Plating method

Abstract

Provided is a technique capable of uniformizing the height of bumps.　A plating method according to the present invention includes: acquiring an opening density change direction Dr2; holding a substrate Wf in which the opening density change direction has been acquired in a substrate holder 30; immersing the substrate held by the substrate holder inside a plating solution Ps facing the anode; executing a first plating process in which a power source 80 supplies a positive direction current while rotating the substrate holder and stirring the plating solution by a stirring mechanism 60; executing a second plating process in which the power source supplies a reverse current pulse while stirring the plating solution by the stirring mechanism with the rotation of the substrate holder stopped in a state in which the opening density change direction becomes non-parallel to the flow direction Dr1 of the plating solution stirred by the stirring mechanism; and executing the first plating process again.

Description

Plating Method

[0001] The present invention relates to a plating method.

[0002] Conventionally, plating methods for plating a substrate have been known (see, for example, Patent Documents 1, 2, and 3). A plating apparatus used in such a plating method includes, for example, a plating tank that stores a plating solution and in which an anode is disposed, a substrate holder that holds a substrate serving as a cathode facing the anode, a power source configured to supply current between the substrate and the anode, and an agitation mechanism configured to agitate the plating solution (see, for example, Patent Documents 1 and 2).

[0003] Patent Documents 2 and 3 also disclose techniques for forming bumps by depositing metal on a substrate by plating. Patent Documents 2 and 3 also disclose techniques for controlling a power supply so that forward current and reverse current pulses are supplied to a substrate and an anode in a plating method using a plating solution containing an accelerator that accelerates plating.

[0004] Japanese Patent No. 7079388 Japanese Patent No. 7357824 Japanese Patent Laid-Open No. 2006-131926

[0005] In recent years, there has been a demand for uniform height of bumps formed on a substrate by plating, and in this respect, there is room for improvement in conventional techniques.

[0006] The present invention has been made in view of the above, and one of its objects is to provide a technique that can make the height of bumps uniform.

[0007] (Aspect 1) To achieve the above object, a plating method according to one aspect of the present invention includes: acquiring an opening density change direction, which is a direction in which the opening density of a photoresist layer provided on a substrate changes; holding the substrate, for which the opening density change direction has been acquired, in a substrate holder; immersing the substrate held by the substrate holder in a plating solution of a plating tank containing a plating solution containing an accelerator that accelerates plating and in which an anode is disposed, so that the substrate faces the anode; rotating the substrate holder and stirring the plating solution with a stirring mechanism, while stirring the substrate and the photoresist layer. The method includes: performing a first plating process by causing a power supply configured to supply current between the anode and the plating solution to supply a forward current for depositing metal from the plating solution onto the substrate; performing a second plating process by causing the power supply to supply a reverse current pulse, which is a current flowing in pulses in the opposite direction to the forward current, while stirring the plating solution with the stirring mechanism, while stopping the rotation of the substrate holder in a state where the direction of change in opening density is non-parallel to the direction of flow of the plating solution stirred by the stirring mechanism; and performing the first plating process again.

[0008] According to this aspect, it is possible to make the height of the bumps formed by the metal deposited on the substrate uniform.

[0009] (Aspect 2) In the aspect 1, in the second plating process, the direction of change in the opening density may be perpendicular to the direction of flow of the plating solution stirred by the stirring mechanism.

[0010] (Aspect 3) In the above-described aspect 1 or aspect 2, the stirring mechanism may include a paddle configured to stir the plating solution in the plating tank by reciprocating movement, and the direction in which the paddle reciprocates may be used as the direction of flow of the plating solution stirred by the stirring mechanism in the second plating process.

[0011] 6A is a perspective view showing the overall configuration of a plating apparatus according to an embodiment; FIG. 6B is a schematic view showing the overall configuration of a plating apparatus according to an embodiment; FIG. 7B is a schematic view showing an example of an opening pattern of a photoresist layer according to an embodiment; FIG. 7A and FIG. 7B are diagrams showing an example of a time waveform of a current supplied from a power supply to an anode and a substrate according to an embodiment; FIG. 7B is a graph showing an example of measuring the height of bumps in each pattern region when multiple bumps are formed on a substrate having a photoresist layer as exemplified in FIG. 6B; FIG. 7C is an example of a flowchart showing a plating method according to an embodiment; FIG. 8A is a schematic plan view showing the direction of change in opening density of a substrate according to an embodiment; FIG. 8B is a schematic view showing the degree of uniformity of bump heights depending on the angle between the direction of change in opening density of the substrate and the direction of flow of the plating solution during stirring.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are diagrammatically illustrated to facilitate understanding of the characteristics of the components, and the dimensional ratios of the components may not be the same as those in reality. In addition, some of the drawings show an X-Y-Z Cartesian coordinate system for reference. In these Cartesian coordinate systems, the Z direction corresponds to the upward direction, and the -Z direction corresponds to the downward direction (the direction in which gravity acts).

[0013] Fig. 1 is a perspective view showing the overall configuration of a plating apparatus 1000 according to an embodiment. Fig. 2 is a plan view (top view) showing the overall configuration of the plating apparatus 1000 according to an embodiment. As shown in Figs. 1 and 2, the plating apparatus 1000 includes a load port 100, a transfer robot 110, an aligner 120, a pre-wet module 200, a pre-soak module 300, a plating module 400, a cleaning module 500, a spin rinse dryer 600, a transfer device 700, and a control module 800.

[0014] The load port 100 is a module for loading substrates stored in a cassette such as a FOUP (not shown) into the plating apparatus 1000 and unloading substrates from the plating apparatus 1000 to the cassette. In this embodiment, four load ports 100 are arranged horizontally, but the number and arrangement of the load ports 100 are optional. The transfer robot 110 is a robot for transporting substrates, and is configured to transfer substrates between the load port 100, the aligner 120, the pre-wet module 200, and the spin rinse dryer 600. When transferring substrates between the transfer robot 110 and the transfer device 700, the transfer robot 110 and the transfer device 700 can transfer the substrates via a temporary stage (not shown).

[0015] The aligner 120 is a module for aligning the positions of the substrate's orientation flat, notch, and the like in a predetermined direction. In this embodiment, two aligners 120 are arranged horizontally, but the number and arrangement of the aligners 120 are optional. The prewet module 200 wets the surface of the substrate to be plated with a treatment liquid such as pure water or degassed water before plating, thereby replacing air within a pattern formed on the substrate surface with the treatment liquid. The prewet module 200 is configured to perform a prewet process that replaces the treatment liquid within the pattern with a plating liquid during plating, thereby making it easier to supply the plating liquid within the pattern. In this embodiment, two prewet modules 200 are arranged vertically, but the number and arrangement of the prewet modules 200 are optional.

[0016] The presoak module 300 is configured to perform a presoak process, which involves etching away, for example, an oxide film with high electrical resistance present on the surface of a seed layer formed on the surface of a substrate to be plated before plating, using a treatment solution such as sulfuric acid or hydrochloric acid to clean or activate the surface of the substrate to be plated. In this embodiment, two presoak modules 300 are arranged vertically, but the number and arrangement of the presoak modules 300 are optional. The plating module 400 applies plating to the substrate. In this embodiment, two sets of 12 plating modules 400 are arranged vertically, three vertically and four horizontally, for a total of 24 plating modules 400, but the number and arrangement of the plating modules 400 are optional.

[0017] The cleaning module 500 is configured to perform a cleaning process on the substrate to remove plating solution and the like remaining on the substrate after plating. In this embodiment, two cleaning modules 500 are arranged vertically, but the number and arrangement of the cleaning modules 500 are optional. The spin rinse dryer 600 is a module for drying the substrate after cleaning by rotating it at high speed. In this embodiment, two spin rinse dryers 600 are arranged vertically, but the number and arrangement of the spin rinse dryers 600 are optional. The transport device 700 is a device for transporting substrates between multiple modules within the plating apparatus 1000. The control module 800 is configured to control the multiple modules of the plating apparatus 1000 and can be configured, for example, as a general computer or a dedicated computer equipped with an input / output interface with an operator.

[0018] An example of a series of plating processes performed by the plating apparatus 1000 will be described. First, a substrate stored in a cassette is loaded into the load port 100. Next, the transfer robot 110 removes the substrate from the cassette in the load port 100 and transfers the substrate to the aligner 120. The aligner 120 aligns the positions of the orientation flat, notch, and the like of the substrate to a predetermined direction. The transfer robot 110 delivers the substrate, whose direction has been aligned by the aligner 120, to the pre-wet module 200.

[0019] The pre-wet module 200 performs a pre-wet process on the substrate. The transport device 700 transports the substrate that has been subjected to the pre-wet process to the pre-soak module 300. The pre-soak module 300 performs a pre-soak process on the substrate. The transport device 700 transports the substrate that has been subjected to the pre-soak process to the plating module 400. The plating module 400 platings the substrate.

[0020] The transfer device 700 transfers the substrate after plating to the cleaning module 500. The cleaning module 500 performs a cleaning process on the substrate. The transfer device 700 transfers the substrate after cleaning to the spin rinse dryer 600. The spin rinse dryer 600 dries the substrate. The transfer robot 110 receives the substrate from the spin rinse dryer 600 and transfers the dried substrate to a cassette on the load port 100. Finally, the cassette containing the substrate is removed from the load port 100.

[0021] It should be noted that the configuration of the plating apparatus 1000 described in FIGS. 1 and 2 is merely an example, and the configuration of the plating apparatus 1000 is not limited to the configurations shown in FIGS.

[0022] Next, a description will be given of the plating module 400. Since the multiple plating modules 400 included in the plating apparatus 1000 according to this embodiment have the same configuration, only one plating module 400 will be described.

[0023] Fig. 3 is a schematic diagram showing the configuration of the plating module 400 in the plating apparatus 1000. Specifically, Fig. 3 schematically shows the plating module 400 in a state before the substrate Wf is immersed in the plating solution Ps. Fig. 4 is a schematic diagram showing the state after the substrate Wf is immersed in the plating solution Ps.

[0024] 3 and 4 is, for example, a plating apparatus (a so-called cup-type plating apparatus) in which the substrate Wf is immersed in the plating solution Ps with its surface oriented horizontally. However, the configuration of the plating apparatus 1000 is not limited to this, and may be, for example, a plating apparatus in which the substrate Wf is immersed in the plating solution Ps with its surface oriented non-horizontally (for example, vertically relative to the ground).

[0025] 3 and 4, a plating module 400 of a plating apparatus 1000 includes a plating tank 10, an overflow tank 20, a substrate holder 30, and a paddle 70 as an example of an agitation mechanism 60. As shown in FIG. 3, the plating module 400 also includes a rotation mechanism 40, a tilting mechanism 45, and an elevation mechanism 50. As shown in FIG. 3, the plating module 400 also includes sensors 130. As shown in FIG. 4, the plating module 400 also includes a power supply 80 and a plating solution flow mechanism 90.

[0026] The plating tank 10 according to this embodiment is a bottomed container with an opening at the top. Specifically, the plating tank 10 has a bottom wall 10a and an outer peripheral wall 10b extending upward from the outer periphery of the bottom wall 10a, with the upper portion of the outer peripheral wall 10b being open. The shape of the outer peripheral wall 10b of the plating tank 10 is not particularly limited, but the outer peripheral wall 10b according to this embodiment has a cylindrical shape, for example. A plating solution Ps is stored inside the plating tank 10.

[0027] The plating solution Ps may be any solution containing ions of the metal elements that make up the plating film, and specific examples thereof are not particularly limited. In this embodiment, copper plating is used as an example of plating, and a copper sulfate solution is used as an example of plating solution Ps. The plating solution Ps may also contain certain additives.

[0028] The plating solution Ps may contain, for example, an accelerator that accelerates plating (specifically, an accelerator that accelerates the formation of a plating film). For example, SPS (bis(3-sulfopropyl)disulfide) or the like may be used as the accelerator.

[0029] An anode 11 is disposed inside the plating tank 10. The specific type of the anode 11 is not particularly limited, and may be an insoluble anode or a soluble anode. In the present embodiment, an insoluble anode is used as an example of the anode 11. The specific type of the insoluble anode is not particularly limited, and platinum, iridium oxide, or the like may be used.

[0030] As illustrated in Figures 3 and 4, an ion resistor 12 may be disposed above the anode 11 inside the plating tank 10. Specifically, as illustrated in the partially enlarged view of Figure 4, the ion resistor 12 is configured as a porous plate member having a plurality of holes 12a (pores). The holes 12a are provided so as to connect the lower surface and the upper surface of the ion resistor 12.

[0031] The ion resistor 12 is provided to homogenize the electric field formed between the anode 11 and the substrate Wf serving as the cathode. By disposing the ion resistor 12 in the plating tank 10 as in this embodiment, it is possible to easily homogenize the thickness of the plating film (plating layer) formed on the substrate Wf.

[0032] As illustrated in Figures 3 and 4, a membrane 16 may be disposed inside the plating tank 10 above the anode 11 and below the ionic resistor 12. In this case, the membrane 16 divides the interior of the plating tank 10 into an anode chamber 17a below the membrane 16 and a cathode chamber 17b above the membrane 16. The anode 11 is disposed in the anode chamber 17a, and the ionic resistor 12 and the substrate Wf are disposed in the cathode chamber 17b. The membrane 16 is configured to allow ionic species, including metal ions, contained in the plating solution Ps to pass through the membrane 16 while inhibiting non-ionic plating additives contained in the plating solution Ps from passing through the membrane 16. For example, an ion exchange membrane can be used as such a membrane 16.

[0033] 4, the plating solution flow mechanism 90 is configured to flow the plating solution Ps in the plating tank 10. As an example, the plating solution flow mechanism 90 according to this embodiment includes a first flow mechanism 91a and a second flow mechanism 91b.

[0034] The first flow mechanism 91a is a mechanism for causing the plating solution Ps in the anode chamber 17a to flow. The second flow mechanism 91b is a mechanism for causing the plating solution Ps in the cathode chamber 17b to flow. The first flow mechanism 91a is connected to the anode chamber 17a via a pipe 92a. The second flow mechanism 91b is connected to the cathode chamber 17b via a pipe 92b. The first flow mechanism 91a and the second flow mechanism 91b each include a pump or the like for pressure-feeding the plating solution Ps.

[0035] 3 and 4, the plating tank 10 is provided with a supply port for supplying the plating solution Ps to the plating tank 10. Specifically, the outer peripheral wall 10b of the plating tank 10 according to this embodiment is provided with a first supply port 13a for supplying the plating solution Ps to the anode chamber 17a and a second supply port 13b for supplying the plating solution Ps to the cathode chamber 17b. The plating solution Ps discharged from the first discharge port 14a is pressure-fed by the first flow mechanism 91a and is again supplied to the anode chamber 17a from the first supply port 13a.

[0036] The overflow tank 20 is a bottomed container disposed outside the plating tank 10. The overflow tank 20 is provided to temporarily store the plating solution Ps that has exceeded the upper end of the outer wall 10b of the plating tank 10 (i.e., the plating solution Ps that has overflowed from the plating tank 10). The plating solution Ps stored in the overflow tank 20 is discharged from the second outlet 14b, then pressure-fed by the second flow mechanism 91b, and again supplied to the cathode chamber 17b from the second supply port 13b.

[0037] The substrate holder 30 holds the substrate Wf as a cathode so that the surface Wfa to be plated of the substrate Wf faces the anode 11. In this embodiment, the surface Wfa to be plated of the substrate Wf is specifically provided on the surface (lower surface) facing downward of the substrate Wf.

[0038] The substrate holder 30 is connected to a rotation mechanism 40. The rotation mechanism 40 is a mechanism for rotating the substrate holder 30. "R1" illustrated in FIG. 3 is an example of the rotation direction of the substrate holder 30. A known rotation motor or the like can be used as the rotation mechanism 40. The tilt mechanism 45 is a mechanism for tilting the rotation mechanism 40 and the substrate holder 30. The lifting mechanism 50 is supported by a support shaft 51 extending in the vertical direction. The lifting mechanism 50 is a mechanism for raising and lowering the substrate holder 30, the rotation mechanism 40, and the tilting mechanism 45 in the vertical direction. A known lifting mechanism such as a linear actuator can be used as the lifting mechanism 50.

[0039] The control module 800 includes a microcomputer, which includes a processor 801, a storage device 802 as a non-transitory storage medium, etc. The control module 800 controls the operation of the plating module 400 by operating the processor 801 based on instructions from a program stored in the storage device 802.

[0040] 3, the sensors 130 detect various types of information used for various controls of the control module 800 and transmit the detection results to the control module 800. The sensors 130 include, for example, a current sensor that detects the current value (A) between the anode 11 and the substrate Wf, and a voltage sensor that detects the voltage value (V) between the anode 11 and the substrate Wf.

[0041] The sensors 130 also include a speed sensor for detecting the movement speed (rpm or m / sec) of the paddle 70. The sensors 130 also include a rotation speed sensor for detecting the rotation speed (rpm) of the substrate holder 30. The sensors 130 also include a flow rate sensor for detecting the flow rate (m / sec) of the plating solution Ps in the plating tank 10. Specifically, the flow rate sensors include a flow rate sensor for detecting the flow rate of the plating solution Ps in the anode chamber 17a and a flow rate sensor for detecting the flow rate of the plating solution Ps in the cathode chamber 17b.

[0042] The sensors 130 also include an angle sensor for detecting the rotation angle of the substrate holder 30. By acquiring the detection result of this angle sensor, the control module 800 can obtain the rotation angle (rotation position) of the substrate holder 30, and thereby can also obtain the rotation angle (rotation position) of the substrate Wf held by the substrate holder 30.

[0043] 4, the power supply 80 is electrically connected to the substrate Wf and the anode 11, and is configured to supply current between the substrate Wf and the anode 11. The operation of the power supply 80 is controlled by a control module 800.

[0044] The control module 800 of this embodiment controls the power supply 80 so that, during the "plating process" in which plating is performed on the substrate Wf, a "forward current" for depositing metal from the plating solution Ps onto the substrate Wf and a "reverse current pulse" which is a current flowing in pulses in the opposite direction to the forward current are supplied.

[0045] 5 is a schematic plan view of the paddle 70. Referring to FIGS. 3, 4, and 5, the paddle 70 is disposed between the substrate Wf and the anode 11 (specifically, in the present embodiment, as an example, between the substrate Wf and the ion resistor 12). The paddle 70 is driven by a driving device 77 that receives instructions from a control module 800. Driving the paddle 70 agitates the plating solution Ps in the plating tank 10.

[0046] The paddle 70 according to the present embodiment is, for example, driven alternately in a "first direction (in the present embodiment, the X direction as an example)" parallel to the substrate Wf and a "second direction (in the present embodiment, the −X direction as an example)" opposite to the first direction. That is, the paddle 70 according to the present embodiment moves back and forth in the X-axis direction as an example.

[0047] 5, the paddle 70 according to this embodiment includes, as an example, a plurality of stirring members 71a extending in a direction (the direction of the Y axis) perpendicular to the first and second directions of the paddle 70. A gap is provided between adjacent stirring members 71a. One end of each of the stirring members 71a is connected to a connecting member 72a, and the other end is connected to a connecting member 72b.

[0048] However, the configuration of the paddle 70 is not limited to this, and various known paddles such as those exemplified in Patent Document 1 can be used.

[0049] The paddle 70 only needs to be disposed inside the plating tank 10 at least when stirring the plating solution Ps, and does not need to be disposed inside the plating tank 10 all the time. For example, when the driving of the paddle 70 is stopped and the plating solution Ps is not stirred by the paddle 70, the paddle 70 may not be disposed inside the plating tank 10.

[0050] Note that "the moving speed of the paddle 70 is N (rpm)" specifically means that the paddle 70 makes one reciprocating movement (i.e., the paddle 70 starts from a predetermined position, moves, for example, in a first direction, then moves in a second direction, moves in the first direction again, and returns to the predetermined position) N times per minute. The faster the moving speed of the paddle 70, the stronger the stirring strength of the plating solution Ps by the paddle 70. In other words, the moving speed of the paddle 70 is an example of the "stirring strength of the plating solution Ps."

[0051] Fig. 6A is a schematic diagram for explaining the surface structure of the substrate Wf. Specifically, Fig. 6A is a schematic cross-sectional view showing bumps 143 formed on the substrate Wf by plating. Specifically, the bumps 143 are formed from a metal (e.g., Cu) deposited on the substrate Wf.

[0052] As illustrated in Fig. 6(A), a thin metal seed layer 140 is provided in advance on the entire surface of the substrate Wf according to this embodiment. During plating, power is supplied to the surface of the substrate Wf via this seed layer 140. A photoresist layer 141 is provided on the surface of the seed layer 140 opposite the substrate Wf side. The photoresist layer 141 has openings 142 in areas where bumps 143 are to be formed. Note that "φ" illustrated in Fig. 6(A) is the diameter (μm) of the openings 142 in the photoresist layer 141, and "BH" is the height (μm) of the bumps 143.

[0053] 6B is a schematic diagram showing an example of an opening pattern in the photoresist layer 141. No. 1 and No. 2 in FIG. 6B show examples in which the diameter φ of the openings 142 is relatively small (for example, 30 μm), while No. 3 and No. 4 show examples in which the diameter φ of the openings 142 is relatively large (for example, 75 μm). Comparing No. 1 and No. 2, the openings 142 are arranged at a higher density in No. 1 than in No. 2. Comparing No. 3 and No. 4, the openings 142 are arranged at a higher density in No. 3 than in No. 4.

[0054] The substrate Wf provided with the photoresist layer 141 as described above is held by the substrate holder 30 and immersed in the plating solution Ps in the plating tank 10 to perform the plating process. During the plating process, the surface of the substrate Wf, except for the openings 142 in the photoresist layer 141, is shielded from the plating solution Ps by the photoresist layer 141. As a result, a plating film grows only in the openings 142 in the photoresist layer 141, thereby forming bumps 143 on the substrate Wf. Note that the photoresist layer 141 may be removed after the plating process.

[0055] 7A and 7B are diagrams illustrating an example of a time waveform of a current output from the power supply 80 according to this embodiment and supplied to the anode 11 and the substrate Wf. As illustrated in FIGS. 7A and 7B, in response to an instruction from the control module 800, the power supply 80 supplies a forward current during a first period T1. The "forward direction" refers to the direction in which a current flows through the plating solution Ps from the anode 11 to the substrate Wf. Therefore, during the first period T1, metal ions in the plating solution Ps are reduced on the plating surface Wfa of the substrate Wf, causing a metal (bump 143) to deposit on the plating surface Wfa, forming a plating film.

[0056] The length of the first period T1 may be a length that occupies the majority of the total time during which the plating process is performed, so that the plating film substantially grows. In other words, the sum of the lengths of the second period T2 and the third period T3, which will be described later, may be negligible compared to the length of the first period T1. The magnitude of the forward current may be, for example, a constant current value throughout the first period T1. Alternatively, the current value of the forward current may be controlled to change over time.

[0057] During a second period T2, which is provided midway through the first period T1, the power supply 80 receives instructions from the control module 800 to supply a current in the opposite direction to the forward current, i.e., a reverse current pulse. For example, the length of the second period T2, i.e., the pulse width of the reverse current pulse, may be approximately 0.1 seconds to several seconds. During the second period T2, in contrast to the reduction reaction of metal ions during the first period T1, some of the metal from the plating film formed on the substrate Wf during the first period T1 is redissolved in the plating solution Ps, and the accelerator (one of the additives contained in the plating solution Ps) that adhered to the outermost surface of the plating film during the reduction reaction is desorbed from the plating film surface. It is desirable to set the current value of the reverse current pulse to a value that sufficiently achieves accelerator desorption.

[0058] 7(B), the power supply 80 may stop supplying current during a third period T3 following the second period T2. That is, during the third period T3, current does not flow in either the forward or reverse direction through the plating solution Ps. As with the second period T2, the length of the third period T3 is extremely short compared to the first period T1, and may be, for example, about 0.1 seconds to several seconds. During the third period T3, the accelerator desorbed from the plating film surface diffuses within the plating solution Ps.

[0059] After the second period T2 or the third period T3, the power supply 80 again supplies a forward current until the predetermined plating time is completed, for example, until the thickness of the formed plating film reaches a predetermined target film thickness.

[0060] Fig. 8 is a graph showing an example of measuring the height (BH) of the bumps 143 in each pattern region when multiple bumps 143 are formed on a substrate Wf having a photoresist layer 141 as exemplified in Fig. 6(B). On the vertical axis of Fig. 8, the height (BH) of each bump 143 corresponding to each of pattern regions P1, P2, P3, and P4 in Fig. 6(B) specifically indicates the average value of the heights of the multiple bumps 143 included in that pattern region.

[0061] The graph on the left of Figure 8 shows the measurement results when a forward current was supplied throughout the entire plating process to form bump 143, and the graph on the right of Figure 8 shows the measurement results when a reverse current pulse was supplied once during the plating process to form bump 143.

[0062] 8, among all the pattern regions, the height (BH) of the bump 143 in pattern region P1 is the smallest, and the height (BH) of the bump 143 in pattern region P4 is the largest. This is because the smaller the diameter φ of the openings 142 and the higher the arrangement density of the openings 142, the more difficult it becomes for metal ions to be sufficiently replenished into the openings 142, resulting in a lower formation rate of the plating film. Here, the difference between the maximum and minimum heights (BH) of the bumps 143 is defined as the "bump height variation (ΔBH)."

[0063] 8, it can be seen that when a reverse current pulse is supplied during the plating process (the graph on the right in FIG. 8), the bump height variation (ΔBH) is smaller than when a reverse current pulse is not supplied (the graph on the left in FIG. 8). Thus, by supplying a reverse current pulse, it is possible to make the height of the bumps 143 uniform.

[0064] 10 is a schematic plan view illustrating the "opening density change direction (Dr2)," which is the direction in which the opening density of a photoresist layer 141 provided on a substrate Wf changes. As an example, in FIG. 10 , the openings 142 in the photoresist layer 141 include a "region Ar1" (i.e., a region where the opening density is "sparse") where the opening density is lower than a predetermined value, and a "region Ar2" (i.e., a region where the opening density is "dense") where the opening density is higher than the opening density of region Ar1. In this case, the opening density change direction (Dr2) is the direction from region Ar1 to region Ar2 (or the direction from region Ar2 to region Ar1).

[0065] Here, the inventors' research has revealed that when a reverse current pulse is supplied, the degree of uniformity of the height of the bumps 143 varies depending on the angle (α1) formed between the "opening density change direction (Dr2)" and the flow direction (Dr1) of the plating solution Ps during stirring (for details, see the description of the experimental results explained in FIG. 11 below). Therefore, in this embodiment, in order to effectively uniform the height of the bumps 143, the plating method explained below in FIG. 9 is performed.

[0066] 9 is an example of a flowchart for explaining the plating method according to the present embodiment. First, the user (operator) obtains the "opening density change direction (Dr2)", which is the direction in which the opening density of the photoresist layer 141 provided on the substrate Wf changes (step S10).

[0067] When obtaining the opening density change direction (Dr2), for example, if information regarding the opening density is described in the specifications of the substrate Wf, the user may obtain the opening density change direction (Dr2) based on these specifications, etc. Alternatively, the user may obtain (i.e., measure) the opening density change direction (Dr2) by observing the substrate Wf visually or using a microscope, etc.

[0068] After step S10, the user or the control module 800 causes the substrate holder 30 to hold the substrate Wf for which the opening density change direction (Dr2) has been acquired (step S20).

[0069] The substrate Wf is held by the substrate holder 30 so that, for example, an orientation flat provided on the substrate Wf faces a predetermined direction of the substrate holder 30. In other words, the substrate Wf is held by the substrate holder 30 in a manner that allows the orientation of the substrate Wf (the direction of the orientation flat) to be determined. Therefore, when the substrate Wf is held by the substrate holder 30, the control module 800 can determine in which direction the opening density change direction (Dr2) of the substrate Wf faces.

[0070] Next, the control module 800 immerses the substrate Wf held by the substrate holder 30 in the plating solution Ps in the plating tank 10 so that the substrate Wf faces the anode 11 (step S30).

[0071] Next, the control module 800 executes the first plating process (step S40). Specifically, in step S40, the control module 800 causes the power source 80 to supply a forward current for a predetermined time while causing the stirring mechanism 60 (e.g., the paddle 70) to stir the plating solution Ps and the rotation mechanism 40 to rotate the substrate holder 30. This results in the formation of a plating film (specifically, bumps 143) on the substrate Wf.

[0072] Next, the control module 800 executes the second plating process (step S50). Specifically, in step S50, the control module 800 stops the rotation of the substrate holder 30 in a state where the opening density change direction (Dr2) is non-parallel to the flow direction (Dr1) of the plating solution Ps stirred by the stirring mechanism 60, and then causes the power supply 80 to supply a reverse current pulse while stirring the plating solution Ps with the stirring mechanism 60.

[0073] In addition, the "opening density change direction (Dr2)" being non-parallel to the "direction of flow of plating solution Ps (Dr1)" means, in other words, that the "opening density change direction (Dr2)" is neither the same direction as nor the opposite direction to the "direction of flow of plating solution Ps (Dr1)."

[0074] Specifically, referring to Figure 10, the control module 800 according to this embodiment stops the rotation of the substrate holder 30 at an angle such that the angle (α1) between the opening density change direction (Dr2) and the flow direction of the plating solution Ps (Dr1) is greater than 0 degrees and less than 180 degrees.

[0075] 10, as an example, the rotation of the substrate holder 30 is stopped so that the opening density change direction (Dr2) and the flow direction (Dr1) of the plating solution Ps are perpendicular (α1 is 90 degrees). With the rotation of the substrate holder 30 stopped in this manner, the control module 800 causes the stirring mechanism 60 to stir the plating solution Ps while causing the power supply 80 to supply a reverse current pulse.

[0076] In this embodiment, the "flow direction (Dr1) of the plating solution Ps stirred by the stirring mechanism 60" specifically coincides with the "direction (Dr1) in which the paddle 70 reciprocates." Therefore, the "direction (Dr1) in which the paddle 70 reciprocates" may be used as the "flow direction (Dr1) of the plating solution Ps stirred by the stirring mechanism 60."

[0077] That is, in this case, in step S50, the control module 800 stops the rotation of the substrate holder 30 in a state where the opening density change direction (Dr2) is non-parallel to the direction (Dr1) in which the paddle 70 moves back and forth, and then causes the plating solution Ps to be stirred by the stirring mechanism 60 while supplying a reverse current pulse to the power supply 80.

[0078] Referring to FIG. 9, after step S50, the control module 800 executes the first plating process again (step S60).

[0079] The control module 800 may repeatedly execute steps S40, S50, and S60 in FIG. 9 multiple times.

[0080] 11A and 11B are diagrams illustrating how the degree of uniformity of the height of the bumps 143 changes depending on the angle (α1) between the opening density change direction (Dr2) and the flow direction (Dr1) of the plating solution Ps during stirring. The vertical axes of FIGS. 11A and 11B represent the within-die uniformity (the difference between the maximum and minimum heights of the bumps 143).

[0081] 11A shows the results of an experiment using a substrate Wf with a relatively large degree of variation in the aperture ratio of the bumps 143 (substrate Wf with an eight-fold difference in aperture ratio within the die), while FIG. 11B shows the results of an experiment using a substrate Wf with a relatively small degree of variation in the aperture ratio of the bumps 143 (substrate Wf with a three-fold difference in aperture ratio within the die).

[0082] Sample No. 1 in FIG. 11A shows experimental results obtained when only the first plating process was performed (i.e., when only a forward current was supplied). Sample No. 2 shows experimental results obtained when the plating method according to this embodiment (FIG. 9) was performed. Specifically, in Sample No. 2, the angle (α1) in the second plating process in step S50 was set to 90 degrees. Sample No. 3 shows experimental results obtained when steps S10 to S60 of the flowchart in FIG. 9 were performed, but the angle (α1) in the second plating process in step S50 was set to zero degrees (or 180 degrees). In other words, Sample No. 2 is an example, and Samples No. 1 and No. 3 are comparative examples.

[0083] A comparison of Sample No. 1 with Sample No. 2 and Sample No. 3 reveals that the supply of a reverse current pulse during plating can reduce the value of intra-die uniformity (i.e., it can be seen that it is possible to make the height of the bumps 143 uniform). Furthermore, a comparison of Sample No. 2 with Sample No. 3 reveals that the value of intra-die uniformity changes depending on the value of the angle (α1) formed during the second plating process.

[0084] Furthermore, as can be seen from a comparison between Sample No. 2 and Sample No. 3, Sample No. 2 has a lower intra-die uniformity value than Sample No. 3. This shows that stopping the rotation of the substrate holder 30 during the second plating process in a state where the opening density change direction (Dr2) is non-parallel to the flow direction (Dr1) of the plating solution Ps during stirring, as in Sample No. 2, can reduce the intra-die uniformity value compared to stopping the rotation of the substrate holder 30 in a state where the opening density change direction (Dr2) is parallel to the flow direction (Dr1) of the plating solution Ps during stirring, as in Sample No. 3.

[0085] This is thought to be because, during the second plating process, when the direction of change in opening density (Dr2) is non-parallel to the direction of flow of plating solution Ps during stirring (Dr1), the plating solution Ps present on the surface of the substrate Wf (i.e., the surface of the plating film) can be stirred more uniformly across the entire surface of the substrate Wf than when it is not, and as a result, the accelerator can be desorbed uniformly and effectively from the surface of the plating film, resulting in a smaller value of intra-die uniformity.

[0086] Sample No. 4 in FIG. 11B shows experimental results obtained when only the first plating process was performed (i.e., when only a forward current was supplied). Sample No. 5 shows experimental results obtained when the plating method according to this embodiment (FIG. 9) was performed. Specifically, in Sample No. 5, the angle (α1) in the second plating process in step S50 was set to 90 degrees. Sample No. 6 shows experimental results obtained when steps S10 to S60 of the flowchart in FIG. 9 were performed, but the angle (α1) in the second plating process in step S50 was set to zero degrees (or 180 degrees). In other words, Sample No. 5 is an example, and Samples No. 4 and No. 6 are comparative examples.

[0087] A comparison of Sample No. 4 with Sample No. 5 and Sample No. 6 reveals that the supply of reverse current pulses during plating can reduce the value of within-die uniformity. Furthermore, a comparison of Sample No. 5 with Sample No. 6 reveals that the value of within-die uniformity changes depending on the value of the angle (α1) during the second plating process.

[0088] Furthermore, as can be seen from a comparison between sample No. 5 and sample No. 6, stopping the rotation of the substrate holder 30 during the second plating process when the opening density change direction (Dr2) is non-parallel to the flow direction (Dr1) of the plating solution Ps during stirring, as in sample No. 5, can reduce the value of intra-die uniformity compared to stopping the rotation of the substrate holder 30 when the opening density change direction (Dr2) is parallel to the flow direction (Dr1) of the plating solution Ps during stirring, as in sample No. 6.

[0089] As described above, it can be seen that the value of the angle (α1) formed when the second plating process is performed changes the in-die uniformity, that is, the degree of uniformity of the height of the bumps 143.

[0090] In this embodiment, the angle (α1) during the second plating process is 90 degrees, but is not limited to this. The angle (α1) is not particularly limited as long as it is greater than 0 degrees and less than 180 degrees. The angle (α1) can be determined in advance by experimentation to find a value that will best achieve uniformity in the height of the bumps 143, and this value can be set as the angle (α1).

[0091] When the relationship between the angle (α1) and the uniformity of the height of the bumps 143 was investigated, it was found that the closer the value of the angle (α1) is to 90 degrees, the more uniform the height of the bumps 143 tends to be. Therefore, from the viewpoint of uniformity of the height of the bumps 143, the angle (α1) is preferably a value selected from the range of 40 degrees or more and 135 degrees or less, more preferably a value selected from the range of 80 degrees or more and 100 degrees or less, and even more preferably 90 degrees.

[0092] According to the present embodiment as described above, the height of the bumps 143 can be made uniform.

[0093] Although the embodiments and modifications of the present invention have been described in detail above, the present invention is not limited to such specific embodiments and modifications, and various further modifications and changes are possible within the scope of the present invention as defined in the claims.

[0094] REFERENCE SIGNS LIST 10 Plating tank 11 Anode 30 Substrate holder 60 Stirring mechanism 70 Paddle 80 Power supply 141 Photoresist layer 142 Opening Ps Plating solution Wf Substrate Dr1 Flow direction of plating solution stirred by stirring mechanism Dr2 Opening density change direction

Claims

1. A plating method comprising: acquiring an opening density change direction, which is a direction in which the opening density of a photoresist layer provided on a substrate changes; holding the substrate, for which the opening density change direction has been acquired, in a substrate holder; immersing the substrate held by the substrate holder in a plating solution of a plating tank containing a plating solution containing an accelerator that promotes plating and in which an anode is disposed, so that the substrate faces the anode; performing a first plating process by rotating the substrate holder and stirring the plating solution with a stirring mechanism, and causing a power source configured to supply a current between the substrate and the anode to supply a forward current for depositing metal from the plating solution onto the substrate; stopping the rotation of the substrate holder in a state in which the opening density change direction is non-parallel to the direction of flow of the plating solution stirred by the stirring mechanism, and causing the power source to supply a reverse current pulse, which is a current that flows in pulses in the opposite direction to the forward current, while stirring the plating solution with the stirring mechanism; and performing the first plating process again.

2. The plating method according to claim 1, wherein in the second plating process, the direction of change in opening density is perpendicular to the direction of flow of the plating solution stirred by the stirring mechanism.

3. The plating method according to claim 1, wherein the stirring mechanism includes a paddle configured to stir the plating solution in the plating tank by reciprocating movement, and the direction in which the paddle reciprocates is used as the direction of flow of the plating solution stirred by the stirring mechanism in the second plating process.

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