Local Modification of Microstructure and of Properties by FIB-CVD
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Local Modification of Microstructure and of Properties by FIB-CVD H. Wanzenboeck, S. Harasek, H. Langfischer, B. Basnar, W. Brezna, J. Smoliner, and E. Bertagnolli Vienna University of Technology Institute for Solid State Electronics Floragasse 7/1 - 1040 Vienna ABSTRACT The focused ion beam has been acknowledged as a versatile tool for local sputtering as well as local deposition of material. A beam diameter below 10 nm is feasible and renders FIB a powerful tool for microstructure fabrication and generation. This experimental study investigates the geometrical limitations of FIB processing as well as the implications on the processed material. The high energetic ions of the primary beam also change the properties of the processed material due to implantation and atomic mixing. The incorporation of Ga from the FIB may be beneficial in the case of deliberate implantation or unfavorable as a chemical impurity. Higher doses of ion irradiation caused amorphisation of the material. The effects of FIB processing on the substrates as well as deposited structures are illustrated. INTRODUCTION Focused ion beams (FIB) increasingly find applications in microelectronics re-engineering, in rapid prototyping of circuits and in repair of photomasks. They can also be used to initiate a chemical vapor deposition to fabricate structures down to the 100 nm regime [1]. A special characteristic is the implantation of ions originating from the FIB into the substrate material leading to atomic mixing. Higher ion doses may lead to significant amorphisation of crystalline substrates. It is known that the implantation of Ga and amorphisation by atomic mixing significantly influence material properties and electric characteristics of microelectronic devices [2,3]. This work aims at identifying and quantifying the amorphisation and implantation effects and beneficial aspects of the ion beam processing. EXPERIMENTAL A FIB system with (base pressure 2x10-7 Torr) utilizing a liquid metal ion source emitting Ga+ ions from a tip was used for this study. The ion energy was 50 keV at an ion current between 10 and 300 pA. The beam was focused down to 200 nm diameter or below. By scanning the focused beam, only pre-selected areas were exposed to the impinging 50 keV ions. As substrates we used bulk doped n-Si(100) wafers with a specific resistivity of 10 Ω*cm or bulk doped p-Si(100) wafers with 14 Ω*cm. In the first experiment the thickness of the damaged layer was investigated using transmission electron microscopy (TEM). Using a FIB-milled lamella of a Si wafer we have fabricated and imaged the cross-section through this lamella showing the amorphous layer on the sidewall. For this damage study the Ga-ion beam was impinging under an 85°-grazing angle. The FIB processed surface was covered with silicon nitride as protection.
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In a second experiment the surface roughness of a FIB irradiated Si surface was imaged by atomic force microscopy (AFM). The small ion dose used did not effect any sputtering. The focused beam was scanned with
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