Fine Line Structures Research Articles

High-Frequency Acoustic Imaging Using Adhesive-Free Polymer Transducer.

The piezoelectric polymer PVDF and its copolymers have a long history as transducer materials for medical and biological applications. An efficient use of these polymers can potentially both lower the production cost and offer an environment-friendly alternative for medical transducers which today is dominated by piezoelectric ceramics containing lead. The main goal of the current work has been to compare the image quality of a low-cost in-house transducers made from the copolymer P(VDF-TrFE) to a commercial PVDF transducer. Several test objects were explored with the transducers used in a scanning acoustic microscope, including a human articular cartilage sample, a coin surface, and an etched metal film with fine line structures. To evaluate the image quality, C- and B-scan images were obtained from the recorded time series, and compared in terms of resolution, SNR, point-spread function, and depth imaging capability. The investigation is believed to provide useful information about both the strengths and limitations of low-cost polymer transducers.

Design and Demonstration of Glass Panel Embedding for 3D System Packages for Heterogeneous Integration Applications

Abstract This article demonstrates a next-generation high-performance 3D packaging technology with smaller form factor, excellent electrical performance, and reliability for heterogeneous integration. High-density logic-memory integration, today, is built predominantly using interposers which are fundamentally limited in assembly pitch and interconnect lengths, and they also are expensive as the package sizes increase. On the other hand, high-frequency applications continue to use laminates which are also limited by package size and ability to integrate many components. Wafer-level fan-out (WLFO) packaging promises better performance and form factor at lower costs, but current WLFO packages are mold-based and hence are limited to small packages. This article presents a 3D packaging technology using glass panel embedding (GPE) for high-performance with potential for large body size heterogeneous integration applications. The tailorable coefficient of thermal expansion of glass allows a reliable direct board attach of large GPE packages that not only benefits the form factor and signal speed but also provides radical benefits to power delivery. Unlike interposers and silicon bridges, GPE packages are not bump-limited and can support I/O densities comparable with backend-of-line with silicon-like redistribution wiring at much lower costs. The fundamental limitations such as die shift and poor dimensional stability of current organic WLFO packages are addressed by parametric process improvements to reduce die shift to <2 μm while also improving the RDL surface planarity for high-yielding fine-line structures and integrating through glass via (TGV) in the fan-out region for 3D packaging. This article describes the fabrication process for 3D GPE, leading to demonstration of a technology using embedding of chips with all-Cu interconnections at 40-μm I/O pitch with TGVs at 300-μm pitch, thus enabling double-side RDL and assembly of chips to achieve three levels of device integration.

Design and demonstration of Glass Panel Embedding for 3D System Packages for heterogeneous integration applications

Abstract This paper demonstrates a next generation high-performance 3D packaging architecture with smaller form factor, excellent electrical performance and reliability for heterogeneous integration. High density Logic-HBM integration, today, is built predominantly using interposers which are fundamentally limited in assembly pitch and interconnect lengths, and they also are expensive as the package sizes increase. On the other hand, high-frequency applications continue to use laminates which are again limited by package size and ability to integrate many components. WLFO promises better performance and form factor at lower costs, but current WLFO packages are mold-based and hence are limited to small packages. This paper presents the first demonstration of 3D Glass Panel Embedding (GPE) technology for high-performance large package applications involving heterogeneous integration. The tailorable CTE of glass allows a reliable direct board SMT of large GPE packages that not only benefits form factor and signal speed, but also provides radical benefits to power delivery. Unlike interposers and silicon bridges, GPE packages are not bump limited and can support BEOL-like I/O densities with Silicon-like RDL at much lower costs. The fundamental limitations like die-shift and poor dimensional stability of current organic WLFO packages are addressed by parametric process improvements to reduce die-shift to <2 um while also improving the RDL surface planarity for high-yielding fine-line structures. This paper describes the fabrication process for 3D GPE, leading to demonstration of a technology using embedding of chips with all-Cu interconnections at 40um I/O pitch while also enabling double-side assembly of chips to achieve 3 levels of device integration.

Ultra-fine Line Multi-Redistribution Layers with 10 μm Pitch Micro-Vias for Wafer Level and Panel Level Packaging realized by an innovative Excimer Laser Dual Damascene Process

Abstract Multi-chip integrated Fan-Out packages and high I/O CSPs demands for higher routing density on wafer level. Due to that, the classical mask aligner lithography and photosensitive thin-film polymers used for BEOL reach its limits and new technologies and materials are necessary to generate lines and space down to two μm. These multi-metal layers set also higher demands on the mechanical properties of the materials. This paper presents a new excimer laser dual damascene process for ultra-fine routing for BEOL. Various materials like low cure temperature polyimide, BCB and 15-μm thick dry-film ABF material are structured by using an excimer laser stepper with a reticle mask to realize feature size below four μm with a high throughput. Micro-vias with a diameter below five μm are realized with high aspect ratio, which overcome the photolithographic limitations of the common used photosensitive thin-film polymers. The laser structuring allows to use innovative dielectric materials for WLP with optimized mechanical and electrical parameters for example inorganic filled polymers like dry-film ABF materials, which do not have to be photosensitive. The ablations depth per laser pulse and the cross-section of the ablated structures in dependence of the ablation parameters was investigated. The depth of embedded lines was set by number of pulses aside of integrated micro-vias. The lines and micro-vias were metallized with copper by galvanic process and the following CMP step removes the copper outside the ablated structures. The CMP removes only the copper and the metal of the seed-layer, which has the functions of an adhesion and barrier layer, stays intact. The under-etching of the conventional wet etch seed layer removal is a major problem for the fine line structures realized by the Laser Dual Damascene process. Due to that, the removal of the seed layer (usually titan) was investigated and it could be shown, that this layer can be removed by the excimer laser system. The stepper like system allows a sub-micron alignment accuracy with no need of a capture pad of the embedded lines. Test structures have been designed and fabricated with lines and spaces below 10 μm to demonstrate the dense multi-layer routing capability where the excellent reliability can be proven by air to air thermal cycling (from −55°C up to 125°C), current leakage and electro migration test.

Aerosol Printing of High Resolution Films for LTCC-Multilayer Components

For the electronic packaging of sensor stable and cost-efficient fine-line printing technologies on LTCC and high frequency laminates are needed. Especially common technologies like screen printing and thin film techniques are unsuitable for fine structures or too expensive. In addition there is no direct write technology for 3D-LTCC-designs as well as for high reliability Co-firing structures. Closing this gap the aerosol printing technology is used to print high resolution conductors on planar and non-planar substrates. Aerosol printing is a direct write non-contact printing technology of functional layers. After a pneumatic atomization the ink is transformed into 1 to 5 μm droplets. The resulting, continuous aerosol stream is focused by a sheath gas in the printing head. Thus the long standoff distance between substrate and deposition tip of max. 5 mm allows the 3D-printing on non-planar substrates. With optimized inks and printing parameters line widths of 10 μm are achievable. This paper will present applications for aerosol printed functional layers on LTCC. These are, for example, aerosol printed films embedded in co-fired LTCC, fine line structures for high frequency applications and the evaluation of printed 3D-structures like LTCC-stairways. Furthermore the 90 degree contacting of unconventional sensor designs will be presented.

Aerosol Printing of High Resolution Films for LTCC-Multilayer Components

For the electronic packaging of sensor stable and cost-efficient fine line printing technologies on LTCC and high frequency laminates are needed. Especially common technologies like screen printing and thin film techniques are unsuitable for fine structures or too expensive. In addition, there is no direct write technology for 3D LTCC designs as well as for high reliability cofiring structures. Closing this gap, aerosol printing technology is used to print high resolution conductors on planar and nonplanar substrates. Aerosol printing is a direct write noncontact printing technology of functional layers. After pneumatic atomization, the ink is transformed into 1–5 μm droplets. The resulting continuous aerosol stream is focused by a sheath gas in the printing head. Thus, the long standoff distance between the substrate and the deposition tip of max. 5 mm allows 3D printing on nonplanar substrates. With optimized inks and printing parameters, line widths of 10 μm are achievable. This paper will present applications for aerosol printed functional layers on LTCC. These are, for example, aerosol printed films embedded in cofired LTCC, fine line structures for high frequency applications, and the evaluation of printed 3D structures like LTCC stairways. Furthermore, the 90° contact of unconventional sensor designs will be presented.

Development of Electronic Substrates for Medical Device Applications

There is a strong desire to develop advanced electronic substrates that can meet the growing demand for miniaturization, high-speed performance, and flexibility for medical devices. To accomplish this, new packaging structures need to be able to integrate more dies with greater function, higher I/O counts, smaller pitches, and high reliability, while being pushed into smaller and smaller footprints. As a result, the microelectronics industry is moving toward alternative, innovative approaches as solutions for squeezing more function into smaller packages. In the present study, we are developing flexible packages for a variety of medical applications. Here we discuss several classes of flexible materials that can be used to form high-performance flexible packaging. In addition, copper thinner than 5 μm is routinely used, with copper layers as thin as 0.2 μm used as a seed layer for semi-additive approaches. The use of semi-additive circuitization facilitates manufacture of fine-line circuit features, and traces narrower than 12μm have been produced routinely. A smooth copper-polymer interface is ideal for high speed applications and for fine line etching. Selection of an appropriate material provides good copper adhesion to the base film. Flexible materials with 1 or 2 metal layers provide the smallest possible roll diameter for systems such as catheters. Compatibility with well developed, high performance electronic materials represents a key advantage of flexible electronics systems that are enabled by high density fine line structures rather than unusual materials. Electrical interconnection between the chip and package can be made by a number of means. Solder-coated Cu-micro pillars for a variety of finer pitch applications are being developed. Cu micro pillars are grown through the dielectric or silicon and subsequently coated with solder to produce finer pitch 3D-interconnects. The paper also describes a novel approach for the fabrication of flexible electronics on PDMS substrates. The paper discusses the fabrication of PDMS substrates using different circuit patterns and geometries. Rozalia/Ron ok move from 2.5/3D to FC/WLP 12-21-11.

Electroluminescent light sources via soft lithography

PurposeMicrocontact printing is a process used to print high‐resolution protein arrays for biosensors. The paper aims to investigate using these techniques to print electrically conductive fine line structures for electroluminescent (E/L) light sources.Design/methodology/approachThe viability of using microcontact printing as a process for electronics fabrication is investigated. Polydimethylsiloxane stamps inked with alkanethiol compounds form self‐assembled monolayers on substrate surfaces, acting as the resist to subsequent etching processes. The printed lines are characterized with regard to their performance as high‐electric field generators in electroluminescent displays.FindingsIt has been demonstrated that microcontact printing is a cheap, repeatable process for fabricating electronic devices. The results demonstrate the viability of the process to fabricate electric field generator structures for E/L light sources with reduced driving voltages.Originality/valueThe paper demonstrates that microcontact printing can produce electrically conductive fine‐line structures with high resolution, confirming its viability in printed electronics manufacture.

Two-Dimensionally Position-Controlled Excimer-Laser-Crystallization of Silicon Thin Films on Glassy Substrate

Nucleus positions have been two-dimensionally controlled in excimer-laser-crystallized Si thin-films on a glassy substrate. The position along one direction on the surface was controlled by intensity gradient of the excimer-laser light. The position control along the other direction was achieved by pre-patterning of the Si thin film as fine line structures and by heating the space between the lines with a light absorption layer. SiON was suitable as an absorption layer for KrF excimer-laser light. The grains grown were as long as 7 mm, even for ultra-thin (50-nm-thick) Si films.

Nanolithographic patterning of Au films with a scanning tunneling microscope

We present a new lithographic technique with a scannning tunneling microscope (STM), allowing us to pattern thin evaporated Au films at the nanometer scale. The electron beam produced by the STM tip is used to expose a very thin layer of ω-tricosenoic acid. Only four monolayers of the acid, which acts as an electron sensitive, negative resist, are deposited on top of the Au films using the Langmuir–Blodgett technique. We have verified the influence of the exposure conditions on the quality of the fabricated fine-line structures with a linewidth down to 15 nm. We can also measure the electrical properties of narrow Au lines which interconnect large predefined contact pads. As expected, the low-temperature magnetoresistance is strongly influenced by quantum interference effects.

Adhesion and fracture analysis of metal/polyimide fine line structures

Finite element analysis has been employed to study the adhesion and fracture behavior observed for metal/polyimide line structures formed by depositing Au/Cr lines on biphenylenetetracarboxylic dianhydride-phenylenediamine as a function of line width and line thickness. The key features can be attributed to the various mechanical environment induced at the interface. The results distinguish conditions where the edge effect becomes significant for line widths less than the substrate film thickness, while the bulk effect becomes dominant for line thicknesses larger than 0.25 of the substrate film thickness. Both effects reduce interfacial strain and deformation energy induced in the metal lines, leading to metal line delamination of the corresponding structures occurring at a higher applied strain. Due to the plastic yield of the metal, the interfacial stress behavior is found to be relatively insensitive as a function of the line dimension, and it cannot account for the delamination behavior observed. In contrast, the deformation energy induced in the metal shows a clear dependence on the applied strain. It continues to increase with applied strain, even after the maximum stress level is reached. Correlating with experiments, the energy in the metal line is about 2–10 J/m2 at the onset of metal line delamination for all structures with different widths and thicknesses. This value is comparable to the total bond energy between the metal and polyimide atoms along the interface, suggesting a correlation between the adhesion energy and the chemical bond strength of the interface. The deformation energy stored in the polyimide is an order-of-magnitude higher than that in the metal, so it dominates the energetics of the fracture process. In addition, the energy profile along the interface shows that maximum deformation occurs in the vicinity of the metal line edge where fracture occurs. These results emphasize the important role of the energetics in controlling the delamination and fracture of the interface.

Molecular structure and thermal/mechanical properties of polymer thin films

The molecular structure and chain packing morphology are shown to be the fundamental factors in determining the thermal-mechanical properties of polymer thin films. This is demonstrated for two polyimides, PMDA-ODA and BPDA-PDA, which have contrasting molecular structures with semi-flexible and rigid rod-like chain morphologies. We first examine the effect of molecular structure on the chain morphologies, then the influence of chain morphology on the materials properties. By examining the degree of anisotropy in materials properties between the lateral and vertical directions with respect to the film plane, a clear correlation between molecular structure and properties is observed. This is further manifested in the fracture behavior of metal-polyimide fine line structures, where the fracture characteristics are found to be largely controlled by the mechanical properties of the polyimide. A strong polyimide, BPDA-PDA, is found to have a fracture toughness about threefold higher than a soft polyimide, PMDA-ODA.

Stress Evolution During the Formation and Transformation of Titanium Silicide

AbstractThe evolution of stress vs. temperature was measured during the formation of TiSi2 in the reaction of Ti with (100) Si and with polycrystalline Si, and during the phase transformation from C49 to C54 TiSi2. The formation of C49 TiSi2 causes an increase in compressive stress, followed by relaxation before the transformation to C54 TiSi2, which causes no significant stress change. C54 TiSi2 is shown to be elastic in the temperature range of 750–860 °C. This difference in the deformation mechanisms of C49 and C54 TiSi2 affects the morphological stability of TiSi2 in fine line structures.

Image Intensifier Based Digital Chest Radiography

Contrast- and edge-enhanced digital monitor images from an image intensifier system for chest radiography were compared to conventional radiograms using visual grading analysis. Eleven observers graded the visibility of rounded opacities, the carinal region, fine line structures, and also compared the overall quality of images from 20 patients. The results showed significantly better visibility on the digital monitor for the rounded opacities and the mediastinum compared to the conventional radiograms. The overall quality of the digital images was also considered better. However, the digital images showed significantly inferior visibility for the line structures in comparison with the conventional radiograms. Our study indicates that the present contrast- and edge-enhanced digital images, with a spatial resolution of 1,024 x 1,024 pixels and a contrast resolution of 8 bits, are superior to conventional radiograms for the visualization of mediastinal anatomy and rounded opacities. The clinical importance of the inferior visibility of fine line structures is not clear.

Broad area, intense electron beam source for high resolution, high throughput semiconductor lithography

Electron beam lithography using a robust, high current density (≳10 A/cm2), high brightness (≳1010 A/m2 rad2), broad area (≳1 cm diam) electron beam source is reported. The electron beam is produced during the hollow cathode discharge phase of a backlighted thyratron. The generated beam propagates in soft vacuum (<200 mTorr) and is collimated using cylindrical dielectric waveguides, resulting in uniform intensity over an area exceeding ∼1 cm2, along with a small divergence angle (<1.5°). Masked lithography for replication of fine line structures has been achieved, demonstrating the potential for a high throughput (∼30–40 wafers/h), high resolution (<0.25 μm) lithography system that is competitive with more complex x-ray and short wavelength optical systems.

Measurement of thermal stress and stress relaxation in confined metal lines. II. Stress relaxation study

The bending beam technique and stress analysis developed for stress measurements of fine line structures have been applied to investigate stress relaxation in confined Al (2 at. % Cu) line structures on a Si substrate. The observed relaxation of the line structure is compared with corresponding unpassivated and passivated layered film structures. The overall behavior of all structure is similar, showing an initial plastic deformation, then a fast relaxation in sequence with a log(time) slow relaxation. The kinetics of these relaxation processes are found to decrease due to the presence of the passivation and a higher degree of dielectric layer confinement. In addition, the relaxation behavior of the principal stress components of the line structure is anisotropic and does not vary monotonically with the annealing temperature. The results are attributed to the relaxation mechanism and interaction at the metal/dielectric interface.

Reactive ion etching of β-SiC in CCl2F2/O2

For the first time, the reactive ion etching (RIE) of β-SiC in CCI2F2/O2 gas mixture is reported. The addition of oxygen to the CC12F2 does not appear to enhance the etch rate, however, the RF power and the DC bias conditions prove to be the dominant factors for controlling the etch rate. In addition, fine line structures with vertical walls and smooth etched surfaces are achieved.

Image Intensifier Based Digital Chest Radiography

Contrast- and edge-enhanced digital monitor images from an image intensifier system for chest radiography were compared to conventional radiograms using visual grading analysis. Eleven observers graded the visibility of rounded opacities, the carinal region, fine line structures, and also compared the overall quality of images from 20 patients. the results showed significantly better visibility on the digital monitor for the rounded opacities and the mediastinum compared to the conventional radiograms. the overall quality of the digital images was also considered better. However, the digital images showed significantly inferior visibility for the line structures in comparison with the conventional radiograms. Our study indicates that the present contrast- and edge-enhanced digital images, with a spatial resolution of 1024 × 1024 pixels and a contrast resolution of 8 bits, are superior to conventional radiograms for the visualization of mediastinal anatomy and rounded opacities. the clinical importance of ...

Fine line structures of ceramic films formed by patterning of metalorganic precursors using photolithography and ion beams

Fine line structures of ceramic thin films were fabricated by patterning of metalorganic precursors using photolithography and ion beams. A trilevel structure was developed with an outer resist layer to transfer patterns, a silver delineated layer as an implantation mask, and a planar resist layer protecting the precursor film from chemical attacking and sputtering. Ion irradiation through the Ag stencil rendered metal carboxylates insoluble in 2-ethylhexanoic acid, permitting patterning of the precursor film with patterning features on micron scales. The potential of this technique was demonstrated in patterning of Bi2Sr2CaCu2O8+x and Pb(Zr0.53Ti0.47) thin films.

Dry etching of β-SiC in CF4 and CF4+O2 mixtures

Dry etching of cubic (100)β-SiC single crystal thin films produced via chemical vapor deposition (CVD) has been performed in CF4 and CF4+O2 mixtures, in both the reactive ion etching (RIE) and plasma etching modes. The latter process yielded measurable etch rates, but produced a dark surface layer which appears, from the results of secondary ion mass spectrometry, to be residual SiC. The RIE samples had no residual layer, but Auger electron spectroscopy did reveal a C-rich surface. The optimal RIE conditions were obtained with 10 sccm of pure CF4 at 40 mTorr and a power density of 0.548 W/cm2, giving an etch rate of 23.3 nm/min. Neither the increase of temperature between 293 and 573 K, nor the incremental addition of O2 to CF4 to 50%, produced any strong effect on the etch rates of SiC during RIE. Pictorial evidence of fine line structures produced by RIE of β-SiC films are also presented.