Plasma processing apparatus and plasma processing method

1. A plasma processing method using an etching amount detecting unit for processing a film to be processed comprising a layers structure preliminarily arranged on an upper surface of a wafer mounted in a processing chamber inside a vacuum vessel, by using plasma generated in the processing chamber, wherein the layers structure comprises the film to be processed and an underlying film which comprises SiO 2 as a material, the method comprising steps of:

detecting an intensity of interference light of plural wavelengths obtained from a surface of the wafer during the processing;

detecting time-series data of time-derivative based on the intensity of the interference light of plural wavelengths detected at an arbitrary time during the processing;

detecting actual differential waveform pattern data using wavelengths as a parameter by using the time series data regarding the plural wavelengths;

calculating a residual film thickness at the arbitrary time using a result of comparing detective differential waveform pattern data with the actual differential waveform pattern data, wherein the detective differential waveform pattern data is produced using two basic differential waveform pattern data of the intensity of the interference light using wavelengths of the interference light as parameters, each of the two basic differential waveform pattern data being indicative of residual thicknesses of the films to be processed that are contained in each of two separate layers of the layers structure, wherein the underlying film thicknesses of each of the two separate layers are different, the detective differential waveform pattern data being preliminarily prepared prior to the processing of the wafer, and wherein the two basic differential waveform pattern data are interpolated by using a ratio of minimum differences between each of the two basic differential waveform pattern data and the actual differential waveform pattern data to thereby produce detective differential waveform pattern data; and

determining by the etching amount detecting unit whether or not an endpoint of the processing has been reached by using the residual film thickness thus calculated and terminating the processing if the endpoint has been reached.

2. The plasma processing method according to claim 1 , wherein

at each of a plurality of times during the processing, the detective differential waveform pattern data is produced using the two basic differential waveform pattern data; and

the residual thickness at the each time is calculated using a result of comparing the detective differential waveform pattern data with the actual differential waveform pattern data at the each time.

3. The plasma processing method according to claim 1 , wherein

at the arbitrary time, the detective differential waveform pattern data and the actual differential waveform pattern data are compared with each other and a residual thickness which is corresponding to a differential waveform pattern at which a difference as a result of comparison therebetween becomes minimum is stored as a residual film thickness at the arbitrary time,

by using the residual film thickness at the arbitrary time and the residual film thickness at a time prior to the arbitrary time, a residual thickness at the arbitrary time is calculated again, and

determination is made as to whether the target of the processing has been reached by using the residual film thickness calculated again.