Abstract:
A plasma processing apparatus includes a processing chamber the inside of which is maintained in a vacuum; a mounting table configured to mount a target substrate and serve as a lower electrode in the processing chamber; a circular ring-shaped member provided at the mounting table so as to surround a peripheral portion of the target substrate; an upper electrode arranged to face the lower electrode thereabove; and a power feed unit for supplying a high frequency power to the mounting table. The apparatus performs a plasma process on the target substrate by plasma generated in the processing chamber. The circular ring-shaped member includes at least one ring-shaped groove configured to adjust an electric field distribution to a desired distribution in a plasma generation space, and the groove is formed in a surface of the circular ring-shaped member and the surface is on an opposite side to the plasma generation space.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Japanese Patent Application No. 2009-128355 filed on May 27, 2009, and U.S. Provisional Application Ser. No. 61/228,636 filed on Jul. 27, 2009, the entire disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to a circular ring-shaped member for a plasma process configured to surround a peripheral portion of a target substrate on which a plasma process is performed in a plasma processing chamber, and a plasma processing apparatus including the same. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a manufacturing process of a semiconductor device or a FPD (Flat Panel Display), there has been widely used a plasma processing apparatus for etching, deposition, oxidation, sputtering, or the like. As one of the plasma processing apparatuses, there has been known a plasma etching apparatus in which an upper electrode and a lower electrode are arranged parallel to each other within a processing vessel or reaction chamber, a target substrate (semiconductor wafer, glass substrate or the like) is mounted on the lower electrode, and a high frequency voltage for plasma generation is applied to either or both of the upper electrode and the lower electrode via a matching unit in most cases. 
         [0004]    Generally, a plurality of gas discharge holes is provided in the upper electrode and an etching gas excited into plasma is discharged to the entire substrate through the gas discharge holes so as to etch the entire surface of the target substrate at the same time. 
         [0005]    Typically, in a parallel plate type plasma etching apparatus, an upper electrode and a lower electrode are arranged parallel to each other, and a high frequency voltage for generating plasma is applied to the upper electrode or the lower electrode via a matching unit. Electrons accelerated by a high frequency electric field between both the electrodes, secondary electrons emitted from the electrodes, or heated electrons collide with molecules of a processing gas and are ionized, so that the processing gas is excited into plasma. By radicals or ions in the plasma, a required microprocessing such as an etching process is performed on a surface of a substrate. 
         [0006]    As semiconductor integrated circuits are miniaturized, high density plasma under a low pressure is required in a plasma process. For example, in a capacitively coupled plasma processing apparatus, a plasma process of a higher efficiency, a higher density, and a lower bias power is required. Further, as semiconductor chips become large-sized and target substrates have large diameters, plasma of a larger diameter is required, and, thus, chambers (processing vessels) also become scaled up. 
         [0007]    However, in the large-diameter plasma processing apparatus along with the large-diameter target substrate, an intensity of an electric field at a central portion of an electrode (upper electrode or lower electrode) tends to be higher than that of an electric field at an edge portion thereof. As a result, there is a problem in that a density of the generated plasma at the central portion of the electrode is different from a plasma density at the edge portion thereof. Therefore, a resistivity of the plasma becomes low at a portion in which plasma density is high, and a current is also concentrated on a corresponding portion of a facing electrode. Accordingly, there is a problem in that a non-uniformity of the plasma density becomes serious. 
         [0008]    Furthermore, as the chamber becomes scaled up along with the large-diameter target substrate, there is a problem in that a plasma density at a central portion of the target substrate is different from a plasma density at a peripheral portion thereof in an actual etching process due to a flow of a processing gas caused by a temperature distribution. 
         [0009]    The non-uniformity of the plasma density causes a difference in an etching rate of the target substrate, and particularly, it causes a deterioration of a device yield obtained from the peripheral portion of the target substrate. 
         [0010]    In this regard, various researches for a configuration of an electrode have been conducted until now. For example, in order to solve the above-described problem, there has been known a technique of providing a high resistance member at a central portion of a main surface of a high frequency electrode (see Patent Document 1). According to this technique, the high resistance member is provided at the central portion of the main surface (plasma contact surface) of the electrode connected with a high frequency power supply, so that an intensity of an electric field at the central portion of the main surface of the electrode is relatively lowered as compared to an intensity of an electric field at an outer peripheral portion thereof. Therefore, non-uniformity of an electric field distribution can be corrected. 
         [0011]    Further, in a plasma processing apparatus disclosed in Patent Document 2, a dielectric member is embedded in a main surface of an electrode facing a processing space such that impedance against a high frequency power supplied from the main surface of the electrode to the processing space is relatively high at an central portion of the electrode and relatively low at an edge portion of the electrode. With this configuration, uniformity of an electric field distribution can be improved. 
         [0012]    Meanwhile, in order to improve uniformity of a plasma density distribution at the edge portion of a target substrate, the plasma processing apparatus includes a circular ring-shaped member such as a focus ring, provided so as to surround an outer periphery of a wafer mounted on a mounting table within the processing chamber. By way of example, the focus ring may have a double-circle structure including a ring-shaped inner focus ring positioned on inner side and a ring-shaped outer focus ring positioned so as to surround an outer periphery of the inner focus ring. Generally, the inner focus ring may be made of a conductive material such as silicon and the outer focus ring may be made of an insulating material such as quartz. 
         [0013]    The inner focus ring has a function to concentrate plasma on the wafer, and the outer focus ring serves as an insulator confining the plasma on the wafer. 
         [0014]    During a plasma process, a temperature of the outer focus ring increases due to heat transferred from the plasma. If the temperature is not stable, a radical density in the vicinity of the outer focus ring becomes non-uniform and a plasma density at an outer peripheral portion of the wafer becomes non-uniform as well. As a result, an effect of the plasma process at the central portion of the wafer is different from that at the outer peripheral portion thereof, and, thus, it becomes difficult to perform the plasma process on the wafer uniformly. 
         [0015]    Therefore, in Patent Document 3, a ring-shaped groove is formed in an outer focus ring so as to reduce a heat capacity of the outer focus ring, so that a temperature of the outer focus ring is rapidly increased and is easily maintained high by heat transferred from plasma. With this configuration, uniformity of the plasma density at a peripheral portion of the wafer can be achieved and deposits on the focus ring can be removed at the earliest stage of a production lot. 
         [0016]    Patent Document 1: Japanese Laid-open Publication No. 2000-323456
   Patent Document 2: Japanese Laid-open Publication No. 2004-363552   Patent Document 3: Japanese Laid-open Publication No. 2007-67353   
 
         [0019]    However, in a high frequency discharge type plasma processing apparatus as disclosed in Patent Documents 1 and 2, since a high resistance member is provided at a central portion of a main surface of a high frequency electrode, there is a problem in that a large quantity of a high frequency power is consumed (energy loss) due to Joule&#39;s heat. 
         [0020]    In accordance with a technique in which a dielectric member is embedded in the main surface of an electrode as disclosed in Patent Documents 1 and 2, a characteristic of an impedance distribution on the main surface of the electrode is determined by a material and a shape profile of the dielectric member. Therefore, there is a problem in that such a technique can not respond flexibly to various kinds of processes or variation of process conditions. 
         [0021]    Further, in Patent Document 3, a groove is formed in an outer focus ring so as to reduce a heat capacity. Accordingly, uniformity of a plasma density distribution at a peripheral portion of a wafer can be obtained due to increase and stabilization of a temperature in a short time. 
         [0022]    However, in order to obtain the uniformity of the plasma density distribution at the peripheral portion of the wafer, not only the temperature needs to be stabilized but a distribution or an intensity of an electric field at the peripheral portion of the wafer also need to be adjusted to a desired level. 
         [0023]    In Patent Document 3, by providing the groove in the outer focus ring so as to reduce the heat capacity, stability of the temperature can be obtained. However, the uniformity of the plasma density distribution caused by the stability of the temperature is obtained only while the temperature is stabilized, which does not mean that the distribution or intensity of the electric field is adjusted to a desired level. Therefore, in Patent Document 3, a problem of adjusting the electric field distribution to a desired level can not be solved. 
         [0024]    Furthermore, in Patent Document 3, the groove is formed in the outer focus ring so as to reduce the heat capacity, so that uniformity of the plasma density distribution can be obtained. However, in order to secure an etching rate or a deposition rate of a desired level at the end portion of the wafer, an electric field distribution on a top surface in the vicinity of the end portion of the wafer needs to be adjusted to a desired level, which has not been solved in Patent Document 3. 
       BRIEF SUMMARY OF THE INVENTION 
       [0025]    In view of the foregoing, the present disclosure provides a circular ring-shaped member for a plasma process capable of improving uniformity and production yield in the plasma process by adjusting an electric field distribution at a peripheral portion of a wafer to a desired level, and a plasma processing apparatus. 
         [0026]    In accordance with an aspect of the present disclosure, there is provided a circular ring-shaped member for a plasma process to surround a peripheral portion of a target substrate to be plasma-processed. The circular ring-shaped member includes at least one ring-shaped groove configured to adjust an electric field distribution to a desired distribution in a plasma generation space. The groove may be formed in a surface of the circular ring-shaped member and the surface may be on an opposite side to the plasma generation space. Since the ring-shaped groove is formed in the circular ring-shaped member configured to surround the peripheral portion of the target substrate to be plasma-processed, the electric field distribution at the peripheral portion of the target substrate can be changed. 
         [0027]    The groove may be formed in an inner peripheral portion of the circular ring-shaped member. Since the groove is formed in the circular ring-shaped member in contact with the target substrate, it is possible to adjust the electric field distribution at the peripheral portion of the target substrate more favorably. 
         [0028]    Further, impedance of the circular ring-shaped member may be adjusted to be a desired value depending on a shape of the groove. The impedance varies depending on the shape of the groove, thereby adjusting the electric field distribution. 
         [0029]    The groove may be formed to have a predetermined width, starting from a position between an inner end of the circular ring-shaped member and a position in a range of about 30% or less of a width of the circular ring-shaped member in a diametric direction. If the groove is formed at a position exceeding about 30% of the width of the circular ring-shaped member, starting from the inner end of the circular ring-shaped member in contact with the target substrate, it becomes difficult to adjust the electric field distribution at the peripheral portion of the target substrate. 
         [0030]    Further, the groove may be formed to have a predetermined width which is about 80% or less of a width of the circular ring-shaped member, starting from an inner end of the circular ring-shaped member in a diametric direction. If the groove is formed to exceed about 80% of the width of the circular ring-shaped member, starting from the inner end of the circular ring-shaped member in contact with the target substrate, the groove has less effect on the electric field distribution at the peripheral portion of the target substrate. 
         [0031]    A depth of the groove may be about 70% or less of a thickness of the circular ring-shaped member. When the groove is formed in the circular ring-shaped member, if the depth of the groove (a length in a vertical direction when the circular ring-shaped member is provided in a horizontal direction) exceeds about 70% of the thickness of the circular ring-shaped member, a lifetime of the circular ring-shaped member is shortened by abrasion caused by a plasma impact. 
         [0032]    Further, the circular ring-shaped member may be made of at least one of quartz, carbon, silicon, silicon carbide, and a ceramic material. 
         [0033]    In accordance with another aspect of the present disclosure, there is provided a plasma processing apparatus including a processing chamber the inside of which is maintained in a vacuum condition; a mounting table configured to mount thereon a target substrate and serve as a lower electrode in the processing chamber; a circular ring-shaped member provided at the mounting table so as to surround a peripheral portion of the target substrate; an upper electrode arranged to face the lower electrode thereabove; and a power feed unit for supplying a high-frequency power to the mounting table. The plasma processing apparatus performs a plasma process on the target substrate by plasma generated in the processing chamber. The circular ring-shaped member may include at least one ring-shaped groove configured to adjust an electric field distribution to a desired distribution in a plasma generation space. The groove may be formed in a surface of the circular ring-shaped member and the surface may be on an opposite side to the plasma generation space. Since the ring-shaped groove is formed in the circular ring-shaped member configured to surround the peripheral portion of the target substrate to be plasma-processed, the electric field distribution at the peripheral portion of the target substrate can be changed. 
         [0034]    The groove may be formed in an inner peripheral portion of the circular ring-shaped member. Since the groove is formed in the circular ring-shaped member in contact with the target substrate, it is possible to adjust the electric field distribution at the peripheral portion of the target substrate more favorably. 
         [0035]    Further, impedance of the circular ring-shaped member may be adjusted to be a desired value depending on a shape of the groove. The impedance varies depending on the shape of the groove, thereby adjusting the electric field distribution. 
         [0036]    The groove may be formed to have a predetermined width, starting from a position between an inner end of the circular ring-shaped member and a position in a range of about 30% or less of a width of the circular ring-shaped member in a diametric direction. If the groove is formed at a position exceeding about 30% of the width of the circular ring-shaped member, starting from the inner end of the circular ring-shaped member in contact with the target substrate, it becomes difficult to adjust the electric field distribution at the peripheral portion of the target substrate. 
         [0037]    Further, the groove may be formed to have a predetermined width which is about 80% or less of a width of the circular ring-shaped member, starting from an inner end of the circular ring-shaped member in a diametric direction. If the groove is formed to exceed about 80% of the width of the circular ring-shaped member, starting from the inner end of the circular ring-shaped member in contact with the target substrate, the groove has less effect on the electric field distribution at the peripheral portion of the target substrate. 
         [0038]    A depth of the groove may be about 70% or less of a thickness of the circular ring-shaped member. When the groove is formed in the circular ring-shaped member, if the depth of the groove (a length in a vertical direction when the circular ring-shaped member is provided in a horizontal direction) exceeds about 70% of the thickness of the circular ring-shaped member, a lifetime of the circular ring-shaped member is shortened by abrasion caused by a plasma impact. 
         [0039]    Further, the circular ring-shaped member may be made of at least one of quartz, carbon, silicon, silicon carbide, and a ceramic material. 
         [0040]    In accordance with the plasma processing apparatus of the present disclosure, the etching rate or deposition rate at the peripheral portion of the wafer can be adjusted easily and freely by adjusting the electric field distribution at the peripheral portion of the wafer, thereby improving uniformity or production yield in the plasma process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    The disclosure may best be understood by reference to the following description taken in conjunction with the following figures: 
           [0042]      FIG. 1  is a longitudinal cross sectional view showing a configuration of a plasma processing apparatus in accordance with an embodiment of the present disclosure; 
           [0043]      FIG. 2A  is a cross sectional view of a conventional focus ring; 
           [0044]      FIG. 2B  is a cross sectional view of a groove-formed focus ring; 
           [0045]      FIGS. 3A to 3C  show shapes of grooves; 
           [0046]      FIG. 4  is a graph showing an etching rate of an oxide film; 
           [0047]      FIG. 5  is a graph showing an etching rate of a nitride film; 
           [0048]      FIGS. 6A and 6B  provide graphs showing a characteristic of a sputtering rate; and 
           [0049]      FIGS. 7A and 7B  provide graphs showing a characteristic of a deposition rate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    Hereinafter, an embodiment applying a plasma processing apparatus in accordance with the present disclosure to an etching apparatus will be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited thereto. 
         [0051]      FIG. 1  shows a schematic overall configuration of a plasma processing apparatus  1  in accordance with the embodiment of the present disclosure. The plasma processing apparatus includes a cylindrical processing chamber the inside of which can be airtightly sealed and is made of, e.g., aluminum or stainless steel. In this case, a capacitively coupled plasma processing apparatus of a lower electrode dual frequency application type is employed, but the present disclosure is not limited thereto. For example, a plasma processing apparatus of an upper and lower electrode dual frequency application type or a plasma processing apparatus of a single frequency application type may be employed. 
         [0052]    Within the processing chamber, a susceptor  2  configured to support a semiconductor wafer (hereinafter, referred to as “wafer”)  15  as a target substrate is horizontally placed. The susceptor  2  is made of a conductive material such as aluminum and serves as an RF electrode. Installed on a top surface of the susceptor  2  is an electrostatic chuck  16  made of a dielectric material such as ceramic so as to hold the wafer  15  by an electrostatic attracting force. An internal electrode  17  formed of a conductive film made of a conductive material such as copper or tungsten is embedded in the electrostatic chuck  16 . The susceptor  2  is supported by a cylindrical holder  3  made of an insulating material such as ceramic. The cylindrical holder  3  is supported by a cylindrical support  4  of the processing chamber. Installed on a top surface of the cylindrical holder  3  is a focus ring  5  configured to surround the top surface of the susceptor  2  in a ring shape. 
         [0053]    Around the outside of the focus ring  5 , a circular ring-shaped cover ring  25  is installed. 
         [0054]    The electrostatic chuck  16  is used as a heat exchange plate for adjusting a temperature of the wafer  15  by exchanging heat with the wafer  15  in contact with each other. The focus ring  5  serving as one of circular ring-shaped members for a plasma process is installed around the outside of the wafer  15 . In this embodiment, the single focus ring  5  is provided, but it may be possible to use a double focus ring which is divided into an outer focus ring and an inner focus ring. The focus ring  5  can be made of, e.g., Si, SiC, C or SiO 2  depending on the wafer  15 . 
         [0055]    Between a sidewall of the processing chamber and the cylindrical support  4 , a ring-shaped exhaust line  6  is provided. At the entrance or on the way to the exhaust line  6 , a ring-shaped baffle plate  7  is provided. A bottom portion of the exhaust line  6  is connected with an exhaust device  9  via an exhaust pipe  8 . The exhaust device  9  includes a vacuum pump such as a turbo molecular pump, and, thus, a plasma processing space within the processing chamber can be depressurized to a predetermined vacuum level. Further, a gate valve  11  configured to open and close a transfer port  10  for loading/unloading the wafer  15  is installed outside the sidewall of the processing chamber. 
         [0056]    A rear surface (bottom surface) of the susceptor  2  and an upper electrode  21  are connected with upper ends of circular column-shaped or cylindrical-shaped power feed rods  14   a  and  14   b  extending from output terminals of matching units  13   a  and  13   b,  respectively. First and second high frequency power supplies  12   a  and  12   b  used in a dual frequency application type are electrically connected with the susceptor  2  and the upper electrode  21  via the matching units  13   a  and  13   b  and the power feed rods  14   a  and  14   b , respectively. The power feed rods  14   a  and  14   b  are made of a conductive material such as copper or aluminum. 
         [0057]    The first high frequency power supply  12   a  outputs a first high frequency power having a relatively high frequency of, e.g., about 60 MHz for generating plasma above the susceptor  2 . The second high frequency power supply  12   b  outputs a second high frequency power having a relatively low frequency of, e.g., about 2 MHz for attracting ions to the wafer  15  on the susceptor  2 . The matching unit  13   a  performs matching between impedance of the first high frequency power supply  12   a  and impedance of a load (mainly, electrode, plasma, and chamber), and the matching unit  13   b  performs matching between impedance of the second high frequency power supply  12   b  and the impedance of the load. 
         [0058]    The electrostatic chuck  16  is configured such that the internal electrode  17  formed of a sheet-shaped or mesh-shaped conductor is embedded in a film-shaped or plate-shaped dielectric member. The electrostatic chuck  16  is integrally fixed to or integrally formed on the top surface of the susceptor  2 . The internal electrode  17  is electrically connected with a DC power supply and a power feed line such as a coated line provided outside the processing chamber, and, thus, the wafer  15  can be attracted to and held on the electrostatic chuck  16  by a Coulomb force generated by a DC voltage applied from the DC power supply. 
         [0059]    At a ceiling portion of the processing chamber, the upper electrode  21  is provided to face parallel to the susceptor  2 . The upper electrode  21  is formed in a circular plate shape having a hollow structure (hollow portion) at the center thereof, and a plurality of gas discharge holes  22  is formed in its bottom surface, thereby functioning as a shower head. An etching gas supplied from a processing gas supply unit is introduced into the hollow portion in the upper electrode  21  through a gas inlet line  23  and uniformly distributed and supplied from the hollow portion to the processing chamber through the gas discharge holes  22 . Further, the upper electrode  21  is made of, e.g., Si or SiC. 
         [0060]    A heat transfer gas such as a He gas is supplied between the electrostatic chuck  16  and the rear surface of the wafer  15  from a heat transfer gas supply unit (not illustrated) through a gas supply line  24 . The heat transfer gas accelerates heat conduction in the electrostatic chuck  16 , i.e., between the susceptor  2  and the wafer  15 . 
         [0061]    A main feature of this plasma processing apparatus is that the focus ring  5 , in which a circular ring-shaped groove is formed, is used so as to obtain an impedance characteristic capable of forming an intensity and distribution of an electric field most suitable for a characteristic of the wafer  15  or various kinds of plasma processes. 
         [0062]      FIG. 2A  is a cross sectional view of a conventional focus ring which has been used in a conventional plasma process, and  FIG. 2B  is a cross sectional view of a groove-formed focus ring in accordance with an embodiment of the present disclosure. All the focus rings illustrated in  FIGS. 2A and 2B  are single (or referred to as “integrated type”) focus rings. However, the present disclosure is not limited to the single focus ring and, for example, may be applied to either or both of two separate focus rings which are divided into an inner focus ring and an outer focus ring. The focus ring may be made of, for example, the same material (Si) as the wafer  15 , or any one of quartz, carbon, silicon carbide, and ceramic materials (yttria (Y 2 O 3 ) or silica). The focus ring  5  is mounted on the electrostatic chuck  16  so as to support a peripheral end portion of the wafer  15 . 
         [0063]    There will be explained the groove-formed focus ring in accordance with the embodiment of the present disclosure with reference to  FIG. 2B . In the groove-formed focus ring illustrated in  FIG. 2B , a groove  51  is formed on a surface (rear surface of the focus ring) in contact with the electrostatic chuck  16 . Desirably, such a groove may be formed on the rear surface of the focus ring. That is because that if a groove-formed surface is exposed to plasma ions, the groove may be eroded (worn out) by a plasma ion impact and, thus, a shape of the groove may be deformed. Further, that is because that if the groove is formed by a cutting process or the like, dust caused by the plasma ion impact may be highly generated as compared to the other surface. 
         [0064]    In  FIG. 2B , a depth of the groove  51  (length in a vertical direction when the focus ring  5  is installed in a horizontal direction) is desirably about 70% or less of a thickness of the focus ring and more desirably about 50% or less. If the depth of the groove  51  exceeds about 70%, a lifetime of the focus ring  5  may be shortened by abrasion caused by a plasma impact. Further, in order to secure hardness of the focus ring, the depth of the groove is desirably about 70% or less. Furthermore, the depth of the groove  51  of the groove-formed focus ring illustrated in  FIG. 2B  is about 0.4 mm, which is about one-ninth ( 1/9) of a thickness of the focus ring  5 , i.e., about 3.6 mm. 
         [0065]    Moreover, a width of the groove  51  in a diametric direction may be about 80% or less of a width of the focus ring in a diametric direction. For example, the width of the groove  51  of the groove-formed focus ring illustrated in  FIG. 2B  is about 40 mm, which corresponds to about two-fifth (⅖) (40%) of a width of the focus ring  5 , i.e., about 100 mm. 
         [0066]    In addition, the groove  51  may be formed from an end of the focus ring at the install position of the wafer  15  or from a position in the range of about 30% or less of the width of the focus ring in a diametric direction. That is because that by forming the groove  51  from the end portion as close as possible, in such a range that is not affected by the ion impact, an electric field distribution on a surface of the wafer  15  can be adjusted more easily. 
         [0067]    As described above, the groove  51  may be formed in a certain shape suitable to optimize the electric field distribution on the surface of the wafer  15 .  FIGS. 3A to 3C  show shapes of grooves in accordance with the present disclosure.  FIG. 3A  shows a case where a groove  51  is formed in a semi-elliptic shape from the vicinity of an inner end portion of a focus ring  5 .  FIG. 3B  shows a case where a trapezoid-shaped groove  51  is formed at an inner end portion of a focus ring  5  and a rectangular groove  51  is formed outside thereof in a diametric direction. Further,  FIG. 3C  shows a case where three circular hollow grooves  51  are successively formed inside a focus ring  5 . The present disclosure is related to a technique of forming a groove in a focus ring so as to obtain a desired electric field distribution, and, thus, it may be possible to form an optimal groove for a desired electric field distribution. 
       Experimental Example 1 
       [0068]    As a focus ring to be installed in the plasma processing apparatus  1 , a couple of the focus rings  5  illustrated in  FIG. 2B  were prepared. A heat transfer sheet having a heat conductivity of about 1 W/MK was almost fully filled in a groove  51  of one focus ring. It will be referred to as “groove-formed focus ring of 1 W type” in the specification hereinafter. Further, a heat transfer sheet having a heat conductivity of about 17 W/MK was almost fully filled in a groove  51  of the other focus ring. It will be referred to as “groove-formed focus ring of 17 W type” in the specification hereinafter. Furthermore, as a comparative example, the conventional focus ring illustrated in  FIG. 2A  was prepared. It will be referred to as “conventional focus ring” in the specification hereinafter. 
         [0069]    Then, three sheets of blanket wafers (hereinafter, referred to as “wafer Ox”) having a diameter of about 300 mm with an oxide film formed thereon and three sheets of blanket wafers (hereinafter, referred to as “wafer Ni”) having a diameter of about 300 mm with a nitride film formed thereon were prepared. The conventional focus ring, the groove-formed focus ring of 1 W type, and the groove-formed focus ring of 17 W type were installed around the blanket wafers Ox and Ni, respectively; a processing gas of C 4 F 6 /Ar/O 2 (18/225/10) was supplied; and a plasma process was performed on each of the wafers Ox and the wafers Ni for about 60 seconds. Here, a temperature of an upper electrode, a temperature of a wall surface of a processing chamber, and a temperature of a bottom surface of an electrostatic chuck were about 60° C., 60° C., and 45° C., respectively. 
         [0070]      FIG. 4  is a graph showing etching rates of the wafers Ox and  FIG. 5  is a graph showing etching rates of the wafers Ni under the above-described plasma process conditions. In the horizontal axis of the graphs in  FIGS. 4 and 5 , a point “O” represents a central point of the wafer and the right and left sides in a diametric direction from that point are represented in millimeters up to 150 mm. The vertical axis represents an etching rate (nm/min) of an oxide film or an etching rate (nm/min) of a nitride film. 
         [0071]    As depicted in  FIG. 4 , when the conventional focus ring was installed around the wafer Ox and the plasma process was performed thereon, an etching rate of the oxide film is about 187 nm/min at the central portion of the wafer and is increased toward the end portion thereof. At a position about 30 mm away from the end portion of the wafer, the etching rate has the maximum value of about 195 nm/min. From that position to the farthest end portion, the etching rate is approximately constant. 
         [0072]    Meanwhile, when the groove-formed focus ring of 1 W type was installed around the wafer Ox and the plasma process was performed thereon, the etching rate is approximately the same as the etching rate (about 187 nm/min) of the conventional focus ring at the central portion of the wafer, but the etching rate is increased toward the end portion thereof. At a position about 30 mm away from the end portion of the wafer, the etching rate is about 197 nm/min. From that position to the farthest end portion, the etching rate is sharply increased and is about 218 nm/min at the farthest end portion. 
         [0073]    The etching rate of the groove-formed focus ring of 17 W type has approximately the same characteristic as that of the groove-formed focus ring of 1 W type as illustrated in  FIG. 4 . 
         [0074]      FIG. 5  is a graph showing an etching rate of a nitride film when the conventional focus ring was installed around the wafer Ni and the plasma process was performed under the above-described conditions. As shown in  FIG. 5 , the etching rate is about −2 nm/min at the central portion of the wafer, which means that CxFy has been deposited at the central portion of the wafer. Further, the etching rate is decreased to a larger minus value (deposition rate of CxFy is increased) toward the end portion thereof. From a position about 50 mm away from the end portion of the wafer to the farthest end portion, the deposition rate is increased. 
         [0075]    Meanwhile, when the groove-formed focus ring of 1 W type was installed around the wafer Ni and the plasma process was performed thereon, the etching rate has a slightly bigger minus value (about −4 nm/min) at the central portion of the wafer than that of the conventional focus ring. However, the etching rate comes to have plus values from minus values as it goes to the end portion. That is, at a position about 25 mm away from the end portion of the wafer, the deposition rate and the etching rate becomes substantially the same, and the etching rate is increased toward the end portion of the wafer from that position. 
         [0076]    The etching rate of the groove-formed focus ring of 17 W type on the wafer Ni has a different etching rate but approximately the same characteristic as that of the groove-formed focus ring of 1 W type. 
         [0077]    In view of the foregoing, the following facts have been proved. A difference in the heat conductivity of the heat transfer sheet embedded in the groove  51  does not make a big difference in the etching characteristic. That is because that the groove  51  formed in the focus ring  5  does not cause a change in its heat capacity but causes a change in the impedance of the focus ring  5 , so that an electric field distribution in its vicinity is varied by a change of the impedance. As a result, an intensity of the plasma (electric charge) impact on the wafer  15  is changed. Therefore, if a shape of the groove  51  is changed so as to obtain a desired electric field distribution according to a material to be plasma-processed, a desired electric field distribution can be formed at a desired position. Accordingly, the plasma process can be uniformly performed on the wafer  15 . 
       Experimental Example 2 
       [0078]    Subsequently, as a focus ring  5  to be installed in the plasma processing apparatus  1 , the groove-formed focus ring of 1 W type and the groove-formed focus ring of 17 W type were prepared in the same manner as experimental example 1, and as a comparative example thereof, the conventional focus ring was also prepared to find characteristics of a sputtering rate. 
         [0079]    Then, three sheets of blanket wafers having a diameter of about 300 mm were prepared in the same manner as the experimental example 1. Thereafter, the conventional focus ring, the groove-formed focus ring of 1 W type, and the groove-formed focus ring of 17 W type were installed around the blanket wafers, respectively; a plasma processing chamber was depressurized to about 35 millitorr; a processing gas of Ar/O 2  (1225/15) was supplied; and a plasma process was performed on each of the blanket wafers for about 60 seconds. Here, a temperature of an upper electrode, a temperature of a wall surface of the processing chamber, and a temperature of a bottom surface of an electrostatic chuck were about 60° C., 60° C., and 45° C., respectively. 
         [0080]      FIGS. 6A and 6B  are graphs each showing a characteristic of a sputtering rate in case of using the above-described three kinds of focus rings under the above-stated plasma process conditions. In the horizontal axis of the graphs in  FIGS. 6A and 6B , a point “O” represents a central point of the wafer and the right and left sides in a diametric direction from that point are represented in millimeters up to 150 mm. The vertical axis represents a sputtering rate in a unit of nm/min. 
         [0081]    As shown in  FIG. 6A , when the conventional focus ring was installed around the blanket wafer and the plasma process was performed thereon, the sputtering rate is about 15 mm/min at the central portion of the wafer and is decreased toward the end portion thereof. From a position about 40 mm away from the end portion of the wafer, the sputtering rate is sharply decreased and is about 13 nm/min at the farthest end portion. 
         [0082]    Meanwhile, when the groove-formed focus ring of 1 W type was installed around the blanket wafer and the plasma process was performed thereon, the sputtering rate is about 17 nm/min at the central portion of the wafer. From a position about 40 mm away from the end portion of the wafer, the sputtering rate is gradually decreased. However, from a position about 10 mm away from the end portion of the wafer to the farthest end portion, the sputtering rate is increased and is about 19 nm/min at the farthest end portion, which shows a characteristic contrary to that of the conventional focus ring. 
         [0083]    The sputtering rate of the groove-formed focus ring of 17 W type has approximately the same characteristic as that of the groove-formed focus ring of 1 W type. 
         [0084]      FIG. 6B  is a graph showing normalized sputtering rates in case of using the three kinds of focus rings illustrated in  FIG. 6A . As shown in  FIG. 6B , a difference in the heat conductivity of the heat transfer sheet embedded in the groove  51  does not make a big difference in the sputtering rate characteristic. Therefore, the groove  51  formed in the focus ring  5  does not cause a change in its heat capacity but causes a change in the impedance of the focus ring  5 , so that an electric field distribution in its vicinity can be varied by the change of the impedance. As a result, it is deemed that an intensity of the plasma impact is changed, resulting in a change of the sputtering rate. 
       Experimental Example 3 
       [0085]    Subsequently, as a focus ring  5  to be installed in the plasma processing apparatus  1 , the groove-formed focus ring of 1 W type and the groove-formed focus ring of 17 W type were prepared in the same manner as experimental examples 1 and 2, and as a comparative example thereof, the conventional focus ring was prepared to find characteristics of a deposition rate. 
         [0086]    Then, three sheets of blanket wafers having a diameter of about 300 mm were prepared. The conventional focus ring, the groove-formed focus ring of 1 W type, and the groove-formed focus ring of 17 W type were installed around the blanket wafers, respectively; a plasma processing chamber was depressurized to about 35 millitorr; a processing gas including C 4 F 6 /Ar (18/1225) was supplied; and a plasma process was performed on each of the blanket wafers for about 60 seconds. Here, a temperature of an upper electrode, a temperature of a wall surface of the processing chamber, and a temperature of a bottom surface of an electrostatic chuck were about 60° C., 60° C., and 45° C., respectively. 
         [0087]      FIGS. 7A and 7B  are graphs each showing a characteristic of a deposition rate when the above-described three kinds of focus rings, i.e., the conventional focus ring, the groove-formed focus ring of 1 W type, and the groove-formed focus ring of 17 W type, were installed around each of the blanket wafers under the above-stated plasma process conditions. In the horizontal axis of the graphs in  FIGS. 7A and 7B , a point “O” represents a central point of the wafer and the right and left sides in a diametric direction from that point are represented in millimeters up to 150 mm. The vertical axis represents a deposition rate in a unit of nm/min. 
         [0088]    As shown in  FIG. 7A , when the conventional focus ring was installed around the blanket wafer and the plasma process was performed thereon, the deposition rate is about nm/min at the central portion of the wafer and is gradually increased toward the end portion thereof. From a position about 50 mm away from the end portion of the wafer, the deposition rate is sharply increased and is about 105 nm/min at the farthest end portion. 
         [0089]    Meanwhile, when the groove-formed focus ring of 1 W type was installed around the blanket wafer and the plasma process was performed thereon, at the central portion of the wafer, the deposition rate is about 80 nm/min, which is approximately the same deposition rate as that of the conventional focus ring. However, on the contrary to the conventional focus ring, from a position about 50 mm away from the end portion of the wafer, the deposition rate is decreased and is about 70 nm/min at the farthest end portion. 
         [0090]    The deposition rate of the groove-formed focus ring of 17 W type has approximately the same characteristic as that of the groove-formed focus ring of 1 W type as depicted in  FIG. 7A . 
         [0091]      FIG. 7B  is a graph showing normalized deposition rates of the three kinds of focus rings illustrated in  FIG. 7A . As can be seen from  FIG. 7B , a difference in the heat conductivity of the heat transfer sheet embedded in the groove  51  does not make a big difference in the deposition rate characteristic as mentioned in experimental examples 1 and 2. Therefore, the groove  51  formed in the focus ring  5  does not cause a change in its heat capacity but causes a change in the impedance of the focus ring  5 , so that an electric field distribution in its vicinity can be varied by the change of the impedance. As a result, it is deemed that an intensity of the plasma impact is changed, resulting in a change in the deposition rate. 
         [0092]    In view of the foregoing, by forming a groove in a focus ring and changing a shape of the groove, a desired electric field distribution can be formed at a desired position. Therefore, it is obvious that an etching rate or a deposition rate can be adjusted to be a desired value at a desired position. 
         [0093]    The present disclosure is not limited to a plasma etching apparatus but can be applied to other plasma processing apparatuses for plasma CVD, plasma oxidation, plasma nitridation, sputtering or the like. Further, a target substrate of the present disclosure is not limited to a semiconductor wafer but can be any one of various kinds of substrates for flat panel display, a photo mask, a CD substrate, and a print substrate.