Copper-Based Metallization for ULSI Applications
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will be replaced by other materials such as Cu, Au, or superconductors for on-chip interconnection. Copper is a candidate for on-chip interconnection in the upper-level metallization because of its low bulk electrical resistivity and its resistance to electromigration.Itslowerresistivityofl.67/afi • cm, versus 2.65 fj.il • cm for aluminum, allows higher current density to be imposed on copper wiring, with smaller line widths and minimized interconnection or RC delay of the devices. Many obstacles to the use of copper still exist in VLSI and ULSI processing. For instance, copper dry etching is difficult because the vapor pressure of most copper halides is low at room temperature. The relatively low interfacial reaction temperatures between copper and most contact materials cause a serious thermal stability problem in copper-based metallization. This issue of the MRS Bulletin focues on the search for novel copper deposition, etching, and patterning processes, the characterization of copper microstructure, and an understanding of the materials in-
teractions and corrosion protection involving copper. In recent years, great effort has gone into depositing high-quality copper thin films. High deposition rates, low-temperature processing, low cost, good selectivity, and step coverage are the major concerns in the deposition of copper films. The article by Kaloyeros and Fury describes the art of chemical vapor deposition of copper. Electroless copper deposition with an alkaline-free deposition solution is introduced by Cho, Kang, Wong, and ShachamDiamand. Copper patterning is another challenge in copper-based metallization. The article by Hampden-Smith and Kodns describes new chemical approaches to copper etching. An inlaid copper scheme using planarization by chemical-mechanical polishing is introduced by Murarka, Steigerwald, and Gutmann. Recent interest in copper-based metallization for ULSI technology has also stimulated extensive studies on its thermal stability issues. The implementation of diffusion barriers, adhesion promoters, and passivation layers in copperbased metallization is highly desirable. The article by Li and Mayer highlights recent progress on refractory metal nitride encapsulation in copper wiring. The objective of this issue is to provide readers with an overview of some active areas in copper-based metallization for ULSI applications. Although copper has many advantages over aluminum as an on-chip interconnection material, many obstacles on the road to copper implementation in ULSI applications need to be overcome. Since the copper-based on-chip interconnect technology covers a wide spectrum, from materials science issues to VLSI processing, an extensive collaboration between universities and the semiconductor industry is important. We hope that this issue of the MRS Bulletin reflects the current research progress and will enhance further collaborations. •
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Advanced Metallization for ULSI Applications 1992 Proceedings of the Conference held
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