Beam Current Increases Research Articles

New development in ion implantation and RTP equipment for high productivity

The productivity of semiconductor processing equipment can be expressed as the product of three factors: yield, throughput and availability. In this article new systems and equipment features for high productivity, developed at Varian for ion implantation and rapid thermal processing, will be reviewed. Yield-related features will be highlighted by real-time monitoring and control capabilities for critical process issues, such as uniformity, wafer charging, wafer temperature control, particulates, etc. Throughput enhancement features, such as those provided by increased beam current, new wafer cooling technology, high-speed wafer handling with integral wafer orientation and centering functions, and automation, will be presented. Availability improvements will focus on such system design aspects as control systems (including diagnostics, predictive maintenance and user-friendly setup capability), intelligent wafer-handling technology, vacuum system design and serviceability features. In the selection of examples particular emphasis will be placed on features of our new high-current ion implanter.

Enhanced ionization freeman ion source

We developed modifications to a standard Freeman ion source which increased the plasma electron temperature and density by minimum factors of 1.5 and 1.1, respectively. The improvement in these fundamental plasma parameters resulted in a greater than 40% increase in B + currents from boron trifluoride gas and substantial usable beam current increases in B 2+, P 2+, and As 2+. A large increase in triple charge currents was also present in the extracted beam. Ion source lifetime tests were performed at 1 mA scanned B + wafer current with a 125 mm aperture on an Eaton NV-6200 Ion Implanter. Filament lifetime was observed to be in excess of 50 h. Further, erosion was more uniformly distributed along the filament length and tests indicate that the extracted ion beam uniformity was increased along the extraction slit. Therefore, we conclude that our modifications to the standard Freeman ion source also increased discharge uniformity.

Particle simulation of a high-power gyrotron oscillator

A self consistent and time-dependent particle code has been developed to simulate the beam-wave dynamics in a gyrotron oscillator. The code is first applied to investigate the effect of the self-consistent field profile on the scaling of the cavity-filling rate with beam current. The fixed-field theory predicts that the transient-wave growth rate depends linearly on the beam current. The simulation results agree with the theoretical prediction at low beam currents. As the beam current increases, the modified field profile changes the nature of the gain scaling from linear to nonlinear. At higher beam currents, the excited wave is observed to exhibit the behavior of the modulated oscillation, due to unequal couplings to the forward- and backward-going waves by the beam. Associated with such amplitude modulation is a periodic variation of the self-consistent field profile. At still higher beam currents, the system becomes chaotic, showing the effect of periodic doubling. Simulation results are presented for the efficiency, the self-consistent field profile, and the scaling of the transient growth rate with the beam current. >

Microstructure of polycrystalline silicon implanted with As ions at high and low temperatures

Ion implantation is an important process for doping polycrystalline silicon layers during IC device fabrication. The use of higher beam currents is desirable from the process point of view to achieve shorter implant times. An important consideration of using Increased beam current, with its resultant higher implant temperature, is the effects on the layer's electrical properties and microstructures. In order to better understand this phenomenon two sets of samples implanted at room temperature and 400°C were investigated by transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) and spreading resistance analysis (SEA). Both sets were implanted at 190 KeV with an As ion dose of 2 x 1016/cm2 into a 220 nm thick polycrystalline silicon layer overlying an oxide layer on a Si wafer substrate. These sample were then annealed at 975°C for 1 hr in a nitrogen atmosphere.

Beam extraction experiments from microwave ion sources

With the aim of designing a new ion source for ampere-class beams, the beam extraction characteristics of standard coaxial-type microwave ion sources were investigated in detail at energies lower than 10 keV. It was found that this source has the capability of providing Ar+ beams of 200 mA at the acceleration voltage of 7.0 kV and the microwave power of 850 W. The obtainable beam current increases with a decrease of gap width between positive and negative electrodes. Moreover, it is shown that the microwave ion source is suitable for obtaining high-current beams of single-charged ions. Both the plasma source and extraction electrode diameters for 1-A beam are estimated to be about 13 cm. The required microwave power is about 6 kW.

The shower-beam concept

A concept is proposed for Electron-Beam Pattern Generators for increasing the theoretical writing speed at least one order of magnitude. The basic writing strategy is variable shaped single beam. A two dimensional array of high brightness electron sources is used. The individual emitters can be adressed seperately, the brightness can be modulated very quickly. The source is imaged at the mid-plane of the objective lens. The increase of total beam current which is necessary for the high writing speed is realized by (1) modulating the source brightness to keep the beam current constant while the shape surface varies, (2) optimizing the beamlet diameters and distances in the objective lens for minimal trajectory displacement effect and (3) correction of spherical aberration of the final lens either by the individual beamlet energy or using a gauze or foil correction element in the objective lens.

Injection and Capture of Electrons in the UCI Stellatron

An l=2 stellatron accelerator is under experimental study. The stellarator field has a strength of up to 10 kG and a rotational transform angle ? ~ 0.1. Electrons are injected from either a thermionic emitter or a field-emission cathode placed inside the torus. Typically, a 20 kV, 2-4 ?s pulse is applied to the hot cathode which emits ~ 3 A. A 2 MeV, 200 A beam is formed due to betatron acceleration which immediately follows the injection. The injection voltage is raised to 60 kV with the cold cathode emitting ~ 30 A for ~ 0.4 ?s. A significant increase in beam current is not observed. A beam in excess of 500 A is generated by injecting plasma and electrons simultaneously at the beginning of the stellarator field and starting the betatron acceleration after the plasma has diffused throughout the torus.

Increased Intensity Performance of the Brookhaven AGS

With the advent of H- injection into the Brookhaven AGS, circulating beams of up to 3 × 1013 protons at 200 MeV have been obtained. Rf capture of 2.2 × 1013 and acceleration of 1.73 × 1013 up to the transition energy (? 8 GeV) and 1.64 × 1013 to full energy (? 29 GeV) has been achieved. This represents a 50% increase over the best performance obtained with H+ injection. The increase in circulation beam current is obtained without filling the horizontal aperture. This allows the rf capture process to utilize a larger longitudinal phase space area (? 1 eV sec/bunch vs ? 0.6 eV sec with H+ operation). The resulting reduction in relative longitudinal density partially offsets the increase in space charge effects at higher currents. In order to make the capture process independent of injected beam current, a dynamic beam loading compensation loop was installed on the AGS rf system. This is the only addition to the synchrotron itself that was required to reach the new intensity records. A discussion of injection, the rf capture process, and space charge effects is presented.

The Superhilac Upgrade Project

This project will increase the uranium output of the Bevalac heavy-ion facility from the currently available 107 to 5×107 ions/pulse, allowing accurate Lamb shift measurements to be made in U90+ and U91+ with important applications to the testing of quantum electrodynamics and the development of an x-ray laser. The injected beam intensity will be increased to make better use of the 10emA output space-charge limit of the Wideroe linac. Components will include a new high current MEtal Vapor Vacuum Arc (MEVVA) ion source1 along with an improved high current, high voltage Cockcroft-Walton power supply to handle the increased beam current. The Low Energy Beam Transport (LEBT) line will be upgraded with additional focusing to manage the increased space-charge forces and with an improved vacuum to reduce charge exchange losses. Finally, the phase matching between the 23MHz Wideroe linac and the 70MHz Alvarez linac will be improved by the addition of the appropriate buncher cavities. Physics design is underway and detailed engineering is scheduled to begin in October 1985, with installation slated for the 1986 summer shutdown.

Beam Intensity Increases at the Intense Pulsed Neutron Source Accelerator

The Intense Pulsed Neutron Source (IPNS) accelerator system has managed a 40% increase in time average beam current over the last two years. Currents of up to 15.6 ?A (3.25 × 1012 protons at 30 Hz) have been successfully accelerated and cleanly extracted. Our high current operation demands low loss beam handling to permit hands-on maintenance. Synchrotron beam handling efficiencies of 90% are routine. A new H- ion source which was installed in March of 1983 offered the opportunity to get above 8 ?A but an instability caused unacceptable losses when attempting to operate at 10 ?A and above. Simple techniques to control the instabilities were introduced and have worked well. These techniques are discussed below. Other improvements in the regulation of various power supplies have provided greatly improved low energy orbit stability and contributed substantially to the increased beam current. These improvements are discussed in a paper1 presented at this conference.

Studies of emission-line profiles from ion-excited neon gas targets

The widths of some atomic emission lines from ion-beam-excited Ne-gas targets have been studied. The line width is a linear function of the pressure within the pressure region studied (20–500 kPa). The line broadening depends on the spectral line studied. A reduction in the line width was observed with increasing beam current. This was interpreted as being due to a density reduction caused by the beam. The results were applied to calculate the temperature of the gas at the point of light emission.

Nonsteady processes in cyclotron-resonance maser with opposing waves

The delay effects in a CRM, just as in any other microwave electron device with distributed interaction of electrons and a high-frequency field, with in CRM with opposing waves cause steady-state oscillation to become replaced (as the beam current increases) by self-modulation of radiation, and the latter, upon further increase of the beam current, to be in turn replaced by stochastic oscillations. These conclusions demonstrate the need for further study of nonsteady processes in a CRM with developed interaction space.

High Voltage Electron Beam Writing for Submicron Design Rule VLSI Fabrications

The advantages of high voltage electron beam lithography in submicron VLSI fabrications have been established. By electron beam lithography with 50 kV acceleration voltage, vertically walled PMMA pattern is obtained at a relatively low dose, 50 µC/cm2. This fact, combined with the increase in beam current, brings about the improvement of throughput in 50 kV writing by a factor of 5 over 20 kV writing. Proximity effect is markedly reduced in 50 kV writing. The pattern size variation due to the proximity effect is within 0.05 µm for line patterns ranging from 10 µm to 0.25 µm. Vertically walled PMMA pattern of 0.25 µm space, which is equal in size to the beam spot, is obtained at 50 µC/cm2 in 50 kV writing. In addition, it is shown that radiation damage of MOSFET's due to the 50 keV beam is essentially the same as that due to 20 keV beam.

Considerations on space charge effect for high current variable shaped beam forming

Variable shaped beam schemes are very promising for advanced VLSI pattern generation. In such a device, beam blurring caused by the space charge effect becomes greater as the beam current increases and the focal length of the electron lens is varied as the beam current changes. In order to keep the beam blurring within a permissible amount, refocusings are required whenever beam sectional areas are changed dramatically. However, it is often difficult to complete refocusing in negligible short time in comparison with the shot time of an element pattern and total exposure time is influenced considerably. Investigating the results of computer simulations and fundamental experiments, it is found that beam blurring caused by defocusing is almost proportional to the deviation of the beam current from that at the optimum focusing point and is kept under the permissible value in certain intervals of beam current. Considering this characteristic, the defocusing problem can be improved significantly by rearranging the exposure sequence of pattern elements so that the frequency of dramatic shape change becomes minimum.

Triple slit scheme for high current variable-shaped beam forming

Variable-shaped beam schemes are very promising for advanced VLSI pattern generation. Some of them are made up of two beam shaping apertures, beam shaping deflectors, and projection lenses. In such devices, exposure speed is proportional to the total beam current finally projected onto the target. When the beam current is increased in this scheme, beam blurring caused by space charge effect becomes greater as the beam current increases. The observed beam blurring becomes much greater on the edges corresponding to the sides of the first beam shaping aperture than on those of the second one. A new beam shaping scheme is proposed for reducing this blurring. In this scheme, auxiliary beam shaping means are provided in the upper stream of the previously developed beam shaping system. The beam is preshaped by the new scheme so as to reduce the beam current between the first and the second beam shaping apertures by an amount which is the sum of the finally required and marginal portions, and a clearer beam shape can be formed on the target. Furthermore, to shorten the path length of electrons for reducing the above blurring, a construction method for an octupole electrostatic deflector is developed. In this method, newly designed isolating and supporting mechanisms for electrodes are adopted so as to minimize the size of the deflectors, which are sufficiently minute to be placed in the electron lens and to shorten the path length of electorn beam.

Increasing the ion beam current from a multidipole source

The ion beam current from a multidipole source can be increased by the injection of low-energy primary electrons. By optimizing the injection energy, an increase in beam current of approximately 35% has been achieved.

Kinescope Spot Size as it Relates to Picture Quality

The degradation of kinescope spot size (spot blooming) with increasing beam current is a well known phenomenon that has significant bearing on kinescope resolution. For purposes of improving kinescope design evaluation and production lot monitoring, it is desirable to quantify the effects of beam current on picture quality. The basis for this paper is the assumption that kinescope performance can be defined in terms of its spatial frequency response. Computer oriented techniques which are employed to analyze a light output profile of the spot and calculate the associated spatial frequency response of the kinescope are discussed. In addition, the non-linear effects of the human eye are considered. Advantages and disadvantages of both techniques are examined and some typical measurements are shown.

Energy Distribution of Positive Ions Extracted from a Hot Cathode Gas Discharge Ion Source

An electrostatic parallel plate energy analyzer was used for measuring the energy distribution of Ar+ ions in a beam extracted from a nonmagnetic, hot cathode, gas discharge ion source under various conditions of source pressure, anode voltage, and anode current. A large number of energy distribution curves were obtained as X-Y recordings. The curve shape depends upon source conditions, though not strongly when the pressure is greater than 3×10−3 Torr with an anode voltage above 50 V (for argon) and an anode current of at least 200 mA. When conditions are optimum, the ion energy distribution curve is a narrow peak with a tail that gradually diminishes towards lower energies over an interval of approximately 30 eV. The actual value of the optimum full width at half maximum was found to be 1.1 eV by extrapolation to zero beam energy. The shape of the curve is such that more than 81% of the beam ions have energies within a 10 eV interval. The source can be used to increase beam currents greatly in certain types of magnetic deflection mass spectrometers without extreme loss of mass resolution due to ion beam energy spread.

Two new tubes for high-speed analogue multiplication

Two new tubes for high-speed analogue multiplication at frequencies up to 200kc/s are described. The electrostatic field configurations required for multiplication are generated by special electrode systems which use plane electrodes, and are therefore relatively simple to construct and to mount with accuracy. The nonlinear error in prototype versions of these tubes is less than 2% of maximum output for one tube, and less than 3% for the other. The phase lag in the output with respect to either input is less than 2° for frequencies up to 200kc/s, and, with increased beam currents, the tubes are capable of operating at higher frequencies without an increase in the phase lag.It is anticipated that, with greater constructional care, an error of less than 1% of maximum output can be achieved.

Eine möglichkeit zur stromerhöhung beim elektronen-synchrotron

The desirability of a constant acceleration vector in the electric field of an electron synchrotron at high currents is discussed. Parameters available for influencing particle dynamics, and perhaps applications to oscillation damping at the beginning of acceleration and to increasing beam current, are described. (M.C.G.)