A large-area rectangular modified-magnetron-type (MMT) radio frequency (RF) plasma source is newly developed and the properties are investigated in detail for producing a large-area uniform plasma. A quite uniform plasma with density variation less than several percent is produced in front of the rectangular substrate of 830 x 650 mm(2). The spatial plasma uniformity is controlled znot only by employing an upper auxiliary electrode but also by putting permanent magnets on the auxiliary electrode in several patterns. We now produce more uniform plasma by using auxiliary permanent magnets put on the upper auxiliary lid electrode.