According to an aspect of the invention, there is provided a polishing liquid for polishing a barrier metal material on an interlayer insulation material, the polishing liquid having a pH of from 2. The buoyancy control system may utilize an incompressible fluid that is transferred between a first internal reservoir and an external chamber to affect buoyancy of the underwater vehicle. The controllable current source provides an output current according to a control signal and produces a feedback signal according to the output of the controllable current source. This may result in a total isolation of the foundation from the earthquake wave energy.