Yasuji Matsui

Flame Structure and Diamond Growth Mechanism of Acetylene Torch

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.

The Growth Mechanism of Diamond Crystals in Acetylene Flames

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.

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

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.

An experimental study on pyro-acoustic amplification of premixed laminar flames

Abstract A premixed, laminar methane-air flame was excited by a speaker-driver unit, and the gain and the phase of pyro-acoustic amplification were measured with microphones located both upstream and downstream of the flame for parameters of burner port radius, flow velocity, and mixture strength. It has been found that the plot of amplification versus excitation frequency shows a jagged shape with peaks and valleys. To describe this experimental behavior, an equation has been derived using a mathematical model of an axially symmetric premixed flame and the concept of “transfer function” of the flame. The results of calculation with this equation are shown to be in good agreement with experimental data. Furthermore, the transfer function obtained in the present work is compared with those suggested by other investigators.

Proposal for pattern layout rule in application of alternating phase-shift mask

An important pattern layout rule in application of alternating phase shift mask (PSM) is proposed. The images of semi- randomly aligned patterns show poor characteristics in defocus and mask fidelity. For an example, lines and spaces patterns with uniform bright and non-uniform dark widths showed significantly large CD variation with defocus. And lines and spaces patterns with uniform dark and non-uniform bright widths showed completely asymmetrical CD-focus characteristics. It has been revealed by the comparison between experimental data and the simulated results that the asymmetrical characteristics are caused by the spherical aberration in projection optics.

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

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.

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

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.

Measurement of SiH2 Densities in an RF-Discharge Silane Plasma Used in the Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Film

Silylene (SiH2) radicals have been detected by intracavity laser absorption spectroscopy in a parallel plate RF-discharge system used in the chemical vapor deposition of hydrogenated amorphous silicon. By the use of two different calibration methods, an absolute density ranging from 2×108 to 6×109 cm-3 has been obtained as a function of the input RF power and of the partial pressure of SiH4. The flux of SiH2 onto the substrate electrode estimated from the gradient of the spatial distribution is less than 1013 cm-2 s-1. This suggests that its direct contribution to the film deposition is small, although it plays an important role in gas phase reactions.

Spectroscopic study of prompt nitrogen oxide formation mechanism in hydrocarbon-air flames

Abstract Total emission intensities of OH∗, CH∗, C2∗, NH∗, and CN∗ in the reaction zone, saturation currents, unburned hydrocarbons, and NOx in the exhaust gases were measured in atmospheric pressure, hydrocarbon-air flames with and without added fuel N (NO and NH3). It has been found that the overall temperature dependence of prompt NO is about 10 kcal/mol for any mixture strength and that NO concentrations are not very dependent on the kind of fuel (CH4, C3H8, and C4H10). The total amount of CH radicals produced in the reaction zone is estimated by comparing NH∗ emission intensity with NO for the flame of added fuel nitrogen, and it is shown that the amount is uniquely determined by the mixture strength without depending on the flame temperature and is also scarcely influenced by fuel. Furthermore, the amount of prompt NO is proportional to that of total CH radicals for fuel-rich, stoichiometric, and lean flames of three different fuels. The above two experimental facts strongly suggest the CH-origin prompt NO formation mechanism (i.e., CH + N2 → HCN + N), and the rate constant is estimated to be k = 4 × 1011 exp (−13,600/RT) cm3/mol s−1 by comparing the amount of prompt NO with that of saturation current.

Application of nitrogen implantation to ULSI

Abstract Nitrogen is not a commonly used ion species in Si ULSI. It cannot be used as an n-type dopant because of its low solubility in Si. However, it shows interesting properties such as the suppression of boron diffusion when applied to source/drain doping and the nitridation of gate oxide when applied to gate doping. In this report, first, the effects of nitrogen preimplantation to the formation of boron-doped shallow p+n junctions are described. The technique is successfully applied to 0.25 μm PMOSFETs, forming shallow junctions and thus suppressing short channel effects. Next, the effects of nitrogen implantation into p+ poly-Si gates are studied. The implanted nitrogen diffuses to the gate oxide during annealing and nitrides the gate oxide. As a result, boron penetration through the gate oxide is suppressed and the reliability and hot carrier resistance are improved.