Auger attachment for 68,000 lb. excavator - 2 ft. hole by 20 deep

Need to dig some 2 ft. wide by 20 ft. deep piling holes. Would like to use my 290G Deere. Who makes augers to clip on the excavator. Or do I have to use a drill when going that deep? Guessing I have to take the arm off to run this attachment and lift the bit out when full of dirt every 3-5 deep deep? Digga is the only one I'm finding. Like to rent it for 2-3 days kinda deal.

Auger attachment for 68,000 lb. excavator - 2 ft. hole by 20 deep