Your cat may be itching in general and chosen that at his spot to attack, he may do it as a started habit due to stress, or it could be another reason.
While you can try a collar, unless you try to get to the root of the problem, he is likely to pick another place to attack that he can reach in spite of his collar.
You might consider if he has a food or litter allergy. Some cats have a problem with wheat gluten, so you might try an elimination of that, if it is in his food (even commercial wet food often has it in there- I've found some of the pouched Whiskas don't have that gluten, but not all). You might try sprinkling a little flaxseed meal in his food (flax oil has omega fatty acids good for inflammation).
You might try to make sure his skin is not too dry. (Is it dry where you live right now? Do you bathe him using a product that might be drying out his skin?)
You might try a little neosporin on the wound as it is quite possible some infection is there and put a thick baby shirt on his back (our cat finally stopped biting in that area by that method but she gets at a hind leg presently).
Hey Pips,
If its abscessed and that's why he keeps on scratching, you need to get him on some Antibiotics. But if you're ABSOLUTELY sure its not infected, call the Animal Shelter closest to you and see if you can get a free medical collar (shame cone) to put on him tell it heals.