The present disclosure relates to some embodiments of a method for improving processing efficiency of a cluster tool. The method comprises transferring a first lot of wafers from a transfer load lock to a designated storage load lock and transferring a second lot of wafers from the transfer load lock to the designated storage load lock while the first lot of wafers is in the transfer load lock or the designated storage load lock. The designated storage load lock has the same structure as the transfer load lock and respectively has an inner load lock portal at an interface with the first transfer chamber and an outer load lock portal on a sidewall of a front end interface. The inner load lock portal of the designated storage load lock is retained opened during processing. The outer load lock portal of the designated storage load lock is retained closed during processing.