Patent ID: 7101257

Claim:
A substrate polishing apparatus comprising: a rotatable polishing table against which a substrate is pressed, said rotatable polishing table having a fluid chamber provided at a light emitting and light-receiving position thereof; a light-emitting and light-receiving device to emit measurement light from said rotatable polishing table to the substrate and to receive reflected light from the substrate; a first passage for a high flow rate, said first passage introducing a fluid, through which the measurement light and the reflected light pass, to said fluid chamber of said rotatable polishing table; a second passage for a low flow rate, said second passage being restricted as compared to said first passage for the high flow rate which introduces the fluid to said fluid chamber; a rotational angle sensor for detecting an angular position of said rotatable polishing table in a rotation direction of said rotatable polishing table; and a switching unit for switching into which of said first and second passages the fluid is introduced based on a detection signal of said rotational angle sensor.