A 2-D scalable, VHF/UHF compatible, capacitively coupled plasma source for large-area applicaiton

摘要

A novel plasma source topology is described. The design is similar to a traditional capacitive diode, except the powered electrode is divided into a 2-dimensional tile array. Neighbouring tiles are powered 180-degree out of phase. Current coupled to the plasma through one tile is canceled by the neighboring tile, resulting in zero net current into the plasma and substrate. In this way, wavelength-effects causing center-to-edge voltage non-uniformities are avoided. This breaks the relationship between substrate size and rf frequency, enabling high-VHF to UHF frequency capacitive plasma sources for application to large area substrates. Plasma density profiles for a 300mm size system have good uniformity at 400 MHz, where the plasma loaded wavelength is about 50mm. The electromagnetic coupling in this configuration is considered. A 600x720 mm~2 multi-tile plasma source operated at 162 MHz is used to deposit PECVD Silicon with a narrow plasma gap (as low as 6mm) giving good uniformity films, without the 1/4-wavelength voltage non-uniformity effects.