Selected Area Deposition Research Articles

In-situ temperature-dependent sheet resistance study of Cu films in oxygen ambient for heterogeneous integrations

Controlling and preventing Cu oxidation is crucial for improving the performance and reliability of Cu–Cu bonding. Ni-B films were selectively deposited on Cu films to block the Cu oxidation. The resistivity changes of the Cu films in N2 and O2 ambient were measured by using a four-point probe in the in situ temperature-dependent resistance measurements at the temperature from room temperature to 400 °C. The resistivity changes of the 100 nm thick Cu films without Ni-B increased rapidly at a higher temperature (284 °C) in the O2 ambiance. The change of resistivity-increase of 100 nm thick Cu with ∼50 nm thick Ni-B (top) film was lower than the Cu films without Ni-B films due to the blocking diffusion of O2 atoms by the Ni-B films. The resistivity-change and oxidation barrier properties were studied using scanning electron microscopy, FIB, transmission electron microscopy, EDX, and secondary ion mass spectroscopy tools. The proposed article will be helpful for the upcoming advancement in Cu–Cu bonding using selected-area deposition.

(Invited) Aligning Dense Arrays of Semiconducting Carbon Nanotubes for Logic and RF Technologies

Semiconductors are materials with electrical conductivity that can be switched on and off, that have allowed for nearly all electronics. However, most semiconductor devices utilize silicon, a microelectronics technology more half a century old. Silicon is now being extended to its limit and cannot meet the needs of next-generation devices.Carbon nanotubes are nanoscale semiconducting wires that conduct more electricity per area than silicon and more rapidly switch between on and off states with less voltage, making them ideal for next-generation fast, low-energy logic and high-speed, linear RF devices. However, no one has yet been able create a process for employing nanotubes commercially. In raw form, nanotubes are disordered and tangled and thus do not conduct electricity well. For nanotubes to be most useful, they must be lined up in the same direction in a single layer so that electricity can rapidly and efficiently travel through them. This has been a long-standing roadblock.This talk will present recent discoveries at the University of Wisconsin on (1) purifying and aligning semiconducting nanotubes into massively parallel arrays and (2) the research and development of semiconducting carbon nanotubes for logic and radio frequency technologies. We have pioneered nanotube array fabrication technologies that enable the (a) partial alignment of nanotubes (±30˚) via shear (demonstrated 100 mm wafer-scale); (b) finer alignment (±6˚) at liquid-liquid interfaces (demonstrated 100 mm size-scale); and, (c) the selected-area deposition of nanotube arrays (±7˚) in lithographically-defined patterns combining topographical and chemical features (demonstrated 25 mm size-scale). Most recently, we have discovered a powerful new mechanism for driving the self-assembly of nanotubes into aligned arrays, by coaxing them to form two-dimensional liquid-crystals. We have uncovered that when nanotubes are segregated to liquid-liquid interfaces, mesogenic interactions cause them to self-align (within +/-5.7 degrees so far) and self-assemble into dense arrays (> 100 per micron) like those needed for microelectronics. The assembled nanotubes are easily integrated on silicon substrates at room-temperature and integrated into high-performance devices.APL (2014); ACS Nano (2014); Science Advances (2016); Langmuir (2017); Adv Elect Materials (2019); Science Advances (2021); Nanoscale Advances (2021); JAP (2022). Highlights by Bloomberg News https://youtu.be/VsUF_CBJq50 (2022); US Patent 10,873,026; US Patent 10,074,819; US Patent 9,673,399.

Selected Area Deposition of High Purity Gold for Functional 3D Architectures.

Selected area deposition of high purity gold films onto nanoscale 3D architectures is highly desirable as gold is conductive, inert, plasmonically active, and can be functionalized with thiol chemistries, which are useful in many biological applications. Here, we show that high-purity gold coatings can be selectively grown with the Me2Au (acac) precursor onto nanoscale 3D architectures via a pulsed laser pyrolytic chemical vapor deposition process. The selected area of deposition is achieved due to the high thermal resistance of the nanoscale geometries. Focused electron beam induced deposits (FEBID) and carbon nanofibers are functionalized with gold coatings, and we demonstrate the effects that laser irradiance, pulse width, and precursor pressure have on the growth rate. Furthermore, we demonstrate selected area deposition with a feature-targeting resolutions of ~100 and 5 µm, using diode lasers coupled to a multimode (915 nm) and single mode (785 nm) fiber optic, respectively. The experimental results are rationalized via finite element thermal modeling.

Nanoparticle gas phase electrodeposition: Fundamentals, fluid dynamics, and deposition kinetics

This communication uncovers missing fundamental elements and an expanded model of gas phase electrodeposition; a relatively new and in large parts unexplored process, which combines particle generation, transport zone and deposition zone in an interacting setup. The process enables selected area deposition of charged nanoparticles that are dispersed and transported by a carrier gas at atmospheric pressure conditions. Two key parameters have been identified: carrier gas flow rate and spark discharge power. Both parameters affect electrical current carried by charged species, nanoparticle mass, particle size and film morphology. In combination, these values enable to provide an estimate of the gas flow dependent Debye length. Together with Langmuir probe measurements of electric potential and field distribution, the transport can be described and understood. First, the transport of the charged species is dominated by the carrier gas flow. In close proximity, the transport is electric field driven. The transition region is not fixed and correlates with the electric potential profile, which is strongly dependent on the deposition rate. Considering the film morphology, the power of the discharge turns out to be the most relevant parameter. Low spark power combined with low gas flow leads to dendritic film growth. In contrast, higher spark power combined with higher gas flow produces compact layers.

Study of a nanocrystalline cobalt coating prepared by area-selective electrodeposition.

Nanocrystalline Co coatings were successfully prepared on the surface of a steel substrate by droplet contact electrodeposition. Area-selective electrodeposition is performed by electrolyte drops contacting the surface of the substrate. By analyzing the current–time curve during the preparation of the coating, the influence of the selected area deposition pattern on the current–time curve is summarized. Meanwhile, microscopic observation, phase composition analysis, and performance testing of the coating were performed. The results show that the control procedure and deposition method directly affect the organization, morphology, and quality of the coating. The limited electrodeposition area and its continuous movement increase the nucleation rate and limit the growth of crystal nuclei. Therefore, the area-selective electrodeposition method has great advantages in preparing nanocrystals. The nanocrystalline Co coating was prepared on the surface of a steel substrate, and the surface hardness and corrosion resistance were improved.

Selective growth of diamond by hot filament CVD using patterned carbon film as mask

Selected-area deposition (SAD) of diamond films was achieved on silicon substrates with carbon film mask by hot filament chemical vapor deposition. Needle tip scraped lines were used to grow diamond films. Scanning electron microscope (SEM) investigation demonstrates that highly selective and sharp edged diamond films were produced. The results also demonstrate that the proper substrate temperature is very important for diamond selective growth in this deposition process. Since the enhancement of diamond growth was not observed on the needle tip scraped area of Si wafer with diamond powder scratching, the selective growth was considered to be closely correlated to silicon carbide formed during carbon film deposition and the residual carbon in the scraped area.

Selected area deposition of multiwalled carbon nanotubes from solution

A simple method is described for the area-selective deposition of multiwalled carbon nanotubes (MWCNTs) from solution. Selectivity is achieved by functionalizing the MWCNTs with groups that adsorbs preferentially on specific areas of a patterned substrate. Well-characterized octadecylester-functionalized MWCNTs are adsorbed directly from solution on to the substrate. The non-polar hydrocarbon chains interact more strongly with non-polar hydrogen-terminated Si surfaces than do polar oxide surfaces and this gives rise to area-selective adsorption of the MWCNTs on a patterned Si/SiO 2 substrate. Potential applications of this method and its application for other types of patterned substrates are discussed.

Selected-Area Deposition of Fibrous Carbon Nanomaterials from Ethanol Vapor at Substrate Temperatures below 500°C

Selected-area deposition of fibrous carbon nanomaterials at reduced substrate temperatures via pyrolysis of ethanol vapor is studied. The results demonstrate that, in a reactor fitted with an internal high-temperature heater, deposition is possible at substrate temperatures down to 330–350°C, which is about 150°C lower in comparison with conventional, externally heated reactors.

Electron emitters synthesized by selected area deposition of carbon nanotubes on silicon substrates

We have successfully attained patterned carbon nanotubes grown on two-dimensional Ni arrays of square blocks of various sizes on Si by a microwave-heated chemical vapor deposition process. The Ni blocks are either freestanding or isolated by the silicon dioxide. For patterned carbon nanotube emitters, grown on freestanding Ni blocks, the emission current–density increases with the size of the Ni blocks. To the contrary, patterned carbon nanotube emitters grown on 2 μm by 2 μm Ni blocks isolated by the silicon diode have exhibited an emission behavior as excellent as the un-patterned emitters; both emitters have very low turn-on and threshold fields being at ∼0.1 V/μm and ∼1.50 V/μm, respectively and can emit current density exceeding 120 mA/cm 2.

New insights into selected-area deposition of diamond films by means of selectiveseeding

Polycrystalline diamond films have been patterned on a polished Si substrate bymeans of selective seeding via hot-filament chemical vapour deposition. Inaddition to the process of selective seeding, the CH4/H2 concentration and thesizes of the patterns have effects on the selectivity. The mechanism of selectivegrowth of diamond is also discussed in this paper.

Field emission from well-aligned carbon nanotips grown in a gated device structure

Vertically well-aligned, high-aspect-ratio carbon nanotips have been directly grown upward on the gated device structure with 4 μm gate aperture. The nanotips rapidly nucleate and grow without any catalyst. In addition, selected area deposition of nanotips is achieved by using a Pt layer as inhibitor in the bias-assisted microwave plasma chemical vapor deposition. The field emission current of nanotips on the gated structure is 154 μA (at a gate-to-cathode voltage of Vgc=50 V). This results from the following reasons: (i) short gate-tips spacing, (ii) small gate aperture, and (iii) the high-aspect ratio of nanotips.

Study of carbon nanoemitters using CO2–CH4 gas mixtures in triode-type field emission arrays

In this study, we used methane/carbon dioxide gas mixtures to deposit nanoemitters on the gate-structured metal–insulator–semiconductor (MIS) diodes. Due to the nanoemitters growing in a high carbon concentration gas source of CH4/CO2, the growth rate is better than conventional mixtures by using hydrocarbons diluted in hydrogen. Moreover, the bias also promotes the growth rate in the CH4/CO2 gas mixtures. In addition, selected area deposition (SAD) of emitters was successfully achieved by using the Pt layer as inhibitor in the bias assisted microwave plasma chemical vapor deposition (BAMPCVD). The field emission current and the current density of nanoemitters on field emission arrays (FEAs) are 154 μA and 490 mA cm−2, respectively. This may be due to the following reasons: (I) short gate-emitter spacing; (II) small gate aperture; and (III) emitter with a sharp feature.

Properties of electron field emitters prepared by selected area deposition of CVD diamond carbon films

Selected area depositions (SAD) of diamond films were successfully achieved on silicon by two different approaches. In the first case, a standard lift-off technique employing a patterned SiO2 layer was used as a mask, and in the second case commercial ink-jet printer technology was adapted to be used to seed diamond nano-grit onto silicon. Patterned, boron-doped diamond pads roughly 5.6 μm in diameter were formed by CVD growth on patterned SiO2/Si substrates and found to be composed of closely packed carbon clusters approximately 250–800 nm in size each containing 50-nm particles embedded in them. The patterned diamond film seeded by ink-jet printing formed after CVD growth with in situ boron-doping, dots (85 μm in diameter) containing poly-crystals in the nanometre range. The resulting patterned diamond films were characterised by Raman and scanning electron microscope (SEM) analysis and then configured as cold cathode field emitters to determine their electron emission performance. The results suggest that patterned diamond films produced by ink-jet printing offer a simpler method for fabricating planar diamond emitter arrays with field emission and conduction properties which could be tailored to improve the performance and fabrication cost of cold field emitters in state-of-the-art field emission displays.

Nitrogen-doped diamond films selected-area deposition by the plasma-enhanced chemical vapor deposition process

Abstract The nitrogen-doped diamond films have been successfully synthesized by using urea as the nitrogen source. Selected-area deposition of diamond nuclei was formed by using a SiO 2 layer as the masking material. Diamond pads, around 9 μm in diameter, were obtained when the N-doped diamond films were deposited on these patterned diamond nuclei using the chemical vapor deposition process. An emission current density as high as 200 μA/cm 2 , with a turn-on field of around 8 V/μm, was obtained. However, the diamond emitters broke down easily, which is ascribed to the localized melting of the substrate materials surrounding the diamond pads.

Selected-area Deposition of Diamond Films on Silicon Nitride-coated Silicon Substrates Using Negatively Biased Microwave Plasma Enhanced Chemical Vapor Deposition Technique

Selected-area deposition (SAD) of diamond films has been successfully grown on silicon substrates, using silicon-rich nitride (SiN) precoatings and a negatively biased microwave plasma enhanced chemical vapor deposition technique. However, diamond growth is limited on stoichiometric nitride ( Si3N4) precoatings, which are ascribed to the insulation of these layers. The application of a negative bias voltage is thus blocked. Lowering the total pressure in the CH4/H2 mixture from 75 Torr to 60 Torr significantly suppresses the nucleation of diamonds on the Si-substrate, without modifying it on the SiN-substrate, so that a high selectivity (>200) SAD diamond film is obtained. Optical emission spectroscopy (OES) indicates that the large etching rate on the Si-surface, due to the reduction in the carbonaceous-to-hydrogen ratio, is the main factor of nucleation suppression. Scanning electron microscopy (SEM) and Raman spectroscopy indicate that the SAD and the quality of diamonds is optimized under deposition conditions such as 60 Torr total pressure, 2500 W microwave power, CH4-to-H2=15:300 sccm and 120 VDC bias.

Electron field emission characteristics of planar diamond film array synthesized by chemical vapor deposition process

Selected area deposition of diamond films on silicon substrates was successfully achieved using the patterned Pt layer as a nucleation inhibitor in the chemical vapor deposition process. The planar diamond film array thus made possesses good electron field emission properties, that is, emission current density of (Je)Si=150 μA/cm2 (under 23.6 V/μm) and turn on field of (Eo)Si=10 V/μm. Precoating a thin Au layer (20 nm) on a Si surface further increased the emission current density to (Je)Au/Si=960 μA/cm2 (under 23.6 V/μm) with (Eo)Au/Si=10 V/μm. The effective work functions (φ) estimated by Fowler–Nordheim plots of the I–V characteristics are (φ)Si=0.059 eV and (φ)Au/Si=0.085 eV. The emission properties of both planar diamond film arrays satisfy the requirement for applying as the electron emitters in the flat panel displays.

Selected-area deposition of diamond films on [formula omitted] surfaces with microwave plasma enhanced CVD

Selected-area deposition (SAD) of diamond films with selectivity greater than 200 was achieved on patterned SiN Si surface, using microwave plasma CVD method. Among the important parameters that can modify the plasma characteristics, the total pressure and CH 4-to-H 2 ratio were observed to influence the selected-area deposition behaviors most significantly. The number density of diamonds grown on Si surface decreased rapidly as the total pressure reduced from 75 Torr to 60 Torr. The selectivity of SAD diamond films increased as the CH 4-to-H 2 ratio increased from 9:300 sccm to 15:300 sccm. These phenomena were accounted for by the decrease in proportion of ion species with CH 4-to-H 2 ratio such that the formation of sp 3 bonds on Si surfaces is suppressed. Scanning electron microscopy (SEM) and Raman spectroscopy indicated that the quality of diamonds grown to SiN surface was optimized for the SAD films deposited under 2500 W microwave power with CH 4-to-H 2 = 15:300 sccm.

Selected-area deposition of multiple active films for conductometric microsensor arrays

A new generation of planar conductometric gas sensors is being developed which combines active semiconducting oxide films with Si-micromachined ‘micro-hotplate’ array structures. These devices are tailored for a variety of applications by tuning both the composition of multiple types of active films and the temperature cycles programmed for individual elements within an array. In this paper we described and demonstrate the approach, and present results for, a chemical vapor deposition (CVD)-based self-lithographic microfabrication method. This method is being examined as a highly efficient and compatible means of depositing oxide films and low-coverage catalytic metal overlayers on the microsensor elements of micro-hotplate arrays. Real-time monitoring of the film growth processe is provided by conductance measurements, and surveys of processing/property relationships can be performed in a very effective manner to determine optimal fabrication methods for multiple-active material arrays.

Nucleation and selected area deposition of diamond by biased hot filament chemical vapor deposition

This paper describes a process for uniformly enhancing the nucleation density of diamond films on silicon (Si) substrates via dc-biased hot filament chemical vapor deposition (HFCVD). The Si substrate was negatively biased and the tungsten (W) filaments were positively biased relative to the grounded stainless steel reactor wall. It was found that by directly applying such a negative bias to the Si substrate in a typical HFCVD process, the enhanced diamond nucleation occurred only along the edges of the Si wafer. This resulted in an extremely nonuniform nucleation pattern. Several modifications were introduced to the design of the substrate holder, including a metal wire-mesh inserted between the filaments and the substrate, in the aim of making the impinging ion flux more uniformly distributed across the substrate surface. With such improved growth system designs, uniform enhancement of diamond nucleation across the substrate surface was realized. In addition, the use of certain metallic wire mesh sizes during biasing also enabled patterned or selective diamond deposition.

Fabrication and characterization of diamond film thermistors

Diamond film thermistors were fabricated from polycrystalline diamond films grown on sintered Si3N4 by microwave plasma chemical vapor deposition. An undoped diamond layer and a zigzag or rectangular pattern of B-doped semiconducting diamond were successively deposited by a selected-area deposition technique. For ohmic electrodes, a Ti/Au bilayer was used. The resistance-temperature characteristics were measured from room temperature to 300 °C. It was found that the temperature coefficient of a diamond film thermistor with a B-doped diamond layer grown using 0.1 ppm B2H6 as dopant gas was higher than those of platinum resistive temperature detectors and SiC film thermistors.