Patent Publication Number: US-2020294842-A1

Title: Plasma Processing Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-046350, filed on Mar. 13, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a plasma processing apparatus. 
     BACKGROUND 
     In an apparatus for applying high-frequency power, technology for suppressing abnormal discharge has been proposed (see, e.g., Patent Documents 1 to 3). Patent Document 1 discloses a sputter apparatus in which an upper shield is disposed between a backing plate for supporting a target and a shield for protecting a chamber inner wall from sputter particles, interposing a gap. The upper shield is provided with a through hole connecting the gap to the inside of the chamber, whereby it is possible to prevent gas generated from an O-ring from passing through a gap between the upper shield and the target, thereby preventing abnormal discharge via gas. 
     Patent Document 2 discloses, when a gas flow path for an introduction of a processing gas is provided in a dielectric window which transmits electromagnetic waves into a chamber in a form of a number of longitudinal grooves, a sufficiently high gas conductance is obtained while effectively preventing backflow or abnormal discharge of plasma in the gas flow path. 
     Patent Document 3 discloses adjusting a gap between an outer peripheral surface of a protrusion member and an inner peripheral surface of a side wall of an upper container to 2.5 mm≤d≤5 mm, setting a thickness of a vertical portion to 3 mm≤t≤8 mm, or adjusting a protrusion length of a cylindrical portion of the protrusion member to a length that is able to cover the vertical portion of the inner peripheral surface of the side wall, thereby controlling the electric field strength at the periphery of the dielectric plate. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document Japanese Laid-Open Patent Publication No. 2005-264177 
     Patent Document Japanese Laid-Open Patent Publication No. 2016-015496 
     Patent Document International Publication No. WO 2009/099186 
     SUMMARY 
     According to embodiments of the present disclosure, there is provided a plasma processing apparatus that applies high-frequency power, the plasma processing apparatus including: a stage provided in a chamber and having a heater therein, the stage being configured to place a substrate thereon; and an annular member provided around the stage to be spaced apart therefrom and formed of a dielectric material, wherein at least one annular groove is formed in a lower surface of the annular member in a radial direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
         FIG. 1  is a schematic cross-sectional view illustrating an exemplary plasma processing apparatus according to an embodiment. 
         FIGS. 2A to 2F  are views illustrating examples of surroundings of stages according to a comparative example, an embodiment and its modification. 
         FIG. 3  is a view illustrating an exemplary electric field around a stage according to a comparative example. 
         FIG. 4  is a circuit configuration diagram for describing a displacement current around a stage according to an embodiment. 
         FIGS. 5A to 5C  are views illustrating annular members according to an embodiment in comparison with a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and redundant descriptions may be omitted. 
     [Plasma Processing Apparatus] 
     A plasma processing apparatus  100  according to an embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a schematic cross-sectional view illustrating an example of a plasma processing apparatus  100  according to an embodiment. The plasma processing apparatus  100  includes a chamber  1 . The chamber  1  includes a container  12  and a lid  11 . The container  12  and the lid  11  are made of, for example, aluminum, and the lid  11  is provided in an opening of the container  12  having a bottom. The chamber  1  and the lid  11  is sealed by an O-ring  13 . As a result, the inside of the chamber  1  is configured to be sealable in a vacuum state. On the inner walls of the container  12  and the lid  11 , a film having corrosion resistance to plasma may be formed. Ceramics such as aluminum oxide and yttrium oxide may be used for the film. 
     The container  12  has four stages S, and  FIG. 1  illustrates two of the four stages. Each stage S is formed in a flat disk shape, and a wafer W is placed thereon. The stage S is formed of a dielectric material such as alumina (Al 2 O 3 ). Inside the stage S, a heater  20  for heating the wafer W is embedded. The heater  20  is configured with, for example, a ceramic sheet-shaped or plate-shaped resistance heating element, which is supplied with electric power from a power supply part so as to generate heat, and heats the placement surface of the stage S so as to heat the wafer W to a predetermined process temperature suitable for film formation. For example, the heater  20  heats the wafer W placed on the stage S to a temperature between 100 degrees C. to 300 degrees C. 
     The stage S has a support  22  extending downward from the center of the lower surface, penetrating the bottom portion of the container  12 . The support  22  is supported, at one end thereof, on a lifter  35 . When the lifter  35  raises and lowers the support  22 , the stage S is moved up and down between the processing position where processing of a wafer W is performed (the position illustrated in  FIG. 1 ) and the delivery position where the delivery of the wafer W is performed. In addition, it is possible to adjust the distance (gap) between the stage S and an upper electrode  14  using the lifter  35 . 
     The delivery position is a position of each stage S indicated by the two-dot chain line in  FIG. 1 . At this position, the delivery of the wafer W to/from an external transport mechanism is performed through a loading/unloading port. The stage S is formed with through holes through which the shafts of lifting pins  30  pass, respectively. 
     In the state in which the stage S has been moved from the processing position of the wafer W (see  FIG. 1 ) to the delivery position of the wafer W, the heads of the lifting pins  30  protrude from the placement surface of the stage S. As a result, the heads of the lifting pins  30  support the wafer W from below the wafer W, lift the wafer W from the placement surface of the stage S, and deliver the wafer W to an external transport mechanism. 
     Four upper electrodes  14 , which also function as shower heads, are provided above respective stages S and below the lid  11  so as to face respective stages S. Each upper electrode  14  is formed of a conductor such as aluminum and is substantially disk-shaped. Each upper electrode  14  is supported by the lid  11 . In each stage S, a mesh-shaped metal electrode plate  21  is embedded in parallel with the heater  20 . Thus, the stage S also functions as a lower electrode facing the upper electrode  14 . 
     A large number of gas supply holes  16  are provided in each upper electrode  14 . Under the control of a valve V and a flow controller MFC, a film forming gas (reactive gas) having a predetermined flow rate and output from the gas supply part  15  is introduced into gas inlets  18  through the gas line  17  at a predetermined timing. The introduced gas passes through the through holes  19  formed in the lid  11  and the flow paths  24  formed between the upper surfaces of the upper electrodes  14  and the lid  11 , and is introduced into the container  12  from a large number of gas supply holes  16 . 
     In addition, an RF power supply  36  is connected to each upper electrode  14  via a matcher  37 , and high-frequency power having a frequency of, for example, 0.4 MHz to 2450 MHz is applied to the upper electrode  14  from the RF power supply  36 . The gas introduced into the container  12  is turned into plasma by high-frequency power. With the plasma generated in the spaces between the upper electrodes  14  and the stages S, plasma processing such as film forming process is performed on the wafers W on the stages S. 
     Around each stage S, an annular member  40  made of a dielectric material such as quartz is provided to be spaced apart from the stage S (see the gaps  44  in  FIG. 1 ). An exhaust manifold  41  is disposed on each annular member  40  and at the outer periphery of each upper electrode  14 .The annular member  40  and the exhaust manifold  41  are formed integrally, and are fixed to the side wall of the container  12  and the outer periphery of the upper electrode  14 . 
     The exhaust manifold  41  is formed of ceramics, and has an exhaust path  42  in the circumferential direction. The gas that passed through the exhaust path  42  passes through a plurality of exhaust ports  43  provided between the exhaust manifold  41  and the annular member  40 , passes under the stage S, flows toward the exhaust port  6  in the bottom portion of the container  12 , and is discharged from the exhaust port  6  to the outside of the chamber  1  by a vacuum pump  45 . The exhaust port  43  may be a single exhaust port that is not divided into multiple ports and opens in the circumferential direction to the stage S. 
     In addition, although the example in which a single exhaust port  6  is provided in the bottom portion of the chamber  1  has been described, the present disclosure is not limited thereto. For example, one or more exhaust ports  6  may be provided in the ceiling portion of the chamber  1 , or one or more exhaust ports  6  may be provided in the bottom portion and the ceiling portion of the chamber  1 . 
     The plasma processing apparatus  100  may further include a controller  50 . The controller  50  may be a computer including, for example, a processor, a storage part such as memory, an input device, a display device, and a signal input/output interface. The controller  50  controls each part of the plasma processing apparatus  100 . In the controller  50 , an operator may perform, for example, a command input operation in order to manage the plasma processing apparatus  100 , using the input device. In addition, in the controller  50 , the operation situation of the plasma processing apparatus  100  may be visualized and displayed by the display device. The storage part stores a control program and recipe data. The control program is executed by the processor in order to execute various kinds of processing in the plasma processing apparatus  100 . The processor executes the control program so as to control each part of the plasma processing apparatus  100  according to the recipe data. 
     [Abnormal Discharge and Countermeasure] 
     Next, with reference to  FIGS. 2A to 2F , abnormal discharge, which is likely to occur around a stage S, and a countermeasure therefor will be described.  FIGS. 2A to 2F  are views illustrating examples of surroundings of stages S according to an embodiment and a modification and a comparative example.  FIGS. 2A and 2B  illustrate an exemplary configuration of the stage S and its surroundings according to a comparative example.  FIGS. 2C and 2D  illustrate an exemplary configuration of the stage S and its surroundings according to the present embodiment.  FIGS. 2E and 2F  illustrate an exemplary configuration of the stage S and its surroundings according to a modification of the present embodiment. 
     The high-frequency power output from the RF power supply  36  illustrated in  FIG. 1  is applied to the upper electrode  14 . As a result, as illustrated in  FIGS. 2A and 2B , a displacement current (hereinafter, referred to as “displacement current  3 ”) flows between the upper electrode  14  and the stage S, which functions as a lower electrode. The displacement current is represented by the flow of an electric field, that is, the time derivative of an electric field. 
     In addition, the high frequency waves output from the RF power supply  36  flow on the surfaces of the metal lid  11  and the container  12  outside the upper electrode  14  and propagate through the exhaust manifold  41 . As a result, an electric field is generated in the exhaust manifold  41  formed of ceramics. 
     According to Ampere-Maxwell&#39;s law, a displacement current, which is the time derivative of the electric field, flows in an alternating electric field even in a dielectric material such as ceramics. Accordingly, the displacement currents in the two directions illustrated in  FIGS. 2A and 2B  (hereinafter, the displacement current at the inner side (upper electrode  14  side) illustrated in  FIGS. 2A and 2B  is referred to as “displacement current  1 ” and the displacement current at the outer side is referred to as “displacement current  2 ”) flow in the exhaust manifold  41 . 
     In addition, as illustrated in  FIGS. 2A and 2B , a displacement current (hereinafter, referred to as “displacement current  4 ”) flows from the center of the stage S toward the outside of the stage S, and a displacement current (hereinafter, referred to as “displacement current  1 ”) flows downward from the center of the stage S. 
     The displacement current  3  flows between the upper electrode  14  and the electrode plate  21  of the stage S, and contributes to the generation of plasma. Therefore, the displacement current  3  is preferably large. In contrast, when the displacement current  4  is large, a strong electric field is generated in the gap  44  between the stage S and the annular member  40  as illustrated in  FIG. 3 . The electric field generated in the gap  44  is indicated by E slit . In particular, the surroundings of the stage S are configured to disturb the displacement current because the dielectric constants are changed in such a manner of the stage S of a dielectric→the gap  44  of the vacuum space→the annular member  40  of a dielectric. Thus, the electric field E slit becomes stronger in the structural portion of the gap  44 . 
     For example, assuming that the dielectric constant of alumina is ε Al2O3 , the dielectric constant of vacuum is ε 0 , and the electric field generated in the stage made of alumina is E Al2O3 , the electric field E slit  generated in the gap  44  is expressed by Equation (1) as follows. 
         E   slit =(ε Al2O3 /ε 0 )× E   Al2O3    (1)
 
     According to Equation ( 1 ), the electric field E slit  generated in the gap  44  becomes larger as the dielectric constant of the dielectric of the stage S becomes greater than the dielectric constant ε 0 of vacuum, and abnormal discharge is likely to occur around the stage S. For example, since the dielectric constant ε Al2O3  of the dielectric of the stage S with respect to the dielectric constant ε 0 of vacuum is about 10, when the stage S is formed of alumina, the electric field E slit  generated in the gap  44  around the stage S is about 10 times as large as the electric field E Al2O3 generated in the stage S. 
     In particular, two metals of the heater  20  and the electrode plate  21  are embedded in the stage S in the horizontal direction. In this case, a strong displacement current  4  is likely to occur in the stage S. Therefore, in the present embodiment, a configuration is adopted in which the impedance in the transmission path of the displacement current around the stage S, i.e., the stage S→the gap  44 →the annular member  40 , is increased. 
     This makes it possible to suppress occurrence of abnormal discharge around the stage S. In addition, this makes it possible to reduce the displacement current in the vacuum portion other than the displacement current  3  flowing between the upper electrode  14  and the stage S as much as possible, and thus increase the displacement current  3  and enhance the plasma generation efficiency. 
       FIGS. 2C and 2D  illustrate an exemplary configuration around the stage S according to the present embodiment.  FIG. 2C  is an enlarged view of the inside of the dotted frame E in  FIG. 1 . As illustrated in a further enlarged view in  FIG. 2D , in the lower surface  140  of the annular member  40  according to the present embodiment, a plurality of annular grooves  40   a  are provided in the vicinity of the gap  44  in the radial direction. Each of the grooves  40   a  are formed in a slit shape. In  FIGS. 2C and 2D , three annular grooves  40   a  are formed in the radial direction. However, the number of annular grooves  40   a  is not limited thereto. The number of annular grooves  40   a  may be one or two or may be four or more. The grooves  40   a  have the same width and the same depth, and are formed concentrically. 
     In the comparative example of  FIGS. 2A and 2B , the annular member  40  has no groove. In this case, the displacement current I d1 flowing through the gap  44 , which is a vacuum space, is represented by the following equation, and is substantially equal to the displacement current I flowing through the stage S as illustrated in the circuit on the left side of  FIG. 4 . 
     
       
         
           
             
               
                 
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     Meanwhile, in the present embodiment of  FIGS. 2C and 2D , by forming three annular grooves  40   a  opened in the lower surface  140  of the annular member  40 , the flow of the displacement current I′ flowing in the stage S (the displacement current  4  illustrated in  FIG. 2A ) can be disturbed, as illustrated in  FIG. 4 . That is, as illustrated in the series circuit on the right side of  FIG. 4 , it is possible to obtain a configuration in which the electric field in the annular member  40  is distributed by the grooves  40   a , and thus the impedance of the transmission path of the displacement, i.e., the stage S→the gap  44 →the annular member  40 , increases. That is, the impedance increases in the vicinity of the grooves  40   a , and the displacement current I d1 flowing through the gap  44  decreases. Accordingly, the displacement current I d1 flowing through the gap  44  in this case is substantially equal to the displacement current I′ (displacement current  4 ) flowing through the stage S, and is much smaller than the displacement current I flowing through the gap  44  in the configuration of the comparative example illustrated in  FIGS. 2A and 2B . From the foregoing, with the annular member  40  according to the present embodiment, it is possible to reduce the displacement current I d1 flowing through the gap  44 . 
     In addition, as illustrated in  FIG. 2D , the annular member  40  extends downward at a portion where the grooves  40   a  are formed, and forms a step  40   b  on the lower surface of the annular member. Thus, the lower surface  140  of the annular member  40  is lower than the lower surface  141  of the stage S in the portion of the step  40   b . With such a configuration and the grooves  40   a , the electric field generated by the high-frequency waves passing through the annular member  40  is distributed, and the impedance is increased at the end of the annular member  40 . This makes it possible to obtain a structure in which the displacement current I′ (displacement current  4 ) is difficult to flow from the stage S to the annular member  40 . 
     As described above, the annular member  40  according to the present embodiment functions as an insulating member that reflects high-frequency waves. This makes it possible to weaken the electric field strength in the gap  44  between the stage S and the annular member  40 , and thus suppress the occurrence of abnormal discharge around the stage S. 
     [Modification] 
     Next, a modification illustrated in  FIGS. 2E and 2F  will be described. For example, as illustrated in  FIGS. 2E and 2F , the stage S may have a ceramic connection member Sb extending downward from an end portion, and the annular member  40  may be provided around the connection member Sb with a distance from the connection member Sb. The annular member  40  may have a step, as illustrated in  FIGS. 2E and 2F . 
     As the thicknesses of the stage S and the annular member  40  around the gap  44  increase, the impedance decreases, and the displacement current easily passes therethrough. Thus, the electric field in the gap  44  becomes stronger. Accordingly, in this modification, a thin ceramic connection member Sb is provided below the end of the stage S. This may allow the connection member Sb to function as a capacitor so as to increase the impedance and to make it difficult to pass the displacement current. In addition, by making the annular member  40  thinner and providing a step, the impedance is further increased, whereby it is possible to enhance the function of the annular member  40  as an insulating member that reflects high-frequency waves. This makes it possible to weaken the electric field strength in the gap  44  between the stage S and the annular member  40 , and thus suppress the occurrence of abnormal discharge around the stage S. 
     In addition, the configuration according to the present embodiment and the configuration according to the modification may be combined and applied. Furthermore, the annular members  40  according to  FIGS. 5A and 5B  and the configuration according to the modification may be combined and applied. 
     The annular members  40  illustrated in  FIGS. 5A and 5B  have two annular grooves  40   a . The grooves  40   a  illustrated in  FIG. 5B  are deeper than the grooves  40   a  illustrated in  FIG. 5A . However, all the adjacent grooves  40   a  have the same width and the same depth. 
     It is preferable that the width of the two annular grooves  40   a  illustrated in  FIGS. 5A and 5B  is substantially equal to or approximately equal to the interval (gap  44 ) between the stage S and the annular member  40 . In addition, it is preferable that the interval between the grooves  40   a  is substantially equal to or approximately equal to the gap  44 . 
     As illustrated in  FIG. 5C , when the width of a groove  200   a  provided in an annular member  200  is significantly larger than the gap  44 , the electric field is concentrated to the groove  200   a , and abnormal discharge is likely to occur around the groove  200   a  and the gap  44 . Accordingly, a single groove  40   a  may be provided in the annular member  40 , but the width thereof is preferably substantially equal to or approximately equal to the interval (gap  44 ) between the stage S and the annular member  40 . 
     As described above, with the plasma processing apparatuses  100  according to the present embodiment and the modification, by forming the grooves  40   a  in the lower surface of the annular member  40  provided around the stage S with a distance from the stage S, the electric field generated by the high frequency waves passing through the annular member  40  is distributed. This makes it possible to lower the electric field strength of the gap  44  between the stage S and the annular member  40 , and thus reduce the displacement current flowing through the stage S. Thus, it is possible to prevent abnormal discharge. 
     The plasma processing apparatus of the present disclosure is applicable to any of an atomic layer deposition (ALD) type apparatus, a capacitively coupled plasma (CCP) type apparatus, an inductively coupled plasma (ICP) type apparatus, a radial line slot antenna type apparatus, an electron cyclotron resonance plasma (ECR) type apparatus, and a helicon wave plasma (HWP) type apparatus. 
     The plasma processing apparatus according to the present disclosure is not limited to the apparatus that is capable of simultaneously processing four wafers W placed on the four stages illustrated in  FIG. 1 . For example, the plasma processing apparatus according to the present disclosure may be an apparatus that is capable of simultaneously processing two or more wafers W placed on two or more stages S arranged to face the upper electrodes  14 , respectively. In addition, the plasma processing apparatus according to the present disclosure may be an apparatus that is capable of sequentially processing one wafer W placed on one stage S arranged to face the upper electrode  14 , respectively. 
     According to an aspect, it is possible to prevent abnormal discharge. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.