BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an electroplating method for simultaneously plating both the face and reverse sides of a substrate which has a through-hole vertically penetrating in its interior to fill a plated film of metal such as copper or the like into the through-hole.
2. Description of the Related Art
A technique of forming a plurality of through-vias of a metal, vertically penetrating through a substrate, is known as a method to electrically connect the layers of a multi-layer stack of substrates such as semiconductor substrates. It is customary to make vertical through-vias in a substrate by simultaneously plating both the face and reverse sides of a substrate, which has through-holes vertically penetrating in its interior, thereby to fill a plated film of metal into the through-holes.
There is known an electroplating apparatus for producing through-vias (see Japanese Patent No. 4138542). This electroplating apparatus includes a substrate holder for holding a substrate while exposing certain areas on its face and reverse sides and sealing peripheral areas around the certain areas, and a pair of anodes disposed in facing relation to the face and reverse sides, respectively, of the substrate that is held by the substrate holder. The substrate held by the substrate holder and the anodes are immersed in a plating solution, and then voltages are applied between the substrate and the anodes to simultaneously plate the face and reverse sides of the substrate, which has vertical through-holes defined therein, embedding metal such as copper in the through-holes.
FIGS. 1A through 1D are diagrams illustrating, in a sequence of process steps, a process for filling a plated film into a through-hole defined in a substrate to form a through-via therein (see Japanese Patent No. 4248353).
As shown in FIG. 1A, a substrate W is prepared which includes a base 100 with a vertical through-hole 100a defined therein, and a barrier layer 102 made of Ti or the like and a seed layer 104, as an electric feed layer, which cover all the surfaces of the base 100 including inner surfaces of the through-hole 100a. The face and reverse sides of the substrate W are simultaneously plated to deposit a plated film 106 of metal such as copper or the like on the face and reverse sides of the substrate W and in the through-hole 100a, as shown in FIG. 1B. The plated film 106 in the through-hole 100a has its maximum thickness at its center along the in-depth direction thereof. Then, as shown in FIG. 1C, the plated film 106 is grown until the tip ends of layers of the plated film 106 that have grown from the wall surfaces of the through-hole 100a are joined to each other at the center of the through-hole 100a along the in-depth direction thereof. The center of the through-hole 100a along the in-depth direction thereof is thus blocked by the plated film 106, forming recesses 108 above and below the closed region. The plating process is further continued to grow the plated film 106 in the recesses 108 until the recesses 108 are filled up with the plated film 106, as shown in FIG. 1D. In this manner, a through-via made up of the plated film 106 is produced in the substrate W.
There has been proposed an electroplating method for filling through-holes defined in a substrate with a plated film of metal (see Japanese Patent Laid-Open Publication No. 2008-513985). According to this electroplating method, a forward pulsed current is supplied to flow between a substrate as a cathode and an anode, and a reverse pulsed current, which flows in an opposite direction to the forward pulsed current, is also is supplied to flow between the substrate and the anode, for thereby fully or substantially fully filling the center of the through-hole.
There has also been proposed a method to prevent whiskers from being generated in plating a printed wiring substrate or the like with copper (see Japanese Patent Laid-Open Publication No. 2010-95775). According to this method, a DC power source for applying a DC voltage between a cathode and an anode has its polarity reversible. The printed wiring substrate is electroplated alternately under a normal DC voltage and a reversed DC voltage, i.e., alternately in a normal electrolyzing cycle in which the printed wiring substrate serves as a cathode and a reverse electrolyzing cycle in which the printed wiring substrate serves as an anode.
SUMMARY OF THE INVENTION In order to form a through-via in the form of a plated film free of defects such as voids or the like therein in a substrate, as shown in FIGS. 1A through 1D, it is ideal that the plated film be grown preferentially at the center of the through-hole along the in-depth direction thereof until the center of the through-hole 100a is blocked by the plated film 106, and then the plating process be further continued. However, it is generally practically difficult to attempt to meet the ideal requirements and at the same time to fill the plated film efficiently into the through-hole to shorten the time required to perform the plating process. Stated otherwise, the conventional electroplating processes have failed to achieve both the ideal filling of the plated film into the through-hole and the efficient filling of the plated film into the through-hole with a higher average plating current during plating.
The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide an electroplating method for efficiently filling a plated film into a through-hole with a higher average plating current during plating to shorten the time required to perform the plating process and also ideally filling the plated film into the through-hole.
In order to achieve the above object, the present invention provides an electroplating method comprising: immersing a substrate with a through-hole defined therein in a plating solution in a plating tank; disposing a pair of anodes in the plating solution in the plating tank in facing relation to face and reverse sides, respectively, of the substrate in the plating solution; performing a plurality of plating processes, each for a predetermined period, on the face and reverse sides of the substrate by supplying pulsed currents respectively between the face side of the substrate and one of the anodes which faces the face side of the substrate, and between the reverse side of the substrate and the other of the anodes which faces the reverse side of the substrate; and performing a reverse electrolyzing process on the face and reverse sides of the substrate between adjacent ones of the plating processes by supplying currents in an opposite direction to the pulsed currents in the plating processes respectively between the face side of the substrate and one of the anodes which faces the face side of the substrate, and between the reverse side of the substrate and the other of the anodes which faces the reverse side of the substrate.
Since the plural plating processes are performed, each for a predetermined period, on the face and reverse sides of the substrate by supplying pulsed currents respectively between the face side of the substrate and one of the anodes which faces the face side of the substrate, and between the reverse side of the substrate and the other of the anodes which faces the reverse side of the substrate, it is possible to fill a plated film into the through-hole efficiently with an increased average current value for thereby shortening a period of time required to plate the substrate. The reverse electrolyzing process performed between the plating processes is effective to dissolve plated films deposited on corners of the through-hole. Therefore, it is possible to ideally fill the plated film into the through-hole by growing the plated film preferentially at the center of the through-hole along the in-depth direction thereof.
In a preferred aspect of the present invention, each of the pulsed currents comprises a PR pulsed current represented by an alternate repetition of a current flowing in a forward direction and a current flowing in a reverse direction.
The reverse electrolyzing process is repeatedly performed between the plating processes using the PR pulsed currents, thereby preventing fine irregularities from being produced by an abnormal deposition on microscopic surfaces of the plated film and hence preventing fine voids from being formed in the plated film due to such fine irregularities.
In a preferred aspect of the present invention, each of the pulsed currents comprises an on/off pulsed current represented by an alternate repetition of the supply and non-supply of a plating current which flows in a forward direction.
Since the on/off pulsed current provides non-plating periods for supplying no plating current in the plating process, the metal ion concentration in the plating solution within the through-hole is recovered in the non-plating period for thereby preventing defects such as voids or the like from being formed in the plated film.
In a preferred aspect of the present invention, each of the pulsed currents comprises a composite pulsed current represented by a combination of two pulsed currents having different current values.
Since the plated film is continuously grown in the plating process with the composite pulsed current, the plated film is prevented from being dissolved into the plating solution in the plating process.
In a preferred aspect of the present invention, the plating processes together with the reverse electrolyzing process are performed to gradually increase an average current density as the substrate is progressively plated.
As the through-hole is gradually filled with the plated film in the plating process, the substantive aspect ratio of the through-hole changes. When the substantive aspect ratio of the through-hole changes, it is possible to efficiently fill the plated film into the through-hole in a manner to match the changing substantive aspect ratio by increasing the average current density in the plating process. Consequently, the period of time required to plate the substrate can be further shortened.
In a preferred aspect of the present invention, the reverse electrolyzing process is performed a plurality of times before and after a normal electrolyzing cycle in which a pulsed current is supplied in the forward direction.
The reverse electrolyzing process is performed with a negative cathode current density in the range from −30 to −40 ASD at a pulse pitch in the range from 0.1 to 10 ms, for example. Depending on the aspect ratio of a through-hole defined in the substrate, it may not be possible to ideally fill a plated film preferentially at the center of the through-hole in the in-depth direction thereof according to a reverse electrolyzing process at a pulse pitch that is shorter than 1.0 ms. However, if the reverse electrolyzing process is repeatedly performed a plurality of times at a pulse pitch shorter than 1.0 ms before and after a normal electrolyzing cycle in which a pulsed current is supplied in the forward direction, then it is possible to ideally fill a plated film into such a through-hole.
According to the present invention, as described above, the plural plating processes are performed, each for a predetermined period, on the face and reverse sides of the substrate by supplying pulsed currents respectively between the face side of the substrate and one of the anodes which faces the face side of the substrate, and between the reverse side of the substrate and the other of the anodes which faces the reverse side of the substrate. Accordingly, it is possible to fill a plated film into the through-hole efficiently with an increased average current value for thereby shortening a period of time required to plate the substrate. The reverse electrolyzing process performed between the plating processes is effective to dissolve plated films deposited on corners of the through-hole. Therefore, it is possible to ideally fill the plated film into the through-hole by growing the plated film preferentially at the center of the through-hole along the in-depth direction thereof.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A through 1D are diagrams illustrating, in a sequence of process steps, a process for filling a plated film into a through-hole defined in a substrate to form a through-via therein;
FIG. 2 is a vertical sectional front view schematically showing an electroplating apparatus which is used to carry out an electroplating method according to the present invention;
FIG. 3 is a front view of a substrate holder of the electroplating apparatus shown in FIG. 2;
FIG. 4 is a plan view of the substrate holder of the electroplating apparatus shown in FIG. 2;
FIG. 5 is a bottom view of the substrate holder of the electroplating apparatus shown in FIG. 2;
FIG. 6 is a cross-sectional view taken along line K-K of FIG. 3;
FIG. 7 is a view of the substrate holder as viewed along the arrow A in FIG. 6;
FIG. 8 is a view of the substrate holder as viewed along the arrow B in FIG. 6;
FIG. 9 is a view of the substrate holder as viewed along the arrow C in FIG. 6;
FIG. 10 is a cross-sectional view taken along line D-D of FIG. 7;
FIG. 11 is a cross-sectional view taken along line E-E of FIG. 7;
FIG. 12 is a cross-sectional view taken along line F-F of FIG. 3;
FIG. 13 is a cross-sectional view taken along line G-G of FIG. 7;
FIG. 14 is a cross-sectional view taken along line H-H of FIG. 8;
FIG. 15 is a front view of an anode holder, which is holding an insoluble anode therein, of the electroplating apparatus shown in FIG. 2;
FIG. 16 is a cross-sectional view of the anode holder, which is holding the insoluble anode therein, of the electroplating apparatus shown in FIG. 2;
FIG. 17 is an enlarged cross-sectional view of the main portion of another substrate holder;
FIG. 18 is an enlarged cross-sectional view of the main portion of the substrate holder shown in FIG. 17;
FIG. 19 is an enlarged cross-sectional view of the main portion of the substrate holder shown in FIG. 17;
FIG. 20 is a graph showing the relationship between the cathode current density and time for an example of a plating current that is supplied between a substrate surface and an anode;
FIG. 21 is an enlarged fragmentary cross-sectional view showing the manner in which a plated film is grown preferentially at the center of a through-hole along the in-depth direction thereof when a reverse electrolyzing process is performed after a plating process;
FIG. 22 is an enlarged fragmentary cross-sectional view schematically showing the manner in which fine irregularities are produced by an abnormal deposition on microscopic surfaces of the plated film in the plating process;
FIG. 23 is a graph showing the relationship between the cathode current density and time for another example of a plating current that is supplied between a substrate surface and an anode;
FIGS. 24A and 24B are enlarged fragmentary cross-sectional views schematically showing the manner in which a plated film embedded in a through-hole is excessively dissolved into the plating solution until finally voids are formed in the plated film;
FIG. 25 is a graph showing the relationship between the cathode current density and time for still another example of a plating current that is supplied between a substrate surface and an anode;
FIG. 26 is a graph showing the relationship between the cathode current density and time for yet another example of a plating current that is supplied between a substrate surface and an anode;
FIG. 27 is a graph showing the relationship between the cathode current density and time for yet still another example of a plating current that is supplied between a substrate surface and an anode;
FIG. 28 is a graph showing the relationship between the cathode current density and time for a further example of a plating current that is supplied between a substrate surface and an anode;
FIG. 29 is a graph showing the relationship between the cathode current density and time for a still further example of a plating current that is supplied between a substrate surface and an anode;
FIG. 30 is a graph showing the relationship between the cathode current density and time for a yet further example of a plating current that is supplied between a substrate surface and an anode;
FIG. 31 is a graph showing the relationship between the cathode current density and time for a yet still further example of a plating current that is supplied between a substrate surface and an anode; and
FIG. 32 is a graph showing the relationship between the cathode current density and time for another example of a plating current that is supplied between a substrate surface and an anode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the drawings. FIG. 2 is a vertical sectional front view schematically showing an electroplating apparatus 50 which is used to carry out an electroplating method according to the present invention. As shown in FIG. 2, the electroplating apparatus 50 includes a plating tank 51 holding a plating solution Q therein, and a substrate holder 10 holding a substrate W such as a semiconductor wafer or the like and suspended vertically in the plating solution Q. The plating solution Q with the substrate holder 10 immersed therein has a surface level L at the upper end of the plating tank 51, as shown in FIG. 2. Two insoluble anodes 52 supported on respective anode holders 58 are disposed in the plating tank 51 in facing relation to respective opposite surfaces, i.e., face and reverse sides, of the substrate W held by the substrate holder 10. As shown in FIG. 3, the substrate holder 10 includes a first holding member 11 having a circular hole 11a defined therein and a second holding member 12 having a circular hole 12a defined therein. The first holding member 11 and the second holding member 12 serve to hold the substrate W therebetween. The insoluble anodes 52 are circular in shape and substantially identical in size to the circular holes 11a, 12a in the first and second holding members 11, 12.
Two regulation plates 60 made of an insulating material are disposed between the substrate holder 10 and the respective insoluble anodes 52 in the plating tank 51. The regulation plates 60 have respective circular holes defined therein which are similar in shape to the circular holes 11a, 12a in the first and second holding members 11, 12. The insoluble anodes 52 are electrically connected to respective wires 61a extending from respective terminals of plating power sources 53 each capable of changing the direction in which a current supplied thereby and also changing the value of the current. The plating power sources 53 have other terminals electrically connected to respective wires 61b which are connected respectively to terminal plates 27, 28 (see FIG. 3) of the substrate holder 10. The plating power sources 53 are also electrically connected to a controller 59 which individually controls the plating power sources 53.
Two stirring paddles 62 are disposed between the substrate W held by the substrate holder 10 and the respective regulation plates 60 in the plating tank 51. The stirring paddles 62 are movable back and forth parallel to the substrate W held by the substrate holder 10 for stirring the plating solution Q. The electroplating apparatus 50 also includes an outer tank 57 disposed around the plating tank 51 for holding the plating solution Q which has overflowed the plating tank 51. The plating solution Q, which has overflowed the plating tank 51 into the outer tank 57, is circulated through a constant-temperature unit 55 and a filter 56 back into the plating tank 51 from its bottom by a plating solution circulation pump 54.
FIG. 3 is a front view of a substrate holder 10. FIG. 4 is a plan view of the substrate holder 10. FIG. 5 is a bottom view of the substrate holder 10. FIG. 6 is a cross-sectional view taken along line K-K of FIG. 3. FIG. 7 is a view of the substrate holder 10 as viewed along the arrow A in FIG. 6. FIG. 8 is a view of the substrate holder 10 as viewed along the arrow B in FIG. 6. FIG. 9 is a view of the substrate holder 10 as viewed along the arrow C in FIG. 6. FIG. 10 is a cross-sectional view taken along line D-D of FIG. 7. FIG. 11 is a cross-sectional view taken along line E-E of FIG. 7. FIG. 12 is a cross-sectional view taken along line F-F of FIG. 3. FIG. 13 is a cross-sectional view taken along line G-G of FIG. 7. FIG. 14 is a cross-sectional view taken along line H-H of FIG. 8.
As shown in FIG. 3, the first holding member 11 and the second holding member 12, each of a planar shape, of the substrate holder 10 have respective lower ends pivotally coupled to each other by a hinge mechanism 13. The hinge mechanism 13 has two hooks 13-1 of synthetic resin, e.g., HTPVC, which are fixed to the second holding member 12. The hooks 13-1 are angularly movable supported on a lower end of the first holding member 11 by a hook pin 13-2 made of stainless steel, e.g., SUS 303. The first holding member 11 is made of synthetic resin, e.g., HTPVC, and has a substantially pentagonal shape. The circular hole 11a is centrally defined in the first holding member 11, as shown in FIG. 7. As shown in FIG. 3, a T-shaped hanger 14 made of synthetic resin, e.g., HTPVC, is integrally formed with an upper end of the first holding member 11. The second holding member 12 is made of synthetic resin, e.g., HTPVC, and has a substantially pentagonal shape. The circular hole 12a is centrally defined in the second holding member 12.
When the first holding member 11 and the second holding member 12 are turned about the hinge mechanism 13 into superposed relation to each other, i.e., when the substrate holder 10 is closed, the first holding member 11 and the second holding member 12 are held together by left and right clamps 15, 16. The left and right clamps 15, 16, each made of synthetic resin, e.g., HTPVC, have respective groove 15a, 16a for receiving therein the side marginal edges of the first holding member 11 and the second holding member 12 that are superposed one on the other. The left and right clamps 15, 16 have lower ends angularly movably supported on the lower ends of the opposite sides of the first holding member 11 by respective pins 17, 18.
As shown in FIG. 7, a seal ring 19 is mounted on a surface of the first holding member 11 which faces the second holding member 12, and extends around the hole 11a. As shown in FIG. 9, a seal ring 20 is mounted on a surface of the second holding member 12 which faces the first holding member 11, and extends around the hole 12a. The seal rings 19, 20 are made of rubber, e.g., silicone rubber. An O-ring 29 is mounted on the surface of the second holding member 12 which faces the first holding member 11, and extends around the seal ring 20.
The seal rings 19, 20, each of a rectangular cross-sectional shape, have respective ridges 19a, 20a projecting radially inwardly from and extending along inner circumferential edges thereof. When the first holding member 11 and the second holding member 12 are superposed one on the other with the substrate W interposed therebetween, the ridges 19a, 20a press the respective surfaces of the substrate W and are held in close contact therewith, defining a watertight space free of the plating solution Q between the O-ring 29 and the ridges 19a, 20a that are positioned radially outwardly of the holes 11a, 12a. As shown in FIGS. 7 and 10, eight substrate guide pins 21 for positioning the substrate W are mounted on the surface of the first holding member 11 which faces the second holding member 12, radially outwardly of the hole 11a, and project through the seal ring 19.
As shown in FIGS. 7, 11 and 12, six conductive plates 22 are mounted on the surface of the first holding member 11 which faces the second holding member 12 around the hole 11a. As shown in FIG. 11, three out of the six conductive plates 22 are held in electric contact with the seed layer 104 (see FIGS. 1A through 1D) on one of the surfaces, e.g., the face side, of the substrate W through conductive pins 23. As shown in FIG. 12, the other three conductive plates 22 held in electric contact with the seed layer 104 on the other surface, e.g., the reverse side, of the substrate W through conductive pins 23.
The three conductive plates 22 which are held in electric contact with the seed layer 104 on one of the surfaces, e.g., the face side, of the substrate W are electrically connected to respective electrode terminals 27a, 27b, 27c (see FIG. 4) provided on the terminal plate 27 of the hanger 14 through insulative covered wires 26 extending through a wire slot 25 (see FIG. 13). The other three conductive plates 22 which are held in electric contact with the seed layer 104 on the other surface, e.g., the reverse side, of the substrate W are electrically connected to respective electrode terminals 28a, 28b, 28c (see FIG. 4) provided on the other terminal plate 28 of the hanger 14 through insulative covered wires 26 extending through a wire slot 25 (see FIG. 13). As shown in FIGS. 7 and 13, the insulative covered wires 26 are held in position by wire holders 30 made of a synthetic resin, e.g., PVC.
The substrate holder 10 operates as follows: When the first holding member 11 and the second holding member 12 are turned about the hinge mechanism 13 away from each other, i.e., when the substrate holder 10 is open, the substrate W is placed in an area on the first holding member 11 which is surrounded by the eight substrate guide pins 21. The substrate W is now positioned in place on the first holding member 11. The first holding member 11 and the second holding member 12 are turned about the hinge mechanism 13 toward each other, i.e., the substrate holder 10 is closed. The left and right clamps 15, 16 are then angularly moved about the pins 17, 18 until the side marginal edges of the first holding member 11 and the second holding member 12 are inserted in the respective grooves 15a, 16a of the left and right clamps 15, 16. The substrate W, which is positioned in place on the first holding member 11, is now held between the first holding member 11 and the second holding member 12.
The O-ring 29 and the ridges 19a, 20a of the seal rings 19, 20 jointly define a watertight space free of the plating solution Q therebetween. At this time, the outer circumferential edge area of the substrate W, which is positioned radially outwardly of the ridges 19a, 20a, is positioned in the watertight space, and the surface areas of the opposite surfaces of the substrate W, which are coextensive with the holes 11a, 12a of the first holding member 11 and the second holding member 12, are exposed to the holes 11a, 12a. The three of the six conductive plates 22, which are held in electric contact with the seed layer 104 on one of the surfaces of the substrate W, are electrically connected to the electrode terminals 27a, 27b, 27c provided on the terminal plate 27 of the hanger 14, and the other three conductive plates 22, which are held in electric contact with the seed layer 104 on the other surface of the substrate W, are electrically connected to the electrode terminals 28a, 28b, 28c provided on the terminal plate 28 of the hanger 14.
FIG. 15 is a front view of the anode holder 58, which is holding the insoluble anode 52 therein, of the electroplating apparatus shown in FIG. 2, and FIG. 16 is a cross-sectional view of FIG. 15. In this embodiment, in order to prevent anodes from being dissolved by an additive(s) of the plating solution, the insoluble anodes 52, each of which comprises an anode body of titanium coated with iridium oxide, for example, are used.
As shown in FIGS. 15 and 16, each of the anode holders 58 includes a holder body 70 having a central hole 70a defined therein, a closure plate 72 disposed on a reverse side of the holder body 70 and closing the central hole 70a, a circular support plate 74 disposed in the central hole 70a of the holder body 70 and holding the insoluble anode 52 on its surface such that the insoluble anode 52 is positioned in the central hole 70a, and an annular anode mask 76 mounted on a face side of the holder body 70 in surrounding relation to the central hole 70a. The support plate 74 has a channel 74a defined therein which houses therein a conductive plate 78 which is electrically connected to the wire 61a extending from the plating power source 53. The conductive plate 78 extends to a central area of the support plate 74 where the conductive plate 78 is electrically connected to the insoluble anode 52.
A separating membrane 80 in the form of a neutral membrane is disposed in covering relation to the surface of the insoluble anode 52 that is positioned in the central hole 70a of the holder body 70. The separating membrane 80 has its peripheral edge gripped in position by the holder body 70 and the anode mask 76, and is fastened to the holder body 70. The anode mask 76 is fastened to the holder body 70 by screws 82, and the closure plate 72 is also fastened to the holder body 70 by screws.
When the anode holder 58 is immersed in the plating solution Q, the plating solution Q enters a gap between the insoluble anode 52 and the support plate 74 in the central hole 70a of the holder body 70.
The insoluble anode 52 and the separating membrane 80 are used for the following reasons: An additive to be added to the plating solution Q includes a component for promoting the formation of monovalent copper, which impairs the function of other additives because it causes oxidative decomposition of the other additives. As a result, soluble anodes cannot be used. When insoluble anodes are used, the insoluble anodes produce an oxygen gas in the vicinity thereof, and part of the produced oxygen gas is dissolved into the plating solution Q, increasing the concentration of dissolved oxygen. The increased concentration of dissolved oxygen tends to cause oxidative decomposition of the additives. Therefore, the separating membrane 80 in the form of a neutral membrane is desirably disposed in covering relation to the surface of the insoluble anode 52 to prevent the components of the additives near the substrate W from being adversely affected even if they are subject to oxidative decomposition in the vicinity of the insoluble anode 52.
It is also desirable to bubble or aerate the plating solution Q in the vicinity of the insoluble anode 52 with air or nitrogen supplied via, e.g., an aeration tube, not shown, for preventing the concentration of dissolved oxygen from being unduly rising on the insoluble anode 52 side.
Since the surface of the insoluble anode 52 held by the anode holder 58 is covered with the separating membrane 80 and the insoluble anode 52 is disposed to allow the separating membrane 80 to face the substrate W that is held by the substrate holder 10 and disposed in the plating tank 51, it is possible to prevent an oxygen gas from being produced in the vicinity of the insoluble anode 52 and dissolving into the plating solution when the plating solution Q is bubbled or aerated and hence to prevent the concentration of dissolved oxygen in the plating solution Q from increasing.
The electroplating apparatus 50 thus constructed operates as follows: The substrate holder 10, which is holding the substrate W whose face and reverse sides are exposed, is placed in the plating solution Q in the plating tank 51 such that one of the surfaces of the substrate W, e.g., the face side thereof, faces one of the insoluble anodes 52 and the other surface of the substrate W, e.g., the reverse side thereof, faces the other insoluble anode 52. The plating power sources 53 supply plating currents that are controlled by the controller 59 respectively between the face side of the substrate W and the insoluble anode 52 which faces the face side of the substrate W, and between the reverse side of the substrate W and the insoluble anode 52 which faces the reverse side of the substrate W, thereby simultaneously plating the face and reverse sides of the substrate W. If necessary, when the face and reverse sides of the substrate W are plated, the stirring paddles 62 are moved back and forth parallel to the substrate W to stir the plating solution Q. In this manner, as shown in FIGS. 1A through 1D, a plated film 106 is grown in the through-hole 100a defined in the substrate W.
FIGS. 17 through 19 show enlarged cross-sectional views of another substrate holder taken in different cross-sectional planes, respectively. The substrate holder shown in FIGS. 17 through 19 is different from the above-described substrate holder as follows: As shown in FIG. 17, the substrate holder includes elastic conductive plates 90, 92 having respective proximal ends fastened to the first holding member 11 and the second holding member 12, instead of the conductive pins 22, 23 shown in FIGS. 11 and 12. When the substrate W is held by the first holding member 11 and the second holding member 12, distal free ends of the elastic conductive plates 90, 92 are elastically held against the face and reverse sides, respectively, of the substrate W in electric contact with the seed layers 104 (see FIGS. 1A through 1D) on the face and reverse sides of the substrate W.
As shown in FIGS. 18 and 19, the substrate holder also includes seal ring holders 94, 96 for holding the seal rings 19, 20, respectively. The seal ring holders 94, 96 are fastened to the first holding member 11 and the second holding member 12, respectively. The seal ring holders 94, 96 have respective arrays of alternate guide teeth 97, 98 for positioning the substrate W, instead of the substrate guide pins 21 shown in FIGS. 7 and 10. The guide teeth 97, 98 are disposed at respective positions along the circumferential direction of the seal ring holders 94, 96. The guide teeth 97, 98 have respective tapered surfaces 97a, 98a on inner peripheral surfaces thereof near free ends thereof. When the substrate W is held by the first holding member 11 and the second holding member 12, the outer circumferential edge of the substrate W is held in contact with and guided by the tapered surfaces 97a, 98a to position the substrate W.
FIG. 20 shows the relationship between the cathode current density and time for an example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The plating current, which is supplied between the reverse side of the substrate W and the insoluble anode 52 which faces the reverse side of the substrate W, is held in synchronism with the plating current which is supplied between the face side of the substrate W and the insoluble anode 52 which faces the face side of the substrate W. However, these plating currents do not need to be synchronized with each other, and hence the present invention should not be limited by whether the above plating currents are to be synchronized with each other or not. The relationship between the cathode current density and time will be described with reference to FIG. 20 for a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation thereto.
In the example shown in FIG. 20, a plating process A in which a pulsed current is supplied between the surface of the substrate W and the insoluble anode 52 for plating the surface of the substrate W for a predetermined period of time, and a reverse electrolyzing process B in which a current is supplied in a direction opposite to the current supplied in the plating process A between the surface of the substrate W and the insoluble anode 52 are alternately repeated. The predetermined period of time for which the plating process A is carried out is in the range from 50 to 100 ms, for example, and the predetermined period of time for which the reverse electrolyzing process B is carried out is in the range from 0.1 to 10 ms, or preferably from 0.5 to 1 ms, for example.
As indicated by the imaginary lines in FIG. 20, a quiescent period C of 0.05 ms, for example, in which no current is supplied between the surface of the substrate W and the insoluble anode 52 may be inserted after the reverse electrolyzing process B and before the plating process A. The quiescent period C can uniformize a metal ion distribution in the plating solution Q within the through-hole for efficiently filling the plated film into the through-hole. The quiescent period C may be inserted for its advantages in each of other examples to be described below.
In the example shown in FIG. 20, the plating process A is carried out, using a PR pulsed current which is represented by an alternate repetition of normal electrolyzing cycles at a pulse pitch P1 in which the plating current flows in a forward direction, i.e., a plating direction, with a positive cathode current density D1 in the range from 1 to 3 ASD (A/dm2), for example, and reverse electrolyzing cycles at a pulse pitch P2 in which the plating current flows in a reverse direction with a negative cathode current density D2 in the range from −0.05 to −4 ASD, for example. The pulse pitch P2 in the reverse electrolyzing cycles of the PR pulsed current is of 0.5 ms, for example. The reverse electrolyzing process B is carried out with a single pulse at a pulse pitch P3 in the range from 0.1 to 10 ms, preferably from 0.5 to 1 ms, with a negative cathode current density D3 in the range from −30 to −40 ASD, for example.
Since the reverse electrolyzing process B with the negative cathode current density D3 in the range from −30 to −40 ASD, for example, is carried out after the plating process A, as indicated by the imaginary lines in FIG. 21, a plated film 106a, which tends to be deposited at the corners of the through-hole 100a, is dissolved into the plating solution Q, thereby allowing the plated film 106 to grow preferentially at the center of the through-hole 100a along the in-depth direction thereof, as indicated by the solid lines in FIG. 21.
As schematically shown in FIG. 22, fine irregularities 106b are liable to be produced by an abnormal deposition on microscopic surfaces of the plated film 106 in the plating process. However, those fine irregularities 106b are prevented from being produced by the reverse electrolyzing cycles with the negative cathode current density D2 in the range from −0.05 to −4 ASD, for example, according to the example shown in FIG. 20. The fine irregularities 106b due to an abnormal deposition would otherwise be joined to each other, forming fine voids in the plated film.
FIG. 23 shows the relationship between the cathode current density and time for another example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 23 is different from the example shown in FIG. 20 in that a reverse electrolyzing process B1 is carried out by applying two pulses each at a pulse pitch P4 in the range from 0.1 to 10 ms, for example, preferably from 0.5 to 1.0 ms before and after a normal electrolyzing cycle in which the plating current is applied in the forward direction.
The reverse electrolyzing process B with the negative cathode current density D3 in the range from −30 to −40 ASD, as shown in FIG. 20, is carried out with the single pulse at the pulse pitch P3 in the range from 0.1 to 10 ms. If the pulse pitch P3 is greater than 1 ms, then as schematically shown in FIG. 24A, the plated film 106 is excessively dissolved into the plating solution, forming excessively dissolved regions 112. As shown in FIG. 24B, the excessively dissolved regions 112 have their open ends closed, tending to produce cat-eyed voids 114 within the plated film 106 embedded in the through-hole 110a. Therefore, the pulse pitch P3 should preferably in the range from 0.1 to 1.0 ms, and more preferably in the range from 0.5 to 1.0 ms.
However, depending on the aspect ratio of a through-hole defined in the substrate W, it may not be possible to perform an ideal embedding process for ideally embedding a plated film preferentially at the center of the through-hole along the in-depth direction thereof according to a reverse electrolyzing process using a single pulse having a pulse pitch that is shorter than 1.0 ms. The reverse electrolyzing process B1 that is carried out by applying two pulses, each at the pulse pitch P4 shorter than 1.0 ms, as shown in FIG. 23, makes it possible to ideally fill a plated film into such a through-hole.
FIG. 25 shows the relationship between the cathode current density and time for still another example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 25 includes three different plating processes, i.e., a plating process (first plating process) A1 in a first zone until the plated film 106 in the through-hole 100a is joined substantially at the center thereof along the in-depth direction of the through-hole 100a, as shown in FIGS. 1A through 1C, a plating process (second plating process) A2 in a second zone for embedding the plated film 106 to a predetermined thickness in the recesses 108 in the through-hole 100a, as shown in FIGS. 1C and 1D, and a plating process (third plating process) A3 in a third zone in which the danger of a pinch-off is reduced after the stage shown in FIG. 1D.
In FIG. 25, the first plating process A1, the second plating process A2 and the third plating process A3 are shown as being carried out once each before and after the reverse electrolyzing process B (see FIG. 20). However, each of the first plating process A1, the second plating process A2 and the third plating process A3 is actually carried out a number of times before and after the reverse electrolyzing process B. This also applies to each of other examples to be described below.
In the example shown in FIG. 25, each of the first plating process A1, the second plating process A2 and the third plating process A3 is carried out with an on/off pulsed current which is represented by an alternate repetition of the supply and non-supply of a plating current which flows in the forward direction, i.e., the plating direction, and has a positive cathode current density D1 in the range from 1 to 3 ASD, for example. The on/off pulsed current in the first plating process A1 has a pulse pitch P5 shorter than the pulse pitch P6 of the on/off pulsed current in the second plating process A2 (P5<P6), and the pulse pitch P6 of the on/off pulsed current in the second plating process A2 is shorter than the pulse pitch P7 of the on/off pulsed current in the third plating process A3 (P6<P7). The on/off pulsed currents in the first, second and third plating processes A1, A2, A3 have respective downtime pitches P8, P9, P10 of the respective on/off pulsed currents equal to each other (P8=P9=P10). Therefore, the cathode current density on average increases stepwise. Alternatively, the cathode current density on average may increase gradually linearly.
Since the on/off pulsed currents provide non-plating periods for supplying no plating current in the overall plating process, the metal ion concentration in the plating solution within the through-hole is recovered in the non-plating periods, for thereby preventing defects such as voids or the like from being formed in the plated film. As the through-hole is gradually filled with the plated film in the plating process, the substantive aspect ratio of the through-hole changes. When the substantive aspect ratio of the through-hole changes, it is possible to efficiently fill the plated film into the through-hole in a manner to match the changing substantive aspect ratio of the through-hole by increasing the cathode current density on average in the plating process. Consequently, the period of time required to plate the substrate can be further shortened.
It is generally known in the art to increase the plating current density stepwise as the plating process progresses. However, it is difficult to inhibit the generation of monovalent copper over a full range of plating current densities from a low plating current density to a high plating current density. According to this example, since the cathode current density has a constant peak value to inhibit the generation of monovalent copper, the plating solution can be prevented from being degraded.
FIG. 26 shows the relationship between the cathode current density and time for yet another example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 26 is different from the example shown in FIG. 25 in that the reverse electrolyzing process B1 shown in FIG. 23 is carried out by applying two pulses each at the pulse pitch P4 in the range from 0.1 to 10 ms, for example, preferably from 0.5 to 1.0 ms, instead of the reverse electrolyzing process B shown in FIG. 25 with the single pulse at the pulse pitch P3 in the range from 0.1 to 10 ms, preferably from 0.5 to 1 ms, for example.
FIG. 27 shows the relationship between the cathode current density and time for yet still another example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 27 is different from the example shown in FIG. 25 in that the first, second and third plating processes A1, A2, A3 have respective processing times which are equal to each other, the on/off pulsed current in the first plating process A1 has a pulse pitch P5 shorter than the pulse pitch P6 of the on/off pulsed current in the second plating process A2 (P5<P6), the pulse pitch Po of the on/off pulsed current in the second plating process A2 is shorter than the pulse pitch P7 of the on/off pulsed current in the third plating process A3 (P6<P7), the downtime pitch P8 of the on/off pulsed current in the first plating process A1 is longer than the downtime pitch P9 of the on/off pulsed current in the second plating process A2 (P8>P9), and the downtime pitch P9 of the on/off pulsed current in the second plating process A2 is longer than the downtime pitch P10 of the on/off pulsed current in the third plating process A3 (P9>P10). Therefore, the cathode current density on average increases stepwise.
FIG. 28 shows the relationship between the cathode current density and time for a further example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 28 is different from the example shown in FIG. 25 in that it uses a composite pulsed power source for supplying a first plating current with a positive cathode current density D1 ranging from 1 to 3 ASD, for example, and a second plating current with a positive cathode current density D4 ranging from 0.1 to 0.5 ASD, for example, instead of the power source for supplying the on/off pulsed current by repeating the supply and non-supply of a plating current which flows in the forward direction, i.e., the plating direction, and has a positive cathode current density D1 in the range from 1 to 3 ASD, for example.
Since the composite pulsed power source is used to continuously supply a weak current in the range from 0.1 to 0.5 ASD, for example, rather than stopping to supply the plating current, the plated film is continuously grown in the plating process. Therefore, the plated film is prevented from being dissolved into the plating solution in the plating process.
FIG. 29 shows the relationship between the cathode current density and time for a still further example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 29 is different from the example shown in FIG. 25 in that a PR pulsed current is supplied by repeating normal electrolyzing cycles with a positive cathode current density D1 in the range from 1 to 3 ASD, for example, and reverse electrolyzing cycles with a negative cathode current density D2 in the range from −0.05 to −4 ASD, for example, rather than the on/off pulsed current supplied by repeating the supply and non-supply of a plating current with a positive cathode current density in the range from 1 to 3 ASD, for example.
FIG. 30 shows the relationship between the cathode current density and time for a yet further example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 30 is different from the example shown in FIG. 25 in that it carries out first, second and third plating processes A1, A2, A3 successively, by supplying a DC plating current with a positive cathode current density D1 in the range from 1 to 3 ASD, for example, the first, second and third plating processes A1, A2, A3 having respective processing times that are progressively longer in this order (A1<A2<A3).
Depending on the aspect ratio of a through-hole, the structure of a plating underlayer, the nature of the plating solution, etc., there may be no need to provide a quiescent period between reverse electrolyzing processes. If no quiescent period is required, then a plating current may be supplied between the surface of the substrate W and the insoluble anode 52 to achieve the relationship between the cathode current density and time shown in FIG. 30 for thereby shortening the time required to perform the plating process to efficiently fill the plated film into the through-hole.
FIG. 31 shows the relationship between the cathode current density and time for a yet still further example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 31 is different from the example shown in FIG. 20 in that when the plated film 106 is embedded to a predetermined thickness in the recesses 108 in the through-hole 100a, as shown in FIG. 1D, so that the danger of a pinch-off is reduced, for example, the reverse electrolyzing process B is followed by a plating process A4 which is carried out by supplying a DC plating current with a positive cathode current density D1 in the range from 1 to 3 ASD, for example. At the stage wherein the danger of a pinch-off is reduced, the embedding of the plated film in the through-hole 100a in the substrate W is essentially completed, as shown in FIG. 1D, and dimples left on the surface of the substrate are to be finally filled up. At this time, it is not necessary to supply a DC plating current to equalize the cathode current density with a previous pulse peak current density, but a DC plating current may be supplied to make the cathode current density higher than a previous pulse peak current density, thereby shortening the time required to perform the plating process.
FIG. 32 shows the relationship between the cathode current density and time for another example of a plating current that is supplied between a surface of the substrate W and the insoluble anode 52 disposed in facing relation to the surface of the substrate W. The example shown in FIG. 32 is different from the example shown in FIG. 27 in that the third plating process A3 is performed by supplying a DC plating current with a positive cathode current density D1 in the range from 1 to 3 ASD, for example, thereby shortening the time required to perform the plating process.
Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
