Abstract : Today, large-scale processing with high density and uniform plasma is necessary for surface treatments that need highly uniform etching or deposition rates. Thus, the objective of this new kind of plasma is to produce a sheet of high density, uniform plasma in the 100 Pa pressure range. Plasma scaling up can be achieved by distributing elementary microwave plasma sources over bi or tri-dimensional networks. This concept is applied to a planar reactor comprising 4 × 3 microwave plasma sources distributed according to a square lattice matrix configuration (with a lattice mesh of 40 mm). In each elementary plasma source, the plasma is produced at the end of a coaxial applicator implemented perpendicularly to the planar source. In the low microwave power range and high pressure range, a localized plasma with azimutal symmetry can be observed around each coaxial applicator. When increasing the microwave power, the localized plasmas expand and then meet together to produce a sheet of uniform plasma. Argon plasmas, that can be sustained in the medium pressure range from 7.5 to 750 Pa, were characterized by using Langmuir probes. The sheet of plasma thus obtained becomes uniform at a distance from the source plane of 15-20 mm, i.e., less than half the lattice mesh of the matrix network. Results show that the plasma can reach densities between 10^12 and 10^13 cm^-3 with a uniformity better than ± 3.5 % at 20 mm from the source plane. The decrease in the electron temperature observed when increasing the microwave power can be justified by the apparition of a two-step ionization mechanism via argon metastable atoms, whose temperature and concentration were measured by laser diode absorption spectroscopy. Analytical and numerical one dimension modelling was presented and permits to justify the assumptions on creation and loss mechanisms. Finally, in order to test matrix plasmas for applications to surface treatments, films of SiOCH and SiNCH were deposited by PACVD in order to evaluate the deposition rate and the uniformity of the films. The deposition rates obtained exceed the µm/min and the films are uniform.