Large-area (> 40 cm in diam) high-density (similar to 10(12)) plasmas are produced by 2.45 GHz microwave discharge, usually under a large dielectric plate which is needed to excite surface waves propagating along the plasma-dielectric interface. However, such a dielectric plate is often unfavorable in practical applications. This article reports a technique for producing surface wave plasmas, in a metal vessel without using such a dielectric plate. When the microwave is injected from slot antennas without a dielectric plate, the plasma is locally generated around the slots with relatively low densities even at high incident powers. This problem is solved by introducing periodic grooves in a flat metal wall, which dramatically improve the plasma uniformity and increase the electron density as high as the dielectric plate case. The dispersion relation and surface impedance are compared between the dielectric wall case and the metal wall case, while the periodic groove effect is treated in an equivalent circuit model and physically explained.