Plasma processing apparatus and temperature measuring method and apparatus used therein

A plasma processing apparatus comprising:

• a vacuum chamber in which a substrate is to be accommodated and processed by a plasma;
• a mounting table provided in the vacuum chamber for mounting the substrate thereon, the mounting table including an RF plate made of an electrically conductive material;
• a base plate provided below the mounting table and having a space therebetween;
• a temperature measuring unit including:
• a light source,
• a splitter for dividing a light beam from the light source into a measurement beam and a reference beam,
• a reference beam reflector for reflecting the reference beam from the splitter,
• an optical path length altering unit for altering an optical path length of the reference beam reflected from the reference beam reflector,
• an optical fiber for irradiating the measurement beam onto the substrate, a collimator provided at an outlet of the optical fiber, and
• a light detecting unit for detecting an interference between the measurement beam reflected from the substrate and the reference beam reflected from the reference beam reflector;
• an airtightly sealed temperature measuring window provided in the mounting table for optically communicating a top surface and a bottom surface of the mounting table to transmit the measurement beam therethrough;
• a plurality of connection members connecting the mounting table and the base plate, the connection members being provided inside the space between the mounting table and the base plate;
• and a power feed bar connected to a central portion of the RF plate and to which a high frequency power is applied to supply the high frequency power to the RF plate,
• wherein a space above the mounting table is set to be maintained under a vacuum atmosphere, and the space between the mounting table and the base plate is set to be maintained under a normal pressure atmosphere,
• wherein the collimator is fixed to the base plate at a position corresponding to the temperature measuring window, thereby measuring a temperature of the substrate via the temperature measuring window by the temperature measuring unit,
• wherein the plasma processing apparatus further comprises a prism located at the mounting table and configured to bend an optical path of the measurement beam to a horizontal path and to a vertical path to irradiate the measurement beam onto the substrate to enable a temperature at a central portion of the substrate that is above the power feed bar to be measured,
• wherein the temperature measuring unit is configured to measure at least two portions of the substrate along a radial direction of the substrate, and said at least two portions of the substrate includes the central portion of the substrate,
• wherein the vacuum chamber has therein a facing electrode facing the mounting table and a cell located on the facing surface of the facing electrode and made of silicon which transmits an infrared ray therethrough such that measurement beams emitted from the mounting table are reflected from a top surface and a bottom surface of the cell, and wherein the temperature measuring unit measures a temperature of the cell based on reflected measurement beams from the top surface and the bottom surface of the cell via the substrate on the mounting table and the temperature measuring window.