“Enlightenment” is an inaccurate translation of bodhi which means awake. So a Buddha is, literally, someone who is awake. In Zen, we don’t rest on our laurels — ooooh, I’ve had an experience of awakening and I’m done! Nope. Every time we have this kind of experience of awakening, we need to practice harder to deepen our awakening. Some forms of Zen emphasize awakening experiences (in Japanese, called kensho). Korean Zen tends to take them in stride. 

For more information see https://en.wikipedia.org/wiki/Enlightenment_in_Buddhism