High Aspect Ratio Contact Research Articles

Novel Enhancement Opportunities in the Thermal and Electrical Conductivity of α-Al-CNTs+AgNPs Nanocomposites

In this study, effort was made to develop novel, cutting-edge composite materials consisting of conducting Al-CNTs and green synthesis silver nanoparticles (AgNPs). Spark plasma sintering (SPS) and very intense ball milling were used to develop the composites. The nanocomposites' microstructure, thermal and electrical conductivity were determined. Al-4%CNTs was refined into finer grains when AgNPs are present. The Al-4%CNTs+2%Ag.NPs composite produces a higher dislocation density because of the production of sub-grain. Al-AgNPs + CNTs can be used to make conductors with a high aspect ratio and lower contact resistance at the CNT junctions. It was established that enhanced electrical and thermal conductivity can be obtained using the developed AgNPs from sustainable materials to increase the dispersion of CNTs in Al for the production of high tensile conductors.

Method for improving dry etching end point detection based on change in time accumulation correlation of plasma emitting wavelengths

This study proposes an optical emission spectroscopy (OES) analysis methodology to improve the ability to detect etching endpoints during high-level semiconductor plasma etching processes. Representative etching endpoint detection methods using single wavelength intensity or multiple wavelength intensity ratio changes include a low signal-to-noise ratio, high plasma instability, a small etching open area, and weak by-product emission signal problems due to deep etching under high-level process conditions such as high aspect ratio contact etching (HARC). As a result, it is difficult to detect the etching endpoint due to the very small or noisy change in the intensity over time due to the process progress of the wavelength selected by OES to detect the etching endpoint. In this study, a method of deriving an accumulative time correlation value according to process progress between selected wavelengths was developed by selecting all wavelengths observed in a specific wavelength region such as ultraviolet region in a spectrum emitted from plasma during a plasma etching process. After classifying the entire correlation signal groups derived as a pair of two intensity peak wavelengths into a dynamic time wrapping algorithm, the intensity change rate of the signal according to the process time was observed by selecting the signal with the most sensitive time change rate during the process. During the vertical nand flash memory manufacturing process, a test wafer for the purpose of detecting the etching endpoint was manufactured and evaluated under the conditions of the cell metal contact etching process, which is a high-level HARC etching process. As a result, it was confirmed that the signal selected by deriving the time accumulative correlation method had a high intensity change rate and a signal-to-noise ratio over time compared to a single wavelength or a plurality of wavelength ratio signals. The method proposed in this study is expected to contribute to process optimization by contributing to improving the ability to detect etching endpoints in high-level plasma etching processes in the future.

Improving detection of plasma etching end point using light compensation on optical emission spectra

When the high aspect ratio contact, called as HARC, hole dry etching process with a high degree of difficulty is carried out in the high performance memory manufacturing process, there is a problem that the sensitivity of the optical signal detection is low due to the small open ratio and the high aspect ratio of the hole when detecting the etching end point signal using the plasma light emission. In particular, due to the fluorocarbon polymer characteristics of fluorocarbon gas, such as C4F6, C4F8, C3F8, and CH2F2, which is mainly used in the HARC hole dry etching process, the viewport, which is a part to which the optical lens is connected to measure the plasma light emitting signal with optical emission spectroscopy, called as OES, can be contaminated with the fluorocarbon polymer coating. As a result of this viewport clogging phenomenon, the intensity of the optical signal collected gradually decreases during the process (∼4%), and thus the sensitivity of the etching end point signal indicating that the etching process is terminated gradually decreases. In this study, a xenon flashlamp for optical signal compensation was additionally applied to the existing OES structure to improve the detection of the etching end point during the HARC hole dry etching process. This can improve the detection sensitivity of the OES etching end point by monitoring the viewport clogging phenomenon in real time and compensating for the reduction of the collected OES signal. The pattern wafer for testing used to verify the effect of the etching end point consists of a structure in which a mold layer sequentially stacked with Si3N4, SiO2, and SiO2 are mixed as a single layer, and as a result of the experiment, it was confirmed that the detection sensitivity of the etching end point applied with the optical signal compensation method was 18% improved from the signal measured only by the existing OES. The method is expected to improve the detection sensitivity of etching end point during the next generation high difficulty HARC hole etching process to improve the plasma etching process control method.

Novel technology of high-aspect-ratio etch utilizing coverage-controllable atomic layer deposition

We demonstrated a coverage-controllable sidewall protective film by controlling the degree of oxidation during plasma-enhanced SiO2 atomic layer deposition (ALD) as a novel technology to suppress bowing in a high-aspect-ratio-contact (HARC) hole etch process. By depositing SiO2 protective film with atomic order on only the top-local region of patterns, to suppress bowing was achieved during HARC etch without the shrinkage of the bottom critical dimension (CD) and etch-stop. In addition, we investigated the parameters that determine the ALD coverage to estimate the coverage profile of sidewall protective film. By analyzing the relationship between activation time and ALD film thickness at each AR, we confirmed that the coverage is determined by the transport of oxygen radical based on the Knudsen transport model. Furthermore, we developed an ALD simulator from the transport model, and successfully estimated the coverage of protective film during etching to improve the verticality of the HARC profile with small bowing-bottom CD bias.

Various evolution trends of sample thickness in fluorocarbon film deposition on SiO2

Recently, fluorocarbon (FC) film deposition on a SiO2 surface has become one of the most important processes in semiconductor manufacturing because the formation of a passivation layer on SiO2 during the deposition process plays a crucial role in atomic layer etching and high aspect ratio contact (HARC) etching, areas that are attracting intense interest in the semiconductor industry. In this work, various trends of sample thickness change, namely, decreasing, increasing, and anomalously increasing trends with time, were observed during FC film deposition on a SiO2 surface. The total thickness including both SiO2 and FC film was found to change during the deposition process in various ways depending on the plasma conditions. This can be successfully explained by considering the mechanism of SiO2 etching with FC plasma, taking into account the dependence of the SiO2 etch rate on FC film thickness. This result is expected to be utilized in semiconductor processes such as HARC etching where a precise control of film thickness is needed.

Characterization of SiO2 Etching Profiles in Pulse-Modulated Capacitively Coupled Plasmas.

Although pulse-modulated plasma has overcome various problems encountered during the development of the high aspect ratio contact hole etching process, there is still a lack of understanding in terms of precisely how the pulse-modulated plasma solves the issues. In this research, to gain insight into previously observed phenomena, SiO2 etching characteristics were investigated under various pulsed plasma conditions and analyzed through plasma diagnostics. Specifically, the disappearance of micro-trenching from the use of pulse-modulated plasma is analyzed via self-bias, and the phenomenon that as power off-time increases, the sidewall angle increases is interpreted via radical species density and self-bias. Further, the change from etching to deposition with decreased peak power during processing is understood via self-bias and electron density. It is expected that this research will provide an informative window for the optimization of SiO2 etching and for basic processing databases including plasma diagnosis for advanced plasma processing simulators.

Formulation and Evaluation of Diluted Sulfuric-Peroxide-HF (DSP+) Mixtures for Cleaning High-Aspect Ratio Contacts in 3D NAND

In this study, organic strip, particle removal efficiency and wettability were investigated at different mixing concentrations of diluted Sulfuric-Peroxide-HF (DSP+) solutions with and without the addition of IPA. Organic strip evaluation was carried out with KrF photoresist (PR), and the strip rate was increased rapidly with the increase in H2SO4 concentration mixed with DI water (DIW). The effects of H2O2 and IPA addition on diluted H2SO4 were observed below 30 vol% of H2SO4. The thickness of PR was increased with the addition of H2O2 to the solutions and the strip rate was increased when IPA was added. Silica particles were used to evaluate particle removal efficiency. The concentration of HF was the predominant factor of increasing PRE, and the addition of H2SO4 and H2O2 assisted in obtaining high PRE, while IPA addition reduced PRE. Decreasing of contact angle was observed with an increase of IPA addition to DSP+ solutions, and improved wettability of DSP+ solutions was expected to effectively clean particles in high-aspect-ratio (HAR) contact holes.

Silver dendrites based electrically conductive composites, towards the application of stretchable conductors

Abstract Among reported stretchable conductors, electrically conductive composites (ECCs) have the advantages of low cost, simplicity in circuit design and fabrication, and good reliability. However, the resistivity of conventional stretchable ECCs usually increases during stretching as a result of the loss of contact between neighboring conductive fillers. Here we prepared stretchable ECCs filled with silver dendrites. Due to the high aspect ratio, hierarchy structure, and multiple contact points in all dimensions, ECCs filled with silver dendrites have lower percolation threshold compared with conventional ECCs filled with silver particles or flakes. Moreover, ECCs filled with silver dendrites show a unique decrease in resistivity during stretching. The resistivity can decrease from 5 × 10−4 Ω·cm to as low as 1.1 × 10−4 Ω·cm at 100% elongation. Due to the high conductivity during stretching, the ECCs are used to prepare stretchable capacitors and antennas, demonstrating the stable electrical performance of ECCs under strain.

A unified semi-global surface reaction model of polymer deposition and SiO2 etching in fluorocarbon plasma

We propose a semi-global surface reaction model to capture simultaneous polymer deposition and oxide etching in fluorocarbon plasma. The critical parameters of this model within reasonable ranges can be determined using predesigned experimental data with plasma diagnostics in inductively coupled fluorocarbon plasma. This model can describe the transition behavior from polymer deposition to oxide etch self-consistently without ad-hoc assumptions, providing better insight into abnormal etching behaviors in high aspect ratio contact hole etching, such as sidewall bowing and twisting toward next generation of memory devices in semiconductor industries.

Contact Resistance Improvement for Advanced Logic by Integration of Epi, Implant and Anneal Innovations

ABSTRACTAs advanced CMOS scaling with FinFETs continues beyond the 10/7nm nodes, contact resistance (Rc) remains a dominant component affecting device performance. The FinFET Source/Drain (S/D) contact area has become smaller with fin pitch scaling, resulting in drastically increased Rc. To achieve higher drive currents and fully realize the performance gain from FinFET architectural changes, it is critical to continue to reduce contact resistivity (ρc) < 1.0x10-9 Ω.cm2 for both NMOS and PMOS. In this paper, we review the recent trends for ρc reduction for advanced CMOS devices and discuss approaches that have demonstrated reduction in ρc, such as in-situ heavily doped epitaxial films for S/D, advanced ion implantation and laser anneals. The implant techniques include pre-amorphization implants (PAI), dopant boosting implants, cryogenic (-100°C) implants for damage engineering and plasma doping (PLAD) for conformal doping of high aspect ratio (HAR) contacts. With such high levels of doping from epi and implants, advanced laser anneals are key for epitaxial regrowth and formation of metastable alloys for dopant supersaturation or segregation in top layers. Millisecond laser anneal (MSA) improves dopant activation and nanosecond laser anneal (NLA) permits superactivation, and both have become key enablers for ρc reduction. This paper also reviews two alternative contact approaches: dual silicide scheme and wrap-around contact (WAC), as potential pathways to further reduce Rc for advanced CMOS nodes.

Process Development of Radical Based Dry Clean for Advanced 3D NAND Fabrication

As semiconductor device scaling marching toward sub-5 nm logic, 128+ layers 3D NAND, and advanced 1x nm DRAM technology nodes, wafer surface cleaning and residue removal in nanoscale, high aspect ratio structures become increasingly critical. Dry clean technologies are developed as alternatives for traditional wet clean applications with significant advantages in process extendibility and environmental friendliness. Furthermore, in comparison with gas only processes, radicals are considered as attractive precursors for dry clean applications due to their high reactivity en route to a high cleaning efficiency. In this work we report a novel inductively coupled remote plasma source design for radical based dry clean applications. The inductively couple plasma (ICP) source yields a high gas dissociation efficiency and a high radical density. Plasma potential and electron temperature are minimized with a unique grounded Faraday shield design and can be further suppressed with a pulsed plasma operation. Ions and electrons generated in the plasma are effectively filtered by charge separation grids, thus only leaving high flux radicals to impinge onto the wafer surface. Different radical chemistries are developed for selective removal of different dielectric, metal, and semiconductor materials, specifically for efficient cleaning inside nanoscale and high aspect ratio structures in advanced semiconductor devices. Here we report the following applications tailored toward 3D NAND manufacturing. Pre-epitaxial deposition clean in high-aspect-ratio channel holes: The requirements are to remove SiOx-like residues and damaged silicon layer at the bottom of high-aspect-ratio channel holes without damage to the exposed SiO2/SiN stacks. The aspect ratio of channel holes can exceed 50:1. A multi-step process is developed based on remote plasma chemistries containing hydrogen and fluorine radicals, in conjunction of a RF bias on wafer surface to improve directionality. SiOx-like residues of various thickness are initially completely removed at the bottom of high-aspect ratio structures. With a customized radical chemistry and a unique anisotropic process, there is no sidewall SiN/SiO2 damage and a minimal CD change. Followed by a selective removal of damaged silicon layer and surface contamination from prior etch process, a pristine and coherent surface can be prepared for the subsequent epitaxial deposition. Contact hole clean: The main objective is to remove amorphous silicon or silicon oxide interface layer at bottom of high aspect ratio contact hole structures in order to minimize metal contact resistance. The aspect ratio of contact hole structures can exceed 50:1 in advanced 3D NAND devices. Device process flow requires a high selectivity towards tungsten. A fluorine-containing remote plasma process was developed to effectively remove oxidized Si residues, create enough gouging depth, and maintain contact hole structure integrity at the same time. Contact resistance is significantly reduced with the radical based dry clean process.

Process Development of Radical Based Dry Clean for Advanced 3D NAND Fabrication

As semiconductor device scaling marching toward sub-5 nm logic, 128+ layers 3D NAND, and 1x nm DRAM, wafer surface cleaning and residue removal in nanoscale, high aspect ratio (AR) structures become increasingly critical. Dry plasma clean technologies based on reactive radicals are developed as alternatives for traditional wet clean applications with significant advantages in process extendibility and environmental friendliness. Here we report a novel inductively coupled remote plasma design for radical based dry clean applications. A high gas dissociation efficiency and a high radical density were achieved with controllable radical component, energy, and reactivity. Two applications, including residue clean in high aspect ratio channel holes and contact holes (AR ~ 50:1), are tailored for 3D NAND manufacturing. Complete removal of oxide and polymeric residues, smooth and pristine Si surface, and considerably reduce contact resistance can be simultaneously achieved with the customized clean chemistries. Applications in mass production have been accomplished.

Direct 3D Printing of Hybrid Nanofiber-Based Nanocomposites for Highly Conductive and Shape Memory Applications

Three-dimensional (3D) printing with conductive polymer nanocomposites provides an attractive strategy for the "on-demand" fabrication of electrical devices. This paper demonstrates a family of highly conductive multimaterial composites that can be directly printed into ready-to-use multifunctional electrical devices using a flexible solvent-cast 3D printing technique. The new material design leverages the high aspect ratio and low contact resistance of the hybrid silver-coated carbon nanofibers (Ag@CNFs) with the excellent 3D printability of the thermoplastic polymer. The achieved nanocomposites are capable of printing in open air under ambient conditions, meanwhile presenting a low percolation threshold (i.e., <6 vol %) and high electrical conductivity (i.e., >2.1 × 105 S/m) without any post-treatments. We further find that this hybrid Ag@CNF-based nanocomposite shows a quick and low-voltage-triggered electrical-responsive shape memory behavior, making it a great candidate for printing electroactive devices. Multiple different as-printed Ag@CNF-based highly conductive nanocomposite structures used as high-performance electrical devices (e.g., ambient-printable conductive components, microstructured fiber sensors, flexible and lightweight scaffolds for electromagnetic interference shielding, and low-voltage-triggered smart grippers) are successfully demonstrated herein. This simple additive manufacturing approach combined with the synergic effects of the multimaterial nanocomposite paves new ways for further development of advanced and smart electrical devices in areas of soft robotics, sensors, wearable electronics, etc.

Surface‐treated kaolin minerals as a complement or substitute to glass fibers in thermoplastics

Glass fiber (GF)‐related mold abrasion and tool wear make it undesirable for certain thermoplastics applications. Furthermore, fiber attrition during processing and orientation sensitivity raise concerns over compromised performance. In this study, kaolin minerals with varying properties and surface‐treatments are tested to potentially replace GFs in nylon composites. Composites are melt‐compounded and injection molded using lab‐scale and industrial‐scale equipment. Mechanical properties (tensile, flex, impact), heat distortion temperature, and thermal decomposition using thermogravimetric analysis (TGA) are used to comparatively characterize kaolin composite formulations against 30% weight GF composites. Kaolin minerals with high aspect ratio and good interfacial contact are found to show strength and modulus improvements up to 80% that of GF. Additionally, low aspect ratio kaolin composites were found to surpass GF composites in impact strength. A synergistic effect is found between high and low aspect ratio kaolin that can potentially lead to further enhancement in properties with the added possibility of blending minerals to customize composite performance. Such findings suggest that kaolin minerals can be used to customize the properties of composites in manners previously unattainable through GF usage alone. Scale up trials show potential for kaolin to replace GFs at industrial levels. POLYM. ENG. SCI., 59:E330–E338, 2019. © 2018 Society of Plastics Engineers

Enhancement of vertical integration density by engineered BSOI wafers

The lateral and vertical integration density of bulk microelectromechanical systems (MEMS) using bonded silicon-on-insulator (BSOI) wafers is significantly enhanced if the handle wafer is used as an electrical redistribution layer. Therefore isolated conductive paths should be integrated in the handle wafer, which are connected to the surface of the BSOI-wafer by high aspect ratio contacts (VIAs) through the device layer of the BSOI-wafer. In the present study we report on a fabrication process for customer specific designed BSOI wafers with VIAs from the device to the handle layers. Wafer bonding, wafer edge shaping and thinning of the wafers, which are critical processes for the fabrication of the BSOI-wafers, are discussed. The contacts to the handle wafer through the 75 µm thick device layer are created by 10 µm wide and 75 µm deep trenches filled with highly doped n-type poly-silicon. From current–voltage measurements an ohmic behaviour of the contacts with a resistance of around 120 Ω is demonstrated.

(Invited) Process and Integration of Dielectrics Required for 10nm and Beyond Scaling

Over the past decade traditional scaling by simple linear shrinking has effectively ceased as IC makers have adopted new 3-dimensional device structures, complex integration schemes and new processes and materials for an expanding number of applications in order to overcome fundamental physical limits. This trend will accelerate as devices are scaled to a level approaching atomic dimensions. Dielectric materials with tailored properties are required to meet future device needs. And deposition processes that are self-limited (e.g. Atomic Layer Deposition (ALD)), or self-directed (e.g. selective deposition) will enable those materials to be used in scaled 3D devices. Highly tailored ALD processes are being investigated to fabricate functional material layers. Interspersed treatments and doping to make ternary materials may be used to modify the physical and electrical properties of ALD films further in order to optimize the resulting physical or electrical properties. To improve device contacts, ultra-thin dielectrics and metal layers may be deposited inside of high aspect ratio contact structures in order to provide lower contact resistivity- or may be used to provide solutions for integration of new contact structures. Selective deposition processes can be used to deposit functional materials only where they are needed, thus reducing the patterning burden during IC manufacturing. Future use of new transistor channel materials, such as III-V and Ge, will require the use of ALD gate dielectrics with compatible treatment schemes in order to passivate defects and provide EOT scaling inside of ultra-high ratio replacement gate structures. Examples of these and similar processes will be described and discussed with the goal of discerning a path beyond 10nm devices.

Biaxial reinforcements for polybutene-1 medical-tubes achieved via flow-design controlled morphological development of incorporated polystyrene: In-situ microfibrillation, alignment manipulation and performance optimization

Abstract By means of goal-directed flow designing and morphology controlling, this paper opened up an efficient method of continuously mass-producing biaxially reinforced polystyrene (PS)/polybutene-1(PB-1) tubes for medical application. The experimental results showed that the PS microfibers were in-situ formed by imposing a specific convergent flow onto the off-die PS/PB-1 blend melt, exhibiting excellent dispersion, high aspect ratio and good interfacial contact. As a result, the ultimate axial strength (UAS) of the microfibrillar PS/PB-1 tubes was enhanced from 29.9 MPa of conventional neat PB-1 tubes to 41.3 MPa. Moreover, by introducing the rotating mandrel or die to modify the flow to helical convergent flow, the formed PS microfiber deviated from axial direction to further improve hoop damage strength (HDS) performances. Particularly, via counter-helical convergent flow extrusion controlled by the counter-rotating mandrel and die system, the opposite-handed helical configuration of PS microfibers was brought out to eliminate the inter-fiber relative slip. As a result, the PS/PB-1 composite tubes exhibited remarkably reinforced mechanical performances in both UAS (40.3PMa) and HDS (34.9 MPa) tests, improved by 34.8% and 48.5% compared to Conv-E neat PB-1. These results suggest that such bi-axially reinforced microfibrillar tubes could be of benefit to ensure the structural integrity of artificial medical tubing systems.

Study on spatial distribution of plasma parameters in a magnetized inductively coupled plasma

Spatial distributions of various plasma parameters such as plasma density, electron temperature, and radical density in an inductively coupled plasma (ICP) and a magnetized inductively coupled plasma (M-ICP) were investigated and compared. Electron temperature in between the rf window and the substrate holder of M-ICP was higher than that of ICP, whereas the one just above the substrate holder of M-ICP was similar to that of ICP when a weak (&amp;lt;8 G) magnetic field was employed. As a result, radical densities in M-ICP were higher than those in ICP and the etch rate of oxide in M-ICP was faster than that in ICP without severe electron charging in 90 nm high aspect ratio contact hole etch.

Reducing the aspect ratio of contact holes by in situ low-angle cross sectioning

Auger analysis of high-aspect ratio contact holes of integrated microelectronic devices is a challenging analytical task. Due to geometrical shadowing the primary electron beam and the energy analyser have not the required direct line of sight to the analysis area simultaneously. To solve this problem sample preparation is needed to flatten the three-dimensional geometry. Here the new approach of in situ low-angle cross sectioning is applied. By this method material gets removed inside the Auger instrument while the sample is sputtered by Ar+ ions at nearly grazing incidence utilizing the edge of a mask, which partly covers the sample. A very shallow bevel with respect to the sample surface is produced. Thus along the bevel contact holes with suitable aspect ratios are available for the Auger analysis.

Study on contact distortion during high aspect ratio contact SiO2 etching

As pattern density is increased in semiconductor integrated circuits (ICs) and pattern sizes are decreased to nanometer scale, high aspect ratio contact etching has become one of the most difficult processes in nanoscale IC fabrication. The increase in aspect ratio of the contact oxide etching raises problems such as low mask selectivity, microloading, pattern degradation, and etch stops. In this study, the authors investigated the effect of various oxide etch conditions such as mask materials, mask thickness, and oxide etch processes, on contact profile degradation. The results showed that greater contact pattern distortion occurred as the aspect ratio of the etched oxide was increased. The use of amorphous carbon instead of amorphous silicon as the etch mask, and the use of a more carbon-rich gas composition, lessened pattern distortion. The polymer deposited at the interface between the mask layer and the oxide layer appeared to significantly affect the degree of contact pattern distortion. By adding an in-situ polymer removal step during the overetch of a multistep contact oxide etch process with a 20:1 aspect ratio, about a 7% improvement in pattern distortion could be obtained without changing other conditions.