A device for trapping nano-particles formed in processing plasmas for reduction of nano-waste Shinya Iwashita, Kazunori Koga, Masaharu Shiratani ⁎ Department of Electronics, Kyushu University, Hakozaki, Fukuoka, 812-8581, Japan Available online 6 September 2006 Abstract Removal of nano-particles is important from the viewpoint that nano-materials may be hazardous to health when they deposit within the respiratory system. We have developed a method for measuring a sticking probability of nano-particles to a wall. The probability of nano-particles above 2 nm in size to a stainless-steel wall is close to 100% at a low ambient pressure below about 160 Pa. Based on this result, we have developed a device for trapping nano-particles formed in low pressure processing plasmas in order to reduce nano-waste, that is, waste of nm in size. The device traps nano-particles by collision and attachment of nano-particles to its surface. The trapping efficiency of the device for nano- particles above 2 nm in size is more than 99.8% at a low ambient pressure below about 160 Pa. © 2006 Elsevier B.V. All rights reserved. PACS: 89.60.Ec; 81.07.Ta Keywords: Nano-particle; Plasma process; Environment; Sticking probability 1. Introduction Removal of nano-waste, that is, waste of nm in size is important, because nano-materials may be hazardous to health when they deposit within the respiratory system. Although many removal methods have been developed in aerosol technology and particle technology areas, the removal of nano-materials is difficult [1]. Moreover, nano-materials formed in plasmas can be in the three charge states, that is, negative, positive, and neutral [2]. Kurimoto et al. developed a negatively-charged fine particle collector to remove negatively-charged particles in low pressure plasmas [3]. However, we still need a removal method effective in removing nano-materials in the three charge states. This paper reports a sticking probability of nano-particles and a particle trapping filter which removes nano-particles formed in low pressure processing plasmas in order to reduce such nano-waste. 2. Sticking probability of particles Firstly, we have produced nano-particles using low pressure processing plasmas and studied their sticking probability to walls as well as their transport efficiency. The experimental setup is shown in Fig. 1. Test nano-particles are generated using H 2 + SiH 4 pulsed discharges and then they are transported toward the downstream region by a gas flow. They are trapped on two stainless-steel meshes of a transparency of T =35% in the downstream region. A sticking probability s(d) of nano- particles having sizes between d and d + Δd is deduced from the following equation, S ðdÞ¼ 1 1−T 1− n 2 ðdÞ n 1 ðdÞ   ð1Þ where Δd is an interval of particle size, n 1 (d) and n 2 (d) are densities of particles, having sizes between d and d + Δd, trapped on the mesh 1 and mesh 2, respectively. We have experimentally confirmed that the sticking probability to the mesh is the same as that to wall such as Si, SiO 2 , and stainless steel. The particle density has been obtained by an ex-situ method using a high resolution transmission electron microscope (HRTEM, JEOL: JEM-2010) [4]. Fig. 2 shows typical images of nano-particles and their size distributions. The mean-size of the nano-particles can be controlled by changing the duration of pulsed discharge, because their size increases with the duration [5]. Fig. 3 shows the dependence of apparent sticking probability of nano-particles on their size as a parameter of a gas velocity V g . Surface & Coatings Technology 201 (2007) 5701 – 5704 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +81 92 642 3950; fax: +81 92 642 3973. E-mail address: siratani@ed.kyushu-u.ac.jp (M. Shiratani). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.060