1. Field of the Invention
The present invention relates to the deposition of a layer on a substrate. More specifically, the invention relates to deposition of a doped layer on a substrate.
2. Background of the Related Art
Consistent and fairly predictable improvement in integrated circuit design and fabrication has been observed in the last decade. One key to successful improvements is multilevel interconnect technology, which provides the conductive paths between the devices of an integrated circuit (IC) and other electronic devices. The conductive paths, or features, of an IC typically comprise horizontal interconnects (also referred to as lines) and vertical interconnects (also referred to as contacts or vias). The shrinking dimensions of features, presently in the sub-quarter micron range, has increased the importance of reducing capacitive coupling between interconnect lines and reducing resistance in the conductive features.
Aluminum has traditionally been the choice of conductive materials used in metallization. However, smaller feature sizes have created a need for a conductive material with lower resistivity than aluminum. Copper is now being considered as an interconnect material to replace or complement aluminum because copper has a lower resistivity (1.7 xcexcxcexa9-cm compared to 3.1 xcexcxcexa9-cm for aluminum) and higher current carrying capacity.
As a result of the desirability of using copper for semiconductor device fabrication, current practice provides for sputtering high purity copper targets. High purity is considered desirable in order to ensure that the low resistivity of copper is not affected by contaminants. However, the inventors have discovered that high purity copper films suffer from electromigration. Electromigration refers to the solid diffusion of ions in the presence of electric fields. Atoms in a conductive material are displaced as a consequence of a direct momentum transfer from the conduction electrons in the direction of their motion. The large flux of electrons interacts with the diffusing atoms in the metal lattice and sweeps these atoms in the direction of electron flow. The transport of mass causes removal of material in some locations, which generates voids and the accumulation of material in other locations. As a result, electromigration causes failures by opening interconnect lines.
Therefore, there is a need for an improved copper based target material which mitigates the problems of electromigration.
The present invention generally provides a method and apparatus for forming a target material having enhanced hardness. The target material is well suited for sputtering processes wherein a portion of the material is deposited on a substrate such as by physical vapor deposition (PVD) or Ionized Metal Plasma (IMP) PVD.
In one aspect, the invention provides a method of sputtering a layer on a substrate, comprising generating a plasma in a substrate processing chamber, sputtering material from a conductive target, the target comprising a material having a vickers hardness between about 100 and about 250, and depositing the sputtered material on the substrate. In one embodiment, the target includes copper and another material selected from the group of magnesium, zinc, aluminum, iron, nickel, silicon and combinations thereof.
In yet another aspect, a conductive material having enhanced hardness is deposited on a substrate. The material comprises at least copper and has a vickers hardness of between about 100 and about 250. In one embodiment, the material comprises primarily copper combined with another material selected from the group of magnesium, zinc, aluminum, iron, nickel, silicon and combinations thereof.