Study of Ni Metallization in Macroporous Si Using Wet Chemistry for Radio Frequency Cross-Talk Isolation in Mixed Signal Integrated Circuits.

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of selected ultra-high-aspect-ratio macroporous regions that were electrochemically etched in p- Si substrates. The metallization process was conducted by means of wet chemistry in an alkaline aqueous solution containing Ni2+ without reducing agent. It is found that at elevated temperature during immersion, Ni2+ was rapidly reduced and deposited into macroporous Si and a conformal metallization of the macropore sidewalls was obtained in a way that the entire porous Si framework was converted to Ni. A conductive moat was as a result incorporated into p- Si substrate. The experimentally measured reduction of crosstalk in this structure is 5~18 dB at frequencies up to 35 GHz

Selective electroless nickel deposition on copper as a final barrier/bonding layer material for microelectronics applications

A low cost, selective electroless metallisation of integrated circuit (IC) copper bond pads with nickel and gold is demonstrated. This metallurgy can function as a barrier layer/bondable material when deposited as a thin layer or as the chip bump for flip chip applications when deposited to greater heights. Four alternative activation steps for selective electroless nickel deposition on bond pad copper are demonstrated. Selective low cost deposition has been achieved with a proprietary electroless plating bath developed at NMRC and three commercial baths on both sputtered copper substrates and electrolessly deposited copper on titanium nitride barrier layer material

Interfacial Electrochemistry and Surface Characterization: Hydrogen Terminated Silicon, Electrolessly Deposited Palladium & Platinum on Pyrolyzed Photoresist Films and Electrodeposited Copper on Iridium

Hydrogen terminated silicon surfaces play an important role in the integrated circuit (IC) industry. Ultra-pure water is extensively used for the cleaning and surface preparation of silicon surfaces. This work studies the effects of ultra-pure water on hydrogen passivated silicon surfaces in a short time frame of 120 minutes using fourier transform infrared spectroscopy – attenuated total reflection techniques. Varying conditions of ultra-pure water are used. This includes dissolved oxygen poor media after nitrogen bubbling and equilibration under nitrogen atmosphere, as well as metal contaminated solutions. Both microscopically rough and ideal monohydride terminated surfaces are examined. Hydrogen terminated silicon is also used as the sensing electrode for a potentiometric sensor for ultra-trace amounts of metal contaminants. Previous studies show the use of this potentiometric electrode sensor in hydrofluoric acid solution. This work is able to shows sensor function in ultra-pure water media without the need for further addition of hydrofluoric acid. This is considered a boon for the sensor due to the hazardous nature of hydrofluoric acid. Thin carbon films can be formed by spin coating photoresist onto silicon substrates and pyrolyzing at 1000 degrees C under reducing conditions. This work also shows that the electroless deposition of palladium and platinum may be accomplished in hydrofluoric acid solutions to attain palladium and platinum nanoparticles on a this film carbon surface for use as an electrode. Catalysis of these substrates is studied using hydrogen evolution in acidic media, cyclic voltammetry, and catalysis of formaldehyde. X-ray diffractometry (XRD) is used to ensure that there is little strain on palladium and platinum particles. Iridium is thought to be a prime candidate for investigation as a new generation copper diffusion barrier for the IC industry. Copper electrodeposition on iridium is studied to address the potential of iridium as a copper diffusion barrier. Copper electrodeposition is studied using a current-transient technique to obtain insight into the nucleation and growth mechanism. Copper on iridum was annealed up to 600 degrees C. X-ray photoelectron spectroscopy and XRD confirm that electrodeposited copper exists in a metallic state. XRD shows that copper exists in the characteristic face-centered cubic (111) form. XRD also confirms the stability of the copper-iridium interface with no new peaks after annealing, which is indicative that no interaction occurs. Scanning electron microscopy, and Scotch ® Tape peel tests confirm the uniformity and strength of copper on iridium even after annealing to 600 degrees C

Surface and molecular modification of polyimides via graft copolymerization and functionalization

Ph.DDOCTOR OF PHILOSOPH

Cu/Ni/Au multilayers by electrochemistry: A crucial system in electronics - A critical review

International audienc

Chemical approaches for doping nanodevice architectures

Advanced doping technologies are key for the continued scaling of semiconductor devices and the maintenance of device performance beyond the 14 nm technology node. Due to limitations of conventional ion-beam implantation with thin body and 3D device geometries, techniques which allow precise control over dopant diffusion and concentration, in addition to excellent conformality on 3D device surfaces, are required. Spin-on doping has shown promise as a conventional technique for doping new materials, particularly through application with other dopant methods, but may not be suitable for conformal doping of nanostructures. Additionally, residues remain after most spin-on-doping processes which are often difficult to remove. In-situ doping of nanostructures is especially common for bottom-up grown nanostructures but problems associated with concentration gradients and morphology changes are commonly experienced. Monolayer doping (MLD) has been shown to satisfy the requirements for extended defect-free, conformal and controllable doping on many materials ranging from traditional silicon and germanium devices to emerging replacement materials such as III-V compounds but challenges still remain, especially with regard to metrology and surface chemistry at such small feature sizes. This article summarises and critically assesses developments over the last number of years regarding the application of gas and solution phase techniques to dope silicon-, germanium- and III-V-based materials and nanostructures to obtain shallow diffusion depths coupled with high carrier concentrations and abrupt junctions

Solution-Based Photo-Patterned Gold Film Formation on Silicon Nitride

Silicon nitride fabricated by low-pressure chemical vapor deposition (LPCVD) to be silicon-rich (SiNx), is a ubiquitous insulating thin film in the microelectronics industry, and an exceptional structural material for nanofabrication. Free-standingcompelling, particularly when used to deliver forefront molecular sensing capabilities in nanofluidic devices. We developed an accessible, gentle, and solution-based photo-directed surface metallization approach well-suited to forming patterned metal films as integral structural and functional features in thin-membrane-based SiNx devices—for use as electrodes or surface chemical functionalization platforms, for example—augmenting existing device capabilities and properties for a wide range of applications

Surface functionalization of crystalline silicon substrates

In this work, various chemical and electrochemical methods were demonstrated to attach application-specific organic monolayers to crystalline silicon substrates. In one study, alkyl monolayers were anodically electrografted or thermally grafted onto planar (100) silicon substrates using Grignard precursors. The results show electrografted methyl monolayers provide a stable Si-C termination, resisting oxidation on (100) surfaces for approximately 55 days in air. The alkyl termination could provide a potential alternative to defective native oxides and kinetically unstable hydride surfaces. A mechanism involving two electron transfers per grafting event was established for both the thermal and electrochemical routes. In another study, unsaturated organic functional groups (phenylacetylene, 5-hexynoic acid) were cathodically electrografted onto planar (100) silicon substrates. Although cathodic grafting mechanism is considerably different, its voltammetric behavior (hysteresis, onset potential shifts) appears similar to anodic grafting process. Experimental results show both anodic and cathodic grafting methods may be applied to pattern the silicon surfaces in situ. Dielectric templates such as polystyrene microspheres or polydimethylsiloxane stamps were used to obtain high throughput, nanoscale monolayer patterns on silicon surfaces. The patterned monolayers may be further used to immobilize biological enzymes via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) chemistry or to direct selective copper electrodeposition or etching on silicon. Established grafting mechanisms were applied to functionalize nanoscale silicon anodes in lithium batteries to improve capacity retention with charge/discharge cycling. Silicon anodes present a safe, high-capacity alternative to conventional carbonaceous anodes; however, a significant capacity loss (\u3e20% initial value) is observed within the first few cycles, primarily due to 300% volume expansion upon lithiation. Silicon nanowires with atleast one dimension \u3c300 nm may withstand the volume expansion effects but may not completely eliminate the capacity fade. This residual fade is mainly a result of protective solid electrolyte interphase (SEI) layer formed on the anode surface due to electrolyte dissociation. Various ex situ and in situ functionalized silicon surfaces were investigated to establish engineered silicon-SEI interface with improved chemical, mechanical and electrical aspects. The work shows silicon lithiation is a function of surface chemistry and in situ methyl siloxane functionalization offers improved capacity retention with nanoscale silicon anodes in lithium batteries

Modern Applications of Novel Electroless Plating Techniques

This dissertation is composed of three distinct but closely related topics on the electrochemical metallization of substrates. The first topic solves the longstanding problem of galvanic corrosion in connection with exploiting the advantageous properties of magnesium {Mg} alloys and is of vital interest to the automotive and aerospace sectors. The second topic provides a new approach to the selective electroless metallization of silicon {Si} in connection with solar cells and other electronic devices. The third topic details a novel method of metal thin film formation using wet chemistry techniques which allow for the deposition of alternating metal layers of different and similar nobility from a single electrolyte. Future possible avenues of investigation are suggested for each of the three topics. The resolution of the galvanic corrosion issue, as presented within herein, is based on the direct electroless deposition of metal thin films less active than the Mg alloy substrates. Claddings of copper {Cu}, nickel boron {Ni-B}, and phosphorous {P} alloys including: nickel {Ni-P}, cobalt {Co-P}, nickel-zinc Ni-Zn-P}, and other ternary alloys, were successfully deposited directly on Mg alloy surfaces. The electroless coating of Mg alloys was accomplished using minimal pre-treatments and made use of the naturally active properties of Mg-based substrates. Qualitative measures of the corrosion resistance of Ni-Zn-P coatings on Mg alloys demonstrated superior resistance to galvanic corrosion compared to uncoated surfaces. The selective electroless metallization of Si is accomplished with the selective removal of the silicon oxide {SiO x } by means of mechanical scribing thereby exposing Si. The exposure of Si provides a catalytic surface for the electroless deposition of gold {Au}, and silver {Ag}, and other metals. The mechanical scribing provides an inexpensive avenue for the selective metallization of Si for solar cells. The novel method of depositing alternating metal layers of both different and similar nobility is achieved by combining electroplating and electroless deposition within a single electrolyte. The technique, termed here hybrid electro-electroless deposition (HEED), provides coatings previously unobtainable using wet electrochemical techniques. The application of HEED is of interest for the provision of sacrificial coatings on Mg alloys for corrosion protection within the transportation sector