Metallization Systems on Cvd-Diamond Substrates for Application in Multichip Modules
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W. D. BROWN, H. A. NASEEM, A. P. MALSHE, J. H. GLEZEN, AND W. D. HINSHAW High Density Electronics Center (HiDEC) and the Department of Electrical Engineering, The University of Arkansas, Fayetteville, Arkansas 72701 ABSTRACT Because of its high thermal conductivity, free-standing CVD-diamond is an extremely attractive material for application as the substrate in multichip modules (MCMs). However, this material does present some technological challenges, one being the development of reliable metallization systems. In this work, adherent metallization systems, such as Au/Ti, Au/Ti-W, Au/Ni-Cr, Au/Cr and Cu/Cr have been produced at low temperatures. Thin adhesion/seed metal layers were deposited using sputtering and evaporation techniques. Gold and copper metallization of several microns thickness was accomplished by electroplating over the thin metal layer. Postdeposition annealing of both the adhesion/seed layer and plated metallization systems were performed at temperatures up to 500'C in an effort to enhance adhesion and determine the impact of subsequent high temperature operations on reliability issues such as intermetallic diffusion, delamination, and the impact of surface microcavities. Extremely adherent Au/Cr and Cu/Cr metallization systems appropriate for use in MCM technology were developed. INTRODUCTION The rapid changes in the electronics industry are generally driven by the attractiveness of smaller, faster, and lighter weight electronic systems.
Consequently, multichip packaging
technology is receiving widespread attention. The use of multichip modules (MCMs) promises to increase packaging density and system performance beyond what is otherwise possible with advances in VLSI and surface mount technology [1]. As is the case for most advanced technologies, the drive toward high performance multichip modules has given rise to a number of engineering challenges. In advanced MCMs, where high speed and high power chips are mounted shoulder to shoulder on large circuit boards, fast heat spreading and removal become major issues. Typically, substrate material choices for MCMs have been limited to silicon, A12 0 3 , and to a much lesser extent, AIN, SiC, and glass/ceramics. However, as the power dissipation of ICs continues to increase, heat dissipation and removal will be major issues, particularly in future 3-D MCMs. The excellent thermal conductivity of diamond, coupled with its unusual combination of electrical and mechanical properties, makes it an ideal substrate material for solving thermal management problems in MCMs. The use of diamond substrates should also make 3-dimensional MCMs a reality. Diamond As A Substrate Recent breakthroughs in CVD diamond deposition technology make it possible to fabricate free-standing diamond substrates. In order to successfully utilize these substrates for MCMs, one 59 Mat. Res. Soc. Symp. Proc. Vol. 391 ©1995 Materials Research Society
must be able to deposit and photolithographically define interconnect metallization on their surface. Currently available diamond fi
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