Nickel Silicide Contacts Research Articles

Empirical Model of Low-Ohmic Nickel-Based Contact Formation on N-Type 4H-SiC Depending on Thermal Budget

In this work, an empirical model of structural and material composition of low-ohmic nickel silicide contact formation on n-type 4H-SiC by laser annealing as well as by RTA is presented. For this purpose, systematic studies with different annealing parameters were performed. The development of the empirical model is based on results from characterization of the nickel silicide by FIB-SEM, TEM, XRD analysis as well as electrical characteristics received from 4-point-measurements.

Formation and crystallographic orientation of NiSi2–Si interfaces

The transport properties of novel device architectures depend strongly on the morphology and the quality of the interface between contact and channel materials. In silicon nanowires with nickel silicide contacts, NiSi2–Si interfaces are particularly important as NiSi2 is often found as the phase adjacent to the silicide–silicon interface during and after the silicidation. The interface orientation of these NiSi2–Si interfaces as well as the ability to create abrupt and flat interfaces, ultimately with atomic sharpness, is essential for the properties of diverse emerging device concepts. We present a combined experimental and theoretical study on NiSi2–Si interfaces. Interfaces in silicon nanowires were fabricated using silicidation and characterized by high-resolution (scanning) transmission electron microscopy. It is found that {111} interfaces occur in ⟨110⟩ nanowires. A tilted interface and an arrow-shaped interface are observed, which depends on the nanowire diameter. We have further modeled NiSi2–Si interfaces by density functional theory. Different crystallographic orientations and interface variations, e.g., due to interface reconstruction, are compared with respect to interface energy densities. The {111} interface is energetically most favorable, which explains the experimental observations. Possible ways to control the interface type are discussed.

Experimental demonstration of a tapered silicon core–shell nanowire solar cell enhanced by a nickel silicide contact

A wholly passivated silicon core–shell nanowire solar cell incorporating a nickel silicide (NiSi) contact shows reduced series resistance. The configuration’s highly ordered vertical nanowire array is produced by the top-down method on a silicon solar-cell surface. The prepared samples demonstrate reflectance of ∼65 % to 7%. The sample without the NiSi contact has a high short-circuit current density of 31.0 mA / cm2. The cells with ∼5 nm NiSi show an improved fill factor of 70%, contributing to a high power-conversion efficiency of 10.8%.

Thermal Stability of Copper–Nickel and Copper–Nickel Silicide Contacts for Crystalline Silicon

Copper is a low-cost, low-damage alternative to Ag paste for front-side metallization of crystalline Si (c-Si) solar cells, but requires conductive diffusion barriers like Ni or NiSi. Thermal stabi...

Ultra Thin Poly-Si Nanosheet Junctionless Field-Effect Transistor with Nickel Silicide Contact.

This study demonstrated an ultra thin poly-Si junctionless nanosheet field-effect transistor (JL NS-FET) with nickel silicide contact. For the nickel silicide film, two-step annealing and a Ti capping layer were adopted to form an ultra thin uniform nickel silicide film with low sheet resistance (Rs). The JL NS-FET with nickel silicide contact exhibited favorable electrical properties, including a high driving current (>107A), subthreshold slope (186 mV/dec.), and low parasitic resistance. In addition, this study compared the electrical characteristics of JL NS-FETs with and without nickel silicide contact.

ChemInform Abstract: Solid‐state Reaction of Nickel Silicide and Germanide Contacts to Semiconductor Nanochannels

The surge in advancing the materials science of solid-state reactions for nanoscale contacts to advanced semiconductor devices necessitates a comprehensive dissemination and discussion on recent progress. The objective of this work is to review the notable developments in compound and alloy contact formation to nanoscale nanowire channels made of germanium, silicon, and their heterostructures, and to develop a unifying framework for understanding the significantly distinct reaction behaviors from those commonly observed in bulk. The Ni-based compound and alloy contacts are used as a platform to highlight the size-relevant, thermodynamic, and kinetic differences, and their key material, reaction, and electronic parameters and properties are summarized. Special attention is given to the interplay between the compound/alloy contact structure and the resultant electronic properties.

Simulations Based on the Cooptimization Procedure for Plated Contacts With a NiSi Interface

A cooptimization procedure has been developed for industrial solar cells metalized using a nickel seed layer thickened by a plated silver layer. A theoretical contact resistivity model for NiSi nickel silicide contacts was first computed and inserted into classical power loss equations. Optical, resistive, and recombination losses were then simulated with a standard set of parameters used in production. This procedure allows the generation of efficiency and silver consumption contour plots for homogeneous and selective emitters. For both, general guidelines are given for the optimization of the doping profile, the finger spacing, and the finger thickness.

Cold Silicon Preamorphization Implant and Presilicide Sulfur Implant for Advanced Nickel Silicide Contacts

We report the first demonstration of a nickel silicide (NiSi) contact formation technique using cold silicon (Si) preamorphization implant (PAI) combined with presilicide sulfur (S) implant. The cold Si PAI suppresses the agglomeration of NiSi film at elevated temperatures. Presilicide S implant and its segregation at the interface of NiSi and n-type Si (n-Si) after silicidation significantly lowers the effective Schottky barrier height (Φ n B ) for electrons at the NiSi/n-Si contact. The S atoms in Si could be modeled as donor-like traps near the NiSi/n-Si interface, and a simulation study was performed to explain the reduction of Φ n B caused by S.

Controllable doping and wrap-around contacts to electrolessly etched silicon nanowire arrays

Top-down electroless chemical etching enables non-lithographic patterning of wafer-scale nanostructured arrays, but the etching on highly doped wafers produces porous structures. The lack of defect-free nanostructures at desired doping and the difficulties in forming reliable electrical side-contacts to the nanostructure arrays limits their integration into high performance nanoelectronics. We developed a barrier layer diffusion technique to controllably dope wafer-scale silicon nanowire arrays (1017–1020 cm−3) produced by chemically etching lightly doped silicon wafers. In order to achieve low resistance top-side electrical contacts to the arrays, we developed a two step tip-doping procedure to locally dope the tips (∼1020 cm−3) to metallic levels. The dopant concentration is characterized by depth profiling using secondary ion mass spectroscopy and four-point probe electrical measurements. Further, array scale electrical measurements show that the tip-doping lowers the specific contact resistivity (∼10−5 Ω cm2) since the metallic tips enable direct tunneling of electrons across the nickel silicide contacts to the nanowire arrays. This work provides a scalable and cost-effective doping approach to control charge injection and charge conduction in nanowire arrays, thus advancing their integration into various device applications.

Solid-state reaction of nickel silicide and germanide contacts to semiconductor nanochannels

The surge in advancing the materials science of solid-state reactions for nanoscale contacts to advanced semiconductor devices necessitates a comprehensive dissemination and discussion on recent progress. The objective of this work is to review the notable developments in compound and alloy contact formation to nanoscale nanowire channels made of germanium, silicon, and their heterostructures, and to develop a unifying framework for understanding the significantly distinct reaction behaviors from those commonly observed in bulk. The Ni-based compound and alloy contacts are used as a platform to highlight the size-relevant, thermodynamic, and kinetic differences, and their key material, reaction, and electronic parameters and properties are summarized. Special attention is given to the interplay between the compound/alloy contact structure and the resultant electronic properties.

Ultrasound assisted nickel plating and silicide contact formation for vertical multi-junction solar cells

Vertical multijunction (VMJ) silicon solar cells (SC) are considered the most preferred among all known single-crystal ones for using in various photovoltaic systems under conditions of highly concentrated sunlight. The techniques of ultrasound assisted nickel plating (USNiP) of mirror polished silicon wafers and their subsequent vacuum annealing for VMJ SC ohmic contacts creating were tested by X-ray diffractometry, scanning electron microscopy and dark current–voltage characteristics. The feasibility of utilizing nickel electroplating in the sulfamate electrolyte for the NiSi ohmic contact made on the mirror polished silicon wafers with n+–p junctions on both sides have been experimentally confirmed. Ultrasound assistance of the nickel plating insured the enhancement of NiSi adhesion and improving the quality of the ohmic contacts.

Fully passivated radial junction nanowire silicon solar cells with submerged nickel‐silicide contact for efficiency enhancement

Presented is a silicon solar cell model with fully passivated radial junction nanowire surface decoration and submerged nickel-silicide contact. Numerical simulations using a finite-difference time-domain method have been done to investigate the spectral responses of the solar cell model. The experimental results indicate that, with proper nickel-silicide thickness, the fill factor of the cell can be improved considerably without much degradation on short circuit current density. Under AM 1.5G illumination, the silicon nanowire solar cell device with 50 Å nickel-silicide contact has short circuit current density of 26.3 mA/cm2, open circuit voltage of 586 mV and fill factor of 70.0%, contributing to power conversion efficiency of 10.8%, which is 19% higher than the control device without the nickel-silicide contact.

Contact Resistance Reduction for Strained N-MOSFETs With Silicon-Carbon Source/Drain Utilizing Aluminum Ion Implant and Aluminum Profile Engineering

We demonstrate a novel technique to reduce the nickel silicide (NiSi) contact resistance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">con</sub> in strained n-channel MOSFETs (n-FETs) with silicon carbon (Si:C) stressors, where a presilicide aluminum (Al) implant is performed and the Al profile is found to be affected by carbon (C). Al diffusion during silicidation is retarded by the presence of C and a high Al concentration is retained within the NiSi:C film, which is considered to be the main reason for electron barrier height Φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bn</i> reduction in NiSi:C contacts. Ge preamorphization implant prior to Al implant further reduces the Φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bn</i> to 0.44 eV. Integration of this technique in n-FETs with Si:C stressors achieves a 50% reduction in source/drain series resistance and 12% enhancement in saturation drive current. Negligible impact on the device short-channel effects is observed. When Al segregates at the NiSi/Si interface, the hole barrier height Φ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bp</i> is lowered, and such an Al profile can be used for the p-FETs. Al profile engineering shows a promise as a single-metal-silicide solution for selective <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">con</sub> optimization in CMOS.

Nickel silicide contacts formed by excimer laser annealing for high efficiency solar cells

ABSTRACTDriven by the relatively high cost of silver (Ag), interest has grown in the photovoltaic (PV) industry to substitute conventional screen printed (SP) Ag front contacts with copper (Cu) plated contacts. The approach chosen here applies selective laser ablation of the front anti‐reflection coating (ARC), then forming self‐aligned nickel silicides (NiSix) contacts, and thickening the lines by Cu plating to achieve the desired line conductivity. A successful implementation of this scheme requires annealing to form NiSix with low contact resistance. However, it has been shown that industrial shallow emitters can be damaged severely upon conventional annealing of nickel. In this paper, we show that by using large area excimer laser annealing (ELA), NiSix contacts can be formed on industrial shallow emitters without the associated junction degradation. On the basis of sheet resistance, transmission electron microscopy, and lifetime measurements, we demonstrate that NiSix formation by ELA can be achieved in narrow contact openings without damaging the passivation and reflectance properties of the neighboring ARC. In addition, the thresholds for NiSix formation for different Ni thicknesses are quantified by rigorous finite element simulations and compared with experimental data. Finally, high efficiency passivated emitter and rear cell type solar cells featuring a shallow 85 Ω/sq emitter have been processed on large area CZ–Si using laser ablation of the ARC and subsequent NiSix formation by ELA. These cells show an average efficiency gain of 0.4%abs compared with cells processed with reference SP contacts. In this work, the best performing cell with the ELA process reached 20.0% energy conversion efficiency. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Emitter Requirements for Nickel Contacts on Silicon Solar Cells-A Simulation Study

A unified model for the nickel-silicon theoretical contact resistivity was computed, using a 0.6eV Schottky barrier height, and compared to recent experimental data. This model was subsequently inserted in a classical co- optimization procedure. Numerical simulations were combined with analytical power losses equations to find out the effect of homogeneous emitter doping profile on an ideal lab-scale silicon solar cell. According to this work, an optimized emitter for plated contacts on a 10μm wide nickel seed layer should have a junction depth ranging from 0.5 to 4μm and a surface doping from 4 x 1018 to 2 x 1019 cm-3. This broad range allows getting more than 25.5% and up to 25.9% theoretical efficiency on a 2 x 2cm2 silicon solar cell metallized with 10μm thick fingers. Finally, contour plots were also simulated using a larger Schottky barrier height in order to figure out the effect of the nickel silicide contact interface on solar cell properties.

Vertically Grown Multiwalled Carbon Nanotube Anode and Nickel Silicide Integrated High Performance Microsized (1.25 μL) Microbial Fuel Cell

Microbial fuel cells (MFCs) are an environmentally friendly method for water purification and self-sustained electricity generation using microorganisms. Microsized MFCs can also be a useful power source for lab-on-a-chip and similar integrated devices. We fabricated a 1.25 μL microsized MFC containing an anode of vertically aligned, forest type multiwalled carbon nanotubes (MWCNTs) with a nickel silicide (NiSi) contact area that produced 197 mA/m(2) of current density and 392 mW/m(3) of power density. The MWCNTs increased the anode surface-to-volume ratio, which improved the ability of the microorganisms to couple and transfer electrons to the anode. The use of nickel silicide also helped to boost the output current by providing a low resistance contact area to more efficiently shuttle electrons from the anode out of the device.

Comparison of nickel silicide and aluminium ohmic contact metallizations for low-temperature quantum transport measurements

We examine nickel silicide as a viable ohmic contact metallization for low-temperature, low-magnetic-field transport measurements of atomic-scale devices in silicon. In particular, we compare a nickel silicide metallization with aluminium, a common ohmic contact for silicon devices. Nickel silicide can be formed at the low temperatures (<400°C) required for maintaining atomic precision placement in donor-based devices, and it avoids the complications found with aluminium contacts which become superconducting at cryogenic measurement temperatures. Importantly, we show that the use of nickel silicide as an ohmic contact at low temperatures does not affect the thermal equilibration of carriers nor contribute to hysteresis in a magnetic field.

Schottky barrier height tuning of silicides on p-type Si (100) by aluminum implantation and pulsed excimer laser anneal

We investigate the tuning of Schottky barrier height (SBH) of nickel silicide formed by pulsed excimer laser anneal of nickel on silicon implanted with aluminum (Al). A wide range of laser fluence was investigated, and it has been found that laser fluence influences the distribution of Al within the silicide and at the silicide/silicon interface. This in turn affects the effective whole SBH (ΦBp) at the silicide/silicon junction. High Al concentration at the silicide/silicon interface and high temperature for nano-second duration to achieve Al activation while keeping the Al concentration within the silicide low is vital for achieving low ΦBp. We demonstrate the achievement of one of the lowest reported ΦBp of ∼0.11 eV. This introduces a new option for forming nickel silicide contacts with reduced contact resistance at low thermal budget for possible adoption in future metal-oxide-semiconductor transistor technologies.

Silicon Carbide Vertical JFET with Self-Aligned Nickel Silicide Contacts

Trenched implanted vertical JFETs (TI-VJFETs) with self-aligned gate and source contacts were fabricated on commercial 4H-SiC epitaxial wafers. Gate regions were formed by aluminium implantation through the same silicon oxide mask which was used for etching mesa-structures. Self-aligned nickel silicide source and gate contacts were formed using a silicon oxide spacer formed on mesa-structure sidewalls by anisotropic thermal oxidation of silicon carbide followed by anisotropic reactive ion etching of oxide. Fabricated normally-on 4H-SiC TI-VJFETs demonstrated low gate leakage currents and blocking voltages exceeding 200 V.

Phase Change Random Access Memory Devices with Nickel Silicide and Platinum Silicide Electrode Contacts for Integration with CMOS Technology

Phase change random access memory (PCRAM) cells utilizing nickel monosilicide (NiSi) or platinum monosilicide (PtSi) as the bottom electrode as well as a heater material was demonstrated. Electrical and simulation results demonstrate the feasibility of employing silicides as a bottom electrode/heater in a PCRAM. The memory cells fabricated attained promising results such as low programming currents and sufficient resistance ratio between the crystalline (SET) and amorphous (RESET) states. A low RESET current of and a SET current of were obtained for contact dimensions of , while a resistance ratio of 2 orders of magnitude could be achieved employing PtSi as the bottom electrode. This work therefore enables the integration of PCRAM directly on the silicided drain regions of field effect transistors, facilitating compact integration in complementary metal-oxide-semiconductor (CMOS) technology with reduced process complexity and cost.