Method of forming contact plug in semiconductor device

1. A method of forming a contact plug of a semiconductor device, comprising the steps of:

forming a source/drain junction unit on a semiconductor substrate housing a surface;

forming an interlayer insulation film being one layer over the semiconductor substrate including the source/drain junction unit;

forming a contact hole by etching the interlayer insulation film;

forming a material for the contact plug over the interlayer insulation film;

forming a contact plug having a top surface in the contact hole by using an etch back process to expose a top surface of the interlayer insulation film;

selectively etching the interlayer insulation film using a wet etch process using an etchant so that the top surface of the contact plug becomes higher than the top surface of the interlayer insulation film; and

forming a metal layer on the interlayer insulation film including the contact plug.