Method of measuring pore depth on the surface of a polishing pad

A method of measuring pore depth on the surface of a polishing pad during processing, wherein the polishing pad is disposed on a rotation plate of a polishing machine, the method comprising:

• providing a planar ultrasound sensing device disposed a predetermined distance above the surface of the polishing pad;
• sending out a plurality of ultrasound signals to the surface of the polishing pad and pores therein;
• receiving a plurality of reflected signals from the pad surface and constituent pores;
• determining the difference between pore depth and the surface to establish first depth difference data according to the time delay in the reflected signals;
• rotating the polishing pad and sending, receiving and determining the difference between pore depth and the surface to establish second to Nth depth difference data;
• computing the size of the pores on the polishing pad according to the first to Nth depth difference data;
• and
• converting the first to Nth depth difference data into a relational image relative to the surface and the pores of the polishing pad.