Patent Publication Number: US-2012031889-A1

Title: Mounting table structure and processing apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to a processing apparatus for performing a heat treatment, e.g., a plasma treatment or a film formation, on a target object such as a semiconductor wafer and a mounting table structure used in the processing apparatus. 
     BACKGROUND OF THE INVENTION 
     Generally, in order to manufacture a semiconductor device such as an integrated circuit (IC), various treatments such as a film formation, an etching process, a heat treatment and a modification process are repeatedly performed on a target object such as a semiconductor wafer with or without using a plasma. As a consequence, a desired circuit device and the like can be manufactured. 
     For example, in a single wafer processing apparatus for performing a heat treatment on semiconductor wafers one by one, a mounting table structure having a resistance heater or the like embedded therein is installed in a vacuum evacuable processing chamber. A specific processing gas is supplied to a semiconductor wafer mounted on a top surface of the mounting table structure, and various heat treatments are performed on the wafer under specific process conditions with or without using a plasma (see Japanese Patent Application Publication Nos. S63-278322, H7-78766, H6-260430, 2004-356624, and H10-209255). 
     In this case, the semiconductor wafer is exposed to a high temperature environment and a corrosive gas such as a cleaning gas and an etching gas is used in the processing chamber. Accordingly, ceramic such as aluminum nitride (AlN) tends to be used for the mounting table structure on which the semiconductor wafer is mounted. In a case where a heater or an electrostatic chuck electrode is provided in the mounting table structure, it is integrally embedded in the ceramic. 
     An example of a conventional processing apparatus and mounting table structure will be described.  FIG. 9  schematically illustrates a conventional general processing apparatus using a plasma.  FIG. 10  is a plan view showing a resistance heater of the mounting table structure.  FIG. 9  illustrates a plasma processing apparatus as an example of the processing apparatus, wherein a mounting table structure for mounting a semiconductor wafer W on a top surface thereof is provided in a cylindrical processing chamber  2 . A shower head  6  serving as a gas introduction unit is provided at a ceiling portion of the processing chamber  2 , and a necessary gas is injected through gas injection holes  6 A formed on a bottom surface of the shower head  6 . A high frequency power supply  8  having a frequency of, e.g., 13.56 MHz for plasma generation is connected to the shower head  6 , and the shower head  6  serves as an upper electrode. 
     Further, a gas exhaust port  10  is provided at a bottom portion of the processing chamber  2  to evacuate the atmosphere inside the processing chamber  2 . A gate valve  12  configured to be opened and closed in loading and unloading of the wafer W is provided at one side of a sidewall of the processing chamber  2 . An observation window  14  formed of, e.g., quartz glass to observe the inside of the chamber is provided at the other side of the sidewall of the processing chamber  2 . The mounting table structure  4  includes a mounting table body  16  for mounting the wafer W thereon, and a support column  18  standing upright on a bottom portion of the chamber to support the mounting table body  16 . The mounting table body  16  is formed of ceramic such as AlN having a heat resistance and corrosive resistance. An electrode  20  serving as a lower electrode and a chuck electrode of an electrostatic chuck is embedded in the mounting table body  16 . A heating unit  22  having a resistance heater  24  is embedded in the mounting table body  16  below the electrode  20  to heat the wafer W. 
     As shown in  FIG. 10 , the resistance heater  24  forming the heating unit  22  includes a resistance heater  24 A and a resistance heater  24 B which are respectively provided in an inner peripheral zone and an outer peripheral zone concentrically separated from each other. The resistance heaters  24 A and  24 B of the respective zones are individually controlled to enhance the in-plane uniformity of the temperature of the wafer W. 
     Attachment ports (not shown) for attaching various measurement devices, e.g., the gate valve  12  and the observation window  14 , are appropriately provided in respective portions of the sidewall of the processing chamber  2 . Such portions have thermal conditions different from those of other portions of the sidewall. For example, a portion to which the gate valve  12  is attached tends to have a lower temperature because the gate valve  12  is repeatedly opened and closed for loading and unloading of the wafer W. A portion having the observation window  14  may have a temperature different from an ambient temperature because the quartz glass which forms the observation window  14  has a specific heat different from that of metal (e.g., an aluminum alloy) which forms the sidewall of the processing chamber  2 . Under these circumstances, a peripheral portion of the wafer W may be adversely affected locally and thermally by an attachment portion of the gate valve  12  and an attachment portion of the observation window which have different temperatures from that of the peripheral portion. 
     However, the resistance heater  24 B of the outer peripheral zone for controlling the temperature of the peripheral portion of the wafer W as described above can control only the entire temperature. Accordingly, when the peripheral portion of the wafer is locally affected by the different thermal conditions, it is difficult to effectively compensate the imbalance in temperature, and it leads to a reduction in the in-plane uniformity of the wafer temperature. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mounting table structure and a processing apparatus capable of controlling a temperature distribution in a peripheral portion of a target object by a simple configuration. 
     In accordance with an aspect of the present invention, there is provided a mounting table structure for mounting a target object to perform a heat treatment on the target object in a processing chamber, the mounting table structure including: a mounting table body on which the target object is mounted and which is divided into a plurality of concentric heating zones; a plurality of resistance heaters provided in the mounting table body to correspond to the heating zones respectively; a plurality of power feed lines which supply electric powers to the resistance heaters, the power feed lines connected to each of the resistance heaters of the heating zones being different from one another; and a heater control unit provided to independently control the electric powers supplied to the resistance heaters for each of the heating zones. 
     The resistance heaters include an outermost peripheral resistance heater that is arranged in an outermost peripheral heating zone of the heating zones, and the outermost peripheral resistance heater extends along a circumferential direction of the outermost peripheral heating zone. Further, the power feed lines include a plurality of outermost peripheral power feed lines to supply electric powers to the outermost peripheral resistance heater. The outermost peripheral power feed lines are respectively connected to a plurality of different positions of the outermost peripheral resistance heater in the circumferential direction, so that the outermost peripheral resistance heater is divided into a plurality of heater sections by the positions, and the heater control unit is configured to individually control electrical states of the respective outermost peripheral power feed lines. 
     The outermost peripheral resistance heater may be a heater with no ends continuously extending along an entire circumference of the outermost peripheral heating zone. 
     Further, the heater control unit may have a plurality of different power supply states for the outermost peripheral resistance heater, each of the power supply states is a combination of the electrical states of the respective outermost peripheral power feed lines, and the heater control unit may be configured to switch the power supply states by time division control. 
     Further, the outermost peripheral resistance heater may be divided into an even number of the heater sections. The heater control unit may have a power supply state to allow currents to flow in all of the heater sections of the outermost peripheral resistance heater. The heater control unit may have a power supply state to allow currents to flow in selected two of the heater sections opposite to each other. The heater control unit may have a power supply state to allow currents to flow in selected two of the heater sections adjacent to each other. 
     Further, the outermost peripheral resistance heater may be divided into an odd number of the heater sections. The heater control unit may have a power supply state to allow currents to flow in selected two of the heater sections adjacent to each other. 
     Further, the heater control unit may have a power supply state to set one or more of the outermost peripheral power feed lines in a floating state. 
     Further, the outermost peripheral resistance heater may be divided into three or more heater sections. 
     Further, the mounting table body may be formed of a ceramic material or quartz. 
     In accordance with another aspect of the present invention, there is provided a processing apparatus for performing a heat treatment on a target object, the apparatus including: an evacuable processing chamber; the above-described mounting table structure provided in the processing chamber to mount the target object; and a gas introduction unit which introduces a gas into the processing chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a processing apparatus having a mounting table structure in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view schematically showing an inside of a processing chamber. 
         FIGS. 3A and 3B  are plan views showing an arrangement of resistance heaters serving as a heating unit. 
         FIG. 4  illustrates a relationship between power supply states and electrical states of outermost peripheral power feed lines when an outermost peripheral zone is divided into four sections. 
         FIGS. 5A and 5B  illustrate examples of variation in power supply states when a specific heater section is controlled to be maintained at a high temperature or low temperature. 
         FIG. 6  illustrates examples of the power supply states when at least one of the outermost peripheral power feed lines is set in a floating state. 
         FIG. 7  schematically illustrates a case where the resistance heater of the outermost peripheral zone is divided into three parts. 
         FIG. 8  illustrates a relationship between power supply states and electrical states of the outermost peripheral power feed lines when the outermost peripheral zone is divided into three sections. 
         FIG. 9  illustrates a conventional general processing apparatus using a plasma. 
         FIG. 10  is a plan view showing a resistance heater of a mounting table structure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a mounting table structure and a processing apparatus in accordance with an embodiment of the present invention will be described in detail with reference to the accompanying drawings.  FIG. 1  illustrates a processing apparatus having a mounting table structure in accordance with the embodiment of the present invention.  FIG. 2  is a cross-sectional view schematically showing an inside of a processing chamber.  FIGS. 3A and 3B  are plan views showing an arrangement of resistance heaters serving as a heating unit. 
     In this embodiment, a parallel plate plasma processing apparatus will be described as an example of the processing apparatus in accordance with the embodiment of the present invention. As illustrated in  FIG. 1 , a parallel plate plasma processing apparatus  30  includes a processing chamber  32  formed of, e.g., an aluminum alloy in a cylindrical shape. A gas exhaust space  34  is formed at the center of a bottom portion of the processing chamber  32  and defined by a downwardly extending defining wall  36  of a cylindrical shape having a bottom surface. The bottom surface of the defining wall  36  becomes a part of the bottom portion of the processing chamber  32 . A gas exhaust port  38  is provided at a sidewall of the defining wall  36 . The gas exhaust port  38  is connected to a gas exhaust pipe  40  in which a pressure control valve or a vacuum pump (not shown) are provided, so that the processing chamber  32  can be vacuum evacuated to a desired pressure. 
     A loading/unloading opening  42  through which a target object, e.g., a semiconductor wafer W is loaded and unloaded is formed at a sidewall of the processing chamber  32  as also shown in  FIG. 2 . A gate valve  44  is provided at the loading/unloading opening  42 . The gate valve  44  is opened and closed in loading and unloading of the wafer W. An observation window  47  is provided at a portion of the sidewall of the processing chamber  32 , opposite to a portion of the sidewall at which the gate valve  44  is provided. The observation window  47  formed of, e.g., quartz glass is airtightly provided via a seal member  45  such as an O ring, so that an inside of the processing chamber  32  can be observed if necessary. Various components such as ports (not shown) for attachment of various measuring instruments, which lead to thermal imbalance, are formed at the sidewall of the processing chamber  32 . 
     A ceiling of the processing chamber  32  is opened, and a shower head  48  serving as a gas introduction unit is installed at the opened ceiling via an insulating member  46 . A seal member  50  such as an O ring is interposed between the shower head  48  and the insulating member  46  to maintain airtightness inside the processing chamber  32 . A gas inlet port  52  is provided at an upper portion of the shower head  48 , and a plurality of gas injection holes  54  is provided at a gas injection surface of a lower portion of the shower head  48  to inject a desired processing gas toward a processing space S. Although one room is formed in the shower head  48  in the illustrated example, a shower head having a plurality of rooms therein to separately supply different gases into the processing space S without mixing the gases in the shower head  48  may be provided. 
     The shower head  48  serves as an upper electrode for plasma generation. Specifically, the shower head  48  is connected to a high frequency power supply  58  for plasma generation via a matching circuit  56 . The frequency of the high frequency power supply  58  is, e.g., 13.56 MHz, but it is not limited thereto. A mounting table structure  60  in accordance with the embodiment of the present invention is provided in the processing chamber  32  to mount the semiconductor wafer W thereon. The mounting table structure  60  has a circular plate-shaped mounting table body  62  for directly mounting the wafer W on its top surface, i.e., a mounting surface. The mounting table body  62  is supported by a support column  64  standing upright on the bottom portion of the processing chamber  32 . 
     A pin elevating mechanism  66  is provided below the mounting table body  62  to lift up and support the wafer W in loading and unloading of the wafer W. The pin elevating mechanism  66  has, e.g., three elevating pins  68  (only two pins are illustrated in the example) which are equi-spaced in a circumferential direction of the mounting table body  62 . Lower end portions of the elevating pins  68  are supported by a pin base plate  70  of, e.g., a circular arc shape. The pin base plate  70  is connected to an elevation rod  72  passing through the bottom portion of the processing chamber  32 . The elevation rod  72  is attached to an actuator  74  which moves the elevation rod  72  up and down. A bellows  76  that is expansible and contractible to allow a vertical movement of the elevation rod  72  while maintaining airtightness inside the processing chamber  32  is provided at a part of the bottom portion of the processing chamber  32  through which the elevation rod  72  passes. 
     Pin insertion through holes  78  are provided in the mounting table body  62  to correspond to the elevating pins  68 . The elevating pins  68  inserted through the pin insertion through holes  78  move up from the mounting surface of the mounting table body  62  by vertically moving the elevation rod  72 , thereby elevating the wafer W. 
     The mounting table body  62  and the support column  64  are entirely formed of a material, e.g., a ceramic material or quartz, having an excellent heat resistance without causing metal contamination. The support column  64  has a cylindrical shape and the upper end of the support column  64  is bonded to a central portion of a lower surface (rear surface) of the mounting table body  62  by, e.g., thermal diffusion bonding. A lower end portion of the support column  64  is connected to a peripheral portion of an opening  82  formed at the bottom portion of the processing chamber  32  by bolts or the like (not shown) via a seal member  80  such as an ring to maintain airtightness inside the processing chamber  32 . One of aluminum nitride (AlN), aluminum oxide (Al 2 O 3 ), silicon carbide (SiC) and the like may be used as the ceramic material. 
     A chuck electrode  84  of an electrostatic chuck and resistance heaters  88  serving as a heating unit are embedded in the mounting table body  62 . The chuck electrode  84  is provided right below the mounting surface to generate an electrostatic force for attracting and holding the wafer W. The resistance heaters  88  for heating wafer W are provided below the chuck electrode  84 . 
     In this embodiment, the chuck electrode  84  also serves as a lower electrode for plasma generation. The chuck electrode  84  is connected to a DC power supply (not shown) for generating a high voltage for attracting and holding the wafer W through a power feed line for a chuck and a high frequency power supply (not shown) for applying a bias voltage for attracting ions of a plasma. 
     The resistance heaters  88  are connected to power feed lines L (L 1  to L 6 ). The power feed lines L are extracted out of the processing chamber  32  through the cylindrical support column  64 . Each of the power feed lines L is connected to a heater control unit  92  having a heater power supply, a computer and the like to control the electric power supplied to the resistance heaters  88 , thereby controlling the temperature of the wafer W. A thermocouple (not shown) for the temperature control is provided at a lower portion of the mounting table body  62 , and the output of the thermocouple is inputted to the heater control unit  92 . A nonreactive gas such as N 2  and Ar is supplied into the support column  64  to thereby prevent corrosion of the power feed lines L and the like. 
     As shown in  FIGS. 3A and 3B , the mounting table body  62  is divided into a plurality of concentric heating zones (hereinafter, referred to as “zones”). In the illustrated example, the mounting table body  62  is divided into two concentric (circular) zones, i.e., a circular inner peripheral zone  94  provided at a central portion of the mounting table body  62  and a ring-shaped outer peripheral zone  96  surrounding the inner peripheral zone  94 . In the illustrated example, since the outer peripheral zone  96  is located at the outermost periphery, the outer peripheral zone  96  is an outermost peripheral zone. 
     The resistance heaters  88  include a resistance heater  98  provided in the inner peripheral zone  94  and a resistance heater  100  provided in the outer peripheral zone  96 . The resistance heaters  98  and  100  provided in different zones are connected to the different power feed lines L, respectively. In this case,  FIG. 3A  illustrates an arrangement of all of the resistance heaters  98  and  100 , and  FIG. 3B  illustrates only an arrangement of the resistance heater  100  provided in the outer peripheral zone  96 . 
     Both ends of the resistance heater  98  of the inner peripheral zone  94  are connected to power feed lines L 5  and L 6 , respectively. The resistance heater  98  continuously extends in a zigzag shape throughout the whole region of the inner peripheral zone  94  without disconnection from one end connected to the power feed line L 5  to the other end connected to the power feed line L 6 . 
     The resistance heater  100  arranged in the outer peripheral zone  96  serving as an outermost peripheral zone, i.e., an outermost peripheral resistance heater, continuously extends throughout the entire circumference along a circumferential direction of the outer peripheral zone  96  (meanderingly in the outer peripheral zone  96  in the illustrated example), and entire shape thereof is a ring (annular) shape with no ends. Further, an arrangement pattern of each of the resistance heaters  98  and  100  is not particularly limited to the above example. The resistance heater  100  serving as the outermost peripheral resistance heater (hereinafter, also referred to as an “outermost peripheral resistance heater”) is connected, at a plurality of circumferential positions, to power feed lines L 1  to L 4  different from the power feed lines L 5  and L 6  for the inner peripheral zone  94 . That is, the outermost peripheral resistance heater  100  is divided into a plurality of heater sections at the connection points with the power feed lines L 1  to L 4 . 
     In the illustrated example, the outermost peripheral resistance heater  100  is connected to the four (even number) power feed lines L 1 , L 2 , L 3  and L 4  at the equi-spaced positions thereof, respectively, to divide the outermost peripheral resistance heater  100  into four heater sections  100 A,  100 B,  100 C and  100 D. Since the power feed lines L 1  to L 4  are connected to the outermost peripheral resistance heater  100 , they are also referred to as outermost peripheral power feed lines. 
     The outermost peripheral power feed lines L 1  to L 4  extend to a central portion of the mounting table body  62 , and are inserted into and pass through the cylindrical support column  64  to be connected to the heater control unit  92 . Various combinations of the electric powers supplied to the heater sections  100 A to  100 D (currents flowing in the heater sections  100 A to  100 D) can be achieved by controlling the electrical states of the outermost peripheral power feed lines L 1  to L 4 . 
     The thermocouple (not shown) is provided at the rear surface (lower surface) of the mounting table body  62  as described above. The temperature measurement results obtained by the thermocouple are inputted to the heater control unit  92 , and the entire temperature of the mounting table body  62  is controlled based on the measurement results. Further, the thermocouple may be provided in each zone. Moreover, the thermocouple may be provided in each zone and also provided in each of the heater sections  100 A to  100 D in the outermost peripheral zone. 
     The entire operation of the plasma processing apparatus  30  is controlled by an apparatus controller  102  having, e.g., a computer and the like. Programs of the computer for performing a control operation are stored in a storage medium  104  such as a flexible disc, compact disc (CD), a hard disc, a flash memory or DVD. Specifically, start and stop of gas supply, a gas flow rate, a supply and power of microwaves or high frequency power, a process temperature and a process pressure and the like are controlled by the instructions transmitted from the apparatus controller  102 . Further, the heater control unit may be operated under the control of the apparatus controller  102 . 
     Next, the operation of the plasma processing apparatus having the above configuration will be described with reference to  FIGS. 4 to 5B .  FIG. 4  illustrates a relationship between power supply states and the electrical states of the outermost peripheral power feed lines when the outermost peripheral zone is divided into four sections.  FIGS. 5A and 5B  illustrate examples of variation in power supply states when a specific heater section is controlled to be maintained at a high or a low temperature. 
     First, the unprocessed wafer W is loaded into the processing chamber  32  through the gate valve  44  and the loading/unloading opening  42  while being supported by a transfer arm (not shown). After the wafer W is delivered onto the lifted elevating pins  68 , the wafer W is mounted on the upper surface of the mounting table body  62  of the mounting table structure  60  by moving down the elevating pins  68 . 
     Then, various processing gases, e.g., film forming gases, are supplied to the shower head  48  while controlling their flow rates, and injected through the gas injection holes  54  to the processing space S. Further, the processing chamber  32  or the gas exhaust space  34  is vacuum evacuated by continuously operating the vacuum pump (not shown) provided to be connected to the gas exhaust pipe  40 . Further, an inner pressure of the processing space S is maintained at a predetermined process pressure by controlling the opening degree of the pressure control valve (not shown). In this case, the temperature of the wafer W is maintained at a specific process temperature. That is, the resistance heaters  88  serving as the heating unit  86  of the mounting table body  62  are heated by applying voltages to the resistance heaters  88  from the heater control unit  92  having the heater power supply through the power feed lines L 1  to L 6 , thereby heating the entire mounting table body  62 . 
     Consequently, the wafer W mounted on the mounting table body  62  is heated to an increased temperature. In this case, the temperature of the wafer W is measured by the thermocouple (not shown) provided in the mounting table body  62 , and the temperature control is performed by the heater control unit  92  based on the measurement results. The temperature control states in this case will be described later. 
     Further, in order to perform a plasma process, a high frequency voltage is applied between the shower head  48  serving as the upper electrode and the mounting table body  62  serving as the lower electrode by driving the high frequency power supply  58 , such that a plasma is generated in the processing space S. At the same time, a high DC voltage is applied to the chuck electrode  84  of the electrostatic chuck to attract and hold the wafer W by an electrostatic force. In this state, a desired plasma process is performed. Further, ions of the plasma can be attracted to the wafer W by applying a high frequency power to the chuck electrode  84  of the mounting table body  62  from a high frequency bias power supply (not shown). Accordingly, the plasma process, e.g., a film formation, is performed on the surface of the wafer W. 
     Further, as described above, while the plasma process such as a film formation or the like is performed on the wafer W, the electric powers are individually controlled and supplied from the heater control unit  92  to the respective resistance heaters  98  and  100  corresponding to the respective zones  94  and  96  by feedback control. In this embodiment, a switching device such as a thyristor is included in the heater control unit  92 , and the electric powers may be supplied in pulse shapes to the resistance heaters  98  and  100  by time division by driving the switching device. 
     The electric power is supplied to the resistance heater  98  of the inner peripheral zone  94  by feedback control through the power feed lines L 5  to L 6 , and the temperature of the inner peripheral zone  94  is controlled as a whole. 
     On the other hand, the outermost peripheral resistance heater  100  of the outermost peripheral zone (outer peripheral zone)  96  is divided into the four heater sections  100 A to  100 D in the circumferential direction. The power supply state of each of the heater sections  100 A to  100 D can be changed by individually controlling each of the electrical states (e.g., potentials) of the four outermost peripheral power feed lines L 1  to L 4 . 
     As described above with reference to  FIGS. 9 and 10 , in the conventional mounting table structure, a component such as the gate valve  12  and the observation window  14  provided at the sidewall or the like of the processing chamber  2  causes thermal imbalance, so that the temperature of a peripheral region of the wafer close to the component locally increases or decreases compared to other regions, thereby reducing the in-plane uniformity of the temperature of the wafer. 
     However, in the mounting table structure in accordance with the embodiment of the present invention, as described above, the outermost peripheral resistance heater  100  of the outermost peripheral zone  96  is divided into a plurality of, e.g., four, heater sections  100 A to  100 D, and the power supply control, i.e., temperature control of each of the heater sections  100 A to  100 D can be individually performed. Accordingly, even though there is a component such as the gate valve  44  and the observation window  47  causing thermal imbalance as described above, it is possible to correct the thermal imbalance to thereby suppress such imbalance and improve the in-plane uniformity of the temperature of the wafer W. 
     The power supply state of each of the heater sections of the outermost peripheral resistance heater  100  will be described in detail with reference to  FIGS. 4 to 5B .  FIG. 4  illustrates potentials (applied voltages) of the outermost peripheral power feed lines L 1  to L 4  in each state. The presence of a pulse indicates that a voltage (e.g., 200 V) is applied to the power feed line, and the absence of a pulse indicates that a voltage applied to the power feed line is zero, that is, the power feed line is grounded. 
     Further, in this case, states S 1  to S 7  are shown as examples of the power supply states, and a current flow direction of each state is indicated by an arrow in each of the heater sections. The states S 1  to S 7  are appropriately selected such that the temperature of the outermost peripheral zone  96  is controlled by switching the selected states in a time division manner. 
     In state S 1 , a voltage is applied to the outermost peripheral power feed lines L 1  and L 3  and a zero voltage is applied to the outermost peripheral power feed lines L 2  and L 4 , thereby allowing currents to flow in all of the heater sections  100 A to  100 D. In this case, the temperature of the outermost peripheral zone  96  is uniformly increased. Further, by applying a voltage to the outermost peripheral power feed lines L 2  and L 4  instead of the outermost peripheral power feed lines L 1  and L 3 , it is also possible to allow currents to flow in all of the heater sections  100 A to  100 D, though in an opposite direction. 
     In state S 2 , a voltage is applied to the outermost peripheral power feed lines L 3  and L 4  and a zero voltage is applied to the outermost peripheral power feed lines L 1  and L 2 . Accordingly, currents flow in the heater sections  100 B and  100 D and do not flow in the heater sections  100 A and  100 C. That is, in this case, the currents may flow in a pair of the selected heater sections  100 B and  100 D opposite to each other. Further, by applying a voltage to the outermost peripheral power feed lines L 1  and L 2  instead of the outermost peripheral power feed lines L 3  and L 4 , it is also possible to allow currents to flow in the heater sections  100 B and  100 D, though in an opposite direction. In state S 2 , it is possible to heat only the heater sections  100 B and  100 D. 
     In state S 3 , a voltage is applied to the outermost peripheral power feed lines L 1  and L 4  and a zero voltage is applied to the outermost peripheral power feed lines L 2  and L 3 . Accordingly, currents flow in the heater sections  100 A and  100 C and do not flow in the heater sections  100 B and  100 D. That is, in this case, the currents may flow in a pair of the selected heater sections  100 A and  100 C opposite to each other. Further, by applying a voltage to the outermost peripheral power feed lines L 2  and L 3  instead of the outermost peripheral power feed lines L 1  and L 4 , it is also possible to allow currents to flow in the heater sections  100 A and  100 C, though in an opposite direction. In state S 3 , it is possible to heat only the heater sections  100 A and  100 C. 
     In state S 4 , a voltage is applied to the outermost peripheral power feed lines L 1 , L 2  and L 3  and a zero voltage is applied to the outermost peripheral power feed line L 4 . Accordingly, currents flow in the heater sections  100 C and  100 D and do not flow in the heater sections  100 A and  100 B. That is, in this case, the currents may flow in a pair of the selected heater sections  100 C and  100 D adjacent to each other. In state S 4 , it is possible to heat only the heater sections  100 C and  100 D. 
     In state S 5 , a voltage is applied to the outermost peripheral power feed lines L 1 , L 3  and L 4  and a zero voltage is applied to the outermost peripheral power feed line L 2 . Accordingly, currents flow in the heater sections  100 A and  100 B and do not flow in the heater sections  100 C and  100 D. That is, in this case, the currents may flow in a pair of the selected heater sections  100 A and  100 B adjacent to each other. In state S 5 , it is possible to heat only the heater sections  100 A and  100 B. 
     In state S 6 , a voltage is applied to the outermost peripheral power feed lines L 1 , L 2  and L 4  and a zero voltage is applied to the outermost peripheral power feed line L 3 . Accordingly, currents flow in the heater sections  100 B and  100 C and do not flow in the heater sections  100 A and  100 D. That is, in this case, the currents may flow in a pair of the selected heater sections  100 B and  100 C adjacent to each other. In state S 6 , it is possible to heat only the heater sections  100 B and  100 C. 
     In state S 7 , a voltage is applied to the outermost peripheral power feed lines L 2 , L 3  and L 4  and a zero voltage is applied to the outermost peripheral power feed line L 1 . Accordingly, currents flow in the heater sections  100 A and  100 D and do not flow in the heater sections  100 B and  100 C. That is, in this case, the currents may flow in a pair of the selected heater sections  100 A and  100 D adjacent to each other. In state S 7 , it is possible to heat only the heater sections  100 A and  100 D. 
     Further, the power supply states, e.g., three states of state S 2 →state S 7 →state S 4  (regardless of the order) as shown in  FIG. 5A , may be combined and controlled by time division, thereby heating only the heater section  100 D to a higher temperature compared to those of the heater sections  100 A to  100 C. Further, arrows of  FIG. 5A  indicate directions of current as in  FIG. 4 . Therefore, in the same manner as the above, it is possible to heat only one of the heater sections  100 A to  100 C to a higher temperature compared to those of the other heater sections by appropriately combining the power supply states. 
     Further, the power supply states, e.g., four states of state S 5 →state S 6 →state S 3 →state S 1  (regardless of the order) as shown in  FIG. 5B , may be combined and controlled by time division, thereby heating only the heater section  100 D to a lower temperature compared to those of the heater sections  100 A to  100 C. Further, arrows of  FIG. 5B  indicate directions of current as in  FIG. 4 . Therefore, in the same manner as the above, it is also possible to heat only one of the heater sections  100 A to  100 C to a lower temperature compared to those of the other heater sections by appropriately combining the power supply states. 
     Further, it is possible to control the electric power supplied to each of the heater sections  100 A to  100 D by varying a pulse width of the pulse-shaped power applied to each of the outermost peripheral power feed lines L 1  to L 4 , i.e., varying a duty ratio. Actually, it is preferable to perform the temperature control of the outermost peripheral zone  96  by varying the power supply states and controlling a duty ratio to vary the pulse width of the applied power. 
     For example, in a case where the temperatures of the peripheral portions of the wafer W, e.g., the heater sections  100 A and  100 C, corresponding to the gate valve  44  and the observation window  47  opposite to each other in the sidewall of the processing chamber  32  tend to decrease, temperature compensation is performed on the corresponding portions by increasing the current flowing time, e.g., as shown in state S 3 , to make the electric powers supplied to the heater sections  100 A and  100 C larger than the electric powers supplied to the other heater sections  100 B and  100 D. 
     Accordingly, since the amount of heat supplied to the peripheral portion of the wafer W corresponding to the gate valve  44  or the observation window  47  increases, it is possible to make a uniform temperature distribution in the circumferential direction of the peripheral portion of the wafer W corresponding to the outer peripheral zone. Consequently, it is possible to increase the in-plane uniformity of the temperature of the wafer W including the inner peripheral zone. Further, the above-described states S 1  to S 7  are merely exemplary and the combination of the voltage application states and the zero voltage application states in the outermost peripheral power feed lines L 1  to L 4  can be arbitrarily set. 
     By performing the control of the electric power supplied to the outermost peripheral resistance heater  100  as described above, it is possible to uniformly maintain the temperature distribution in the circumferential direction of the peripheral portion of the wafer W even though the peripheral portion of the wafer W is affected by the non-uniform heat supplied from the sidewall of the processing chamber  2 . Consequently, it is possible to improve the in-plane uniformity of the temperature of the wafer W. 
     Further, it is possible to simplify the arrangement of the outermost peripheral resistance heater  100  and the outermost peripheral power feed lines L 1  to L 4 . The outermost peripheral resistance heater may be formed of a plurality of (e.g., four) resistance heaters and the electric powers supplied to the plurality of resistance heaters may be individually controlled. In this case, however, it is required to provide a considerably large number of outermost peripheral power feed lines in the mounting table body  62 . For example, in a case where the outermost peripheral resistance heater is divided into four heater sections in the present embodiment, four outermost peripheral power feed lines are required. On the other hand, in case of using four resistance heaters separated from each other, eight outermost peripheral power feed lines are required. Further, it is troublesome to arrange a plurality of resistance heaters separated from each other. 
     Therefore, in accordance with the embodiment of the present invention, it is possible to simply install the outermost peripheral resistance heater and the outermost peripheral power feed lines, and reduce the time and cost required for the manufacture of the mounting table body. Meanwhile, there is no particular difference in controlling the heater control unit  92  between a case of using the four resistance heaters separated from each other and a case where the outermost peripheral resistance heater is divided into four heater sections as in the present embodiment. 
     (Case where Electrical States of Power Feed Lines Include Floating State) 
     The electrical state of each of the outermost peripheral power feed lines described in  FIGS. 4 to 5B  is one of a state in which a specific voltage is applied and a state in which a zero voltage is applied (ground). In addition to the two states, the electrical states may include a floating state (in which no voltage is applied to the outermost peripheral power feed line, and at the same time the outermost peripheral power feed line is not grounded to thereby making the power feed line electrically float).  FIG. 6  illustrates examples of the power supply states when at least one of the outermost peripheral power feed lines is set in a floating state. In  FIG. 6 , “F” indicates a floating state and the others indicate the same as those shown in  FIG. 4 . 
     In state S 11 , one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 1  is set in a floating state, a voltage is applied to another one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 4 , and a zero voltage is applied to the remaining outermost peripheral power feed lines, e.g., the outermost peripheral power feed lines L 2  and L 3 . 
     In this case, currents flow in the heater sections  100 A,  100 C and  100 D and no current flows in the heater section  100 B. Further, the heater sections  100 A and  100 D are connected in series to each other. The current flowing in the heater sections  100 A and  100 D is a half (½) of the current flowing in the heater section  100 C (the electric power applied to each of the heater sections  100 A and  100 D is ¼ of the electric power applied to the heater section  100 C. 
     In state S 12 , one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 1  is set in a floating state, a voltage is applied to two other ones of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed lines L 2  and L 4 , and a zero voltage is applied to the remaining outermost peripheral power feed line, e.g., the outermost peripheral power feed line L 3 . In this case, currents flow in the heater sections  100 B and  100 C and do not flow in the heater sections  100 A and  100 D. 
     In state S 13 , two of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed lines L 3  and L 4  are set in a floating state, a voltage is applied to another one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 1 , and a zero voltage is applied to the remaining outermost peripheral power feed line, e.g., the outermost peripheral power feed line L 2 . In this case, currents flow in all of the heater sections  100 A to  100 D. In this case, the heater sections  100 B,  100 C and  100 D are connected in series between the outermost peripheral power feed lines L 1  and L 2  involved in the current supply. The current flowing in the heater sections  100 B,  100 C and  100 D is ⅓ of the current flowing in the heater section  100 A (the electric power applied to each of the heater sections  100 B,  100 C and  100 D is 1/9 of the electric power applied to the heater section  100 A). 
     In state S 14 , two of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed lines L 1  and L 2  are set in a floating state, a voltage is applied to another one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 3 , and a zero voltage is applied to the remaining outermost peripheral power feed line, e.g., the outermost peripheral power feed line L 4 . In this case, currents flow in all of the heater sections  100 A to  100 D as in state S 13 . Further, the heater sections  100 D,  100 A and  100 B are connected in series between the outermost peripheral power feed lines L 3  and L 4  involved in the current supply. The current flowing in the heater sections  100 D,  100 A and  100 B is ⅓ of the current flowing in the heater section  100 C (the electric power applied to each of the heater sections  100 D,  100 A and  100 B is 1/9 of the electric power applied to the heater section  100 C). 
     In state S 15 , two of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed lines L 1  and L 3  are set in a floating state, a voltage is applied to another one of the outermost peripheral power feed lines, e.g., the outermost peripheral power feed line L 4 , and a zero voltage is applied to the remaining outermost peripheral power feed line, e.g., the outermost peripheral power feed line L 2 . 
     In this case, currents flow in all of the heater sections  100 A to  100 D. Further, the heater sections  100 A and  100 D are connected in series and the heater sections  100 B and  100 C are connected in series between the outermost peripheral power feed lines L 4  and L 2  involved in the current supply. 
     As described above, the power supply states of the states S 11  to S 15  and the power supply states shown in  FIG. 4  may be combined and controlled by time division, so that the temperature control is more specifically performed. Further, the states S 11  to S 15  are merely examples of the outermost peripheral power feed lines, at least one of which is set in a floating state, and it is not limited thereto. 
     In other words, in this case, five states of the states S 11  to S 15  are representatively illustrated. Since the heater sections  100 A to  100 D and the outermost peripheral power feed lines L 1  to L 4  have rotational symmetry, it is obvious to obtain the same power supply pattern when the power supply pattern shown in the states S 11  to S 15  is rotated by 90 degrees. 
     (Embodiment in which Outermost Peripheral Zone is Divided into Three Sections) 
     Although the case where the resistance heater of the outermost peripheral zone is divided into even number (four) of sections has been described in the above embodiment, the resistance heater of the outermost peripheral zone may be divided into odd number (e.g., three) of sections.  FIGS. 7 and 8  illustrate such a case, wherein  FIG. 7  schematically illustrates the case where the resistance heater of the outermost peripheral zone is divided into three sections, and  FIG. 8  illustrates a relationship between the power supply states and the states of the outermost peripheral power feed lines when the outermost peripheral zone is divided into three sections. Further,  FIG. 8  illustrates a diagram in the same way as those shown in  FIGS. 4 and 6 . 
     As illustrated in  FIG. 7 , in this embodiment, three outermost peripheral power feed lines L 1 , L 2  and L 3  are connected to the outermost peripheral resistance heater  100  such that the outermost peripheral resistance heater  100  is divided into three heater sections  100 A,  100 B and  100 C in its circumferential direction. 
     For example, the power supply states shown in  FIG. 8  can be realized in this embodiment. In state S 21 , a voltage is applied to two of the outermost peripheral power feed lines L 1  to L 3 , e.g., the outermost peripheral power feed lines L 1  and L 3 , and a zero voltage is applied to the outermost peripheral power feed line L 2 . In this case, currents may flow in the two selected heater sections  100 A and  100 B adjacent to each other. In the state S 21 , it is possible to heat only the heater sections  100 A and  100 B. 
     In state S 22 , a voltage is applied to two of the outermost peripheral power feed lines L 1  to L 3 , e.g., the outermost peripheral power feed lines L 1  and L 2 , and a zero voltage is applied to the outermost peripheral power feed line L 3 . In this case, currents may flow in the two selected heater sections  100 B and  100 C adjacent to each other. In the state S 22 , it is possible to heat only the heater sections  100 B and  100 C. 
     In state S 23 , a voltage is applied to two of the outermost peripheral power feed lines L 1  to L 3 , e.g., the outermost peripheral power feed lines L 2  and L 3 , and a zero voltage is applied to the outermost peripheral power feed line L 1 . In this case, currents may flow in the two selected heater sections  100 A and  100 C adjacent to each other. In the state S 23 , it is possible to heat only the heater sections  100 A and  100 C. 
     In state S 24 , a voltage is applied to one of the outermost peripheral power feed lines L 1  to L 3 , e.g., the outermost peripheral power feed line L 1 , and a zero voltage is applied to the outermost peripheral power feed lines L 2  and L 3 . In this case, currents may flow in the two selected heater sections  100 A and  100 C adjacent to each other. In the state S 24 , it is possible to heat only the heater sections  100 A and  100 C. 
     The heater sections heated in the state S 24  are the same as those in the state S 23 , but the directions of currents in two states S 23  and S 24  are opposite. Further, it is apparent that it is possible to obtain the same power supply pattern as that of the state S 24  by applying a voltage to only one of the other outermost peripheral power feed lines L 2  and L 3  instead of the outermost peripheral power feed line L 1 . 
     In state S 25 , a case including the outermost peripheral power feed line set in a floating state (F) is illustrated as an example. A voltage is applied to one of the outermost peripheral power feed lines L 1  to L 3 , e.g., the outermost peripheral power feed line L 1 , a zero voltage is applied to the outermost peripheral power feed line L 3 , and the outermost peripheral power feed line L 2  is set in a floating state. In this case, currents may flow in all of the heater sections  100 A to  100 C, thereby heating the heater sections  100 A to  100 C. 
     In this case, the heater sections  100 A and  100 B are connected in series between the outermost peripheral power feed lines L 1  and L 3  involved in the current supply. The current flowing in the heater sections  100 A and  100 B are ½ of the current flowing in the heater section  100 C (the electric power applied to each of the heater sections  100 A and  100 B is ¼ of the power applied to the heater section  100 C). Further, it is apparent that it is possible to obtain the same current supply pattern as that of the state S 25  by applying a voltage to any one of the three outermost peripheral power feed lines L 1  to L 3  and setting any other one of the outermost peripheral power feed lines in a floating state. 
     Further, the outermost peripheral resistance heater has been divided into three or four sections in the above-described embodiments. However, the number of the divided sections may be an even or odd number equal to or greater than three without being limited thereto. 
     Further, the mounting table body  62  is divided into two concentric heating zones of the inner peripheral zone and the outer peripheral zone in the above-described embodiments. However, the mounting table body  62  may be divided into three or more concentric heating zones, wherein the heating zone located at the outermost periphery is an outermost peripheral heating zone, and a resistance heater arranged in the outermost peripheral heating zone, i.e., an outermost peripheral resistance heater, is divided into a plurality of heater sections along its circumferential direction. 
     Further, the outermost peripheral power feed lines L 1  to L 4  extend to the central portion of the mounting table body  62  such that the resistance heater  98  of the inner peripheral zone is not interfered therewith in the above-described embodiments. However, if the resistance heater  98  of the inner peripheral zone and the outermost peripheral resistance heater  100  are arranged in two layers having different heights in a thickness direction, there is no need for the outermost peripheral power feed lines L 1  to L 4  to be arranged such that the resistance heater  98  of the inner peripheral zone is not interfered therewith. Thus, the freedom in design is increased. 
     Further, although the mounting table structure has the support column  64  in the above-described embodiments, the mounting table structure may be configured without having the support column  64 . The material of the mounting table body  62  may be metal such as aluminum and an aluminum alloy without being limited to a ceramic material or quartz. 
     Further, although a voltage is applied by pulse control (digital control) in the above-described embodiments, analog control for varying an amplitude of the application voltage may be used instead of or in combination with the digital control. 
     Further, although one electrode serves as both of the electrostatic chuck and the lower electrode in the above-described embodiments, the electrode may be separately provided for each of the electrostatic chuck and the lower electrode. Further, the processing apparatus of the present invention is not limited to the parallel plate plasma processing apparatus as described above. That is, the present invention may be applied to a plasma process using high frequency waves or microwaves in an etching apparatus, a film forming apparatus and the like for forming different types of films. 
     Further, the present invention may be applied to a processing apparatus using no plasma, e.g., a thermal CVD film forming apparatus, a thermal oxidation apparatus, an annealing apparatus and a modification apparatus. In this case, a lower electrode is unnecessary. Further, although a target object is a semiconductor wafer in the above-described embodiments, the semiconductor wafer further includes a silicon substrate, or a compound semiconductor substrate such as GaAs, SiC and GaN substrates. Further, the target object may be a ceramic substrate or a glass substrate used in a liquid crystal display.