To extend the scaling limit of thermal SiO/sub 2/ in the ultrathin regime when the direct tunneling current becomes significant, members of this author's research team at Yale University, in collaboration with the Jet Process Corporation, embarked on a program to explore the potential of silicon nitride as an alternative gate dielectric. In this paper, high-quality silicon nitride (or oxynitride) films made by a novel jet vapor deposition (JVD) technique are described. The JVD process utilizes a high-speed jet of light carrier gas to transport the depositing species onto the substrate to form the desired films. The film composition has been determined to consist primarily of Si and N, with some amounts of O and H. Metal-nitride-Si (MNS) capacitors based on the JVD nitride films deposited directly on Si exhibit relatively low densities of interface traps, fixed charge, and bulk traps. The interface traps at the nitride/Si interface exhibit different properties from those at the SiO/sub 2//Si interface in several aspects. In contrast to the conventional CVD silicon nitride, the high-field I-V characteristics of the JVD silicon nitride fit the Fowler-Nordheim (F-N) tunneling theory over four to five orders of magnitude in current, but do not fit at all the Frenkel-Poole (F-P) transport theory. This is consistent with the much lower concentration of electronic traps in the JVD silicon nitride. Results from the carrier separation experiment indicate that electron current dominates the gate current with very little hole contribution. Both theoretical calculation and experimental data indicate that the gate leakage current in JVD silicon nitride is significantly lower than that in silicon dioxide of the same equivalent oxide thickness. The breakdown characteristics of the JVD nitride are also respectable. Compared to their MOSFET counterparts, MNS transistors exhibit reduced low-field transconductance but enhanced high-field transconductance, perhaps due to the presence of border traps. As expected, the JVD silicon nitride films exhibit very strong resistance to boron penetration and oxidation at high temperatures. These properties, coupled with its room-temperature deposition process, make JVD silicon nitride an attractive candidate to succeed thermal SiO/sub 2/ as an advanced gate dielectric in future generations of ULSI devices.

Making silicon nitride film a viable gate dielectric

The present invention is directed to methods for patterning a substrate by imprint lithography. Imprint lithography is a process in which a liquid is dispensed onto a substrate. A template is brought into contact with the liquid and the liquid is cured. The cured liquid includes an imprint of any patterns formed in the template. In one embodiment, the imprint process is designed to imprint only a portion of the substrate. The remainder of the substrate is imprinted by moving the template to a different portion of the template and repeating the imprint lithography process.

Step and repeat imprint lithography processes

This paper presents a critical review of the basic data concerning the physics and chemistry of low pressure SiH 4 glow discharges used to deposit hydrogenated amorphous silicon films (a-Si:H). Starting with an updated table of thermochemical data, we analyze the gas-phase elementary processes consisting of i) electron-molecule collisions, ii) ion-molecule collisions, iii) neutral-neutral collisions, iv) other electron and ion collisions involving electron-ion and ion-ion recombination, electron attachment on radicals and detachment of anions, and v) cluster growth kinetics in dusty plasmas. Experimental data or theoretical estimates are given and discussed in terms of cross-sections. collision and reaction rate constants, and transport coefficients. We also analyze the surface processes and reaction probabilities of ions, radicals and molecules.

Cross-Sections, Rate Constants and Transport Coefficients in Silane Plasma Chemistry

Effective utilization of methane remains one of the long-standing problems in catalysis. Over the past several years, various routes, both direct and indirect, have been considered for the conversion of methane to value-added products such as higher hydrocarbons and oxygenates. This review will focus on the range of issues dealing with thermal and catalytic decomposition of methane that have been addressed in the last few years. Surface science studies (molecular beam methods and elevated-pressure reaction studies) involving methane activation on model catalyst systems are extensively reviewed. These studies have contributed significantly to our understanding of the fundamental dynamics of methane decomposition. Various aspects of the nonoxidative methane to higher hydrocarbon conversion processes such as high-temperature coupling and two-step low-temperature methane homologation have been discussed. Decomposition of methane results in the production of COx-free hydrogen (which is of great interest to sta...

Nonoxidative Activation of Methane

A plasma jet has been developed which deposits silica films at up to at 760 Torr and 115 to C. The jet operates by feeding oxygen and helium gas between two coaxial electrodes that are driven by a 13.56 MHz radio frequency source at 40 to 500 W. Tetraethoxysilane is mixed with the effluent of the plasma jet and directed onto a substrate located 1.7 cm downstream. The properties of the silica films, as determined by infrared spectroscopy and capacitance measurements, are comparable to those of thermally grown silicon dioxide films at C.

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Deposition of silicon dioxide films with an atmospheric-pressure plasma jet

To understand the diamond growth mechanism in C2H2/O2 flame, we carried out gas analyses for various mixture ratios (R=C2H2/O2) with laser-induced fluorescence and mass spectrometric techniques. These measurements show that CO and H2 are the dominant gases in the feather, and that C2H2 and C-containing radicals (e.g., C2H, CR, Cn, n=1-3) are minor species. Their concentrations are found to be consistent with the equilibrium values estimated by the adiabatic calculation. The feather is formed by the inter-diffusion and reactions between these C-radicals and O-radicals (e.g., O and OH), which are produced in the intermediate zone by the oxidation with O2 supplied through the secondary flame. It is also found that R-dependences of the diamond growth rate is in good agreement with those of CH and C2 concentrations in the feather.

Flame structure and diamond growth mechanism of acetylene torch

To discuss the diamond growth mechanism in acetylene flames, numerical calculations are carried out, including both gaseous reactions in the boundary layer near a water-cooled substrate and overall surface reactions on a growing crystal. It is shown that stable species such as CH4 and C2H4 are rapidly produced in the layer, followed by the methyl radical formation according to the fast partial equilibrium of the reaction, CH4+H\rightleftarrowsCH3+H2. The comparison between the calculated and the measured CH4 concentrations upon the substrate has revealed that C-radicals adsorbed on the diamond surface are etched by H-atoms to form CH4, though the surface reactions do not have a significant effect on the gaseous concentrations. The dependences of the growth rate both on the substrate temperature and on the C2H2/O2 ratio are shown to be explainable by the CH3-precursor model.

https://iopscience.iop.org/article/10.1143/JJAP.29.1552/pdf

The Growth Mechanism of Diamond Crystals in Acetylene Flames

The precursors of the a-Si:H film in SiH4 plasma-enhanced CVD are investigated by use of trench coverage analysis. The cross sectional profile of deposited film in a trench is simulated by a direct Monte-Carlo method using the radical sticking probability β as an adjustable parameter. A comparison with the experimental results has shown that the trench coverage profiles are reproduced well by the model if two kinds of radicals, i.e., SiH3 and SiH2, are deposited independently on the substrate with the respective sticking probabilities of 0.1 and 1.0. The experimentally observed dependence of the trench profile on the plasma condition can be explained by the change in the radical deposition ratio, which becomes SiH3/SiH2=1/1 in pure SiH4 at low rf power and decreases to 1/2-1/3 in SiH4 diluted in Ar at high rf power. The above change in the contribution of two kinds of radicals to the deposition is also supported by the chemical kinetic calculation of the gas phase reactions and the radical transport to the substrate.

https://iopscience.iop.org/article/10.1143/JJAP.28.212/pdf

A Study on Radical Fluxes in Silane Plasma CVD from Trench Coverage Analysis

Thin films of (Ba, Sr)TiO3 with high dielectric constant were prepared on Pt/SiO2/Si substrates of 6-inch-diameter by chemical vapor deposition using liquid sources. Ba(DPM)2 and Sr(DPM)2 dissolved into tetrahydrofuran were vaporized in a vaporizer at 523 K, and Ti(O-i-C3H7)4 was bubbled at 313 K. The mixture of the source vapors with O2 and N2O was supplied to the reactor (10 Torr) at uniform velocities through a shower-type nozzle, which realized uniform profiles in the deposited film thickness and composition. The electrical properties are significantly influenced by the film composition, and the typical properties obtained for a 800-A-thick film prepared at the substrate temperature of 823 K are an equivalent SiO2 thickness t eq of 5.2 A, a leakage current J L of 2.4× 10-6 A/cm2 (at 1.65 V), and a dielectric loss tan δ of 0.07.

Preparation of (Ba, Sr)TiO3 Thin Films by Chemical Vapor Deposition Using Liquid Sources

The decomposition process of tetraethylorthosilicate (TEOS) and ozone at atmospheric pressure was measured in a closed vessel by in-situ Fourier-transform infrared absorption (FT-IR) analysis, and the changes of the deposition rate and the overall sticking probability β of the film precursor were obtained along the flow direction in a flow-type reactor. It has been found that the film precursors are formed by TEOS decomposition with O-atoms and/or ozone in the gas phase, and that CH3CHO may be the first product, followed by the oxidation to CO2 and H2O via HCHO. It is also shown that the film quality changes along the flow direction, that is, O-H bonds in the film decrease and the β-value increases as the reaction proceeds. These results may show that there are several kinds of precursors, and the sticky (unstable) precursors become dominant in the later stages.

https://iopscience.iop.org/article/10.1143/JJAP.31.2925/pdf

Yasuji Matsui

Papers

Flame structure and diamond growth mechanism of acetylene torch

The Growth Mechanism of Diamond Crystals in Acetylene Flames

A Study on Radical Fluxes in Silane Plasma CVD from Trench Coverage Analysis

Preparation of (Ba, Sr)TiO3 Thin Films by Chemical Vapor Deposition Using Liquid Sources

Reaction Mechanism of Chemical Vapor Deposition Using Tetraethylorthosilicate and Ozone at Atmospheric Pressure