Can I tile over Linoleum felt paper on a concrete slab?
It is not uncommon to apply a coat of embossing compound over a firmly bonded vinyl floor, then tile right over it. It certainly is not my favorite method, but as long as the existing vinyl is well adhered and not curling at sides etc. the tile should stay down well.

Since you have already removed most of the vinyl, I would not worry too much about some left behind backer. Get as much off as you can, and don't leave any loose paper. If any of the leftovers will soften easily with water, soak them a bit and remove it. Other than that, if it is stuck good, go ahead and tile over it.