Method and apparatus for plasma processing
The invention provides a plasma processing apparatus capable of minimizing the non-uniformity of potential distribution around wafer circumference, and providing a uniform process across the wafer surface. The apparatus is equipped with a focus ring formed of a dielectric, a conductor or a semiconductor and having RF applied thereto, the design of which is optimized for processing based on a design technique clarifying physical conditions for flattening a sheath-plasma interface above a wafer and the sheath-plasma interface above the focus ring. A surface voltage of the focus ring is determined to be not less than a minimum voltage for preventing reaction products caused by wafer processing from depositing thereon. The surface height, surface voltage, material and structure of the focus ring are optimized so that the height of an ion sheath formed on the focus ring surface is either equal or has a height difference within an appropriate tolerance range to the height of the ion sheath formed on the wafer surface. Optimization of the structure is realized by setting up an appropriate tolerance range taking into consideration the variation caused by consumption of the focus ring.
1. A plasma processing apparatus for plasma processing an object, the plasma processing apparatus comprising:
a processing stage upon which the object to be processed is placed;
a focus ring disposed on the processing stage and surrounding the object to be processed;
an RF power supply for applying RF bias to the object to be processed and to the focus ring;
means for performing an equivalent circuit analysis and acquiring both a voltage on a surface of the object to be processed and the focus ring, and a sheath height on the surface of the object to be processed and the focus ring,
means for performing a two dimensional plasma analysis and a two dimensional electric field analysis, based on a result of the equivalent circuit analysis;
means for optimizing a configuration of the focus ring based on results of the two dimensional plasma analysis and the two dimensional electric field analysis, and based on a plasma-sheath interface flattening condition for making a first voltage drop of an RF voltage from the processing stage to a plasma-sheath interface above the object to be processed equal to a second voltage drop of an RF voltage from the processing stage to a plasma-sheath interface above the focus ring; and
means for making a sum of a surface height of the object to be processed and a sheath height of the surface of the object to be processed equal to a sum of a surface height of the focus ring and the sheath height of the surface of the focus ring,
wherein the first voltage drop is calculated based on a voltage on a surface of the object to be processed, and
wherein the second voltage drop is calculated based on a voltage on a surface of the focus ring.