Patent Publication Number: US-2021183631-A1

Title: Plasma processing apparatus and plasma processing method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2019-227677 filed on Dec. 17, 2019, the entire disclosures of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The various aspects and embodiments described herein pertain generally to a plasma processing apparatus and a plasma processing method. 
     BACKGROUND 
     Patent Document 1 describes a technique of removing a deposit on a non-plasma surface in a space at an outside of an insulated plasma processing chamber by generating plasma from a fluorocarbon gas and supplying the generated plasma into the space at the outside of the plasma processing chamber. 
     Patent Document 1: Japanese Patent Laid-open Publication No. 2018-195817 
     SUMMARY 
     In an exemplary embodiment, a plasma processing apparatus includes a chamber, a heater and a heater power supply. The chamber is configured to process a substrate by using a plasma. The heater is disposed in a region within the chamber which is not exposed to the plasma and a radio frequency power. The heater power supply is configured to supply a pulsed power to the heater. 
     The foregoing summary is illustrative only and is not intended to be any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  is a diagram schematically illustrating an example of a cross section of a plasma processing apparatus according to an exemplary embodiment; 
         FIG. 2  is a diagram illustrating an example of a layout of a heater according to the exemplary embodiment; 
         FIG. 3  is a diagram illustrating an example of a temperature variation of the heater according to the exemplary embodiment; 
         FIG. 4  is a diagram illustrating an example of a pulsed power to be supplied to the heater according to the exemplary embodiment; 
         FIG. 5  is a diagram illustrating an example of heating by the heater according to the exemplary embodiment; 
         FIG. 6  is a diagram illustrating an example of temperature variations of a front surface and a rear surface of a member according to the exemplary embodiment; 
         FIG. 7  is a diagram illustrating an example of a test object according to the exemplary embodiment; 
         FIG. 8  is a diagram illustrating an outline of an experiment according to the exemplary embodiment; 
         FIG. 9  is a diagram illustrating a schematic layout of the heater and the test object according to the exemplary embodiment; 
         FIG. 10  is a diagram illustrating an experimental result according to the exemplary embodiment; and 
         FIG. 11  is a diagram schematically illustrating an example of a cross section of a plasma processing apparatus according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part of the description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current exemplary embodiment. Still, the exemplary embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     Hereinafter, exemplary embodiments of a plasma processing apparatus and a plasma processing method according to the present disclosure will be described in detail with reference to the accompanying drawings. Further, it should be noted that the plasma processing apparatus and the plasma processing method according to the present disclosure are not limited to the exemplary embodiments. 
     A by-product is generated when a plasma processing is performed, and the generated by-product is scattered around within a chamber, ending up with being attached to the chamber. Thus, there is known a technique of cleaning the by-product by using plasma, as described in Patent Document 1, for example. In a region within the chamber which is not exposed to the plasma and a radio frequency (radio frequency) power applied to form the plasma, however, the by-product is difficult to remove even if the plasma is used. As a result, the by-product may be easily deposited in that region. Though the deposited by-product needs to be removed regularly with a scraper or the like, there arises a risk that a harmful gas or the like may be generated. 
     In this regard, there has been a demand for a technique capable of suppressing deposition of the by-product in the region within the chamber which is not exposed to the plasma and the radio frequency power. 
     First Exemplary Embodiment 
     &lt;Configuration of Plasma Processing Apparatus&gt; 
     An example of a plasma processing apparatus according to a first exemplary embodiment will be described. The present exemplary embodiment will be explained for an example where the plasma processing apparatus etches a substrate by using a plasma as a plasma processing. Here, the substrate is a wafer.  FIG. 1  is a diagram schematically illustrating an example of a cross section of a plasma processing apparatus  10  according to the exemplary embodiment. The plasma processing apparatus  10  shown in  FIG. 1  is a capacitively coupled plasma processing apparatus. 
     The plasma processing apparatus  10  is equipped with a chamber  12 . The chamber  12  has a substantially cylindrical shape, and is made of, by way of non-limiting example, aluminum and hermetically sealed. An internal space of the chamber  12  is configured as a processing space  12   c  in which a plasma processing is performed. A film having plasma-resistance is formed on an inner wall surface of the chamber  12 . This film may be an alumite film or an yttrium oxide film. The chamber  12  is grounded. An opening  12   g  is formed in a sidewall of the chamber  12 . When a wafer W is carried into the processing space  12   c  from an outside of the chamber  12  or when the wafer W is carried out from the processing space  12   c  to the outside of the chamber  12 , the wafer W passes through the opening  12   g . A gate valve  14  is provided at the sidewall of the chamber  12  to open or close the opening  12   g.    
     Within the chamber  12 , a substrate support  13  configured to support the wafer W is provided near a center of the chamber  12 . The substrate support  13  includes a supporting member  15  and a stage  16 . The supporting member  15  has a substantially cylindrical shape and is provided on a bottom of the chamber  12 . The supporting member  15  is made of, by way of non-limiting example, an insulating material. Within the chamber  12 , the supporting member  15  is extended upwards from the bottom of the chamber  12 . The stage  16  is provided within the processing space  12   c . The stage  16  is supported by the supporting member  15 . 
     The stage  16  is configured to hold the wafer W placed thereon. The stage  16  includes a lower electrode  18  and an electrostatic chuck  20 . The lower electrode  18  includes a first plate  18   a  and a second plate  18   b . Each of the first plate  18   a  and the second plate  18   b  is made of a metal such as, but not limited to, aluminum, and has a substantially disk shape. The second plate  18   b  is provided on the first plate  18   a  and electrically connected with the first plate  18   a.    
     The electrostatic chuck  20  is provided on the second plate  18   b . The electrostatic chuck  20  includes an insulating layer and a film-shaped electrode embedded in the insulating layer. The electrode of the electrostatic chuck  20  is electrically connected with a DC power supply  22  via a switch  23 . A DC voltage from the DC power supply  22  is applied to the electrode of the electrostatic chuck  20 . If the DC voltage is applied to the electrode of the electrostatic chuck  20 , an electrostatic attracting force is generated in the electrostatic chuck  20  and attracts the wafer W toward the electrostatic chuck  20 , thus allowing the wafer W to be held on the electrostatic chuck  20 . Further, a heater may be embedded within the electrostatic chuck  20 , and this heater may be connected to a heater power supply provided at an outside of the chamber  12 . 
     A focus ring  24  is provided on a peripheral portion of the second plate  18   b . The focus ring  24  is a substantially annular plate. The focus ring  24  is disposed to surround an edge of the wafer W and the electrostatic chuck  20 . The focus ring  24  is configured to improve etching uniformity. The focus ring  24  may be formed of such a material as, but not limited to, silicon or quartz. 
     A path  18   f  is formed within the second plate  18   b . A temperature control fluid is supplied via a pipeline  26   a  into the path  18   f  from a chiller unit provided at an outside of the chamber  12 . The temperature control fluid supplied into the path  18   f  is returned back into the chiller unit via a pipeline  26   b . That is, the temperature control fluid is circulated between the path  18   f  and the chiller unit. By controlling a temperature of this temperature control fluid, a temperature of the stage  16  (or the electrostatic chuck  20 ) and a temperature of the wafer W are adjusted. As an example of the temperature control fluid, Galden (registered trademark) may be used. 
     The plasma processing apparatus  10  is provided with a gas supply line  28 . The gas supply line  28  supplies a heat transfer gas such as, but not limited to, a He gas from a heat transfer gas supply device into a gap between a top surface of the electrostatic chuck  20  and a rear surface of the wafer W. 
     The plasma processing apparatus  10  is further equipped with a shower head  30 . The shower head  30  is disposed above the stage  16 . The shower head  30  is supported at an upper portion of the chamber  12  with an insulating member  32  therebetween. The shower head  30  may include an electrode plate  34  and a supporting body  36 . A bottom surface of the electrode plate  34  is in direct contact with a processing space  12   c . The electrode plate  34  is provided with a multiple number of gas discharge holes  34   a . This electrode plate  34  may be made of a material such as, but not limited to, silicon or silicon oxide. 
     The supporting body  36  is configured to support the electrode plate  34  in a detachable manner, and is made of a conductive material such as aluminum. A gas diffusion space  36   a  is provided within the supporting body  36 . A multiple number of gas through holes  36   b  extend downwards from the gas diffusion space  36   a  to communicate with the gas discharge holes  34   a . The supporting body  36  is provided with a gas inlet opening  36   c  through which a gas is introduced into the gas diffusion space  36   a . A gas supply line  38  is connected to the gas inlet opening  36   c.    
     The gas supply line  38  is connected to a gas source group  40  via a valve group  42  and a flow rate controller group  44 . The gas source group  40  includes a plurality of gas sources for various kinds of gases for use in plasma etching. The valve group  42  includes a plurality of valves, and the flow rate controller group  44  includes a plurality of flow rate controllers such as mass flow controllers or pressure control type flow rate controllers. Each of the gas sources belonging to the gas source group  40  is connected to the gas supply line  38  via a corresponding valve belonging to the valve group  42  and a corresponding flow rate controller belonging to the flow rate controller group  44 . The gas source group  40  supplies the various kinds of gases for the plasma etching into the gas diffusion space  36   a  of the supporting body  36  through the gas supply line  38 . The gases introduced into the gas diffusion space  36   a  are supplied from the gas diffusion space  36   a  into the chamber  12  through the gas through holes  36   b  and the gas discharge holes  34   a  while being distributed in a shower shape. 
     A first radio frequency power supply  62  is connected to the lower electrode  18  via a matching device  63 . Further, a second radio frequency power supply  64  is connected to the lower electrode  18  via a matching device  65 . The first radio frequency power supply  62  is a power source configured to generate a radio frequency power for plasma formation. In the plasma processing, the first radio frequency power supply  62  supplies the radio frequency power having a preset frequency ranging from 27 MHz to 100 MHZ, e.g., 40 MHz to the lower electrode  18  of the stage  16 . The second radio frequency power supply  64  is a power source configured to generate a radio frequency power for ion attraction (bias). The second radio frequency power supply  64  supplies the radio frequency power having a predetermined frequency lower than the first radio frequency power supply  62  ranging from 400 kHz to 13.56 MHz, e.g., 3 MHz to the lower electrode  18  of the stage  16 . In this way, the stage  16  is configured to be capable of applying the dual radio frequency powers having the different frequencies from the first radio frequency power supply  62  and the second radio frequency power supply  64 . The shower head  30  and the stage  16  serve as a pair of electrodes (an upper electrode and a lower electrode). 
     The supporting body  36  of the shower head  30  is connected to a variable DC power supply  68  via a low pass filter (LPF)  66 . The variable DC power supply  68  is configured to turn on/off a power feed by an on/off switch  67 . A current/voltage of the variable DC power supply  68  and an on/off operation of the on/off switch  67  are controlled by a controller  70  to be described later. Further, when plasma is formed in the processing space as the radio frequency powers from the first radio frequency power supply  62  and the second radio frequency power supply  64  are applied to the stage  16 , the on/off switch  67  is turned on by the controller  70  when necessary, and a preset DC voltage is applied to the supporting body  36 . 
     An exhaust port  51  is formed at a bottom of the chamber  12  next to the substrate support  13 . The exhaust port  51  is connected with an exhaust device  50  via an exhaust line  52 . The exhaust device  50  includes a pressure controller such as a pressure control valve and a vacuum pump such as a turbo molecular pump. The exhaust device  50  is capable of decompressing the chamber  12  to a required pressure level by evacuating the chamber  12  through the exhaust port  51  and the exhaust line  52 . 
     The chamber  12  is provided with a baffle plate  48  at an upstream of the exhaust port  51  with regard to a flow of an exhaust gas toward the exhaust port  51 . The baffle plate  48  is disposed between the substrate support  13  and an inner side surface of the chamber  12 , surrounding the substrate support  13 . The baffle plate  48  is, for example, a plate-shaped member and may be formed by coating a surface of an aluminum base member with ceramics such as Y 2 O 3 . The baffle plate  48  is made of a member having multiple number of slits, a mesh member, or a member having a multiple number of punching holes, so the exhaust gas can pass through the baffle plate  48 . An internal space of the chamber  12  is partitioned by the baffle plate  48  into the processing space  12   c  in which the wafer W is processed by using the plasma; and an exhaust space connected with an exhaust system such as the exhaust line  52  and the exhaust device  50  configured to evacuate the chamber  12 . 
     A heater  55  is provided in a region within the chamber  12  which is not exposed to the plasma and the radio frequency powers. As an example, the heater  55  is disposed in the exhaust space. The heater  55  may be, by way of non-limiting example, an infrared heater such as a carbon wire heater. The heater  55  is disposed to surround the substrate support  13  while being spaced apart from the inner side surface of the chamber  12 , the bottom of the chamber  12 , the substrate support  13  and the baffle plate  48 . That is, the heater  55  is provided along a side surface of the substrate support  13  while being distanced apart from the chamber  12 , the substrate support  13  and the baffle plate  48  lest the heater  55  should be in contact with the chamber  12 , the substrate support  13  and the baffle plate  48 . The heater  55  is connected to a heater power supply  56  via a wiring  57 . The heater  55  generates heat by a power supplied from the heater power supply  56 , and radiates infrared rays and heats members nearby. The heater power supply  56  supplies the power to the heater  55  in a pulse shape under the control of the controller  70  to be described below. Furthermore, the heater power supply  56  may be a DC power supply or a radio frequency power supply. 
     The plasma processing apparatus  10  is further equipped with the controller  70 . The controller  70  may be, by way of example, a computer including a processor, a storage, an input device, a display device, and so forth. The controller  70  controls the individual components of the plasma processing apparatus  10 . In the controller  70 , a command or the like may be inputted by an operator through the input device to manage the plasma processing apparatus  10 . Further, in the controller  70 , an operational status of the plasma processing apparatus  10  can be visually displayed by the display device. Further, control programs for controlling various processings to be performed in the plasma processing apparatus  10  by the processor and recipe data are stored in the storage of the controller  70 . As the processor of the controller  70  executes the control programs and controls the individual components of the plasma processing apparatus  10  according to the recipe data, a required processing is performed in the plasma processing apparatus  10 . 
     As mentioned above, in the plasma processing, a by-product is generated as the plasma processing is performed, and the generated by-product is scattered around within the chamber  12  and attached thereto. There is known a technique of cleaning this by-product by using plasma, as described in Patent Document 1, for example. In the cleaning using the plasma, however, it is difficult to remove the by-product from a region within the chamber  12  which is not exposed to the plasma and the radio frequency powers. By way of example, since the plasma and the radio frequency powers are blocked by the baffle plate  48 , the plasma and the radio frequency powers may not reach a space under the baffle plate  48  within the chamber  12 . Therefore, the by-product may be easily deposited under the baffle plate  48  within the chamber  12 . 
     As a resolution, in the plasma processing apparatus  10 , the heater  55  is placed in the region which is not exposed to the plasma and the radio frequency powers. For example, in the present exemplary embodiment, the heater  55  is disposed in the space under the baffle plate  48  within the chamber  12 . 
       FIG. 2  is a diagram illustrating a layout of the heater  55  according to the exemplary embodiment.  FIG. 2  shows the space under the baffle plate  48  within the chamber  12  and the vicinity thereof. In the space under the baffle plate  48  within the chamber  12 , the by-product may be easily deposited on a region  80  on the inner side surface of the chamber  12 . On this ground, the heater  55  is placed at a preset distance from the region  80  within the chamber  12  where the by-product may be easily deposited. 
     The heater  55  generates heat when the power is supplied from the heater power supply  56 .  FIG. 3  is a diagram illustrating an example of a temperature variation of the heater  55  according to the exemplary embodiment.  FIG. 3  shows the temperature variation after the power is supplied to the carbon wire heater used as the heater  55 . As can be seen from  FIG. 3 , if the power is supplied, a temperature of the carbon wire heater increases rapidly to 1000° C. in about 3 seconds. 
     If the heater power supply  56  supplies the power to the heater  55 , the heater  55  generates the heat, and the region  80  on the inner side surface of the chamber  12  is heated by the heat from the heater  55 . Accordingly, adhesion of the by-product is suppressed or the by-product is removed. 
     If the power is continuously supplied to the heater  55  from the heater power supply  56  to suppress adhesion of the by-product or remove the by-product, the heat in the region  80  on the inner side surface of the chamber  12  is transferred to an outer surface of the chamber  12 , resulting in an increase of a temperature of the outer surface of the chamber  12 . For example, an outer surface of the chamber  12  corresponding to the region  80  may be heated to a high temperature. If the outer surface of the chamber  12  is excessively heated, a countermeasure such as providing a heat insulator on the outer surface of the chamber  12  or the like is required for the sake of safety of the apparatus. Thus, it is desirable to maintain the outer surface of the chamber  12  at a temperature equal to or less than a preset tolerance temperature (e.g., 50° C.) which is regarded as being safe. 
     For the purpose, the heater power supply  56  supplies the pulsed power to the heater  55 .  FIG. 4  is a diagram illustrating an example of the pulsed power which is supplied to the heater according to the exemplary embodiment. The controller  70  turns on/off the supply of the power by the heater power supply  56 , thus allowing the pulsed power to be supplied to the heater  55 . 
     By disposing the heater  55  within the chamber  12 , a heating time can be shortened, and an inner surface of the chamber  12  can be heated efficiently. Further, by repeating heating/cooling by the heater  55  by way of supplying the pulsed power to the heater  55 , a temperature rise of the outer surface of the chamber  12  can be suppressed. A frequency of the pulsed power may be set to be equal to or lower than, e.g., 0.05 Hz. 
       FIG. 5  is a diagram showing an example of heating by the heater  55  according to the exemplary embodiment.  FIG. 5  illustrates a flat plate-shaped member  12   h  as a copy of the sidewall of the chamber  12 . The member  12   h  is made of the same metal (for example, aluminum) as the chamber  12  and has a thickness of 10 mm. A surface of the member  12   h  at a right-hand side of  FIG. 5  is referred to as a front surface, and a surface at a left-hand side of  FIG. 5  is referred to as a rear surface. The heater  55  is placed at a position 50 mm apart from the front surface of the member  12   h . In this configuration, the front surface of the member  12   h  corresponds to an inner wall surface of the chamber  12 . The rear surface of the member  12   h  corresponds to an outer wall surface of the chamber  12 . 
     When the pulsed power is supplied to this heater  55 , since the heat from the heater  55  is directly irradiated to the front surface of the member  12   h , a temperature of the front surface of the member  12   h  varies in response to a turning-on/off of the power supply. Meanwhile, since a temperature of the rear surface of the member  12   h  is changed by the heat transferred from the front surface thereof, a temperature variation of this rear surface is not as big as the temperature variation of the front surface.  FIG. 6  is a diagram illustrating an example of the temperature variations of the front surface and the rear surface of the member  12   h  according to the exemplary embodiment. In a power-on period during which the power supply is on, the temperature of the front surface of the member  12   h  increases rapidly due to the heat radiated from the heater  55 . In a power-off period in which the power supply is off, on the other hand, the temperature of the front surface of the member  12   h  decreases rapidly as the heat is diffused within the member  12   h . Meanwhile, since the heat radiation to the front surface of the member  12   h  from the heater  55  is stopped before the temperature of the rear surface of the member  12   h  increases rapidly due to the heat transferred from the front surface, the temperature of the rear surface of the member  12   h  no longer increases after being raised gently. 
     Thus, by adjusting the power-on period and the power-off period appropriately, the temperature of the front surface of the member  12   h  can be temporarily raised to a temperature at which the by-product is removed in the power-on period, while the temperature of the rear surface of the member  12   h  is maintained at a temperature equal to or lower than the tolerance temperature. The front surface of the member  12   h  corresponds to the inner wall surface of the chamber  12 . The rear surface of the member  12   h  corresponds to the outer wall surface of the chamber  12 . Thus, it is possible to temporarily increase the temperature of the inner wall surface of the chamber  12  up to the temperature at which the by-product is removed in the power-on period, while maintaining the temperature of the outer wall surface of the chamber  12  at the temperature equal to or lower than the tolerance temperature. 
     The controller  70  controls the heater power supply  56  to supply the pulsed power to the heater  55  while adjusting the power-on period and the power-off period appropriately. By way of example, a proper cycle of the power-on period and the power-off period is calculated through an experiment or the like. The controller  70  controls the heater power supply  56  to supply the pulsed power to the heater  55  with the calculated cycle. The controller  70  controls the heater power supply  56  to repeat an operation of turning-off the power supply after keeping on the power supply until the region  80  on the inner side surface of the chamber  12  is heated by the heat from the heater  55  to the temperature at which the by-product attached to the region  80  in the plasma processing volatilizes. By way of example, the controller  70  controls the heater power supply  56  to repeat the turning-on/off of the power supply such that, in the power-on period, the region  80  reaches the temperature at which the by-product volatilizes and the outer surface of the chamber  12  corresponding to the region  80  becomes equal to or lower than the tolerance temperature. For instance, when the by-product generated by the plasma processing is a titanium-based by-product, the controller  70  controls the heater power supply  56  to increase the temperature of the region  80  on the inner side surface of the chamber  12  to 80° C. to 100° C. temporarily in the power-on period. 
     Accordingly, the plasma processing apparatus  10  is capable of suppressing deposition of the by-product onto the region  80  on the inner side surface of the chamber  12 . Further, the plasma processing apparatus  10  is also capable of suppressing the temperature of the outer surface of the chamber  12  corresponding to the region  80  to the tolerance temperature or less. 
     Moreover, though the present exemplary embodiment has been described for the example where deposition of the by-product on the region  80  on the inner side surface of the chamber  12  is suppressed, the present exemplary embodiment is not limited thereto. The heater  55  can be placed at any region within the chamber  12  where the deposition of the by-product needs to be suppressed. By disposing the heater  55  at a position corresponding to the region within the chamber  12  which is not exposed to the plasma and the radio frequency powers and supplying the pulsed power to the heater  55  from the heater power supply  56 , the by-product can be suppressed from being deposited on the region within the chamber  12  which is not exposed to the plasma and the radio frequency powers. 
     Further, the inside of the chamber may be cleaned by using plasma. As an example, in the cleaning, a plasma processing is performed in the state that the wafer W is not placed in the chamber  12 , or in the state that a dummy wafer is placed therein. In this cleaning, the controller  70  may control the heater power supply  56  to supply the pulsed power to the heater  55 , thus accelerating removal of the by-product. For example, when the wafer W is plasma-processed, the controller  70  controls the heater power supply  56  to supply the power until the region not exposed to the plasma and the radio frequency powers reaches a first temperature in the power-on period during which the heater power supply  56  is on. For example, the first temperature is a temperature at which adhesion of the by-product is suppressed. Further, when the inside of the chamber  12  is cleaned with the plasma in the state that the wafer W is not placed within the chamber  12  or in the state that the dummy wafer is placed therein, the controller  70  controls the heater power supply  56  to supply the power until the region not exposed to the plasma and the radio frequency powers reaches a second temperature in the power-on period during which the heater power supply  56  is on. As an example, the second temperature is a temperature at which the removal of the by-product is accelerated. The second temperature may be set to be higher than the first temperature. By way of example, if the by-product generated by the plasma processing is the titanium-based by-product, the temperature of the region  80  on the inner side surface of the chamber  12  is increased up to 80° C. to 100° C. temporarily in the power-on period during which the heater power supply  56  is on, when the wafer W is plasma-processed. Accordingly, the titanium-based by-product generated when the plasma processing is performed can be suppressed from being attached to the region  80 . Meanwhile, when the cleaning is performed, the temperature of the region  80  on the inner side surface of the chamber  12  is temporarily increased up to 100° C. to 120° C. in the power-on period during which the heater power supply  56  is on. As a result, the removal of the titanium-based by-product attached to the region  80  can be accelerated. 
     Now, a specific example will be explained. In the following, an experiment where a temperature is measured by using a test object having a flat plate shape as a copy of the sidewall of the chamber  12  will be explained.  FIG. 7  is a diagram illustrating an example of the test object according to the exemplary embodiment.  FIG. 7  shows a structure of a flat plate-shaped test object  90 . An aluminum (A5052) flat plate having a size of 360 mm×200 mm and a thickness of 10 mm is used as the test object  90 . An upper side and a lower side of the test object  90  in  FIG. 7  are defined as an inner side and an outer side, and a left side and a right side of the test object  90  in  FIG. 7  are defined as an upper side and a lower side. The test object  90  is provided with thermocouples for measuring a temperature respectively provided at five front-surface positions of the test object  90 : a position F 1  (front center) near a center of a front surface thereof and positions F 2  (front upper side), F 3  (front inner side), F 4  (front lower side) and F 5  (front outer side) 40 mm apart from the position F 1  to the upper side, the inner side, the lower side and the outer side, respectively. Further, the test object  90  is also provided with thermocouples for measuring a temperature which are respectively provided at a rear-surface position B 1  (rear center) corresponding to the front-surface position F 1 , a rear-surface position B 2  (rear inner side) corresponding to the front-surface position F 3 , and a rear-surface position B 3  (rear outer side) corresponding to the front-surface position F 5 . The positions B 2  and B 3  are located 40 mm apart from the position B 1  near a center of a rear surface to the inner side and the outer side, respectively. 
       FIG. 8  is a diagram for describing an outline of the experiment according to the exemplary embodiment. In the experiment, heating is performed by the heater  55  placed at a position 55 mm away from the front surface of this test object  90 . A carbon wire heater is used as the heater  55 . The heater  55  is disposed through a glass pipe  91  to correspond to regions on the front surface of the test object  90  where the thermocouples are provided.  FIG. 9  is a diagram showing a schematic layout of the heater  55  and the test object  90  according to the exemplary embodiment. The heater  55  is disposed through the transparent zigzag glass pipe  91  to face the regions of the positions F 1  to F 5  while being distanced 50 mm apart from the front surface of the test object  90 . 
     In the experiment, a power having a current value of 20 A is supplied to the heater  55  when the power is on, and a current value is set to be OA when the power is off. In this way, the on/off powers are supplied in a pulse shape. 
       FIG. 10  is a diagram showing an experimental result according to the exemplary embodiment. A variation of the current value supplied to the heater  55  is shown in a lower portion of  FIG. 10 . Further, measurement results at the front-surface five positions F 1  to F 5  by the thermocouples placed on the front surface of the test object  90 , and measurement results at the rear-surface three positions B 1  to B 3  by the thermocouples placed on the rear surface of the test object  90  are shown in  FIG. 10 . 
     As shown in  FIG. 10 , a temperature of the front surface of the test object  90  can be varied in response to the turning on/off of the power supply, and the front surface of the test object  90  can be temporarily increased in a power-on period up to a temperature where a by-product is removed. By way of example, the temperatures at the front-surface positions F 1  (front center), F 2  (front upper side) and F 5  (front outer side) are temporarily increased in the power-on period up to 80° C. or higher at which the titanium-based by-product is removed. Meanwhile, the temperatures at the rear surface positions (rear center, rear outer side, and rear inner side) are maintained equal to or lower than 50° C. 
     Thus, in the plasma processing apparatus  10 , by placing the heater  55  within the chamber  12  appropriately and supplying the pulsed power to the heater  55 , deposition of the by-product within the chamber  12  can be suppressed. 
     As stated above, the plasma processing apparatus  10  according to the exemplary embodiment is equipped with the chamber  12 , the heater  55 , and the heater power supply  56 . The chamber  12  is configured to process the wafer W by using the plasma. The heater  55  is disposed to corresponding to the region within the chamber  12  which is not exposed to the plasma and the radio frequency powers. The heater power supply  56  is configured to supply the pulsed power to the heater  55 . With this configuration, the plasma processing apparatus  10  is capable of suppressing deposition of the by-product in the region within the chamber  12  which is not exposed to the plasma and the radio frequency powers. 
     Further, the plasma processing apparatus  10  is further equipped with the exhaust port  51  and the baffle plate  48 . The chamber  12  is evacuated through the exhaust port  51 . The baffle plate  48  is disposed at the upstream of the exhaust port  51  with regard to the flow of the exhaust gas within the chamber  12  toward the exhaust port  51 . The heater  55  is provided at the downstream of the baffle plate  48  with regard to the flow of the exhaust gas toward the exhaust port  51 . Accordingly, the plasma processing apparatus  10  is capable of suppressing the by-product from being deposited in the region at the downstream of the baffle plate  48  where the by-product may be easily deposited. 
     Furthermore, the plasma processing apparatus  10  is further equipped with the substrate support  13 . The substrate support  13  is disposed within the chamber  12  and supports the wafer W. The baffle plate  48  is disposed to surround the substrate support  13  between the substrate support  13  and the inner side surface of the chamber  12 . The heater  55  is placed between the baffle plate  48  and the exhaust port  51 , surrounding the substrate support  13 . With this configuration, the plasma processing apparatus  10  according to the exemplary embodiment is capable of suppressing deposition of the by-product in the region around the substrate support  13  under the baffle plate  48 . 
     Moreover, the heater power supply  56  repeats the operation of turning-off the power supply after keeping on the power supply until the region not exposed to the plasma and the radio frequency powers is heated by the heat from the heater  55  to the temperature at which the by-product volatilizes. Accordingly, in the plasma processing apparatus  10  according to the present exemplary embodiment, deposition of the by-product in the region not exposed to the plasma and the radio frequency powers can be suppressed. 
     In addition, the heater power supply  56  repeats the turning-on/off of the power supply such that, in the power-on period, the temperature of the region which is not exposed to the plasma and the radio frequency powers reaches the temperature at which the by-product volatilizes while the temperature of the outer surface of the chamber  12  corresponding to the region which is not exposed to the plasma and the radio frequency powers becomes equal to or lower than the tolerance temperature. Accordingly, the plasma processing apparatus  10  according to the exemplary embodiment is capable of suppressing deposition of the by-product in the region which is not exposed to the plasma and the radio frequency powers. Further, the plasma processing apparatus  10  according to the exemplary embodiment is capable of maintaining the outer surface of the chamber  12  equal to or lower than the tolerance temperature. 
     The exemplary embodiments disclosed so far are illustrative in all aspects and not limited thereto. In fact, the above exemplary embodiments can be embodied in various forms. Further, the above-described exemplary embodiments may be omitted, substituted, or changed in various forms without departing from the scope of the appended claims 
     By way of example, the above-exemplary embodiment has been described for the example where the cycle of the power-on period and the power-off period for the power supplied to the heater  55  from the heater power supply  56  is appropriately adjusted and set in advance. However, the exemplary embodiment may not be limited thereto. A temperature may be measured by using a temperature sensor, and the power-on period and the power-off period may be controlled based on the measured temperature. By way of example, the heater  55  is placed to correspond to a target region within the chamber  12  where deposition of the by-product needs to be suppressed. Further, the temperature sensor is provided at the target region within the chamber  12  and an outer surface of the chamber  12  corresponding to the target region. The heater power supply  56  may repeat, in the pulse shape, turning-off the power supply after keeping on supplying the power to the heater  55  from the heater power supply  56  until the temperature measured by the temperature sensor provided in the target region reaches the temperature at which the by-product volatilizes. Further, the heater power supply  56  may lengthen the power-off period as the temperature measured by the temperature sensor provided at the outer surface of the chamber  12  approaches the tolerance temperature. 
     Additionally, the above exemplary embodiment has been described for the example where the plasma processing apparatus  10  is the capacitively coupled plasma processing apparatus. However, the exemplary embodiment is not limited thereto and applicable to any of various kinds of plasma processing apparatuses. By way of example, the plasma processing apparatus  10  may be any of various kinds of plasma processing apparatuses such as an inductively coupled plasma processing apparatus, a plasma processing apparatus configured to excite a gas by a surface wave such as a microwave, and so forth. 
     Further, in the above-described exemplary embodiment, the first radio frequency power supply  62  and the second radio frequency power supply  64  are connected to the lower electrode  18 . However, a configuration of the plasma source is not limited thereto. By way of example, the first radio frequency power supply  62  for plasma formation may be connected to the shower head  30 . Further, the second radio frequency power supply  64  for ion attraction (bias) may not be connected to the lower electrode  18 . 
     In addition, in the above-described exemplary embodiment, an inter-electrode distance between the shower head  30  serving as an upper electrode and the stage  16  serving as a lower electrode is fixed. However, the exemplary embodiment is not limited thereto. In a parallel plate type plasma processing apparatus, the inter-electrode distance between the upper electrode and the lower electrode affects a plasma processing characteristic of a substrate. Thus, the plasma processing apparatus  10  may be configured to be capable of varying the inter-electrode distance between the shower head  30  and the stage  16 .  FIG. 11  is a diagram schematically illustrating an example of a cross section of a plasma processing apparatus according to another exemplary embodiment. A plasma processing apparatus  10  shown in  FIG. 11  includes a substrate support  13  and a shower head  30 . The substrate support  13  is disposed within the chamber  12  near a center thereof, and supports a wafer W. Though not shown, the substrate support  13  has the same configuration as that of  FIG. 1 , and a radio frequency power is applied to this substrate support  13  when plasma is formed. The shower head  30  is disposed to face the substrate support  13 . The shower head  30  and the substrate support  13  serve as an upper electrode and a lower electrode, respectively. Furthermore, the plasma processing apparatus  10  is further equipped with an elevator  200  configured to move the shower head  30  up and down. The elevator  200  is configured to move the shower head  30  up and down between a ceiling of the chamber  12  and the substrate support  13 . The shower head  30  is provided with a bellows  210  which surrounds the elevator  200 . The bellows  210  is airtightly connected to a ceiling wall of the chamber  12  and a top surface of the shower head  30 . The chamber  12  has therein a cylindrical wall  220  surrounding the shower head  30 , a processing space  12   c  and the substrate support  13 . An exhaust port  51  is provided at a bottom of a side portion of the chamber  12 . The exhaust port  51  is connected with an exhaust device  50  via an exhaust line  52 . The exhaust device  50  evacuates the chamber  12  through the exhaust port  51  and the exhaust line  52 , thus allowing the inside of the chamber  12  to be decompressed to a required pressure level. 
     The chamber  12  is provided with a baffle plate  48  at an upstream of the exhaust port  51  with regard to a flow of an exhaust gas toward the exhaust port  51 . The baffle plate  48  is disposed between an inner surface of a lower portion of the cylindrical wall  220  and the substrate support  13  to surround the substrate support  13 . The chamber  12  is partitioned by the baffle plate  48  into a processing space  12   c  in which the wafer W is processed by using the plasma and an exhaust space connected with an exhaust system such as the exhaust line  52  and the exhaust device  50  configured to evacuate the chamber  12 . The processing space  12   c  is a space formed by a bottom surface of the shower head  30 , the cylindrical wall  220 , the baffle plate  48  and the substrate support  13 . The processing space  12   c  is a space formed by, for example, the bottom surface of the shower head  30 , an inner surface of the cylindrical wall  220 , the baffle plate  48  and the substrate support  13 . The exhaust space is a space formed by, for example, an inner wall surface of the chamber  12 , the corresponding surface cylindrical wall  220 , an upper portion of a peripheral portion of the shower head  30 , and the ceiling of the chamber  12 . 
     Here, in cleaning using plasma, it is difficult to remove a by-product in a region within the chamber  12  which is not exposed to the plasma and radio frequency powers. Thus, a heater  55  is disposed in the region within the chamber  12  not exposed to the plasma and the radio frequency power. As an example, the heater  55  is disposed in the exhaust space. For example, the heater  55  is provided in a space  230  formed by an outer side of the cylindrical wall  220 , the shower head  30 , and the ceiling of the chamber  12 . With this configuration, the plasma processing apparatus  10  is capable of suppressing deposition of the by-product in the space  230 . Moreover, the plasma processing apparatus  10  is capable of suppressing a temperature of an outer surface of the chamber  12  corresponding to the space  230  to equal to or less than a tolerance temperature. 
     Further, though the above-described plasma processing apparatus  10  is the plasma processing apparatus configured to perform etching as the plasma processing, the exemplary embodiment may be applicable to various of other kinds of plasma processing apparatuses configured to perform a plasma processing. For example, the plasma processing apparatus  10  may be a single-wafer deposition apparatus configured to perform chemical vapor deposition (CVD), an atomic layer deposition (ALD), a physical vapor deposition (PVD), or the like, or may be a plasma processing apparatus configured to perform plasma annealing, plasma implantation, or the like. 
     Moreover, in the above-described exemplary embodiments, though the substrate is the semiconductor wafer, the substrate is not limited thereto. By way of example, the substrate may be any of various other kinds of substrates such as a glass substrate. 
     According to the exemplary embodiment, it is possible to suppress the by-product from being deposited in the region within the chamber which is not exposed to the plasma and the radio frequency power. 
     From the foregoing, it will be appreciated that various exemplary embodiments of the present disclosure have been described herein for the purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various exemplary embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.