Plasma processing apparatus

The present invention relates to a plasma processing apparatus for performing plasma processing to a processing object such as a wafer or the like.

As apparatuses for performing surface treatment of processing objects such as wafers or the like, there have been known plasma processing apparatuses. A plasma processing apparatus operates to produce plasma under a reduced-pressure atmosphere to allow a surface of a processing object to be subjected to etching processing or the like by physical and chemical actions of the plasma. Plasma is generated by applying a high-frequency voltage to an upper electrode or lower electrode while the internal pressure within a sealed processing chamber of the plasma processing apparatus is reduced to a specified pressure with a plasma-generation gas (hereinafter, referred to simply as ‘gas’) fed thereto.

For such plasma processing, it is desirable in some cases to generate high-density plasma depending on the aim of processing. For example, in plasma etching targeted for silicon substrates such as wafers or the like, a process of uniformly spraying and feeding a relatively high-pressure gas to a surface of a silicon wafer is used with a view to improving the processing efficiency.

Known parallel-plate electrode members suited for such plasma processing formed of a gas-permeable porous plate which is a sintered body of ceramic particles (see, e.g., Japanese unexamined patent publication No. 2002-231638 A, JP 2003-7682 A and JP 2003-282462 A). With the use of such a porous plate, it becomes possible to uniformly generate high-density plasma so that a stable plasma processing is carried out with high etching efficiency.

With a processing object set on a stage which is the lower electrode within the processing chamber, as plasma processing is started by applying a high-frequency voltage to the upper electrode or lower electrode, the porous plate provided on one side closer to the upper electrode, which is a counter electrode to the lower electrode, rapidly increases in temperature. Whereas the porous plate typically has a diameter of about 220 mm or 320 mm and a thickness of about 2 to 10 mm, the porous plate does not increase in temperature uniformly as a whole, but does increase in temperature first rapidly in vicinities of a central portion of a counter surface (normally, lower surface) confronting the lower electrode (typically, rapidly increases from normal temperature to approximately 200° C. for about 30 seconds), and then increases in temperature gently at an outer edge portion of the porous plate more slowly than in the vicinities of the central portion. As a result, strain due to nonuniform temperature increases occurs to the porous plate, so that cracks might occur at the outer edge portion of the porous plate (for example, radial cracks occur to outer peripheral edge portions because the porous plate is generally a disc-shaped). This might cause the porous plate to be fractured and thus damaged, disadvantageously.

Accordingly, an object of the present invention, lying in solving the above problem, is to provide a plasma processing apparatus in which damage due to occurrence of cracks in an outer edge portion of a porous plate caused by thermal expansion due to rapid temperature increases in plasma processing can be prevented, thus allowing a stable plasma processing to be carried out.

According to a first aspect of the present invention, there is provided a plasma processing apparatus comprising a first electrode unit having a placement surface on which a processing object is to be placed, and a second electrode unit facing the placement surface of the first electrode unit, and a processing vessel that defines a processing chamber in which the first and second electrode units are to be located, wherein a plasma-generation gas is supplied into a plasma processing space between the first and second electrode units so as to generate a plasma and then plasma processing on the processing object is performed,

the second electrode unit comprising:

• • a body portion having a gas supply port communicating with a gas supply passage;
  • a porous plate which is placed so as to cover the gas supply port and face the plasma processing space and which has gas permeability such that the gas supplied from the gas supply port is supplied to the plasma processing space through inside thereof; and
  • a support member which supports the porous plate on its outer edge portion so that the porous plate is fixedly placed to the body portion, wherein

a plurality of cutout portions are formed in the outer edge portion of the porous plate at a specified interval pitch so as to extend through the plate in a thicknesswise direction thereof.

According to a second aspect of the present invention, there is provided the plasma processing apparatus as defined in the first aspect, wherein