Method for making a well disposed over a sensor

A method for forming a well providing access to a sensor pad, the method comprising:

• patterning a first photoresist layer over a dielectric structure disposed over the sensor pad;
• etching a first access into the dielectric structure and over the sensor pad, the first access having a first characteristic diameter;
• depositing a bottom anti-reflective coating following etching the first access, wherein the bottom anti-reflective coating is at least partially disposed in the first access;
• patterning a second photoresist layer over the dielectric structure after depositing a bottom anti-reflective coating;
• and
• etching a second access over the dielectric structure and over the sensor pad, the second access having a second characteristic diameter, the first and second accesses overlapping, a diameter ratio of the first characteristic diameter to the second characteristic diameter being not greater than 0.7, the first access exposing the sensor pad, the second access having a bottom depth less than a bottom depth of the first access.