A subhalf-micron gap filling process for copper (Cu) films was developed by using an electron cyclotron resonance (ECR) plasma sputtering method. The achieved Cu film had a resistivity as low as that of bulk Cu and an excellent, void-free filling property in a 0.5-μm-wide trench. This result is because the distance between the target and wafer was longer than conventional sputtering; the plasma could be generated at low pressure (
