Low-pressure Chemical Vapor Deposition Process Research Articles

Effects of Polycrystalline Silicon Plug Defect on DRAM Characteristics

This study first demonstrates the effect of polycrystalline silicon plug defects, including voids and seams in dynamic random access memory (DRAM) storage node contact (SNC), on product characteristics. The defect portion of SNC has increased continually due to a reduction in the contact area, an increase in the doping concentration, and low-pressure chemical vapor deposition (LPCVD) process limitations. We validate the effect through defect removal experiments. Numerous methods, such as the cyclic deposition/etch/deposition process of silicon, ion implantation, and laser annealing, are used. The experiments are successful without any side effects using a high-density laser annealing process. The contact resistance of the sample-removed polysilicon defect decreases by 59% and the cell drain current increases by 6%. In addition, the overlap capacitance of the drain node and cell gate edge (Cov) variations by the SNC dopant diffusion forming the source and drain junction of the cell transistor is improved by 6%. Finally, we conduct the row precharge delay from the last data-in (tRDL) time delay reliability test using mass production test technology and it was confirmed that the contact area standard that satisfies the product quality target is improved by 10%. We propose a new direction for polycrystalline silicon SNC development for a sub-20-nm DRAM device based on this experiment.

Optical, structural and composition properties of silicon nitride films deposited by reactive radio-frequency sputtering, low pressure and plasma-enhanced chemical vapor deposition

We present a comparative study of optical properties of silicon nitride thin films deposited by reactive radio-frequency (R-RF) sputtering, low pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD). For LPCVD process, two different proportions of mixed gases were used (LPCVD (A) and LPCVD (B) processes) and PECVD deposition were conducted in three regimes: low frequency (LF), mixed frequency and high frequency. Dielectric functions were extracted from ellipsometric measurements for the wavelength range from ultraviolet to near-infrared wavelengths, spanning from 210 nm to 1690 nm. To understand how different deposition parameters affect the optical properties of thin films, additional structures and composite analysis was done by using X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, X-ray reflectometry, atomic force microscopy, reflection electron energy loss spectroscopy, Fourier-transform infrared spectroscopy and stress measurements. The series of analysis show that the influence of deposition method on optical properties is significant especially for in the range of 200 nm–400 nm. For these UV wavelengths, LPCVD (A)-deposited films give a transparency window at the shortest wavelength up to 275 nm, while R-RF-sputtering and PECVD (LF) lead to transparency windows starting up to 320 nm wavelengths. Hence, appropriate techniques and recipes should be selected to account for various peculiarities in optical and structural properties of silicon nitride films towards their potential applications in photonic and nanostructured systems.

Tailoring the nanostructure of plasma-deposited CoOX-based thin films for catalytic applications – A step forward in designing nanocatalysts

Among the heterogeneous catalysts based on non-noble metals, cobalt oxides, mainly in the Co3O4 form, are particularly promising materials. Herein, we developed a facile bottom-up approach to synthesize a novel and sophisticated Co3O4-based thin-film material with a tailored nanostructure that is crucial for catalytic properties. The films were produced using a low-pressure plasma-enhanced chemical vapor deposition (PECVD) process that was thoroughly analyzed. The as-deposited films, in the amorphous form composed of Co, O, C, and H atoms (called CoOX-based films), were thermally treated (calcined), transforming them into films containing Co3O4 nanocrystallites. For a fundamental understanding of the transformation process, the calcination was performed in a controlled manner by Raman spectroscopy using the Raman laser as a heat source. An original model to describe the formation of Co3O4 nanocrystallites was proposed. We have shown that the concentration of Co3O4 and also the number and size of its nanocrystallites in the films can be rationally tailored to the specific needs by selecting the parameters of the PECVD and calcination processes. Our research provides a practical strategy for the molecular design of nanostructured thin-film catalysts in a controllable way using the PECVD process.

Self-Catalytic Growth of Elementary Semiconductor Nanowires with Controlled Morphology and Crystallographic Orientation.

While the orientation-dependent properties of semiconductor nanowires have been theoretically predicted, their study has long been overlooked in many fields owing to the limits to controlling the crystallographic growth direction of nanowires (NWs). We present here the orientation-controlled growth of single-crystalline germanium (Ge) NWs using a self-catalytic low-pressure chemical vapor deposition process. By adjusting the growth temperature, the orientation of growth direction in GeNWs was selectively controlled to the ⟨110⟩, ⟨112⟩, or ⟨111⟩ directions on the same substrate. The NWs with different growth directions exhibit distinct morphological features, allowing control of the NW morphology from uniform NWs to nanoribbon structures. Significantly, the VLS-based self-catalytic growth of the ⟨111⟩ oriented GeNW suggests that NW growth is possible for single elementary materials even without an appropriate external catalyst. Furthermore, these findings could provide opportunities to investigate the orientation-dependent properties of semiconductor NWs.

Effect of the Field Oxidation Process on the Electrical Characteristics of 6500V 4H-SiC JBS Diodes

The effect of the field oxidation process on the electrical characteristics of 6500V 4H-SiC JBS diodes is studied. The oxide thickness and field plate length have an effect on the reverse breakdown voltage of the SiC JBS diode. According the simulation results, we choose the optimal thickness of the oxide layer and field plate length of the SiC JBS diode. Two different field oxide deposition processes, which are plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD), are compared in our paper. When the reverse voltage is 6600V, the reverse leakage current of SiC JBS diodes with the field oxide layer obtained by LPCVD process is 0.7 μA, which is 60% lower than that of PECVD process. When the forward current is 25 A, the forward voltage of SiC JBS diodes with the field oxide layer obtained by LPCVD process is 3.75 V, which is 10% higher than that of PECVD process. There should be a trade-off between the forward and reverse characteristics in the actual high power and high temperature applications.

Graphene growth with no intended carbon precursor feeding into the LPCVD process: causes, solutions, and effects

In this research, we have investigated the unintended graphene nucleation problem and its damaging effects on monolayer graphene synthesis in low-pressure chemical vapor deposition (LPCVD) process. This problem is the growth of graphene on the copper surface with no carbon feedstock. A new source of undesired carbon species was identified which has not been addressed so far. The hydrogen-rich heating stage was diagnosed as the onset of the unintended nucleation for the first time owing to the determinant catalytic role of hydrogen in this stage. It was found out that this problem leads to uncontrollable growth of multilayer graphene, growth of defective graphene film and also inhibition of the reliable synthesis of monolayer graphene. We managed to grow enhanced-quality monolayer graphene by developing some innovative solutions to the problem containing a general solution based on the hydrogen effects in the heating stage. The results reveal a significant decrease in the unintended nucleation density from ∼2000 to almost zero domains per 100 × 100 μm2 copper area. Furthermore, Raman, HRTEM and SAED analysis confirm the defect-free growth of monolayer graphene after employing the solutions. These findings could pave the way for the reliable synthesis of high-quality monolayer graphene as well as large-sized graphene domains.

Partial Pressure Assisted Growth of Single-Layer Graphene Grown by Low-Pressure Chemical Vapor Deposition: Implications for High-Performance Graphene FET Devices.

An attempt has been made to understand the thermodynamic mechanism study of the low-pressure chemical vapor deposition (LPCVD) process during single-layer graphene (SLG) growth as it is the most debatable part of the CVD process. The intensive studies are being carried out worldwide to enhance the quality of LPCVD-grown graphene up to the level of mechanically exfoliated SLG. The mechanism and processes have been discussed earlier by several research groups during the variation in different parameters. However, the optimization and mechanism involvement due to individual partial pressure-based effects has not been elaborately discussed so far. Hence, we have addressed this issue in detail including thermodynamics of the growth process and tried to establish the effect of the partial pressures of individual gases during the growth of SLG. Also, optical microscopy, Raman spectroscopy, and atomic force microscopy (AFM) have been performed to determine the quality of SLG. Furthermore, nucleation density has also been estimated to understand a plausible mechanism of graphene growth based on partial pressure. Moreover, the field-effect transistor (FET) device has been fabricated to determine the electrical properties of SLG, and the estimated mobility has been found as ∼2595 cm2 V–1 s–1 at n = −2 × 1012 cm–2. Hence, the obtained results trigger that the partial pressure is an important parameter for the growth of SLG and having various potential applications in high-performance graphene FET (GFET) devices.

Stress-released Si3N4 fabrication process for dispersion-engineered integrated silicon photonics.

We develop a stress-released stoichiometric silicon nitride (Si3N4) fabrication process for dispersion-engineered integrated silicon photonics. To relax the high tensile stress of a thick Si3N4 film grown by low-pressure chemical vapor deposition (LPCVD) process, we grow the film in two steps and introduce a conventional dense stress-release pattern onto a ∼400nm-thick Si3N4 film in between the two steps. Our pattern helps minimize crack formation by releasing the stress of the film along high-symmetry periodic modulation directions and helps stop cracks from propagating. We demonstrate a nearly crack-free ∼830nm-thick Si3N4 film on a 4" silicon wafer. Our Si3N4 photonic platform enables dispersion-engineered, waveguide-coupled microring and microdisk resonators, with cavity sizes of up to a millimeter. Specifically, our 115µm-radius microring exhibits an intrinsic quality (Q)-factor of ∼2.0×106 for the TM00 mode and our 575µm-radius microdisk demonstrates an intrinsic Q of ∼4.0×106 for TM modes in 1550nm wavelengths.

Performance of different layers of graphene as protective coating for copper wire

Graphene can be used as an anti-oxidation and anti-corrosion layer due to its impermeability to oxygen or etchant and its atomically thin thickness. In this study, monolayer, bi-layer, and multilayer graphene were grown on copper (Cu) wire samples using a low-pressure chemical vapor deposition (LPCVD) process, and their performances for copper wire protection were characterized experimentally. The results show that multilayer graphene provided anti-oxidation protection up to 350 °C under continuous heating of 30 min. The etching time of copper wire with multilayer-graphene protection doubled comparing to their bare Cu wire counterparts. Furthermore, multilayer graphene protection significantly reduced the contact resistance between twisted-pair copper wires.

Growth of Large-Scale Praseodymium Hexaborides (PrB6) Nanowires and Enhanced Field-Emission Performance

Large-scale PrB6 nanowires were fabricated by an effective, catalyst-free, and a simple low-pressure chemical vapor deposition (LPCVD) process. These nanowires, characterized in detail by various analytical instruments, demonstrated the large aspect ratio and high single-crystalline grown along the [001] crystal direction perpendicular to the (001) crystal plane. The field electron emission equipment tests manifest that the asgrown PrB6 products have a low turn-on field (Eto, 2.32 V/μm), a threshold field (Ethr, 4.28 V/μm), a high field enhancement factor (β, 2336), as well as a stable current-density (J) of field-emission. The relationships of the field electron emission parameters, such as J, Eto, and β versus cathode gap (d), have been established when d is increased from 500 μm to 800 μm. The outstanding properties suggest that the PrB6 products may be promising emitters in the cold-field-emission cathode application.

Analysis of boron profiles as function of nitrogen content in silicon

In this paper, the Secondary Ion Mass Spectroscopy (SIMS) technique is used to study the experimental depth concentration profiles of boron, nitrogen, and other expected atoms in amorphous nitrogen doped silicon (NiDoS) layers deposited at Td = 460 °C by low-pressure chemical vapor deposition (LPCVD) process from disilane. It has been observed that the reduction of implanted boron penetration is important when the film deposition temperature is low and the nitrogen in-situ doping step is initially improved. And, the simulation results with the experientially measured projected range values using SIMS are in good agreement.

SiO2 layer effect on atomic layer deposition Al2O3-based resistive switching memory

In this letter, we demonstrated improved resistive switching (RS) characteristics for a complementary metal-oxide-semiconductor compatible Ni/Ti/Al2O3/SiO2/Si device structure. The robust SiO2 layer deposited by the additional low-pressure chemical vapor deposition process can improve the RS characteristics such as the endurance cycle, current level, and on/off ratio. Moreover, the multilevel capability is enhanced in the bilayer structure; the larger the reset stop voltage, the greater the on/off ratio demonstrated. Furthermore, for practical RS operation, several resistance states were obtained by adjusting the pulse amplitude. This property is desirable for highly integrated nonvolatile memory applications.

Transfer-Free, Large-Scale Growth of High-Quality Graphene on Insulating Substrate by Physical Contact of Copper Foil.

High-quality, large-area, single-layer graphene was directly grown on top of a quartz substrate by a low-pressure chemical vapor deposition (CVD) process using Cu vapor as a catalyst. In this process, continuous generation and supply of highly concentrated Cu vapor is the key to the growth of large-scale, high-quality graphene. It was achieved by direct physical contact, or "touch-down," of a Cu foil with an underlying sacrificial SiO2 /Si substrate, and the target quartz substrate was placed on top of the Cu foil, eventually having a quartz/Cu/SiO2 /Si sandwich structure. To establish the reaction mechanism, a test growth was performed without the quartz substrate, which revealed that Cu is diffused through the SiO2 layer of the sacrificial SiO2 /Si substrate to form liquid-phase Cu-Si alloy that emits massive Cu vapor. This Cu vapor catalyzes thermal decomposition of supplied CH4 gas.

Characteristic Study of Silicon Nitride Films Deposited by LPCVD and PECVD

This paper analyzes and compares the characteristics of silicon nitride films deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD), with special attention to the hydrogenation and chemical composition of silicon nitride films. Three different LPCVD processes at various DCS and NH3 gas flow rates and deposition temperatures, together with PECVD using SiH4 and NH3 and ICP CVD using SiH4 and N2, were compared. The silicon nitride film deposition rate decreases with an increasing NH3/DCS ratio in LPCVD, which also leads to an increase in the refractive index and a decrease in the residual stress in the film. There is nearly no hydrogen incorporated in the LPCVD films, which differs from PECVD and ICP CVD that show significant Si-H and N-H bonds. The chemical composition of silicon nitride films is mostly Si-rich, except for the LPCVD process at high NH3/DCS ratio with near stoichiometric chemistry.

Fabrication and electrochemical characterization of super-capacitor based on three-dimensional composite structure of graphene and a vertical array of carbon nanotubes

We have demonstrated a three-dimensional composite structure of graphene and carbon nanotubes as electrodes for super-capacitors. The goal of this study is to fabricate and test the vertically grown carbon nanotubes on the graphene layer acting as a spacer to avoid self-aggregation of the graphene layers while realizing high active surface area for high energy density, specific capacitance, and power density. A vertical array of carbon nanotubes on silicon substrates was grown by a low-pressure chemical vapor deposition process using anodized aluminum oxide nanoporous template fabricated on silicon substrates. Subsequently, a graphene layer was grown by another low-pressure chemical vapor deposition process on top of a vertical array of carbon nanotubes. The Raman spectra confirmed the successful growth of carbon nanotubes followed by the growth of high-quality graphene. The average measured capacitance of the three-dimensional composite structure of graphene-carbon nanotube was 780 µFcm−2 at 100 mVs−1.

Effect of Graphene Modified Cu Current Collector on the Performance of Li4Ti5O12 Anode for Lithium-Ion Batteries.

Interface design between current collector and electroactive materials plays a key role in the electrochemical process for lithium-ion batteries. Here, a thin graphene film has been successfully synthesized on the surface of Cu current collector by a large-scale low-pressure chemical vapor deposition (LPCVD) process. The modified Cu foil was used as a current collector to support spinel Li4Ti5O12 anode directly. Electrochemical test results demonstrated that graphene coating Cu foil could effectively improve overall Li storage performance of Li4Ti5O12 anode. Especially under high current rate (e.g., 10 C), the Li4Ti5O12 electrode using modified current collector maintained a favorable capacity, which is 32% higher than that electrode using bare current collector. In addition, cycling performance has been improved using the new type current collector. The enhanced performance can be attributed to the reduced internal resistance and improved charge transfer kinetics of graphene film by increasing electron collection and decreasing lithium ion interfacial diffusion. Furthermore, the graphene film adhered on the Cu foil surface could act as an effective protective film to avoid oxidization, which can effectively improve chemical stability of Cu current collector.

Impact of LPCVD TEOS Thickness on Vt-Pushout in Flash Memory Cell due to Mechanical Stress

This paper reports on the dependence of cycling or endurance in flash memory with the stress induced by low-pressure chemical vapor deposition (LPCVD) process. The deposited 12.5nm tetraethyl orthosilicate (TEOS) layer served as sacrificial oxide during source/drain (S/D) implantation, which was then subsequently removed. However, this deposited TEOS layer has been found to induce a stress on the channel which affects the flash memory cycling or endurance performance.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

Spatial batch optimal design based on self-learning gaussian process models for LPCVD processes

Low pressure chemical vapor deposition (LPCVD) is one of the most important processes during semiconductor manufacturing. However, the spatial distribution of internal temperature and extremely few samples makes it hard to build a good-quality model of this batch process. Besides, due to the properties of this process, the reliability of the model must be taken into consideration when optimizing the MVs. In this work, an optimal design strategy based on the self-learning Gaussian process model (GPM) is proposed to control this kind of spatial batch process. The GPM is utilized as the internal model to predict the thicknesses of thin films on all spatial-distributed wafers using the limited data. Unlike the conventional model based design, the uncertainties of predictions provided by GPM are taken into consideration to guide the optimal design of manipulated variables so that the designing can be more prudent. Besides, the GPM is also actively enhanced using as little data as possible based on the predictive uncertainties. The effectiveness of the proposed strategy is successfully demonstrated in an LPCVD process.

Superior oxidation resistance, mechanical properties and residual stresses of an Al-rich nanolamellar Ti0.05Al0.95N coating prepared by CVD

The influence of microstructure on thermal and oxidation properties of Ti1-xAlxN hard coatings is not fully understood. In this work, an Al-rich Ti0.05Al0.95N coating with a unique self-organized microstructure of alternating soft hexagonal (w) AlN and hard cubic (fcc) TiN nanolamellae synthesized by a low-pressure chemical vapor deposition (CVD) process is analyzed in terms of oxidation resistance, microstructure and phase stability, hardness as well as residual stresses. Multiple coating samples on hard metal substrates were oxidized in ambient air for 1h at temperatures in the range of 700–1200°C. Exceptionally good oxidation resistance up to 1050°C was found, whereas above 1100°C a localized surface degradation caused by the substrate–air interaction with very characteristic oxide blisters was observed. A coating hardness of about 29GPa remained in all unaffected surface areas for temperatures up to 1050°C. This is interpreted by the specific lamellae microstructure that retained a nanocomposite character even after lamellae partly decomposed during annealing. Depth-resolved stress and phase characterization performed by cross-sectional X-ray nanodiffraction in the as-deposited Ti0.05Al0.95N revealed a strong compressive residual stress gradient of up to −2GPa at the coating surface which homogenized but remained still compressive after annealing at 1050°C. Finally, it is demonstrated that the unique dense nanocomposite microstructure is responsible for the superior oxidation behavior as well as high compressive stresses in the Ti0.05Al0.95N coating.