Plasma window performance and scaling for an accelerator-based neutron source.

A "plasma window" was developed for use with a SHINE accelerator-based neutron source. In this work, the design of the plasma window is presented along with results demonstrating successful operation in deuterium over a range of aperture diameters (5-12 mm), gas flow rates (3.5 to 12.5 slm), and input powers (10-55 kW). An empirically determined relationship between the aperture diameter, deuterium gas flow rate, input power, and plasma window pressure differential is also presented.

Molecular ion sources for low energy semiconductor ion implantation (invited).

Smaller semiconductors require shallow, low energy ion implantation, resulting space charge effects, which reduced beam currents and production rates. To increase production rates, molecular ions are used. Boron and phosphorous (or arsenic) implantation is needed for P-type and N-type semiconductors, respectively. Carborane, which is the most stable molecular boron ion leaves unacceptable carbon residue on extraction grids. A self-cleaning carborane acid compound (C4H12B10O4) was synthesized and utilized in the ITEP Bernas ion source resulting in large carborane ion output, without carbon residue. Pure gaseous processes are desired to enable rapid switch among ion species. Molecular phosphorous was generated by introducing phosphine in dissociators via 4PH3 = P4 + 6H2; generated molecular phosphorous in a pure gaseous process was then injected into the HCEI Calutron-Bernas ion source, from which P4(+) ion beams were extracted. Results from devices and some additional concepts are described.

Development of the ion source for cluster implantation.

Bernas ion source development to meet needs of 100s of electron-volt ion implanters for shallow junction production is in progress in Institute for Theoretical and Experimental Physics. The ion sources provides high intensity ion beam of boron clusters under self-cleaning operation mode. The last progress with ion source operation is presented. The mechanism of self-cleaning procedure is described.

Gas feeding molecular phosphorous ion source for semiconductor implanters.

Phosphorus is a much used dopant in semiconductor technology. Its vapors represent a rather stable tetratomic molecular compound and are produced from one of the most thermodynamically stable allotropic forms of phosphorus-red phosphorus. At vacuum heating temperatures ranging from 325 °C, red phosphorus evaporates solely as P4 molecules (P4/P2 ∼ 2 × 10(5), P4/P ∼ 10(21)). It is for this reason that red phosphorus is best suited as a source of polyatomic molecular ion beams. The paper reports on experimental research in the generation of polyatomic phosphorus ion beams with an alternative P vapor source for which a gaseous compound of phosphorus with hydrogen - phosphine - is used. The ion source is equipped with a specially designed dissociator in which phosphine heated to temperatures close to 700 °C decomposes into molecular hydrogen and phosphorus (P4) and then the reaction products are delivered through a vapor line to the discharge chamber. Experimental data are presented reflecting the influence of the discharge parameters and temperature of the dissociator heater on the mass-charge state of the ion beam.

Molecular phosphorus ion source for semiconductor technology.

This paper presents results on the generation of molecular phosphorus ion beams in a hot filament ion source. Solid red phosphorous is evaporated mainly as tetra-atomic molecules up to a temperature of 800°C. Thus, one of the main conditions for producing maximum P(4)(+) fraction in the beam is to keep the temperature of the phosphorous oven, the steam line and the discharge chamber walls no greater than 800°C. The prior version of our ion source was equipped with a discharge chamber cooling system. The modified source ensured a P(4)(+) ion beam current greater than 30% of the total beam current.

Boron ion source based on planar magnetron discharge in self-sputtering mode.

An ion source based on a planar magnetron sputtering device with thermally isolated target has been designed and demonstrated. For a boron sputtering target, high target temperature is required because boron has low electrical conductivity at room temperature, increasing with temperature. The target is well-insulated thermally and can be heated by an initial low-current, high-voltage discharge mode. A discharge power of 16 W was adequate to attain the required surface temperature (400 degrees C), followed by transition of the discharge to a high-current, low-voltage mode for which the magnetron enters a self-sputtering operational mode. Beam analysis was performed with a time-of-flight system; the maximum boron ion fraction in the beam is greater than 99%, and the mean boron ion fraction, time-integrated over the whole pulse length, is about 95%. We have plans to make the ion source steady state and test with a bending magnet. This kind of boron ion source could be competitive to conventional boron ion sources that utilize compounds such as BF(3), and could be useful for semiconductor industry application.

Carborane beam from ITEP Bernas ion source for semiconductor implanters.

A joint research and development of steady state intense boron ion sources for hundreds of electron-volt ion implanters has been in progress for the past 5 years. The difficulties of extraction and transportation of low energy boron beams can be solved by implanting clusters of boron atoms. In Institute for Theoretical and Experimental Physics (ITEP) the Bernas ion source successfully generated the beam of decaborane ions. The carborane (C(2)B(10)H(12)) ion beam is more attractive material due to its better thermal stability. The results of carborane ion beam generation are presented. The result of the beam implantation into the silicon wafer is presented as well.

Bernas ion source discharge simulation.

As the technology and applications continue to grow up, the development of plasma and ion sources with clearly specified characteristic is required. Therefore comprehensive numerical studies at the project stage are the key point for ion implantation source manufacturing (especially for low energy implantation). Recently the most commonly encountered numerical approach is the Monte Carlo particle-in-cell (MCPIC) method also known as particle-in-cell method with Monte Carlo collisions. In ITEP the 2D3V numerical code PICSIS-2D realizing MCPIC method was developed in the framework of the joint research program. We present first results of the simulation for several materials interested in semiconductors. These results are compared with experimental data obtained at the ITEP ion source test bench.

Experimental comparison of time-of-flight mass analysis with magnetic mass analysis.

A series of experiments was carried out in which both a magnetic analyzer (mass separator) and a time-of-flight (TOF) spectrometer were used for ion charge/mass spectral analysis of the ion beam formed by a dc Bernas ion source made for semiconductor implantation. The TOF analyzer was a detachable device that provides rapid analysis of charge-to-mass composition of moderate energy ion beams. The magnetic analyzer was a massive device using a 90 degrees -sector bending magnet with radius of the central orbit of 35 cm. Comparison of these two methods for measuring ion beam composition shows good agreement.

Status of ITEP decaborane ion source program.

The joint research and development program is continued to develop steady-state ion source of decaborane beam for ion implantation industry. Both Freeman and Bernas ion sources for decaborane ion beam generation were investigated. Decaborane negative ion beam as well as positive ion beam were generated and delivered to the output of mass separator. Experimental results obtained in ITEP are presented.

Ion sources for energy extremes of ion implantation.

For the past four years a joint research and development effort designed to develop steady state, intense ion sources has been in progress with the ultimate goal to develop ion sources and techniques that meet the two energy extreme range needs of meV and hundreads of eV ion implanters. This endeavor has already resulted in record steady state output currents of high charge state of antimony and phosphorus ions: P(2+) [8.6 pmA (particle milliampere)], P(3+) (1.9 pmA), and P(4+) (0.12 pmA) and 16.2, 7.6, 3.3, and 2.2 pmA of Sb(3+)Sb(4+), Sb(5+), and Sb(6+) respectively. For low energy ion implantation, our efforts involve molecular ions and a novel plasmaless/gasless deceleration method. To date, 1 emA (electrical milliampere) of positive decaborane ions was extracted at 10 keV and smaller currents of negative decaborane ions were also extracted. Additionally, boron current fraction of over 70% was extracted from a Bernas-Calutron ion source, which represents a factor of 3.5 improvement over currently employed ion sources.