Polishing apparatus and polishing method
A polishing apparatus is used for polishing and planarizing a substrate such as a semiconductor wafer on which a conductive film such as a copper (Cu) layer or a tungsten (W) layer is formed. The polishing apparatus includes a polishing table having a polishing surface, a motor for rotating the polishing table, a top ring for holding a substrate and pressing the substrate against the polishing surface, a film thickness measuring sensor disposed in the polishing table for scanning a surface of the substrate, and a computing device for processing signals of the film thickness measuring sensor to compute a film thickness of the substrate.
1. A polishing method for polishing a substrate by pressing the substrate against a polishing surface on a rotating polishing table, the polishing method comprising:
scanning the substrate with a film thickness measuring sensor disposed in the polishing table and outputting a sensor signal;
generating a representative value from the sensor signal of the film thickness measuring sensor generated during a previous rotation of the polishing table;
outputting a corrected signal, the corrected signal having the representative value when a value of the sensor signal of the film thickness measuring sensor generated during a current rotation of the polishing table is larger than the representative value and having the value of the sensor signal of the film thickness measuring sensor generated during the current rotation of the polishing table when the value of the sensor signal of the film thickness measuring sensor generated during the current rotation of the polishing table is smaller than the representative value; and
computing a film thickness of the substrate from the outputted corrected signal.
2. The polishing method according to claim 1 , wherein scanning data on the substrate obtained by the film thickness measuring sensor is divided into a plurality of zones having a size larger than a die formed on the substrate, and said computing of the film thickness of the substrate comprises processing a sensor signal of the film thickness measuring sensor in each of the plurality of zones on the substrate using a respective representative value generated in each of the plurality of zones.
3. The polishing method according to claim 1 , wherein said generating of the representative value comprises generating the representative value from the sensor signal of the film thickness measuring sensor generated during an immediately preceding rotation of the polishing table.
4. The polishing method according to claim 1 , wherein said generating of the representative value comprises generating the representative value by adding a predetermined correction value to a minimum value of the sensor signal of the film thickness measuring sensor within a certain period of time.
5. The polishing method according to claim 4 , wherein said generating of the representative value comprises obtaining the predetermined correction value by multiplying a difference between a maximum value and the minimum value of the sensor signal of the film thickness measuring sensor within the certain period of time by a predetermined coefficient.
6. The polishing method according to claim 1 , wherein the film thickness measuring sensor comprises at least one of an eddy current sensor, an optical sensor and a microwave sensor.
7. The polishing method according to claim 1 , wherein the film thickness measuring sensor comprises an eddy current sensor.