When processing a substrate (wafer) in a semiconductor manufacturing process in a vacuum condition, temperature is controlled to make the surface temperature of the substrate uniform and to enhance processing uniformity. Temperature may be controlled by forming a coolant flow path within a substrate stage for mounting a substrate, allowing a coolant to flow through the flow path and cooling the surface of the substrate mounted on the substrate stage with radiant heat radiating from the substrate stage.
For example, Japanese Laid-Open Patent Publication No. (Hei) P9-17770 (hereinafter, JP9-17770A) discloses a plasma processing apparatus in which two concentric coolant flow paths are formed within a substrate stage. The temperature of the coolant flowing through the outer flow path differs from that of the coolant flowing through the inner flow path. Thus, the peripheral portion of a substrate exposed to radiant heat radiating from the inner wall of a chamber is cooled more heavily than the central portion of the substrate, thereby making the surface temperature of the substrate uniform.
In the plasma processing apparatus disclosed in JP9-17770A, however, the two coolant flow paths, through which coolants differing in temperature flow, are arranged adjacent to each other within one substrate stage. Thus, the temperatures of the two coolant flow paths affect each other, and there is a concern that the cooling operations of the central portion and the peripheral portion of the substrate cannot be independently controlled. In other words, it becomes impossible to precisely manage and control the temperatures of the central portion and the peripheral portion of the substrate mounted on the substrate stage. This makes it difficult to have the temperature of the substrate uniform over the entire surface since the temperature of the peripheral portion of the substrate is greatly influenced by the radiant heat radiating from the inner wall of a chamber while the temperature of the central portion of the substrate is less affected by the radiant heat. Thus, since the conditions of the entire surface of the substrate are not kept uniform when processing the substrate, there is a problem that the substrate cannot be processed uniformly. The integral formation of the substrate stage within the plasma processing apparatus is also the reason why the temperatures of the two coolant flow paths have an influence on each other and the temperatures of the central portion and the peripheral portion of the substrate cannot be independently controlled. Further, since the two coolant flow paths are provided independently, coolant supply and discharge pipes are required for the inlet ports and the outlet ports of the respective coolant flow path, which poses a problem that the number of pipes required in the plasma processing apparatus is increased and the piping arrangement becomes complicated.
In the plasma processing apparatus disclosed in, e.g., JP9-17770A, the substrate is usually held on the substrate stage by an electrostatic chucking method or the like. Thus, a temperature change in the substrate stage tends to directly cause a temperature change in the substrate surface. This makes it fairly easy to manage and control the temperature of the substrate surface. In contrast, in a substrate processing apparatus of the type in which a substrate is held on a substrate stage with a gap left between the substrate and the substrate stage, the temperature of the substrate surface is managed and controlled by radiant heat radiating from the substrate stage. In this case, a temperature change in the substrate stage does not directly lead to a temperature change in the substrate surface. Accordingly, there is a need to more precisely manage and control the temperature of the substrate stage.