Richard J. Buss

Reactive sticking coefficients for silane and disilane on polycrystalline silicon

Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition‐rate measurements using molecular beam scattering and a very low‐pressure cold‐wall reactor. The RSCs have nonlinear Arrhenius temperature dependencies and decrease with increasing flux at low (710 °C) temperatures. Several simple models are proposed to explain these observations. The results are compared with previous studies of the SiH4/Si(s) reaction and low‐pressure chemical vapor deposition‐rate measurements.

Modeling the plasma chemistry of C2F6 and CHF3 etching of silicon dioxide, with comparisons to etch rate and diagnostic data

A detailed chemical reaction mechanism is reported that describes the C2F6 and CHF3 plasma etching of silicon dioxide, which is widely used in the fabrication of microelectronic devices. The gas-phase part of the C2F6 mechanism involves 28 species and 132 reactions, while the surface part involves 2 materials, 6 species, and 85 reactions. Rate parameters are generally taken from independent studies in the literature, or estimated from rates measured for related species. Zero-dimensional simulations using these mechanisms compare well with a large body of etch rate and diagnostic measurements in three different high-density plasma reactors. The diagnostic measurements include electron and negative ion absolute densities, CF, CF2, and SiF densities, gas temperatures, and ion current densities. An analysis of the dominant reaction paths shows the importance of gas-phase electron impact reactions and the need to include reactions of the etch-product species. On the surface, the etching reactions are dominated...

Laser studies of the reactivity of SiH with the surface of a depositing film

A new method for studying the interaction of radicals with the surface of a depositing film is presented. This method combines spatially resolved laser spectroscopy with molecular beam techniques and is demonstrated by measuring the state‐resolved reactivity of SiH molecules with the surface of a depositing amorphous hydrogenated silicon film. SiH molecules from a silane glow discharge react at the surface with greater than 0.94 probability. The spatial distribution of the desorbing SiH is consistent with a cosine angular distribution. No dependence of reactivity on rotational state of the SiH was observed.

SIMULATIONS OF BCL3/CL2/AR PLASMAS WITH COMPARISONS TO DIAGNOSTIC DATA

A reaction mechanism is reported that describes BCl3/Cl2/Ar plasmas used in the etching of metal lines in microelectronics fabrication processes. Although many of the fundamental electron-impact cross sections for this system are not well known, a reasonable set of reaction paths and rate coefficients has been derived to describe low-pressure reactors with high plasma density. The reaction mechanism describes 59 possible gas-phase events and 18 plasma-surface interactions. A well-mixed reactor model is used to develop the reaction set and to test it against absolute experimental measurements of electron and Cl− densities, as well as relative measurements of BCl and Cl radicals in an inductively coupled research reactor. The experimental data cover a wide range of operating conditions and gas mixtures. The model provides quantitative agreement with measurements over the whole range of conditions and diagnostics, capturing most of the observed trends. In addition, the model predicts relative ion ratios and ...

Chemical kinetics in chemical vapor deposition: growth of silicon dioxide from tetraethoxysilane (TEOS)

Abstract Chemical reactions in the gas-phase and on surfaces are important in the chemical vapor deposition (CVD) of materials for microelectronic applications. General approaches for modeling the homogeneous and heterogeneous kinetics in CVD are discussed. A software framework for implementing the theory utilizing the CHEMKIN suite of codes is presented. Specific examples are drawn from the CVD of SiO 2 using tetraethoxysilane (TEOS). Experimental molecular beam reactive-sticking coefficient studies were employed to extract surface-reaction rate constants. Numerical simulations were used to analyze the molecular-beam experiments and low-pressure tube furnace data, illustrating the general modeling approach.

Properties of micrometer-thick plasma-polymerized tetrafluoroethylene films

Several physical properties of thin plasma‐polymerized films have been measured using a new fiber‐optic‐based technique. Films of plasma‐polymerized tetrafluoroethylene (PPTFE) deposited on the end of an optical fiber form an optical cavity, the reflectivity of which is very sensitive to the film thickness. The fiber is used as an in situ monitor of the deposition rate in the plasma and, after removal from the plasma, the mechanical properties of the film can be measured. With this measurement technique the thermal expansion of the film normal to its surface as well as the swelling of the film when exposed to an array of organic solvents have been determined. A significantly smaller thermal‐expansion coefficient and larger degree of swelling are observed relative to bulk PTFE. X‐ray photoelectron spectroscopy measurements show that the fluorocarbon chains are highly branched and have a fluorine‐to‐carbon ratio of 1.45. These results suggest that the plasma‐polymerized films are not crystalline and are hea...

Glow-discharge synthesis of silicon nitride precursor powders

A radio-frequency glow discharge is used for the synthesis of submicron, amorphous, silicon nitride precursor powders from silane and ammonia. Powders are produced with a range of Si/N ratios, including stoichiometric, Si-rich, and N-rich, and contain substantial amounts of hydrogen. The powders appear to be similar to silicon diimide and are easily converted to oxide by water vapor. The powders lose weight and crystallize to a mixture of {alpha} and {beta}-Si{sub 3}N{sub 4} after prolonged heating at 1600{degree}C. Studies of spectrally and spatially resolved optical emission from the plasma are reported.

Kinetics of the micromirror chemical sensor

Abstract Most chemical sensors involve a sensitizing coating that interacts with the chemical species to be detected to produce a change in some physical parameter which can then be measured. The speed of response of the sensor depends to a large extent on the nature of this chemical interaction. Here we explore the kinetics of the micromirror chemical sensor, a reflective-type optical-fiber sensor, for two different interactions: (1) the detection of hydrogen at high concentrations using palladium films; (2) organic vapor detection using a plasma-polymerized fluorocarbon film. For hydrogen detection, where the palladium films are very thin (∼ 10 nm), the kinetics are determined by the complex nature of the surface chemistry; the presence of oxygen changes the speed of the sensor response. For organic vapor detection, the fluorocarbon film is much thicker (∼1 μm) and the speed of response is determined by diffusion of the organic molecules through the fluorocarbon film.

Synthesis of silicon nitride particles in pulsed radio frequency plasmas

Silicon nitride (hydrogenated) particles are synthesized using a pulsed 13.56 MHz glow discharge. The plasma is modulated with a square‐wave on/off cycle of varying period to study the growth kinetics. In situ laser light scattering and ex situ particle analysis are used to study the nucleation and growth. For SiH4/Ar and SiH4/NH 3 plasmas, an initial very rapid growth phase is followed by slower growth, approaching the rate of thin film deposition on adjacent flat surfaces. The average particle size can be controlled in the 10–100 nm range by adjusting the plasma‐on time. The size dispersion of the particles is large and is consistent with a process of continuous nucleation during the plasma‐on period. The large polydispersity is also reported for silicon particles from silane and differs from that reported in other laboratories. The silicon nitride particle morphology is compared to that of silicon and silicon carbide particles generated by the same technique. Whereas Si particles appear as rough cluste...

Laser studies of the reactivity of SiO with the surface of a depositing film

The reactivity of SiO produced in a SiCl4/O2 plasma with the surface of a depositing silicon oxide film has been measured to be near zero for surface temperatures of 25–500 °C using the IRIS technique (imaging of radicals interacting with surfaces). This method combines spatially resolved laser-induced fluorescence with molecular beam techniques. The SiO desorbs from the surface with a spatial distribution consistent with a cosine angular distribution.