Ion emission and electric field characteristics in the liquid metal ion source with a new suppressor electrode Byeong Seong Cho a , Hyun Joo Oh a , Han S. Uhm a , Seung Oun Kang a , Changjo Kim b , Yoon Choi b , Eun Ha Choi a, * a Charged Particle Beam and Plasma Laboratory, Dept. of Electrophysics, Kwangwoon University, 447-1 Wolgye-Dong, Nowon-Gu, Seoul 139-701, Republic of Korea b A-Tech System,175-25, Cheongcheon-Dong 2, Bupyeong-Gu, Incheon, Republic of Korea article info Article history: Received 26 July 2010 Received in revised form 18 March 2011 Accepted 24 March 2011 Available online 1 April 2011 Keywords: Liquid metal ion source Focused ion beam Suppressor Electric field Field ion emission abstract The liquid metal ion sources (LMIS) in focused ion beam (FIB) system have many advantages of high current density, high brightness and low ion energy spread. There are two electrodes being emitter and extractor for field ion emission in LMIS. But several LMIS have a new electrode called the suppressor. Characteristics of LMIS with a suppressor are investigated in terms of the electric field change due to the suppressor. The threshold and extinguishing voltages are investigated under the varying a suppressor voltage for a specified source voltage, and also currentevoltage (IeV) characteristics have been observed in terms of the voltage difference between the source and extractor for the various suppressor voltages. It is found that the emission current decreases as the suppressor voltage increases since the increase in the suppressor voltage reduces the electric field. It is also noted that the threshold and extinguishing volt- ages are increased as the suppressor voltage increases. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Liquid metal ion source (LMIS) has been studied for the ion implantation, the surface analysis, the ion microscope, and micro- fabrication because of high current density, high brightness and low ion energy spread. Ion beam is emitted by the strong field in a high voltage electrode which is composed of a sharp needle type electrode (source) and a plane extractor [1e3]. The beam characteristics have been studied in many aspects but the influ- ence of a suppressor electrode on the ion extraction has not been thoroughly investigated. In this paper, we introduce a suppressor electrode, and the relation between an electric field and a suppressor voltage and currentevoltage (IeV) curve are investigated. Fig. 1 shows a schematic of experimental set-up for power supply and electrode systems in LMIS with a suppressor elec- trode. There are three electrodes of source, extractor and suppressor to emit a liquid metal gallium ion. A source is applied high voltage V S from 0 V to 15 kV. An extractor is the electrode to extract ion from the source. It is floated on the source because of fixing an ion potential energy and changing an ion emission current simultaneously. The voltage difference between the source and the extractor is a threshold or an ignition or voltage V. A suppressor is a new electrode to change an electric field on the source. It is also floated on the source voltage and called a suppressor voltage V Sup . 2. Study of electric field in terms of source and suppressor positions in extractor We have investigated the proper suppressor position for the emission of liquid metal ion beams. The suppressor electrode has been located between the extractor and the source. The suppressor can be located above the source end, as in Fig. 2. The suppressor is also located at the same horizontal line as the end of the source, as in Fig. 3, and it is also be located below the source end, as in Fig. 4. The voltage applied to the source and the suppressor is 10 kV. The voltage difference between the source and the extractor electrode is also set to be 10 kV. The distance between the suppressor and the extractor electrode r 1 is fixed to be 700 mm, even though it may also give a big influence on the electric field profile, and the distance r between the source and the extractor electrode varies 1100 mm, 700 mm and 300 mm. The electric fields from the simulation have been calculated on the end-region of the tip under the vacuum environment. In Figs. 2 and 3, there is insufficient electric field to emit ion from the source because the suppressor is floated on the * Corresponding author. E-mail address: ehchoi@kw.ac.kr (E.H. Choi). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.03.069 Current Applied Physics 11 (2011) S172eS176