My cat keeps opening the same wound on his neck and I don't know what to do

So my cat is nearly 5 years old, and he occasionally scratches his neck. The first time was when he was younger, like 2, and now at 4. He's an indoor cat and very healthy, but his back claws are long, and the vet has stated he doesn't need clipping since he sheds them off and doesn't need to. However, whenever he scratches, he causes a small gash in his neck, which, when healing, does itch over time, causing him to scratch more and more, removing patches of hair. Right now it's like the length of a penny, but I'm worried it'll grow and we have a flower cone collar that's plush so he's comfortable and he doesn't touch it BUT as soon as I take it off after a few hours, he goes right back to scratching it and I'm very new to this so any info will be greatly appreciated.