High-Rate Etching of Mn-Zn Ferrite by Laser-Induced Chemical Reaction in CC1 2 F 2 Atmosphere
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HIGH-RATE ETCHING OF Mn-Zn FERRITE BY LASER-INDUCED CHEMICAL REACTION IN CCl 2 F2 ATMOSPHERE Y. F. LU, M. TAKAI, S. NAGATOMO*, AND S. NAMBA Faculty of Engineering Science and Research Center for Extreme Materials, Osaka University, Toyonaka, Osaka 560, Japan *On leave from D. S. Scanner Co., Ltd., Fukushima 5-3-7, Fukushima-ku, Osaka 553, Japan ABSTRACT Maskless dry etching of Mn-Zn ferrite in dichlorodifluoromethane (CCl 2F 2 ) by Ar+-ion laser (514.5 nm-line) irradiation has been investigated to obtain high etching rates and aspect-ratios of etched grooves. The etching reaction was found to be thermochemical and caused by Cl radicals thermally decomposed from CCI 2 F2 gas. High etching rates of up to 360 pm/s, which is about one order of magnitude higher than that in a CC1 4 gas and even higher than that in a H3 PO4 solution, have been achieved. A high aspect-ratio of up to 12 was obtained. Definite gas pressure and dwell time are necessary to fabricate a smooth groove. INTRODUCTION Laser-induced microfabrication, as a new fabrication method for the microstructures of semiconductors, metals, and insulators, has been widely investigated in recent years [1-4]. Like semiconductors, ceramics are another important kinds of materials in the electronic industry. For example, ferrite is used as an important material for magnetic heads in the information storage system. Our previous studies on laser-induced processing of ferrite materials provided a new method to microfabricate this material with high process-rate, high precision and low damage, in which laser-induced etching of ferrite in a CCI 4 gas atmosphere or in a H3 PO4 aqueous solution [5-8], and laser-induced deposition of buried Si0 2 line in ferrite [9] were performed. This paper shows a new approach to etch the ferrite material by laser irradiation in a CCl F gas atmosphere instead of other reactive halogen compounds. Since CC67F is chemically stable at room temperature, much 2 safer to human body than CCI 4 [10] and does not stain the metal parts in the vacuum system, it is considered to be more suitable for the industrial applications than CCI 4 . Furthermore, CCl 2 F2 has high vapor pressure in room temperature up to 4000 Torr which may promote etching reaction, whereas CC1 4 has a vapor pressure below 100 Torr. The sample used in this study is a single crystal ferrite, which is superior in mechanical and magnetic characteristics to conventionally used polycrystal ferrite. For example, single crystal ferrite has higher magnetic susceptibility, higher wear resistance and is free of grains. The etching behavior in CC1 2 F will be compared with those in laserinduced dry etching in CC1 4 and we? etching in a H3 PO4 aqueous solution. EXPERIMENTAL The schematic diagram of the experimental system is shown in figure 1. The experimental system includes an Ar+-ion laser, a convex lens, a quartz window containing vacuum chamber, a pumping system and an etchant gas supplying system. Single crystal Mn-Zn ferrite (MnO : ZnO : Fe 2 03 = 31;17;52) samples, (100) oriented,
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