Patent Publication Number: US-2023160089-A1

Title: Apparatus for plating and method of controlling apparatus for plating

Description:
TECHNICAL FIELD 
     The present disclosure relates to an apparatus for plating and a method of controlling the apparatus for plating. 
     BACKGROUND ART 
     Cup-type electroplating apparatus has been known as one example of plating apparatus. In the cup-type electroplating apparatus, a substrate (for example, a semiconductor wafer) held by a substrate holder in such an arrangement that a surface to be plated of the substrate faces down is soaked in a plating solution, and a voltage is applied between the substrate and an anode, so that a conductive film (plating film) deposits on the surface of the substrate. In this type of plating apparatus, rotating the substrate holder and the substrate forms a solution current in the vicinity of the surface of the substrate and thereby uniformly supplies a sufficient amount of ion to the substrate. A paddle reciprocating parallel to the surface of the substrate (Patent Document 1) may be provided, in order to further enhance the solution current in the vicinity of the surface of the substrate. 
     RELATED ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Publication No. 2019-151874 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case of forming the solution current by the rotation of the substrate, a phenomenon that the conductive film is inclined in a direction of the solution current is likely to occur. This is because an upper convection layer of the plating solution becomes thick and a lower diffusion layer becomes thin on a downstream side in the direction of the solution current, due to the direction of convection of the convection layer inside of an opening of a resist on the substrate. As a result, the amount of plating inversely proportional to the thickness of the diffusion layer increases on the downstream side. 
     Furthermore, in the case of using the paddle, there may be a significant field shielding effect on a specific location of a paddle, due to the frequency of the reciprocating motion of the paddle and the number of rotations of the substrate per unit time (frequency of the substrate). Especially, when the frequency of the reciprocating motion of the paddle is an integral multiple of the frequency of the substrate, a beam of the paddle consistently stops at an identical location of the substrate when the paddle stops at respective ends of the reciprocating motion. The field shielding effect is thus likely to be significantly increased at the location/position and to lower the uniformity in thickness of the plating film. 
     The present invention is provided by taking into account the problems described above. One object is to reduce the adverse effect of a solution current by the rotation of a substrate on the uniformity in thickness of a plating film. One object is to reduce the adverse effect of field shielding of a paddle on the uniformity in thickness of the plating film. One object is to reduce the adverse effects of the solution current by the rotation of the substrate and the adverse effect of field shielding of the paddle on the uniformity in thickness of the plating film. 
     Solution to Problem 
     According to one aspect, there is provided an apparatus for plating that is configured to plate a substrate and comprises a plating tank; an anode placed in the plating tank; a rotation mechanism configured to rotate the substrate in a first direction and in a second direction that is opposite to the first direction; and a control device configured to control the rotation mechanism, such that a time period when the substrate is rotated in the first direction becomes equal to a time period when the substrate is rotated in the second direction or such that a time integrated value of a rotation speed in the first direction becomes equal to a time integrated value of a rotation speed in the second direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating the overall configuration of a plating apparatus according to an embodiment; 
         FIG.  2    is a plan view illustrating the overall configuration of the plating apparatus according to the embodiment; 
         FIG.  3    is a schematic diagram illustrating one example of a plating module according to the embodiment; 
         FIG.  4    is a schematic diagram illustrating control of the rotation speed of a substrate according to the embodiment; 
         FIG.  5    is a schematic diagram illustrating control of a plating film in different combinations of forward rotation and reverse rotation of the substrate; 
         FIG.  6    is a graph showing a positional relationship between a paddle and the substrate when the rotation speed of the substrate is changed; 
         FIG.  7    is a schematic diagram illustrating an example of controlling the rotation speed of the substrate; 
         FIG.  8    is a schematic diagram illustrating an example of controlling the rotation speed of the substrate; 
         FIG.  9    is a schematic diagram illustrating an example of controlling the rotation speed of the substrate; 
         FIG.  10    is an exemplary flowchart of setting the rotation speed of the substrate; 
         FIG.  11    is an exemplary flowchart of setting the rotation speed of the substrate; 
         FIG.  12    is an exemplary flowchart of a plating process; 
         FIG.  13    is a schematic diagram illustrating the effect of a flow direction of a plating solution on a plating film 
         FIG.  14    is a schematic diagram illustrating a positional relationship between the paddle and the substrate when the frequency of reciprocating motion of the paddle is an integral multiple of the frequency of the rotation of the substrate; and 
         FIG.  15    is a graph showing the positional relationship between the paddle arid the substrate when the frequency of the reciprocating motion of the paddle is an integral multiple of the frequency of the rotation of the substrate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments of the present disclosure with reference to drawings. In the drawings described below, identical or equivalent components are expressed by identical reference signs, and duplicated description is omitted. 
       FIG.  1    is a perspective view illustrating the overall configuration of the plating apparatus of this embodiment.  FIG.  2    is a plan view illustrating the overall configuration of the plating apparatus of this embodiment. As illustrated. in  FIGS.  1  and  2   , a plating apparatus  1000  includes load ports  100 , a transfer robot  110 , aligners  120 , pre-wet modules  200 . pre-soak modules  300 , plating modules  400 , cleaning modules  500 , spin rinse dryers  600 , a transfer device  700 , and a control module  800 . 
     The load port  100  is a module for loading a substrate housed in a cassette, such as a FOUP, (not illustrated) to the plating apparatus  1000  and unloading the substrate from the plating apparatus  1000  to the cassette. While the four load ports  100  are arranged in the horizontal direction in this embodiment, the number of load ports  100  and arrangement of the load ports  100  are arbitrary. The transfer robot  110  is a robot for transferring the substrate that is configured to grip or release the substrate between the load port  100 , the aligner  120 , and the transfer device  700 . The transfer robot  110  and the transfer device  700  can perform delivery and receipt of the substrate via a temporary placement table (not illustrated) to grip or release the substrate between the transfer robot  110  and the transfer device  700 . 
     The aligner  120  is a module for adjusting a position of an orientation flat, a notch, and the like of the substrate in a predetermined direction. While the two aligners  120  are disposed to be arranged in the horizontal direction in this embodiment, the number of aligners  120  and arrangement of the aligners  120  are arbitrary. The pre-wet module  200  wets a surface to be plated (or a plating surface) of the substrate before a plating process with a process liquid, such as pure water or deaerated water, to replace air inside a pattern formed on the surface of the substrate with the process liquid. The pre-wet module  200  is configured to perform a pre-wet process to facilitate supplying the plating solution to the inside of the pattern by replacing the process liquid inside the pattern with a plating solution during plating. While the two pre-wet modules  200  are disposed to be arranged in the vertical direction in this embodiment, the number of pre-wet modules  200  and arrangement of the pre-wet modules  200  are arbitrary. 
     For example, the pre-soak module  300  is configured to remove an oxidized film having a large electrical resistance present on, a surface of a seed layer firmed on the surface to be plated of the substrate before the plating process by etching with a process liquid, such as sulfuric acid and hydrochloric acid, and perform a pre-soak process that deans or activates a surface of a plating base layer. While the two pre-soak modules  300  are disposed to be arranged in the vertical direction in this embodiment, the number of pre-soak modules  300  and arrangement of the pre-soak modules  300  are arbitrary. The plating module  400  performs the plating process on the substrate. There are two sets of the  12  plating modules  400  arranged by three in the vertical direction and by four in the horizontal direction, and the total  24  plating modules  400  are disposed in this embodiment, but the number of plating modules  400  and arrangement of the plating modules  400  are arbitrary. 
     The cleaning module  500  is configured to perform a cleaning process on the substrate to remove the plating solution or the like left on the substrate after the plating process, While the two cleaning modules  500  are disposed to be arranged in the vertical direction in this embodiment, the number of cleaning modules  500  and arrangement of the cleaning modules  500  are arbitrary. The spin rinse dryer  600  is a module for rotating the substrate after the cleaning process at high speed and drying the substrate. While the two spin rinse dryers are disposed to be arranged in the vertical direction in this embodiment, the number of spin rinse dryers and arrangement of the spin rinse dryers are arbitrary. The transfer device  700  is a device for transfer the substrate between the plurality of modules inside the plating apparatus  1000 . The control module  800  is configured to control the plurality of modules in the plating apparatus  1000  and can be configured of, for example, a general computer including input/output interfaces with an operator or a dedicated computer. 
     An example of a sequence of the plating processes by the plating apparatus  1000  will be described. First, the substrate housed in the cassette is loaded on the load port  100 . Subsequently, the transfer robot  110  grips the substrate from the cassette at the load port  100  and transfers the substrate to the aligners  120 . The aligner  120  adjusts the position of the orientation flat, the notch, or the like of the substrate in the predetermined direction. The transfer robot  110  grips or releases the substrate whose direction is adjusted with the aligners  120  to the transfer device  700 . 
     The transfer device  700  transfers the substrate received from the transfer robot  110  to the pre-wet module  200 , The pre-wet module  200  performs the pre-wet process on the substrate. The transfer device  700  transfers the substrate on which the pre-wet process has been performed to the pre-soak module  300 . The pre-soak module  300  performs the pre-soak process on the substrate. The transfer device  700  transfers the substrate on which the pre-soak process has been performed to the plating module  400 . The plating module  400  performs the plating process on the substrate. 
     The transfer device  700  transfers the substrate on which the plating process has been performed to the cleaning module  500 . The cleaning module  500  performs the cleaning process on the substrate. The transfer device  700  transfers the substrate on which the cleaning process has been performed to the spin rinse dryer  600 . The spin rinse dryer  600  performs the drying process on the substrate. The transfer device  700  grips or releases the substrate on which the drying process has been performed to the transfer robot  110 . The transfer robot  110  transfers the substrate received from the transfer device  700  to the cassette at the load port  100 . Finally, the cassette housing the substrate is unloaded from the load port  100 . 
       FIG.  3    is a schematic diagram illustrating one example of the plating module according to the embodiment. As shown in  FIG.  3   . the plating module  400  according to the embodiment is a face-down type or cup type plating module. The plating solution is, for example, a copper sulfate solution, and a plating film is, for example, a copper film. The plating film may, however, be any platable metal, and the plating solution may be selected according to the type of the plating film. 
     The plating module  400  includes a plating tank  401 , a substrate holder (substrate holding tool)  403 , and a plating solution storage tank  404 . The substrate holder  403  is configured to hold a substrate  402 , such as a wafer, in such a manner that a surface to be plated of the substrate  402  faces down. The plating module  400  is provided with a motor  411  configured to rotate the substrate holder  403  in a circumferential direction. The motor  411  receives supply of electric power from a non-illustrated power supply. The motor  411  is controlled by the control module  800  to control rotations of the substrate holder  403  and of the substrate  402  held by the substrate holder  403 . In other words, the control module  800  controls the rotation of the motor  411  and thereby controls the number of rotations per unit time (also called as the rotational frequency or the rotation speed) of the substrate  402 . Rotating the substrate  402  forms a solution current or flow of the plating solution in the vicinity of the surface of the substrate and uniformly supplies a sufficient amount of ion to the substrate. An anode  410  is placed in the plating tank  401  to be opposed to the substrate  402 . 
     The plating module  400  also includes a plating solution receiving tank  408 . The plating solution in the plating solution storage tank  404  is supplied through a filter  406  and a plating solution supply pipe  407  via a bottom portion of the plating solution  401  into the plating tank  401  by means of a pump  405 . The plating solution flowing over from the plating tank  401  is received in the plating solution receiving tank  408  and is returned to the plating solution storage tank  404 . 
     The plating module  400  is also provided with a power supply  409  that is connected with the substrate  402  and the anode  410 . When a predetermined voltage is applied from the power supply  409  to between the substrate  402  and the anode  410  with rotation of the substrate holder  403  by the motor  411 , plating current flows between the anode  410  and the substrate  402  to form a plating film on the surface to be plated of the substrate  402 . 
     Furthermore, a plate  10  for adjustment of electric field where a plurality of apertures are provided is placed between the substrate  402  and the anode  410 . A paddle  412  is placed between the substrate  402  and the plate  10 . The paddle  412  is driven by a driving mechanism  413  to be reciprocated parallel to the substrate  402 , so as to stir the plating solution and form a stronger solution current on the surface of the substrate  402 . The driving mechanism  413  includes a motor  413   a  configured to receive supply of electric power from a non-illustrated power supply, a rotation-linear motion converting mechanism  413   b,  such as a ball screw, configured to convert the rotation of the motor  413   a  into linear motion, and a shaft  413   c  linked with the rotation-linear motion converting mechanism  413   b  and the paddle  412  and configured to transmit the power of the rotation-linear motion converting mechanism  413   b  to the paddle  412 . The control module  800  controls the rotation of the motor  413   a  and thereby controls the speed of the reciprocating motion of the paddle  412 . 
       FIG.  13    is a schematic diagram illustrating the effect of a flow direction of the plating solution on the plating film. A seed layer is provided on the surface of the substrate  402 , although being omitted from the illustration of  FIG.  13   . When the substrate  402  is rotated in a direction of an arrow A, the plating solution flows in one direction shown by an arrow B in the vicinity of the surface of the substrate  402  and forms a spiral convection in one direction shown by a spiral arrow B′ inside of an opening  402   b  of a resist  402   a.  In the opening  402   b,  this convection forms a convection layer Q 1  of the plating solution and also forms a diffusion layer Q 2  of the plating solution under the convection layer Q 1  (as shown by an upper drawing of  FIG.  13   ). In the diffusion layer Q 2 , copper ion (Cu 2 +) is diffused, and copper plating (Cu) deposits on the seed layer of the substrate  402  that is exposed on a bottom face of the opening  402   b  (as shown by a lower drawing of  FIG.  13   ). The convection of the plating solution in the convection layer Q 1  causes the diffusion layer Q 2  to become thinner on a downstream side in a direction of solution current B (on an upstream side in a direction of substrate rotation A) and to become thicker on an upstream side in the direction of solution current B (on a downstream side in the direction of substrate rotation A). With regard to the deposition rate of plating in the opening  402   b,  the supply amount of copper ion from the convection layer Q 1  where the copper icon concentration is fixed to a plating surface where the copper icon concentration is low (or is substantially zero) is a rate-limiting factors. In the case where the diffusion rate of copper ion to the plating surface is fixed, the supply amount of copper ion to the plating surface increases with a decrease in thickness of the diffusion layer Q 2  (with a decrease in distance from a boundary between the convection layer Q 1  and the diffusion layer Q 2  to the plating surface). The deposition rate of plating in the opening  402   b  is inversely proportional to the thickness of the diffusion layer Q 2 , so that the plating film formed becomes thicker on the downstream side in a direction of solution current B (on upstream side in the direction of substrate rotation A) and becomes thinner on the upstream side in the direction of solution current B (on the downstream side in the direction of substrate rotation A) as shown by the lower drawing of  FIG.  13   . As described above, the direction of solution current caused by the rotation of the substrate is likely to affect the uniformity in the thickness of the plating film. 
       FIG.  14    is a schematic diagram illustrating a positional relationship between the paddle and the substrate when the frequency of the reciprocating motion of the paddle  412  is an integral multiple of the frequency of the rotation of the substrate  402 . In  FIG.  14   , a left-side drawing illustrates an initial state of the substrate  402  and the paddle  412 . and a right-side drawing illustrates a state of the substrate  402  and the paddle  412  after one rotation (one period) of the substrate  402 .  FIG.  14    shows that the paddle  412  reciprocates a number of times N and returns to an identical position on the substrate  402  during one period or one rotation of the substrate  402 , when the frequency of the reciprocating motion of the paddle  412  is N-times the frequency of the rotation of the substrate  402 .  FIG.  15    is a graph showing the positional relationship between the paddle and the substrate when the frequency of the reciprocating motion of the paddle  412  is an integral multiple of the frequency of the rotation of the substrate  402 . In this graph, the abscissa shows the time, and the ordinate shows the positions of the substrate  402  and the paddle  412 . A curve W shows a change in position of a specific location of the substrate  402  with time, and a curve P shows a change in position of a specific location (for example, a left end beam) of the paddle  412  with time. Apexes of the curve P indicate stop positions where the paddle  412  stops at a left end and at a right end. This graph shows that the stop positions of the paddle  412  at the left end and at the right end consistently overlap with the specific location of the substrate  402  and that the paddle  412  consistently stops at the same position on the substrate  402 . Accordingly, when the frequency of the reciprocating motion of the paddle  412  is an integral multiple of the frequency of the rotation of the substrate  402 , the beam of the paddle  412  consistently stops at the same location on the substrate  402  at the time when the paddle  412  stops at the left end and at the right end. This is likely to cause a significantly large field shielding effect at this location on the substrate  402  and to affect the uniformity in the thickness of the plating film. 
     In order to solve these problems, this embodiment is configured to rotate the substrate  402  forward and rearward and to control the rotation of the substrate  402  (the motor  411 ), such that the rotation time of the substrate  402  in a direction of forward rotation RF becomes equal to the rotation time of the substrate  402  in a direction of reverse rotation RR and/or a time-integrated value of the rotation speed in the direction of forward rotation RF becomes equal to a time-integrated value of the rotation speed in the direction of reverse rotation RR. 
       FIG.  4    is a schematic diagram illustrating control of the rotation speed of the substrate according to the embodiment. In this diagram, the ordinate shows a rotation speed V of the substrate  402 , and the abscissa shows a time t. Sa is a time integrated value of the speed V in the direction of forward rotation RF (the area of the speed V in the direction of forward rotation RF in a V-t plane), Sb is a time integrated value of the speed V in the direction of reverse rotation RR (the area of the speed V in the direction of reverse rotation RR in the V-t plane), When a plurality of forward rotation periods RF are included in a plating time/period it, Sa is a sum of time integrated values of the speed V in the plurality of forward rotation periods RF. When a plurality of reverse rotation periods RR are included in the plating time/period Tt, Sb is a sum of time integrated values of the speed V in the plurality of reverse rotation periods RR. The plating time/period Tt means an actual plating time/period T when the plating current is applied to actually perform plating or means a total time/period of the actual plating time/period T and a time/period TS 1  and; or a time/period TS 2  when the substrate is rotated without applying plating current before and/or after plating. In the actual plating time/period T, however, the plating current is not necessarily applied throughout the entire period but is applied at required timings according to a process. 
     In this illustrated example, the rotation of the substrate  402  is controlled, such that the time integrated value Sa of the speed V in the direction of forward rotation RF becomes equal to the time integrated value Sb of the speed V in the direction of reverse rotation RR. This diagram illustrates an example where the substrate  402  is rotated once in the direction of forward rotation RF and once in the direction of reverse rotation RR. The substrate  402  may, however, be rotated multiple times in the direction of forward rotation RF and multiple times in the direction of reverse rotation RR. In the latter case, the control is made with respect to the entirety of the multiple rotations in the direction of forward rotation RF and the multiple rotations in the direction of reverse rotation RR, such that a total time integrated value of the speed V in the direction of forward rotation RF (a sum of integrated values of the respective rotations) becomes equal to a total time integrated value of the speed V in the direction of reverse rotation RR (a scan of integrated values of the respective rotations). Curve profiles (change profiles) of the rotation speed in the respective rotations may be identical with one another or may be different from one another. A change profile of the rotation speed of each forward rotation may be identical with or may be different from a change profile of the rotation speed of each reverse rotation. 
     When the change profile of the rotation speed in the direction of forward rotation RF is identical with the change profile of the rotation speed in the direction of reverse rotation RR in  FIG.  4   , control may be made such that a rotation time in the direction of forward rotation RF becomes equal to a rotation time in the direction of reverse rotation RR In the case where the substrate  402  is rotated multiple times in the direction of forward rotation RF and multiple times in the direction of reverse rotation RR. When the change profile of the rotation speed of each rotation in the direction of forward rotation RF is identical with the change profile of the rotation speed of each rotation in the direction of reverse rotation RR, control may be made such that a rotation time of each rotation in the direction of forward rotation RF becomes equal to a rotation time of each rotation in the direction of reverse rotation RR. 
       FIG.  5    is a schematic diagram illustrating control of the plating film in different combinations of the forward rotation and the reverse rotation of the substrate. Controlling the rotation speed shown in  FIG.  4    cancels out the effects of the directions of rotations of the substrate  402  in a plating time Tt of the substrate  402  (total plating time). As shown in  FIG.  5   . in the case of rotation of the substrate  402  in the direction of forward rotation RF, the thickness of the plating film formed is thicker on an upstream side in the direction of forward rotation RF and is thinner on a downstream side in the direction of forward rotation RF. In the case of rotation of the substrate  402  in the direction of reverse rotation RR, the thickness of the plating film formed is thicker on an upstream side in the direction of rearward rotation RR (on the downstream side in the direction of forward rotation RF) and is thinner on a downstream side in the direction of rearward rotation RR (on the upstream side in the direction of forward rotation RF). The degree of unevenness in the thickness of the plating film is proportional to the time integrated values of the rotation speed V in the forward rotation and in the rearward rotation over the plating time Tt. Accordingly, making the time integrated value of the rotation speed V in the forward rotation equal to the time integrated value of the rotation speed V in the rearward rotation over the plating time Tt cancels out the unevenness of the film thickness due to the solution current caused by the rotation of the substrate and equalizes the thickness of the plating film formed over the total plating time Tt. A difference in thickness of the diffusion layer Q 2  (i.e., a plating growth rate) between the upstream side and the downstream side in the opening  402   b  may be varied with the growth of the thickness of the plating film. It is accordingly desirable to repeat the forward rotation and the reverse rotation (switchover of the direction of rotation) multiple times as frequently as possible. 
     In the example of  FIG.  4   , the control is made to make the integrated value Sa of the forward rotation equal to the integrated value Sb of the reverse rotation and is optionally made to change the rotation speed V to multiple different rotation speeds in each of the direction of forward rotation and the direction of reverse rotation. Such control suppresses or prevents the beam of the paddle  412  from consistently stopping at the same location on the substrate  402  when the paddle  412  stops at the left end and at the right end. In this illustrated. example, a plurality of steps that are maintained at different fixed rotation speeds for preset time periods are provided. In the case where three or more different fixed rotation speeds are set, however, the fixed rotation speeds may be partly equal to each other. For example, the rotations in the direction of forward rotation and/or in the direction of reverse rotation may have curve profiles with repetition of an increase and a decrease in the fixed rotation speed. In the example of  FIG.  4   . with respect to the rotations in the direction of forward rotation and/or in the direction of reverse rotation, the rotation speed V may be one fixed rotation speed. 
     According to the embodiment, as long as the time integrated value of the rotation speed in the direction of forward rotation is made equal to the time integrated value of the rotation speed in the direction of rearward rotation with respect to the entire plating time Tt fir plating one substrate, the curve profile of the rotation speed may be any arbitrary curve profile (characteristics including the number of steps, the acceleration in each step, fixed rotation speeds, time durations of the fixed rotation speeds, and the acceleration during speed reduction (deceleration)) in each repetition of forward rotation and rearward rotation. It is preferable that each forward rotation/each reverse rotation has a plurality of steps in the rotation speed (multiple fixed rotation speeds) in terms of suppressing or preventing the beam of the paddle  412  from consistently stopping at the same location on the substrate  402 . 
       FIG.  6    is a graph showing the positional relationship between the paddle and the substrate when the rotation speed of the substrate is changed. The rotation control of  FIG.  4    changes the rotation speed V to the multiple different fixed rotation speeds with respect to the rotations in each of the direction of forward rotation and the direction of reverse rotation. This suppresses or prevents the beam of the paddle  412  from consistently stopping at the same location on the substrate  402  when the paddle  412  stops at the left end and at the right end. In  FIG.  6   , the abscissa shows the time, and the ordinate shows the positions of the substrate  402  and the paddle  412 . A curve P shows a time change in the position of a specific location (for example, the left end beam) of the paddle  412 . A curve W 1  shows a displacement by rotation of a specific location of the substrate  402  at a rotation speed V 1 , and a curve W 2  shows a displacement by rotation of the specific location of the substrate  402  at a rotation speed V 2  (not equal to V 1 ). As understood from this graph, changing the rotation speed V changes the location on the substrate  402  where the beam of the paddle  412  is stopped when the paddle  412  stops at the left end and at the right end. 
       FIG.  7    is a schematic diagram illustrating an example of controlling the rotation speed of the substrate. This diagram shows a time change in the rotation speed V when a plating time is expressed by Tt and the plating time Tt includes one unit period (also called forward rotation reverse rotation period) consisting of a forward rotation period RF and a reverse rotation period RR. The plating time Tt may be equal to an actual plating time T when the plating current is applied to actually perform plating or may be equal to a total time of the actual plating time and a time TS 1  and/or a time TS 2  when the substrate is rotated, without applying plating current before and/or after plating. TS 1  is provided to replace a liquid and/or a gas inside of the opening  402   b  of the resist  402   a  with the plating solution. In this example, one unit period (number of repetitions=1) is included in the plating time Tt. A plurality of unit periods may, however, be included in the plating time Tt. The actual plating time T, and the time TS 1  and the time TS 2  having only the rotation of the substrate are determined in advance by experiment or by simulation. 
     In the example of  FIG.  7   , a curve of the rotation speed V in the forward rotation period RF and a curve of the rotation speed V in the reverse rotation period RR are symmetric with respect to a time axis. The curve of the rotation speed V in the reverse rotation period RR is obtained by symmetrically folding back the curve of the rotation speed V in the forward rotation period RF with respect to the time axis and translating a starting point of the curve of the rotation speed V in the reverse rotation period RR to an end point of the curve of the rotation speed V in the forward rotation period RF along the time axis. In this example, inputting the number of steps n, an acceleration a in each step, a rotation speed V in each step and a constant speed time Δt with regard to the forward rotation period RF enables a curve in the reverse rotation period RR that has an inverted symmetrical shape with respect to the time axis (the number of steps n, the acceleration a in each step, the rotation speed V in each step and the constant speed time Δt) to be automatically calculated. 
     In the example of  FIG.  7   , in each of the forward rotation period RF and the reverse rotation period RR, the number of steps n=2 and the number of repetitions m=1. The number of steps n shows the number of periods when the substrate is rotated at multiple fixed rotation speeds in one forward rotation period/reverse rotation period. The number of repetitions m shows the number of times of repeating the unit period consisting of one forward rotation period RF and one reverse rotation period RR. In the example of  FIG.  7   , with regard to the forward rotation period RF, step  1  includes a period when the rotation of the substrate is accelerated at an acceleration a 1  and a period when the substrate is subjected to constant speed rotation at a fixed rotation speed V 1  for a constant speed time Δt 1 . Step  2  includes a period when the rotation of the substrate is accelerated at an acceleration a 2  and a period when the substrate is subjected to constant speed rotation at a fixed rotation speed V 2  for a constant speed time Ate, After completion of step  2 , the rotation of the substrate is decelerated (i.e. the rotation speed is reduced) at an acceleration −a n+1 . In the reverse rotation period RR, similar rotation control to that of the forward rotation period RF is performed with inverting the direction of acceleration and the direction of rotation speed from those in the forward rotation period RF. More specifically, with regard to the reverse rotation period RR, step  1  includes a period when the rotation of the substrate is accelerated at an acceleration −a 1  and a period when the substrate is subjected to constant speed rotation at a fixed rotation speed −V 1  for the constant speed time Δt 1 . Step  2  includes a period when the rotation of the substrate is accelerated at an acceleration −a 2  and a period when the substrate is subjected to constant speed rotation at a fixed rotation speed −V 2  for the constant speed time Δt 2 . After completion of step  2 , the rotation of the substrate is deceleration at an acceleration a n+1 . In this example, a 1 , a 2 , . . . , a n , a n+1 , V 1  and V 2  are positive values. The larger value of the acceleration a n+1  during speed reduction (deceleration) is more preferable. The motion of the substrate in the course of switching over between forward rotation and reverse rotation is the motion in a direction of weakening the solution current. It is thus preferable to increase the acceleration a n+1  in the course of switching over between forward rotation and reverse rotation as large as possible (it is preferable to decrease a time period required for switching over between forward rotation and reverse rotation as short as possible). According to another embodiment, the control during speed reduction (deceleration) may be control in a plurality of control steps to have multiple fixed rotation speeds, as in the case of the control during acceleration (speed increasing). 
     In the example of  FIG.  7   , the respective parameters satisfy an expression given below: 
         Tt={ΣV   k   /a   k   +ΣΔt   k   +V   n   /a   n+1 }×2 m    (1)
 
     where Tt denotes the plating time, n denotes the number of steps, m denotes the number of repetitions, k denotes an integer of not less than 1, V k  denotes the rotation speed in a step k, Δt k  denotes the constant speed time in the step k, V n  denotes the rotation speed in a step n, a n+1  denotes the acceleration during speed reduction deceleration), and Σ denotes summation of k=1 to n. In parentheses of a right side, a first term indicates a total time period required for acceleration, a second term indicates a total constant speed time of the respective steps, and a third term indicates a deceleration time. 
       FIG.  8    is a schematic diagram illustrating an example of controlling the rotation speed of the substrate. In the example of  FIG.  7   , the curve of the rotation speed V in the reverse rotation period RR is obtained by folding back the curve of the rotation speed V in the forward rotation period RF with respect to the time axis. As shown in  FIG.  8   , the curve of the rotation speed in the reverse rotation period RR may be obtained by rotating the curve of the rotation speed V in the forward rotation period RF by  180  degrees (to be symmetric with respect to an end point in the forward rotation period RF). 
       FIG.  9    is a schematic diagram illustrating another example of controlling the rotation speed of the substrate.  FIG.  9    shows a time change in the rotation speed V in the case of the number of steps n=2 and the number of repetitions m=1. as in the example of  FIG.  7   . In this example, the acceleration and the constant speed time in the respective steps are set to a fixed acceleration a and a fixed constant speed time Δt, and an acceleration a during speed reduction (deceleration) is a constant. The larger value of the acceleration a, during speed reduction (deceleration) is more preferable. According to another embodiment, the control during speed reduction (deceleration) may be control in a plurality of control steps to have multiple fixed rotation speeds, as in the case of the control during acceleration (speed increasing). The motion of the substrate in the course of switching over between forward rotation and reverse rotation is the motion in the direction of weakening the solution current. It is thus preferable to increase the acceleration a, in the course of switching over between forward rotation and reverse rotation as large as possible. In this example, a, V 1  and V 2  are positive values, and a, is a negative value. In this example, the curve of the rotation speed V in the forward rotation period RF and the curve of the rotation speed V in the reverse rotation period RR are symmetric with respect to the time axis, as in the example of  FIG.  7   . The settings of this example may, however, be also applied to the curve of the rotation speed V in the forward rotation period RF and the curve of the rotation speed V in the reverse rotation period RR that are rotated relative to each other by 180 degrees, as in the example of  FIG.  8   . In the example of  FIG.  9   , inputting three (three different) parameters among four (four different) parameters, i.e., the rotation speed V in each step, the acceleration a in each step, the constant speed time Δt in each step, and the number of repetitions m of the unit period, relative to a specified plating time Tt and a specified number of steps n automatically calculates one remaining parameter. 
     In the example of  FIG.  9   , the respective parameters satisfy an expression given below: 
         Tt={V   n   /a+Δt×n+V   n   /a   s }×2 m    (2)
 
     where Tt denotes the plating time, n denotes the number of steps, m denotes the number of repetitions, a denotes a common acceleration in the respective steps during acceleration (speed increasing), V n  denotes the rotation speed in a step n (maximum value of the rotation speed), Δt denotes a common constant speed time in the respective steps, and as denotes an acceleration during speed reduction (deceleration). In parentheses of a right side, a first term indicates a total time period required for acceleration, a second term indicates a total constant speed time of the respective steps, and a third term indicates a deceleration time. 
       FIG.  10    is an exemplary flowchart of setting the rotation speed of the substrate in the example of  FIG.  7   . This control flow may be performed by the control module  800  described above. This control flow may be performed in cooperation of the control module  800  with another control device inside or outside of the plating apparatus or may be performed by a control device inside or outside of the plating apparatus other than the control module  800 . The same applies to the subsequent flowcharts. 
     At S 100 , the control flow sets the plating time Tt, the total number of steps n included in one forward rotation period RF. and the number of repetitions in of the unit period, and also sets a target step number k=1. The plating time Tt is equal to the actual plating time T when the plating current is applied to actually perform plating or is equal to the total time of the actual plating time T and the time TS 1  and/or the time TS 2  when the substrate is rotated without applying plating current before and/or after plating. 
     The control flow subsequently performs the processing of S 110  to S 130  and sets an acceleration a k , a constant speed time Δt k  and a rotation speed V k  in each step k (S 110 ) with changing k from 1 to n (S 130 ). The control flow sets an acceleration −a n+1  during speed. reduction (deceleration) (SI 10 ) when it is determined at S 130  that k=n+1. When k=the control flow has a negative answer No at  5120  and proceeds to S 140 . At S 140 , the control flow calculates a time period T k =V k /a k +Δt k  (k=1, . . . , n) required for each step and a time period V n /a n+1  required for speed reduction (deceleration). The respective parameters are set to satisfy Expression (1) given above by the processing of S 110  to S 140 . For example, the processing of S 110  to S 140  is repeated until the respective parameters satisfy Expression (1) given above. 
     The control flow subsequently performs a process of folding back the curve of the rotation speed V in the forward rotation period RF with respect to the time axis (as shown in  FIG.  7   ), calculates an acceleration, a constant speed time, and a rotation speed in each step k and an acceleration during speed reduction (deceleration) in the reverse rotation period RR (S 150 ), and completes a recipe of the substrate rotation control (S 160 ). In the example of  FIG.  8   , the control flow rotates the curve of the rotation speed V in the forward rotation period RF by 180 degrees, calculates an acceleration, a constant speed time, and a rotation speed in each step k and an acceleration during speed reduction (deceleration) in the reverse rotation period RR, and completes a recipe of the substrate rotation control. 
       FIG.  11    is an exemplary flowchart of setting the rotation speed of the substrate in the example of  FIG.  9   . At S 200 , the control flow sets a plating time Tt and a total number of steps n included in one forward rotation period RF (or in one reverse rotation period RR). The plating time Tt is equal to the actual plating time T when the plating current is applied to actually perform plating or is equal to the total time of the actual plating time T and the time TS 1  and/or the time TS 2  when the substrate is rotated without applying plating current before and/or after plating. 
     At S 210 , sets three (three different) parameters among four (four different) parameters, i.e., the accelerations a and the rotation speed V k  in each step (k=1, . . . n), the constant speed time At and the number of repetitions m shown in  FIG.  9   . The acceleration a. denotes an acceleration during acceleration (speed increasing), and the acceleration a, denotes an acceleration during speed reduction (deceleration). The acceleration a during acceleration (speed increasing) and the constant speed time At are common values in the respective steps, and a s  is a fixed value. 
     The control flow subsequently calculates one remaining parameter to satisfy Expression (2) given above (S 220 ) and completes a recipe of the substrate rotation control (S 230 ). 
       FIG.  12    is an exemplary flowchart of a plating process. At S 300 , the plating process carries the substrate  402  into the plating tank  401  and mounts the substrate  402  to the substrate holder  403 . After setting the plating current, the plating time, the respective parameters of the substrate rotation control (shown in  FIGS.  7  to  11   ) and the like at S 310 , the plating process performs plating with rotating the substrate  402 , based on the set plating current, the set plating time, the respective set parameters of the substrate rotation control and the like (S 320 ). After completion of plating, the plating process carries out the plated substrate (S 330 ). The plating time at S 310  may be set to the actual plating time T or may be set to the plating time Tt determined by taking into account the period TS 1  and/or the period TS 2  with only rotation of the substrate, in addition to the actual plating time T, as described above, 
     At least aspects described below are provided from the description above. 
     According to one aspect, there is provided an apparatus for plating that is configured to plate a substrate and comprises a plating tank; an anode placed in the plating tank; a rotation mechanism configured to rotate the substrate in a first direction and in a second direction that is opposite to the first direction; and a control device configured to control the rotation mechanism, such that a time period when the substrate is rotated in the first direction becomes equal to a time period when the substrate is rotated in the second direction, and/or such that a time integrated value of a rotation speed in the first direction becomes equal to a time integrated value of a rotation speed in the second direction. 
     According to the configuration of this aspect, during plating of the substrate, a total time when the substrate is rotated in a direction of forward rotation is equal to a total time when the substrate is rotated in a direction of reverse rotation, or a time integrated value of the rotation speed in the direction of forward rotation is equal to a time integrated value of the rotation speed in the direction of rearward rotation. This configuration accordingly suppresses or prevents the phenomenon that the surface of a plating film is inclined due to the direction of the current of the plating solution. This is because the amount of inclination of the plating film surface during the forward rotation is superimposed on the amount of inclination of the plating film surface during the reverse rotation in the plating time, so as to cancel out the inclination of the plating film surface. 
     According to one aspect, the control device may perform a unit period once or multiple times during plating of the substrate, wherein the unit time may include a first direction rotating period when the substrate is continuously rotated in the first direction and a second direction rotating period when the substrate is continuously rotated in the second direction. 
     The configuration of this aspect performs the unit period once or multiple times, so as to alternately perform the rotation in the first direction and the rotation in the second direction. The number of times when the unit period is performed may be regulated according to a process. Performing the unit period multiple times enables the inclination of a surface of a plating film caused by rotation in one direction to be reduced by rotation in a reverse direction, before the inclination of the surface of the plating film is increased by rotation in one direction. This configuration thus planarizes the surface of the plating film with the higher accuracy. For example, performing the unit period multiple times suppresses or prevents the plating film from being significantly inclined by rotation in one direction and from affecting a solution current and thereby planarizes the surface of the plating film with the higher accuracy. 
     According to one aspect, the control device may control the first direction rotating period and/or the second direction rotating period in a plurality of steps with regard to part or entirety of the unit period, wherein each of the steps may have a constant speed period when the substrate is rotated at a fixed rotation speed, and at least two steps may have different fixed rotation speeds. 
     The configuration of this aspect switches over the rotation speed of the substrate between a plurality of rotation speeds and thereby suppresses or prevents a beam of a paddle from consistently stopping at an identical location of the substrate, due to a frequency of a reciprocating motion of the paddle and a rotation speed (frequency) of the substrate. This configuration accordingly suppresses or prevents a phenomenon of increasing the field shielding effect on a specific location of the substrate. As a result, this suppresses or prevents reduction of the uniformity in the thickness of the plating film due to the increasing field shielding effect at the specific location of the substrate. 
     According to one aspect, at least two steps among the plurality of steps may have different constant speed times. 
     The configuration of this aspect enables the constant speed time to be more appropriately set according to the frequency of the paddle and the frequency of the substrate with a view to further reducing the field shielding effect. This configuration also facilitates regulation of the constant speed time in each step so as to correspond to the plating time. 
     According to one aspect, the plurality of steps may respectively have an identical constant speed time. 
     The configuration of this aspect further facilitates the rotation control of the substrate. 
     According to one aspect, at least two steps among the plurality of steps may have different accelerations to increase the rotation speed to the fixed rotation speed in each step. 
     The configuration of this aspect enables the acceleration to be more appropriately set according to the frequency of the paddle and the frequency of the substrate with a view to further reducing the field shielding effect. This configuration also facilitates relation of the acceleration in each step so as to correspond to the plating time. 
     According to one aspect, the plurality of steps may respectively have an identical acceleration to increase the rotation speed to the fixed rotation speed in each step, 
     The configuration of this aspect further facilitates the rotation control of the substrate. 
     According to one aspect, at least two unit periods may have different change characteristics in rotation speed. The change characteristic in rotation speed means a curve profile (change profile) of the rotation speed illustrated in  FIG.  4    or in each of  FIGS.  7  to  9    and includes the number of steps, an acceleration, a fixed rotation speed, and a constant speed time, in each step, and an acceleration during speed reduction (deceleration). 
     The configuration of this aspect has different change patterns in rotation speed between the unit periods. This configuration more effectively disperses the location on the substrate where the beam of the paddle stops and thus more effectively suppresses the phenomenon of increasing the field shielding effect at a specific location of the substrate. 
     According to one aspect, the first direction rotating period and the second direction rotating period may have different change characteristics in rotation speed with regard to part or entirety of the unit periods. 
     The configuration of this aspect has different change patterns in rotation speed between the first direction rotating period and the second direction rotating period. This configuration more effectively disperses the location on the substrate where the beam of the paddle stops and thus more effectively suppresses the phenomenon of increasing the field shielding effect at a specific location of the substrate. 
     According to one aspect, when inputting a number of steps, a fixed rotation speed in each step, an acceleration in each step to increase the rotation speed of the substrate to the fixed rotation speed, and a constant speed time in each step with regard to the first direction rotating period, the control device may automatically calculate a number of steps, a fixed rotation speed in each step, an acceleration in each step, and a constant speed time in each step with regard to the second direction rotating period, which corresponds to a change curve in such a shape that is obtained by symmetrically folding back a time change curve of the rotation speed in the first direction rotating period with respect to a time axis. 
     When the respective parameters in the forward rotation are set, the configuration of this aspect automatically calculates the respective parameters in the reverse rotation. This configuration accordingly simplifies setting of the parameters. This configuration also causes the substrate to be rotated at rotation speeds of the identical change characteristics in the forward rotation and in the reverse rotation and thereby enhances the uniformity in the thickness of the plating film. 
     According to one aspect, when inputting three (three different) parameters among four (four different) parameters, i.e., a fixed rotation speed in each step, an acceleration in each step to increase the rotation speed of the substrate to the fixed rotation speed in each step, a constant speed time in each step, and a number of repetitions of the unit period, the control device may automatically calculate one remaining parameter, wherein the acceleration and the constant speed time may be common among the respective steps. 
     The configuration of this aspect shares the common acceleration and the common constant speed time among the respective steps and inputs three parameters out of the tour parameters, so as to automatically calculate one remaining parameter and complete a recipe of rotation control. This configuration simplifies the setting of the parameters. 
     According to one aspect, there is provided a method of controlling an apparatus for plating that is configured to plate a substrate, while rotating the substrate. The method comprises controlling rotation of the substrate, such that a time period when the substrate is rotated in a first direction becomes equal to a time period when the substrate is rotated in a second direction or such that a time integrated value of a rotation speed in the first direction becomes equal to a time integrated value of a rotation speed in the second direction. This aspect has functions and advantageous effects described above. 
     According to one aspect, there is provided a non-volatile storage medium storing therein a program that causes a computer to perform a method of controlling an apparatus for plating that is configured to plate a substrate, while rotating the substrate. The non-volatile storage medium stores the program that causes the computer to control rotation of the substrate, such that a time period when the substrate is rotated in a first direction becomes equal to a time period when the substrate is rotated in a second direction or such that a time integrated value of a rotation speed in the first direction becomes equal to a time integrated value of a rotation speed in the second direction. This aspect has functions and advantageous effects described above. 
     Although the embodiments of the present invention have been described based on some examples, the embodiments of the invention described above are presented to facilitate understanding of the present invention, and do not limit the present invention. The present invention can be altered and improved without departing from the subject matter of the present invention, and it is needless to say that the present invention includes equivalents thereof. In addition, it is possible to arbitrarily combine or omit respective constituent elements described in the claims and the specification in a range where at least a part of the above-mentioned problem can be solved or a range where at least a part of the effect is exhibited. 
     REFERENCE SIGNS LIST 
       100  load port 
       110  transfer robot 
       120  aligner 
       200  pre-wet module 
       300  pre-soak module 
       400  plating module 
       401  plating tank 
       402  substrate 
       403  substrate holder (substrate holding tool) 
       404  plating solution storage tank 
       405  pump 
       406  filter 
       407  plating solution supply pipe 
       408  plating solution receiving tank 
       409  power supply 
       413  driving mechanism 
       413   a  motor 
       413   b  rotation-linear motion converting mechanism 
       413   c  shaft 
       500  cleaning module 
       600  spin rise dryer 
       700  transfer device 
       800  control module 
       1000  plating apparatus