Plasma confinement in a capacitively coupled VHF plasma reactor

Summary form only given. In order to minimize chamber contamination, to reduce cleaning time and cost, and to minimize process drift it is crucial to confine plasma in the process chamber preventing plasma penetrating to the downstream chamber. Plasma can be confined using physical confinement ring and/or by impedance confinement. In order to quantify the confinement level, we define the density ratio as the ratio of maximum plasma density below the confinement ring to that in the process chamber. The lower the density ratio, the better the plasma confinement. In order to design plasma confinement ring, plasma simulation has been performed to analyze the effectiveness of various confinement ring designs for a very high frequency capacitively coupled reactor. A confinement ring also increases chamber flow resistance adversely affecting the process window. Flow simulation has been performed to calculate pressure on wafer plane for different confinement ring gap widths. The confinement ring design is optimized not only to confine plasma but also to reduce flow resistance. To further improve the plasma confinement an innovative concept of impedance confinement has been analyzed using plasma simulation. An impedance parameter has been defined, and the density ratio is calculated. The impedance parameter has been optimized so as to achieve highly confined plasma. The impedance parameter can be controlled to increase plasma confinement during etch process, and to decrease plasma confinement during cleaning, as necessary