cm . __ __ EB . . . . .A. :.,. ~::::.::~:;j:+::: .::.:; ,.,..,. :::p.. . .:‘:: >’ ::: ::_; : ...A . .:., :.,.::: applied zyxwvutsrqponm surface science ELSEVIER Applied Surface Science loO/lOl (1996) 360-364 Charging phenomenon of insulators in negative-ion implantation Yoshitaka Toyota * , Hiroshi Tsuji, Shoji Nagumo, Yasuhito Gotoh, Junzo Ishikawa zyxwvutsrqpo Deparrment of Elecrronic Science zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA nnd Et~girwering, Kyoro Uniwrsi&.Yoslzidrr-honina~hi. .SU~JW hx. Kyro 606-01, Japan Received 15 August 1995: accepted 24 October 1995 Abstract The energy distribution of secondary electrons emitted from an insulator during negative-ion implantation was measured. According to secondary-electron-energy analysis. the charging voltage of insulator was estimated from the measured energy distribution. The experimental results in negative-carbon-ion implantation showed that the charging voltages of a quartz glass plate and a photoresist film on silicon substrate are several negative volts in the energy range from 5 to 35 keV and decrease gradually with increasing ion energy. The low negative charging voltage of insulator and the most probable energy of the secondary-electron energy distribution during negative-ion implantation are discussed using a charging model based on an electric double layer. 1. Introduction The preliminary experiment on insulators by a secondary-electron-energy analysis was carried out to estimate the charging voltage of an insulator from the measured energy distribution. As a result, the charging voltage of insulators, such as quartz glass and photoresist, was considered to be several nega- tive volts, which is the opposite to an isolated elec- trode at several positive volts. The low charging voltage during negative-ion implantation is consid- ered to be due to the charge equilibrium between incoming charges (negative ions) and outgoing charges (secondary electrons with high energy). However, the opposite polarity proves that the charg- ing model of an isolated electrode [4] does not apply to the case of an insulator. * Corresponding author. Tel.: +81-75-7535021: fax: +81-75- 751 1576: e-mail: ytoyota@kuee.kyoto-u.ac.jp. In the preliminary experiment, the accuracy of the experimental apparatus, in particular the energy ana- lyzer. was low. Hence, the charging mechanism which causes the negative charging was not under- stood enough. In this paper, the measurement appara- tus reformed to increase the accuracy is described. In addition to measuring the energy distribution of sec- ondary electrons to evaluate the charging voltage of insulator, a charging model of insulator in the charge equilibrium is discussed. 2. Charging voltage evaluation by secondary-elec- tron-energy analysis 2. I. M easurement principle and apparatus Ion bombardment with materials brings secondary electron emission from the surface. The secondary electrons have not only kinetic energy but also po- tential energy which is measured from the ground 0169-4332/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SOl69-4332(96)00242-5