Analysis of Structural Transformations in High Fluence Nitrogen Ion Implanted Aluminium
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ANALYSIS OF STRUCTURAL TRANSFORMATIONS IN HIGH FLUENCE NITROGEN ION IMPLANTED ALUMINIUM L. CALVO', A. PEREZ-RODRIGUEZ', A. ROMANO-RODRIGUEZ', J.R. MORANTEAND J. MONTSERRAT* LCMM, Dept. Ffsica Aplicada i Electrbnica, Universitat de Barcelona, Avda. Diagonal, 645-647, E-08028-Barcelona, Spain "" Centro Nacional de Microelectr6nica CNM-CSIC, Campus UAB, E-08193 Bellaterra, Spain ABSTRACT The structural analysis of Al layers on Si obtained by sputtering at different 2 conditions and implanted with nitrogen (with doses of 2.5x10'7 and 5x10 17 N2 ' ions/cm , energy 150 keV, room temperature) is performed by SRP, SIMS and TEM measurements. The correlation between these measurements shows the formation of AIN crystalline precipitates already at the substoichiometric dose. SRP and TEM reveal the presence of a buried layer with resistivity higher than the Al matrix, with a high concentration of AIN precipitates. The morphology of this layer is affected by surface roughness. For the higher dose, a buried continuous AIN polycrystalline dielectric layer is formed. Moreover, the SIMS measurements suggest a gettering effect of Si in the buried layer. INTRODUCTION Ion implantation constitutes a well known process for the improvement of the surface properties of metals, such as microhardness and corrosion resistance. In the case of Al, the implantation of a high dose of nitrogen has an additional interest for the synthesis of AlN layers. The direct synthesis of comnounds by high dose ion implantation constitutes a very interesting approach for o b t a i n i n g complex structures [1]. Although initially it was essentially involved in the development of Silicon on Insulator (SOI) technologies (SiO2 and Si3N4 layers in Si), nowadays it has been successfully applied to many other systems, including AIN in Al [2-8]. The interest in this compound is due to its optical and mechanical properties, which make it suitable for electronic applications: large direct gap, good thermal conductivity and chemical stability up to very high temperature. Therefore, it has potential interest as a good dielectric for active and passive components in semiconductor devices, and for the development of optoelectronic devices in the ultraviolet region. Moreover, AlN is also a piezoelectric material with a high acoustic velocity, which makes it interesting for surfacewave acoustic devices. The synthesis of AIN layers by high dose N ion implantation has been reported by different authors [2-8]. According to their data, the distribution in the implanted material, the formation of AIN and its structure are features which depend strongly on the ion implantation conditions (energy, dose and temperature), as well as on the characteristics of the Al matrix (crystalline nature and orientation, grain size, presence of impurities...) [2,5,9]. Clearly, the development of the potentialities of this technology for the production of electronic devices needs a thorough knowledge and understanding of this dependence. Mat. Res. Soc. Symp. Proc. Vol. 311. ©1993 Materials Resea
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