Step Coverage Research Articles

Hard mask and lithographic capabilities improvement by amorphous carbon step coverage optimization in high aspect ratio device pattern

Due to the complexity of micro control unit (MCU), the fabrication process of MCU has become very challenging, and in particular the hard mask (HM) and lithographic technologies. Therefore, it is very important to improve the performance of the two processes. The performances of the HM and lithographic processes strongly depend on the step coverage (S/C) of HM. Poor HM S/C will directly impact the protection provided by HM on device patterning during the etching process and overlay marks during photoresist (PR) rework. The application of C2H2 base amorphous carbon (a-C) to form the HM instead of C3H6 base a-C can achieve better sidewall and bottom S/C due to the fact that C2H2 base a-C has superior sticking coefficient (higher carbon to hydrogen (C/H) ratio). Furthermore, the silicon (Si) center damaging problem in device patterning is alleviated by the good S/C performance of C2H2 base a-C. Experimental results have demonstrated that the overlay mark is not damaged with five PR reworks with the application of C2H2 base a-C. Furthermore, a process parameter design of experiment (DOE) for C2H2 base a-C to obtain the trends of sidewall and bottom S/C is proposed. The presented experimental results show that bad sidewall S/C of a-C film induces the Si edge damage in high aspect ratio device patterning. The proposed DOE will allow us to optimize the C2H2 base a-C process to improve the S/C by 49%–91% better than the unoptimized process. This helps to reduce the amount of device pattern damage significantly.

Kinetic effects of methanol addition on supercritical fluid deposition of TiO2

Methanol-assisted supercritical fluid deposition of TiO2 (TiO2-SCFD), which had previously provided uniformly thick films on deep trenches with an aspect ratio (AR) above 30, was kinetically analyzed. To assess the overall reaction kinetics, a novel analytical scheme exploiting micro/macrocavities and flow/closed reactors was developed. Two reaction paths were thereby revealed: surface reaction of the precursor and consecutive reactions starting from homogeneous reactions of the precursor in the fluid (fluid-phase reaction), followed by the surface reaction of the intermediate species. Compared with the original TiO2-SCFD, methanol addition enhanced the surface reaction rate constant and thus growth rate, although the step coverage was slightly deteriorated. Nevertheless, it still had good step coverage on the high-aspect-ratio features (e.g., a step coverage of 85% on a trench with an AR of 50). Methanol addition is an effective way to promote the growth rate insofar as conformal deposition has been ensured on the targeted structure.

Using the light scattering properties of multi-textured AZO films on inverted hemisphere textured glass surface morphologies to improve the efficiency of silicon thin film solar cells

We report the light scattering characteristics of multi-textured aluminum-doped zinc oxide (AZO) thin films with high optical transmittance, haze ratio and step coverage for amorphous silicon thin film solar cells (a-Si TFSCs). Multi-textured AZO films were deposited on inverted hemisphere textured (IHT) glass surface morphologies. Multi-textured process was used to create modulated surface morphologies with micro and nano-features useful for the light scattering in visible as well as near-infrared wavelength region. Highly transparent IHT glass surface morphologies with high haze ratio were prepared by wet chemical etching of periodic glass substrates. Total transmittance of the IHT glass substrates showed higher average values (91.38–93.40%) as compared to that of bare glass (90.94%) in the visible wavelength region due to lower reflectance. Multi-textured AZO films showed higher rms roughness 100.479 nm, optical transmittance 82.60% and haze ratio 75.09% in the visible wavelength region. X-ray photoelectron spectroscopic analysis of multi-textured AZO thin films was used to study the atomic compositions and chemical binding states. Multi-textured AZO films with high transmittance and haze ratio were used as front transparent conductive oxide layers for the fabrication of a-Si TFSCs using an absorber layer thickness of 400 nm. Multi-textured AZO films deposited on the optimal textured glass surface morphologies yield the maximum performance of a-Si TFSCs as; Voc = 871 mV, Jsc = 16.55 mA/cm2, FF = 66.6% and η = 9.61%. An enhancement of photocurrent was noticed from 15.64 to 16.55 mA/cm2 for the a-Si TFSCs deposited on as deposit AZO to optimal textured AZO films.

SiO2 tunneling and Si3N4/HfO2 trapping layers formed with low temperature processes on gate-all-around junctionless charge-trapping flash memory devices

The SiO2 tunneling and Si3N4/HfO2 trapping layers formed with low temperature (LT) processes on operation characteristics of gate-all-around (GAA) junctionless (JL) charge trapping (CT) flash memory devices were studied in this work. The devices with an Ω-nanowire configuration were also compared. The faster operation speeds and larger memory windows are achieved by a GAA configuration. However, the worse retention characteristics for GAA devices may be caused by the SiO2 and Si3N4 layer with worse step coverage, which are formed by the LT processes. The coverage issues of dielectrics deposited with LT processes in GAA JL CT flash devices need solutions for 3D memory applications.

Novel Cyclosilazane-Type Silicon Precursor and Two-Step Plasma for Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride.

We designed cyclosilazane-type silicon precursors and proposed a three-step plasma-enhanced atomic layer deposition (PEALD) process to prepare silicon nitride films with high quality and excellent step coverage. The cyclosilazane-type precursor, 1,3-di-isopropylamino-2,4-dimethylcyclosilazane (CSN-2), has a closed ring structure for good thermal stability and high reactivity. CSN-2 showed thermal stability up to 450 °C and a sufficient vapor pressure of 4 Torr at 60 °C. The energy for the chemisorption of CSN-2 on the undercoordinated silicon nitride surface as calculated by density functional theory method was -7.38 eV. The PEALD process window was between 200 and 500 °C, with a growth rate of 0.43 Å/cycle. The best film quality was obtained at 500 °C, with hydrogen impurity of ∼7 atom %, oxygen impurity less than 2 atom %, low wet etching rate, and excellent step coverage of ∼95%. At 300 °C and lower temperatures, the wet etching rate was high especially at the lower sidewall of the trench pattern. We introduced the three-step PEALD process to improve the film quality and the step coverage on the lower sidewall. The sequence of the three-step PEALD process consists of the CSN-2 feeding step, the NH3/N2 plasma step, and the N2 plasma step. The H radicals in NH3/N2 plasma efficiently remove the ligands from the precursor, and the N2 plasma after the NH3 plasma removes the surface hydrogen atoms to activate the adsorption of the precursor. The films deposited at 300 °C using the novel precursor and the three-step PEALD process showed a significantly improved step coverage of ∼95% and an excellent wet etching resistance at the lower sidewall, which is only twice as high as that of the blanket film prepared by low-pressure chemical vapor deposition.

Performance of WCN diffusion barrier for Cu multilevel interconnects

The electrical and thermal properties of a WCN diffusion barrier have been studied for Cu multilevel interconnects. The WCN has been prepared using an atomic layer deposition system with WF6–CH4–NH3–H2 gases and has a very low resistivity of 100 µΩ cm and 96.9% step coverage on the high-aspect-ratio vias. The thermally stable WCN maintains an amorphous state at 800 °C and Cu/WCN contact resistance remains within a 10% deviation from the initial value after 700 °C. The mean time to failure suggests that the Cu/WCN interconnects have a longer lifetime than Cu/TaN and Cu/WN interconnects because WCN prevents Cu migration owing to the stress evolution from tensile to compressive.

Sulfur poisoning of Ni/Gadolinium-doped ceria anodes: A long-term study outlining stable solid oxide fuel cell operation

This work presents an analysis of the long-term behavior of nickel/gadolinium-doped ceria (CGO) anode-based solid oxide fuel cells (SOFC) under sulfur poisoning conditions. A parameter study of sulfur-induced irreversible long-term degradation of commercial, high-performance single cells was carried out at 900 °C for different H2/N2/H2S fuel gas atmospheres, current densities and Ni/CGO anodes. The poisoning periods of the cells varied from 200 to 1500 h. The possibility of stable long-term Ni/CGO anode operation under sulfur exposure is established and the critical operating regime is outlined. Depending on the operating conditions, two degradation phenomena can be observed. Small degradation of the ohmic resistance was witnessed for sulfur exposure times of approximately 1000 h. Moreover, degradation of the anode charge transfer resistance was observed to be triggered by the combination of a small anodic potential step and high sulfur coverage on Ni. The microstructural evolution of altered Ni/CGO anodes was examined post-mortem by means of SEM and FIB/SEM, and is correlated to the anode performance degradation under critical operating conditions, establishing Ni depletion, porosity increase and a tripe phase boundary density decrease in the anode functional layer. It is shown that short-term sulfur poisoning behavior can be used to assess long-term stability.

О СТАНОВЛЕНИИ ЖАНРА МУЗЫКАЛЬНОЙ КОМЕДИИ В КАБАРДИНО-ЧЕРКЕССКОЙ ДРАМАТУРГИИ

The article is devoted to the study of the questions of origin, formation and development of a musical comedy, which remain the least studied in Adyghe literary criticism. In this regard, attention is focused on the genre identity of the Kabardino-Circassian comedy as a kind of dramatic art. It is established that, unlike the Adyghe and Circassian comedy, the Kabardian comedy has accumulated more experience and has become the heritage of the music world much earlier. In this connection, the main attention in the paper is paid precisely to the problem of scientific coverage of the first steps of Kabardian musical comediography.

Nano crystalline diamond MicroWave Chemical Vapor Deposition growth on three dimension structured silicon substrates at low temperature

Nano crystalline diamond (NCD) films grown at a temperature below 400 °C can open new applications on temperature sensitive substrates such as polymers or low-melting point alloys. One requirement for the applicative use of NCD is the ability of depositing on a structured substrate having high aspect ratio. This work presents a study on the three dimensional (3D) conformity of NCD deposition at low temperature (350 °C) and low pressure (30 Pa). Silicon wafers have been structured using a mask-less photolithography and (hardmask-less) Deep Reactive Ion Etching (DRIE) process and seeded with nano-diamond particles. The NCD films were grown on these 3D patterned Si substrates with various trench geometries to provide means of determining the limiting geometries of this technique. By measuring the step coverage with changing trench width, a threshold for conformal NCD growth can be determined. The NCD films at the bottom of the 100 μm deep trenches were continuous down to an aspect ratio of 1:7.

Atomic layer deposition of copper thin film and feasibility of deposition on inner walls of waveguides

Copper thin films were deposited by plasma-enhanced atomic layer deposition at low temperature, using copper(I)-N,N′-di-sec-butylacetamidinate as a precursor and hydrogen as a reductive gas. The influence of temperature, plasma power, mode of plasma, and pulse time, on the deposition rate of copper thin film, the purity of the film and the step coverage were studied. The feasibility of copper film deposition on the inner wall of a carbon fibre reinforced plastic waveguide with high aspect ratio was also studied. The morphology and composition of the thin film were studied by atomic force microscopy and x-ray photoelectron spectroscopy, respectively. The square resistance of the thin film was also tested by a four-probe technique. On the basis of on-line diagnosis, a growth mechanism of copper thin film was put forward, and it was considered that surface functional group played an important role in the process of nucleation and in determining the properties of thin films. A high density of plasma and high free-radical content were helpful for the deposition of copper thin films.

Design rules for vertical interconnections by reverse offset printing

Formation of vertical interconnections by reverse offset printing was investigated, particularly focusing on the transfer step, in which an ink pattern is transferred from a polydimethylsiloxane (PDMS) sheet for the step coverage of contact holes. We systematically examined the coverage of contact holes made of a tapered photoresist layer by varying the hole size, the hole depth, PDMS elasticity, PDMS thickness, printing speed, and printing indentation depth. Successful ink filling was achieved when the PDMS was softer, and the optimal PDMS thickness varied depending on the size of the contact holes. This behaviour is related to the bell-type uplift deformation of incompressible PDMS, which can be described by contact mechanics numerical simulations. Based on direct observation of PDMS/resist-hole contact behaviour, the step coverage of contact holes typically involves two steps of contact area growth: (i) the PDMS first touches the bottom of the holes and then (ii) the contact area gradually and radially widens toward the tapered sidewall. From an engineering perspective, it is pointed out that mechanical synchronisation mismatch in the roll-to-sheet type printing invokes the cracking of ink layers at the edges of contact holes. According to the above design rule, ink filling into a contact hole with thickness of 2.5 µm and radius of 10 µm was achieved. Contact chain patterns with 1386 points of vertical interconnections with the square hole size of up to 10 µm successfully demonstrated the validity of the technique presented herein.

Step coverage of the barrier films deposited onto patterned photoresist

In this study, silicon oxynitride (SiOxNy) films and three-paired organosilicon/SiOxNy multilayered structures prepared by the plasma-enhanced chemical vapor deposition were respectively deposited onto the polyethylene terephthalate and silicon substrate with overcut and undercut patterned photoresist to mimic the packaging of the patterned organic light emitting diodes (OLEDs) and surface contaminants. The step coverage at the bottom and sidewall surface was conducted from the cross-sectional scanning electron microscopy observations. A methodology for investigating the position-dependent coverage at the concave region of the sidewall surface on the undercut patterns was developed. The increase in the water vapor transmission when these barrier structures were deposited onto polyethylene terephthalate substrate was linked to the decrease in their coverage at the sidewall surface, which was ascribed to the reduction in the diffusion path for water vapor permeation. It also was demonstrated that the degradation in the barrier property was significant as those structures coated onto the undercut patterns originating from the precursors hardly arrived at the concave region. However, although the film growth at the concave region of the sidewall surface was limited, paired organosilicon/SiOxNy structures still showed a superior barrier property to that of single SiOxNy film as the appearance of the organosilicon film in the paired structure was favorable to prolonging the diffusion length for water vapor permeation. The investigation into the barrier structures coated onto the patterned surface was beneficial for better understanding the package reliability on the patterned OLED devices.

High performance few-layer MoS2 transistor arrays with wafer level homogeneity integrated by atomic layer deposition

Wafer-level integration of 2D transition metal disulfide is the key factor for future large-scale integration of the continuously scaling-down devices, and has attracted great attention in recent years. Compared with other ultra-thin film growth methods, atomic layer deposition (ALD) has the advantages of excellent step coverage, uniformity and thickness controllability. In this work, we synthesized large-scale and thickness-controllable MoS2 films on sapphire substrate by ALD at 150 °C with molybdenum hexcarbonyl and hexamethyldisilathiane (HMDST) as precursors followed by high-temperature annealing in sulfur atmosphere. HMDST is introduced for the first time to enable a toxic-free process without hazardous sulfur precursors such as H2S and CH3SSCH3. The synthesized MoS2 retains the inherent benefits from the ALD process, including thickness controllability, reproducibility, wafer-level thickness uniformity, and high conformity. Finally, field-effect transistor (FET) arrays were fabricated based on the large-area ALD MoS2 films. The top-gate FETs exhibited excellent electrical performance such as high on/off current ratio over 103 and peak room-temperature mobility up to 11.56 cm2 V−1 s−1. This work opens up an attractive approach to realize the application of high-quality 2D materials with wafer scale homogeneity.

A method of controlling the hole size of nanopores array on anodic aluminum oxide

Solid-state nanopores are promising for applications in molecular biology and treatment of water pollution. Many techniques represented cannot fabricate nanopores array. In this work, we demonstrated a novel, cost-efficient and convenient technique to control the hole size of anodic aluminum oxide (AAO). It was based on the insufficient step coverage of plasma enhanced chemical vapor deposition (PECVD). Nanopores around 8 nm were obtained after depositing SiO2 for 150 s. The distributions of the hole sizes were fitted with Gaussian function and mean sizes were extracted. The relation between hole size and deposition time was fitted. Generally, the hole size decreased linearly with the increasing deposition time. ESI-CFD was used to simulate this deposition process. The simulation agreed well with the experimental results. The result shows that this technique is promising for getting a large uniform nanopore array under 10 nm.

Conformal deposition of lithium phosphate thin film electrolytes for 3D solid state batteries by MOCVD

A metal-organic chemical vapor deposition (MOCVD) process was developed to deposit high quality lithium phosphate (Li3PO4) thin films using lithium dipivaloylmethanate (Li(DPM)), triethyl phosphate (TEP) and H2O as the precursor materials. The use of water as an activating agent helps stimulate the formation of a lithium phosphate structure and tailor the process to the reaction-controlled regime. Consequently, lithium phosphate thin films were deposited uniformly with ~46% step coverage on trenched substrates with an aspect ratio of 6:1, demonstrating the feasibility of the three-dimensional (3D) deposition of Li3PO4 by MOCVD. In the temperature range of 300–450°C, an increase in temperature led to the development of crystallinity, increased growth rate, and decreased lithium concentration. The concentrations of Li, P, and O were homogeneous along the film depth. The films deposited at 400°C exhibited the highest ionic conductivity (5×10−8Scm−1) due to the optimal elemental ratio and crystallinity. The method developed in this study can also be applied for the uniform deposition of other materials on 3D geometries by using suitable activating agents.

Silicon Nitride Deposition for Flexible Organic Electronic Devices by VHF (162\u2009MHz)-PECVD Using a Multi-Tile Push-Pull Plasma Source

Depositing a barrier film for moisture protection without damage at a low temperature is one of the most important steps for organic-based electronic devices. In this study, the authors investigated depositing thin, high-quality SiNx film on organic-based electronic devices, specifically, very high-frequency (162 MHz) plasma-enhanced chemical vapor deposition (VHF-PECVD) using a multi-tile push-pull plasma source with a gas mixture of NH3/SiH4 at a low temperature of 80 °C. The thin deposited SiNx film exhibited excellent properties in the stoichiometry, chemical bonding, stress, and step coverage. Thin film quality and plasma damage were investigated by the water vapor transmission rate (WVTR) and by electrical characteristics of organic light-emitting diode (OLED) devices deposited with SiNx, respectively. The thin deposited SiNx film exhibited a low WVTR of 4.39 × 10−4 g (m2 · day)−1 for a single thin (430 nm thick) film SiNx and the electrical characteristics of OLED devices before and after the thin SiNx film deposition on the devices did not change, which indicated no electrical damage during the deposition of SiNx on the OLED device.

Deposition of a Diamond-Like-Carbon Film by Ion Plating and Investigation on its Adhesiveness

Diamond-like-carbon (DLC) films are promising as coating materials. Ion plating, an excellent method in terms of adhesiveness, step coverage, and deposition rate, can form not only pure metal films but also oxide films, nitride films, and carbonized films. In this study, which aimed to form a DLC film with good adhesiveness and a diamond crystal structure, a DLC film, with a SiC interlayer formed by ion plating with introduction of tetramethylsilane (TMS), was formed. It was experimentally revealed that as the interlayer thickness increases, the crystal structure in the DLC film becomes more diamond rich, and the adhesiveness of the DLC film and substrate is thereby improved.

Highly conformal and high-ionic conductivity thin-film electrolyte for 3D-structured micro batteries: Characterization of LiPON film deposited by MOCVD method

This paper reports a lithium phosphorus oxynitride (LiPON) thin-film electrolyte deposited using a metalorganic-chemical vapor deposition (MOCVD) method for 3D-structured micro batteries. It is shown that the MOCVD-LiPON film has both highly-conformal step coverage on a patterned substrate with line/space=2μm/2μm and aspect ratio=1 (51±3 nm) and high-ionic conductivity for very thin films deposited at 4.7 nm/min (5.9×10-6 S/cm for 190 nm and 5.3×10-6 S/cm for 95 nm). Detailed material characterization attributes the enhancement in ionic conductivity to a decrease in nanocrystallite size and improvement in chemical-composition uniformity in the film. In addition, electrochemical characterization of an all-solid-state thin-film battery fabricated with the 190 nm-thick LiPON film (Si substrate/Ti/Pt/LiCoO2/LiPON/a-Si:H/Cu) demonstrates that the LiPON film can successfully act as the electrolyte for lithium-ion batteries. Therefore, the MOCVD-LiPON film is a promising candidate material to realize 3D-structured micro batteries in the near future.

Analysis of arrayed nanocapacitor formed on nanorods by flow-rate interruption atomic layer deposition

Flow-rate interruption (FRI) atomic layer deposition (ALD) technique was adopted to fabricate AZO/Al2O3/AZO thin film on a ZnO nanorod array template at low temperature. The high quality amorphous dielectric Al2O3 layer was deposited at 50°C. The template with an average of 0.73μm in length was made by a simple hydrothermal method on a c−plane sapphire with an AZO seed layer. Using Polystyrene (PS) microspheres were served as a mask to form vertical and well-aligned ZnO nanostructures. Field-emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) images show ALD to have achieved good step coverage and thickness control in the thin films structure coating. The capacitance density of the arrayed template nanocapacitor increased more than 100% than those of the thin film capacitor at an applied frequency of 10 kHz. These results suggest that the ZnO-arrayed template could enhance energy storage capability by providing significant surface area. This structure provides a concept for high surface-area nanocapacitor applications.

Properties of Lithium Phosphorus Oxynitride Films Prepared By Metalorganic Chemical Vapor Deposition Method

3D-structured thin-film batteries draw attention to applications like IoT, wearable, and medical devices because of their having non-flammability, electrochemical stability, and flexibility; furthermore, their capacity density can be enhanced by designing the structure, e.g. the aspect ratio (AR) of trench and pillar structures. For realizing 3D-structured batteries with high-capacity density, the step coverage for high AR-patterned structures is a crucial process parameter. In the case of conventional physical vapor deposition (PVD) method, the coverage is not conformal enough to deposit onto a high AR-patterned surface. On the other hand, chemical vapor deposition (CVD) method is attractive to deposit much more conformal films than PVD. In this study, properties of lithium phosphorus oxynitride (LiPON), which is a promising thin-film electrolyte material due to high-chemical stability and nontoxicity, films deposited using metalorganic (MO) CVD are investigated in detail. In this experiment, utilized precursors were lithium tert-butoxide, tris(dimethylamino)phosphine, O2, and NH3. Chemical composition and microstructure of prepared films were evaluated by various analytical methods such as XPS, RBS/NRA, Raman spectroscopy, and XRD. In addition, electrochemical properties of the film were evaluated by AC impedance (Nyquist plot) and cyclic voltammetry methods. Using this MOCVD system, Li4.1PO4.2N0.7 film with 7.5 nm of crystallite size and 5.0 nm/min of deposition rate shows 5.9x10-6 S/cm at 200 nm and 3.3x10-6 S/cm at 50 nm of ionic conductivity, and an excellent step coverage on a patterned substrate is also shown by SEM and EDX (Fig. 1). These results demonstrate the LiPON film deposited by MOCVD would be successfully available for 3D-structured thin-film batteries. Figure 1