Hydrogenated amorphous silicon nitride films, prepared in various commercially available plasma enhanced chemical vapor deposition systems, have been investigated in terms of different deposition conditions.The full characterization of these gate insulators has been carried out by different techniques.Experimental data and interesting findings obtained from this study are presented.Indeed, some valuable relationships between physico-chemical and mechanical properties have been established.Special attention has been devoted to the influence of hydrogen on these properties.

Hydrogenated amorphous silicon nitride films, prepared in various commercially available plasma enhanced chemical vapor deposition systems, have been investigated in terms of different deposition conditions.The full characterization of these gate insulators has been carried out by different techniques.Experimental data and interesting findings obtained from this study are presented.Special attention has been devoted to the influence of hydrogen on optical and electrical properties.

Plasma silicon nitride (P-SiN) films were prepared from SiH4/NH3 mixtures in a large volume microwave plasma (LMP) apparatus, at substrate temperatures T2 ranging from ambient to 250°C.Under otherwise nominally identical fabrication conditions, deposition rates were 10 to 25 times greater than those reported by others for radio- or audio-frequency plasmas.Based on film compositions, determined by elastic recoil detection (ERD), and measurements of such properties as density, refractive index, etch rate in dilute HF, and moisture permeation coefficient, our best P-SiN films (produced at T2 ≥ 200°C) are very similar to those reported in the literature.

Over the past several years, numerous new materials have been prepared by the glow discharge decomposition of gaseous species.Among these, a material with extraordinary though as yet unfulfilled potential is hydrogenated amorphous carbon(a-C:H).As a metastable state between the two naturally occurring carbons, graphite and diamond, a-C:H can display a wide range of phyical characteristics.Film optical and electronic properties are a strong function of deposition parameters, where 2.l>Eopt >0.9eV.and 1016 >ρ>106Ω-cm., for films deposited between 75 and 375C.Occasionally referred to as “diamond-like”, such films can be extraordinarily hard and virtually impervious to chemical attack.The interrelation of film structure on the atomic level and macroscopic film properties will be discussed, with emphasis on the current controversy over whether such material is indeed diamond-like in its microscopic ordering.

The emission spectra of various hydrocarbon plasmas used in the growth of amorphous hydrogenated carbon (α-C:H) thin films have been measured.The presence of CH, H, H2, and C2 species in the plasma have been observed.The chemical composition of the α-C:H films was determined by combustion analysis and shows roughly equal atomic concentrations of H and C and a surprising large concentration of 0.The plasma emission spectra and chemical composition results can be partially understood in terms of relative bond strengths of the different molecules involved, and these results give some insights into the growth kinetics of α-C:H thin films.

Optical emission analysis and mass spectroscopy was applied to study the rf-glow discharge in hydrocarbons used for the deposition of amorphous hydrogenated carbon (a-C:H).The mass spectra of the positively charged ions in the plasma are characteristic for the hydrocarbon used - e.g.benzene, hexane, or methane.In contrast, the properties of the deposited a-C:H film, such as refractive index, are independent of the precursor gas.Spatially resolved optical measurements show strong emission from C, C2, and CH in the vincinity of the negatively self-biased cathode (substrate) irrespective of the precursor used.Based on these findings we conclude that the fragmentation of the impinging energetic hydrocarbons is one of the key mechanisms for the formation of hard, strongly cross-linked a-C:H films.

The amorphous dielectrics a-C:H and BN were deposited on III–V semiconductors.Optical band gaps as high as 3 eV were measured for a-C:H generated by C4 H10 plasmas; a comparison was made with bad gaps obtained from films prepared by CH4 glow discharges.The ion beam deposited BN films exhibited amorphous behavior with band gaps on the order of 5 eV.

Film compositions were studied by Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS).The optical properties were characterized by ellipsometry, UV/VIS absorptiofr, and IR reflection and transmission.Etching rates of a-C:H subjected to O2 discharges were determined.

It is desirable to develop detailed models of glow discharge chemical reactors in order to understand the many complex interactions that govern reactor performance.One important part of an overall model of the plasma reactor is the description of the discharge physical structure including charged particle densities, energies and the self-consistent electric field.The continuum or fluid equation approach to this problem is presented in this paper and potential problems with this approach are discussed.Results from recent simulations of a 13.56 MHz rf discharge are presented.The behavior of the electrons in the quasineutral plasma and their interaction with the self-consistent field are highlighted.It is shown that the rf power dissipation peaks at the plasma-sheath boundary, and the implications of this for the validity of estimates of mean electron density from equivalent rf rcircuit models is discussed.

The transport of ions through a rf-plasma sheath was simulated using a Monte Carlo method to determine the distribution of ion bombardment energy and impingement angle.Several types of ion-molecule interactions were tested to determine their effect on the distributions: elastic hard-sphere scattering, elastic potential-field interactions (based upon reported literature values obtained by drift tube measures), and charge transfer.The type of elastic scattering does not significantly change the angular distributions; however, the scattering cross-sections changes as a function of ion energy (or sheath E/P) for the potential-field interactions.The fraction of collisions giving charge exchange makes a large difference in the simulated directionality as well as a factor of two difference in the average bombardment energy.

A simple kinetic dry etching model accounting for generation, loss, and transport of the reactive and by-product species is developed.To demonstrate and evaluate the model, the etching of silicon using SF6+O2+Ar in the plasma etch mode is investigated.

Continuity equations for the concentration of electrons, positive ions, and negative ions were constructed and solved to predict rf breakdown voltages and the electrical properties of SF, discharges.These balances for the three types of charged species include terms for convection (electric field-driven fluxes), diffusion, and reactions (ionization, electron attachment, and negative-positive ion recombination).The mobilities, diffusivities, and reaction rate coefficients necessary for the rf discharge model are based on reported measurements and calculations of these parameters in dc electric fields.The electric fields developed in the rf discharge are calculated from Poisson's equation and applied voltage conditions.Predictions based on this model are compared with measured rf breakdown characteristics of SF6.

Three independent models are presented: One for determining the plasma density and target sheath voltage, one for silicon etching using CF4plus O2, and one for RIE etching of silicon dioxide.

In most dry etching techniques the target and plasma voltages play a large role.In this paper, the dc and rf mechanisms which determine the plasma density, and thus the target voltage, are presented.The mechanisms used are: 1) secondary electron ionization in the sheath, 2) secondary electron ionization in the plasma, 3) ionization by tertiary electrons, 4) I2R heating of the plasma electrons, and 5) sheath heating of plasma electrons.An equivalent circuit for an rf discharge is presented, and the relationship between the plasma voltage and target sheath voltage are discussed.

The mechanisms used to model silicon etching include chemical etching, ion enhanced etching and diffusion of reactive species.Laser induced fluorescence data from G.S.Selwyn will be discussed.These data show spatial resolution of a reactive species in an RIE plasma and show the diffusion effects.

The ion-enhanced etching effect for SiO2, shows a much stronger voltage dependence than that for Si, which is almost independent of voltage.Data from G.Fortuno show that the voltage dependence for SiO2 is similar to that of sputtering.The mechanisms used to model SiO2 etching include the work by G.Fortuno (1985) and that by B.N.Chapman and V.J.Minkiewicz (1978).

The etching of SiO2 was studied during reactive ion etcing (RIE) in an SF plasma.The etch rate of SiO2, the sheath voltage and the wafer temperature were measured as a function of the percentage of SF6 in Ar and as a function of the total pressure.This was done with the purpose of better understanding the etching mechanisms involved.The results are compared with similar experiments carried out with CF4 and Ar [1].Tests to the model formulated will also be given.

A kinetic model, composed of elementary chemical reactions, is derived to predict the etch rate of crystalline silicon with NF3 in a plasma discharge.Experimental data taken from a radial flow plasma etching reactor is used to determine the model's kinetic parameters.The rate constant for atomic fluorine reacting with <100> silicon was determined to be 1410 cm/min at 25 °C, in good agreement with a value obtained by other investigators.

Profile control in polysilicon etching with SF6/O2 and NF3/O2 gas mixtures has been explored as a function of feed gas composition, power, pressure and total flow.Polysilicon appears to etch anisotropically under certain anomalous combinations of these parameters, such as high power/dilute etchant gas composition, low power/high etchant gas composition and high power/high etchant gas composition.Very rapid etch rates (3.5 μm/min) and anisotropic etching were obtained simultaneously in SF6/O2 mixtures at 250 mtorr.In order to provide a rational for explaining these anomalies, a kinetic model for these plasmas has been developed which couples electron impact events in the plasma to gas-phase chemistry and surface reactions of the etching process.Peculiarities in the electron energy distribution function (EEDF) of these gas mixtures, determined by Boltzmann calculations, appear related to the anisotropy under dilute conditions.However, anisotropic etching observed at 250 mtorr and rich SF6 gas mixtures appears more related to anomalies in power deposition to the discharge, possibly including wave interactions or resonant processes.Comparisons between computer simulations and experimental results are presented.

The directional etching of P-doped polysilicon has been studied as a function of power (0.2 – 0.8 W/cm3), pressure (0.2 – 0.4 torr), and CFC13 (FreonR-11) fraction (1 – 20%) in SF6 discharges.Over this parameter space, experimental measures of the etching rate, directionality, plasma impedance, optical emission, and ion-bombardment energy and flux were made.Through Ar actinometry, the concentrations of F and Cl were estimated.Response Surface Methodolgy was used to fit the measurements to polynomial models which were used in the subsequent kinetic modeling of the process.As the fraction of CFCl3 was increased from 1 to 20%, the F concentration fell by a factor of 3 while the Cl concentration increased by a factor of approximately 20.The mask undercut and etching rate, however changed less than a factor of two with the CFCl.increase.The measured average ionbombardment energies were well correlated using discharge currents.

Electron energy distribution functions in molecular rf plasmas (CO, SF6 ) have been calculated by numerically solving the time dependent Boltzmann equation in a wide range of field frequencies up to the establishment of the periodic state.Particular attention is given to the reduction of the modulation degree and phase shift with respect to the rf field of the isotropic distribution function and of some macroscopic quantities as a function of frequency.Time averages of distribution functions and of some macroscopic quantities are then compared with the corresponding results obtained by using the effective field approximation.Finally we discuss the role of the second kind collisions in affecting the results.

An integrated electron kinetics, plasma chemistry, and surface deposition model has been developed to study the relationship between film characteristics and plasma parameters in the plasma enhanced chemical vapor deposition (PECVD) of amorphous hydrogenated silicon (a–Si:H) in low pressure parallel plate RF discharges.The integrated model consists of a Monte-Carlo simulation for the electron distribution function in the RF discharge, a time and spatially dependent plasma chemistry model, and a model for the surface deposition process.The surface model consists of an accounting of the surface density of adsorbed species, and the fractional distribution of various types of bonds (e.g.Si–Si, Si–H, Si–.) in the film.The calculated distribution of radicals in silane discharges will first be discussed.The computed hydrogen content and deposition rates of a-Si:H films from silane and disilane discharges are next discussed and compared to experiment.The dependence of hydrogen content on Rf power and substrate temperature is calculated and agrees well with experiment.Mechanisms are proposed to explain these dependencies.

Experimental measurements and theoretical modeling of methane deposition plasmas have made it possible to determine the most likely homogeneous and heterogeneous chemical reaction paths leading to deposition of hydrogenated carbon from the fragments of electron dissociated methane.The methane plasma was modeled as a plug-flow reactor.Gas phase reactions, diffusive transport, variable surface reflection coefficients, and surface chemical reactions are included in the model which follows a “plug” of gas as it flows through the reactor.Boltzmann equation and Monte Carlo calculations were used to determine the electron energy distribution and the resulting dissociation and ionization rate coefficients averaged over space and time.Experimental measurements of the time dependent electrical properties of the plasma are used as input to the model.Deposition rates, deposition uniformity, downstream mass spectroscopy, and the dependences of these quantities on power and mass flow rates are compared to the model to arrive at a consistent representation of the deposition chemistry.

We describe a plasma enhanced chemical vapor deposition process (PECVD) developed for the low temperature deposition of thin films of silicon oxides, nitrides and oxynitrides.The process, designated as remote PECVD (RPECVD), differs from conventional PECVD in two ways; (a) not all of the process gases are subjected to plasma excitation; and (b) the deposition is done outside of the plasma region.We include an empirical model of the deposition process chemistry and discuss the use of infrared spectroscopy (IR) and Auger electron spectroscopy (AES) to characterize the local atomic structure of the deposited films.