Polishing method

A method of polishing a thin film layer to be polished, which is formed on the surface of a substrate, by pressing said substrate on the surface of a polishing pad and relatively moving said substrate and said polishing pad. said method comprising the steps of:

• directly detecting the distance from the position of a front surface of said thin film layer to be polished to the position of a bottom surface of said thin film layer using a sensor on the way of said polishing;
• calculating the residual thickness of said thin film layer on the basis of said detected distance;
• and
• controlling the processing condition of the subsequent polishing on the basis of the calculated residual thickness of said thin film layer;
• wherein said sensor is provided on the side of said polishing pad in such a manner as to face the surface of said substrate, and the distance between the positions of the front and bottom surfaces of said thin film layer is directly detected as a differential value between the distance from said detector to the front surface of said thin film layer and the distance from said detector to the bottom surface of said thin film layer.