Plating device and plating method

Abstract

The present invention forms a plurality of bumps at a uniform height on a substrate.　A plating device for forming a plating film on a substrate includes: a substrate holder for holding the substrate; a plating tank for storing a plating solution together with the substrate holder; an anode disposed in the plating tank so as to face the substrate held by the substrate holder; a power supply for supplying a plating current between the substrate and the anode; and a control unit. The control unit causes the power supply to output a plating current that repeats a forward current period in which a forward current for causing a metal to be deposited on the substrate from the plating solution is supplied, a reverse current period in which a reverse current pulse flowing in the opposite direction to the forward current is supplied, and a current pause period in which the supply of current is paused partway during a transition from the reverse current pulse to the forward current. The control unit controls the length of the current pause period such that the width of fluctuation of the plating voltage after the reverse current pulse is supplied falls within a predetermined range.

Description

Plating apparatus and plating method

[0001] The present invention relates to a plating apparatus and a plating method. In particular, the present invention relates to a plating apparatus and a plating method for forming bumps on a substrate.

[0002] Metal plating films, such as Cu, are formed on the surface of substrates for semiconductor devices and electronic elements. For example, a substrate to be plated is held in a substrate holder, and the substrate, along with the substrate holder, is immersed in a plating tank containing a plating solution to perform electroplating. The substrate holder holds the substrate so that the plated surface is exposed. An anode is positioned in the plating solution to correspond to the exposed surface of the substrate, and an electroplated film can be formed on the exposed surface of the substrate by applying a voltage between the substrate and the anode.

[0003] For example, a photoresist layer having multiple openings is placed on the surface of a substrate. By plating such a substrate with a photoresist layer, bumps can be formed at the openings.

[0004] Patent No. 7357824

[0005] It is required to form multiple bumps on the substrate at a uniform height.

[0006] According to one embodiment, a plating apparatus for forming a plating film on a substrate is provided, comprising: a substrate holder configured to hold the substrate; a plating tank configured to contain a plating solution together with the substrate holder; an anode disposed in the plating tank so as to face the substrate held by the substrate holder; a power supply configured to supply a plating current between the substrate and the anode; and a control unit, wherein the control unit is configured to output a plating current from the power supply having a repeating cycle of a positive current period in which a positive current is supplied from the plating solution to deposit metal onto the substrate; a reverse current period in which a reverse current pulse flowing in the opposite direction to the positive current is supplied; and a current pause period in which the current supply is paused during the transition from the reverse current pulse to the positive current, and the control unit is further configured to control the length of the current pause period so that the fluctuation range of the plating voltage after the supply of the reverse current pulse falls within a predetermined range.

[0007] This is a perspective view showing the overall configuration of the plating apparatus of this embodiment. This is a plan view showing the overall configuration of the plating apparatus of this embodiment. This is a schematic diagram showing the configuration of the plating module in the plating apparatus. This is a schematic diagram of the plating module showing the state in which the substrate is immersed in the plating solution. This is a schematic diagram showing bumps formed on the substrate by plating the surface of the substrate using the plating apparatus according to one embodiment of the present invention. This is a schematic diagram showing an example of an aperture pattern of the photoresist layer used to form a plurality of bumps. This is a graph showing the time waveform of the plating current output from the power supply and flowing between the anode and the substrate in the plating apparatus according to one embodiment of the present invention. This is a conceptual diagram explaining the principle by which the uniformity of the height of a plurality of bumps is improved by using the plating current of Figure 7. This is a graph showing the time waveform of the plating voltage for one cycle observed when plating is performed using the plating current of Figure 7 in the plating apparatus according to one embodiment of the present invention. This is a graph showing the time waveform of the plating voltage for one cycle observed when plating is performed using the plating current of Figure 7 in the plating apparatus according to one embodiment of the present invention. This is a graph showing an example of a time waveform over multiple cycles of the plating voltage observed when plating is performed using the plating current of Figure 7 in the plating apparatus according to one embodiment of the present invention. This graph shows an example of the time waveform of the plating voltage over multiple cycles when the length of the current pause period is controlled by a control module of a plating apparatus according to one embodiment of the present invention. This graph shows the time waveform of the plating voltage over multiple cycles in another example where the length of the current pause period is controlled by a control module of a plating apparatus according to one embodiment of the present invention.

[0008] Embodiments of the present invention will be described below with reference to the drawings. In the drawings described below, the same or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] Figure 1 is a perspective view showing the overall configuration of the plating apparatus of this embodiment. Figure 2 is a plan view showing the overall configuration of the plating apparatus of this embodiment. As shown in Figures 1 and 2, the plating apparatus 1000 includes a load port 100, a transport 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 transport device 700, and a control module 800.

[0010] The load port 100 is a module for loading substrates stored in cassettes such as FOUPs (not shown) into the plating apparatus 1000, and for unloading substrates from the plating apparatus 1000 into cassettes. In this embodiment, four load ports 100 are arranged horizontally, but the number and arrangement of load ports 100 are arbitrary. The transport robot 110 is a robot for transporting substrates and is configured to transfer substrates between the load port 100, the aligner 120, and the transport device 700. When transferring substrates between the transport robot 110 and the transport device 700, the transfer of substrates can be done via a temporary storage platform (not shown).

[0011] The aligner 120 is a module for aligning the positions of orientation flats and notches on the substrate to a predetermined direction. In this embodiment, two aligners 120 are arranged side by side horizontally, but the number and arrangement of the aligners 120 are arbitrary. The pre-wet module 200 replaces the air inside the patterns formed on the substrate surface with a treatment solution by wetting the surface of the substrate to be plated with a treatment solution such as pure water or degassed water before the plating process. The pre-wet module 200 is configured to perform a pre-wetting process that makes it easier to supply the plating solution inside the patterns by replacing the treatment solution inside the patterns with the plating solution during plating. In this embodiment, two pre-wet modules 200 are arranged side by side vertically, but the number and arrangement of the pre-wet modules 200 are arbitrary.

[0012] The pre-soak module 300 is configured to perform a pre-soak treatment, which involves etching away 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, thereby cleaning or activating the surface of the substrate. In this embodiment, two pre-soak modules 300 are arranged side by side in the vertical direction, but the number and arrangement of the pre-soak modules 300 are arbitrary. The plating module 400 performs the plating treatment on the substrate. In this embodiment, there are two sets of 12 plating modules 400, arranged in a vertical direction of three modules and a horizontal direction of four modules, for a total of 24 plating modules 400, but the number and arrangement of the plating modules 400 are arbitrary.

[0013] The cleaning module 500 is configured to clean the substrate to remove any remaining plating solution after the plating process. In this embodiment, two cleaning modules 500 are arranged side by side in the vertical direction, but the number and arrangement of the cleaning modules 500 are arbitrary. The spin rinse dryer 600 is a module for drying the substrate after the cleaning process by rotating it at high speed. In this embodiment, two spin rinse dryers are arranged side by side in the vertical direction, but the number and arrangement of the spin rinse dryers are arbitrary. The transport device 700 is a device for transporting substrates between multiple modules in the plating apparatus 1000. The control module 800 is configured to control multiple modules of the plating apparatus 1000 and can consist of, for example, a general-purpose computer or a dedicated computer with an input / output interface with an operator.

[0014] An example of a series of plating processes performed by the plating apparatus 1000 will be described. First, substrates stored in cassettes are loaded into the load port 100. Next, the transport robot 110 removes the substrates from the cassettes in the load port 100 and transports them to the aligner 120. The aligner 120 aligns the orientation flats and notches of the substrates to a predetermined direction. The transport robot 110 then transfers the substrates, whose orientation has been aligned by the aligner 120, to the transport device 700.

[0015] The transport device 700 transports the substrate received from the transport robot 110 to the pre-wet module 200. The pre-wet module 200 performs a pre-wet treatment on the substrate. The transport device 700 transports the pre-wet treated substrate to the pre-soak module 300. The pre-soak module 300 performs a pre-soak treatment on the substrate. The transport device 700 transports the pre-soaked treated substrate to the plating module 400. The plating module 400 performs a plating treatment on the substrate.

[0016] The transport device 700 transports the plated substrate to the cleaning module 500. The cleaning module 500 cleans the substrate. The transport device 700 transports the cleaned substrate to the spin rinse dryer 600. The spin rinse dryer 600 dries the substrate. The transport device 700 hands over the dried substrate to the transport robot 110. The transport robot 110 transports the substrate received from the transport device 700 to the cassette in the load port 100. Finally, the cassette containing the substrate is discharged from the load port 100.

[0017] The configuration of the plating apparatus 1000 described in Figures 1 and 2 is merely an example, and the configuration of the plating apparatus 1000 is not limited to the configurations shown in Figures 1 and 2.

[0018] Next, the plating module 400 will be described. Since the multiple plating modules 400 in the plating apparatus 1000 according to this embodiment have similar configurations, only one plating module 400 will be described.

[0019] Figure 3 is a schematic diagram showing the configuration of the plating module 400 in the plating apparatus 1000. Specifically, Figure 3 schematically illustrates the plating module 400 before the substrate Wf is immersed in the plating solution Ps. Figure 4 is a schematic diagram showing the state after the substrate Wf has been immersed in the plating solution Ps.

[0020] The plating apparatus 1000 illustrated in Figures 3 and 4 is, as an example, a type of plating apparatus (a so-called cup-type plating apparatus) in which the substrate Wf is immersed in the plating solution Ps with its surface orientation horizontal. However, the configuration of the plating apparatus 1000 is not limited to this, and for example, it may be a type of plating apparatus in which the substrate Wf is immersed in the plating solution Ps with its surface orientation non-horizontal (for example, perpendicular to the ground).

[0021] The plating module 400 of the plating apparatus 1000 illustrated in Figures 3 and 4 comprises a plating tank 10, an overflow tank 20, a substrate holder 30, and a paddle 70 as an example of a stirring mechanism 60. The plating module 400 also comprises a rotation mechanism 40, a tilting mechanism 45, and a lifting mechanism 50, as illustrated in Figure 3. The plating module 400 also comprises a sensor 130, as illustrated in Figure 3. The plating module 400 also comprises a power supply 80 and a plating solution flow mechanism 90, as illustrated in Figure 4.

[0022] The plating tank 10 according to this embodiment is composed of 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 that extends upward from the outer peripheral edge of the bottom wall 10a, with the upper part 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 as an example. A plating solution Ps is stored inside the plating tank 10.

[0023] The plating solution Ps can be any solution containing ions of the metal elements that constitute the plating film, and its specific examples are not particularly limited. In this embodiment, copper plating is used as an example of a plating process, and copper sulfate solution is used as an example of the plating solution Ps. The plating solution Ps may also contain predetermined additives.

[0024] As an additive to this plating solution Ps, for example, an accelerator that promotes plating (specifically, an accelerator that promotes the formation of a plating film) can be used. As this accelerator, for example, SPS (bis(3-sulfopropyl) disulfide) can be used.

[0025] An anode 11 is placed inside the plating tank 10. The specific type of anode 11 is not particularly limited and may be an insoluble anode or a soluble anode. In this embodiment, an insoluble anode is used as an example of anode 11. The specific type of this insoluble anode is not particularly limited and can be platinum, iridium oxide, or the like.

[0026] As illustrated in Figures 3 and 4, an ion resistor 12 may be positioned 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 made up of 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.

[0027] This ion resistor 12 is provided to homogenize the electric field formed between the anode 11 and the substrate Wf, which acts as the cathode. As in this embodiment, by arranging the ion resistor 12 in the plating tank 10, it is possible to easily homogenize the thickness of the plating film (plating layer) formed on the substrate Wf.

[0028] As illustrated in Figures 3 and 4, a film 16 may be placed inside the plating tank 10 above the anode 11 and below the ion resistor 12. In this case, the inside of the plating tank 10 is divided by the film 16 into an anode chamber 17a below the film 16 and a cathode chamber 17b above the film 16. The anode 11 is placed in the anode chamber 17a, and the ion resistor 12 and substrate Wf are placed in the cathode chamber 17b. The film 16 is configured to allow ionic species containing metal ions contained in the plating solution Ps to pass through the film 16, while suppressing the passage of nonionic plating additives contained in the plating solution Ps. For example, an ion exchange film can be used as such a film 16.

[0029] As illustrated in Figure 4, the plating solution flow mechanism 90 is configured to cause the plating solution Ps in the plating tank 10 to flow. The flow of the plating solution Ps in the plating tank 10 stirs the plating solution Ps in the plating tank 10. The plating solution flow mechanism 90 according to this embodiment includes, as an example, a first flow mechanism 91a and a second flow mechanism 91b.

[0030] The first flow mechanism 91a is a mechanism for flowing the plating solution Ps in the anode chamber 17a. The second flow mechanism 91b is a mechanism for flowing the plating solution Ps in the cathode chamber 17b. The first flow mechanism 91a is in communication with the anode chamber 17a via piping 92a. The second flow mechanism 91b is in communication with the cathode chamber 17b via piping 92b. The first flow mechanism 91a and the second flow mechanism 91b are each equipped with a pump or the like for pressurizing the plating solution Ps.

[0031] Referring to Figures 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 pumped by the first flow mechanism 91a and supplied again to the anode chamber 17a from the first supply port 13a.

[0032] The overflow tank 20 is a bottomed container located outside the plating tank 10. The overflow tank 20 is provided to temporarily store the plating solution Ps that exceeds the upper end of the outer peripheral wall 10b of the plating tank 10 (i.e., the plating solution Ps that overflows from the plating tank 10). The plating solution Ps stored in the overflow tank 20 is discharged from the second outlet 14b, then pumped by the second fluidization mechanism 91b and supplied again to the cathode chamber 17b from the second supply port 13b.

[0033] The substrate holder 30 holds the substrate Wf, which serves as the cathode, such that the plated surface Wfa of the substrate Wf faces the anode 11. In this embodiment, the plated surface Wfa of the substrate Wf is specifically located on the surface (bottom surface) facing downwards.

[0034] The substrate holder 30 is connected to the rotating mechanism 40. The rotating mechanism 40 is a mechanism for rotating the substrate holder 30. For example, the substrate holder 30 rotates in the rotation direction R1 illustrated in Figure 3 by the drive of the rotating mechanism 40. A known rotary motor or the like can be used as the rotating mechanism 40. The tilting mechanism 45 is a mechanism for tilting the rotating mechanism 40 and the substrate holder 30. The lifting mechanism 50 is supported by a support shaft 51 that extends in the vertical direction. The lifting mechanism 50 is a mechanism for raising and lowering the substrate holder 30, the rotating 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.

[0035] The control module 800 is equipped with a microcomputer, which includes a processor 801 and a storage device 802 as a non-temporary storage medium. The control module 800 controls the operation of the plating module 400 by having the processor 801 operate based on program instructions stored in the storage device 802.

[0036] Referring to FIG. 3, the sensor 130 detects various information used for various controls of the control module 800 and transmits the detection result to the control module 800. For example, the sensor 130 may include a current sensor that detects the value of the plating current flowing between the anode 11 and the substrate Wf during the plating process.

[0037] In addition to the current sensor, the sensor 130 may include a voltage sensor that detects the value of the plating voltage during the plating process. The voltage sensor according to the present embodiment is configured to also detect the fluctuation width Wd of the plating voltage.

[0038] The voltage sensor may detect the voltage value between the substrate Wf and the anode 11 as the plating voltage, or may detect the voltage value between the substrate Wf and the reference electrode 18 (see FIG. 4). The voltage sensor is configured to detect the fluctuation width Wd based on such a plating voltage.

[0039] Note that the reference electrode 18 is disposed inside the plating tank 10 and is an electrode that is referenced instead of the anode 11 when detecting a voltage or the fluctuation width of a voltage. The specific location of the reference electrode 18 inside the plating tank 10 is not particularly limited, but in the present embodiment, as an example, it is disposed at a location near the anode 11 of the plating tank 10 (on the bottom wall 10a in the present embodiment).

[0040] As illustrated in FIG. 4, the power supply 80 is electrically connected to the substrate Wf and the anode 11 and is configured to supply a current between the substrate Wf and the anode 11. The operation of the power supply 80 is controlled by the control module 800.

[0041] Figure 5 is a schematic diagram showing bumps formed on a substrate Wf by plating the surface of the substrate Wf using a plating apparatus 1000 according to one embodiment of the present invention. A thin metal seed layer 501 is pre-formed on the entire surface of the substrate Wf, and the surface of the substrate Wf is supplied with power through this seed layer 501 during plating. A photoresist layer 502 is formed on the seed layer 501, and the photoresist layer 502 has an opening 502a in the area where the bumps are to be formed. The substrate Wf with the photoresist layer 502 formed on it is held in a substrate holder 30 and immersed in a plating solution Ps in a plating tank 10 to perform plating. During plating, the portion of the substrate Wf surface other than the opening 502a of the photoresist layer 502 is shielded from the plating solution Ps by the photoresist layer 502. As a result, the plating film grows only on the bottom surface of the opening 502a of the photoresist layer 502, forming bumps 503 on the substrate Wf. The photoresist layer 502 is removed after the plating process (see Figure 5 right).

[0042] Numerous such bumps 503 are formed on the substrate Wf using a photoresist layer 502 having a predetermined aperture pattern. Figure 6 is a schematic diagram showing an example of an aperture pattern of the photoresist layer 502 used to form a plurality of bumps 503. In the aperture pattern shown in Figure 6, small apertures 502a with a small aperture diameter φ (see Figure 5) are densely arranged in pattern region P1, small apertures 502a with a small aperture diameter φ are sparsely arranged in pattern region P2, large apertures 502a with a large aperture diameter φ are densely arranged in pattern region P3, and large apertures 502a with a large aperture diameter φ are sparsely arranged in pattern region P4.

[0043] Depending on the size (i.e., aperture diameter) and density (i.e., number of apertures per unit area) of the openings in the photoresist layer 502, variations may occur in the height (film thickness) of the bumps 503 formed at each opening, even on the same substrate Wf. Therefore, it is necessary to form multiple bumps 503 at a uniform height on the substrate Wf.

[0044] Figure 7 is a graph showing the time waveform of the plating current output from the power supply 80 in a plating apparatus 1000 according to one embodiment of the present invention, which flows between the anode 11 and the substrate Wf. As shown in Figure 7, the power supply 80 outputs a positive current during period T1 (hereinafter, period T1 is referred to as the positive current period). "Positive direction" means the direction in which the current flows through the plating solution Ps from the anode 11 to the substrate Wf. Therefore, during the positive current period T1, metal ions in the plating solution Ps are reduced on the plated surface Wfa of the substrate Wf, causing metal to be deposited on the plated surface Wfa (i.e., a plating film is formed). The length of the positive current period T1 may be a sufficient length of time for the plating film to grow substantially. In other words, the lengths of periods T2 and T3, described later, may be negligible compared to the length of the positive current period T1. The magnitude of the positive current may be a constant current value I1 throughout the entire positive current period T1. Alternatively, the current value I1 of the positive current may be controlled to change over time.

[0045] In the period T2 following the positive current period T1, the power supply 80 outputs a current in the opposite direction to the positive current described above (hereinafter, period T2 is referred to as the reverse current period). During the reverse current period T2, the current maintains a current value I2 with a sign different from I1. The length of the reverse current period T2 is extremely short compared to the positive current period T1. Therefore, the current in the reverse current period T2 is pulsed, and hereinafter, in this specification, this will be referred to as a "reverse current pulse". For example, the length of the reverse current period T2, i.e., the pulse width of the reverse current pulse, may be around 0.1 seconds to several seconds. In the reverse current period T2, contrary to the reduction reaction of metal ions in the positive current period T1, some of the metal in the plating film formed on the plated surface Wfa during the positive current period T1 is redissolved in the plating solution Ps, and the accelerator (one of the additives contained in the plating solution Ps) that was attached to the outermost surface of the plating film during the reduction reaction is detached from the surface of the plating film.

[0046] Furthermore, it is desirable to set the current value I2 of the reverse current pulse to a value that ensures sufficient desorption of the accelerator. Also, when setting the current value I2 to be equal to the current value I1, instead of the power supply 80 that outputs with both positive and negative polarity as described above, a combination of a power supply that outputs with a single polarity and a polarity reversal switch that can reverse the polarity of the output of said power supply may be used.

[0047] Furthermore, during the period T3 following the reverse current period T2, the power supply 80 stops outputting current (hereinafter, period T3 is referred to as the current pause period). That is, during the current pause period T3, no current flows through the plating solution Ps in either the forward or reverse direction. Similar to the reverse current period T2, the length of the current pause period T3 may be extremely short compared to the forward current period T1, for example, it may be only a few seconds long.

[0048] After the current pause period T3, the power supply 80 transitions back to a positive current period T1, outputting a positive current (current value I1). Similarly, the positive current period T1, the reverse current period T2, and the current pause period T3 are repeated in this order. These three periods T1, T2, and T3 are repeated until the predetermined plating time is completed, for example, until the thickness of the formed plating film reaches a predetermined target thickness.

[0049] By performing a plating treatment on a substrate Wf using a plating current having a repeating cycle of a forward current period T1, a reverse current period T2, and a current pause period T3, the height of the multiple bumps 503 formed on the substrate Wf can be made uniform (see Patent Document 1). The reason why the bump heights are made uniform has already been explained in Patent Document 1, but it will be explained again here using Figure 8 as it is a prerequisite for a better understanding of the present invention.

[0050] Figure 8 is a conceptual diagram illustrating the principle by which the uniformity of the heights of the multiple bumps 503 is improved by using the plating current described above. On the plated surface Wfa of the substrate Wf, in areas where the diameter of the openings 502a of the photoresist layer 502 is large and the arrangement density of the openings 502a is low (for example, pattern region P4 in Figure 6), metal ions are more easily replenished into the openings 502a compared to other areas (for example, pattern region P1), resulting in a higher plating film formation rate. Therefore, if a reverse current pulse is not supplied, while a positive current is supplied (i.e., during the positive current period T1), the plating film thickness in areas with large opening diameters and / or low opening density will be thicker than the plating film thickness in areas with small opening diameters and / or high opening density (stage (A) in Figure 8).

[0051] Here, the plating solution Ps contains an accelerator (e.g., SPS (bis(3-sulfopropyl) disulfide) as one of its additives, which has the effect of promoting the formation of the plating film. Such accelerator molecules are concentrated and adsorbed at a constant density on the surface of the plating film, regardless of location, and promote the reduction reaction of metal ions. During the reverse current period T2, when the reverse current pulse is supplied, the accelerator molecules detach from the surface of the plating film and diffuse into and near the opening 502a. At this time, since the accelerator molecules are originally concentrated and adsorbed at a constant density on the surface of the plating film, the local concentration of the accelerator molecules detached from the surface of the plating film inside each opening 502a is constant (stage (B) in Figure 8).

[0052] However, in areas with high aperture density, similarly detached accelerator molecules are present in neighboring apertures 502a, resulting in a small concentration gradient of accelerator molecules near these multiple apertures 502a. Therefore, relatively few of these accelerator molecules diffuse far away from the apertures 502a, and a large number of accelerator molecules remain near the apertures 502a. In contrast, in areas with low aperture density, the influence from neighboring apertures 502a is small, resulting in a large concentration gradient of accelerator molecules near the multiple apertures 502a. Therefore, most of the accelerator molecules detached from the plating film diffuse far away, leaving only a small number of accelerator molecules near the apertures 502a. As a result, during the current pause period T3 when no current flows through the plating solution Ps, the average concentration of accelerator molecules is higher near apertures 502a in areas with high aperture density compared to near apertures 502a in areas with low aperture density. In other words, the difference in aperture density results in a difference in the average concentration of accelerator molecules. Furthermore, differences in the size of the opening 502a also create similar differences in the concentration of the accelerator molecules (when the opening diameter is large, the accelerator molecules diffuse more easily to the outside of the opening 502a, so the concentration of accelerator molecules becomes lower in the vicinity of the larger opening 502a).

[0053] Thus, the concentration of accelerator molecules near the opening 502a differs depending on the structure (i.e., diameter and arrangement density) of the opening 502a where the plating film is formed. Therefore, when a positive current is supplied again after the current pause period T3, the amount of accelerator molecules re-adsorbed onto the plating film surface within the opening 502a will differ depending on the location. Specifically, in areas with a large opening diameter and / or low opening density, the amount of re-adsorbed accelerator molecules is relatively small, while in areas with a small opening diameter and / or high opening density, the amount of re-adsorbed accelerator molecules is relatively large (stage (C) in Figure 8).

[0054] As described above, the detachment of the accelerator occurs uniformly (stage (B)). Therefore, looking at the process from detachment to readsorption as a whole, the density (or amount) of accelerator molecules that have been readsorbed and are present on the surface of the plating film is relatively small at openings 502a located in areas with a large opening diameter and / or low opening density, and relatively large at openings 502a located in areas with a small opening diameter and / or high opening density. Consequently, the effect of the accelerator is greater on the surface of the plating film in areas with a small opening diameter and / or high opening density than in areas with a large opening diameter and / or low opening density, and the plating rate increases (stage (D) in Figure 8). This compensates for the difference in film thickness due to the location of the initially existing plating film (see stage (A)), and as a result, the film thickness of the plating film formed within the openings 502a (i.e., bumps 503) is made uniform regardless of the difference in the structure of the openings 502a (stage (E) in Figure 8).

[0055] As can be understood from the above explanation, in order to equalize the height of the bump 503, it is important to create a density difference in the accelerator molecules that are re-adsorbed after desorption. This density difference is due to the fact that, as mentioned above, the degree to which the desorbed accelerator molecules diffuse farther away from the plating film during the reverse current period T2 and the current pause period T3 differs depending on the location (i.e., depending on the size and arrangement density of the opening 502a).

[0056] Here, as the plating time on the substrate Wf increases, the thickness of the plating film formed on the substrate Wf (i.e., the height of the bump 503) increases, and the depth from the surface of the photoresist layer 502 to the surface of the plating film within the opening 502a of the photoresist layer 502 gradually decreases. As a result, the accelerator molecules detached from the surface of the plating film can diffuse more easily from the inside to the outside of the opening 502a, so the amount of accelerator molecules re-adsorbed decreases, and the density difference depending on the location of the accelerator molecules near the opening 502a formed as a result of diffusion, and consequently the density difference depending on the location of the accelerator molecules re-adsorbed after detachment, gradually decreases. Consequently, the effect of homogenizing the bump height by reverse current pulses and current pauses diminishes as the plating time progresses.

[0057] Figure 9A is a graph showing the time waveform of the plating voltage for one cycle, observed when a plating process is performed using the plating current shown in Figure 7 in a plating apparatus 1000 according to one embodiment of the present invention. As mentioned above, the plating voltage can be measured by the sensor 130 as the voltage value between the substrate Wf and the anode 11, or the voltage value between the substrate Wf and the reference electrode 18. As shown in Figure 9A, when a reverse current pulse is supplied during the plating process, the plating voltage decreases and a minimum value is generated due to the subsequent re-adsorption of the accelerator onto the substrate Wf. This time change in the plating voltage is due to a change in the adsorption state of the additives (accelerator and inhibitor) on the surface of the plating film, which changes the electrical resistance (polarization resistance) of the cathode surface, i.e., the surface of the plating film.

[0058] Specifically, as shown in Figure 9A, the plating voltage changes from a positive voltage V1 to a negative voltage V0 when a reverse current pulse is applied, and then, after a current pause, the positive current is applied again, causing the voltage to temporarily become higher than the original voltage value V1. At this point, that is, immediately after the application of the positive current, the accelerator has hardly re-adsorbed onto the surface of the plating film, and from this state, the re-adsorption of the accelerator gradually progresses. As a result, the electrical resistance of the plating film surface gradually decreases, and therefore the plating voltage decreases. Subsequently, in addition to the accelerator, the inhibitor also begins to adsorb, and the inhibitory effect on plating film formation by the inhibitor becomes stronger. Then, the plating voltage changes from decreasing to increasing with V2 as its extreme value, and gradually increases towards the voltage value V1 corresponding to the positive current.

[0059] In this specification, the difference between the plating voltage V1 immediately before the reverse current pulse is supplied and the minimum value V2 of the plating voltage that occurs after the reverse current pulse is supplied is defined as the plating voltage fluctuation range Wd. Depending on the type of additive contained in the plating solution Ps and the aperture pattern of the photoresist layer 502 on the substrate Wf, the plating voltage may exhibit a time waveform as shown in Figure 9B. In the case of a time waveform as shown in Figure 9B, the plating voltage fluctuation range Wd may be defined as the difference between the plating voltage V1 immediately before the reverse current pulse and the minimum value V2 of the plating voltage after the reverse current pulse, as in the case of Figure 9A, or it may be defined as the difference between the minimum value V2 of the plating voltage and the maximum value V3 of the plating voltage that occurs after the minimum value.

[0060] As described above, the magnitude of the minimum value V2 of the plating voltage that occurs after the supply of the reverse current pulse (i.e., the depth of the dip in the voltage waveform) depends on the amount of accelerator molecules re-adsorbed, and the amount of accelerator molecules re-adsorbed decreases as the plating process time progresses. Consequently, the effect of uniformizing the bump height when plating is performed using the plating current shown in Figure 7 gradually decreases as the plating process time progresses.

[0061] Figure 10 is a graph showing an example of a time waveform of the plating voltage over multiple cycles, observed when a plating process is performed using the plating current as shown in Figure 7 in a plating apparatus 1000 according to one embodiment of the present invention. In the example in Figure 10, the lengths of the positive current period T1, the reverse current period T2, and the current pause period T3 in each cycle are kept constant throughout the entire period of the plating current. As shown in this figure, the minimum value V2 of the plating voltage (the dip in the voltage waveform) becomes shallower over time, and the fluctuation range Wd becomes smaller. Accordingly, the effect of uniformizing the bump height also decreases.

[0062] Therefore, in order to maintain the effect of uniformizing the bump height until the plating process of the substrate Wf is completed, it is necessary to ensure that the fluctuation range Wd of the plating voltage does not fall below a predetermined constant value. To achieve this, the control module 800 of the plating apparatus 1000 according to one embodiment of the present invention controls the length of the current pause period T3 in the plating current output from the power supply 80. Specifically, by shortening the length of the current pause period T3, excessive diffusion of accelerator molecules detached from the surface of the plating film is prevented (even when the depth from the surface of the photoresist layer 502 to the surface of the plating film becomes shallower as the plating progresses), and as a result, the decrease in the amount of accelerator molecules re-adsorbed when a positive current is applied again can be suppressed. This ensures that the density difference depending on the location of the re-adsorbed accelerator molecules is stably formed until the end of the plating process, thereby further uniformizing the bump height.

[0063] Figure 11 is a graph showing an example of the time waveform of the plating voltage over multiple cycles when the length of the current pause period T3 is controlled by the control module 800 of the plating apparatus 1000 according to one embodiment of the present invention. In the example in Figure 11, the lengths of the forward current period T1 and the reverse current period T2 in each cycle are constant over the entire period of the plating current, as in the example in Figure 10. However, the length of the current pause period T3 is constant. ｈａｌｔ In the first half of the entire plating process, period P1, the first time length t ｌｏｎｇ (For example t ｌｏｎｇ It is set to (≥5 seconds), and in the latter half of period P2, the first time length t ｌｏｎｇ A second time length t that is shorter than ｓｈｏｒｔ (For example, 0 seconds ≤ t) ｓｈｏｒｔ The setting is <5 seconds). The timing of the switch from the first half period P1 to the second half period P2 is selected so that the fluctuation range Wd of the plating voltage does not fall below a predetermined constant value. As shown in Figure 11, the fluctuation range Wd of the plating voltage gradually decreases during the first half period P1, but in the second half period P2, the length of the current pause period T3 is set to a shorter second time length t ｓｈｏｒｔBy changing to this, the fluctuation width Wd of the plating voltage that once became small increases again. As a result, a plating process with better bump height uniformity than in the case of the example in FIG. 10 is realized.

[0064] FIG. 12 is a graph showing the time waveform over a plurality of cycles of the plating voltage in another example in which the length of the current pause period T3 is controlled by the control module 800 of the plating apparatus 1000 according to an embodiment of the present invention. The example of FIG. 12 differs from the example of FIG. 11 only in that the plating process period consists of three periods: a first half period P1, an intermediate period P2, and a second half period P3. In the example of FIG. 12, the length t ｈａｌｔ of the current pause period T3 is set to a first time length t ｌｏｎｇ (for example, t ｌｏｎｇ ≧5 seconds) in the first half period P1, and a second time length t ｌｏｎｇ shorter than the first time length t ｍｅｄｉｕｍ (for example, 2 seconds ≦ t ｍｅｄｉｕｍ <5 seconds) in the intermediate period P2, and a third time length t ｍｅｄｉｕｍ even shorter than the second time length t ｓｈｏｒｔ (for example, 0 seconds ≦ t ｓｈｏｒｔ <2 seconds) in the second half period P3. The switching timings from the first half period P1 to the intermediate period P2 and from the intermediate period P2 to the second half period P3 are each selected so that the fluctuation width Wd of the plating voltage does not fall below a predetermined constant value. Also in this example, by gradually changing the length of the current pause period T3 to a shorter time length, the fluctuation width Wd of the plating voltage is maintained at a certain value or more throughout the entire periods P1 to P3. Therefore, similar to the case of FIG. 11, a plating process with better bump height uniformity is realized.

[0065] In Figures 11 and 12 above, the entire period during which the plating process is performed is divided into two or three periods, but it may be divided into four or more periods, and the plating current may be controlled such that the length of the current pause period T3 becomes progressively shorter for each of these divided periods. The plating current may also be controlled such that the length of the current pause period T3 becomes progressively shorter for each cycle of the plating current, which consists of a repeating forward current period T1, a reverse current period T2, and a current pause period T3 (i.e., a period consisting of one set of forward current period T1, reverse current period T2, and current pause period T3).

[0066] Furthermore, the magnitude of the voltage waveform minimum V2 (for example, the first minimum in the latter half of period P2 in the example in Figure 11) that appears immediately after changing the length of the current pause period T3 can vary depending on the length of the current pause period T3 after the change, or the timing of changing the length of the current pause period T3. For example, if the length of the current pause period T3 after the change is made too short compared to the length of the current pause period T3 before the change, the amount of re-adsorption of accelerator molecules will become too large, causing the minimum value V2 of the plating voltage (the dip in the voltage waveform) to become deeper. In this case, the effect of compensating for differences in film thickness depending on the location of the plating film (see stage (D) in Figure 8) becomes excessive, resulting in a loss of uniformity in bump height. Similarly, if the timing of changing the length of the current pause period T3 is too early (i.e., if the length of the current pause period T3 is changed while the dip in the voltage waveform is still sufficiently deep), the amount of re-adsorption of accelerator molecules will increase too much. Therefore, there are both appropriate lower and upper limits for the minimum value V2 of the plating voltage (or the fluctuation range Wd) necessary to uniformize the bump height.

[0067] Therefore, it is advantageous to select the length of the current pause period T3 after modification, and the timing of changing the length of the current pause period T3, so that the fluctuation range Wd of the plating voltage is maintained within a range determined by predetermined appropriate lower and upper limits. For example, it is possible to determine the optimal values ​​for the length of such a current pause period T3 and the timing of the change through experiments using a sample substrate for evaluation, and the control module 800 can operate to control the plating current according to a recipe created based on these optimal values.

[0068] Furthermore, the control module 800 may monitor the actual fluctuation range Wd of the plating voltage and, based on this monitoring, control the length of the current pause period T3 after the change, and / or the timing of changing the length of the current pause period T3, in real time. For example, the control module 800 can acquire the fluctuation range Wd of the plating voltage after each reverse current pulse from the sensor 130. The control module 800 monitors whether the acquired fluctuation range Wd of the plating voltage falls below a predetermined threshold, and when the fluctuation range Wd falls below the threshold, it changes the length of the current pause period T3 in the plating current from the length before the change to the shorter length after the change. In this case, the length of the current pause period T3 after the change may be a length determined by prior experiments as described above, or it may be a length determined in real time based on the current state of the plating apparatus 1000 or plating module 400 (e.g., type, temperature, concentration, etc. of the plating solution Ps) (or the state of the plating apparatus 1000 or plating module 400 from the current state to the present). The control module 800 may also individually adjust the length of the current pause period T3 after each reverse current pulse according to the fluctuation range Wd of the plating voltage acquired from the sensor 130. For example, the control module 800 may control the length of the current pause period T3 of the plating current in real time (for example, by feedback control) so that the fluctuation range Wd of the plating voltage is always constant (or within a predetermined range that can be considered substantially constant).

[0069] Furthermore, the control module 800 may change the stirring intensity of the plating solution Ps by the paddle 70 according to the fluctuation range Wd of the plating voltage obtained from the sensor 130. For example, in the example of Figure 11 described above, the stirring intensity in the latter half of the period P2 may be set weaker than the stirring intensity in the first half of the period P1. By weakening the stirring intensity, the diffusion of accelerator molecules in the plating solution Ps is suppressed. In other words, weakening the stirring intensity has the same effect as shortening the length of the current pause period T3 of the plating current. Therefore, by weakening the stirring intensity in the latter half of the period P2 in the example of Figure 11, the bump height can be made even more uniform.

[0070] While embodiments of the present invention have been described above based on several examples, the embodiments described above are intended to facilitate understanding of the present invention and do not limit it. The present invention can be modified and improved without departing from its spirit, and of course, its equivalents are included. Furthermore, any combination or omission of the components described in the claims and specification is possible to the extent that at least some of the above-mentioned problems can be solved or at least some of the effects can be achieved.

[0071] 1000 Plating apparatus 100 Load port 110 Transfer robot 120 Aligner 200 Pre-wet module 300 Pre-soak module 400 Plating module 500 Cleaning module 600 Spin rinse dryer 700 Transfer device 800 Control module 10 Plating tank 11 Anode 12 Ion resistor 16 Film 17a Anode chamber 17b Cathode chamber 18 Reference electrode 20 Overflow tank 30 Substrate holder 40 Rotation mechanism 45 Tilting mechanism 50 Lifting mechanism 60 Stirring mechanism 70 Paddle 80 Power supply 90 Plating solution flow mechanism 130 Sensor 801 Processor 802 Memory device 501 Seed layer 502 Photoresist layer 503 Bump

Claims

1. A plating apparatus for forming a plating film on a substrate, comprising: a substrate holder configured to hold the substrate; a plating tank configured to contain a plating solution together with the substrate holder; an anode disposed in the plating tank so as to face the substrate held by the substrate holder; a power supply configured to supply a plating current between the substrate and the anode; and a control unit, wherein the control unit is configured to output a plating current from the power supply having a repeating cycle of a forward current period in which a forward current is supplied from the plating solution to deposit metal onto the substrate, a reverse current period in which a reverse current pulse flowing in the opposite direction to the forward current is supplied, and a current pause period in which the current supply is paused during the transition from the reverse current pulse to the forward current; and the control unit is further configured to control the length of the current pause period so that the fluctuation range of the plating voltage after the supply of the reverse current pulse falls within a predetermined range.

2. The plating apparatus according to claim 1, wherein the fluctuation range of the plating voltage is the difference between the plating voltage immediately before each reverse current pulse is supplied and the minimum value of the plating voltage that occurs after the reverse current pulse is supplied, or the difference between the minimum value and the maximum value of the plating voltage that occurs after the minimum value.

3. The plating apparatus according to claim 1 or 2, wherein the plating treatment period for the substrate includes a first plating treatment period and a second plating treatment period that occurs later in time than the first plating treatment period, and the control unit controls the length of the current pause period in the second plating treatment period to be shorter than the length of the current pause period in the first plating treatment period.

4. The plating apparatus according to claim 3, wherein the control unit is further configured to monitor the fluctuation range of the plating voltage for each of the reverse current pulses and to switch from the first plating period to the second plating period based on the monitoring.

5. The plating apparatus according to claim 1 or 2, wherein the control unit is configured to monitor the fluctuation range of the plating voltage for each of the reverse current pulses and to individually adjust the length of the current pause period after each reverse current pulse according to the fluctuation range obtained by the monitoring.

6. The plating apparatus according to claim 1, further comprising a stirring mechanism for stirring the plating solution in the plating tank, wherein the control unit is further configured to change the stirring intensity by the stirring mechanism according to the fluctuation range of the plating voltage.

7. The plating apparatus according to claim 1, wherein the substrate has a metal seed layer and a shielding film that shields the metal seed layer from the plating solution in portions other than the bumps to be formed, such that the plating film formed on the substrate constitutes bumps.

8. The plating apparatus according to claim 7, wherein the shielding film has a pattern corresponding to a plurality of bumps of different diameters.

9. The plating apparatus according to claim 7 or 8, wherein the shielding film has a pattern in which a plurality of bumps to be formed are arranged at different densities.

10. A plating method for forming a plating film on a substrate, comprising: supplying a plating current between the substrate and the anode placed in a plating tank, the current having a repeating cycle of a positive current period in which a positive current is supplied from the plating solution in the plating tank to deposit metal onto the substrate, a reverse current period in which a reverse current pulse flowing in the opposite direction to the positive current is supplied, and a current pause period in which the current supply is paused during the transition from the reverse current pulse to the positive current; and controlling the length of the current pause period so that the fluctuation range of the plating voltage after the supply of the reverse current pulse falls within a predetermined range.

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