Hi Ganesh,
As far as I know, SFTP is not supported as of yet.
1782625 - Is Secure FTP supported with SAP BI4.0 as a Scheduling Destination
1556571 - Does BusinessObjects Enterprise 3.1 support Secure FTP as a scheduling destination as it does with regular FTP?
However you can do a bit of research on the internet to find a workaround .
Regards,
RVS