Unless you have severe perennial weeds like horsetail, brambles, knotweed or bindweed, you don't need to do this as most weeds appear in the top millimetre of soil. Even if you created a raised bed full of sterilised soil, within a few months you would find weeds appearing in it as weed seeds blow around in the air from miles around. You would have to cover your bed completely to prevent this.
As we are surrounded by willow trees here, even pots at the end of the season are full of tiny willow trees as the willow seeds get everywhere.
Depending on what you are growing in your raised bed, it would be better to spend your money on mulches which protect the soil and from which you can handweed the weed seedlings more easily.