Method for controlling a line dimension arising in photolithographic processes

In a photolithographic process utilizing a wafer coated with a chemically amplified photoresist, a method for controlling a line dimension in a photoresist pattern, the method comprising the steps of:

• (1) measuring, at least two times and from at least two angles, time evolving signals comprising intensities of light diffracted from a portion of an exposed patterned area on a wafer, said measuring being performed during a post-exposure bake of the wafer,
• the evolving signals corresponding to vector combinations of
• (i) time dependent light diffracted from the pattern appearing in the photoresist;
• and
• (ii) substantially time invariant light diffracted due to any underlying pattern beneath the photoresist;
• (2) combining the measurements for detecting a change in the signal over time thereby obtaining a measure of the strength of the latent image;
• and
• (3) comparing said measure of the strength of the latent image to a predetermined value correlated to a desired line dimension in the photoresist pattern to terminate the bake when an end point condition is met.