I would have suggested that you merely change the locks and if he breaks in, call the police.
Of course, you can go to a district justice and file an eviction Complaint. In the end, however, once you obtain an eviction notice, which is nothing but a piece of paper ordering your son out of your home, your son may still refuse to leave. In this event you will need to contact the sheriff to have him forcibly removed.
In either case, it appears you will need the authorities to have your son removed from the home.
I know as a mother this will be difficult, but I suggest you cut to the chase, change the locks and let him know you will call the police if he returns. Good Luck.