Polishing apparatus and polishing method

A polishing method comprising:

• measuring a thickness of a film formed on a substrate;
• inputting a desired thickness of the film formed on the substrate;
• storing polishing rate data on at least two lately polished substrates in a storage device, the at least one past substrate being recently polished;
• calculating a polishing rate and an optimal polishing time based on the polishing rate data and the desired thickness of the film formed on the substrate by using a weighted average method which weights the polishing rate data on the at least two lately polished substrates;
• and
• polishing the substrate for the optimal polishing time,
• wherein the weighted average method includes setting a weight coefficient for each lately polished substrate, and
• wherein the weight coefficient for a most recently polished substrate of the at least two lately polished substrates is larger than the weight coefficient for a less recently polished substrate of the at least two lately polished substrates.

A polishing method comprising:

• polishing a first substrate;
• after polishing the first substrate, storing polishing rate data on the first substrate in a storage device;
• after polishing the first substrate, polishing a second substrate;
• after polishing the second substrate, storing polishing rate data on the second substrate in the storage device;
• measuring a thickness of a film formed on a third substrate;
• inputting a desired thickness of the film formed on the third substrate;
• calculating a polishing rate and an optimal polishing time for the third substrate based on the polishing rate data on the first substrate, the polishing rate data on the second substrate, and the desired thickness of the film formed on the third substrate by using a weighted average method in which the polishing rate data on the second substrate is weighted more heavily than the polishing rate data on the first substrate;
• and
• polishing the third substrate for the optimal polishing time.