Dear Prashant:
There are two types of STO (Stock transfer order)
Interplant:
You create the purchase order UB type, create outbound delivery, and receive the goods with reference of this outbound delivery. As the movements is between the same company code is not necessary to create an invoice.
In this case one plant is the supplying plant and the other plant is the receiving plant.
Intercompany:
You create the purchase order NB type, create outbound delivery, invoice the delivery, receive the goods with reference of this outbound. Make the invoice verification (this last step could be automatically)
As the movement is with different company codes is necessary to invoice the requirement from supplying plant to Receivig plant.
Please check it
Antonio Martínez