Method for manufacturing a magnetoresistive sensor

A method for manufacturing a magnetic sensor, the method comprising:

• depositing a series of sensor layers;
• depositing a series of mask layers over the series of sensor layers, the series of mask layers including an under-layer, a Si containing hard mask layer deposited over the under-layer and a photoresist layer deposited over the Si containing hard mask;
• photolithographically patterning the photoresist layer to form a photoresist mask;
• performing a first reactive ion etching to transfer the image of the photoresist mask onto the Si containing hard mask layer to form a patterned hard mask, the first reactive ion etching being performed in a chemistry that includes CF4, CHF3, O2, and He;
• performing a second reactive ion etching to transfer the image of the patterned hard mask onto the under-layer to form a patterned under-layer;
• and then
• performing an ion milling to remove portions of the series of sensor layers that are not protected by the patterned under-layer.