Planar microwave discharges using slot antennas have been investigated as a large-diameter and uniform plasma source for material processing. A plasma with a high uniformity, a large diameter, and high density was obtained by using a multi-slotted planar antenna without forming standing wave of surface waves. A three dimensional calculation of wave propagation in the plasma was also performed with finite-difference time-domain scheme, and shows the close relation with experiment results. (c) 2005 Published by Elsevier B.V.