Plating apparatus and plating method

Abstract

A plurality of bumps are formed on a substrate with a uniform height. A plating apparatus for forming a plating film on a substrate, comprising: a substrate holder configured to hold the substrate; a plating bath configured to accommodate a plating solution together with the substrate holder; an anode disposed in the plating bath so as to face the substrate held by the substrate holder; a power source configured to supply a plating current between the substrate and the anode; and a control unit, wherein the control unit outputs a plating current having a repetition of a forward current period in which a forward current for depositing a metal on the substrate from the plating solution is supplied, a reverse current period in which a reverse current pulse flowing in a direction opposite to the forward current is supplied, and a current interruption period in which current supply is interrupted during the transition from the reverse current pulse to the forward current, from the power source, and the control unit is further configured to control the length of the current interruption period so that a fluctuation range of the plating voltage after the reverse current pulse is supplied falls within a predetermined range. A plating apparatus is provided.

Description

Technical Field

[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.

Background Art

[0002] A metal plating film such as Cu is formed on the surface of a substrate for a semiconductor device or an electronic element. For example, a substrate to be plated is held by a substrate holder, and the substrate together with the substrate holder may be immersed in a plating bath containing a plating solution to perform electroplating. The substrate holder holds the substrate so as to expose the plating surface of the substrate. In the plating solution, an anode is arranged so as to correspond to the exposed surface of the substrate, and a voltage is applied between the substrate and the anode to form an electroplating film on the exposed surface of the substrate.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is required to form a plurality of bumps on the substrate with a uniform height.

Means for Solving the Problems

[0006] According to one embodiment, there is provided an electroplating apparatus for forming a plating film on a substrate, comprising: a substrate holder configured to hold the substrate; a plating bath configured to accommodate a plating solution together with the substrate holder; an anode disposed in the plating bath 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. The control unit is configured to cause the power supply to output a plating current having a repetition of a forward current period in which a forward current for depositing a metal on the substrate from the plating solution is supplied, a reverse current period in which a reverse current pulse flowing in a direction opposite to the forward current is supplied, and a current pause period in which current supply is paused during the transition from the reverse current pulse to the forward current. The control unit is further configured to control the length of the current pause period so that a fluctuation range of the plating voltage after the reverse current pulse is supplied falls within a predetermined range.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9A

Figure 9B

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

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

[0009] FIG. 1 is a perspective view showing the overall configuration of the plating apparatus of the present embodiment. FIG. 2 is a plan view showing the overall configuration of the plating apparatus of the present 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.

[0010] The load port 100 is a module for loading a substrate stored in a cassette such as a FOUP (not shown in the plating apparatus 1000) into the plating apparatus 1000 or unloading the substrate from the plating apparatus 1000 to the cassette. In the present embodiment, four load ports 100 are arranged side by side in the horizontal direction, but the number and arrangement of the load ports 100 are arbitrary. The transfer robot 110 is a robot for transferring the substrate and is configured to transfer the substrate between the load port 100, the aligner 120, and the transfer device 700. When transferring the substrate between the transfer robot 110 and the transfer device 700, the transfer robot 110 and the transfer device 700 can transfer the substrate via a temporary placement table (not shown).

[0011] The aligner 120 is a module for aligning the positions of the orientation flat, notch, etc. of the substrate in a predetermined direction. In the present embodiment, two aligners 120 are arranged side by side in the horizontal direction, but the number and arrangement of the aligners 120 are arbitrary. The pre-wet module 200 wets the surface to be plated of the substrate before the plating process with a processing liquid such as pure water or degassed water, thereby replacing the air inside the pattern formed on the substrate surface with the processing liquid. The pre-wet module 200 is configured to perform a pre-wet process that makes it easier to supply the plating liquid inside the pattern by replacing the processing liquid inside the pattern with the plating liquid during plating. In the present embodiment, two pre-wet modules 200 are arranged one above the other in the vertical direction, but the number and arrangement of the pre-wet modules 200 are arbitrary.

[0012] The presoak module 300 is configured to perform a presoak process of etching and removing an oxide film with a large electrical resistance present on the surface of a seed layer formed on the surface to be plated of a substrate before plating, etc., with a processing solution such as sulfuric acid or hydrochloric acid, and cleaning or activating the plating base surface. In this embodiment, two presoak modules 300 are arranged side by side in the vertical direction, but the number and arrangement of the presoak modules 300 are arbitrary. The plating module 400 performs a plating process on the substrate. In this embodiment, there are two sets of 12 plating modules 400 arranged side by side in three in the vertical direction and four in the horizontal direction, and a total of 24 plating modules 400 are provided, but the number and arrangement of the plating modules 400 are arbitrary.

[0013] 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 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 by rotating it at high speed after the cleaning process. 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 transfer device 700 is a device for transferring the substrate between a plurality of modules in the plating apparatus 1000. The control module 800 is configured to control a plurality of modules of the plating apparatus 1000, and can be composed of, for example, a general computer or a dedicated computer having an input / output interface with an operator.

[0014] An example of a series of plating processes by the plating apparatus 1000 will be described. First, a substrate stored in a cassette is loaded into the load port 100. Subsequently, the transfer robot 110 takes out the substrate from the cassette of the load port 100 and transfers the substrate to the aligner 120. The aligner 120 aligns the positions of the substrate, such as the orientation flat and the notch, in a predetermined direction. The transfer robot 110 delivers the substrate whose direction has been aligned by the aligner 120 to the transfer device 700.

[0015] The transfer device 700 transfers the substrate received from the transfer robot 110 to the pre-wet module 200. The pre-wet module 200 performs a pre-wetting process on the substrate. The transfer device 700 transfers the substrate on which the pre-wetting process has been performed to the pre-soak module 300. The pre-soak module 300 performs a pre-soaking process on the substrate. The transfer device 700 transfers the substrate on which the pre-soaking process has been performed to the plating module 400. The plating module 400 performs a plating process on the substrate.

[0016] The transfer device 700 transfers the substrate on which the plating process has been performed to the cleaning module 500. The cleaning module 500 performs a cleaning process on the substrate. The transfer device 700 transfers the substrate on which the cleaning process has been performed to the spin rinse dryer 600. The spin rinse dryer 600 performs a drying process on the substrate. The transfer device 700 delivers the substrate on which the drying process has been performed to the transfer robot 110. The transfer robot 110 transfers the substrate received from the transfer device 700 to the cassette of the load port 100. Finally, the cassette storing the substrate is unloaded from the load port 100.

[0017] Note 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 in FIGS. 1 and 2.

[0018] Subsequently, the plating module 400 will be described. Since the plurality of plating modules 400 included in the plating apparatus 1000 according to the present embodiment have the same configuration, one plating module 400 will be described.

[0019] FIG. 3 is a schematic diagram showing the configuration of the plating module 400 in the plating apparatus 1000. Specifically, FIG. 3 schematically illustrates 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 a state in which the substrate Wf is immersed in the plating solution Ps.

[0020] The plating apparatus 1000 illustrated in FIGS. 3 and 4 is, for example, a type of plating apparatus (so-called cup type plating apparatus) that immerses a substrate Wf in a plating solution Ps with the surface direction of the substrate Wf being 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 that immerses the substrate Wf in the plating solution Ps with the surface direction of the substrate Wf being non-horizontal (for example, perpendicular to the ground).

[0021] The plating module 400 of the plating apparatus 1000 illustrated in FIGS. 3 and 4 includes a plating tank 10, an overflow tank 20, a substrate holder 30, and a paddle 70 as an example of a stirring mechanism 60. Further, as illustrated in FIG. 3, the plating module 400 includes a rotation mechanism 40, an inclination mechanism 45, and a lifting mechanism 50. Further, as illustrated in FIG. 3, the plating module 400 includes a sensor 130. Further, as illustrated in FIG. 4, the plating module 400 includes a power source 80 and a plating solution flow mechanism 90.

[0022] The plating tank 10 according to the present embodiment is configured by a bottomed container having an opening upward. Specifically, the plating tank 10 has a bottom wall 10a and an outer peripheral wall 10b extending upward from the outer peripheral edge of the bottom wall 10a, and the upper part of the outer peripheral wall 10b is open. Note that 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 the present embodiment has a cylindrical shape as an example. A plating solution Ps is stored inside the plating tank 10.

[0023] The plating solution Ps may be a solution containing ions of a metal element constituting the plating film, and specific examples thereof are not particularly limited. In the present embodiment, as an example of the plating process, copper plating is used, and as an example of the plating solution Ps, a copper sulfate solution is used. Further, the plating solution Ps may contain a predetermined additive.

[0024] As an additive contained in 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) or the like can be used.

[0025] 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, as an example of the anode 11, an insoluble anode is used. The specific type of this insoluble anode is not particularly limited, and platinum, iridium oxide, or the like can be used.

[0026] As illustrated in FIGS. 3 and 4, an ion resistor 12 may be disposed above the anode 11 inside the plating tank 10. Specifically, as illustrated in a partially enlarged view of FIG. 4, the ion resistor 12 is constituted by a porous plate member having a plurality of holes 12a (fine holes). The holes 12a are provided so as to communicate the lower surface and the upper surface of the ion resistor 12.

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

[0028] As illustrated in FIGS. 3 and 4, inside the plating tank 10, a film 16 may be disposed at a location above the anode 11 and below the ion resistor 12. In this case, the inside of the plating tank 10 is partitioned 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 disposed in the anode chamber 17a, and the ion resistor 12 and the substrate Wf are disposed in the cathode chamber 17b. The film 16 is configured to allow ion species including metal ions contained in the plating solution Ps to pass through the film 16 while suppressing the passage of non-ion-based plating additives contained in the plating solution Ps through the film 16. As such a film 16, for example, an ion exchange membrane can be used.

[0029] As illustrated in FIG. 4, the plating solution flow mechanism 90 is configured to flow the plating solution Ps in the plating tank 10. By flowing the plating solution Ps in the plating tank 10, the plating solution Ps in the plating tank 10 is agitated. The plating solution flow mechanism 90 according to the present 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 communicates with the anode chamber 17a via a pipe 92a. The second flow mechanism 91b communicates with the cathode chamber 17b via a pipe 92b. Note that the first flow mechanism 91a and the second flow mechanism 91b each include a pump or the like for pumping the plating solution Ps.

[0031] Referring to FIGS. 3 and 4, the plating bath 10 is provided with a supply port for supplying the plating solution Ps to the plating bath 10. Specifically, on the outer peripheral wall 10b of the plating bath 10 according to the present embodiment, there are provided 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 then supplied again from the first supply port 13a to the anode chamber 17a.

[0032] The overflow tank 20 is constituted by a bottomed container disposed outside the plating bath 10. The overflow tank 20 is provided for temporarily storing the plating solution Ps that has exceeded the upper end of the outer peripheral wall 10b of the plating bath 10 (that is, the plating solution Ps that has overflowed from the plating bath 10). The plating solution Ps stored in the overflow tank 20 is discharged from the second discharge port 14b and then pumped by the second flow mechanism 91b and supplied again from the second supply port 13b to the cathode chamber 17b.

[0033] The substrate holder 30 holds the substrate Wf as a cathode such that the plated surface Wfa of the substrate Wf faces the anode 11. In the present embodiment, the plated surface Wfa of the substrate Wf is specifically provided on the surface (lower surface) facing the lower side of the substrate Wf.

[0034] The substrate holder 30 is connected to the rotation mechanism 40. The rotation mechanism 40 is a mechanism for rotating the substrate holder 30. As an example, the substrate holder 30 rotates in the rotation direction R1 illustrated in FIG. 3 by the drive of the rotation mechanism 40. As the rotation mechanism 40, a known rotation motor or the like can be used. The tilting 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 moving the substrate holder 30, the rotation mechanism 40, and the tilting mechanism 45 up and down in the vertical direction. As the lifting mechanism 50, a known lifting mechanism such as a direct-acting actuator can be used.

[0035] The control module 800 includes a microcomputer, which includes a processor 801, a storage device 802 as a non-temporary storage medium, and the like. The control module 800 controls the operation of the plating module 400 by operating the processor 801 based on the 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 referred to instead of the anode 11 when detecting the voltage or the fluctuation width of the voltage. The specific arrangement 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] FIG. 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 an embodiment of the present invention. A thin metal seed layer 501 is previously formed on the entire surface of the substrate Wf, and the surface of the substrate Wf is powered 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 a portion where bumps are to be formed. The substrate Wf on which the photoresist layer 502 is formed in this way is held by a substrate holder 30 and immersed in a plating solution Ps in a plating bath 10, and plating is performed. During plating, portions of the surface of the substrate Wf other than the opening 502a of the photoresist layer 502 are shielded from the plating solution Ps by the photoresist layer 502. Thereby, a plating film grows only on the bottom surface of the opening 502a of the photoresist layer 502, and bumps 503 are formed on the substrate Wf. Note that the photoresist layer 502 is removed after the plating process (see the right side of FIG. 5).

[0042] A number of such bumps 503 are formed on the substrate Wf using a photoresist layer 502 having a predetermined opening pattern. FIG. 6 is a schematic diagram showing an example of the opening pattern of the photoresist layer 502 used to form a plurality of bumps 503. In the opening pattern shown in FIG. 6, openings 502a having a small opening diameter φ (see FIG. 5) are arranged at a high density in a pattern region P1, openings 502a having a small opening diameter φ are arranged at a low density (i.e., sparsely) in a pattern region P2, openings 502a having a large opening diameter φ are arranged at a high density in a pattern region P3, and openings 502a having a large opening diameter φ are arranged at a low density in a pattern region P4.

[0043] Depending on the size of the openings (i.e., the opening diameter) and the density of the openings (i.e., the number of openings per unit area) provided in the photoresist layer 502, even for the same substrate Wf, the height (film thickness) of the bumps 503 formed in each opening may vary. Therefore, it is required to form a plurality of bumps 503 on the substrate Wf with a uniform height.

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

[0045] In a period T2 following the forward current period T1, the power supply 80 outputs a current in a direction opposite to the above-mentioned forward current (hereinafter, the period T2 is referred to as the reverse current period). The current maintains a current value I2 with a sign different from that of I1 during the reverse current period T2. The length of the reverse current period T2 is a time of an extremely short length compared to the forward current period T1. Therefore, the current in the reverse current period T2 is in a pulse shape, and hereinafter, this is referred to as a "reverse current pulse" in this specification. For example, the length of the reverse current period T2, that is, the pulse width of the reverse current pulse, may be about 0.1 second to several seconds. In the reverse current period T2, contrary to the reduction reaction of metal ions in the forward current period T1, a part of the metal of the plating film formed on the plating surface Wfa in the forward current period T1 redissolves into the plating solution Ps, and an accelerator (one of the additives contained in the plating solution Ps) attached to the outermost surface of the plating film during the reduction reaction detaches from the plating film surface.

[0046] Note that it is desirable to set the current value I2 of the reverse current pulse to a value such that the detachment of the accelerator is sufficiently performed. Also, when setting the current value I2 equal to the current value I1, instead of the power supply 80 that outputs with both positive and negative polarities as described above, a combination of a power supply that outputs with a single polarity and a polarity inversion switch that can invert the polarity of the output of the power supply may be used.

[0047] Furthermore, in a period T3 following the reverse current period T2, the power supply 80 stops current output (hereinafter, the period T3 is referred to as the current pause period). That is, in the current pause period T3, the current does not flow in 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 a time of an extremely short length compared to the forward current period T1, and may be, for example, about several seconds in length.

[0048] After the current pause period T3, the power supply 80 again transitions to the forward current period T1 during which it outputs a forward current (current value I1). Similarly hereinafter, the forward current period T1, the reverse current period T2, and the current pause period T3 are sequentially repeated in this order. The repetition of these three periods T1, T2, and T3 continues until a predetermined plating process time ends, for example, until the thickness of the formed plating film reaches a predetermined target thickness.

[0049] By performing a plating process on the substrate Wf using such a plating current having repetitions of the forward current period T1, the reverse current period T2, and the current pause period T3, it is possible to make the heights of a plurality of bumps 503 formed on the substrate Wf uniform (see Patent Document 1). The reason for the uniformization of the bump height has already been described in Patent Document 1, but for the sake of better understanding of the present invention, it will be described again here with reference to FIG. 8.

[0050] FIG. 8 is a conceptual diagram for explaining the principle by which the uniformity of the heights of a plurality of bumps 503 is improved by using the plating current as described above. On the plating surface Wfa of the substrate Wf, at locations where the diameter of the opening 502a of the photoresist layer 502 is large and where the arrangement density of the openings 502a is low (for example, the pattern region P4 in FIG. 6), compared to other locations (for example, the pattern region P1), metal ions are more easily replenished into the opening 502a, so the formation rate of the plating film is high. Therefore, if no reverse current pulse is supplied, during the period when the forward current is supplied (that is, during the forward current period T1), the plating film thickness at locations where the opening diameter is large and / or the opening density is low becomes thicker than the plating film thickness at locations where the opening diameter is small and / or the opening density is high (stage (A) in FIG. 8).

[0051] Here, in the plating solution Ps, as one of the additives, an accelerator (such as SPS (bis(3-sulfopropyl) disulfide), etc.) having an action of promoting the formation of the plating film is included. Such accelerator molecules are concentrated and adsorbed at a constant density regardless of the location on the surface of the plating film, and promote the reduction reaction of metal ions. In the reverse current period T2 when a reverse current pulse is supplied, the accelerator molecules desorb from the surface of the plating film and diffuse into the inside of the opening 502a and the vicinity thereof. At this time, since the accelerator molecules were originally concentrated and adsorbed at a constant density on the surface of the plating film, the local concentration of the accelerator molecules that have desorbed from the surface of the plating film inside each individual opening 502a is constant (stage (B) in FIG. 8).

[0052] However, in a place where the opening density is high, since there are similarly desorbed accelerator molecules in the neighboring openings 502a, the concentration gradient of the accelerator molecules in the vicinity of these plurality of openings 502a is small. Therefore, among these accelerator molecules, the number of molecules that diffuse far away from the opening 502a is relatively small, and a large number of accelerator molecules remain near the opening 502a. On the other hand, in a place where the opening density is low, since the influence from the neighboring openings 502a is small, the concentration gradient of the accelerator molecules in the vicinity of the plurality of openings 502a is large. Therefore, most of the accelerator molecules that have desorbed from the plating film diffuse far away, and only a small number of accelerator molecules remain near the opening 502a. As a result, during the current pause period T3 when no current flows in the plating solution Ps, in the vicinity of the opening 502a in a place where the opening density is high, the average concentration of the accelerator molecules is higher than that in the vicinity of the opening 502a in a place where the opening density is low. That is, due to the difference in the opening density, a difference occurs in the average concentration of the accelerator molecules. Also, the difference in the size of the opening 502a creates a similar concentration difference of the accelerator molecules (since the larger the opening diameter, the easier it is for the accelerator molecules to diffuse outside the opening 502a, the concentration of the accelerator molecules is lower near the opening 502a with a larger diameter).

[0053] Thus, since the concentration of accelerator molecules in the vicinity of the opening 502a varies according to the structure (i.e., diameter and arrangement density) of the opening 502a where the plating film is formed, when a positive current is supplied again after the current pause period T3, the amount of accelerator molecules re-adsorbed on the surface of the plating film in the opening 502a will vary depending on the location. Specifically, at locations where the opening diameter is large and / or the opening density is low, the amount of re-adsorbed accelerator molecules is relatively small, and at locations where the opening diameter is small and / or the opening density is high, the amount of re-adsorbed accelerator molecules is relatively large (stage (C) in FIG. 8).

[0054] And as described above, the desorption of the accelerator occurs uniformly (stage (B)), so when looking at the overall process from desorption to re-adsorption, the density (or amount) of accelerator molecules that are re-adsorbed and present on the surface of the plating film will be relatively small at the opening 502a arranged at locations where the opening diameter is large and / or the opening density is low, and relatively large at the opening 502a arranged at locations where the opening diameter is small and / or the opening density is high. Therefore, on the surface of the plating film at locations where the opening diameter is small and / or the opening density is high, the action of the accelerator becomes greater than at locations where the opening diameter is large and / or the opening density is low, and the plating rate increases (stage (D) in FIG. 8). As a result, the film thickness difference due to the location of the initially existing plating film (see stage (A)) is compensated, and as a result, regardless of the difference in the structure of the opening 502a, the film thickness of the plating film (i.e., bump 503) formed in the opening 502a is made uniform (stage (E) in FIG. 8).

[0055] As can be understood from the above description, in order to equalize the height of the bump 503, it is important to create a density difference depending on the location for the accelerator molecules re-adsorbed after desorption. And this density difference, as described above, is due to the extent to which the desorbed accelerator molecules diffuse away from the plating film during the reverse current period T2 and the current pause period T3 varying depending on the location (i.e., depending on the size and arrangement density of the opening 502a).

[0056] Here, as the plating treatment time for the substrate Wf elapses and the thickness of the plating film formed on the substrate Wf (i.e., the height of the bump 503) increases, the depth from the surface of the photoresist layer 502 to the surface of the plating film gradually becomes shallower within the opening 502a of the photoresist layer 502. Then, the accelerator molecules detached from the surface of the plating film become more likely to diffuse out from the inside of the opening 502a, so the re-adsorption amount of the accelerator molecules becomes less, and the density difference due to the location of the accelerator molecules near the opening 502a formed as a result of diffusion, and thus the density difference due to the location of the accelerator molecules re-adsorbed after desorption, gradually becomes smaller. As a result, the effect of equalizing the bump height by the reverse current pulse and the current pause will gradually weaken as the plating treatment time elapses.

[0057] FIG. 9A is a graph showing the time waveform for one cycle of the plating voltage observed when plating is performed using the plating current as shown in FIG. 7 in the plating apparatus 1000 according to an embodiment of the present invention. The plating voltage can be measured 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 by the sensor 130 as described above. As shown in FIG. 9A, when a reverse current pulse is supplied during the plating process, due to the subsequent re-adsorption of the accelerator onto the substrate Wf, the plating voltage decreases and a minimum value occurs in the voltage. Such a time change in the plating voltage is caused by a change in the adsorption state of the additives (accelerator and inhibitor) on the plating film surface, resulting in a change in the electrical resistance (polarization resistance) of the surface of the cathode, i.e., the plating film surface.

[0058] Specifically, as shown in FIG. 9A, the plating voltage changes from the positive voltage V1 to the negative voltage V0 by the application of a reverse current pulse, and then becomes a voltage higher than the original voltage value V1 once again by flowing a forward current after the current pause. At this point, that is, immediately after the application of the forward current, almost no accelerator is re-adsorbed on the surface of the plating film, and the re-adsorption of the accelerator gradually proceeds from this state. Therefore, the electrical resistance of the plating film surface gradually decreases, and thus the plating voltage decreases. Thereafter, in addition to the accelerator, the inhibitor also starts to be adsorbed, and the inhibitory effect of the inhibitor on the formation of the plating film becomes stronger. Then, the plating voltage turns from a decrease to an increase with V2 as the extreme value, and gradually increases toward the voltage value V1 corresponding to the forward current.

[0059] In this specification, the difference between the plating voltage V1 immediately before the supply of the reverse current pulse and the minimum value V2 of the plating voltage generated after the supply of the reverse current pulse is defined as the variation width Wd of the plating voltage. Note that depending on the type of additive contained in the plating solution Ps and the opening pattern of the photoresist layer 502 on the substrate Wf, the plating voltage may show a time waveform as shown in FIG. 9B. In the case of the time waveform as shown in FIG. 9B, the variation width Wd of the plating voltage 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 FIG. 9A, or alternatively, 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 generated after the minimum value.

[0060] As described above, the magnitude of the minimum value V2 of the plating voltage generated after the supply of the reverse current pulse (i.e., the depth of the depression in the voltage waveform) depends on the re-adsorption amount of the accelerator molecules, and the re-adsorption amount of the accelerator molecules decreases as the plating treatment time elapses. And thereby, the effect of height uniformity of the bumps in the case of performing the plating treatment using the plating current as shown in FIG. 7 gradually becomes smaller as the plating treatment time elapses.

[0061] FIG. 10 is a graph showing an example of a time waveform over a plurality of cycles of the plating voltage, which is observed when plating treatment is performed using the plating current as shown in FIG. 7 in the plating apparatus 1000 according to an embodiment of the present invention. In the example of FIG. 10, the lengths of the forward current period T1, the reverse current period T2, and the current pause period T3 in each cycle are kept constant over the entire period of the plating current. As shown in this figure, as time passes, the minimum value V2 (the depression in the voltage waveform) of the plating voltage becomes shallower, and the fluctuation width Wd becomes smaller. Along with this, the effect of height uniformity of the bumps also becomes smaller.

[0062] Therefore, in order to maintain the effect of height uniformity of the bumps until the plating treatment of the substrate Wf is completed, it is necessary to ensure that the fluctuation width 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 an 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, (even when the plating progresses and the depth from the surface of the photoresist layer 502 to the surface of the plating film becomes shallower), excessive diffusion of the accelerator molecules detached from the surface of the plating film is prevented. As a result, a decrease in the amount of re-adsorption of the accelerator molecules when a forward current is applied again can be suppressed. Thereby, the density difference due to the location of the re-adsorbed accelerator molecules is stably formed until the end of the plating treatment, and thus further height uniformity of the bumps can be achieved.

[0063] FIG. 11 is a graph showing an example of a time waveform over a plurality of cycles of the plating voltage when the control module 800 of the plating apparatus 1000 according to an embodiment of the present invention controls the length of the current pause period T3. In the example of FIG. 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, similar to the case of the example of FIG. 10. However, the length t halt of the current pause period T3 is the first time length t long (for example, t longis set to be ≥5 seconds), and in the latter period P2, the first time length t long is shorter than the second time length t short (for example, 0 seconds ≤ t short <5 seconds). The switching timing from the first half period P1 to the second half period P2 is selected so that the fluctuation width Wd of the plating voltage does not fall below a predetermined constant value. As shown in FIG. 11, during the first half period P1, the fluctuation width Wd of the plating voltage gradually decreases, but by changing the length of the current interruption period T3 to a shorter second time length t short in the second half period P2, the fluctuation width Wd of the plating voltage that has once decreased increases again. As a result, a plating process with better bump height uniformity is realized compared to the case of the example in FIG. 10.

[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 interruption period T3 is controlled by the control module 800 of the plating apparatus 1000 according to an embodiment of the present invention. The example in FIG. 12 is different from the example in FIG. 11 only in that the plating process period consists of three periods: the first half period P1, the intermediate period P2, and the second half period P3. In the example of FIG. 12, the length t halt of the current interruption period T3 is the first time length t long (for example, t long ≥5 seconds) in the first half period P1, the 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 the 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 timing from the first half period P1 to the intermediate period P2 and from the intermediate period P2 to the second half period P3 is selected so that the fluctuation width Wd of the plating voltage does not fall below a predetermined constant value, respectively. Also in this example, by gradually changing the length of the current interruption 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 period P1 to P3. Therefore, similar to the case of FIG. 11, a plating process with better bump height uniformity is realized.

[0065] In FIGS. 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 gradually decreases for these multiple divided periods. The plating current may be controlled such that the length of the current pause period T3 gradually decreases for each cycle of the plating current (i.e., the period composed of one set of the forward current period T1, the reverse current period T2, and the current pause period T3) consisting of the repetition of the forward current period T1, the reverse current period T2, and the current pause period T3.

[0066] Note that the magnitude of the minimum value V2 of the voltage waveform (e.g., the first minimum value in the latter half period P2 in the example of FIG. 11) that appears immediately after changing the length of the current pause period T3 can vary depending on the length of the changed current pause period T3 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 the accelerator molecules becomes too large this time, and the minimum value V2 (the dent in the voltage waveform) of the plating voltage becomes deeper. In this case, the effect of compensating for the film thickness difference depending on the location of the plating film (see stage (D) in FIG. 8) becomes excessive, and as a result, the uniformity of the bump height is also impaired. Also, the same applies when the timing of changing the length of the current pause period T3 is too early (i.e., when the length of the current pause period T3 is changed while the dent in the voltage waveform is still sufficiently deep) because the amount of re-adsorption of the accelerator molecules increases too much. Therefore, there are both an appropriate lower limit value and an upper limit value required to equalize the bump height for the minimum value V2 (or the fluctuation width Wd) of the plating voltage.

[0067] Therefore, it is advantageous to select the length after the change of the current pause period T3 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 a predetermined appropriate lower limit value and upper limit value. For example, it is possible to determine the optimum values of the length of such a current pause period T3 and the change timing by an experiment using a sample substrate for evaluation in advance, and the control module 800 can operate to control the plating current according to a recipe created based on those optimum values.

[0068] Also, the actual fluctuation range Wd of the plating voltage may be monitored, and based on the monitoring, the length after the change of the current pause period T3 and / or the timing of changing the length of the current pause period T3 may be controlled in real time. For example, the control module 800 can obtain the fluctuation range Wd of the plating voltage after each reverse current pulse from the sensor 130. The control module 800 monitors whether the obtained fluctuation range Wd of the plating voltage falls below a predetermined threshold value, and at the timing when the fluctuation range Wd falls below the threshold value, changes the length of the current pause period T3 in the plating current from the length before the change to a shorter length after the change. At this time, the length after the change of the current pause period T3 may be the length determined by a prior experiment as described above, or may be a length determined in real time based on the state of the current plating apparatus 1000 or plating module 400 (for example, the type, temperature, concentration, etc. of the plating solution Ps). Also, the control module 800 may 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 obtained 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 at any time (for example, by feedback control) so that the fluctuation range Wd of the plating voltage always takes a constant value (or a value within a predetermined range that can be regarded as 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 width Wd of the plating voltage acquired from the sensor 130. For example, in the example of FIG. 11 described above, the stirring intensity in the latter half period P2 may be set weaker than the stirring intensity in the former half period P1. By weakening the stirring intensity, the diffusion of accelerator molecules in the plating solution Ps is suppressed. That is, 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 period P2 of the example of FIG. 11, the bump height can be further equalized.

[0070] As described above, embodiments of the present invention have been described based on several examples. However, the above-described embodiments of the invention are for facilitating the understanding of the present invention and do not limit the present invention. The present invention can be changed and improved without departing from its gist, and it goes without saying that equivalents of the present invention are included. In addition, within the scope of being able to solve at least a part of the above-described problems or achieving at least a part of the effects, any combination or omission of each component described in the claims and the specification is possible.

Description of Reference Numerals

[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 Membrane 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 bath configured to accommodate a plating solution together with the substrate holder; an anode disposed in the plating bath so as to face the substrate held by the substrate holder; a power source configured to supply a plating current between the substrate and the anode; a control unit; the control unit is configured to cause the power source to output a plating current having a repetition of a forward current period in which a forward current for depositing a metal on the substrate from the plating solution is supplied, a reverse current period in which a reverse current pulse flowing in a direction opposite to the forward current is supplied, and a current interruption period in which current supply is interrupted during the transition from the reverse current pulse to the forward current; the control unit is further configured to control the length of the current interruption period so that a variation range of the plating voltage after the reverse current pulse is supplied falls within a predetermined range; a plating apparatus.

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

3. The plating process period for the substrate includes a first plating process period and a second plating process period that is temporally later than the first plating process period; the control unit controls the length of the current interruption period in the second plating process period to be shorter than the length of the current interruption period in the first plating process period, according to claim 1 or 2.

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

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

6. further comprising a stirring mechanism for stirring the plating solution in the plating bath The plating apparatus according to claim 1, 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 a portion other than the bumps to be formed, such that a plating film formed on the substrate constitutes the bumps.

8. The plating apparatus according to claim 7, wherein the shielding film has a pattern corresponding to a plurality of bumps having 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 having a repetition of a forward current period in which a forward current for depositing metal on the substrate from the plating solution in the plating tank is supplied between the substrate disposed in the plating tank and the anode, a reverse current period in which a reverse current pulse flowing in a direction opposite to the forward current is supplied, and a current pause period in which current supply is paused during the transition from the reverse current pulse to the forward current; controlling the length of the current pause period so that the fluctuation range of the plating voltage after the reverse current pulse is supplied falls within a predetermined range; The plating method includes the above steps.

Images