Properties of aluminum films deposited by low energy and high density ion bias sputtering method using cusp magnetic field electrode

To improve both aluminum film properties and step coverage in contact and via holes, a low-energy and high-density ion bombardment bias sputtering method at medium substrate temperature (under 400°C) using a cusp magnetic field electrode was developed. Properties of aluminum films deposited under different conditions are evaluated to determine the correct substrate bias voltage (-50 V) and bias current (20 mA/cm²). By proper selection of processing parameters, aluminum films with high (111) preferred orientation, low mechanical stress, low Ar content, and high electric conductivity can be obtained. A cusp magnetic field electrode designed for this purpose made high-uniformity and high-density substrate bias Ar ion bombardments possible. The aluminum film coverage observed by scanning electron microscopy (SEM) in a via hole with a 2-μm diameter and 1.7-μm depth is over 40% with this method and 20% with conventional magnetron sputtering. The improvement of aluminum coverage was observed with tapered vias that ensure effective bias argon ion bombardments on the aluminum film on the via hole walls