Robert E. Ellefson

Bio: Robert E. Ellefson is an academic researcher from Syracuse University. The author has contributed to research in topics: Ion & Mass spectrometry. The author has an hindex of 9, co-authored 15 publications receiving 319 citations.

Recommended practice for the calibration of mass spectrometers for partial pressure analysis

Abstract: This Recommended Practice addresses issues involved in the use of partial pressure analyzers (PPAs) for quantitative analysis and describes recommended apparatus and procedures for determining resolution and sensitivity of a PPA so that the instrument can be used quantitatively for partial pressure, partial flow and gas composition analysis. This updates previous material in the AVS Standard 2.3-1972 (tentative) by including reference to current pressure transfer standards and computer controlled PPAs. This document presents an introduction to PPAs and how they work, definitions pertinent to the use of PPAs, equipment needed for calibration, instrument setup prior to calibration and the measurement of sensitivity and linearity by various methods. Four methods of calibration of a PPA are described as follows: (1) the direct comparison of the PPA output with a transfer standard pressure gauge, (2) the indirect comparison of PPA readings with readings of a transfer standard pressure gauge separated by a flow...

Miniature quadrupole residual gas analyzer for process monitoring at milliTorr pressures

Abstract: Monitoring of gas composition for processes in the mTorr range is not possible with a conventional residual gas analyzer (RGA) unless a pressure reduction pumping system is used. A miniature sensor, having dimensions compatible with the mean-free path of gas molecules can operate directly at mTorr pressures while being less expensive and more compact than a conventional apparatus. This article describes a quadrupole RGA which is scaled down by a factor of 7 to operate at pressures up to 10 mTorr. This sensor requires different construction methods and drive electronics than a traditional RGA. A unique ion source with high output has been developed. The small sensor has resolution characteristics very similar to standard size models but sensitivity is reduced in proportion to the ratio of cross-sectional area for each quadrupole r0. Response is linear to the mTorr range and a correction method for gas scattering, based on pressure measured by a total pressure gauge included in the ion source design, extend...

Recommended Practice for the Calibration of Mass Spectrometers

Abstract: This Recommended Practice addresses issues involved in the use of partial pressure analyzers (PPAs) for quantitative analysis and describes recommended apparatus and procedures for determining resolution and sensitivity of a PPA so that the instrument can be used quantitatively for partial pressure, partial flow and gas composition analysis. This updates previous material in the AVS Standard 2.3-1972 (tentative) by including reference to current pressure transfer standards and computer controlled PPAs. This document presents an introduction to PPAs and how they work, definitions pertinent to the use of PPAs, equipment needed for calibration, instrument setup prior to calibration and the measurement of sensitivity and linearity by various methods. Four methods of calibration of a PPA are described as follows: (1) the direct comparison of the PPA output with a transfer standard pressure gauge, (2) the indirect comparison of PPA readings with readings of a transfer standard pressure gauge separated by a flow restriction (pressure divider method), (3) comparison of the PPA output response to known gas flow rates. The first three methods may be carried out on a test stand of suitable design or in situ. The fourth method requires that the pumping speed during calibration be the same as the pumping speed during use, and normally implies that the PPA is calibrated in situ. Discussion on gas interactions, sources of nonlinearity, stability of sensitivity and quality assurance methods is given.

Mass spectrometric measurements on inductively coupled fluorocarbon plasmas: Positive ions, radicals and endpoint detection

Abstract: Positive ions and radicals in C2F6 and CHF3 high density discharges were measured using a direct-line-of-sight mass spectrometer The ion energy distributions of the dominant ions were measured as a function of process conditions Appearance potential mass spectrometry was performed to measure trends of the radical densities For C2F6 plasmas CF3 and CF3+are the most abundant neutral and ionic species, respectively CF3 is the most abundant neutral species for a CHF3 plasma, whereas CHF2+ and CF+ are the most abundant ionic species at 600–1000 and 1400 W, respectively Erosion of the quartz coupling window is an important contaminant source for our inductively coupled plasma system For comparison, downstream mass spectrometry was also applied using a closed ion source system since this approach is of interest for real-time monitoring and control Endpoint detection for Si and SiO2 film etching in a CHF3 plasma was investigated using the downstream mass spectrometer system and compared with data obtained

Surface etching mechanism of silicon nitride in fluorine and nitric oxide containing plasmas

Abstract: The etch rate of silicon nitride (Si3N4) in the afterglow of fluorine-containing plasmas is strongly enhanced when both nitrogen and oxygen are added to the remote discharge. This effect is attributed to the formation of nitric oxide (NO), which we identify as a highly reactive precursor for the etching of Si3N4. The Si3N4 etch rate, surface oxidation, and the depletion of the surface of N atoms show a linear dependence on the NO density. In order to determine the products of the NO reaction at the Si3N4 surface, mass spectrometry was performed in immediate proximity to the surface with a specially designed movable sampling orifice. Both SiF4 and N2 are identified as primary etch products, but a smaller amount of N2O was also detected. Based on our results, we suggest that NO enhances the removal of N from the Si3N4 surface by the formation of gaseous N2, and leaving behind an O atom, while the overall surface oxidation remains very low, and the reactive layers are very thin. This modified surface reacts ...

Miniature mass spectrometers

Abstract: We discuss miniaturization in mass spectrometry in terms of the mass analyzer, the mass spectrometer, and the total analytical system. Mass analyzer miniaturization has focused on ion traps. Decreases in mass analyzer size facilitate reduction of the sizes of the other components of a miniature mass spectrometer, especially the radio frequency electronics and vacuum system. Appropriate sample introduction systems are needed for performance optimization. The criteria by which a miniature mass spectrometer is judged include adequate performance in the traditional areas of resolution, detection limits, and specificity; ruggedness; reliability; and fully autonomous operation. Our discussion of the total analytical system emphasizes the removal of the bottleneck of sample preparation and suggests a solution to the combination of sampling, preconcentration, and ionization: ambient ionization methods. We also describe current miniature mass spectrometers.

Miniature mass analyzers

Abstract: Increased efforts are being made to develop miniature mass spectrometers, including those which are hand-portable, and to retain the performance characteristics of traditional laboratory instruments as much as possible in the miniature instruments. This review of miniature mass analyzers emphasizes analytical performance and compares the relative merits of each type of miniature mass analyzer. Miniature instruments discussed include sector, Wien filter, time-of-flight, linear quadrupole, quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometers, as well as combinations of and variations on these major types. Special considerations that apply to small mass analyzers are noted and suggestions are made regarding the possible future development of this field. Copyright 2000 John Wiley & Sons, Ltd.

A Review of SiO2 Etching Studies in Inductively Coupled Fluorocarbon Plasmas

Abstract: A comprehensive overview of results from mechanistic studies on plasma-surface interactions in inductively coupled fluorocarbon plasmas, which are currently widely used for the SiO 2 etching process in semiconductor device manufacturing industry, is presented. The plasma-surface interactions that are covered in this overview range from interactions at the plasma reactor wall and coupling window, which affect the plasma gas phase, to interactions at the substrate level which determine the etching of both blanket surfaces and microscopic features, In particular, the effects of reactor wall temperature and parasitic capacitive coupling on the SiO 2 etching process are addressed. Further, the mechanism of selective SiO 2 to Si and Si 3 N 4 etching on blanket and inclined surfaces is discussed, Finally, it is shown how the SiO 2 etch process in high aspect ratio microstructures differs from the etch process on blanket surfaces.

A parallel miniature cylindrical ion trap array

Abstract: A small mass spectrometer array is described in which each element is a cylindrical ion trap (CIT). The array contains four CITs, each having an inner radius of 2.5 mm, arranged in parallel and operated using a single electronics system under common conditions for trapping and mass analysis. By using an array of identically sized traps, higher ion capacity can be achieved than with a single miniature CIT, but the advantage of lower power and voltage requirements associated with the smaller ion trap is maintained. Overall signal intensity of the array of four traps is compared with that of a two-element CIT array to demonstrate the increased ion capacity of larger arrays. Resolution for m-dichlorobenzene is shown to be ∼180 (full width at half-maximum), with no significant loss in resolution as a result of using multiple CITs. The detection of 5 × 10-9 Torr partial pressure of krypton in argon with a signal-to-noise ratio of ∼30 for the most abundant isotope is shown, demonstrating the applicability of the...