The 100-nm-scale CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) were fabricated using a CH3OH etching process. These MTJs have steep side walls and show clear MR loops. The distributions of magnetic properties of CH3OH etched MTJs were smaller than those of conventional Ar ion etched MTJs

Realization of Silicon Nitride Template for Nanoimprint: A First Result

A first result of realization of silicon nitride templates on 100mm silicon wafer as nanoinprint mold using simple wet etching method is reported in this paper. The process is based on traditional photolithograph and following buffer HF wet etching, which started from a p-type wafer with 400nm thermal silicon oxide, 200nm PECVD silicon nitride and 400nm PECVD silicon oxide sandwich layer. After patterning with lithography, the patterned resist is used as mask for the isotropic underlayer wet etching of silicon dioxide with buffer HF solution. Using the obtained nanosacle silicon dioxide lines as RIE dry etching mask, silicon nitride template of 100nm width with steep sidewalls is successfully realized.

Deep ridge GaN cw‐laser diodes

AbstractThe processing of homoepitaxial grown GaN based laser diodes by means of chemical assisted ion beam etching (CAIBE) is discussed. These laser diodes, emitting in the blue/UV spectral region, have been processed as buried ridge wave guide structures. Both, the influence of process parameters during etching such as the angle of incidence of the ions and gas fluxes as well as the impact of the ridge depth on the device performance will be analysed. Steep and smooth sidewalls of the ridge have been achieved by optimising the process parameters and by etching the ridge through the active region, cw‐lasing has been achieved. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Dependence of Thermal-Cycling-Induced Failure Mechanism on Topological Feature of Passivated Metallic Conductors in Plastic-Encapsulated Microelectronic Devices

This work presents how thermal-cycling-induced cracking in a device pattern is influenced by manipulating the topological feature of passivated metallic conductors. The modification of the topological feature is done by the variation of the sidewall slope of metallic conductors. In order to compare thermal-cycling reliability in two kinds of devices with different surface morphologies, each device is prepared to have pre-existing cracks along its edge region. The propagation behavior of the cracks is then investigated for each device. Discontinuous but fast crack propagation is observed for the device with the poor topological feature (i.e., 70°-sidewall slope) during thermal-cycling from -65 to 150 °C. On the other hand, continuous but limited crack growth is detected for the device with the improved topological feature (i.e., 130°-sidewall slope). The reason why cracking behavior differs, depending on the different re-entrant angle of each device pattern, is explained by numerical calculation. Finite-element method (FEM) work shows that the concentration of shear stress at the re-entrant corner of the passivated metallic conductor with the steep sidewall slope is responsible for such discontinuous crack propagation. Therefore, if the topological feature of passivated metallic conductors is improved, the rapid propagation of the pre-existing crack such as sawing-induced damage into the active device pattern will be effectively prevented to ensure thermal-cycling reliability.

Origin and evolution of closed depressions in central Belgium, European loess belt

AbstractClosed depressions (CDs) are lower lying areas where the sediment eroded from the surrounding soil surfaces draining towards the CD is trapped in the system. CDs have been reported in several regions of the European loess belt and are attributed either to natural processes (e.g. dissolution of subsurface horizons) or to human intervention (e.g. quarrying). Previous studies focussed mainly on cropland areas where, however, only few and largely filled in CDs remain.The objectives of this study were to i) assess the spatial distribution of CDs under forest and cropland, ii) to determine and compare the morphology of CDs under forest and under cropland, and iii) to determine the origin and age of these CDs under forest.In a study area located partly in ancient forest (13 km2) and partly in cropland (29 km2), a systematic survey revealed the presence of 71 CDs under forest (5·3 CD.km−2) and 30 CDs under cropland (1 CD.km−2). Comparison of their morphology showed that CDs under forest were significantly deeper, with steeper sidewalls and a smaller surface area because of the erosion and deposition processes acting on the CDs under cropland. By comparing CDs that had been under cropland for different time intervals, the rate of this morphological evolution could be reconstructed.Analysis of the soil stratigraphy of two representative CDs in the ancient forest area confirmed their origin as quarries. Most probably, calcareous loess was excavated since this soil horizon, about two to five meters thick, was completely absent within the CDs. Dating of the infilling of one CD by optically stimulated luminescence (OSL) shows that the CD filled in between the first century BC and the fourth century AD. This dating corresponds to the dating of sediment deposits in nearby, human‐induced gullies that were attributed to an agricultural land use phase between the 18th century BC and the third century AD.

Critical Dimension Measurement Using New Scanning Mode and Aligned Carbon Nanotube Scanning Probe Microscope Tip

We have developed a new scanning mode and an aligned carbon nanotube tip for atomic force microscopy (AFM) for measuring the critical dimension of deep structures. The aligned carbon nanotube (A-CNT) was assembled in the scanning electron microscope (SEM) chamber. The diameter of the tip is uniformly around 20 nm and the tip attachment angle is within ±1.5° to the sample normal. The aspect ratio (length/diameter) of the tip is greater than 30. The new scanning mode is composed of two functions, namely transporting the tip along the steep trench structure and detecting the sample surface. This mode can faithfully trace the steep side wall using a flexible CNT tip without damaging the tip. The critical dimension (CD) measurements of the shallow trench isolation (STI) were performed using the newly developed scanning mode and the A-CNT tip.

Gallium nitride powerbar transistors with via holes fabricated by laser ablation

Low ohmic through-hole vias are fabricated for AlGaN/GaN HEMT powerbar devices on SiC substrates using laser ablation technique. A complete processing technique has been developed. Through-wafer micro holes with an aspect ratio of 4 were drilled using pulsed UV laser machining. A plating technique on steep side wall could be established. Feasibility and performance of laser drilled via holes were tested with large power devices and proved successful up to the packaging level. The device demonstrated 14 dB of linear gain and a saturated output power of 40 W. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Realization of High-Power Highly Efficient GaInP/AlGaInP Ridge Laser Diodes for Recordable/Rewritable Digital Versatile Discs

Very efficient and reliable GaInP/AlGaInP red multiple-quantum-well laser diodes for recordable/rewritable digital versatile disc (DVD-R/RW) were successfully developed by low-damage fabrication. Because we adopted dry etching instead of conventional chemical wet etching for the steep ridge sidewalls of laser diodes (LDs), devices could be operated at a high output power over 200 mW at 70°C without showing any unstable higher-order transverse modes. In-situ monitoring tools in metal organic chemical vapor deposition (MOCVD) and dry etching were useful for controlling process parameters precisely, which enhances device characteristics and maintains the reproducibility of device fabrication. A very small beam aspect ratio of 1.78 with a very low vertical beam divergence angle of 15.3° at a high output power was achieved by optimizing the two-step n-cladding layer in our LD structures. These low values of the vertical beam divergence angle and aspect ratio are essential for minimizing the coupling loss between the LD and the objective lens in DVD pickups.

Ray waves in a pit lake

The special basin shape of Island Copper mine pit‐lake and its sharp salinity stratification make it an ideal place to investigate ray waves, or internal wave beams, as the more recent oceanographic literature tends to name the observed phenomenon. A first‐mode internal seiche oscillates the deep water vertically over the regular bench structure of the sidewalls at a distinct frequency. Theoretical considerations show the disturbances result in internal wave beams traversing the stratified water body at a known angle. Steep sidewalls prevent the ray waves from being trapped in the beach zone. Instead the reflection at the extremely strong pycnocline creates a vertical interference pattern. Here we numerically derive the vertical length scale of this interference to be 0.43 m. This scale is in full agreement with the repeated turbulence pattern discovered underneath the pycnocline.

Deep etching of epitaxial gallium nitride film by multiwavelength excitation process using F2 and KrF excimer lasers

The deep etching of GaN(0001) thin films epitaxially grown on Al2O3(0001) has been investigated by laser ablation using F2 and KrF excimer lasers. The simultaneous irradiation with F2 and KrF excimer lasers markedly improves etching quality compared with single-KrF excimer laser ablation and provides almost the same quality as that in the case of single-F2 laser ablation with a high etching rate. Additionally, the present method achieves the deep etching of a GaN film of more than 5 μm in depth with steep side walls at an angle of 87° by changing the laser incidence angle.

High-power 660-nm GaInP-AlGaInP laser diodes with low vertical beam divergence angles

We present 660-nm GaInP-AlGaInP ridge multiple-quantum-well laser diodes (LDs) reliably operating at high output power over 200 mW at 70/spl deg/C not showing unstable higher order lateral modes owing to an adoption of a dry etching method instead of a conventional chemical wet etching for realizing steep ridge sidewalls. Employing an optimized two-step n-cladding layer LDs produced very narrow horizontal and vertical beam divergence angles of 8.6/spl deg/ and 15.3/spl deg/, respectively. To the best of our knowledge, this vertical beam divergence angle is the lowest value ever reported in high-power 660-nm LDs operating over 200 mW and is expected to play an important role in minimizing the coupling loss between LD and passive optical components in digital versatile disc system.

A New Forming Strategy to Realise Parts Designed for Deep‐drawing by Incremental CNC Sheet Forming

The work detailed in this paper focuses on a new forming strategy for the CNC incremental sheet forming (ISF) process that is appropriate to form steep flanges, e.g. for parts designed for deep‐drawing. When parts are designed for deep‐drawing, they usually contain steep or rectangular side walls that cannot be manufactured using the standard ISF strategies. Unlike prior approaches to obtain steep flanges through ISF, the present method achieves a rough approximation to the final part already in the preforming stage. This can be accomplished without excessive sheet thinning due to sheet bending and stretching at this stage. As a consequence, additional material can be used for the finishing stages, thus yielding a final part with largely reduced thinning. After basic studies on a simple benchmark problem, the new bending/stretching strategy is tested with an industrially applied part that is usually produced by deep‐drawing. Finally, the ISF workpiece is evaluated against the deep‐drawn component with respect to sheet thickness and geometric accuracy.

High-Power 200mW AlGaInP Laser Diodes with low Operating Current

We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

Metrology of high aspect ratio MEMS

Lack of metrology tools for inspecting high aspect ratio MEMS severely limits the degree to which tolerances of a given part can be examined. Tools such as SEMs, AFMs, vision-based systems, and profilometers are good at examining two-dimensional entities of a part or for calculating surface roughness characteristics. None of these tools, however, can extract full three-dimensional data sets of high aspect ratio MEMS for part inspection. The hardware is either limited by the steep sidewalls of the part or by the simple fact that the acquisition method only collects two-dimensional data. This research proposes a method for extracting three-dimensional information from a part using multiple two-dimensional pointclouds. A fiducial setup is proposed which would allow for the registration of multiple pointclouds. A computer-aided inspection (CAI) software platform has been developed to handle the multiple data sets. The software platform implements a least-squares localization routine to compute the best-fit deviations from the nominal CAD geometry, as well as algorithms to determine the correct alignment between two pointclouds. With this software platform, both form errors of a single pointcloud and geometric errors with respect to multiple pointclouds can be calculated.

Fabrication of super-sharp nanowire atomic force microscope probes using a field emission induced growth technique

A relatively simple and consistent technique based on field emission induced growth has been developed to grow a single metallic nanowire on an atomic force microscope (AFM) tip. A clamping setup with two micromanipulators ensures that the fabrication of a vertically aligned nanowire probe, which is sharp, robust, and with high aspect ratio, can be achieved on different types of AFM cantilevers with different force constants. The controlled growth technique has been used to produce tungsten nanowire AFM probes with great consistency and high reproducibility. The tungsten nanowires were grown to lengths between 100 nm to 1.5 μm with radius of curvature at the tip end typically between 1–2 nm. Experiments using the fabricated tungsten nanowire AFM probe demonstrate its ability to produce high-resolution AFM images and improved profiling of structures with steep sidewalls due to its very sharp tip and high aspect ratio. The technique can be extended to fabricating other types of metallic nanowire AFM probes or even composite nanowire AFM probes by using different precursor gases. Experiments have been successful in fabricating cobalt nanowire AFM probes which are able to produce good high-resolution AFM images as well.

An experimental study of a mesoscale vortex colliding with topography of varying geometry in a rotating fluid

The interaction of a self-propagating barotropic cyclonic vortex with an obstacle has been investigated and the conditions for a vortex to bifurcate into two vortices determined. As in a previous study, after a self-propagating cyclonic vortex came into contact with the obstacle, fluid peeled off the outer edge of the vortex and a so-called “streamer” went around the obstacle in a counterclockwise direction. Under certain conditions, this fluid formed a new cyclonic vortex in the wake of the obstacle, causing bifurcation of the original vortex into two vortices. In the present study we performed three sets of idealized laboratory experiments with the aim of investigating the importance on the bifurcation mechanism of the obstacle’s horizontal cross sectional geometry, the influence of the height of the obstacle, and the importance of the slope of the obstacle sidewalls. The present results suggest that bifurcation occurs only when the obstacle height is equal or larger than 85% of the vortex height and that steep sloping sidewalls do not influence the bifurcation mechanism. In addition, experiments performed using an obstacle with an elliptical horizontal cross section revealed that the relevant parameter governing the occurrence of bifurcation is the length which the “streamer” has to travel around the obstacle, and not the dimension of the obstacle in the direction orthogonal to the motion of the vortex. Collisions of oceanic mesoscale vortices with seamounts often result in major modifications of their structure, having significant impacts on the redistribution of water properties. Observations of a “Meddy” bifurcating after colliding with the Irving Seamount in the Canary Basin show behavior similar to these idealized laboratory experiments. This suggests that these results could be used to explain and predict the outcome of a vortex colliding with seamounts of varying geometry in the ocean.

High-resolution nanowire atomic force microscope probe grownby a field-emission induced process

A technique to grow a nanowire probe on an atomic force microscope (AFM) tip using a field-emission induced growth process has been developed. The simple and highly reproducible technique produces vertically aligned nanowire probes whose length is controlled by the growth duration. Using a cantilever clamping arrangement, nanowire probes can be grown on low-stiffness cantilevers. Experiments using the robust nanowire AFM probe demonstrate its ability to produce high-resolution tapping mode AFM images and improved profiling of structures with steep sidewalls due to its very sharp tip and high aspect ratio. No degradation in imaging performance was observed after a period of continuous scanning and storage.

High-Power 200 mW 660 nm AlGaInP Laser Diodes with Low Operating Current

We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

High-Density Plasma Etching of Iridium Thin Films in a Cl2 / O 2 / Ar Plasma

Dry etching of iridium films using a TiN mask was studied with a gas mix in an inductively coupled plasma. The variations in etch rates and etch profiles of iridium films and TiN masks were investigated as a function of and concentrations. The etch rate of iridium film in this study was in the range 50-100 nm/min. It was found that the ratio of to concentration in an etch gas strongly influenced the etch selectivity of the iridium film relative to the TiN mask, which in turn impacted the etch profile of iridium films. By increasing coil power and bias voltage, or by decreasing gas pressure, the etch rate and selectivity of iridium films were increased and the etch profile was improved. Iridium etching with a residue-free steep sidewall of 70-80° was achieved. © 2003 The Electrochemical Society. All rights reserved.