The authors developed a ceramic upper shower plate used in the microwave-excited high-density plasma process equipment incorporating a dual shower-plate structure to establish a very uniform gas-flow pattern in the process chamber. Thousands of very fine gas-injection holes are implemented on this Al2O3 upper shower plate with optimized allocation to establish a uniform gas-flow pattern of plasma-excitation gases and radical-generation gases for generating intended radicals in the plasma-excitation region. The size of these fine holes must be 50 μm or less in diameter and 8 mm or more in length because these holes perform an essential role: They completely avoid the plasma excitation in these fine holes and upper gas-supply regions resulting from the plasma penetration into these regions from excited high-density plasma, even if very high-density plasma greater than 1×1012 cm-3 is excited just under the ceramic upper shower plate by microwaves supplied from the radial line slot antenna. On the other hand, various process gases, such as material gases for film formations and etching gases, are supplied from the lower shower plate installed in the diffusion plasma region to this very uniform gas-flow pattern region of plasma-excitation gases and radical-generation gases. As a result, the process gases are supplied to the wafer surface in a very effective manner without excess decomposition of those process gas molecules and undesired reaction-product deposition on the inner surface of the process chamber. The process results are improved drastically by introducing the newly developed ceramic upper shower plate. But also, process uniformity on the entire wafer is improved with drastically reducing reaction-product deposition on the inner sur- face of the process chamber.