Patent Publication Number: US-2021183628-A1

Title: Transfer system and transfer method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2019-224553 filed on Dec. 12, 2019, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The various aspects and embodiments described herein pertain generally to a transfer system and a method therefor. 
     BACKGROUND 
     Patent Document 1 describes a semiconductor manufacturing apparatus. This apparatus includes a substrate processing chamber, a focus ring standby chamber, and a transfer device. An electrode is disposed within the substrate processing chamber. A substrate is placed on the electrode. The focus ring standby chamber accommodates therein a multiple number of focus rings. The transfer device transfers the focus ring accommodated in the focus ring standby chamber into the substrate processing chamber without opening the substrate processing chamber to the atmosphere. The focus ring is placed to surround the substrate placed on the electrode.
     Patent Document 1: Japanese Patent Laid-open Publication No. 2006-196691   

     SUMMARY 
     In one exemplary embodiment, there is provided a transfer system configured to transfer a focus ring into a processing apparatus. The transfer system includes a transfer device and a position detection system. The processing apparatus includes a chamber main body; and a placing table disposed within a chamber provided by the chamber main body. The placing table has a substrate placing region and a focus ring placing region surrounding the substrate placing region. The transfer device is configured to transfer the focus ring onto the focus ring placing region. The position detection system includes a light source, multiple optical elements, a driving unit and a controller. The light source is configured to generate measurement light. The multiple optical elements are configured to output the measurement light generated from the light source as output light and configured to receive reflected light. The driving unit is configured to move each of the multiple optical elements to allow each of the optical elements to scan a scanning range from the focus ring placed on the focus ring placing region to the substrate placing region. The controller is configured to calculate, based on the reflected light in the scanning range, a positional relationship between the placing table and the focus ring placed on the focus ring placing region for each of the multiple optical elements. The transfer device is configured to adjust a transfer position of the focus ring onto the focus ring placing region based on the positional relationship calculated by the controller. 
     The foregoing summary is illustrative only and is not intended to be any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  is a diagram illustrating an example of a processing system; 
         FIG. 2  is a diagram illustrating an example of a longitudinal cross sectional configuration of major parts of a processing apparatus; 
         FIG. 3  is a configuration view illustrating an example of a position detection system according to an exemplary embodiment; 
         FIG. 4  is a diagram illustrating an example of scanning using three optical elements; 
         FIG. 5  is a diagram illustrating an example of a scanning range of the position detection system according to the exemplary embodiment; 
         FIG. 6  is a flowchart illustrating an example processing of a focus ring transfer method according to the exemplary embodiment; 
         FIG. 7  is a diagram illustrating an example of determining a transfer position of a focus ring which is transferred by a transfer device; 
         FIG. 8A  and  FIG. 8B  are diagrams illustrating an example where a positional relationship between a placing table and the focus ring is appropriate; 
         FIG. 9A  and  FIG. 9B  are diagrams illustrating an example where a positional relationship between the placing table and the focus ring is inappropriate; 
         FIG. 10  is a diagram illustrating an example of scanning using two optical elements; and 
         FIG. 11A  and  FIG. 11B  are diagrams illustrating an example of calculating a positional relationship as polar coordinates from a result of the scanning using the two optical elements. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part of the description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current exemplary embodiment. Still, the exemplary embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     Hereinafter, various exemplary embodiments will be described. 
     In one exemplary embodiment, there is provided a transfer system configured to transfer a focus ring into a processing apparatus. The transfer system includes a transfer device and a position detection system. The processing apparatus includes a chamber main body; and a placing table disposed within a chamber provided by the chamber main body. The placing table has a substrate placing region and a focus ring placing region surrounding the substrate placing region. The transfer device is configured to transfer the focus ring onto the focus ring placing region. The position detection system includes a light source, multiple optical elements, a driving unit and a controller. The light source is configured to generate measurement light. The multiple optical elements are configured to output the measurement light generated from the light source as output light and configured to receive reflected light. The driving unit is configured to move each of the multiple optical elements to allow each of the optical elements to scan a scanning range from the focus ring placed on the focus ring placing region to the substrate placing region. The controller is configured to calculate, based on the reflected light in the scanning range, a positional relationship between the placing table and the focus ring placed on the focus ring placing region for each of the multiple optical elements. The transfer device is configured to adjust a transfer position of the focus ring onto the focus ring placing region based on the positional relationship calculated by the controller. 
     In the above described transfer system, by allowing the multiple optical elements to scan, the height of the focus ring with respect to the height of the substrate placing region in the scanning range is detected. Based on the variation amount of this height, the positional relationship between the focus ring and the placing table in the scanning rage is calculated. The substrate placing region has the circular shape, and the outer diameter of the substrate placing region and the inner diameter of the focus ring are previously set. Thus, the position detection system is capable of calculating the positional relationship between the focus ring and the placing table by allowing the multiple optical elements to scan, and thus capable of adjusting the transfer position of the focus ring based on this positional relationship. 
     In the exemplary embodiment, the multiple optical elements is three or more optical elements, and each of the multiple optical elements is disposed to output the measurement light to an end portion of the substrate placing region. The controller may be configured to determine, when the focus ring is transferred onto the focus ring placing region, a positional relationship between the placing table and the focus ring held by the transfer device based on the reflected light on a circumference of the substrate placing region. In this case, since the positional relationship between the placing table and the focus ring is determined in the middle of the transfer of the focus ring, the transfer system is capable of suppressing the contact between the placing table and the focus ring. 
     In the exemplary embodiment, the controller may be configured to calculate the positional relationship between the placing table and the focus ring placed on the focus ring placing region as polar coordinates. Since the positional relationship between the focus ring and the placing table is calculated as the polar coordinates, the transfer system is capable of clarifying the distance and the direction in which the position deviation between the focus ring and the placing table is adjusted. 
     In another exemplary embodiment, there is provided a transfer method of transferring a focus ring. The transfer method includes transferring the focus ring onto a focus ring placing region surrounding a substrate placing region on which a substrate is placed; scanning a scanning range from the focus ring placed on the focus ring placing region to the substrate placing region with multiple optical elements each configured to output measurement light as output light and configured to receive reflected light; calculating a positional relationship between the placing table and the focus ring placed on the focus ring placing region based on the reflected light in the scanning range; and deciding a transfer position of the focus ring based on the positional relationship between the placing table and the focus ring placed on the focus ring placing region, which is calculated through the calculating of the positional relationship. 
     Hereinafter, the various exemplary embodiments will be described in detail with reference to the accompanying drawings. In the various drawings, same or corresponding parts will be assigned same reference numerals. 
     First Exemplary Embodiment 
       FIG. 1  is a diagram illustrating an example of a processing system. The processing system S 1  shown in  FIG. 1  is configured to perform a processing on a target object. The target object is a disk-shaped object as a processing target of a processing apparatus. By way of example, the target object is a wafer W (an example of a substrate). The target object may have a slopped peripheral portion (bevel). A treatment or a plasma processing may or may not be previously performed on this target object. 
     The processing system S 1  includes stages  2   a  to  2   d , receptacles  4   a  to  4   d , a loader module LM, load lock chambers LL 1  and LL 2 , process modules PM 1  to PM 6  (an example of the processing apparatus), and a transfer chamber TC. 
     The stages  2   a  to  2   d  are arranged along one side of the loader module LM. The receptacles  4   a  to  4   d  are mounted on the stages  2   a  to  2   d , respectively. Each of the receptacles  4   a  to  4   d  is configured to accommodate wafers W therein. 
     The loader module LM has a chamber wall which forms and confines therein a transfer space which is in an atmospheric pressure state. The loader module LM has a transfer device TU 1  in this transfer space. The transfer device TU 1  is configured to transfer the wafers W between the receptacles  4   a  to  4   d  and the load lock chambers LL 1  and LL 2 . 
     The load lock chambers LL 1  and LL 2  are provided between the load module LM and the transfer chamber TC. Each of the load lock chambers LL 1  and LL 2  provides a preliminary decompression chamber. 
     The transfer chamber TC is connected to the load lock chambers LL 1  and LL 2  via gate valves. The transfer chamber TC is configured as an evacuable decompression chamber, and a transfer device TU 2  is accommodated in this decompression chamber. The transfer device TU 2  is configured to transfer the wafers W between the load lock chambers LL 1  and LL 2  and the process modules PM 1  to PM 6  and between any two of the process modules PM 1  to PM 6 . 
     The process modules PM 1  to PM 6  are connected to the transfer chamber TC via gate valves. Each of the process modules PM 1  to PM 6  is a processing apparatus configured to perform a certain processing such as a plasma processing on the wafer W. 
     In the processing system S 1 , a series of operations when a processing is performed on the wafer W are as follows, for example. The transfer device TU 1  of the loader module LM takes out the wafer W from one of the wafer receptacles  4   a  to  4   d  and transfers the wafer W into either one of the load lock chambers LL 1  and LL 2 . Then, this load lock chamber decompresses the preliminary decompression chamber to a preset pressure. Subsequently, the transfer device TU 2  takes out the wafer W from this load lock chamber and transfers the wafer W into any one of the process modules PM 1  to PM 6 . The wafer W is processed by one or more of the process modules PM 1  to PM 6 . Thereafter, the transfer device TU 2  transfers the wafer W after being processed into either one of the load lock chambers LL 1  and LL 2  from the process module. Then, the transfer device TU 1  transfers the wafer W from the corresponding load lock chamber into any one of the receptacles  4   a  to  4   d.    
     The processing system S 1  is further equipped with a control device MC (an example of a controller). The control device MC may be a computer including a processor, a storage device such as a memory, a display device, an input/output device, a communication device, and so forth. The above-described series of operations of the processing system S 1  are implemented under the control of the control device MC over the individual components of the processing system S 1  according to a program stored in the storage device. 
     Now, a processing apparatus  2  as an example of the process modules PM 1  to PM 6  will be discussed.  FIG. 2  is a longitudinal cross sectional view schematically illustrating a configuration of major components of the processing apparatus  2 . As depicted in  FIG. 2 , the processing apparatus  2  is equipped with a processing vessel  20  (an example of a chamber main body) configured to accommodate therein a wafer W and process it by plasma. 
     The processing vessel  20  forms and confines a processing chamber S (an example of a chamber) therein. The processing chamber S is configured to be evacuable. A placing table  21  for placing the wafer W and a focus ring FR to be described later thereon is provided in the processing chamber S. The placing table  21  has a stepped shape as a peripheral portion of a top surface portion of a cylindrical body is notched along the entire circumference thereof. That is, a portion of the top surface portion other than the peripheral portion is protruded into a cylindrical shape. The placing table  21  has, on a top surface thereof, a substrate placing region  21   a  and a focus ring placing region  21   b.    
     The substrate placing region  21   a  is a region for placing the substrate thereon. The substrate placing region  21   a  has a circular shape centered on an axis of the placing table  21 . The focus ring placing region  21   b  is a region for placing the focus ring FR thereon. The focus ring placing region  21   b  is set to surround the substrate placing region  21   a . The focus ring placing region  21   b  is of a circular ring shape defined by two concentric circles. An inner circle forms a circumference of the substrate placing region  21   a.    
     The substrate placing region  21   a  is protruded higher than the focus ring placing region  21   b . A step is formed between the substrate placing region  21   a  and the focus ring placing region  21   b . As an example, a height of the step is equivalent to a difference between the wafer W and the focus ring FR. That is, the protruded portion forms the substrate placing region  21   a  on which the substrate is placed, and a peripheral portion surrounding this substrate placing region  21   a  forms the focus ring placing region  21   b  on which the focus ring FR is placed. An electrostatic chuck mechanism (not shown) configured to attract the wafer W is provided under the substrate placing region  21   a . Further, an electrostatic chuck mechanism may be provided under the focus ring placing region  21   b  as well. 
     The placing table  21  is made of a conducive material. The placing table  21  is equipped with a RF plate (not shown) to which a high frequency power is applied. The placing table  21  is electrically connected with a high frequency power supply (not shown) via a power feed rod  24 . 
     The focus ring placing region  21   b  sustains the focus ring FR which surrounds the substrate placing region  21   a . The focus ring FR is an annular member. The focus ring FR is configured to improve in-surface uniformity of a plasma processing upon the wafer W. The focus ring FR may be separated from the focus ring placing region  21   b  and replaced by a new focus ring FR in maintenance. The replacement of the focus ring FR is carried out by, for example, the aforementioned transfer device TU 2 . 
     A base plate  25  is provided at a bottom of the processing vessel  20 , and a clearance  26  is provided between the placing table  21  and the base plate  25 . This clearance  26  has an enough width to insulate the placing table  21  and the base plate  25 . Further, a driving mechanism (not shown) for a pusher pin (not shown) is provided in the clearance  26 . The pusher pin receives the wafer W from a transfer arm such as the transfer device TU 2  and places the received wafer W on the substrate placing region  21   a . Further, the pusher pin lifts up the wafer W from the substrate placing region  21   a  and delivers it to the transfer arm. Furthermore, the pusher pin receives the focus ring FR from a transfer arm such as the transfer device TU 2  and places the received focus ring FR on the focus ring placing region  21   b . Further, the pusher pin lifts up the focus ring FR from the focus ring placing region  21   b  and hands it over to the transfer arm. The clearance  26  is not in a vacuum atmosphere but in an atmospheric atmosphere. 
     A facing electrode  27  is disposed above the placing table  21 , facing the placing table  21  at a certain distance therebetween. The facing electrode  27  is configured as a so-called shower head, and is configured to supply a preset processing gas onto the wafer W placed on the substrate placing region  21   a  in a shower shape. The facing electrode  27  is set to have a ground potential, or a high frequency power is applied thereto. 
     A first window  28 A is formed at an upper portion of the facing electrode  27 . The first window  28 A is formed downwards from an upper portion of the processing vessel  20 . The first window  28 A is optically transmissive and has a hermetically sealed structure. The processing vessel  20  is provided with a first through hole  29 A corresponding to the first window  28 A. The first window  28 A and the first through hole  29 A constitute a first light introduction path through which measurement light is irradiated to the processing chamber S. 
     A first optical element  33 A (an example of an optical element) as a constituent component of a position detection system  3  to be described later is disposed at an upper end of the first through hole  29 A. The first optical element  33 A is connected to a light source via a first optical fiber  36 A. The first optical element  33 A irradiates the measurement light to the processing chamber S through the first window  28 A, the first through hole  29 A and the facing electrode  27 . The first optical element  33 A may be, by way of non-limiting example, a collimator or a focuser. The first optical element  33 A is connected with a first actuator  37 A (an example of a driving unit) configured to move the first optical element  33 A in a horizontal direction to allow the first optical element  33 A to scan in this horizontal direction. The first actuator  37 A is an electrically controllable driving device, for example, a stepping motor. 
     In the processing vessel  20 , multiple light introduction paths having the same configuration as the aforementioned first light introduction path are arranged along a circumferential direction of the placing table  21  and the focus ring FR. Specifically, a non-illustrated second window  28 B and a non-illustrated second through hole  29 B as a second light introduction path and a non-illustrated third window  28 C and a non-illustrated third through hole  29 C as a third light introduction path are provided along the circumferential direction of the placing table  21  and the focus ring FR. Further, a second optical element  33 B (an example of the optical element) and a third optical element  33 C (an example of the optical element) are disposed in the second light introduction path and the third light introduction path, respectively. Each of the second optical element  33 B and the third optical element  33 C may be, by way of non-limiting example, a collimator or a focuser. As stated, multiple sets of the window, the through hole and the optical element are provided at the upper portion of the facing electrode  27 . 
       FIG. 3  is a configuration view illustrating an example of the position detection system according to the exemplary embodiment. The position detection system  3  is a system configured to measure a distance from a front surface or a rear surface of the facing electrode  27  to a reflection point by using light interference and detect, based on the measurement result, a positional relationship between the placing table  21  and the focus ring FR, for example. As depicted in  FIG. 3 , the position detection system  3  includes a light source  30 , an optical circulator  31 , an optical switch  32 , the first optical element  33 A, the second optical element  33 B, the third optical element  33 C and a measurement unit  34 . Here, however, the position detection system  3  may not be equipped with the optical switch  32 . 
     The measurement unit  34  is connected with an operation device  35  (an example of the controller). The operation device  35  may be a computer including a processor, a storage device, a display device, an input/output device, a communication device, and so forth. A series of operations of the position detection system  3  to be described later are carried out under the control of the operation device  35  over the individual components of the position detection system  3  according to a program stored in the storage device. The storage device previously stores therein a position of the optical element, an inner diameter of the focus ring FR, a size of the substrate placing region  21   a , and so forth. The information stored in the storage device is used in an operation of the operation device  35 . The operation device  35  and the control device MC shown in  FIG. 1  may be configured as a single body. The light source  30 , the optical circulator  31 , the optical switch  32 , the first optical element  33 A, the second optical element  33 B, the third optical element  33 C and the measurement unit  34  are connected by using optical fibers. 
     The light source  30  is configured to generate measurement light. For example, the light source  30  generates measurement light having a wavelength penetrating a measurement target object. By way of example, a wavelength-sweep light source is used as the light source  30 . The measurement target object may be, by way of example, an object (wafer W), or a part (component) of the processing apparatus  2  such as the focus ring FR or the facing electrode  27 . The measurement target object is made of, by way of non-limiting example, Si (silicon), SiO 2  (quarts), Al 2 O 3  (sapphire), or the like. An example of the measurement light capable of penetrating the object made of such a material is infrared light. 
     The optical circulator  31  is connected to the light source  30 , the optical switch  32  and the measurement unit  34 . The optical circulator  31  propagates the measurement light generated from the light source  30  to the optical switch  32 . As an example, the optical switch  32  has one input terminal and three output terminals. The input terminal is connected to the optical circulator  31 . Further, the three output terminals are connected to the first optical element  33 A, the second optical element  33 B and the third optical element  33 C via the first optical fiber  36 A, the optical fiber  36 B and the optical fiber  36 C, respectively. The optical switch  32  is configured to change an output destination. The optical switch  32  receives the light from the optical circulator  31  through the input terminal and outputs the received light to the three output terminals alternately. 
     Each of the first optical element  33 A, the second optical element  33 B and the third optical element  33 C outputs the measurement light generated from the light source  30  as output light and receives reflected light. To elaborate, each of the first optical element  33 A, the second optical element  33 B and the third optical element  33 C outputs the measurement light, which is controlled to be a convergent ray, to the focus ring FR via the facing electrode  27 . Each of the first optical element  33 A, the second optical element  33 B and the third optical element  33 C then receives the reflected light from the facing electrode  27  and the focus ring FR. The reflected light includes reflected light from the rear surface as well as reflected light from the front surface. Each of the first optical element  33 A, the second optical element  33 B and the third optical element  33 C propagates the received reflected light to the optical switch  32 . 
     The first actuator  37 A (an example of the driving unit), the second actuator  37 B (an example of the driving unit) and the third actuator  37 C (an example of the driving unit) are driven by the operation device  35  to move the first optical element  33 A, the second optical element  33 B and the third optical element  33 C, respectively, to allow the first optical element  33 A, the second optical element  33 B and the third optical element  33 C to scan a preset scanning range. The first optical element  33 A, the second optical element  33 B and the third optical element  33 C are allowed to scan the preset scanning range by the first actuator  37 A, the second actuator  37 B and the third actuator  37 C, respectively. The scanning range is a range from the substrate placing region  21   a  to the focus ring FR, and corresponds to, for example, a width of the first through hole  29 A and the first window  28 A shown in  FIG. 2 .  FIG. 4  is a diagram schematically illustrating an example of scanning using the three optical elements. As shown in  FIG. 4 , the first optical element  33 A is configured to scan within a first scanning range Q 1  extending in a diametrical direction. The second optical element  33 B is configured to scan within a second scanning range Q 2  extending in the diametrical direction at a position spaced apart from the first scanning range Q 1  in the circumferential direction. The third optical element  33 C is configured to scan within a third scanning range Q 3  extending in the diametrical direction at a position spaced apart from the first scanning range Q 1  and the second scanning range Q 2  in the circumferential direction. A scanning direction may be a diametrically outward direction or a diametrically inward direction. 
     Referring back to  FIG. 3 , the optical switch  32  outputs the reflected lights obtained by the first optical element  33 A, the second optical element  33 B and the third optical element  33 C to the optical circulator  31  alternately. The optical circulator  31  outputs each received reflected light to the measurement unit  34 . The measurement unit  34  measures a spectrum of the reflected light obtained from the optical circulator  31 . The spectrum of the reflected light indicates an intensity distribution dependent on a wavelength or a frequency of the reflected light. The measurement unit  34  outputs the spectrum of the reflected light to the operation device  35 . 
     The operation device  35  calculates, for each optical element, a positional relationship between the placing table  21  and the focus ring FR based on the reflected light in the scanning range.  FIG. 5  is a diagram illustrating the scanning range of the position detection system  3  according to the exemplary embodiment. In  FIG. 5 , the scanning of the first optical element  33 A will be explained as an example. The first optical element  33 A is moved within the first scanning range Q 1  ranging from the substrate placing region  21   a  to the focus ring FR while outputting output light. 
     The output light outputted from the first optical element  33 A is reflected by individual parts of the processing apparatus  2  in the scanning range. By way of example, the output light is reflected on the front surface and the rear surface of the facing electrode  27 , the substrate placing region  21   a  of the placing table  21 , and a front surface and a rear surface of the focus ring FR. The first optical element  33 A acquires reflected light at each scanning position. The operation device  35  measures a height of the scanning range based on the spectrum of the reflected light. 
     The operation device  35  measures a distance D A  between the placing table  21  and the focus ring FR in the horizontal direction based on a variation of the height of the scanning range. To elaborate, the operation device  35  measures the distance D A  in the horizontal direction from the substrate placing region  21   a  to a position of a flat upper end portion FRA of the focus ring FR, a position of a flat lower end portion FRB of the focus ring FR, or a position between the flat portions of the focus ring FR which has a varying height. As an example, the operation device  35  measures a distance D A1  from the substrate placing region  21   a  to the flat upper end portion FRA of the focus ring FR. The operation device  35  may measure a distance D A2  to an inclined surface FRE of the focus ring FR or a distance D A3  to the flat lower end portion FRB of the focus ring FR. These distances D A1  to D A3  are examples of the distance D A , and the operation device  35  may alternatively measure the distance with respect to a portion other than the flat portions. 
     The second optical element  33 B and the third optical element  33 C are also allowed to scan in the respective scanning ranges. The operation device  35  measures a distance D B  (D B1 , D B2 , D B3 ) and a distance D C  (D C1 , D C2 , D C3 ) between the placing table  21  and the focus ring FR in the horizontal direction. 
     The operation device  35  calculates the positional relationship based on the distance D between the placing table  21  and the focus ring FR in the horizontal direction which is measured by each optical element. An outer diameter of the substrate placing region  21   a  and an inner diameter of the focus ring FR are previously set. Thus, the positional relationship between the placing table  21  and the focus ring FR are calculated by using the distance D in the horizontal direction, the inner diameter of the focus ring FR and the outer diameter of the substrate placing region  21   a . Specifically, an inner diameter of the flat upper end portion FRA of the focus ring FR is referred to as A FRA , and an outer diameter of the substrate placing region  21   a  is referred to as A 21 . When centers of the substrate placing region  21   a  and the focus ring FR are coincident, the distance D (D A1 , D B1 , D C1 ) in the horizontal direction is calculated by the following expression (1). 
     
       
         
           
             
               
                 
                   
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     Thus, the positional relationship between the placing table  21  and the focus ring FR is calculated based on a difference between the distance D (D A1 , D B1 , D C1 ) in the horizontal direction and a value ((A FRA −A 21 )/2) which is obtained by dividing a difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2. That is, based on differences corresponding to the distances D A1 , D B1 , and D C1 , a deviation amount in center positions of the substrate placing region  21   a  and the focus ring FR and a deviation direction are calculated. For an inner diameter of the inclined surface FRE of the focus ring FR and an inner diameter of the flat lower end portion FRB of the focus ring FR, the aforementioned relationship is also established with respect to the distance D in the horizontal direction corresponding to each position. Thus, at least one of the set of the distances D A1 , D B1 , D C1 , the set of the distances D A2 , D B2 , D C2 , and the set of the D A3 , D B3 , D C3  needs to be measured. 
     The control device MC adjusts a transfer position of the focus ring FR based on the positional relationship between the placing table  21  and the focus ring FR. If the difference between the distance D in the horizontal direction and the value obtained by dividing the difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2 is larger than a preset threshold value, the operation device  35  outputs the difference corresponding to the measurement position of each optical element to the control device MC. In this case, the control device MC adjusts a teaching value (a parameter which controls an operation of the transfer device TU 2 ) of the transfer device TU 2  such that each difference becomes zero (0). 
     The control device MC adjusts the teaching value after the focus ring FR is carried out of the processing chamber S, and then carries the focus ring FR in again after the adjustment of the teaching value is completed. The control device MC may perform the adjustment of the teaching value without carrying the focus ring FR out of the processing chamber S, that is, in the state that the focus ring FR stays in the processing chamber S. The transfer device TU 2  adjusts the transfer position of the focus ring FR through the adjustment of the teaching value by the control device MC. 
     A system  1  configured to transfer the focus ring FR according to the exemplary embodiment includes the transfer device TU 2 , the control device MC and the position detection system  3  described above. The control device MC and the operation device  35  of the position detection system  3  may not be configured as separate bodies. The control device MC may be configured to carry out a part or all of the functions of the operation device  35 . 
     [Operation of System Configured to Transfer Focus Ring] 
       FIG. 6  is a flowchart illustrating an example processing of a method of transferring the focus ring FR according to the exemplary embodiment. The flowchart shown in  FIG. 6  is performed by the system  1  when a new focus ring FR is carried in after a previous focus ring FR is separated from the focus ring placing region  21   b.    
     As shown in  FIG. 6 , the transfer device TU 2  transfers the focus ring FR onto the focus ring placing region  21   b  which surrounds the substrate placing region  21   a  on which the wafer W is placed (process S 10 ). Then, the position detection system  3  performs scanning of the focus ring FR. As an example, the scanning range from the focus ring placing region  21   b  to the focus ring FR is scanned by the three optical elements (process S 20 ). 
     The operation device  35  calculates the positional relationship between the placing table  21  and the focus ring FR based on the distance D between the substrate placing region  21   a  and the focus ring FR in the horizontal direction which is measured by each optical element. This positional relationship is calculated based on the outer diameter of the substrate placing region  21   a , the inner diameter of the focus ring FR and the distance D between the substrate placing region  21   a  and the focus ring FR in the horizontal direction which is measured by each optical element (process S 30 ). 
     The operation device  35  determines, based on the positional relationship between the placing table  21  and the focus ring FR, whether the transfer position of the focus ring FR is appropriate (process S 40 ). If the difference between the distance D in the horizontal direction and the value obtained by dividing the difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2 is equal to or less than the preset threshold value, the operation device  35  makes a determination that the transfer position of the focus ring FR is appropriate. If the transfer position is found to be appropriate (process S 40 : Yes), the processing of the flowchart of  FIG. 6  is ended. 
     If, however, the difference between the distance D in the horizontal direction and the value obtained by dividing the difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2 is larger than the preset threshold value, the operation device  35  makes a determination that the transfer position is inappropriate. If the transfer position is found to be inappropriate (process S 40 : NO), the transfer device TU 2  carries out the focus ring FR (process S 50 ). In this case, the operation device  35  outputs the difference between the distance D in the horizontal direction and the value obtained by dividing the difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2 to the control device MC. 
     The control device MC adjusts the transfer position of the focus ring FR based on the positional relationship between the placing table  21  and the focus ring FR (process S 60 ). The control device MC adjusts the teaching value (a control parameter which controls an operation of the transfer device TU 2 ) of the transfer device TU 2  so that each difference becomes zero (0). After the transfer position of the focus ring FR is adjusted, the focus ring FR is carried in again (process S 10 ). Through these operations, the processes S 10  to S 60  are repeated until the determination that the transfer position is appropriate is made. 
     Second Exemplary Embodiment 
       FIG. 7  is a diagram illustrating an example of determining a transfer position of the focus ring FR being transferred. In a position detection system according to a second exemplary embodiment, a positional relationship between the placing table  21  and the focus ring FR is investigated by three or more optical elements before the focus ring FR is placed on the focus ring placing region  21   b . By way of example, when the focus ring FR is transferred by the transfer device TU 2 , the position detection system investigates the positional relationship between the placing table  21  and the focus ring FR when the focus ring FR is placed on the pusher pin of the focus ring placing region  21   b . The position detection system may investigate the positional relationship between the placing table  21  and the focus ring FR in the state that the focus ring FR is held by the transfer device TU 2 . 
     A first optical element  33 A, a second optical element  33 B, and a third optical element  33 C are disposed at positions where they output output lights to a peripheral portion of the substrate placing region  21   a . The first optical element  33 A, the second optical element  33 B and the third optical element  33 C are arranged such that their irradiation positions are distanced apart from each other in the circumferential direction of the placing table  21 . 
     The operation device  35  investigates the positional relationship between the placing table  21  and the focus ring FR based on reflected light which has reached each optical element.  FIG. 8A  and  FIG. 8B  are diagrams illustrating an example where the positional relationship between the placing table  21  and the focus ring FR is appropriate.  FIG. 8A  is a plan view of the placing table  21  and the focus ring FR, and  FIG. 8B  is a partial cross sectional view of the placing table  21  and the focus ring FR. In  FIG. 8A  and  FIG. 8B , a center position of the substrate placing region  21   a  and a center position of the focus ring FR are coincident. When the positional relationship between the placing table  21  and the focus ring FR is appropriate, the output light is reflected on a peripheral portion of the placing table  21  since the inner diameter of the focus ring FR is larger than the outer diameter of the substrate placing region  21   a . If heights measured by the three optical elements all coincide with a preset height of the substrate placing region  21   a , the operation device  35  makes a determination that the positional relationship between the placing table  21  and the focus ring FR is appropriate. 
       FIG. 9A  and  FIG. 9B  are diagrams illustrating an example where the positional relationship between the placing table  21  and the focus ring FR is inappropriate.  FIG. 9A  is a plan view of the placing table  21  and the focus ring FR, and  FIG. 9B  is a partial cross sectional view of the placing table  21  and the focus ring FR. In  FIG. 9A  and  FIG. 9B , the center position of the focus ring FR is deviated to the right from the center position of the substrate placing region  21   a , so that the inner diameter of the focus ring FR and the outer diameter of the substrate placing region  21   a  are overlapped. When the positional relationship between the placing table  21  and the focus ring FR is inappropriate, the output light is reflected by the focus ring FR. If the height measured by at least one of the three optical elements does not coincide with the preset height of the substrate placing region  21   a , the operation device  35  makes a determination that the positional relationship between the placing table  21  and the focus ring FR is inappropriate. 
     The operation device  35  outputs measurement results of the three optical elements to the control device MC. The control device MC adjusts a teaching value of the transfer device TU 2  based on the measurement results of the three optical elements. The transfer device TU 2  may carry out the focus ring FR from the chamber and then carry the focus ring FR into the chamber again with the adjusted teaching value. Alternatively, the transfer device TU 2  may adjust a holding position of the focus ring FR within the chamber based on the adjusted teaching value. 
     If the focus ring FR is transferred in the state that the positional relationship between the placing table  21  and the focus ring FR is inappropriate, there is a likelihood that the focus ring FR and the placing table  21  come into contact with each other. The position detection system according to the second exemplary embodiment suppresses this contact between the focus ring FR and the placing table  21  by detecting a position of the focus ring FR being transferred. 
     The inventive features described in the second exemplary embodiment may be used in combination with the first exemplary embodiment. The system  1  may investigate the positional relationship between the placing table  21  and the focus ring FR in the process S 10  in  FIG. 6 . For example, before the focus ring FR is placed on the focus ring placing region  21   b  after it is carried into the chamber, the positional relationship between the placing table  21  and the focus ring FR may be investigated by the three or more optical elements. 
     Third Exemplary Embodiment 
       FIG. 10  is a diagram illustrating an example of scanning using two optical elements. In a position detection system according to the third exemplary embodiment, the operation device  35  calculates a positional relationship between the placing table  21  and the focus ring FR based on a distance D between the substrate placing region  21   a  and the focus ring FR in the horizontal direction which is measured by the two optical elements. In the position detection system according to the third exemplary embodiment, a first optical element  33 A is disposed at a position which is not opposite from a second optical element  33 B by 180 degrees with respect to a center position of the substrate placing region  21   a.    
     Even if the number of the optical elements is two, the relationship of the aforementioned expression (1) is still established. Thus, the positional relationship between the placing table  21  and the focus ring FR is calculated based on a difference between the distance D in the horizontal direction and a value obtained by dividing the difference between the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR by 2. 
       FIG. 11A  and  FIG. 11B  are diagrams illustrating an example where the positional relationship is calculated as polar coordinates from scanning results using the two optical elements.  FIG. 11A  is a diagram illustrating a polar coordinate system in which a rotation position θ 0  set with respect to a center position of the substrate placing region  21   a  is defined as a zero coordinate. A first optical element  33 A is disposed at a rotation position θ A . A distance between the substrate placing region  21   a  and the focus ring FR in the horizontal direction at the rotation position θ A  is referred to as Dm. A second optical element  33 B is disposed at a rotation position θ B . A distance between the substrate placing region  21   a  and the focus ring FR in the horizontal direction at the rotation position θ B  is referred to as D B1 . 
       FIG. 11B  is a graph plotted based on the polar coordinates of  FIG. 11A . A vertical axis represents a distance between the substrate placing region  21   a  and the focus ring FR in the horizontal direction, and a horizontal axis indicates a rotation position. When the center positions of the substrate placing region  21   a  and the focus ring FR are coincident, the distance between the substrate placing region  21   a  and the focus ring FR in the horizontal direction is maintained constant. In  FIG. 11B , the distance in the horizontal direction which is maintained constant is, e.g., 1.0 mm. If the center position of the substrate placing region  21   a  and the center position of the focus ring FR are not coincident with each other, the distance in the horizontal direction varies in the shape of a sine wave, as illustrated in  FIG. 11B . The distances D A1  and D B1  in the horizontal direction calculated by scanning of the first optical element  33 A and the second optical element  33 B are indicated as distances at the rotation position θ A  and the rotation position θ B  of the sine wave. 
     In  FIG. 11A  and  FIG. 11B , a deviated distance between the center position of the substrate placing region  21   a  and the center position of the focus ring FR is referred to as R FR , and a deviated rotation position is referred to as θ FR . The distances D A1  and D B1  in the horizontal direction calculated by the scanning of the first optical element  33 A and the second optical element  33 B satisfy relationships indicated by the following expressions (2) and (3) in relation with R FR  and θ FR . 
     
       
         
           
             
               
                 
                   
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     Since the rotation position θ A  and the rotation position θ B  are mounting positions of the optical elements, these positions are already known, and an inner diameter A FR  of the focus ring FR and an outer diameter A 21  of the substrate placing region  21   a  are also already known. Thus, by solving simultaneous equations using the expressions (2) and (3), the operation device  35  is capable of calculating the deviated distance R FR  and the deviated rotation position θ FR . As stated above, by calculating the positional relationship as the polar coordinates, a distance and a direction in which the position deviation between the focus ring FR and the placing table  21  is adjusted becomes clear. 
     MODIFICATION EXAMPLES 
     So far, the various exemplary embodiments have been described. However, the exemplary embodiments are not limiting, and various omissions, substitutions and changes may be made. Further, other exemplary embodiments may be embodied by combining elements in the various exemplary embodiments in a variety of other forms. 
     By way of example, the optical element is not limited to the focuser. The optical element is not particularly limited as long as it has a function of irradiating light to a target object and receiving reflected light therefrom. By way of example, the optical element may be a collimator or the like. Further, a SLD (Super Luminescent Diode) may be used as the light source  30 , and in this case, a spectroscope is used as the measurement unit  34 . The position detection system  3  may measure a distance from the optical element to a reflection position by using light interference with respect to the optical element. 
     The operation device  35  may calculate the positional relationship between the placing table  21  and the focus ring FR held on the focus ring placing region  21   b  as the polar coordinates from a scanning result of the three or more optical elements. As an example, polar coordinates are calculated from a scanning result of a third optical element  33 C in addition to scanning results of the first and second optical elements  33 A and  33 B. If a distance in the horizontal direction, which is calculated as the third optical element  33 C scans in a θ C  direction, is D C1 , the following expression (4) is satisfied. 
     
       
         
           
             
               
                 
                   
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     The operation device  35  is capable of using the simultaneous equations of the expressions (2) and (3), the simultaneous equations of the expressions (3) and (4), and the simultaneous equations of the expressions (2) and (4). Though the rotation position θ A , the rotation position θ B  and the rotation position θ C  are already known as they are mounting positions of the optical elements, there may exist an assembly error of the optical elements or the like. Further, there may be a measurement error as well. The operation device  35  is capable of reducing the error by averaging values of the respective simultaneous equations. The third exemplary embodiment can be applied to the first exemplary embodiment and the second exemplary embodiment. 
     SUMMARY OF EXEMPLARY EMBODIMENTS 
     According to the system and the method of the various exemplary embodiments, by allowing the multiple optical elements to scan, the height of the focus ring FR with respect to the height of the substrate placing region  21   a  is detected. Based on the variation amount of this height, the positional relationship between the focus ring FR and the placing table  21  in the scanning rage is calculated. The substrate placing region  21   a  has the circular shape, and the outer diameter of the substrate placing region  21   a  and the inner diameter of the focus ring FR are previously set. Thus, the position detection system is capable of calculating the positional relationship between the focus ring FR and the placing table  21  by allowing the multiple optical elements to scan, and thus capable of adjusting the transfer position of the focus ring FR based on this positional relationship. 
     According to the system and the method of the second exemplary embodiment, the positional relationship between the focus ring FR and the placing table  21  is investigated in the middle of the transfer of the focus ring FR. Therefore, according to the present system and method, a contact between the focus ring FR and the placing table  21  can be suppressed. 
     According to the system and the method of the third exemplary embodiment, the positional relationship between the focus ring FR and the placing table  21  is calculated as the polar coordinates. Therefore, the system is capable of clarifying the distance and the direction in which the position deviation between the focus ring FR and the placing table  21  is adjusted. 
     According to the present disclosure, it is possible to transfer the focus ring accurately. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting. The scope of the inventive concept is defined by the following claims and their equivalents rather than by the detailed description of the exemplary embodiments. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the inventive concept.