RMAN type sbt_tape?

[bab]

Hi,
I am taking backup from tdp client of Oracle database,RMAN type should be "sbt_tape"? 
is it possible to I can specify type DISK.I want backup should go to diskpool and then 
data should migrate to tapepool.My copygroup- copy distination is pointing 
diskpool,but at the time of backup,it is asking tape?