When a semiconductor device or an FPD (flat panel display) is microprocessed by using a plasma, it is extremely crucial to control a temperature and a temperature distribution of a substrate and a plasma density distribution on a substrate to be processed (a semiconductor wafer, a glass substrate or the like). If the temperature of the substrate is not properly controlled, it is difficult to secure process uniformity on a surface of the substrate, thereby deteriorating a production yield of a semiconductor device or a display device.
Generally, a mounting table or a susceptor for mounting thereon a substrate to be processed inside a chamber of a plasma processing apparatus, especially a capacitively coupled plasma processing apparatus, functions as a high frequency electrode for applying a high frequency power to a plasma space, as a support member for supporting a substrate by an electrostatic adsorption or the like and as a temperature control unit for controlling the substrate at a predetermined temperature by heat conduction. The mounting table serving as the temperature control unit is required to properly compensate a heat distribution caused by a substrate supporting structure or a distribution of heat transfer characteristics on the substrate caused by nonuniformity of a radiant heat from a plasma or a chamber wall.
Conventionally, in order to control a temperature of a top surface of the susceptor (and further a temperature of the substrate), there has been widely used a method for supplying a coolant whose temperature controlled by a chiller unit into a coolant passageway provided inside a susceptor or a susceptor support to be circulated therein. However, the above method is disadvantageous in that it is difficult to change a temperature of the coolant at a high speed and, also, the temperature cannot be raised and lowered at a high speed due to poor responsiveness in temperature control. Recently, a plasma processing, e.g., a plasma etching, requires a method for successively processing a multilayer film on a substrate to be processed inside a single chamber instead of multiple chambers. In order to implement such method, it is crucial to have a technique capable of raising and lowering a temperature of a mounting table at a high speed. For the above reasons, a heater capable of precisely controlling a susceptor temperature and further a substrate temperature at a high speed by controlling Joule heat of a heating element is attracting attention again.
Meanwhile, in case where a lower plate dual frequency application type in which a high frequency power supply is connected to a susceptor in view of plasma control and the above heater in which a heating element is provided in a susceptor in view of temperature control are used at the same time, if a part of a high frequency applied to the susceptor enters a heater power supply via a heater power feed line, an operation or a performance of the heater power supply may deteriorate. Especially, the heater power supply capable of high-speed control performs an ON/OFF control or a switching control with high sensitivity by using a semiconductor switching device such as an SSR (solid state relay) or the like, so that misoperation may easily occur by high frequency noise. To that end, it is common to provide in the heater power feed line a filter circuit for efficiently reducing the high frequency noise.
Generally, such filter circuit includes a plurality of LC low pass filters each having a single coil (inductor) and a single capacitor, the LC low pass filters being connected at multiple stages in the form of a ladder. For example, if the high frequency noise can be reduced by 1/10 in each stage of the LC low pass filter, it can be reduced by 1/100 in a second-stage connection and to 1/1000 in a third-stage connection.
(Patent Document 1) Japanese Patent Application Publication No. 2006-286733
As set for the above, in the conventional plasma processing apparatus, the function of the filter circuit provided in the heater power feed line focuses on reducing the high frequency noise from the high frequency power supply via the susceptor in view of ensuring normal operation and performance of the heater power supply. Thus, a coil having a small inductance and a capacitor having a large capacitance are used in each of the LC low pass filters in the filter circuit.
However, the inventors of the present invention have found, during the development and the evaluation of a plasma processing apparatus using a heater in a susceptor together with applying a high frequency power to a lower plate, that the conventional filter circuit has a problem in processing performance. Namely, they have found that the RF power loss in the conventional filter is so large that it cannot be neglected in the processing performance, in addition to a known fact that a predetermined correlation exists between a processing performance (e.g., an etching rate) and a loss of high frequency power applied from a high frequency power supply to a susceptor (i.e., the processing performance deteriorates as the RF power loss increases). Moreover, the inventors of the present invention have found that the RF power loss in the filter circuit is not determined by the circuit design, and varies even between plasma apparatuses of a same configuration, thereby causing differences in the processing performance. The inventors of the present invention have conducted numerous tests and wholehearted studies by considering the above drawbacks, thereby conceiving the present invention.