Patent Publication Number: US-2009229756-A1

Title: Plasma processing apparatus

Description:
TECHNICAL FIELD 
     This invention relates to a plasma processing apparatus for processing a surface of an object to be processed by generating a plasma discharge under near atmospheric pressure and exposing the object to the plasma discharge. This invention particularly relates to an atmospheric-pressure plasma processing apparatus suitable when the object is composed of a dielectric material such as a glass substrate. 
     BACKGROUND ART 
     Normal-pressure plasma processing apparatus are known in the art for processing a surface of an object such as a glass substrate by generating a plasma discharge under near atmospheric pressure and placing the object in the plasma discharge space. This kind of apparatus typically has a high-voltage electrode and a ground electrode arranged to be opposed to each other. Each of the electrodes has a solid dielectric layer formed in an opposing surface thereof to improve the stability of discharge. The solid dielectric layer is typically composed of a thermally-sprayed alumina or a ceramic plate. In many cases, the ground electrode also serves as a stage for the object to be placed thereon. The high-voltage electrode is disposed to be opposed to the object placed on the ground electrode-cum-stage. When the voltage is supplied to the high-voltage electrode, an electric field is impressed between the high-voltage electrode and the ground electrode-cum-stage, and an atmospheric-pressure plasma discharge is generated. A process gas suitable for the intended processing is introduced into the atmospheric-pressure plasma discharge. The process gas is plasmatized, contacts and reacts with the object, thereby processing the surface of the object. 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2004-228136. 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In recent years, objects to be processed have been enlarged, and accordingly, there has been a demand for enlargement of a ground electrode-cum-stage. Enlargement of the stage requires enlargement of a solid dielectric layer on a top surface thereof. However, it is not easy to form a large-area solid dielectric layer, which inevitably causes increase in manufacturing cost. 
     On the other hand, the objects are typically composed of a dielectric material such as glass. So, if the objects composed of a dielectric material can be utilized as a solid dielectric layer for the stage, there will be no need for disposing a solid dielectric layer on a metal surface of the stage. In this case, it is desirable to completely cover the metal surface of the stage with the object in such a manner that a peripheral portion of the object is a little more protruded than the metal surface of the stage so that an arc discharge can be prevented. 
     However, in this arrangement, no discharge is generated when the electrode is located above or outside of the peripheral portion of the object. When the electrode is moved further inward than the peripheral portion of the object to above an end portion of the metal surface of the stage, a plasma discharge is suddenly generated and a processing is started. Therefore, discharge condition tends to be unstable in a processing start point, i.e. a bordering portion between the peripheral portion and a main portion located further inside. As a result, the bordering portion (end portion of the main portion) may not be properly processed or may be damaged. 
     Means for Solving the Problem 
     In view of the above, according to the present invention, there is provided a plasma processing apparatus for processing a surface of an object to be processed which is mainly composed of a dielectric material by exposing the object to a near atmospheric-pressure plasma discharge, the apparatus comprising: 
     a stage including a first stage portion (main placement portion) having an exposed first metal surface (metallic main placement surface) and a second stage portion (side portion) having a second metal surface (side metal portion) covered with a solid dielectric layer (side dielectric part) and disposed on an outer peripheral portion of the first stage portion, the object being placed on the first metal surface of the first stage portion such that a peripheral portion of the object is protruded toward the second stage portion; and 
     an electrode relatively movable with respect to the stage within a range including a first movement range (first position) in which the electrode is opposed to the first stage portion to generate the plasma discharge and a second movement range (second position) in which the electrode is opposed to the second stage portion. 
     In this arrangement, the object to be processed can be utilized as a solid dielectric layer for the first metal surface of the stage, thus eliminating the necessity of providing a solid dielectric layer composed of a sprayed film or a ceramic plate on the first metal surface. This saves manufacturing cost and makes it easier to enlarge the stage. In this arrangement, an electric field can be impressed between the electrode in the second movement range and the second stage portion. This allows a run up discharge to be generated before the electrode enters the first movement range in preparation for a regular plasma processing. As a result, discharge condition at the beginning of a regular plasma discharge can be stabilized in a bordering portion between the peripheral portion and a main portion located further inside than the peripheral portion in the object. Damage to an end portion of the main portion of the object can be prevented and proper processing of the end portion may be ensured. 
     Preferably, the first metal surface is slightly smaller in area than the object. This allows the main portion of the object to cover the entirety of the first metal surface. Preferably, the peripheral portion of the object is placed on the second stage portion. 
     Preferably, a thickness and a dielectric constant of the solid dielectric layer of the second stage portion are set such that the plasma discharge is generated between the electrode in the second movement range and the second stage portion. 
     This ensures the generation of the run up discharge before the electrode enters the first movement range, thereby surely stabilizing the discharge condition at the end portion of the main portion of the object. 
     Preferably, the solid dielectric layer of the second stage portion includes an inner dielectric portion (peripheral edge placement portion) on which the peripheral portion of the object is to be placed and an outer dielectric portion disposed on an opposite side of the inner dielectric portion from the first stage portion, the outer dielectric portion being more protruded than the peripheral portion of the object. 
     Preferably, of the inner dielectric portion and the outer dielectric portion, at least the outer dielectric portion is disposed corresponding to the second metal surface and covers the second metal surface. 
     This allows the run up discharge to be generated outside of the peripheral portion of the object. 
     Preferably, a ratio of the thickness to the dielectric constant of the outer dielectric portion is substantially the same as a ratio of a thickness to a dielectric constant of the object. 
     This allows the run up discharge to be generated above the outer dielectric portion located further outside than the peripheral portion of the object. 
     Preferably, a ratio of the thickness to the dielectric constant of the outer dielectric portion is substantially the same as a ratio of a thickness to a dielectric constant of the object. 
     Preferably, the dielectric constant and the thickness of the outer dielectric portion are set such that a capacitance per unit area of the outer dielectric portion is equal to a capacitance per unit area of the object. 
     This allows the condition of the run up discharge above the outer dielectric portion to be substantially the same as the condition of the regular discharge above the main portion of the object. 
     Preferably, the electrode has a width astride the outer dielectric portion and the first stage portion in a direction of the relative movement. 
     This allows the electric field to exist not only above the end portion of the main portion of the object but also above the outer dielectric portion when the electrode moves from the second movement range to the first movement range. By this, concentration of electric field above the end portion of the main portion of the object can be prevented and the proper processing of the end portion of the main portion of the object can be ensured. 
     Preferably, the width of the electrode in the direction of the relative movement is at least greater than a width of the inner dielectric portion in the direction of the relative movement. 
     The first metal surface may be more protruded toward the electrode than the second metal surface (contact surface between a second metal portion and the solid dielectric layer). A surface of the outer dielectric portion may be more protruded toward the electrode than the first metal surface. This arrangement is suitable when the dielectric constant of the outer dielectric portion is greater than the dielectric constant of the object. 
     When the dielectric constant of the outer dielectric portion is smaller than the dielectric constant of the object, it is preferable that the contact surface between the second metal portion and the solid dielectric layer is more protruded toward the electrode than the first metal surface. 
     Preferably, a surface of the outer dielectric portion is more protruded toward the electrode than the first metal surface by substantially the same amount as a thickness of the object. 
     This allows flow condition of a process gas between the electrode and the second stage portion during the run up discharge to be substantially the same as the flow condition of the process gas between the electrode and the object during the regular plasma discharge. 
     Preferably, a surface of the inner dielectric portion is flush with the first metal surface. Preferably, the surface of the inner dielectric portion is continuously flush with the first metal surface. 
     This allows the main portion of the object to be surely contacted with the first metal surface and this also allows the peripheral portion of the object to be surely contacted with the inner dielectric portion. This prevents a rear surface of the object and the stage from forming a gap therebetween. 
     The front surface of the inner dielectric portion and the first metal surface may be flush with each other, a rear surface of the inner dielectric portion may be an inclined surface inclined toward the front as the inner dielectric portion extends toward the first stage portion, and a thickness of the inner dielectric portion may be reduced toward the first stage portion (See  FIG. 7 ). 
     This allows an overall dielectric constant of the inner dielectric portion and the peripheral portion of the object placed on the inner dielectric portion to gradually become closer to the dielectric constant of the object alone toward the first stage portion. Accordingly, plasma discharge condition in a run up discharge zone above the peripheral portion of the object can be made closer to the plasma discharge condition in a regular discharge zone toward the regular discharge zone, thereby preventing discontinuity of the discharge condition in a bordering portion between the peripheral portion and the end portion of the main portion of the object. 
     Preferably, the inner dielectric portion and the outer dielectric portion are continuously and integrally formed. 
     This prevents the second metal portion from being exposed at a border between the inner dielectric portion and the outer dielectric portion, thereby preventing a creeping discharge from striking the second metal portion through the border between the inner dielectric portion and the outer dielectric portion. 
     Alternatively, the inner dielectric portion and the outer dielectric portion may be formed separately. 
     Preferably, a step is formed between the inner dielectric portion and the outer dielectric portion. In this arrangement, an end surface of the object can be placed against the step, thereby enabling the precise positioning of the object. 
     Preferably, a first metal portion of the first stage portion and the second metal portion of the second stage portion are in contact with or continuous from each other, and preferably, the second metal portion is disposed on the rear side of the inner dielectric portion. 
     This allows the run up discharge zone and the regular discharge zone of the plasma discharge to be continuous when the electrode is located astride the second movement range and the first movement range, thereby further ensuring proper processing of the end portion of the main portion of the object. 
     Preferably, the stage comprises a stage body made of metal; 
     wherein a portion located further inward than a peripheral portion in the stage body includes the exposed first metal surface to constitute the first stage portion; and 
     wherein the peripheral portion of the stage body includes the second metal surface covered with the solid dielectric layer, the peripheral portion of the stage body and the solid dielectric layer constituting the second stage portion. 
     In this arrangement, the first metal portion of the first stage portion and the second metal portion of the second stage portion can be integrally structured, thereby ensuring the continuity between the run up discharge zone and the regular discharge zone of the plasma discharge when the electrode is located astride the second movement range and the first movement range. 
     Preferably, the electrode is relatively movable within a range including the first movement range, the second movement range and a third movement range located on an opposite side of the second movement range from the first movement range. 
     Preferably, the apparatus further comprises a power supply circuit. Preferably, the power supply circuit starts supplying voltage to the electrode for the plasma discharge when the electrode reaches a predetermined position while the electrode moves from the third movement range toward the first movement range via the second movement range, the predetermined position being located between a position in which the electrode is located astride the second movement range and the third movement range and a position in which the electrode is located immediately before the first movement range. 
     In this arrangement, direction of electric field from the electrode at the start of the voltage supply can be surely directed toward the second metal, and the generation of an abnormal electrical discharge from the electrode can be prevented. Local concentration of the electric field from the electrode on an outer end portion of the second metal can be avoided, and damage to the solid dielectric layer of the second stage portion can be prevented. 
     The electrode may be located astride the second movement range and the third movement range at the predetermined position. In this case, it is preferable that approximately 30 to 70 percent of the electrode is in the second movement range and the rest of the electrode is in the third movement range. 
     Making the percentage of the electrode being placed in the second movement range 30 percent or more surely prevents the abnormal electrical discharge at the start of the voltage supply and surely avoids the concentration of the electric field on portions such as the outer end portion of the second metal. Making the percentage of the electrode being placed in the second movement range 70 percent or less eliminates necessity of making the second stage portion unnecessarily wide. 
     More preferably, approximately 50 percent of the electrode is in the second movement range and the rest of the electrode is in the third movement range. 
     This surely prevents the abnormal electrical discharge from the electrode and surely avoids the concentration of the electric field on the outer end portion of the second metal. 
     The width of the electrode in the direction of the relative movement of the electrode may be greater than, or equal to, or smaller than the width of the second stage portion (i.e. the second movement range) in the direction of the relative movement of the electrode. 
     The predetermined position may be set anywhere between the position astride the second movement range and the third movement range and a position immediately before the first movement range. 
     When the width of the electrode is greater than the width of the second stage portion, the predetermined position may be a position astride the second movement range and the third movement range and at the same time immediately before the first movement range. 
     When the width of the electrode is smaller than the width of the second stage portion, the predetermined position does not have to be a position astride the second movement range and the third movement range. The predetermined position may be a position in which an entirety of the electrode in a width direction is within the second movement range. 
     Preferably, the stage further includes a third stage portion having insulation properties and located on an opposite side of the second stage portion from the first stage portion. Preferably, when the electrode is in the third movement range, the electrode is opposed to the third stage portion. 
     This allows the electrode to stand by above the third stage portion. A passageway for the process gas may be formed outside of the second stage portion, between the electrode and the third stage portion. 
     It is preferable that a front surface of the third stage portion is flush with a front surface of the solid dielectric layer of the second stage portion. 
     According to another aspect of the present invention, there is provided an atmospheric-pressure plasma processing apparatus for processing a surface of an object to be processed which is mainly composed of a dielectric material by exposing the object to a near atmospheric-pressure plasma discharge, the apparatus comprising: 
     a stage including a first stage portion having an exposed first metal surface and a second stage portion having a second metal surface covered with a solid dielectric layer and disposed on an outer peripheral portion of the first stage portion, the object being placed on the first metal surface of the first stage portion such that a peripheral portion of the object is protruded toward the second stage portion; 
     a first electrode relatively movable with respect to the stage within a range including a first movement range in which the electrode is opposed to the first stage portion, a second movement range in which the electrode is opposed to the second stage portion and a third movement range located on an opposite side of the second movement range from the first movement range; 
     a second electrode located more to the third movement range side than the first electrode and relatively movable with respect to the stage in unison with the first electrode over a range including the first movement range, the second movement range and the third movement range; 
     a first power supply circuit that starts supplying voltage to the first electrode for the plasma discharge when the first electrode reaches a predetermined position during an entrance movement in which the first and second electrodes move from the third movement range toward the first movement range via the second movement range, the predetermined position being located between a position in which the first electrode is located astride the second movement range and the third movement range and a position in which the first electrode is located immediately before the first movement range; and 
     a second power supply circuit that starts supplying voltage to the second electrode for the plasma discharge when the second electrode reaches a predetermined position during the entrance movement, the predetermined position being located between a position in which the second electrode is located astride the second movement range and the third movement range and a position in which the second electrode is located immediately before the first movement range. 
     In this arrangement, the object can be utilized as the solid dielectric layer for the first metal surface of the stage, thereby eliminating the necessity of providing a solid dielectric layer composed of a sprayed film or a ceramic plate on the first metal surface. This reduces manufacturing cost and makes it easier to enlarge a stage. An electric field can be impressed between the electrode in the second movement range and the second stage portion. This allows a run up discharge to be generated before the electrode enters the first movement range in preparation for a regular plasma processing. As a result, discharge condition at the beginning of a regular plasma discharge can be stabilized in a bordering portion between the peripheral portion and a main portion located further inside than the peripheral portion in the object. Accordingly, damage to an end portion of the main portion of the object can be prevented and proper processing of the end portion can be ensured. 
     Moreover, the voltage supply to the first electrode is started when the first electrode reaches the predetermined position, which ensures that a direction of electric field from the first electrode is directed toward the second metal. Subsequently, the voltage supply to the second electrode is started when the second electrode reaches the predetermined position, which ensures that a direction of electric field from the second electrode is directed toward the second metal. In this way, by starting the voltage supply to the first and second electrodes in sequence, abnormal electrical discharge and concentration of electric field can be prevented at the beginning of the voltage supply. 
     Types of electrical discharge suitable for the surface processing according to the present invention include corona discharge, creeping discharge, dielectric barrier discharge and glow discharge. Glow discharge under near atmospheric pressure (generally normal pressure) is preferable. Here, the near atmospheric pressure refers to a pressure in the range of 1.013×10 4  to 50.663×10 4  Pa. Considering the ease of pressure control and the simplicity of the structure of the apparatus, a pressure in the range of 1.333×10 4  to 10.664×10 4  Pa is preferable and a pressure in the range of 9.331×10 4  to 10.397×10 4  Pa is more preferable. 
     EFFECT OF THE INVENTION 
     According to this invention, the object can be utilized as the solid dielectric layer for the first metal surface of the stage. This eliminates the necessity of providing a solid dielectric layer composed of a sprayed film or a ceramic plate on the first metal surface. This reduces manufacturing cost and makes it easier to enlarge a stage. In addition, an electric field can be impressed between the electrode in the second movement range and the second stage portion. This allows a run up discharge to be generated in preparation for a regular plasma processing. As a result, discharge condition at the beginning of a regular plasma discharge above the end portion of the main portion of the object can be stabilized. Accordingly, damage to portions including the end portion of the main portion of the object can be prevented and proper processing of the end portion can be ensured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  This is a schematic front cross-sectional view of a normal-pressure plasma processing apparatus according to a first embodiment of the present invention. 
         FIG. 2  This is a front cross-sectional view of the normal-pressure plasma processing apparatus showing the step of placing a substrate on a stage in processing of the substrate by the apparatus. 
         FIG. 3  This is a front cross-sectional view of the normal-pressure plasma processing apparatus showing the step of locating an electrode in a second movement range and a run up discharge generated above an outer dielectric portion in the processing of the substrate by the apparatus. 
         FIG. 4  This is a front cross-sectional view of the normal-pressure plasma processing apparatus showing the steps of covering the entirety of a second stage portion by the electrode and generating the run up discharge above a peripheral portion of the substrate as well in the processing of the substrate by the apparatus. 
         FIG. 5  This is a front cross-sectional view of the normal-pressure plasma processing apparatus showing the steps of locating the electrode astride a location above the second stage portion and a location above an end portion of a first stage portion and generating a regular plasma discharge above an end portion of a main portion of the substrate in the processing of the substrate by the apparatus. 
         FIG. 6  This is a front cross-sectional view of the normal-pressure plasma processing apparatus showing the step of plasma-processing a generally central portion of the main portion of the substrate by the apparatus. 
         FIG. 7  This is a partial schematic front cross-sectional view of a normal-pressure plasma processing apparatus according to a second embodiment of the present invention (a version in which the solid dielectric layer is modified). 
         FIG. 8  This is a partial schematic front cross-sectional view of a normal-pressure plasma processing apparatus according to a third embodiment of the present invention (a version in which the solid dielectric layer is modified). 
         FIG. 9  This is a partial schematic front cross-sectional view of a normal-pressure plasma processing apparatus according to a fourth embodiment of the present invention (a version in which the solid dielectric layer is modified). 
         FIG. 10  This is a schematic front cross-sectional view of a normal-pressure plasma processing apparatus according to a fifth embodiment of the present invention. 
         FIG. 11  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to the fifth embodiment showing the steps of retreating a processing unit to the outside of the stage, placing a substrate on the stage, and starting to move the processing unit toward above the stage in the processing of the substrate by the apparatus. 
         FIG. 12  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to the fifth embodiment showing the step of locating a right electrode in a predetermined position astride the second movement range and a third movement range in the processing of the substrate by the apparatus. 
         FIG. 13  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to the fifth embodiment showing the step of locating a middle electrode in the predetermined position in the processing of the substrate by the apparatus. 
         FIG. 14  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to the fifth embodiment showing the step of locating a left electrode in the predetermined position and the right electrode in a position astride a first movement range and the second movement range in the processing of the substrate by the apparatus. 
         FIG. 15  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to the fifth embodiment showing the steps of locating the entirety of the processing unit within the first movement range and processing the main portion of the substrate with plasma. 
         FIG. 16  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to a variation of the fifth embodiment wherein the predetermined position that is a starting point of voltage supply is a position in which an entirety of each of the electrodes is within the second movement range, showing the right electrode in the predetermined position. 
         FIG. 17  This is a front cross-sectional view of a normal-pressure plasma processing apparatus according to a sixth embodiment of the present invention having a single electrode wider than the second stage portion, showing the step of locating the electrode in the predetermined position astride the second movement range and the third movement range. 
         FIG. 18  This is a front cross-sectional view of the normal-pressure plasma processing apparatus according to a variation of the sixth embodiment wherein the predetermined position of the electrode that is a starting point of voltage supply is a position immediately before the first movement range. 
     
    
    
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
         W substrate (object to be processed) 
         Wa main portion of the substrate 
         Wae end portion of the main portion of the substrate 
         Wb peripheral portion of the substrate 
         M atmospheric-pressure plasma processing apparatus 
           10  processing unit 
           11  electrode 
           11 A electrode 
           11 B electrode 
           11 C electrode 
           12  holder 
           13  solid dielectric plate 
           20  stage 
           20 A stage body 
           21  first stage portion 
           21   a  first metal surface 
           22  second stage portion 
           23  outer frame, third stage portion 
           24  second metal portion 
           24   a  second metal surface 
           25  solid dielectric layer 
           26  inner dielectric portion 
           27  outer dielectric portion 
           30  power supply circuit 
           31 A switch part 
           31 B switch part 
           31 C switch part 
           40  moving mechanism 
         D 1  regular plasma discharge zone 
         D 2  plasma discharge run up zone 
         D 2   a  run up discharge zone 
         D 2   b  run up discharge zone 
         R 1  first movement range 
         R 2  second movement range 
         R 3  third movement range 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A first embodiment of the present invention will be described below. 
       FIG. 1  shows a schematic drawing of a normal-pressure plasma processing apparatus M. The normal-pressure plasma processing apparatus M includes a processing unit  10  and a stage  20 . The processing unit  10  has a high-voltage electrode  11  and a holder  12  holding the electrode  11 . The processing unit  10  and the high-voltage electrode  11  extend in a direction orthogonal to the plane of the drawing of  FIG. 1 . A power supply circuit  30  is connected to the high-voltage electrode  11 . The power supply circuit  30  supplies voltage to the electrode  11  for generating atmospheric-pressure plasma discharge. The supply voltage may be continuous-wave voltage such as sine wave or intermittent wave voltage such as pulse wave. A solid dielectric plate  13  as a solid dielectric layer made of ceramic is disposed on a bottom portion of the processing unit  10  including an under surface of the high-voltage electrode  11 . 
     Although not shown in the drawing, a process gas supply line from the process gas source is connected to the processing unit  10 . Process gas from the process gas supply line is blown downward to the processing unit  10 . A kind of gas suitable for the intended processing is used as the process gas. For example, fluorocarbon compounds such as CF 4  and nitrogen are used for etching processing or for water repellent processing. 
     The stage  20  is located below the processing unit  10 . A gap between an under surface of the processing unit  10  (under surface of the solid dielectric plate  13 ) and the stage  20  is in the order of some millimeters. The gap is exaggerated in the drawing. 
     The stage  20  includes a first stage portion  21 , a second stage portion  22  disposed on an outer peripheral portion of the first stage portion  21  and an outer frame  23  (third stage portion) disposed on an outer peripheral portion of the second stage portion  22 . 
     The first stage portion  21  is made of metal (first metal) such as aluminum and has a quadrangular shape in plan view. A depth of the first stage portion  21  (dimension in the direction orthogonal to the plane of the drawing of  FIG. 1 ) is substantially the same as a length of the electrode  11 . 
     The solid dielectric layer is not provided on a top surface  21   a  of the first stage portion  21  made of metal (first metal surface), and the metal surface  21   a  is exposed. The metal surface  21   a  has a quadrangular shape in plan view and extends horizontally. 
     As shown in the imaginary line in  FIG. 1 , a substrate (object to be processed) W is to be directly placed on the exposed first metal surface  21   a . The substrate W may be composed of a dielectric material such as a glass for a large liquid crystal display or a color filter, having a quadrangular shape in plan view. Relative dielectric constant ∈ w  of the glass composing the substrate W is approximately ∈ w =5. A thickness t w  of the substrate W is, for example, approximately t w =0.7 millimeters. 
     An area of the first metal surface  21   a  (area of the first stage portion  21 ) is slightly smaller than an area of the substrate W. Accordingly, a main portion Wa located further inside than a peripheral portion Wb in the substrate W covers the entirety of the first metal surface  21   a . The peripheral portion Wb of the substrate W protrudes further outward than the first metal surface  21   a , in other words, protrudes toward the second stage portion  22 . The amount of protrusion of the peripheral portion Wb of the substrate from the first metal surface  21   a  is, for example, approximately 10 millimeters. 
     The second stage portion  22  has a second metal  24  and a solid dielectric layer  25 . The second metal  24  is composed of metal such as aluminum. The second metal  24  integrally continues from the first metal composing the first stage portion  21 . The first and second metals  21 ,  24  constitute a stage body  20 A. 
     To be more in detail, the stage  20  includes the stage body  20 A composed of aluminum, etc. and having a quadrangular shape in plan view. A central portion of the stage body  20 A (portion located further inside than a peripheral portion) is the first metal  21  (first stage portion) and the peripheral portion of the stage body  20 A is the second metal  24 . The stage body  20 A (first and second metals  21 ,  24 ) is electrically grounded. Hereby, the stage body  20 A serves as a ground electrode facing the high voltage electrode  11 . 
     A top surface  24   a  of the second metal  24  (second metal surface) of the second stage portion  22  is recessed relative to the first metal surface  21   a  of the first stage portion  21  and a step is formed between the first and second metal surfaces. (The first metal surface  21   a  is more protruded upward than the second metal surface  24   a .) The second metal surface  24   a  is horizontal. 
     The second metal surface  24   a  is provided with the solid dielectric layer  25  thereon. (Of the peripheral portion  24  and the main portion  21  located further inside than the peripheral portion in the stage body  20 A, only the peripheral portion  24  is provided with the solid dielectric layer  25  thereon.) The solid dielectric layer  25  covers the entirety of the second metal surface  24   a . The solid dielectric layer  25  is composed of a ceramic material such as alumina (Al 2 O 3 ). Relative dielectric constant ∈ 25  of the alumina composing the solid dielectric layer  25  is approximately twice the relative dielectric constant of the substrate W and is approximately ∈ 25 =10. 
     The solid dielectric layer  25  has an inner dielectric portion  26  on the first stage portion  21  side and an outer dielectric portion  27  on the outer frame  23  side. The inner and outer dielectric portions  26 ,  27  are continuously and integrally formed. 
     Inner end surface (end surface on the first stage portion  21  side) of the inner dielectric portion  26  is abutted against a step-riser surface between the first metal surface  21   a  and the second metal surface  24   a . A top surface of the inner dielectric portion  26  is flush with the first metal surface  21   a.    
     The peripheral portion Wb of the substrate W is to be placed on the top surface of the inner dielectric portion  26 . 
     The outer dielectric portion  27  is thicker than the inner dielectric portion  26 . The outer dielectric portion  27  is more protruded upward than the top surface of the inner dielectric portion  26  and the first metal surface  21   a . A step is formed between the outer dielectric portion  27  and the inner dielectric portion  26 . The step is located further inside than an outer end portion of the second metal  24  (on the first stage portion  21  side). 
     A peripheral surface of the substrate W is placed against a step-riser surface between the outer dielectric portion  27  and the inner dielectric portion  26 . A height of the step between the outer dielectric portion  27  and the inner dielectric portion  26  is substantially the same as a thickness of the substrate W. Accordingly, a top surface of the outer dielectric portion  27  and a top surface of the substrate W are generally flush with each other. 
     The outer dielectric portion  27  is located further outside than the substrate W. 
     An outer end surface of the outer dielectric portion  27  is more protruded outward than the second metal  24 . The outer frame  23  composed of insulator material such as resin is disposed on outer side surfaces of the outer dielectric portion  27  and the second metal  24 . 
     A thickness/dielectric constant ratio of the outer dielectric portion  27  is set substantially the same as a thickness/dielectric constant ratio of the substrate W. This makes a discharge condition above the second stage  22  substantially the same as the discharge condition above the first stage  21 . Accordingly, when the dielectric constant of the solid dielectric layer  25  is twice the dielectric constant of the substrate W, the thickness of the outer dielectric portion  27  is set substantially twice the thickness of the substrate W. When the relative dielectric constant of the substrate W made of glass is in an approximate range of ∈ w =5.3 to 6.5 and the thickness of the substrate W is in an approximate range of t w =0.5 to 0.7 millimeters and the relative dielectric constant of the solid dielectric layer  25  is in an approximate range of ∈ 25 =9 to 11, then the thickness of the outer dielectric portion  27  is set to be in an approximate range of t 27 =0.69 to 1.45 millimeters. For example, when the relative dielectric constant of the substrate W is approximately ∈ w =5 and the thickness of the substrate W is approximately t w =0.7 millimeters, the thickness of the outer dielectric portion  27  of the solid dielectric layer  25  made of alumina having the relative dielectric constant of approximately ∈ 25 =10 is set to be approximately t 27 =1.4 millimeters. 
     A width in a right and left direction of the second stage portion  22  is smaller than a width in a right and left direction of the high-voltage electrode  11 . This means that the high-voltage electrode  11  has a width astride the second stage portion  22  and the first stage portion  21 . 
     As shown in  FIG. 1 , the normal-pressure plasma processing apparatus M further includes a moving mechanism  40 . The moving mechanism  40  is connected to the processing unit  10 . The processing unit  10  is reciprocally moved by the moving mechanism  40  in the right and left direction (direction orthogonal to a longitudinal direction of the electrode  11 ) as indicated by arrows in  FIGS. 2 to 6 . This means that the high-voltage electrode  11  is relatively moved in the right and left direction with respect to the stage  20 . A range of the relative movement of the high-voltage electrode  11  includes a first movement range R 1  in which the electrode  11  is opposed to the first stage portion  21  and a second movement range R 2  in which the electrode is opposed to the second stage portion  22  (see  FIGS. 3 to 5 ). The high voltage electrode  11  in  FIG. 5  is opposed to an end portion of the first stage portion  21  and the second stage portion  22  and is located astride the first movement range R 1  and the second movement range R 2 . 
     Alternatively, the movement mechanism  40  may be connected to the stage  20 , and the stage  20  may be reciprocally moved in the right and left direction. 
     To process the surface of the substrate W using the normal-pressure plasma processing apparatus M of the construction described above, as shown in  FIG. 2 , firstly, the processing unit  10  is retreated to the outside (left, for example) of the stage  20 , and the substrate W is placed on the stage  20 . The main portion Wa located further inside than the peripheral portion Wb in the substrate W is directly placed on the first metal surface  21   a  of the stage body  20 A. The peripheral portion Wb is placed on the inner dielectric portion  26  of the second stage portion  22 . Since the top surface of the inner dielectric portion  26  and the first metal surface  21   a  are continuous and flush with each other, formation of a gap between a rear surface of the substrate W and the stage  20  can be prevented. The end surface of the substrate W is placed against the step riser surface between the inner dielectric portion  26  and the outer dielectric portion  27 . This allows the substrate W to be precisely positioned. The top surface (front surface) of the substrate W is to be flush with the top surface of the outer dielectric portion  27 . 
     Next, the processing unit  10  is moved by the moving mechanism  40  in the direction of the arrow (right direction) of  FIG. 2 . Then, as shown in  FIG. 3 , the high-voltage electrode  11  enters the second movement range R 2  in which the high-voltage electrode  11  is opposed to the second stage portion  22 . At this timing, the voltage is supplied to the high-voltage electrode  11  from the power supply circuit  30 . The timing for starting the voltage supply is preferably when the high-voltage electrode  11  has not yet reached above the end portion of the substrate W and located above the second stage portion  22  (preferably above the outer dielectric portion  27 ). This allows an electric field to be impressed between the high-voltage electrode  11  and the second metal  24  below the high-voltage electrode  11 , and an atmospheric-pressure plasma discharge is generated therebetween. The atmospheric-pressure plasma discharge initially is generated only above the outer dielectric portion  27  of the solid dielectric layer  25 . Consequently, a run up plasma discharge D 2  can be generated outside the substrate W. At this time, the outer dielectric portion  27  serves as the solid dielectric layer on a surface of the second metal  24 , thereby contributing to the stability of discharge. By properly setting the thickness and the dielectric constant of the outer dielectric portion  27 , the condition of the discharge can be made to be substantially the same as a discharge condition of a regular plasma discharge D 1  above the substrate W, which is to be described later. Since the top surface of the outer dielectric portion  27  and the top surface of the substrate W are flush with each other, a gap between the processing unit  10  in a second position and the outer dielectric portion  27  can be the same as a gap between the processing unit  10  in a first position and the substrate W. This allows the flow condition of the process gas at the time of the run up discharge D 2  to be substantially the same as the flow condition of the process gas at the time of the regular plasma discharge D 1  to be described later. 
     As shown in  FIG. 4 , as the processing unit  10  is moved in the direction of arrow, the high-voltage electrode  11  is moved to be placed above the peripheral portion Wb of the substrate W as well. This causes the run up discharge D 2  to be extended to above the peripheral portion Wb of the substrate W. The process gas is introduced to the run up discharge zone D 2 , and a front surface of the peripheral portion Wb of the substrate is plasma processed. At this time, the peripheral portion Wb of the substrate, together with the inner dielectric portion  26 , serves as a solid dielectric layer on the surface of the second metal  24 , thereby contributing to the stability of discharge. 
     Although the electrode  11  is located astride the outer dielectric portion  27  and the inner dielectric portion  26  at this time, the second metal  24  is prevented from being struck by a creeping discharge, etc. since the second metal  24  is completely covered by the outer dielectric portion  27  and the inner dielectric portion  26  which are continuously and integrally formed. 
     A total dielectric constant of the peripheral portion Wb of the substrate and the inner dielectric portion  27  is somewhat different from the dielectric constant of the outer dielectric portion  27  alone and also different from a dielectric constant of the main portion Wa of the substrate alone. This causes the discharge condition above the peripheral portion to be slightly different from the discharge condition of the run up discharge D 2  above the outer dielectric portion  27  or the discharge condition of the regular plasma discharge D 1  above the main portion Wa of the substrate. However, it does not pose a problem since the condition of the peripheral portion Wb of the substrate is not relevant to the quality of product. 
     As shown in  FIG. 5 , as the processing unit  10  is further moved in the direction of arrow, the high-voltage electrode  11  comes to a position astride the second movement range R 2  and an end portion of the first movement range R 1 . This causes an electric field to be impressed between the high-voltage electrode  11  and the end portion of the first stage portion  21 . As a result, the regular atmospheric-pressure plasma discharge D 1  is generated between the processing unit  10  and an end portion Wae (portion bordering with the peripheral portion Wb) of the main portion Wa of the substrate W. The process gas is introduced to the regular plasma discharge zone D 1 , and the end portion Wae of the main portion of the substrate W is plasma-processed. 
     The regular plasma processing starts from the end portion Wae of the main portion of the substrate W. At the beginning of the regular plasma processing, width of the overlap area between the high voltage electrode  11  and the first stage portion  21  is small. Thus the regular discharge zone D 1  is narrow. On the other hand, at this point, the high-voltage electrode  11  is also opposed to the second stage portion  22 . Accordingly, the electric field is maintained between the high-voltage electrode  11  and the second stage portion  22 . The run up discharge D 2  remains to be generated. This prevents the electric field from concentrating only on the narrow regular discharge zone D 1 . By this, damage to the power supply circuit  30  at the beginning of the regular plasma processing is prevented. The discharge condition above the end portion Wae of the main portion of the substrate W is stabilized. Prior to the regular plasma discharge D 1 , the run up discharge D 2  above the second stage portion  22  raises a temperature of the electrode  11 . This causes a solid dielectric plate  13  made of ceramic to be dried and so on in preparation for the discharge. This further stabilizes the discharge condition above the end portion Wae of the main portion of the substrate W. Moreover, since the run up discharge zone D 2  and the regular discharge zone D 1  are continuous, the plasma can communicate between these two discharge zones D 1 , D 2 . As a result, substantially homogeneous plasma can be obtained across the discharge zones. This allows the end portion Wae of the main portion of the substrate W to be processed in the same manner as a central portion of the substrate W, thereby promoting homogeneity of processing. 
     As shown in  FIG. 6 , the processing unit  10  is further moved in the direction of arrow. Then, the entirety of the electrode  11  is located in the first movement range R 1  to be opposed only to the first stage portion  21 . The regular plasma discharge D 1  is generated between the electrode  11  in the first movement range R 1  and the main portion Wa of the substrate W to allow the main portion Wa of the substrate W to be plasma-processed. At this time, the main portion Wa of the substrate W serves as a solid dielectric layer for the first stage portion  21 . This eliminates the necessity of providing a solid dielectric layer on the first metal surface  21   a , thus reducing manufacturing cost. In this way, the stage  20  can be easily enlarged to accommodate the increase in area of the substrate W. 
     The processing unit  10  is further moved in the direction of arrow to reach above an end portion on the opposite side (right side in  FIG. 6 ) of the stage  20 . In this way, the entirety of the main portion Wa of the substrate W can be plasma-processed. 
     The processing unit  10  may be reciprocated in the right and left direction according to need. 
     After the processing has finished, the processing unit  10  is retreated to the outside of the stage  20  and the substrate W is dismounted. 
     Other embodiments of the present invention will be described hereinafter. Same reference numerals are used to designate elements corresponding to those in the previously described embodiment and detailed explanations are omitted for such elements. 
       FIG. 7  shows a second embodiment of the present invention. In this embodiment, a bottom surface of the inner dielectric portion  26  of the solid dielectric layer  25  is an inclined surface inclined upward toward the inner end portion (opposite side from the outer dielectric portion  27 ). The inner dielectric portion  26  has a triangular cross-sectional configuration reduced in thickness toward the inner end portion. Then, the total dielectric constant of the inner dielectric portion  26  and the peripheral portion Wb of the substrate W placed on the inner dielectric portion  26  is gradually reduced toward the inner end portion of the inner dielectric portion  26  to be closer to the dielectric constant ∈ w  of the substrate W alone. 
     In this way, plasma discharge condition in the run up discharge zone D 2   a  above the peripheral portion Wb of the substrate W can be gradually made closer to the condition of the regular plasma discharge D 1  toward the main portion Wa of the substrate. This prevents discontinuity in the discharge condition in the boundary between the peripheral portion Wb and the end portion Wae of the main portion of the substrate W, further stabilizing the discharge condition in the end portion Wae of the main portion of the substrate W, thus promoting further homogenization of the processing. 
       FIG. 8  shows a third embodiment of the present invention. In this embodiment, the second metal  24  of the second stage portion  22  is formed of metal separately from the stage body  20 A which constitutes the first stage portion  21 . An inner end portion of the second metal  24  is in abutment with and direct contact with the first stage portion  21 . An earth wire is provided in the first stage portion  21 . The second metal  24  is electrically grounded via the first stage portion  21 . Alternatively, an earth wire may be directly connected to the second metal  24 . 
     The inner dielectric portion  26  and the outer dielectric portion  27  of the solid dielectric layer  25  are formed individually. The inner dielectric portion  26  is made of ceramic such as alumina and has a frame configuration with L-shaped cross-section. The peripheral portion Wb of the substrate W is to be placed against the frame-shaped inner dielectric portion  26 . 
     A step for fitting the inner dielectric portion  26  thereonto is formed in an inner end side of the top surface of the second metal  24 . 
     The outer dielectric portion  27  is a solid dielectric plate composed of ceramic, etc. and placed on the top surface of the second metal  24 . The outer dielectric portion  27  may be a sprayed film sprayed onto the top surface of the second metal  24 . A dielectric constant of the solid dielectric constituting the outer dielectric portion  27  is smaller than that of the substrate W. A thickness of the outer dielectric portion  27  is smaller than that of the substrate W. Accordingly, a thickness/dielectric constant ratio of the outer dielectric portion  27  is substantially the same as a thickness/dielectric constant ratio of the substrate W. The top surface of the second metal  24  is located higher than the first metal surface  21   a  such that the top surface of the outer dielectric portion  27  is flush with the top surface of the substrate W. 
       FIG. 9  shows a fourth embodiment of the present invention. In the first to the third embodiments, the second metal  24  is located astride a rear of the outer dielectric portion  27  of the solid dielectric layer  25  and the rear of the inner dielectric portion  26 . On the other hand, in the fourth embodiment, the second metal  24  is disposed only at the rear of the outer dielectric portion  27 . No metal that could be a ground electrode is provided on the rear of the inner dielectric portion  26 . The second metal  24  is spaced from the first stage portion  21  by a distance corresponding to a width of the inner dielectric portion  26 . An earth wire is connected to the second metal  24  independently of the first stage portion  21 . 
     According to the fourth embodiment, the run up discharge D 2  is generated only above the outer dielectric portion  27  and not generated above the inner dielectric portion  26  or above the peripheral portion Wb of the substrate W. On the other hand, the electrode  11  is wide enough to be located astride a position above the outer dielectric portion  27  and a position above the first stage portion  21 . Accordingly, when an electric field is impressed between an end portion at the front in a direction of travel of the electrode  11  (right end portion in  FIG. 9 ) and an end portion of the first stage portion  21 , the electric field remains to be impressed between an end portion at the rear in the direction of travel of the electrode  11  (left end portion) and the second metal  24 . The run up discharge D 2  above the outer dielectric portion  27  continues to be generated. Accordingly, the electric field does not concentrate on above the end portion of the first stage portion  21 . Moreover, the end portion at the front in the direction of travel of the electrode  11  passes above the outer dielectric portion  27  before reaching above the end portion of the first stage portion  21 . While passing above the outer dielectric portion  27 , the end portion at the front in the direction of travel of the electrode  11  is heated by the run up discharge D 2 , and an end portion at the front in the direction of travel of the solid dielectric plate  13  is dried. This helps a stable plasma discharge D 1  to be generated above the end portion Wae of the main portion Wa of the substrate W, thus promoting a proper surface processing of the end portion Wae. 
       FIG. 10  shows a fifth embodiment of the present invention. The processing unit  10  of a normal-pressure plasma processing apparatus M of the fifth embodiment includes three (a plurality of) high-voltage electrodes  11 ,  11 ,  11 . To distinguish these three electrodes  11 ,  11 ,  11 , the electrode on the right is referred to as  11 A, the middle electrode is referred to as  11 B, and the electrode on the left is referred to as  11 C (see  FIGS. 11 to 15 ). 
     Each electrode  11  has a quadrangular cross-section and extends in a direction orthogonal to the plane of the drawing of  FIG. 10 . A solid dielectric layer of ceramic, not shown, as the solid dielectric layer is provided on the under surface of each of the electrodes  11 . The three electrodes  11 ,  11 ,  11  are arranged in the right and left direction at equal intervals. 
     The three electrodes  11  are connected to a common power supply circuit  30 . The power supply circuit  30  supplies voltage to the electrodes  11  for generating an atmospheric-pressure plasma discharge. The power supply circuit  30  has three (a plurality of) switch parts  31  corresponding to electrodes  11 . The switch part  31 A is connected to the electrode  11 A. The switch part  31 B is connected to the electrode  11 B. The switch part  31 C is connected to the electrode  11 C (see  FIGS. 11 to 15 ). 
     A gap between the electrodes  11 ,  11  adjacent to each other in the right and left direction is greater than the actual gap between the under surface of the processing unit  10  (under surface of the solid dielectric layer of each electrode  11 ) and the stage  20 . 
     The first stage portion  21  of the stage  20  and the second metal portion  24  of the second stage portion  22  located further outside than the first stage portion  21  are individually formed of metal and abutted with and joined to each other. The second metal  24  is electrically grounded via the first stage portion  21 . Alternatively, the second metal  24  may be directly connected to an earth wire without going through the first stage portion  21 . 
     The first metal constituting the first stage portion  21  and the second metal  24  of the second stage portion  22  may be integrally and continuously formed. The stage  20  may include the stage body made of metal such as aluminum, with the central portion of the stage body (portion located further inside than the peripheral portion) serving as the first metal  21  (first stage portion) having the exposed surface and the peripheral portion of the stage body serving as the second metal  24  covered with the solid dielectric layer  25 . 
     The width of the inner dielectric portion  26  of the second stage portion  22  in the right and left direction (width of the peripheral portion Wb of the substrate) is smaller than the width of each electrode  11  in the right and left direction. 
     A width of the outer dielectric portion  27  in the right and left direction is greater than the width of each electrode  11  in the right and left direction and smaller than a distance between a left end portion of the left electrode  11 C and a right end portion of the right electrode  11 A. 
     The second metal  24  of the second stage portion  22  is not necessarily provided on the rear side (under surface) of the inner dielectric portion  26  as long as it is provided on the rear side (under surface) of the outer dielectric portion  27 . The inner dielectric portion  26  and the outer dielectric portion  27  may be individually formed and may have different dielectric constant values. 
     Outer end portions of the second metal  24  and the solid dielectric layer  25  of the second stage portion  22  are flush with each other. An outer frame made of a dielectric material such as resin, i.e. a third stage portion  23  is disposed on outer side surfaces of the second metal  24  and the solid dielectric layer  25 . 
     Alternatively, the outer dielectric portion  27  of the solid dielectric layer  25  may be more protruded outward than the second metal  24 . 
     Moreover, in the fifth embodiment, the three electrodes  11 ,  11 ,  11  of the processing unit  10  are moved reciprocally in the right and left direction (direction orthogonal to a longitudinal direction of the electrodes  11 ) in unison by a moving mechanism  40 . As shown in  FIGS. 11 to 15 , a movement range of each electrode  11  includes the first movement range R 1  opposed to the first stage portion  21 , the second movement range R 2  opposed to the second stage portion  22  and a third movement range R 3  opposed to the third stage portion  23 . 
     Alternatively, the processing unit  10  and, in extension, the electrodes  11 ,  11 ,  11  may be fixed, and the moving mechanism  40  may be connected to the stage  20  such that stage  20  may be reciprocally moved in the right and left direction. 
     To process the surface of the substrate W with the normal-pressure plasma processing apparatus M of the fifth embodiment, as shown in  FIG. 11 , firstly, all of the switch parts  31 A to  31 C corresponding to electrodes  11 A to  11 C are set to off, the processing unit  10  is retreated to the outside (left, for example) of at least the second stage portion  22  of the stage  20 , and the substrate W is placed on the stage  20 . To be more specific, the main portion Wa located further inside than the peripheral portion Wb in the substrate W is placed on the first metal surface  21   a  of the first stage portion  21 , and the peripheral portion Wb is placed on the inner dielectric portion  26  of the second stage portion  22 . Since the top surfaces of the first metal surface  21   a  and the inner dielectric portion  26  are continuous and flush with each other, formation of a gap between the rear surface of the substrate W and the stage  20  can be prevented. The end surface of the substrate W is abutted against the step riser surface between the inner dielectric portion  26  and the outer dielectric portion  27 . Accordingly, the substrate W can be precisely positioned. The top surface (front surface) of the substrate W becomes flush with the top surface of the outer dielectric portion  27 . 
     Next, the processing unit  10  is moved by the moving mechanism  40  in the direction of the arrow (right direction) of  FIG. 11 . 
     In the course of moving, as shown in  FIG. 12 , the right electrode  11 A reaches a predetermined position astride the second movement range R 2  corresponding to the second stage portion  22  and the third movement range R 3  corresponding to the third stage portion  23 . At this predetermined position, approximately 30 to 70 percent of the electrode  11 A is located in the second movement range R 2 , and the rest of the electrode  11 A is located in the third movement range R 3 . Preferably, approximately 50 percent of the electrode  11 A is located in the second movement range R 2 , and the rest of the electrode  11 A is located in the third movement range R 3 . At this timing, the switch part  31 A is set to on to start voltage supply to the right electrode  11 A from the power supply circuit  30 . This causes an electric field to be impressed between the right electrode  11 A and the second metal  24  of the second stage portion  22 . Since 30 percent or more, preferably 50 percent of the right electrode  11 A is opposed to the second metal  24 , direction of electric field from the electrode  11 A can be precisely directed toward the second metal  24 . This prevents an abnormal electrical discharge from being applied to surrounding metal members from the electrode  11 A. Voltage is not supplied when the entirety of the electrode  11 A is outside of the second movement range R 2 . Even when a portion of the electrode  11 A is in the second movement range R 2 , voltage is not supplied as long as the electrode  11 A is located to the left of the predetermined position. Voltage supply is started only when the electrode reaches the predetermined position. This prevents local concentration of the electric field from the electrode  11 A on the outer end portion of the second metal  24 , thereby preventing damage to the solid dielectric layer  25 . 
     The impression of the electric field mentioned above causes the atmospheric-pressure plasma discharge to be generated between the right electrode  11  and the outer dielectric portion  27 . This causes a run up plasma discharge D 2  to be generated outside of the substrate W. At this time, the second metal  24  serves as a ground electrode for the electrode  11 . The outer dielectric portion  27  serves as a solid dielectric layer on the second metal surface  24   a , thereby contributing to the stability of discharge. By properly setting the thickness and the dielectric constant of the outer dielectric portion  27 , the condition of the discharge can be made to be substantially the same as a discharge condition of a regular plasma discharge D 1  above the substrate W to be described later. Since the top surface of the outer dielectric portion  27  and the top surface of the substrate W are flush with each other, a gap between the processing unit  10  in a second position and the outer dielectric portion  27  can be made the same as a gap between the processing unit  10  in a first position and the substrate W. This allows the flow condition of the process gas at the run up discharge D 2  to be substantially the same as the flow condition of the process gas at the regular plasma discharge D 1  to be described later. 
     The run up discharge D 2  starts when 70 percent or less of the electrode  11 A is placed in the second movement range R 2 . This eliminates the necessity of making the second stage portion  22  unnecessarily wide. 
     The processing unit  10  is moved further to the right while the switch part  31 A is kept on to continue voltage supply to the right electrode  11 A. As the right electrode  11 A is moved to the right, the run up discharge zone D 2  between the electrode  11 A and the second stage portion  22  is moved to the right as well. Then, as shown in  FIG. 13 , the middle electrode  11 B reaches the predetermined position astride the second movement range R 2  and the third movement range R 3 . At this timing, the switch part  31 B is set to on to start voltage supply to the middle electrode  11 B from the power supply circuit  30 . This allows an electric field to be impressed between the middle electrode  11 B and the second metal  24  while preventing an abnormal electrical discharge from the middle electrode  11 B and the concentration of the electric field, and thus generating the run up discharge D 2  between the middle electrode  11 B and the outer dielectric portion  27 . 
     The processing unit  10  is moved further to the right while the switch parts  31 A,  31 B are kept on to respectively continue voltage supply to the right and middle electrodes  11 A,  11 B. As the processing unit  10  is moved to the right, the run up discharge zone D 2  between the right electrode  11 A and the second stage portion  22  and the run up discharge zone D 2  between the middle electrode  11 B and the second stage portion  22  are moved to the right, too. Then, as shown in  FIG. 14 , the left electrode  11 C reaches the predetermined position astride the second movement range R 2  and the third movement range R 3 . At this timing, the switch part  31 C is set to on to start voltage supply to the left electrode  11 C from the power supply circuit  30 . This allows an electric field to be impressed between the left electrode  11 C and the second metal  24  while preventing an abnormal electrical discharge from the left electrode  11 C and the concentration of the electric field, and thus generating the run up discharge D 2  between the left electrode  11 C and the outer dielectric portion  27 . 
     As mentioned above, when each of the electrodes  11 A,  11 B,  11 C is positioned further to the third movement range R 3  side than the predetermined position astride the second movement range R 2  and the third movement range R 3 , voltage is not supplied to the electrode; and every time when the electrode reaches the predetermined position, the voltage supply to the electrode is started, thereby generating the run up discharge D 2 ; and then when the electrode is positioned further to the first movement range R 1  side than the predetermined position, voltage supply is continued to maintain the discharge. 
     As shown in  FIG. 14 , generally at the same time as when the left electrode  11 C reaches the predetermined position, the right electrode  11 A reaches above the peripheral portion Wb of the substrate W. This causes the run up discharge D 2  to be generated between the right electrode  11 A and the peripheral portion Wb of the substrate. The process gas is introduced between the right electrode  11 A and the peripheral portion Wb of the substrate, and the front surface of the peripheral portion Wb of the substrate is plasma processed. At this time, the peripheral portion Wb of the substrate together with the inner dielectric portion  26  serve as a solid dielectric layer on the surface of the second metal  24 , thereby contributing to the stability of discharge. 
     Here, the total dielectric constant of the peripheral portion Wb of the substrate and the inner dielectric portion  26  is somewhat different from the dielectric constant of the outer dielectric portion  27  alone and also different from the dielectric constant of the main portion Wa of the substrate alone. This means that the condition of the discharge D 2   b  is slightly different from the discharge condition of the run up discharge D 2  above the outer dielectric portion  27  or the discharge condition of the regular plasma discharge D 1  above the main portion Wa of the substrate. However, it does not pose a problem since the condition of the peripheral portion Wb of the substrate is not relevant to the quality of product. 
     As shown in  FIG. 14 , the right electrode  11 A comes to a position astride the second movement range R 2  and the first movement range R 1 . Hereby, an electric field is also impressed between the right electrode  11 A and an end portion of the first stage portion  21 . As a result, the regular atmospheric-pressure plasma discharge D 1  is generated between the right electrode  11 A and the end portion Wae of the main portion Wa (portion bordering with the peripheral portion Wb) of the substrate W. The process gas is introduced to the regular plasma discharge zone D 1 , and the end portion Wae of the main portion of the substrate is plasma-processed. 
     At the initial stage of the regular plasma processing, the run up discharge D 2  or D 2   b  between the electrode  11 A and the second stage portion  22  remains to be generated. This prevents the concentration of the electric field on the narrow regular discharge zone D 1 . This prevents damage to the power supply circuit  30  and serves to stabilize the discharge condition above the end portion Wae of the main portion of the substrate. Prior to the regular plasma discharge D 1 , the temperature of the electrode  11 A is raised by the run up discharge D 2  above the second stage portion  22 . This causes a solid dielectric layer made of ceramic, which is not shown, on the surface of the electrode  11 A to be dried and so on in preparation for the discharge. This serves to further stabilize the discharge condition above the end portion Wae of the main portion of the substrate. Since the run up discharge zone D 2  (including D 2   b ) and the regular discharge zone D 1  defined by discharge of the electrode  11 A are continuous, the plasma can communicate between the discharge zones D 1 , D 2 . Substantially homogeneous plasma can be obtained. In this way, the end portion Wae of the main portion of the substrate can be processed in the same manner as the central portion of the substrate W, and thereby homogeneous processing can be achieved. 
     The processing unit  10  is further moved in the right direction, and the entirety of the right electrode  11 A is located in the first movement range R 1 , and the middle electrode  11 B is located astride the second movement range R 2  and the first movement range R 1 . Then, the plasma discharge D 2   b  is generated between the middle electrode  11 B and the peripheral portion Wb of the substrate, and further, the plasma discharge D 1  is generated between the middle electrode  11 B and the end portion Wae of the main portion of the substrate. 
     Subsequently, the entirety of the middle electrode  11 B is located in the first movement range R 1 , and the left electrode  11 C is located astride the second movement range R 2  and the first movement range R 1 . Then, the plasma discharge D 2   b  is generated between the left electrode  11 C and the peripheral portion Wb of the substrate, and further, the plasma discharge D 1  is generated between the left electrode  11 C and the end portion Wae of the main portion of the substrate. 
     Then, as shown in  FIG. 15 , the entirety of the processing unit  10  is located in the first movement range R 1 , the electric field is impressed between each of the electrodes  11 A,  11 B,  11 C and the first stage portion  21 , and the regular plasma discharge D 1  is generated between each of the electrodes  11 A,  11 B,  11 C and the main portion Wa of the substrate. This allows surfaces of portions of the main portion Wa of the substrate positioned under the electrodes  11 A,  11 B,  11 C to be plasma processed. At this time, the substrate W serves as the solid dielectric layer for the first stage portion  21 . This eliminates the necessity of providing a solid dielectric layer on the first metal surface  21   a , thus reducing manufacturing cost. In this way, the stage  20  can be easily enlarged to accommodate the increase in area of the substrate W. 
     The processing unit  10  is further moved in the direction of arrow toward the end portion on the opposite side (right side in  FIG. 10 ) of the stage  20 . Although not shown in the drawing, in the end portion on the opposite side, as each of the electrodes  11  reaches the predetermined position astride the second movement range R 2  and the third movement range R 3 , the corresponding switch part  31  is set to off, and the voltage supply to the electrode  11  is stopped. 
     The voltage supply to the electrodes above the end portion on the opposite side of the stage  20  may be stopped when each of the electrodes  11  reaches a predetermined position astride the first movement range R 1  and the second movement range R 2 . 
     When all of the electrodes  11  reach the end portion on the opposite side of the stage  20 , the entirety of the substrate W is plasma-processed. 
     The processing unit  10  may be reciprocated in the right and left direction according to need. 
     After the processing has finished, the processing unit  10  is retreated to the outside of the stage  20  and the substrate W is dismounted. 
     As shown in  FIG. 16 , the width in the right and left direction of each of the electrodes  11 ,  11 ,  11  is smaller than the width in the right and left direction of the second stage portion  22 , and by extension, smaller than a width in the right and left direction of the second movement range R 2 . Accordingly, there is a zone in which the entire width of the electrode  11  is positioned within the second movement range R 2 . Therefore, the predetermined position which sets timing for voltage supply may be shifted in the direction of the first movement range R 1  from the position in which the electrode  11  is located astride the second movement range R 2  and the third movement range R 3  to a position in which the entire width of the electrode  11  is positioned within the second movement range R 2 . In other words, voltage supply to the electrode  11  and the generation of the run up discharge D 2  may be started when the entire width of the electrode  11  is in the second movement range R 2 . 
     In this way, direction of electric field from the electrode  11  at the start of the voltage supply can be surely directed toward the second metal  24  of the second stage portion  22 , thereby surely preventing the abnormal electrical discharge from being generated from the electrode  11 . At the same time, a concentration of electric field on portions such as the outer end portion of the second metal can be surely avoided. 
     In a sixth embodiment as shown in  FIG. 17 , the processing unit  10  includes only one electrode  11 . A width of the electrode  11  in the right and left direction is greater than the width of each of the electrodes  11 A,  11 B,  11 C of the fifth embodiment in the right and left direction and, moreover, greater than a width of the second stage portion  22  in the right and left direction. Accordingly, when the front end portion in a direction of travel (right end portion) of the electrode  11  reaches a point immediately before the first movement range R 1 , the rear end portion in the direction of travel (left end portion) of the electrode  11  is still in the third movement range R 3 , and the electrode  11  is located astride the second movement range R 2  and the third movement range R 3  (see  FIG. 18 ). 
     The power supply circuit  30  includes only one switch part  31 , through which the electrode  11  is connected to the power supply circuit  30 . 
     In the sixth embodiment, when the single wide electrode  11  is positioned in the third movement range R 3 , the switch part  31  is set to off, and voltage supply to the electrode  11  is stopped. When the electrode  11 , being moved in the direction of arrow (right direction) in  FIG. 17 , reaches the predetermined position astride the second movement range R 2  and the third movement range R 3 , the switch part  31  is set to on to start the voltage supply to the electrode  31  to generate a run up discharge D 2  between the electrode  31  and the second stage portion  22 . The predetermined position may be set to be a position where, for example, approximately 30 to 70 percent of the wide electrode  11  is in the second movement range R 2 , and the rest of the wide electrode  11  is in the third movement range R 3 . When the wide electrode  11  reaches the predetermined position, the voltage supply is started. Preferably, as shown in  FIG. 17 , the predetermined position may be a position where approximately 50 percent of the wide electrode  11  is in the second movement range R 2  and the rest of the wide electrode  11  is in the third movement range R 3 . When the wide electrode  11  reaches the predetermined position, the voltage supply is started. By this, generation of an abnormal electrical discharge from the wide electrode  11  and a concentration of an electric field on the outer end portion of the second metal  24  can be surely prevented. 
     More preferably, as shown in  FIG. 18 , the predetermined position is set to be a position where the wide electrode  11  is immediately before the first movement range R 1 , and when the wide electrode  11  reaches the predetermined position, the voltage supply is started. By this, generation of the abnormal electrical discharge from the wide electrode  11  and the concentration of the electric field on the outer end portion of the second metal  24  can be further surely prevented, thereby further enhancing safety. 
     The voltage supply is continued while the wide electrode  11  is located more to the first movement range R 1  side than the predetermined position. In this way, a surface of the substrate W can be plasma processed. 
     The present invention is not limited to the above described embodiments and various modifications are possible. 
     For example, the object to the processed W is not necessarily entirely composed of a dielectric material as long as it is mainly composed of a dielectric material, and especially as long as the surface to be processed (surface) is mainly composed of a dielectric material. Some metal may be disposed on the surface. Metal may be embedded in the object to be processed W, which will cause almost no problem as long as the metal is not exposed outside. Such objects W may include a liquid crystal panel and a liquid crystal module constituting a liquid crystal display and a panel and a module constituting a plasma display, an organic electroluminescence display and a field emission display. 
     A metal surface of the first stage portion  21  is not necessarily entirely exposed as long as the first stage portion  21  has an exposed metal surface. A portion of the metal surface may be coated with a solid dielectric layer or an insulator which does not serve as the solid dielectric layer (a tape, paint or an insulating thin film used in a field of semiconductor, for example). Here the “solid dielectric layer” refers to a solid dielectric coated on a metal body of an electrode and serves to prevent an abnormal electrical discharge such as an arc discharge to obtain a stable glow discharge. 
     Different features of the first to sixth embodiments may be combined. For example, the single-member solid dielectric layer  25  of the first or the second embodiment may be combined with the individually formed first stage portion  21  and the second metal  24  of the third embodiment; the inner dielectric portion  26  of the third embodiment may be formed such that its width is reduced toward the inner end thereof (opposite side from the outer dielectric portion  27 ) as with the second embodiment; and the thickness and the dielectric constant of the outer dielectric portion  27  of the third embodiment may be made greater than those of the substrate W as with the first embodiment. 
     In the fifth embodiment, the number of the electrodes does not have to be one or three. Two or more than four electrodes may be used. Preferably, two or more electrodes are arranged along the direction of relative movement with respect to the stage. When one of the two or more electrodes serves as a first electrode, another electrode arranged behind it in the relative movement direction (on the third movement range side) serves as a second electrode. 
     In the fifth embodiment, the power supply circuit  30  may be provided for each of the plurality of electrodes. The power supply circuit for the first electrode is a first power supply circuit and the power supply circuit for the second electrode is a second power supply circuit. Of course, as shown in  FIG. 10 , the first power supply circuit and the second power supply circuit may be realized by one common power supply circuit. 
     INDUSTRIAL APPLICABILITY 
     This invention may be applied to cleaning, property modification (hydrophilization, hydrophobilization, etc.), film-forming, etching, ashing, etc. of a surface of a substrate by use of plasma in manufacturing of semiconductor substrates or liquid crystal substrates, for example.