The trend in semiconductor fabrication is toward faster and more complex devices. Increased operating speeds are typically attained through the fabrication of devices having small feature sizes, and through the use of a variety of electrically conductive metals. A multitude of different metals and metal alloys are now in use which increase device operating speeds, and in some cases, provide a diffusion barrier to protect the devices from contamination. Further, complex metallization structures are being used to form electrical interconnection to the various components found in an integrated circuit. The need for complex metallization systems has occurred, in part, as a result of the need to form many overlying layers of conductive interconnects to electrically couple the vast number of device components in an integrated circuit.
The process technology fused to form the metallization structures must have the capability to produce metal films of high purity. The deposited metal films must not only be highly electrically conductive, but also must possess the necessary optical reflectivity characteristics to enable high definition photolithographic processing. In order to meet the film quality requirements demanded in semiconductor fabrication, sputter deposition has become a widely used technique. A metal sputtering process is typically carried out in an ultra-high vacuum environment in which processing parameters, such as metal film deposition rates and morphological characteristics of the metal film, can be carefully controlled. Using a state of the art sputtering process, a metal film can be rapidly deposited onto the surface of a semiconductor substrate, while controlling the grain size and film thickness uniformity with a high degree of precision. Additionally, the sputter deposition process is adaptable to the formation of metal alloy films, either by using multi-component sputtering targets, or by introducing reactive gases into the sputter deposition system.
Although a sputtering system can be adapted to produce a variety of metals and metal alloys, the deposition of certain metals and their alloys can be accompanied by high levels of contamination during the sputter deposition process. For example, many refractory metals do not adhere well to metal surfaces commonly present in a sputter deposition chamber. During a sputter deposition process, in addition to depositing a metal layer on the semiconductor substrate, the metal being deposited from a sputtering target also coats the exposed metal surfaces within the sputter deposition chamber. If the sputtered metal does not adhere well to the metal surfaces within the deposition chamber, the sputtered metal can continuously peel away from the chamber surfaces and contaminate the film deposited on the semiconductor substrate.
One method of preventing film contamination from sputtering system components, is to disassemble the components of the chamber and individually coat the components with a metal having good adhesion properties. The individually coating of metal components requires that the vacuum chamber be open to ambient atmosphere, and each individual component removed and disassembled. In addition to requiring a large amount of time, and associated loss of production capacity, the individual component coating method exposes the coated components to oxygen in the ambient atmosphere. The coating metal can oxidize during periods prior to reinstallation into the sputtering apparatus. Aluminum is a commonly used adhesion metal, which readily oxidizes to form aluminum oxide. The formation of aluminum oxide is undesirable because aluminum oxide does not have the adhesion properties of elemental aluminum.
Another component passivation approach is to fabricate the internal components of the sputtering system from a metal which inherently has good adhesive properties. However, the fabrication of internal components from an adhesive metal is expensive and can compromise the structural integrity of the sputter deposition system. Additionally, whenever the sputtering system is open to atmosphere, the internal components can be subject to oxidation. Accordingly, further development of sputter deposition processes is necessary to provide high-purity sputter deposited metal films, while avoiding excessive expense and loss of production time.