Ion Current Density Distribution Research Articles

Ion Current Density and Ion Energy Distributions at the Electron Cyclotron Resonance Position in the Electron Cyclotron Resonance Plasma

Extremely highly selective phosphorus-doped polycrystalline silicon etching is achieved at the electron cyclotron resonance (ECR) position in a newly developed ECR plasma etching system. To characterize these etching results, the ion current density and the ion energy distribution in a ECR plasma are measured. Microwave power is absorbed completely at the ECR position. Therefore, the ECR position has maximum ion current density in an ECR plasma. Moreover, the mean ion energy and the width of ion energy distribution has minimum values at the ECR position. The ECR position in the ECR plasma can satisfy a high ion current density and a low ion energy at the same time. These characteristics correspond to the etching results.

Damage Caused by Stored Charge during ECR Plasma Etching

The influence of stored charge caused by changing the plasma parameter can be accurately shown by measuring the leakage current in CMOS-inverter integrated circuits. The leakage current increase is due to nonuniform ion current density distribution and self-bias voltage at the point of ECR plasma discharge turn-off. Positive charge ions are stored by the ion current density difference on a wafer. Moreover, a large voltage across the gate oxide is generated by the self-bias voltage at the point of ECR plasma discharge turn-off, and finally degrades the gate oxide.

Dual ion beam deposition of oxide, nitride, and carbide films

Compound films such as oxides, nitrides, and carbides have been prepared in a dual ion beam (DIB) deposition system, which contains an ionized cluster beam (ICB) source and an ionized gas beam (IGB) source. The characteristic of the DIB system and the properties of compound films such as SiOx, TiNx, and C were investigated. The ion current density distribution was measured at acceleration voltages from 0 to 10 kV by an array of Faraday cups at the substrate position. Uniform ion current distributions over 5-in. diam substrates have been obtained for ICB of Au, Cu, and Si and IGB of CH4, N2, and O2. The composition of SiOx films prepared by DIB approaches stoichiometric SiO2 with increasing oxygen ion current density. The crystalline structure of TiNx films changes gradually from TiN to Ti2N as the atomic flux ratio of (N/Ti) decreases. The Knoop hardness values of TiN and C films prepared at 200 °C are over 1700 and 3000 kg/mm2, respectively. Therefore the advantages of using the DIB deposition system for low-temperature compound film growth include control over film composition and crystalline structure with excellent physical properties. Ion irradiation during film growth by both metal and gas beams enhances chemical reaction kinetics on the substrate.

Optimized eight-inch extraction system for reactive ion beam etching

A methodology of ion extraction system optimization is proposed, taking into account the influence of the ion density variation in plasma at the plasma sheath. Software tools for extraction grids design and machining have been developed, allowing compensation for the current, divergence, and deflection of a single beamlets. Simulation was used to predict the properties of the three-grid single beamlet. The measurement of the radial ion saturation current density distribution in plasma using a double Langmuir probe for an axial magnetic field up to 16 mT, vacuum chamber pressure ranging from 4×10−5 to 2×10−3 and rf power from 100 to 900 W has been performed. These distributions were used to calculate the grid compensation functions. An extraction system was optimized for the reference magnetic field in the air coil B=7.20 mT, vacuum chamber pressure p=2.0×10−4 mbar, rf power Prf=500 W, and net acceleration voltage Vnet=300 V with argon as a working gas. The ion current density distributions for optimized and nonoptimized extraction systems have been measured and compared with predictions of the model. A maximum detectable variation in the ion current density across the 8 in. target can be reduced to < 3%.

Quantification of sputter depth profiles by means of wedge crater sputtering—a new technique for depth scale calibration

AbstractAn essential part of depth profile quantification is the conversion of sputtering time into depth, for which a simple method is described. It requires an ion gun providing a sufficient fine focusable ion beam. A suitable beam control produces a wedgelike distribution of ion current density in a raster field which is large compared to the ion beam cross‐section. A “wedge crater” is sputtered in this way in addition to the “normal crater” for depth profiling. The wedge crater profile obtained of surface profilometer measurements provides the sputtering time–depth relation. Moreover the sputtering rate as a function of depth may be deduced from wedge crater profile. Application of the method to SIMS depth profiling in multilayer thin film systems shows its usefulness in depth scale calibration and intensity correction. Small expenditure and universal applicability are advantages in comparison with other methods.

Radial current distribution at a planar magnetron cathode

Experiments and theory are used to investigate the radial distribution of current at the cathode of a cylindrically symmetric, planar magnetron discharge. We have developed a simple model of the distribution of incident ions at the cathode, in the form of an integral equation. Energetic electrons, produced by secondary electron emission when ions strike the cathode, are accelerated into the discharge through a thin sheath. The Hamiltonian motion of the energetic electrons in the magnetic field determines the birthplace of discharge ions, and thus, the distribution of ion current density at the cathode. The radial current distribution has been measured for various magnetic fields using a radially staggered array of sixteen 1-mm-diam current probes imbedded in a 9-in.-diam cathode. In agreement with the model, the current distribution is peaked at the radius at which the magnetic field is tangent to the cathode plate, and the width of the distribution scales as the square root of the energetic electron Larmor radius.

Broad ion beam modeling for extraction optics optimization and etching process simulation

A model for calculating the ion–current density distribution of a broad-beam ion source at the target level is proposed. Three model parameters related to a single beamlet such as the beam divergence, the maximum ion–current density in the beamlet center, and a possible misalignment between the different grids are needed to describe the overall extraction performance. These parameters were determined partially with the axcel simulation code or experimentally via etch tests. In this work the model parameters have been determined for a capacitively coupled filamentless 13.56 MHz rf source operated with argon at low power levels ranging from 20–100 W and low acceleration voltages (100–1000 V). However, the model proposed is applicable also for other types of ion sources, for different extraction grid sets with varying geometry and a wide range of working conditions. Intensity profiles predicted by the above model show good agreement with experimental results.

磁気中性点による散乱効果を用いたイオン源の基本特性

Two types of ion sources with a single magnetron injection gun-type-thermionic cathode were fabricated and tested. The cathode was positioned on the extended line of the cylindrical axis. These sources have magnetic multipole linecusps with different directions. One of them had azimuthally oriented magnetic field, and the other had axially oriented one. The measurement of ion current density and ion energy distribution revealed that the beam profile became a hollow-beam whose intensity increases in proportion to discharge current, and that the ion source with azially oriented magnetic field produces ion beams 450 times higher than those with azimuthally oriented magnetic field. Single extraction grid-ion source is also compared in extracted beam profile with the two grid-ion source.

Ion milling source with slot extraction system

An ion source with a slot extracting system for micromachining and surface treatment applications has been designed and built. It has an ion extracting system which does not change its geometry when heated. The slot extracting electrodes have been made of Mo rods mounted in a way that allows for thermal elongation without distortion. The source was tested using an array of 49 Faraday cages. Measurements of the ion current density distribution have been made for helix- and meander-shaped cathode filaments. The source has been designed for the energy range 500–1000 V and for an ion current density of 2 mA/cm2. The ion beam divergence in the direction perpendicular to the slots is 5° and in the direction parallel to the slots is about 7°.

Computational simulation of mass spectral peak shape

On the base of a statistical modelling method the computational algorithm of an ion current density distribution, a shape of a mass spectral peak obtained due to an ion beam movement relative to a receiver slit, a mass spectrometer transmission and resolution is described. The state of an ion beam at a source output slit is defined by the volume in a beam parameter six-dimensional space. Ion trajectories in electric and magnetic sector fields are computed analytically considering fringing effects. Resolution is determined by an equal intensity peak converging method.

Influence of Wind and Conductor Potential on Distributions of Electric Field and Ion Current Density at Ground Level in DC High Voltage Line to Plane Geometry

Influence of Wind and Conductor Potential on Distributions of Electric Field and Ion Current Density at Ground Level in DC High Voltage Line to Plane Geometry

Influence of Wind and Conductor Potential on Distributions of Electric Field and Ion Current Density at Ground Level in DC High Voltage Line to Plane Geometry

Lateral profiles of electric field and ion current density at ground level were measured precisely in a unipolar/bipolar line to plane geometry under different wind conditions and different dc voltages. Furthermore, the relationship between the field and current density is discussed. In the case of unipolar line in still air, the normalized profiles are approximately independent of the magnitude of the applied voltage and the linear dimensions of the gap, but they are strongly influenced in the bipolar case. The wind effect on the current profile is greatest at voltages close to corona onset for each experimental arrangemeht. The experimental results suggest that the usual wind extends the region of the ionic current flowing . e. the right-of- ay required for HVDC transmis-sion lines) by a factor of two or more as compared with that with no wind.

General plasma characteristics of a Berkeley multifilament ion source

The general plasma characteristics of a Berkeley Multifilament Ion Source are presented. The measurements are obtained via a pulsed electrostatic-probe data-acquisition system, and in part conclude: (a) The electron distribution function consists of a bulk component of thermal electrons (kTe∼3–5 eV) comprising 90–97% of the total electron population (depending on operating conditions), plus a nonthermal high-energy tail, which is a monotonically decreasing function of energy, and contains a small but experimentally significant electron population at energy values 10–15 eV above maximum cathode fall. (b) Overall source performance, i.e., the spatial distribution of plasma potential, plasma density, and ion current density, approximately follows steady-state low-pressure discharge theory assuming spatially uniform ion production.

Gas discharge ion source. I. Duoplasmatron

The effects of the plasma expansion cup on the operation of a duoplasmatron ion source have been investigated by measuring the total ion current and the distributions of the ion energy, mass, and current density. A copper expansion cup did not affect the magnetic field near the anode of the ion source and consequently the ion current density distribution was sharply peaked near the center of the cup. Ion energy distributions were approximately symmetrical about anode potential. The dominant ionic species were D(+) (3) and D(+) at low and high arc currents, respectively. Changes in the electrical potential of the copper cup with respect to the anode produced negligible changes in the above data. A mild steel plasma expansion cup caused the magnetic field to diverge and intercept the cup walls, resulting in ion current density distributions that were flatter and more amenable to focusing than the ones with the copper cup. With the steel cup at anode potential, the ion mass distribution was similar to that from the copper cup; however, the ion energy distribution was asymmetrical about the anode potential with a peak about 10-20 V above anode potential. The total ion current from this mode of operation was about one-third the value from the copper cup. If the steel cup assumed floating potential, about 50 V below anode potential, the total current increased to the level observed from the copper cup and the ion energy distribution was similar to that observed with the copper cup but the current density distribution was much flatter than that of the copper cup. The ion mass distribution was 60%-70% atomic ions over the entire arc current range investigated. Based on these data, a modified plasma expansion cup was designed with tapered steel walls lined with a boron nitride insert. The overall performance of the duoplasmatron ion source with this cup was superior to any of the previous three modes of operation. The improved design uses a molybdenum anode insert which is far superior to copper in regard to erosion over extended operating times. A total beam current of 200 mA was produced at an arc current of 24 A.

Gas discharge ion source. II. Duopigatron

Ion source performance characteristics consisting of total ion current, ion energy distribution, mass distribution, and ion current density distribution have been measured for several models of a duopigatron. Variations on the duopigatron design involved plasma expansion cup material and dimensions, secondary cathode material, and interelectrode spacings. Of the designs tested, the one with a copper and molybdenum secondary cathode, and a mild steel plasma expansion cup proved to give the best results. The ion current density distribution was peaked at the center of the plasma expansion cup and fell off to 80% of the peak value at the cup wall for a cup 15.2 mm deep. A total ion current of 180 mA consisting of 60%-70% atomic ions was produced with an arc current of 20 A and source pressure of 9.3 Pa. More shallow cups produced a larger beam current and a more sharply peaked ion current density distribution. Typical ion energy distributions were bellshaped curves with a peak 10-20 V below anode potential and with ion energies extending 30-40 V on either side of the peak.

Factors affecting beam shape and quality

The beam shape and quality are affected by hash, ripple, ion intensity distribution and geometrical and operational factors. Hash, which was found to be localized mainly at the sides of the beam (parasitic divergence β), must be stopped by an appropriate diaphram to improve the image quality. The magnitude of β is strongly dependent on the relative hash. Of all the source parameters, the magnetic field is the dominant factor in determining hash. Ripple in the cathode or arc power supplies of the source leads to a modulation of the beam divergence and consequently to an apparent increase of β. The main result is an equivalent loss of transmission when β is eliminated. Installing effective filters in the cathode and arc supplies of the MEIRA separator reduced the ripple by a factor of 10. Other factors found to increase the value of β for long emission slits were faulty alignment of the electrode with the emission slit and non-uniform current density along this slit. Factors affecting ion current density distribution along the slit are described. Preliminary results are given concerning the variation of features of the divergence curve with operational parameters.

Current density distribution on the cathode surface of a hollow cathode discharge in a longitudinal magnetic field†

ABSTRACT The radial distribution of the positive ion current density J+, on the cathode surface of a hollow cathode discharge in a longitudinal magnetic field, has been measured in air and hydrogen. The characteristic distribution for J+ which shows a maximum away from the axis has been attributed to the effect of the non-uniform electric and uniform magnetic field.

1614. Ion current density distribution along the cathode in a Penning discharge: E M Rudnitskiy, Zh Tekh Fiz, 37 (5), May 1967, 927–931 ( in Russian).

1614. Ion current density distribution along the cathode in a Penning discharge: E M Rudnitskiy, Zh Tekh Fiz, 37 (5), May 1967, 927–931 ( in Russian).

Wall charges and radial distribution of positive ion current on the cathode of a glow discharge

The radial electrostatic field due to wall charges in the dark space region has been shown to determine the radial distribution of the positive ion current density on the cathode surface of an abnormal and an obstructed glow discharge, for large values of the interelectrode distance. Theoretical and experimental estimates have been obtained for the wall potentials developed.