Microelectronic Fabrication Research Articles

Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications.

A protocol has been developed to selectively process low-k SiCOH dielectric substrates in order to activate or deactivate them toward the deposition of thin solid films by chemical (CVD or ALD) means. The original SiCOH surfaces are hydrophobic, an indication that they are alkyl- rather than silanol-terminated and that, consequently, they are fairly unreactive. However, the chemical-mechanical polishing (CMP) sometimes done during microelectronics fabrication renders them hydrophilic and reactive. It was shown here that silylation of the CMP-treated surfaces with any of a number of well-known silylation agents such as HMDS, ODTS, or OTS caps the reactive silanol surface groups and turns them back to being hydrophilic and unreactive. Further exposure of any of the passivated surfaces to a combination of ozone and UV radiation reinstates their hydrophilicity and chemical activity. Importantly, it was also demonstrated that all these changes could be induced without altering the original mechanical, optical, or electrical properties of the samples: atomic force microscopy (AFM) images show no increase in roughness, ellipsometry measurements yield the same values for the index of refraction and dielectric constant, and infrared absorption spectroscopy attests to the preservation of the organic fragments present in the original SiCOH samples. The chemical selectivity of the resulting surfaces was tested for the atomic layer deposition (ALD) of HfO2 films, which could be grown only on the UV/O3 treated substrates.

Nanoscale Silicon-on-Insulator Photo-Activated Modulator Building Block for Optical Communication

The constantly growing use of real-time computing generates constant urge for much faster processors than those which are currently available in the market. Correspondingly, there is an accelerated development of new optics communication related applications and components. The effort to combine those two trends leads to the generation of new optoelectronic nanodevices. Such hybrid devices may allow high operation speed, reduced cross talk and other noises, low operation power, and obviate the need for the existing electro-optical convertors. In this letter, we present the design, simulation, fabrication, and characterization of an optoelectronic device based on silicon which is capable of speeding up the processing capabilities. This novel device is called silicon-on-insulator photo-activated modulator. The nature of the data flow in this device is electronic, while the modulation control command is optic. Since the external voltage in the final configuration design of the device is constant and no RC (electrical average response time) related delay is generated, faster operation rates are anticipated. This novel device can serve as a building block toward the development of optical data processing while breaking through the way to all optic processors based on silicon chips that are fabricated via typical microelectronics fabrication process.

Fabrication of resonator–quantum well infrared photodetector focal plane array by inductively coupled plasma etching

Inductively coupled plasma (ICP) etching has distinct advantages over reactive ion etching in that the etching rates are considerably higher, the uniformity is much better, and the sidewalls of the etched material are highly anisotropic due to the higher plasma density and lower operating pressure. Therefore, ICP etching is a promising process for pattern transfer required during microelectronic and optoelectronic fabrication. Resonator-quantum well infrared photodetectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). To fabricate R-QWIP focal plane arrays (FPAs), two optimized ICP etching processes are developed. Using these etching techniques, we have fabricated R-QWIP FPAs of several different formats and pixel sizes with the required dimensions and completely removed the substrates of the FPAs. Their QE spectra were tested to be 30 to 40%. The operability and spectral non- uniformity of the FPA is ∼99.5 and 3%, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10

A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness

Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate.

Micro/nanoscale electrohydrodynamic printing: from 2D to 3D

Electrohydrodynamic printing (EHDP), based on the electrohydrodynamically induced flow of materials, enables the production of micro/nanoscale fibers or droplets and has recently attracted extensive interest to fabricate user-specific patterns in a controlled and high-efficiency manner. However, most of the existing EHDP techniques can only print two-dimensional (2D) micropatterns which cannot meet the increasing demands for the direct fabrication of three-dimensional (3D) microdevices. The integration of EHDP techniques with the layer-by-layer stacking principle of additive manufacturing has emerged as a promising solution to this limitation. Here we present a state-of-the-art review on the translation of 2D EHDP technique into a viable micro/nanoscale 3D printing strategy. The working principle, essential components as well as critical process parameters for EHDP are discussed. We highlight recent explorations on both solution-based and melt-based 3D EHDP techniques in cone-jet and microdripping modes for the fabrication of multimaterial structures, microelectronics and biological constructs. Finally, we discuss the major challenges as well as possible solutions with regard to translating the 3D EHDP process into a real micro/nanoscale additive manufacturing strategy for the freeform fabrication of 3D structures.

Quantum-correlated photon pairs generated in a commercial 45 nm complementary metal-oxide semiconductor microelectronic chip

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process that also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100-nm) complementary metal-oxide semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultralow CW on-chip pump powers ranging from 4.8 to 400 μW, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single-photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured, with a maximum of 55. In the process of characterizing this source, we also accurately predict pair generation rates from the results of classical stimulated four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with the capability of large volumes and pristine process control, where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.

Sandwich structure based on back-side etching silicon (100) wafers for flexible electronic technology

An SU-8-silicon(100)-SU-8 flexible composite sandwich structure is studied. Besides preventing corrosion to the thin silicon membrane, SU-8 photoresist coated on the silicon membrane improves its flexibility as shown by an ANSYS finite element simulation. Using a plasma enhanced chemical vapor deposited SiO2/Si3N4 composite film as an etch mask on the polished side, a 4ź (100) silicon wafer was thinned to 26 µm without rupture in a 30 wt% KOH solution. The wafer was coated on both sides with 20 µm of SU-8 photoresist and then bent over cylinders with various diameters, to flex the sandwich in a controlled manner. The determined minimal bending radius of the fabricated thin silicon-based sandwich structure is approximately 3.5 mm. The fabrication of this sandwich structure is compatible with conventional microelectronic fabrication processing. Thus, it allows one to thin fully fabricated devices in a post-fabrication process to make high-performance flexible electronics.

Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.

Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy.

Monitoring of organic contamination in the ambient air of microelectronic clean room by proton-transfer reaction/time-of-flight/mass spectrometry (PTR–ToF–MS)

The organic contamination has been recently considered as the most important problem for the photolithography world in the semiconductor industry, especially when the photolithographic methods moved from 130nm node to 32nm node. One of the most common organic compounds found in photolithography areas of the clean room is Trimethylsilanol (TMS), which can adsorb on the optical lenses forming a thin molecular layer, hence causing damages. Salt crystal formation is another potential threat for the optical devices. In the clean rooms, this salt is produced by a light-induced reaction between ammonia and an acid. In the context of semiconductor industry, the involved acid is usually the acetic acid produced by hydrolysis from propylene glycol methyl ether acetate (PGMEA), a commonly used organic compound in the photolithography.Here, we present an innovative analytical method using a state-of-the-art proton-transfer reaction–time-of-flight–mass spectrometer (PTR–ToF–MS) for on-line and continuous survey of volatile organic compounds (VOCs) with an emphasis on TMS and PGMEA. The effect of relative humidity on the detection and fragmentation of these organic compounds was assessed. The new analytical method is operated in a real life clean room environment and the results were compared with those obtained with off-line measurements using automated thermal desorber–gas chromatography–mass spectrometry (ATD–GC–MS) as reference method.The contamination sources were detected and identified, which is of paramount importance for the microelectronic fabrication plant. The trapping efficiency of the chemical filters used for AMCs filtration in the photolithography zone was determined.

Investigation of a Micro Dielectric Barrier Discharge Plasma Actuator for Regional Aircraft Active Flow Control

This paper reports a multitechnique investigation of a micro dielectric barrier discharge plasma actuator (DBDPA) as a promising system to control separated flows. The device was manufactured through a photolithographic technique and its performances and capabilities were compared with the ones of conventional macro DBDPAs. Alternate current operation under sinusoidal voltage excitation was studied in the absence of external flow by means of many experimental techniques like discharge imaging, flow visualizations, particle image velocimetry, infrared thermography, and electrical characterization. The influence of the operating parameters was investigated. The main results underlined that an increase in the voltage amplitude or frequency brought to a rise in the maximum induced velocity, electrical power dissipation, and actuator surface temperature. Moreover, it was assessed that the small heating of the micro DBDPA did not affect the actuated flow. A jet velocity up to 1.36 m/s was obtained at a 9.01 W/m electrical power dissipation per unit electrode length. The device realized by microelectronic fabrication technology allowed reaching a flow velocity magnitude comparable with the one of conventional macro DBDPAs, with a reduction in applied voltage, power dissipation, and actuator size. Furthermore, the induced wall jet was more confined in the area in proximity of the device, because of the limited plasma discharge extension.

Hybrid subtractive micro-patterning of a self-assembled SiO2 nano/microsphere monolayer

Colloidal self-assembly and direct micro-patterning of functional materials have drawn intense interest as an alternative to the conventional photolithography based microelectronics fabrication process. In this paper, we introduce a facile subtractive micro contact printing method to create a patterned colloidal nano/micro sphere monolayer on a wafer scale by combining an additive ‘bottom-up’ self-assembly and subtractive ‘top-down’ printing process. A vacuum-assisted contact printing method enabled precise and uniform pressure control to directly fabricate a large-area micro-patterned hexagonally close packed structure of nano/micro spheres on the target substrate very fast, at low cost, under ambient conditions. In addition, analysis on the hybrid printing pressure and the patterning time has been conducted.

Efficient Cluster based Fault Detection andRecovery in Wireless Sensor Network

In recent years, applications of wireless sensor networks (WSNs) have been increased due to its vast potential to connect the physical world to the virtual world. Also, an advance in microelectronic fabrication technology reduces the cost of manufacturing portable wireless sensor nodes. It becomes a trend to deploy the large numbers of portable wireless sensors in WSNs to increase the quality of service (QOS). In order to maintain the better QOS under failure conditions, identifying and detaching such faults are essential, we proposed a fault recovery corrupted node and Self Healing is necessary. In this proposed system round trip delay techniques used to identify the fault node and maintain the cluster structure in the event of failures caused by energy-drained nodes. Initially, node with the maximum residual energy in a cluster becomes cluster heed and node with the second maximum residual energy becomes secondary cluster heed. Later on, selection of cluster heed and secondary cluster heed will be based on available residual energy. We use NS2 software as simulation platform quantities. Like, energy consumption at cluster and number of clusters is computed in evaluation of proposed algorithm.

Microfabrication by High Rate Anodic Dissolution: Fundamentals and Applications

This paper presents a review of the basic principles of electrochemical metal removal processes and their application in microfabrication. After a brief description of anodic behavior of metals, the influence of mass transport, surface films and current distribution on microfabrication performance are discussed. Some examples of microelectronic component fabrication are presented that demonstrate the challenges and opportunities offered by high rate anodic dissolution processes.

A Soft Approach for Energy Storage and Mobile Healthcare

Wearable devices that match the soft, curvilinear, and time-dynamic nature of human body is an important trend for future technologies, redefining not only the appearance, but also the design and fabrication of microelectronics. In this talk, I will discuss the strategy to transform materials and devices that are conventionally rigid and brittle into a soft format. Specifically, the mechanical properties of rigid systems can be engineered by breaking down their geometry into small islands and subsequently rebuilding the interconnections with flexible/stretchable conducting filaments. This principle can be illustrated by two examples, which represent the latest progress in stretchable energy storage and mobile healthcare: a wirelessly rechargeable lithium ion battery with a record reversible biaxial stretchability up to 300%, and a soft wearable system capable of multifunctional physiological sensing on skin for health monitoring.

Electrodeposition of Cu-Ag Alloy Thin Films Directly on W Diffusion Barrier By Controlling Complexing Agents and Organic Additives

Cu as an excellent electrical conductor has been used for interconnect in Si-based microelectronic devices. Recently Cu alloys instead of Cu have emerged as interconnect material for future microelectronic device fabrication because higher adhesion strength to foreign materials, larger resistance to electromigration, and improved electrical conductivity are required in very narrow interconnect lines. It is known that Cu-Ag alloy among Cu alloys has beneficial properties such as higher electrical conductivity, better formability, higher mechanical strength, and better resistance to electromigration than pure Cu. In this research, we investigate the effect of electrodeposition parameters on the nucleation and growth of Cu-Ag alloy nano-nuclei and the formation of thin, smooth Cu-Ag alloy thin film. Cu-Ag alloys are electrodeposited directly on W diffusion barrier without employing a Cu seed layer. Area density, size, and morphology of Cu-Ag alloy nano-nuclei influence the microstructure, surface roughness, and thickness of Cu-Ag alloy thin film formed on the W diffusion barrier. Sophisticated control of chemical equilibrium of electrolyte is carried out by managing the concentration and type of complexing agent and organic additives. Chelation behavior of Cu and Ag with complexing agent is also studied according to pH of electrolyte. Reduction rate and chemical composition of electrodeposited Cu-Ag alloy are controlled under diffusion-controlled deposition conditions.

Multilayer Scanning Coil Detector for Improved Detection of Surface Pathogen Contamination

This paper presents an investigation into improved pathogen detection on food and food contact surfaces using a multilayer scanning coil detector combined with wireless magnetoelastic (ME) biosensors. In contrast to our previous studies of surface pathogen detection where a single-layer planar coil was employed, a more sensitive detector with a multi-layer coil design was investigated in this work. The two-fold roles of the coil detector are: (1) the application of an alternating magnetic field for the excitation of the ME sensor’s vibration and (2) detection of the resultant magnetic flux changes induced by the vibrating sensor. Surface pathogen detection can then be realized when the sensor comes into contact and binds specifically with the pathogen of interest, causing the sensor’s resonant frequency to decrease. For surfaces with large roughness and curvatures (e.g., leafy greens and cantaloupes), a long stand-off distance (distance between the sensor and detector) may be required. Hence, enhancement in the excitation power and sensitivity of coil detector with a multilayer design is a key to improving the system’s detection capabilities. Furthermore, smaller ME biosensors with higher mass sensitivity can also be measured with this sensitive multilayer coil detector. Several design parameters, including the number of layers, width, height, and spacing of coil turns, were studied. Coils were fabricated using standard microelectronic fabrication techniques (photolithograpy, electroplating, etching and sputtering) and tested.Both theoretical calculations and experimental data showed that the above coil geometric parameters have a significant impact on the signal amplitude and stand-off distance. Finally, with the newly fabricated multilayer coil detector, simultaneous measurement of multiple biosensors on spinach leaf surfaces was demonstrated. This multilayer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.

Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas

Control of ion energy distributions (IEDs) onto the surface of wafers is an ongoing challenge in microelectronics fabrication. The use of capacitively coupled plasmas (CCPs) using multiple radio frequency (rf) power sources provides many opportunities to customize IEDs. In dual-frequency CCPs using a fundamental frequency and its second harmonic, varying the relative voltages, powers, and phases between the fundamental and second harmonic biases have demonstrated potential as control mechanisms for the shape of the IEDs. In this paper, we report on computational and experimental investigations of IED control in dual-frequency and triple-frequency CCPs where the phase between the fundamental and second harmonic frequency voltage waveform is used as a control variable. The operating conditions were 5–40 mTorr (0.67–5.33 Pa) in Ar and Ar/CF4/O2 gas mixtures. By changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects was significant and not only shifted the dc self-bias but also affected plasma uniformity. When changing phases of higher harmonics, the energies and widths of the IEDs could be controlled. With the addition of a 3rd high-frequency source, the plasma density increased and uniformity improved. Computed results for IEDs were compared with experimental results using an ion energy analyzer in systems using rf phase locked power supplies.

Controlling VUV photon fluxes in low-pressure inductively coupled plasmas

Low-pressure (a few to hundreds of millitorrs) inductively coupled plasmas (ICPs), as typically used in microelectronics fabrication, often produce vacuum-ultraviolet (VUV) photon fluxes onto surfaces comparable to or exceeding the magnitude of ion fluxes. These VUV photon fluxes are desirable in applications such as sterilization of medical equipment but are unwanted in many materials fabrication processes due to damage to the devices by the high-energy photons. Under specific conditions, VUV fluxes may stimulate etching or synergistically combine with ion fluxes to modify polymeric materials. In this regard, it is desirable to control the magnitude of VUV fluxes or the ratio of VUV fluxes to those of other reactive species, such as ions, or to discretely control the VUV spectrum. In this paper, we discuss results from a computational investigation of VUV fluxes from low-pressure ICPs sustained in rare gas mixtures. The control of VUV fluxes through the use of pressure, pulsed power, and gas mixture is discussed. We found that the ratio, β, of VUV photon to ion fluxes onto surfaces generally increases with increasing pressure. When using pulsed plasmas, the instantaneous value of β can vary by a factor of 4 or more during the pulse cycle due to the VUV flux more closely following the pulsed power.

Luminescence studies of perovskite structured titanates: A review

Apart from widely known dielectric and ferroelectric properties, the perovskite type materials also constitute a class of materials, which are recently investigated for their optical properties. These materials are being used for fabrication of various microelectronics and optoelectronic devices. Photoluminescence (PL), mechanoluminescence (ML) and thermoluminescence (TL) are such phenomena offering numerous applications in different fields like electro-optics, flat panel displays, LED technology, sensors, dynamic visualization etc. This paper briefly reviews the status and new progress in luminescence studies of ferroelectric materials like barium titanate (BT), barium zirconate titanate (BZT), calcium titanate (CT), calcium zirconate titanate (CZT), lead titanate (PT), lead zirconate titanate (PZT), etc., prepared through various methods.

A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

Wet anisotropic etching based silicon micromachining is an important technique to fabricate freestanding (e.g. cantilever) and fixed (e.g. cavity) structures on different orientation silicon wafers for various applications in microelectromechanical systems (MEMS). {111} planes are the slowest etch rate plane in all kinds of anisotropic etchants and therefore, a prolonged etching always leads to the appearance of {111} facets at the sidewalls of the fabricated structures. In wet anisotropic etching, undercutting occurs at the extruded corners and the curved edges of the mask patterns on the wafer surface. The rate of undercutting depends upon the type of etchant and the shape of mask edges and corners. Furthermore, the undercutting takes place at the straight edges if they do not contain {111} planes. {100} and {110} silicon wafers are most widely used in MEMS as well as microelectronics fabrication. This paper reviews the fabrication techniques of convex corner on {100} and {110} silicon wafers using anisotropic wet chemical etching. Fabrication methods are classified mainly into two major categories: corner compensation method and two-steps etching technique. In corner compensation method, extra mask pattern is added at the corner. Due to extra geometry, etching is delayed at the convex corner and hence the technique relies on time delayed etching. The shape and size of the compensating design strongly depends on the type of etchant, etching depth and the orientation of wafer surface. In this paper, various kinds of compensating designs published so far are discussed. Two-step etching method is employed for the fabrication of perfect convex corners. Since the perfectly sharp convex corner is formed by the intersection of {111} planes, each step of etching defines one of the facets of convex corners. In this method, two different ways are employed to perform the etching process and therefore can be subdivided into two parts. In one case, lithography step is performed after the first step of etching, while in the second case, all lithography steps are carried out before the etching process, but local oxidation of silicon (LOCOS) process is done after the first step of etching. The pros and cons of all techniques are discussed.