Method for processing workpiece

A method for processing comprising:

• providing a workpiece including an etching target layer, a mask provided on the etching target layer, and an opening provided in the mask extending from a top surface of the mask to the etching target layer so as to expose the etching target layer;
• and
• removing the etching target layer, for each atomic layer, through repetitive execution of a sequence including:
• a first process of generating plasma of a first processing gas within a processing container of a plasma processing apparatus where the workpiece is accommodated, and forming a mixed layer containing ions included in the plasma of the first processing gas, on an atomic layer of a surface of the etching target layer through the opening;
• a second process of purging a space within the processing container after execution of the first process;
• a third process of generating plasma of a second processing gas within the processing container, and removing the mixed layer by radicals included in the plasma of the second processing gas after execution of the second process;
• and
• a fourth process of purging the space within the processing container after execution of the third process,
• wherein the etching target layer contains silicon oxide, the first processing gas contains nitrogen, and the second processing gas contains fluorine,
• the plasma of the second processing gas generated in the third process contains the radicals that remove the mixed layer containing silicon nitride, and
• in the first process, a bias voltage is applied to the plasma of the first processing gas so as to form the mixed layer containing the ions on the atomic layer of the surface of the etching target layer.