Potential of Ag Interconnect and Contact Metallization for Various Applications via Cu Additions
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Potential of Ag Interconnect and Contact Metallization for Various Applications via Cu Additions Hauk Han1,2, Yeongseok Zoo1, James W. Mayer1, and Terry L. Alford1,2 1
School of Materials, Arizona State University, Tempe, AZ, 85287-8706
2
Flexible Display Center at ASU, Arizona State University, Tempe, AZ, 85287
ABSTRACT The thermal stability of Ag(Cu) alloy thin films on indium tin oxide (ITO) has been investigated and compared to that of pure Ag thin films on ITO. Atomic force microscopy and Xray diffraction results of annealed films show differences in the evolution of surface morphology and texture with annealing. The presence of Cu atoms in the silver impacts the surface energy and surface diffusion. This results in Ag and Ag(Cu) alloy having very different surface morphology and crystallographic texture. The enhanced texture and thermal stability of the Ag(Cu) alloy constitute its potential use contact as material for MOSFET and for flip-chip lightemitting diodes. INTRODUTION For the development of ultra large-scale integration (ULSI), the concern for electrical resistivity and susceptibility to electromigration is becoming increasingly important to decrease resistance-capacitance (RC) delay time and high power consumption, and to increase reliability. To decrease the RC signal delays, the circuit can be fabricated with a metal having resistivity lower than currently used Al(Cu) alloy. The resistivity of Al alloys (about 3.1 µΩ-cm) is higher than desired for high speed ICs. Silver has been studied as attractive future interconnection material for ULSI because of its lowest resistivity (about 1.57 µΩ-cm for bulk) and higher oxidation resistance than Cu. In the view of electromigration, silver promises to provide an electromigration resistance of at least one order of magnitude better than Al. These properties of Ag make it one of the promising highconductivity candidates to be considered as possible interconnect material for ULSI technology Silver however does not to adhere well to dielectrics and also has a high diffusivity in to SiO2 [1, 2]. More substantially, agglomeration of silver thin films at high temperatures has been considered as a drawback of silver metallization; it can result in an increased electrical resistivity and eventually loss of continuity [3]. If silver agglomeration can be circumvented and diffusion prevented during processing and operation, Ag based metallization can be an optimal solution for future interconnects materials.
This study shows the promise of Ag alloy films as interconnect material for future ULSI applications and reflector material for high efficiency flip chip light emitting diode (FCLED) because of enhanced texture and surface roughness, good reflectivity of Ag, and thermal stability up to 600 ∞C. EXPERIMENT DETAILS The 200 nm Ag and Ag(Cu) thin films were deposited using electron-beam evaporation onto ITO layers which were previously deposited onto clean Si substrates by rf sputtering at room temperature. The samples were annealed for 1 hour in a vac
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