Measurements of secondary electron emission and plasma density enhancement for plasma exposed surfaces using an optically isolated Faraday cup

Qin, Shu; Bradley, Michael P.; Kellerman, P.; Saadatmand, K.

doi:10.1063/1.1431707

Cited by 21 publications

(21 citation statements)

References 11 publications

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“…However, the above-mentioned analytical model and fluid model both neglect the secondary electron emission effect, and till now, few theoretical studies on the secondary electron emission in PSII have been carried out. Moreover, opinions on the effect of secondary electron emission still disagree with each other [59,60] . It is expected that the particle simulation method will accurately calculate the effect of secondary electron emission in PSII.…”

Section: Discussionmentioning

confidence: 97%

Simulation methods of ion sheath dynamics in plasma source ion implantation

Wang¹

2004

Chinese Sci Bull

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Progress of the theoretical studies on the ion sheath dynamics in plasma source ion implantation (PSII) is reviewed in this paper. Several models for simulating the ion sheath dynamics in PSII are provided. The main problem of nonuniform ion implantation on the target in PSII is discussed by analyzing some calculated results. In addition, based on the relative researches in our laboratory, some calculated results of the ion sheath dynamics in PSII for inner surface modification of a cylindrical bore are presented. Finally, new ideas and tendency for future researches on ion sheath dynamics in PSII are proposed.Keywords: plasma sheath simulation, plasma source ion implantation, fluid model, particle simulation, inner surface plasma source ion implantation.Plasma source ion implantation (PSII) has been a well-known technique to modify surface properties of materials. It has many advantages over conventional ion beam implantation, i.e. it is non-line-of-sight accessible, cost-effective and it can be easily operated. In PSII, a target is immersed in a plasma. When a series of negative high-voltage ( 10 100 kV) pulses are applied to the target, ions are extracted directly from the plasma and accelerated to the target for implantation. Since the technique was proposed by Conrad in 1986 [1,2] , many experiments have performed and shown its superiorities in improving the surface hardness, the resistance to wear and corrosion of materials [3 6] .The ion dose and impact energy are the most important factors to determine the result of PSII, and the two factors depend mainly on the dynamics of ion sheath evolution. Therefore, theoretical studies on the ion sheath dynamics emerged and have been continuously developing, giving guidance for the PSII techniques. The physical model of ion sheath forming and expanding in PSII (Fig. 1) is: When a sudden negative voltage is applied to the target, initially, in the time scale of the inverse electron plasma frequency ( pe 1 ), electrons near the target are driven away, on this time scale the ion motion is negligible so that as the electrons recede, they leave behind a region of nearly uniform ion space charge around the target, which is called the "ion-matrix sheath". Subsequently, on the time scale of the inverse ion plasma frequency ( pi 1 ), ions within the sheath are accelerated into the target as they fall through the ion-matrix sheath. This, in turn, drives the sheath-plasma edge further away, exposing new ions that are extracted. Finally, on a longer time scale, the system evolves toward a steady-state Child law sheath. Fig. 1. Schematic diagram of ion sheath evolution in PSII.Based on the above physical model, before the sheath expansion, the ion density in the sheath can be assumed uniform. Thus the sheath thickness, the electric field and potential distributions within the ion-matrix sheath can be calculated by Poisson's equation [1,8 10] . During the period of sheath propagation, the ion velocity, energy, flux, dose and incidence angle at different positions of the target...

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Section: Discussionmentioning

confidence: 97%

Simulation methods of ion sheath dynamics in plasma source ion implantation

Wang¹

2004

Chinese Sci Bull

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“…The values of measured by En and Cheung were comparable with those reported by Szapiro et al, while Shamim and coworkers found values of that were about twice those of Szapiro. Qin et al [16] found that these indirect methods ignore the phenomenon of plasma density enhancement during the high voltage pulse, which in turn increases the secondary yield, and developed a direct method based on a Faraday dosimetry technique for measuring the incident ion flux that automatically incorporates the effect of plasma density enhancement. Qin et al obtained secondary yields with values lower than those obtained by previous PIII methods but still higher than the standard methods.…”

Section: Introductionmentioning

confidence: 99%

Measurement of secondary electron emission yields

Chutopa

Yotsombat

Brown

2003

IEEE Trans. Plasma Sci.

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The authors describe a method for the measurement of secondary electron emission coefficients and demonstrate the use of this approach for the measurement of secondary electron yields for titanium, copper, and carbon ions incident upon an aluminum target. The method is time-resolved in that a series of measurements can be obtained within a single ion beam pulse of several hundred microseconds duration. The metal ion beams were produced with a vacuum arc ion source, and the ratio of secondary electron current to incident ion current was determined using a Faraday cup with fast control of the electron suppressor voltage. The method is relatively simple and readily applied and is suitable for measurements over a wide parameter range. The secondary yields obtained in the present work are of relevance to the measurement of ion current and implantation dose in plasma immersion ion implantation.Index Terms-Ion beam bombardment, ion beams, secondary electron yield, secondary emission, vacuum arc ion source, vacuum arc plasma.

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“…For the pulsed continuous plasma systems used in the PIII process, people can only measure the quiescent plasma parameters without the pulses, 1,6,7 although the impact of the high-voltage pulses on the plasma densities has been qualitatively or semiquantitatively observed 8 and quantitatively measured. 4 Qin, et al used an in situ Faraday cup dosimetry technique to measure the plasma density enhancement factor e.f. ϭ J ion ͑on͒ / J ion ͑off͒ so that the averaged plasma density during the high voltage pulse can be obtained indirectly. 4 In this letter, a time-delayed and time-resolved Langmuir probe measurement was used to measure the evolution of the plasma densities versus time of a dc pulsed, noncontinuous plasma.…”

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confidence: 99%

“…4 Qin, et al used an in situ Faraday cup dosimetry technique to measure the plasma density enhancement factor e.f. ϭ J ion ͑on͒ / J ion ͑off͒ so that the averaged plasma density during the high voltage pulse can be obtained indirectly. 4 In this letter, a time-delayed and time-resolved Langmuir probe measurement was used to measure the evolution of the plasma densities versus time of a dc pulsed, noncontinuous plasma.…”

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confidence: 99%