There are several possibilities for photoresist adhesion problems. Fortunately most are easily corrected. It very well could be that the wafers are either over or under primed. Overpriming usually happens with new types of resist that have very different molecular weight from the old, well established resist process. High resolution resists may have much lower mass and may need significantly shorter priming cycles.
There are a couple of ways of checking your coating. Depending on the type of resist coating equipment you have, you may be able to watch the resist spread during dispense. On an overprimed wafer, the resist will just ball up and run off the wafer instead of spreading out nicely. Another way of monitoring the coating is to stop the process after spread (before the ramp to final spin speed) and look to see if the resist has wetted the entire surface of the wafer.
When experiencing a photoresist adhesion problem, it is good to check the following:
If you still encounter issues, we invite you to ask a question.