1. Magnetron Discharge-Based Boron Ion Source
Alexey Vizir1, Efim Oks1,2, Georgy Yushkov1, and Maxim Shandrikov1
1 Institute of High Current Electronics SD RAS, Tomsk, Russia
2 Tomsk State University of Control Systems and Radioelectronics, Tomsk, Russia
An ion source was designed utilizing a planar magnetron with 2-inch diameter pure boron target. The discharge can operate both in DC and pulsed modes. Boron as a semiconductor has low conductivity at normal conditions, which still is sufficient to start low-current (2 mA) high-voltage (2000 V) DC discharge. Due to the target heat insulation, it gradually rises the temperature to 300 ºC and more, enabling to apply high-current pulses to the discharge gap. An improved time-of-flight methodic was used to measure the ion species in the plasma and the beam. The ion composition of plasma was examined within a wide range of DC and pulse parameters: pulse duration of µs, repetition rate of p.p.s., pulse current up to 100 A. It was shown that with pulse current of more than 10 A boron ions can prevail in the extracted ion beam. The boron ions are mostly singly ionized. The rest sort of ions are singly and doubly charged argon or krypton which were used as working gases.
SEM output voltage oscillogram
A view of the magnetron
Experimental setup
At the DC discharge current of 100 mA, boron ion fraction is less than 1 %. At pulsed discharge current higher than 20 A the ion beam composition indicates that the discharge enters a self-sputtering mode when the target material ions prevail in plasma and the boron ion fraction can exceed 85 %.
Discharge and ion beam currents through a pulse duration. Pressure is 2 mtorr, repetition rate is 20 p.p.s.
Ion beam composition dependence on repetition rate. Pressure is 0.25 mtorr, pulse current is 10 A, gate pulse delay is 12 µs.
Ion beam composition dependence on discharge current. Pressure is 0.5 mtorr, repetition rate is 200 p.p.s., pulse duration is 6 µs.
SUMMARY
Measurements showed that the maximal time-integrated boron ion fraction is reached at the following conditions: pressure of 2 mtorr, pulsed discharge current of 100 A, repetition rate of 10 p.p.s. and pulse duration of 250 µs, which at the same time provide the optimal discharge power to keep the target hot. Relatively low dc discharge current of 1 mA was simultaneously applied, which ensures stable pulsed discharge ignition and, at the same time, provides low time-averaged argon ion fraction. Pulsed ion beam with current of 100 mA and boron ion fraction of more than 85 % is generated using the magnetron discharge with hot pure boron target.
The work was supported by Russian Science Foundation under grant #