JP2007277676A - Electroplating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deposition and holding of bubbles dispersed in a plating solution on a material to be plated by air stirring to reduce occurrence of plating defects such as a void in electroplating on the material to be plated having a via hole or a through-hole. <P>SOLUTION: The material to be plated which has a recessed part or a through-hole is electroplated while carrying out jet stirring and/or mechanical stirring of the plating solution around the material to be plated without entraining air bubbles by setting the arrangement of an anode and the material to be plated so that the air bubbles produced by continuously air-stirring the plating solution around the anode is not shifted to the surroundings of the material to be plated and not caught in the surrounding plating solution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to electroplating on printed wiring boards, wafers, and the like having via holes and through holes, and more particularly to an electroplating method that can reduce the occurrence of plating defects around via holes and through holes as much as possible.

  When, for example, copper plating is performed on a substrate having a via hole or a through hole, various additives are added to the plating solution in order to adjust the plating characteristics in accordance with the shape of the via hole or the through hole. Many of these additives, particularly brighteners and levelers, are reduced during plating, and divalent copper ions are partially reduced to monovalent copper ions. The resulting reduced form of the additive and monovalent copper ions adversely affect the properties of the plating film, so that the reduction reaction is suppressed and the produced reduced form and monovalent copper ions are used for stirring the cathode. A method of oxidizing by air introduced into the air is commonly used.

  In this method, it is effective to dissolve oxygen in the plating solution to suppress the reduction reaction, and since dissolved oxygen can be used as an oxidizing agent for the oxidation reaction, a plating film can be stably formed. For this purpose, it is necessary to maintain the oxygen concentration in the plating solution at a certain level continuously.

  In general, air agitation is employed as a method of supplying oxygen consumed in the oxidation reaction described above and maintaining the oxygen concentration continuously. While stirring the plating solution by this air agitation, oxygen in the plating solution is used. Concentration is maintained at a constant level.

  A large number of bubbles are dispersed in the plating solution by this air agitation, but minute bubbles easily adhere to the substrate, and in particular, if they enter the inside of minute via holes or through holes, If it is held and not easily discharged and the plating proceeds as it is, defects such as voids (no plating) are caused.

  Furthermore, in order to improve the stirring efficiency of the plating solution itself, it is also commonly used in combination with air stirring and jet stirring or mechanical stirring (for example, paddles, squeegees, etc.). When the air bubbles collide with the air bubbles, the air bubbles are crushed to generate fine air bubbles that are more easily penetrated into the via hole or the through hole, thereby increasing the plating defect.

  The prior art document information relating to the present invention includes the following.

JP 2004-143478 A JP 2004-320994 A

  The present invention has been made in view of the above circumstances, and when performing electroplating such as electrolytic copper plating on an object to be plated having a via hole or a through hole, the bubbles dispersed in the plating solution by air agitation are used. It is an object of the present invention to provide a method of electroplating by reducing as much as possible plating defects caused, particularly plating defects around via holes and through holes.

  As a result of diligent investigations to solve the above problems, the present inventor stirred the plating solution when performing electroplating such as electrolytic copper plating on an object to be plated such as a printed wiring board having via holes or through holes. In addition, air agitation and jet agitation and / or mechanical agitation are used together. The plating solution around the object to be plated is agitated by jet agitation and / or mechanical agitation, and the plating solution around the anode is agitated by air agitation. At this time, the arrangement of the anode and the object to be plated is set so that the plating liquid around the object to be plated does not entrain air bubbles dispersed around the anode, and the plating solution around the object to be plated is jetted and stirred. / Or mechanical agitation to prevent bubbles from adhering to and holding the surface of the object to be plated and the narrow parts of the object to be plated such as via holes and through holes. Found that it is possible to suppress the defective plating of voids such, the present invention has been accomplished.

That is, the present invention
[1] A method of electroplating an object to be plated by immersing an object to be plated having a recessed portion or a through-hole in an electroplating solution, wherein the plating solution around the anode is continuously agitated with air. The arrangement of the anode and the object to be plated is set so that air bubbles generated by air agitation move around the object to be plated and are not caught in the surrounding plating solution. An electroplating method characterized by electroplating with jet stirring and / or mechanical stirring without accompanying air bubbles;
[2] The direction of the jet of the plating solution around the object to be plated is set so as not to entrain air bubbles by air agitation, and the jet is stirred so that the jet of the plating solution collides with the object to be plated. ] The electroplating method according to
[3] The electroplating method according to [1], wherein the mechanical stirring is stirring with a paddle or a squeegee.
[4] An air nozzle for air agitation is arranged immediately below or close to the position where the anode is arranged, and a jet nozzle for jet agitation and / or a mechanical agitation tool are arranged close to the object to be plated. 1] to the electroplating method according to any one of [3],
[5] The electroplating method according to any one of [1] to [4], wherein the electroplating solution is an electrolytic copper plating solution, and [6] [1] to [1], wherein the object to be plated is a printed wiring board or wafer. 5] The electroplating method according to any one of the above.

  According to the present invention, in the electroplating to the object to be plated having via holes or through holes, it is possible to prevent the bubbles dispersed in the plating solution by air agitation from being attached to and retained on the object to be plated. Occurrence of plating defects such as voids can be reduced.

Hereinafter, the present invention will be described in more detail.
The electroplating method of the present invention is a method for electroplating an object to be plated by immersing an object to be plated having a recessed portion such as a via hole or a through hole such as a through hole in an electroplating solution. The liquid is continuously stirred by air, and the arrangement of the anode and the plating object is set so that air bubbles generated by this air stirring move around the plating object and are not caught in the surrounding plating solution. Then, the plating solution around the object to be plated is subjected to electroplating while jet stirring and / or mechanical stirring without accompanying air bubbles.

  Here, examples of the electroplating include copper plating, nickel plating, and gold plating. The electroplating method of the present invention can be effectively applied to copper plating, particularly copper sulfate plating. In addition, the plating solution used for these plating can use the thing of a well-known plating solution composition, and can also use a commercial item.

In the present invention, when electrolytic copper sulfate plating is performed by immersing a substrate having a recessed portion such as a via hole or a through hole such as a through hole, for example, when performing via fill plating, copper sulfate (CuSO ₄ ) is used as a copper source. This is effective when sulfuric acid is added to the material and, if necessary, an additive that is easily reduced during plating as an additive such as brightener or leveler.

  In the present invention, the plating solution around the anode is continuously stirred by air stirring. Air stirring of the plating solution around the anode has the following advantages.

(A) When the anode slime is generated, the slime accumulates at the lower end portion of the anode due to gravity and prevents energization in this portion, so that the plating film thickness of the portion of the object to be plated close to the lower end portion becomes thin, and the plating film The thickness distribution becomes worse. By preventing the generation of the anode slime, the deterioration of the film thickness distribution can be suppressed, and the anode maintenance cycle can be extended, thereby improving the productivity.

(B) The oxidation of the reduced form of the additive is promoted and decomposed efficiently so as not to adversely affect the plating. For example, in the case of copper sulfate plating, monovalent copper ions can be oxidized. . Furthermore, the plating solution with reduced reductant can be distributed throughout the plating solution, and the influence of aging of the plating solution can be reduced.

  In the present invention, the plating solution around the object to be plated is continuously stirred by jet stirring and / or mechanical stirring (that is, jet stirring or mechanical stirring or both methods). At this time, the anode and the object to be plated are arranged so as not to entrain air bubbles dispersed around the anode, and the flow direction of the plating solution is set by air stirring, jet stirring and / or mechanical stirring. In particular, in the case of copper sulfate plating, jet stirring is effective. However, the jet stirring of the plating solution around the object to be plated by causing the jet to collide with the object to be plated has the following advantages.

(C) In an object to be plated having a recessed portion or a through hole, a plating solution rich in metal ions such as copper ions is applied to a narrow portion such as a recessed portion such as a via hole or a through hole such as a through hole. Can be supplied automatically. In this case, since the metal ion concentration is hardly lowered even in a narrow portion, it is possible to suppress the film thickness shortage due to the metal ion shortage, the reduction of throwing power (around), the generation of voids, and the like. Further, since the film growth rate is limited by the mass transfer, in this case where the mass transfer is fast, the occurrence of burns hardly occurs even if the current density is increased. As a result, productivity can be improved.

(D) Even in the case where bubbles are attached during immersion of the object to be plated, it can be peeled off by the collision force of the jet.

  In addition, when using the jet flow, if the object to be plated is swung, the flow of the plating solution on the surface of the object to be plated can be prevented from being always in a certain direction. In the case of a plated object, instead of changing the flow of the plating solution by swinging the object to be plated, the flow of the plating solution on the surface of the object to be plated can be changed by mechanical stirring such as a squeegee or paddle. Moreover, by using both jet stirring and mechanical stirring, the flow of the plating solution on the surface of the object to be plated becomes more active, especially in the printed wiring board, the replacement of the plating solution inside via holes and through holes is more active. To be done.

  According to the present invention, by using air agitation and jet agitation and / or mechanical agitation having the advantages as described above, the advantages of each of these agitations can be utilized to the maximum, and further, a recessed portion such as a via hole, or By avoiding the weak points of air stirring and jet stirring in electroplating to the plating object having through-holes such as through-holes, it is possible to electroplate with good productivity without causing poor film thickness and bad plating such as voids. It becomes possible.

  If there is no jet stirring or mechanical stirring, there is no movement of the plating solution in the vicinity of the object to be plated. The phenomenon occurs when the amount is insufficient. Compared to air agitation, jet agitation and mechanical agitation are preferred in that a stronger agitation effect can be obtained.

  In the present invention, as conditions for air agitation, jet agitation, and mechanical agitation, known conditions corresponding to the type of the plating solution, the type of the object to be plated, and the like can be adopted. Moreover, in this invention, in addition to said stirring aspect, a to-be-plated object can also be rock | fluctuated as needed.

Next, the method of the present invention will be described more specifically with reference to the drawings.
1 is a plan view showing an example of a plating tank suitable for the electroplating method of the present invention, FIG. 2 is a cross-sectional view taken along line XX in FIG. 1, and FIG. 3 is taken along line YY in FIG. This example shows an example in which air agitation and jet agitation are used in combination, and a printed wiring board is used as an object to be plated, and plating is performed on both surfaces thereof. In the figure, a power supply and a conducting wire for supplying a current between an object to be plated (cathode) and an anode are not shown.

  1 to 3, the object to be plated (cathode) 11 is immersed in the central part of the plating solution 2 in the plating tank 1, and the jet nozzles 12 and 12 face the front and back surfaces of the object 11 to be plated, respectively. Is provided close to the object 11 to be plated. A jet port 13 (16 in this example (the number of jet ports is not limited)) is provided on the side of the jet nozzle 12 facing the object 11 to be plated, and appropriate means such as a pump. (Not shown), the plating solution 2 is sent to the injection nozzle 12, the plating solution 2 is ejected from the jet port 13 toward the object 11 to be plated, and substantially perpendicularly to the object 11, and the jet is indicated by an arrow in the figure. It collides with the to-be-plated object 11 as shown by these. And the jet which collided with the to-be-plated object 11 flows along the surface and the back surface of the to-be-plated object 11, agitates the plating solution 2 around the to-be-plated object 11, and goes to the outside area | region from the to-be-plated object 11 outer periphery part. It has come to flow.

  Further, 21 and 21 are anode plates, and the anode plates 21 and 21 are disposed in the vicinity of the inner wall of the plating tank 1 so as to face the object 11 to be plated. Air nozzles 22 and 22 are provided along the vicinity of the lower ends of the anodes 21 and 21 and spaced apart from the jet nozzle 12 by a sufficient distance. The air nozzles 22 are provided with air ports 23 (in this example, six air nozzles are provided for each air nozzle (the number of air ports is not limited)). The air bubbles are blown upward from the air port 23, and the plating solution around the anode is agitated by air bubbling.

  The plating solution ejected from the jet nozzle 12 is a plating solution stored in an overflow tank separately provided in the plating tank 1 so that bubbles due to air agitation are not mixed. The plating solution at the bottom of the tank 1 is taken in.

  In the plating method of the present invention, the anode and the object to be plated are arranged so as not to entrain air bubbles dispersed around the anode, and the flow directions of the air and the jet are set. That is, in the case of the above-described example, the air nozzle 22 is plated while avoiding the vicinity area of the object 11 to be plated, the vicinity area of the jet nozzle 12, the area between the object 11 and the jet nozzle 12, and the upper and lower areas thereof. The plating solution 2 which is provided in the vicinity of the inner peripheral wall of the tank 1 and directly hits the object 11 to be plated and does not contain air bubbles, and the plating solution 2 which has collided with the object 11 is separated from the outer peripheral edge of the object 11 to be plated. Since it flows to the inner peripheral wall region of the plating tank 1 toward the outside, the jet impinging on the object to be plated 11 directly hits the air bubbles blown out from the air nozzle 22, and the jet breaks the air bubbles. The air bubbles taken out from the air nozzle 22 by taking in the bubbles are not brought into contact with the workpiece 11.

  Therefore, according to the plating method of the present invention, it is possible to prevent air bubbles from adhering to and holding in the narrow portion formed on the surface of the object to be plated and via holes, through holes, etc. The occurrence of plating defects such as the above can be suppressed.

  In the above example, the case where the jet flow is collided from the jet nozzle in the substantially vertical direction with respect to both the front and back surfaces of the object to be plated is not limited to this. In this case, for example, when there is no concern about bubbles adhering when the workpiece is immersed, the jet is made to collide with the front and back surfaces of the workpiece from the low angle direction. In this case, the jet mainly forms a flow along both the front and back surfaces of the object to be plated, and thereby it is possible to agitate the plating solution around the object to be plated without entraining air bubbles by air agitation. . In particular, air bubbles caused by air agitation move upward (in the antigravity direction) in the plating solution. Therefore, in order to avoid direct collision between the air bubbles and the jet as much as possible, the jet is applied to both the front and back surfaces of the object to be plated. It is effective to make the collision from the low angle direction upward (antigravity direction).

  In addition, when the jet port of the jet nozzle and the air port of the air nozzle are relatively close to each other, in order to avoid direct contact between the jet and the air, the jet flow and the air flow are disturbed so that they do not come into contact with each other. It is also possible to provide a shielding plate. In addition, an air nozzle is not restrict | limited to an above-described example, For example, you may arrange | position in a ring shape along a plating tank inner wall.

  When the distance between the anode and the object to be plated is narrow, the positional relationship between air agitation and jet agitation and / or mechanical agitation installed between them is close, and bubbles caused by air agitation are jet agitation and / or mechanical agitation. The fine bubbles are generated by being entangled and pulverized, and the fine bubbles may adhere to the via hole or the through hole of the substrate to generate a void. Therefore, when the interval between the anode and the object to be plated is narrow, it is preferable to provide a shielding plate between the air outlet and the jet stirring and / or mechanical stirring to prevent entrainment of bubbles.

  Furthermore, the present invention can also be used for single-side plating on an object to be plated such as a wafer. In this case, for example, the embodiment shown in FIGS. 4 is a longitudinal sectional view of the plating tank, FIG. 5 is a transverse sectional view, in which 1 is a plating tank, 2 is a plating solution, 21 is an anode plate disposed near one side wall of the plating tank, 11 Represents an object to be plated disposed near the other side wall of the plating tank 1 so as to face the anode 21, 22 represents an air nozzle, 31 represents a mechanical stirrer such as a paddle or squeegee. In this case, if necessary, a jet is applied to the plating solution between the object to be plated 11 and the mechanical stirrer 31, so that the jet flows near the bottom wall of the plating tank 1 below the object to be plated 11 and the mechanical stirrer 31. The nozzle 12 may be installed.

  In the case of a plating tank for printed circuit boards, the strength of air, liquid depth, jet flow, and strength of mechanical stirring are appropriately selected and are not particularly limited. For example, the distance from the anode to the air outlet: air The distance from the outlet to the jet protrusion port is preferably 1: 2 or more, and the distance from the anode to the cathode is preferably ½ or more of the liquid depth. Also, in the case of a plating tank for wafers, particularly when plating with the wafer oriented vertically (with the wafer thickness direction horizontal): distance from anode to air outlet: distance from air outlet to squeegee = n: 1 (however, , N is preferably (distance from cathode to anode) / (depth of liquid).

  On the other hand, when there is no mechanical stirring, it is preferable that the angle of the jet is perpendicular to the surface of the cathode (to-be-plated object) and the cathode is swung in the direction perpendicular to the jet. In the case of mechanical stirring, it is preferable to set the angle of the jet so that it is perpendicular to the movement of mechanical stirring and perpendicular to the surface of the cathode (to-be-plated). The rocking is preferably performed as much as possible, but is not performed when the accuracy of mechanical stirring is lowered due to the rocking.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to the following Example.

[Example 1]
Using the following copper sulfate plating solution, the object to be plated (printed wiring board) and the anode are arranged as shown in FIGS. 1 to 3, and the jet nozzle and the air nozzle are arranged as shown in FIGS. A substrate having a via hole having a diameter of 150 μm and a depth of 95 μm was electroplated while stirring the plating solution by stirring and air stirring. The plating conditions are as follows. The plating evaluation was performed at two points immediately after the bathing and after dummy plating with a dummy plate for 10 hours.

Copper sulfate plating solution Copper sulfate (CuSO ₄ .5H ₂ O) 80 g / L
Sulfuric acid 200g / L
Additive Sulcup ETN (manufactured by Uemura Kogyo Co., Ltd.)
The additive concentration was analyzed by CVS, and plating was performed while adjusting the ETN-1-A solution = 1 ml / L and ETN-1-B solution = 10 ml / L while replenishing the additive.

Plating conditions Cathodic current density (ASD): 3.0 A / cm ²
Plating temperature: 25 ° C
Plating time: 38 minutes

  The electroplating was performed on a substrate having via holes subjected to normal desmear treatment to chemical copper plating, and throwing power (TP) was evaluated for the plated via holes. The TP evaluation method is as follows. The results are shown in Table 1.

TP evaluation As shown in FIG. 6, the via hole and the surrounding cross section were cut out, the thickness of each plating film of the portion indicated by a, b and c was measured by cross section observation, and calculated from the result by the following formula. .
TP (%) = (c × 2) / (a + b) × 100
In FIG. 6, 41 is a via hole, 42 is a plating film, 43 is a surface laminated copper foil, 44 is a resin layer, and 45 is an internal copper foil.

  Next, the board | substrate which has the said via hole was changed into the SUS board, the copper plating film was formed into a film on the SUS board on the following conditions, and the physical property of the plating film was evaluated with the following method. The results are shown in Table 1.

Plating conditions Cathodic current density (ASD): 3.0 A / cm ²
Plating temperature: 25 ° C
Plating time: 75 minutes

Evaluation of Physical Properties of Film After a SUS plate was lightly polished with an abrasive (Scotch Bright: manufactured by 3M Company), it was subjected to acid cleaning treatment and electrolytic copper plating to form a plating film with a thickness of 50 ± 5 μm. After plating, the plating film was peeled off from the SUS plate and heat treated at 120 ° C. for 2 hours. The film is punched into a dumbbell-shaped test piece of the size shown in FIG. 7, the film thickness is measured with a fluorescent X-ray film thickness meter, the distance between chucks is 40 mm, the pulling speed is 4 mm / min by autograph, and the film is broken. The elongation rate and tensile strength of each were calculated and evaluated by the following equations.
T [kgf / mm ² ] = F [kgf / mm ² ] / (10 [mm] × d [mm])
T: Tensile strength F: Maximum tensile stress d: Film thickness at the center of the test piece E [%] = ΔL [mm] / 20 [mm] × 100
E: Elongation rate ΔL: Length stretched until the film broke

[Comparative Example 1]
The substrate and the anode were disposed at the same positions as in Example 1, and the air nozzle was disposed immediately below the substrate without performing the jet stirring without the jet nozzle, and only the air stirring was performed. In this case, the electroplating is performed in a state in which bubbles caused by air agitation are always in contact with the substrate. Table 1 shows the results of evaluating the plating in the same manner as in Example 1.

[Comparative Example 2]
The substrate and the anode were disposed at the same position as in Example 1, the jet nozzle was disposed at the same position as in Example 1, and the jet stirring was performed. The air nozzle was disposed immediately below the substrate to perform the air stirring. In this case, the electroplating is performed in a state in which bubbles caused by air agitation are always in contact with the substrate. Table 1 shows the results of evaluating the plating in the same manner as in Example 1.

[Comparative Example 3]
The substrate and the anode were disposed at the same position as in Example 1, and the air nozzle was not disposed without disposing the air nozzle, and the jet nozzle was disposed at the same position as in Example 1 and only the jet stirring was performed. Table 1 shows the results of evaluating the plating in the same manner as in Example 1.

It is a top view which shows an example of the plating tank suitable for the electroplating method of this invention. It is sectional drawing along the XX line of FIG. It is sectional drawing along the YY line of FIG. It is a longitudinal cross-sectional view which shows another example of the plating tank suitable for the electroplating method of this invention. It is a cross-sectional view of the plating tank of FIG. It is sectional drawing of a via hole which shows the film thickness measurement location of the film | membrane in evaluation of throwing power (TP) of a via hole. It is a figure which shows the shape and size of the test piece which measured the film physical property.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plating tank 2 Plating solution 11 To-be-plated object 12 Jet nozzle 13 Jet port 21 Anode 22 Air nozzle 23 Air port 31 Mechanical stirring tool

Claims (6)

  A method of electroplating an object to be plated by immersing an object to be plated having a recessed portion or a through-hole in an electroplating solution, wherein the plating solution around the anode is continuously agitated with air, The arrangement of the anode and the object to be plated is set so that the generated air bubbles move around the object to be plated and are not caught in the surrounding plating solution. An electroplating method, wherein electroplating is performed with jet stirring and / or mechanical stirring without being accompanied.   The jet flow agitation is performed such that the jet direction of the plating solution around the object to be plated is set so as not to entrain air bubbles by air agitation and the jet of the plating solution collides with the object to be plated. Electroplating method.   The electroplating method according to claim 1, wherein the mechanical stirring is stirring with a paddle or a squeegee.   The air nozzle for air agitation is disposed at a position immediately below or close to the position where the anode is disposed, and the jet nozzle for jet agitation and / or the stirring tool for mechanical agitation are disposed close to the object to be plated. 4. The electroplating method according to any one of 3 above.   The electroplating method according to any one of claims 1 to 4, wherein the electroplating solution is an electrolytic copper plating solution. 6. The electroplating method according to claim 1, wherein the object to be plated is a printed wiring board or a wafer.

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