<title>Maskless Fabrication Using Focused Ion Beams</title>

Abstract

Maskless Fabrication Using Focused Ion BeamsKenji GAMO and Susumu NAMBAFaculty of Engineering Science, Osaka University, Toyonaka, Osaka, JapanAbstractMaskless patterning of materials using focused ion beams are important to simplifydevice processing and to develope full maskless processing. We have shown that a high speedmaskless patterning can be done using ion beam assisted etching and ion beam modificationtechniques. In this paper, basic characteristics of various liquid metal alloy ion sourcesand a mass separatted focused ion beam system, and maskless patterning techniques for GaAs,Cr films and other materials are reported.IntroductionThere has been an increasing interest in high- brightness focused ion beamsl). This isbecause ion beams can be used in almost all important,device fabrication process such as ionbeam lithography, etching and ion implantation, and moreover, focused ion beams have apotential ability for maskless microfabrication. Focused ion beams are also attractive forapplications to various micro ion beam analysis. Recently much effort has been done todevelop scanning secondary ion spectroscopy and ion microscopy2 -4).High- brightness focused ion beams are formed using liquid metal ion sources and forvarious maskiess microfabrication processing, various ions are required. Relatively rightions are necessary to expose a thick resist layer, heavy ions provide high etching rate, andfor maskless implantation, various dopant ions are required. Recently it is shown thatmany ions can be obtained using metal alloys with a low melting temperature5-7).A maskless etching or pattern fabrication technique is necessary to develop fullmaskless fabrication process techniques. A simple etching technique is to use physicalsputtering effect. However, this technique gives a very slow etching rate, although afocused ion beam provides an advantage to solve problems of etching selectivity betweenmasks and materials to be etched.To improve etching rate, use of chemical effects induced by a collision between ionsand target atoms are important. Examples of these chemical effects are radiation enhancedetching$), ion beam assisted etching9,10), and ion beam modification techniquesl1).In the present paper, basic characteristics of liquid metal alloy ion sources and massseparated focused ion beam system and various maskiess pattern fabrication techniques usingion beam induced chemical effect are presented.Liquid metal alloy ion sourcesFor various practical applications of focused ion beams, liquid metal ion sources arerequired for various elements and to have a long lifetime, as well as a high brightness.The first requirement is now shown to be satisfied by using low temperature metal alloys5