An obstacle to better design and control of plasma processes is our limited ability to monitor surface properties in situ. We describe a new plasma diagnostic technique, photoemission optogalvanic spectroscopy, which can be used to monitor surface contamination, etching rates, and end points. The experiment consists of irradiating a surface with a pulsed excimer or dye laser whose photon energy is above the substrate work function. Photoemission of electrons from the surface is detected by monitoring changes in the discharge current (optogalvanic effect). The technique is characterized by measuring signal strengths as a function of laser intensity, laser wavelength, and bias voltage in vacuum and in an Ar plasma. The technique is used to monitor contamination and etching end points in F-containing plasmas.

Laser-induced fluorescence, LIF, data provide a wide variety of detailed information about physical and chemical reactions and plasmas. In today's technological environment these areas commonly extend from nanosecond laser etching to ion etching (in the low gas density direction), or to combustion gases (near atmospheric pressure). In studying these dynamical processes, the laser probe is nearly ideal; note that one measures a specific species' density as a function of position, velocity, temperature and time within an unperturbed working environment (i.e. high vacuum not required). Examples are derived from our LIF probing of laser etch plumes; the surfaces included sapphire, polymers and benzene (both as a gas and frozen monolayer). LIF results distinguish between diatomic radicals due to thermal vaporization as compared to diatomics from a photochemical decomposition. Beyond the above LIF probing of a laser-etch plume, sophisticated diagnostic techniques such as CARS, multiphoton excitation and ionization, and dissociation immediately followed by optical excitation appear regularly. Enhanced information gathering by laser probing is also demonstrated by the fact that spectroscopic data can be recorded as a 2D picture of a reacting species.

With respect to limitations on laser probing, consider the following: Even though plasmas and etch plumes are luminous, the pulsed nature of laser experiments discriminates heavily against background light and dark current noise. While the various techniques measure relative densities at even very low densities, establishing accurate values for absolute densities is considerably more challenging. (Spectral-linewidth uncertainties are a common culprit.) Perhaps the main limitations on laser probing relate to the patience, dedication and budget of the experimenter.

The chemical vapor deposition process consists of a chemicallyreacting flow in which the fluid mechanics and chemical kinetics are strongly coupled. Laser probes such as Raman spectroscopy and laserinduced fluorescence can be used to measure gas temperature fields and chemical species concentrations, but often the interpretation of such data is difficult because several interacting chemical and physical phenomena are occuring simultaneously. Detailed numerical modeling of the experinmental system under study provides valuable insights into these interactions and allows one to make useful comparisons between experiment and the model to gain a fundamental understanding of the CVD process. Examples of this approach are given for silicon deposition from silane and fluid mechanics diagnostics in a rotating disk CVD reactor.

Spatially resolved concentration profiles of ground-state chlorine atoms were measured in CF3 Cl/Ar RF plasmas using two-photon laser induced fluorescence. A significant Cl gradient was found between the two electrodes under conditions typical for plasma etching. This experimental observation is consistent with previous model predictions which assumed the primary loss of Cl was a second-order surface recombination on the upper electrode which is partially limited by gaseous diffusion.

Laser-induced fluorescence (LIF) is an ideal technique to determine the gas phase concentration of the chemically reactive radical species in processing plasmas. Quantitative species concentration measurements require spectroscopic and collision dynamics data. Experiments to obtain such data for the B2 and Σ+ B′2 Δ states of SiCl are described. Using LIF, the transition strengths, radiative lifetimes, and collisional removal rates are determined. Collisional transfer between the two excited electronic states, B′→B, shows a very unusual quantum state specificity for the final vibrational levels which is quite different for each of the rare gas collision partners (He, Ne, Ar). Such energy transfer makes the B′2 Δ state unsuitable for quantitative LIF diagnostics; however, the B2Σ+ state appears to be an ideal excited state for LIF diagnostic measurements in silicon etching plasmas.

RF plasmas of CFM4 have been investigated by laser-induced fluorescence (LIF). Ground state CF2 and CF radicals have been observed under a variety of experimental conditions, where LIF has enabled spatial and temporal distributions to be found. In addition, absolute concentrations have been measured and the processes of radical production and removal have been examined.

The distribution of ions present in halofluorocarbon (CF4, CF3Cl, CF3Br, CF2Cl2 ) plasmas has been studied by mass analysis of the ions extracted from the discharge. Silicon and silicon dioxide targets have been used to study the discharge chemistry in Reactive Ion Etching (RIE) conditions. In the case of silicon, both fluorine and chlorine participate in the etching; therefore, the discharge is enriched in halocarbon oligomers and etch products containing fluorine, chlorine and bromine. The higher reactivity of fluorine induces the formation of chlorine or bromine-enriched molecules and ions. Chlorine and bromine molecules are formed but their concentration in the discharge is not high due to consumption by etching. The situation is different with the silicon dioxide target. In this case, etching consumes both fluorine and fluorocarbon radicals, leading to the formation of silicon tetrafluoride and carbon oxides. The target, in this case, is “neutral”; the discharge is not enriched in oligomers as for silicon. The tendency to form chlorine and bromine-enriched species is still present and considerable amounts of molecular chlorine and bromine are present in the discharge because they do not participate efficiently in etching.

Mass spectroscopy has been used to diagnose plasma processing atmospheres by detailing the flux of neutral and ion species and the energy distribution of ions impinging upon a substrate immersed in a glow discharge. The institution of a diagnostic tool to investigate the chemical (reactive neutral) and physical (ion) aspects involved in plasma processing is necessary to improve control and reliability in thin film materials processing. Research has focussed on ion-enhanced etching of tungsten thin films in NF3/O2 and the deposition of tungsten by the reaction of WF6 and H2 in rf glow discharge reactions.

Processing plasmas generated by three types of discharges are diagnosed spectroscopically in order to estimate the quantitative relationship between plasma parameters and electrical and optical properties of deposited materials. An rf discharge is capacitively produced by a 13.56 MHz rf oscillator. A microwave generator operating at 2.45 GHz is used to supply power to a discharge cavity. Further a pulsed plasma which is inductively generated by pulsed current ( 70 kA peak ) is applied to study dissociation process in the transient plasma and possibility of a novel processing system. The gases used are methane for amorphous carbon formation and silane for amorphous silicon deposition. Measurements of optical emission spectrum are performed to estimate the processing plasma state by the relative spectral intensity method and the Doppler-broadening method.

Laser diagnostics, including long path infrared diode laser absorption and dye laser induced fluorescence, are able to provide microscopic information on the gas phase of such important semiconductor fabrication processes as plasma etching and plasma enhanced deposition. It is possible to measure temperatures, concentration profiles, and absolute concentrations if independent laboratory measurements of quantitative spectroscopic parameters have been made. Infrared band strength measurements on several molecular radicals important in semiconductor processing systems are described. We also describe a new apparatus which allows multipass absorption and laser induced fluorescence diagnostics of a large volume of plasma.

PACVD techniques for depositing protective coatings are an emerging field in plasma processing technology. Technology transfer is limited by a lack of understanding of the basic mechanisms involved in the gas phase plasma chemistry. The aspects of plasma species concentration and distribution and plasma gas temperature are fragmentary and unclear. Laser diagnostic techniques represent a critical starting point for providing some of this needed information. The techniques are in-situ, nonintrusive, and give excellent spatial and temporal resolution. Numerous diagnostic techniques for detailed coating characterization are available, but a correlation of the PACVD parameters with some of the key coating properties is required. Thus, a predictive capability that is lacking in the present science base can be established together with important phenomenological aspects needed for efficient deposition of high quality protective coatings. As the mechanisms become better understood, use of remote sensors and A.I may then be introduced. This paper will review selected diagnostic techniques available for characterizing these nonequilibrium reactive plasmas and the coatings.

Many industrially important metallurgical processes are accompanied by the emission of light, the analysis of which often supplies useful information concerning the current state of the process while also providing insight into the details of specific process mechanisms. Optical diagnostic techniques are finding an increasingly wide range of application throughout the metallurgical community. This paper discusses the application of emission spectroscopy and imaging techniques to the analysis of such diverse processes as vacuum arc remelting, laser welding, and arc welding. A discussion of these techniques will be presented addressing such subjects as instrumentation, data analysis, the kind of information available and its potential impact on the selection of process parameters. Special attention will be given to discussing the difficulties encountered in applying these diagnostic technologies to “real life” processes in non-laboratory environments.

Carbonization of carbon-carbon composites is presently a slow, costly process. The failure rate and the variation in final material properties are both excessive. The complex physical and chemical changes require new control methods. Real time sensing of material properties can, in combination with a priori expert knowledge, be used to improve real time model estimates of process outcome and to revise the process. The basic elements of the control strategy for real time control of carbonization based on thermal, acoustic, conductivity, and gas chemistry sensors are described. Preliminary results relate real time gas analysis to physical changes.

To implement new process control strategies including Intelligent Processing of Materials, advanced sensors are required to nonintrusively evaluate process and microstructure variables. Researchers increasingly are looking to innovative extensions of traditional nondestructive evaluation technologies, such as ultrasonics, acoustic emission, and eddy current methodologies for this. Here, the nature and characteristics of emerging sensors based upon these new measurement methods are described and examples of their application discussed.

The accurate measurement and control of temperature can be of great importance in most materials manufacturing and processing applications. With present-day technology such measurement almost always requires either physical contact with the subject or an extensive calibration procedure. In many cases contact is either not desirable, because such contact may significantly alter the temperature or other characteristics of the subject, or is not possible because the subject is moving, is too far away, is too hot or is in an otherwise hostile environment. Similarly calibration may not be possible if the characteristics change too much.

Emission spectroscopy and laser-induced fluorescence have been used to monitor the field and tail-flame regions of a Hull-design 1 inductively coupled plasma. This plasma is used for a variety of syntheses 2,3 including SiC, TiC, BN, AlN and diamond. Temporallyand spatially-resolved spectra of both pure Ar and Ar/gas mixtures have been studied as a function of RF power, pressure and flow rate. Preliminary data suggest that the system is far from local thermodynamic equilibrium.

In order to make desirable surface layers by low pressure plasma spraying (LPPS), optimum operating conditions and plasma torch gun designs must be decided upon for understanding LPPS plasma and powder behavior. As the first step of this approach, LPPS plasmas without powders were measured by the Thomson scattering, the Michelson interferometry and a Pitot tube. These diagnostics revealed that LPPS plasma jets may be treated as supersonic neutral gas flows as the first approximation. In addition, the neutral particle temperature Tn and ion temperature Ti were found to be the same as the electron temperature Te, which is 1 eV at an oblique shock wave heating point and 0.2 eV at the sugsequent cooling point. LPPS plasmas and flows were modeled by a computer Simulation of a supersonic nozzle flow, 2nd yielded reasonable understanding of the thermodynamic and fluid-mechanical conditions.

Formation, growth and deposition of particles represent a critical part of several important industrial processes, such as production of carbon black, optical fibers, micro-electronic components, and metal and ceramic powders. Laser diagnostic techniques are utilized to develop a fundamental understanding of these processes.

Formation of carbonaceous soot particles has been studied in laminar, coannular, hydrocarbon diffusion flames. Laser extinction/scattering, laser scattering dissymmetry, and velocimetry measurements have been used to determine particle volume fraction, size, number density and velocity. From this set of data, particle formation and growth rates have been determined for different fuels and at different temperatures. Similar techniques have been used to study silica particle formation in an opposed jet diffusion flame, where silicon is introduced in the form of silane (SiH4) into the fuel stream (H2/Ar); the oxidant is an O2/Ar mixture. The advantage of this geometry is that, along the stagnation point streamline, the flow may be considered one-dimensional. This should allow the extension of the results of this study to practical CVD or MCVD processes for optical fibers. Laser diagnostic techniques are also being used to investigate metal powder atomization processes, and the effect of operating conditions on particle size distribution.

The characterization of silica “sooting” torches used in optical waveguide manufacture by external flame-hydrolysis deposition processes such as Outside Vapor Deposition (OVD) and Vapor-phase Axial Deposition (VAD) prflents a formid.ble high temperature environment at > 2000°C in the presence of > 1012 particles/cm3 of silica. This paper describes the first application of Dynamic Light Scattering (DLS) to probe particle sizes in an actual lightguide burner following the “triple-flame” VAD design. DLS, also termed Photon Correlation Spectroscopy (PCS) or Diffusion Broadening Spectroscopy (DBS), was previously identified as a viable diagnostic tool for in-situ particle measurements in silica-sooting flames by W. L. Flower [1] and through an earlier collaboration between AT&T and the Sandia Combustion Research Facility. In applying DLS, however, our experience with the VAD torch reveals that a specialized experimental method will undoubtedly be required to deal with the inevitable presence of low frequency system instabilities in industrial systems.

The formation and growth of soot particles in combustion systems represents an area of significant research interest. Critical to progress in this area has been the development of suitable optical diagnostic techniques. Principal among these has been the utilization of laser light scattering techniques to obtain particle size and concentration information. When combined with measurements of other quantities such as the velocity, the resulting spatially and temporally resolved measurements can be used to examine particle processes such as coagulation and surface growth. In the present work, the results from studies conducted in laminar diffusion flames involving laser based measurements of the soot particle and velocity fields are reviewed. As an example of the utility of such an approach, these results are used to examine the evolution of the particle surface area for a series of simple hydrocarbon fuels. The results indicate that the available surface area varies strongly with the fuel molecular structure. However, the specific surface growth rate is observed to be similar for all the fuels studied.