Contact Hole Structures Research Articles

Vertically Stackable Ovonic Threshold Switch Oscillator Using Atomic Layer Deposited Ge0.6Se0.4 Film for High-Density Artificial Neural Networks.

Nanodevice oscillators (nano-oscillators) have received considerable attention to implement in neuromorphic computing as hardware because they can significantly improve the device integration density and energy efficiency compared to complementary metal oxide semiconductor circuit-based oscillators. This work demonstrates vertically stackable nano-oscillators using an ovonic threshold switch (OTS) for high-density neuromorphic hardware. A vertically stackable Ge0.6Se0.4 OTS-oscillator (VOTS-OSC) is fabricated with a vertical crossbar array structure by growing Ge0.6Se0.4 film conformally on a contact hole structure using atomic layer deposition. The VOTS-OSC can be vertically integrated onto peripheral circuits without causing thermal damage because the fabrication temperature is <400 °C. The fabricated device exhibits oscillation characteristics, which can serve as leaky integrate-and-fire neurons in spiking neural networks (SNNs) and coupled oscillators in oscillatory neural networks (ONNs). For practical applications, pattern recognition and vertex coloring are demonstrated with SNNs and ONNs, respectively, using semiempirical simulations. This structure increases the oscillator integration density significantly, enabling complex tasks with a large number of oscillators. Moreover, it can enhance the computational speed of neural networks due to its rapid switching speed.

Synaptic Characteristics and Vector‐Matrix Multiplication Operation in Highly Uniform and Cost‐Effective Four‐Layer Vertical RRAM Array

AbstractThis study implements a highly uniform 3D vertically stack resistive random‐access memory (VRRAM) with a four‐layer contact hole structure. The fabrication process of a four‐layer VRRAM is demonstrated, and its physical and electrical properties are thoroughly examined. X‐ray photoelectron spectroscopy and transmission electron microscopy are employed to analyze the chemical distribution and physical structure of the VRRAM device. Multilevel capability, reliable endurance (&gt;104 cycles), and retention (104 s) are successfully obtained. Synaptic memory plasticity, such as spike time‐dependent plasticity, spike rate‐dependent plasticity, excitatory post‐synaptic current, paired‐pulse facilitation, and long‐term potentiation and depression is presented. Finally, the vector‐matrix multiplication (VMM) operation is conducted on a 4 × 12 VRRAM array, according to the low resistance state ratio. It is ascertained that the accuracy drop, which can occur due to VMM error, can be limited to a decrease of less than 0.44% point. Utilizing the high‐density, multilevel, and biological characteristics of VRRAM, it is possible to implement high‐performance neuromorphic systems that require densely integrated synaptic devices.

Alloyed High-k-Based Resistive Switching Memory in Contact Hole Structures

Resistive random-access memory (RRAM) devices are noticeable next generation memory devices. However, only few studies have been conducted regarding RRAM devices made of alloy. In this paper, we investigate the resistive switching behaviors of an Au/Ti/HfTiOx/p-Si memory device. The bipolar switching is characterized depending on compliance current under DC sweep mode. Good retention in the low-resistance state and high-resistance state is attained for nonvolatile memory and long-term memory in a synapse device. For practical switching operation, the pulse transient characteristics are studied for set and reset processes. Moreover, a synaptic weight change is achieved by a moderate pulse input for the potentiation and depression characteristics of the synaptic device. We reveal that the high-resistance state and low-resistance state are dominated by Schottky emissions.

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.

Optical critical dimension metrology for directed self-assembly assisted contact hole shrink

Directed self-assembly (DSA) is a potential patterning solution for future generations of integrated circuits. Its main advantages are high pattern resolution (∼10 nm), high throughput, no requirement of high-resolution mask, and compatibility with standard fab-equipment and processes. The application of Mueller matrix (MM) spectroscopic ellipsometry-based scatterometry to optically characterize DSA patterned contact hole structures fabricated with phase-separated polystyrene-b-polymethylmethacrylate (PS-b-PMMA) is described. A regression-based approach is used to calculate the guide critical dimension (CD), DSA CD, height of the PS column, thicknesses of underlying layers, and contact edge roughness of the post PMMA etch DSA contact hole sample. Scanning electron microscopy and imaging analysis is conducted as a comparative metric for scatterometry. In addition, optical model-based simulations are used to investigate MM elements’ sensitivity to various DSA-based contact hole structures, predict sensitivity to dimensional changes, and its limits to characterize DSA-induced defects, such as hole placement inaccuracy, missing vias, and profile inaccuracy of the PMMA cylinder.

Combined Ligand Exchange and Substitution Reactions in Atomic Layer Deposition of Conformal Ge2Sb2Te5 Film for Phase Change Memory Application

For phase change memories application, Ge–Sb–Te films were prepared by a stable and reliable atomic layer deposition (ALD) method. Ge(OC2H5)4, Sb(OC2H5)3, [(CH3)3Si]3Sb, and [(CH3)3Si]2Te were used to deposit various layers with compositions that can be described by combinations of GeTe2–Sb2Te layers including Ge2Sb2Te5 at a substrate temperature as low as 70 °C. A shift in composition of Sb–Te films from Sb2Te3 to Sb2Te composition was achieved by combining ligand exchange and substitution reaction between Sb in [(CH3)3Si]3Sb and Te in the Sb2Te3 layer. This surface-limited ALD process allowed highly conformal, smooth, and reproducible film growth over a contact hole structure, highlighting the feasibility of phase change memory applications.

Conformal Formation of (GeTe2)(1–x)(Sb2Te3)x Layers by Atomic Layer Deposition for Nanoscale Phase Change Memories

Phase change random access memory appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density phase change memory (≫1 Gb) depends heavily on the thin film growth technique for the phase changing chalcogenide material, most typically containing Ge, Sb and Te (Ge–Sb–Te). Atomic layer deposition (ALD) at low temperatures is the most preferred growth method for depositing such complex materials over surfaces possessing extreme topology. In this study, [(CH3)3Si]2Te and stable alkoxy-Ge (Ge(OCH3)4) and alkoxy-Sb (Sb(OC2H5)3) metal–organic precursors were used to deposit various layers with compositions lying on the GeTe2–Sb2Te3 tie lines at a substrate temperature as low as 70 °C using a thermal ALD process. The adsorption of Ge precursor was proven to be a physisorption type while other precursors showed a chemisorption behavior. However, the adsorption of Ge precursor was still self-regulated, and the facile ALD of the pseudobinary solid solutions with composition (GeTe2)(1-x)(Sb2Te3)x were achieved. This chemistry-specific ALD process was quite robust against process variations, allowing highly conformal, smooth, and reproducible film growth over a contact hole structure with an extreme geometry. The detailed ALD behavior of binary compounds and incorporation behaviors of the binary compounds in pseudobinary solid solutions were studied in detail. This new composition material showed reliable phase change and accompanying resistance switching behavior, which were slightly better than the standard Ge2Sb2Te5 material in the nanoscale. The local chemical environment was similar to that of conventional Ge2Sb2Te5 materials.

Chemically Conformal ALD of SrTiO3 Thin Films Using Conventional Metallorganic Precursors

(STO) thin films were grown on Si wafer, Pt- and Ru-coated Si wafers, respectively, by an atomic layer deposition (ALD) technique using conventional metallorganic precursors, and (TTIP) as Sr- and Ti-precursors, respectively, with a remote-plasma activated vapor as the oxidant at a wafer temperature of 250°C. Patterned Si wafers with contact holes having a diameter of 0.13 and 1 μm depth (aspect ratio of 8) was used in order to test the film-thickness and cation-composition conformalities over the contact hole surface. The ALD behavior of the STO film was critically dependent on the source heating temperature. When the Sr source temperature was [ melting temperature] stoichiometric STO films were deposited with a good process reliability. Excellent film thickness and cation composition conformalities (nonuniformity ) over the severe contact hole structure were obtained by the optimized precursor supply and deposition conditions. It was also observed that most of the input TTIP precursor molecules did not chemically adsorb on the SrO surface, possibly due to oversaturation of the SrO surface by the molecules or thermally modified molecules as a result of the heating process of the when the Sr-source temperature was . This difficulty resulted in a nonuniform cation composition ratio along the contact hole.

Bi1-x-yTixSiyOz (BTSO) Thin Films for Dynamic Random Access Memory Capacitor Applications

Bi1–x–yTixSiyOz (BTSO) thin films were grown on eight inch diameter Ru/SiO2/Si or bare Si wafers by atomic layer deposition (ALD) method using Bi(mmp)3, Ti(mmp)4, and Si(OEt)4 [mmp = 1-methoxy-2-methyl-2-propoxide (OCMe2CH2OMe, Me = methyl); Et = ethyl] as metal alkoxide precursors and ozone (O3) as the oxidant gas. Transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) analysis showed that the as-deposited films are amorphous and the cation compositional ratio of Bi:Ti:Si is 0.38:0.37:0.25 of films deposited at 325 °C on Ru/SiO2/Si Ru substrates. X-ray photoelectron spectroscopy (XPS) shows that the BTSO films are homogeneously dispersed without any phase-separation of the components. The BTSO films show excellent step coverage on a high aspect ratio (4) contact hole structure with a diameter of 300 nm. The leakage current density of BTSO films is on the order of 10–8 A cm–2 at 1 V, meeting present dielectric requirements for a dynamic random access memory storage capacitor with an equivalent oxide thickness of 2.1 nm. From the capacitance–voltage characteristics at 10 kHz of the Pt/BTSO/Ru capacitor, the estimated dielectric constant of amorphous BTSO films is ∼ 24.

레이저 CVD 텅스텐막 증착을 통한 TFT LCD 불량배선 수리

The photodepositioned tungsten film by laser CVD has been carried out the taping test with scotch tape over 10 times. As a result, it exhibited strong adhesion to the under-film such as ITO and SiNx patterned on the LCD substrate. However, it was seriously attacked by alkaline solution used for removing polyimide. And a thickness of laser CVD tungsten film had a close relation to a speed of laser scanning. Also we have improved the success rate of a laser CVD repair with making two pairs of contact hole structure and decreasing laser scanning speed.

Remote plasma enhanced atomic layer deposition of TiN thin films using metalorganic precursor

TiN films were deposited by remote plasma enhanced atomic layer deposition (PEALD) method using tetrakis-dimethyl-amino-titanium precursor and hydrogen, hydrogen/nitrogen mixture, and nitrogen plasmas. Remote PEALD method showed a relatively wide temperature window compared to that of conventional ALD process due to the increased reactivity of reactant gas. TiN films showed significantly lower impurity contents than those of the films deposited by other methods such as plasma enhanced chemical vapor deposition, metalorganic chemical vapor deposition, and conventional ALD using the same precursor. TiN films deposited using N2 plasma showed better characteristics than the films deposited using H2 and H2/N2 mixture plasmas. TiN films deposited by remote PEALD at 250 °C showed the resistivity value as low as about 300 μΩ cm and exhibited excellent conformal step coverage on 0.25-μm-wide and 2.5-μm-deep contact hole structure.

Stoichiometry effects in TiN diffusion barriers

TiN diffusion barriers were deposited via reactive sputtering in an ArN 2 gas mixture. Several TiN films with variation in the stoichiometry were produced and used as a diffusion barrier between a silicon substrate and an aluminium alloy film in order to prevent Al-Si interdiffusion (“spiking”). The quality of the barrier films during further anneal steps was investigated by detection of the diffusion processes and interfacial reactions using Auger electron spectroscopy (AES) depth profiling and by testing the spiking directly on wafers with contact hole structures (“spiking tests”). A correlation between TiN stoichiometry and barrier quality was established; the use of nitrogen-deficient TiN films resulted in a high degree of interdiffusion and a clear tendency towards spiking. In order to counteract barrier failure due to substoichiometric TiN a barrier post-treatment in N 2 was performed and characterized with AES. With this post-treatment an improvement in the barrier performance for substoichiometric TiN films could be achieved.

Excimer laser planarization of AlSi, AlSiTi and AlSiCu alloys

In this work we use a XeCl excimer laser (λ = 308 nm) to planarize three Al alloys, namely AlSi(1%), and AlSi(1%)Ti(0.1%), and AlSi(1%)Cu(0.5%). AlSi(1%) is currently the dominant first level metalization used in production because of its low resistance and compatibility with conventional Si processes. The Ti and Cu are added to suppress hillocking and improve electromigration resistance. Our results show that excellent planarization is achieved for all topologies including submicron contact hole structures, however, for the AlSi alloy spot ablation occurs which is characterized by the removal of metal. This is not seen for the AlSiCu and the AlSiTi alloys. The best morphology is obtained for the AlSiTi alloy with large areas completely free of ablation and pitting, which indicates that excellent planarization over large device areas can be achieved using this alloy.