Chemical Vapor Deposition of Copper Alloys
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CHEMICAL VAPOR DEPOSITION OF COPPER ALLOYS CHRISTOPHER J. SMART, SCOTT K. REYNOLDS, CAROL L. STANIS, AR VIND PA TIL, J. THOR KIRLEIS IBM T.J. Watson Research Center P.O. Box 218, Yorktown Heights, New York, 10598
ABSTRACT Chemical vapor deposition of metals is becoming a desirable alternative to physical deposition techniques (e.g. sputtering, evaporation) for applications in chip wiring. This is due to the possibility of achieving highly conformal coverage and low processing temperatures. Additionally, it is convenient to be able to enhance the physical properties (e.g. corrosion resistance, adhesion, electromigration resistance) of metal films used for chip interconnection by incorporation of an alloying agent. We have investigated the possibility of extending our current copper deposition process to allow for the deposition of copper alloys. By careful selection of the precursors and reactor conditions, simultaneous decomposition of the two compounds to give clean alloy Films is effected. Using this co-deposition method, Cu-Co and Cu-Te alloy films were prepared. Precursor and reaction chemistry are discussed as well as some properties of the resulting films. INTRODUCTION Recently, a number of reports have appeared describing new precursors for the chemical vapor deposition (CVD) of pure copper films. 1.2 Both blanket and selective processes are described, conformality has been demonstrated, and very low deposition temperatures have been achieved. These factors, taken in conjunction with the fact that copper is second only to silver in room temperature conductivity, have lead many to believe that copper will supplant aluminum and aluminum alloys as the chip wiring metal of choice. In switching to copper metallization, benefits would include an improvement in the RC time constant of the circuits involved (by minimization of the wiring delay) as well as an improvement in some physical and mechanical properties (such as electromigration) of copper over aluminum. 3 However, a proposed copper metallization scheme would be anticipated to have its own set of weaknesses. Among these are: susceptibility to corrosion, and poor adhesion to dielectric materials. It has also been suggested that the mobility of copper atoms through the finished structure may be problematic 4 and that the electromigration resistance of copper, while improved over pure aluminum, may still not be sufficiently high. We have taken up the following study of CVD of copper alloys with the intention of maintaining the attractive features of CVD copper (conformality, highly conductive films, low deposition temperature) while at the same time thwarting some of the above-mentioned foibles. EXPERIMENTAL CVD Reactor. All cvd depositions were carried out in a quartz, bell jar reactor which was designed for the deposition of copper and an alloying agent. The main chamber was pumped using an oil vapor diffusion pump, backed by a mechanical, rotary vane pump. Reactor pressure was maintained at 1-5 torr during the depositions. Reaction by-products were isolate
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