Use of Advantageous Impurity Effects in Metallization
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S.P. MURARKA Center for Integrated Electronics and Electronics Manufacturing, Rensselaer Polytechnic Institute, Troy, NY 12180
ABSTRACT Impurities control electrical, mechanical, physical, and chemical properties of the materials. We have manipulated their introduction into semiconductors, insulators, and metals to achieve otherwise unattainable properties. More recently, the continued miniaturization of the solid state devices and circuits have challenged the existing interconnection and contact metallization materials and schemes. These have led to an investigation of new multilevel metallization schemes with lower resistivities and higher reliabilities. In addition, efforts are being made to re-examine the use of newer Al-alloys that may satisfy the resistivity and reliability requirements. This paper will briefly review the existing practices, future needs, and current research activities focused to satisfy these future needs. INTRODUCTION Impurities in materials have played a very significant role in determining the properties of materials that are the backbone of the industrial and electronic revolutions. They provide a means to tailor the properties of natural and pure materials so that new materials with desired capabilities and applicability ranges can be created. Some of the examples are: making of steels from iron; high strength light metal alloys; corrosion resistant alloys; glasses, ceramics, and gems of all kinds; high performance liquids, doping of semiconductors, and electromigration resistant aluminum alloys. It is noted that impurities do not always produce advantageous changes in material. There are many undesirable features of certain impurities in certain materials, such impurities must be and are avoided. Oxidation, corrosion, grain boundary trapping leading to embrittlement, enhancement in chemical reactivity, diffusion, and electrical activity, increase in the electrical resistivity of metals and decrease in electrical resistivity of insulators and semiconductors, lowering of the freezing point, and elevation of the boiling point are some examples of the effects of impurity addition to materials. In this paper, we focus on the advantageous effects of the impurities. After a brief discussion of grain-boundary-impurity effects, special attention will be given to the application (of the impurity concepts) in the metallization schemes for high performance integrated circuits (ICs). Metals are used in ICs to form interconnection wirings. Keeping the resistivity of such metals as low as possible and imparting higher reliability (e.g., corrosion resistance, electromigration and stress migration resistance, and adhesion with the dielectric) will be the goals in selecting the right alloying element. Both copper and aluminum based alloys containing small and controlled amount of impurities will be discussed.
485 Mat. Res. Soc. Symp. Proc. Vol. 405 01996 Materials Research Society
GRAIN BOUNDARIES AND IMPURITIES The properties of the pure elemental and crystalline materials are determined by their
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