Etching method and apparatus

Abstract

An etching method capable of controlling the film thickness of a hard mask layer uniformly is provided. A plasma etching is performed on a native oxide film by using an etching gas containing, for example, CF 4 and Ar while a thickness of a silicon nitride film is being monitored and the etching is finished when the thickness of the silicon nitride film reaches a predetermined value. Then, a plasma etching is performed on a silicon substrate by employing an etching gas containing, for example, Cl 2 , HBr and Ar and using the silicon nitride film as a mask while a depth of a trench is being monitored and the etching is finished when the depth of the trench reaches a specified value.

1 . An etching method of a substrate to be processed including a mask layer having a pattern; a native oxide film to be etched, formed in a groove portion of the pattern; and a silicon layer formed beneath the mask layer and the native oxide film to be etched, wherein the native oxide film is formed on a surface of the silicon layer in the groove portion, the etching method comprising:
 performing a first etching on the mask layer and the native oxide film by using a first plasma and monitoring a thickness of the mask layer during the first etching, wherein the first etching is finished when the thickness of the mask layer is reduced to a threshold value;   performing a second etching on the silicon layer by using a second plasma, wherein the etched mask layer is used as a mask.   
     
     
         2 . The etching method of  claim 1 , wherein the mask layer is a silicon nitride film. 
     
     
         3 . The etching method of  claim 1 , wherein, an etched depth of the silicon layer is monitored during the second etching and the second etching is finished when the etched depth reaches a specified value. 
     
     
         4 . The etching method of  claim 1 , which is applied to a trench etching in shallow trench isolation. 
     
     
         5 . The etching method of  claim 4 , wherein the monitoring of the thickness of the mask layer involves the steps of:
 irradiating a light to the mask layer;   detecting a reflected light from a surface of the mask layer and a reflected light from an interface between the mask layer and the silicon layer;   calculating a spectral reflectance; and   measuring the thickness of the mask layer based on a calibration curve obtained in advance by employing a curve fitting method.