This paper presents a concise and subjective summary of the rapid progress that has been made in the understanding of the essential features of RF discharges. The paper concentrates on introducing the important concepts used in modeling the rf discharge. The discharges have been modeled from several distinctly different approaches. These include circuit, beamdiffusion, plasma fluid or continuum, and particle kinetic models. The treatments have their usefulness depending on the application. The circuit models give easily parameterized results, power deposition, and phase angles between voltage and current, however, they do not describe the important plasma chemistry and the source terms for deposition and etching. The newer continuum models efficiently give self-consistent plasma parameters for higher pressure discharges but synergistic ion and neutral interactions with surfaces are difficult to include. The particle kinetic models can include many effects without approximations, however they need extensive data sets and long computer run times. The coupling of improved diagnostics and the different theories has resulted in a convergence of their conclusions. There are four distinct energy-gain mechanisms in the RF discharge : a bulk plasma excitation; electron beam excitation resulting from secondary emission from ion collisions with the electrodes; wave-riding acceleration on the sheath oscillation (collisional: Kushner); and a noncollisional plasma electron-sheath boundary interaction (Godyak). The relative contributions are sensitive functions of the gas mixture, pressure, frequency and RF voltage.

Selfconsistent fluid models of radiofrequency discharges in helium and silane are presented. The role of the sheath and plasma electric field in the electron energy gain and deposition mechanisms in both cases are discussed.

The electrical resistivity and N content of a-SiN:H films can be controlled by varying the reactor pressure. This appears to be a result of the increased dissociation of the ammonia feed gas by the change in the electron energy spectrum. The effect of ion bombardment of the substrate surface does not result in observable changes in film quality.

Infrared tunable diode laser absorption studies of radicals and stable molecules formed in radio frequency plasmas are being carried out in a laboratory reactor which allows a long absorption path. In this paper we describe studies of CH4 RF plasmas. We report absolute concentration measurements as functions of total pressure and RF power for CH3 and C2H2 in CH4 plasmas, as well as measurements of the CH4 rotational temperature and dissociation fraction.

Laser-based techniques have been developed to directly study the kinetics of the reactions of the mono-silicon hydride radicals SiH, SiH2 and SiH3. A summary of rate constants obtained from these studies is presented along with a discussion of the implications of these results for present mechanistic models of the PECVD of amorphous hydrogenated silicon from silane.

Si atoms and SiO radicals have been monitored in DC ulow discharges via laser-induced fluorescence on the Si 4s 3P0-3P2−3P and SiO A1 π-x1Σ+ (0−0), (1−0) and (1−1) transitions. Production of Si 4s 3P0 in the 193 and 251 nm multiphoton dissociation of silanes has been observed and the implications for Si atom diagnostics discussed.

Spatially resolved Laser Induced Fluorescence and Optical Emission Spectroscopy were applied in an rf silane discharge, for the simultaneous detection of both ground and excited states of SiH radicals. Axial intensity profiles of these radicals were recorded under various conditions. The experimental observations indicate that the two radicals have different generation paths. LIF profiles are considered to represent the generation profile of all the ground state radicals and they were used as such in kinetic calculations.

Rotational temperature (Tr) of nitrogen molecule, equivalent to the gas temperature (Tg), was used for monitoring silicon nitride (SiN) surface temperature during rf glow discharge processing. SiN film characteristics such as deposition rate and etching rate for mixture of hydro-fluoric acid (HF) and ammonium fluoride : (NH4F) were dependent on Tr near the substrate. The Tr increased not only with substrate temperature setting (To) but also with gas mixing ratio of H2/(H2+N2) due to improvement of thermal conductance from heater to substrate in the process chamber.

The chemistry of silicon nitride deposition from ammonia-silane and nitrogensilane mixtures in a glow-discharge plasma was analyzed using special mass spectrometric techniques involving line-of-sight sampling through an orifice in the wafer plane of a parallel-plate reactor. It was found that high rf power is needed to activate the nitrogen source sufficiently, and that silane flow must be held below a certain critical value to ensure an excess of activated nitrogen. This critical value is detectable by the appearance of disilane in the plasma, which is indicative of silane reacting with itself. At low power, silane reacts only with itself, and disilane is the dominant gaseous product. Conversely, disilane-free plasmas in either gas mixture result in films that are nitrogen-rich and free of the Si-H bonding that has been correlated with poor dielectric behavior. Utilization of silane to form SiNxHy is near unity. The aminosilanes, SiH4-n(NH2)n, are the sole gas-phase Si-N products of the ammonia mixture, and the triaminosilane radical, Si(NH2)3, is the key deposition precursor. The precursor is transformed into SiNxHy by way of a temperature-driven chemical condensation reaction at the surface, with the evolution of ammonia. The nitrogen mixture produces no gas-phase Si-N products, and deposition proceeds by the reaction of SiHn radicals and N atoms at the surface. These basic differences in deposition mechanism result in significant and logical differences in the physical and electrical properties of films deposited from the two mixtures.

The structure and composition of plasma deposited (PD) silicon nitride thin films formed using NH3/SiH4, N2/SiH4, and N2/SiH4/H2, discharges are compared. The effect of introducing a DC grounded stainless steel mesh between the parallel electrodes is also discussed. Chemical structure and composition of these films are measured using X-ray Photoelectron Spectroscopy and Fourier Transform Infrared Spectroscopy. Significant changes in film composition are observed with changes in gas composition and with utilization of the screen. When the screen is invoked, variations in film composition are more pronounced for PD silicon nitride films formed using N2 as the nitrogen source. An increase in the N:Si ratio occurs for all films deposited using the screen. This compositional change is reflected in increased N-H and decreased Si-H bonding. Similar changes are also observed in films deposited from a N2/SiH4/H2 discharge compared to films formed using a N2/SiH4 discharge.

We have produced a-Si,N:H alloy films using remote PECVD at a substrate temperature of 200°C with Si/N ratios between 0 (a-Si:H) and 3/4 (Si3N4). Films were prepared using nitrogen or ammonia source-gases, introduced downstream from a helium rf plasma. Nitrogen and hydrogen bonding environments were investigated using infrared absorbance. For films produced from N2, [N] and [H] concentrations were determined by SIMS. A random bonding model is used for a quantitative analysis of Si-H and Si-N bonding distributions, and to estimate the N/Si ratio in films produced from NH3. A comparison of N2 and NH3 source gases for nitrogen incorporation is also presented.

A UHV electron cyclotron resonance (ECR) plasma source has been used to deposit SiNx, SiOxNy and amorphous Si thin films on InP substrates for optoelectronic device applications. High quality dielectric films can be deposited at temperatures significantly lower than conventional techniques, namely less than 110°C. Selected applications pertinent to optoelectronic devices are used to establish the role of ion/electron fluxes in thin film properties.

Silicon nitride films deposited from silane-nitrogen and silane-ammonia mixtures by PECVD contain large amounts of hydrogen. We have determined that adding argon to the gas mixture reduces the amount of hydrogen in the resulting films. Differences in film composition are obviously due to changes in the chemistry of the discharge which was characterized by line-of-sight mass spectrometry, optical emission spectroscopy and plasma double probe measurements. Substrate temperature was fixed at 325°C, pressure was 500 mtorr, the RF power was 0.25 watts cm−2, the silane to nitrogen ratio was varied from 0.003 to 0.02, the silane to ammonia ratio was varied from 0.01 to 0.5, and the argon additions were 10% of the total gas flow. Argon additions to the discharge increased the plasma density in both nitrogen and ammonia plasmas. Optical emission from N2 and Si-H species increased upon the addition of 10% argon to the silane-nitrogen discharge, whereas the N-H emission decreased upon addition of argon to the silane-ammonia discharge. Infrared transmission spectra of films deposited with and without argon show no change in peak position or intensity of Si-H and N-H absorption bands in the spectral range studied, despite a large (over 20%) reduction in hydrogen content, as determined by nuclear profiling, upon the addition of argon. These results suggest that a substantial fraction of the hydrogen in the films is not infrared active. We propose that the reduction in hydrogen content is due to bombardment of the growing film by argon ions, which sputter the adsorbed hydrogen molecules.

We have characterized the step coverage and film quality of (tetraethoxysilane) TEOS-based silicon oxides which are directionally deposited on horizontal surfaces of trench features under oxygen-lean conditions in a high frequency (14 MHz) discharge. The film thickness on the sidewalls depends most strongly on the O2 :TEOS feed ratio. Water uptake after ambient exposure was used as a measure of film quality and the amount of water absorbed in the film correlated well with changes in the refractive index and stress. Oxide quality on horizontal surfaces could be improved by decreasing the TEOS feed or increasing the discharge power, but the sidewall oxide quality could not be improved by these methods. Small NF3 additions to the discharge markedly improved sidewall quality, altered the angle between the sidewall and the bottom of trench features from 90° to ˜115° (tapered profile) and increased the deposition rate, while preserving the directionality of deposition.

Silicon dioxide films deposited from the PECVD reaction of silane and nitrous oxide in the presence of helium were studied to determine the effects of RF power on the deposition process. Increased RF power density yielded oxides which were structurally and chemically more homogeneous. The combination of elevated power density with increased silane concentration resulted in the deposition of films of high electrical and physical integrity at high deposition rates.

Amorphous SiO2 films have been deposited by plasma enhanced chemical vapor deposition (N2O:SiH4 flow rate ratio of 40:1) then 60Co gamma irradiated. We observe paramagnetic defects similar to oxygen vacancy centers which are created at least 100 times more efficiently in as-deposited oxide than in the same oxide annealed for 1 hr in Ar at 950°C. Positive fixed oxide charge creation in samples irradiated in the unbiased mode has a fractional yield of 0.018 defects per electron-hole pair. No enhancement of the positive fixed oxide charge creation is observed when comparing as-deposited and annealed films suggesting that the paramagnetic and electric defects do not have the same physical origin. Comments are made about the potential hazards of using such deposited oxide near a semiconductor surface where surface inversion may occur.

Low-energy (≤ 200 eV) ion irradiation during crystal growth from the vapor phase can be used to provide new chemical reaction pathways, modify film-growth kinetics, and, hence, controllably alter the physical properties of films deposited by a variety of techniques. The latter includes sputter deposition, ion plating, plasma-assisted chemical vapor deposition (PA-CVD), primary-ion deposition (PID), and molecular-beam epitaxy (MBE) using accelerated beam sources. Ion/surface interaction effects such as ion-induced chemistry, trapping, recoil implantation, preferential sputtering, collisional mixing, enhanced diffusion, and alteration in segregation behavior are used to interpret and model experimental results concerning the effects of low-energy particle bombardment on nucleation and growth kinetics, elemental incorporation probabilities, compositional depth distributions, and the growth of metastable phases.

Low temperature processing will be an essential requirement for the device sizes, structures, and materials being considered for future integrated circuit applications. In particular, low temperature silicon epitaxy will be required for new devices and technologies utilizing three-dimensional epitaxial structures and silicon-based heterostructures. A novel technique, Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD), has achieved epitaxial silicon films at a temperature as low as 150°C which is believed to be the lowest temperature to date for silicon epitaxy. The process relies on a stringent ex-situ preparation procedure, a controlled wafer loading sequence, and an in-situ remote hydrogen plasma clean of the sample surface, all of which provide a surface free of carbon, oxygen, and other contaminants. The system is constructed using ultra-high vacuum technology (10-10 Torr) to achieve and maintain contaminantion-free surfaces and films. Plasma excitation of argon is used in lieu of thermal energy to provide energetic species that dissociate silane and affect surface chemical processes. Excellent crystallinity is observed from the thin films grown at 150°C using the analytical techniques of Transmission Electron Microscopy (TEM) and Nomarski interference contrast microscopy after defect etching.

In this paper the reaction kinetics of Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) are investigated. Growth rate characterization has been performed for substrate temperatures of 220 – 400°C, r-f powers from 4 – 8 W, and silane flow rates of 10 – 30 sccm. Growth rate has been found to increase exponentially with r-f power, which is, as yet, unexplained. An approximate square root dependence of growth rate on silane partial pressure agrees with the theory of Claasen et. Al for Chemical Vapor Deposition (CVD) of silicon from silane with an inert carrier gas. From an Arrhenius plot of the temperature dependence of growth rate, we note a change of slope at ∼300°C which we have attributed to the behavior of hydrogen at the silicon surface.

Remote plasma enhancecd chemical vapor deposition techniques have been developed for a wide variety of processes. These include SiO2, Si3N4, Si, Ge, GaN, GaAs, and a-Si:H depositions. This development has been enabled through the use of electron diffraction and electron spectroscopy techniques. These techniques have been used to qualify cleaning procedures prior to epitaxial or dielectric depositions. They have beeii used to qualify epitaxial deposition conditions by defining suitable.temperature and rate conditions. And, they have been used to evaluate cross-contamination issues. In situ techniques have been used in conjunction with ex situ characterizations to identify and correct problems in wafer cleaning, epitaxy, and process integration.