Flooring Tile - 2 layers hardibacker on countertop

Hello
Can I use 1/2" hardibacker instead of plywood as a base for countertops? Right now the cabinents have been framed with 2x4 s for a base they run along the front and back and between each drawer (maybe a little overkill) . I was planning on putting 1/2 inch hardibacker over the cabinets and securing it with screws then apply modified thinset with a 1/4 inch notched trowell then place 1/4 hadibacker over the thinset and securing it with screws. Then lay 12x12 marble tile. My thought was to keep the plywood out so there is less chance of water swelling the base. So is there a specific reason to use plywood (is it moe ridgid than Hardibacker).
so please all you knowledgeable people pleas give me some advice.
Thank you

Use 3/4" plywood with 1/4" hardi thinsetted(unmodified) and screwed. The hardi is not structural like the plywood. If you are concerned about water getting through to the plywood you could redgard the hardi.

I'd like to see another 1/2" of plywood over the 3/4".:)