Method and structure for determining an overlay error

A method comprising:

• obtaining an intermediate structure comprising:
• a first layer;
• a second layer on top of the first layer;
• a masking layer over the second layer;
• a device area comprising:
• a first structure in the first layer having a top surface above a top surface of the first layer;
• the second layer in contact with the first structure such that the first structure is pinned in the second layer;
• and
• a first masking structure in the masking layer, overlapping the first structure;
• and
• an overlay metrology area comprising:
• a third structure in the first layer having a top surface above the top surface of the first layer;
• the second layer, in contact with the third structure, such that the third structure is pinned in the second layer;
• a second masking structure in the masking layer, overlapping the third structure;
• and
• a fifth structure in the first layer having a top surface above the top surface of the first layer;
• optically detecting a first distance between a feature of the second masking structure and a feature of the fifth structure;
• etching the second layer, by using the first masking structure and the second masking structure, so as to form a second structure in contact with the first structure, and a fourth structure in contact with the third structure;
• optically detecting a second distance between (1) a feature of the fourth structure that corresponds to the feature of the second masking structure and (2) the feature of the fifth structure;
• and
• making a comparison of the first distance and the second distance.