Film thickness measuring method, polishing method, fabrication method of thin film magnetic head and substrate for forming the thin film magnetic head

A method of measuring a film thickness comprising the steps of:

• forming, on a surface, a first element formation layer structuring a portion of an element and at least one dummy layer which does not contributes to the structure of the element;
• forming a first planarized layer planarized by polishing a surface until a surface of the first element formation layer and the surface of the dummy layer expose after embedding and coating the first element formation layer and the dummy layer;
• forming a second element formation layer structuring a portion of the element on the first planarized layer;
• forming a second planarized layer planarized by polishing a surface until the surface of the second element formation layer exposes from the embedded layer after embedding and coating the second element formation layer with a predetermined embedding material;
• measuring a film thickness of the embedded layer on the dummy layer;
• and
• measuring a film thickness of the second element formation layer based on the film thickness of the embedded layer.