Photo mask provided with development rate measuring pattern and method for measuring development rate uniformity

A method for measuring development rate uniformity using a photo mask with development rate measuring patterns, each of said patterns comprising a plurality of lug-shaped dots arranged in a first matrix and a plurality of depression-shaped dots arranged in a second matrix, said method comprising the steps of:

• using the photo mask with the development rate measuring patterns in a photolithography process to expose a wafer at center, upper, lower, left and right positions with reference to a center position of the wafer;
• developing the wafer during the photolithography process;
• selecting a reference dot from the plurality of lug-shape dots and the plurality of depression-shape dots that has a minimum dimension and is still distinct from the development rate measuring patterns at the center, upper, lower, left and right positions;
• combining said reference dots from the center, upper, lower, left and right patterns to form a group;
• calculating a development rate uniformity by subtracting the minimum dimension of said reference dots of said group from the maximum dimension of said reference dots of said group.