WO2003033775A1

WO2003033775A1 - Method of copper-plating small-diameter holes

Info

Publication number: WO2003033775A1
Application number: PCT/JP2002/010483
Authority: WO
Inventors: Kenji Nakamura
Original assignee: Shinko Electric Industries Co., Ltd.
Priority date: 2001-10-16
Filing date: 2002-10-09
Publication date: 2003-04-24
Also published as: US20040011654A1; KR20040045390A; JP4148895B2; JPWO2003033775A1; CN1283848C; TW561808B; CN1476492A

Abstract

A method of copper-plating the interiors of small-diameter holes in a material to be plated having small holes by a PPR method using a copper sulphate plating solution containing copper sulphate, sulfuric acid, chlorine ions, a sulfur compound and a surfactant, wherein those portions in the vicinities of small-hole entrances of a sulfur compound adsorbed to the material to be plated are removed by a reverse electrolysis performed within a current density range of 0.1-1A/dm2 to thereby keep a polarizing resistance lower inside the small-diameter holes than in the vicinities of small-diameter hole entrances at a regular electrolysis, whereby uniform-thickness copper-plated films are formed inside small-diameter holes. The interiors of small-diameter holes can be plated satisfactorily at reduced equipment costs without the need of a high-accuracy, large-capacity pulse power supply.

Description

Description Copper plating method for small diameter holes

Technical field

The present invention relates to a method for plating a small diameter hole with copper. Background art

As the wiring density of electronic components has increased, the diameter of through holes and blind vias in wiring boards has become smaller, making it difficult to reliably form plating films inside these. That is, the ordinary plating method has a problem in reliability because the plating thickness in the center of the through hole or the bottom of the via becomes extremely thin. In addition, long-term mounting to increase the thickness of the interior causes additional costs, costs, and the opening is blocked, causing new problems.

To solve these problems, periodically reverse the polarity of electrolysis.

A PPR (Periodic Pulse Reverse) plating method (for example, Japanese Patent Application Laid-Open No. 2000-68651) and a method of performing special stirring have been proposed. The use of pulses in (ms) units has the following issues.

In other words, a high-performance and expensive pulse power source that can continuously switch the polarity at high speed is required.

In addition, it is necessary to synchronize the two power supplies to attach the patterns on the front and back of the board, but it is extremely difficult to synchronize because of the high-speed pulse.

Also, the reverse electrolysis current density is required to be 1 to 5 times the positive electrolysis current density. Therefore, a large power supply is required.

In addition, since the pulse is fast (high frequency), it is necessary to route the wiring in consideration of the loss due to the inductance of the wiring.

In addition, in the case of hanging an object to be coated (substrate) in the plating liquid or rack mounting, the pulse effect does not reach the center of the substrate, so it is not practical o

Moreover, various problems force ^s Mel that set various plating conditions are not easy.

In addition, when a special stirrer is used, it is difficult to uniformly stir all parts, and there is a problem that it is costly.

Disclosure of the invention

Accordingly, an object of the present invention is to eliminate the need for a high-precision, large-capacity pulsed power supply, thereby reducing equipment costs and, at the same time, providing copper plating in a small-diameter hole, which allows good plating in the small-diameter hole. To provide a way.

In order to achieve the above object, a method for plating a small-diameter hole with copper according to the present invention has a small-diameter hole using a copper sulfate plating solution containing copper sulfate, sulfuric acid, chloride ions, sulfur compounds, and a surfactant. in copper Me per way method in small holes applying by Ri copper plated to PPR method in diameter halls of the plated material, the reverse electrolysis carried out at 0. l ~ l current density range of AZ dm ² By separating the sulfur compound adsorbed on the adherend from the sulfur compound near the entrance of the small-diameter hole, the polarization resistance in the small-diameter hole during positive electrolysis is reduced from that near the entrance of the small-diameter hole. It is characterized by forming a copper-plated film with a uniform thickness in the small-diameter hole while keeping it low.

During the reverse electrolysis, the first half reverse electrolysis is performed at a high current density, and the second half reverse electrolysis is performed. Two-stage reverse electrolysis, which is performed at a lower current density than in the first half, is more suitable.

The positive electrolysis is performed for several tens to several hundred seconds, and the reverse electrolysis is performed for several seconds to several tens of seconds.

Doing positive electrolysis 1-2 eight / ^ 1! 1 ² current density range is preferred. It is preferable to use a copper sulfate plating solution having a low electric resistance and a high copper concentration, with a sulfuric acid concentration of 150 to 250 g Zl and a copper sulfate concentration of 130 to 200 g / 1. Is Raniwa, 2 0 0 _g l before and after the sulfuric acid concentration, copper sulfate plated solution was 1 5 0 g Z 1 before and after the copper sulfate concentration is suitable in stability. Also, the inside of the small diameter hole can be filled with copper plating. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a graph showing the relationship between sulfuric acid concentration and plating solution resistance. Fig. 2 is a graph showing the relationship between the concentration of sulfuric acid and the concentration of saturated copper sulfate. Fig. 3 is a graph showing the relationship between the reverse electrolytic potential and the magnitude of the polarization resistance during positive electrolysis.

FIG. 4 is a schematic diagram showing a current waveform in one embodiment of the present invention.

FIG. 5 is a cross-sectional photograph of the through hole of Example 1.

FIG. 6 is a cross-sectional photograph of the through hole of Example 2.

FIG. 7 is a cross-sectional photograph of the through hole of Example 3.

FIG. 8 is a cross-sectional photograph of the through hole of Example 4.

FIG. 9 is a cross-sectional photograph of the through hole of Comparative Example 1.

FIG. 10 is a cross-sectional photograph of the through hole of Comparative Example 2. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the copper sulfate plating solution will be described.

The composition of the copper sulfate plating solution is as follows: copper sulfate as a copper source, sulfuric acid for conductivity adjustment, chlorine ion (chloride) as a suppressor and a surfactant, and a plating accelerator. Consists of functional sulfur compounds.

It is preferable to use a solution with a high copper concentration in order to improve the throwing power of the plating into the small-diameter holes, and to reduce the electric resistance of the plating solution, the larger the amount of sulfuric acid, the better. However, when the amount of sulfuric acid is large, it becomes difficult to dissolve copper sulfate, and when the amount is excessive, copper sulfate is precipitated. Therefore, a balance between the two is required.

FIG. 1 is a graph showing the relationship between the sulfuric acid concentration, the copper sulfate concentration, and the electrical resistance of the plating solution, and is a comparison when the electrical resistance of 5% sulfuric acid is set to 1. FIG. 2 is a graph showing the relationship between the sulfuric acid concentration and the saturated copper sulfate concentration.

As is clear from Fig. 1, when the sulfuric acid concentration is more than 150 g / 1, the electrical resistance is low and almost constant. Therefore, the sulfuric acid concentration is preferably at least 150 g Zl in order to obtain a plating solution having a low electric resistance. In order to obtain a solution with a high copper concentration, the sulfuric acid concentration is preferably set to 250 gZl or less.

The area below the straight line in Fig. 2 is the area that can be used as a copper plating solution. In the above range of sulfuric acid concentration (150 to 250 g Zl), the copper sulfate concentration is approximately Can be dissolved within the range of 130 to 200 g / l. Within the above range, the plating solution can be used stably while maintaining a high copper concentration. It is best to adjust the concentration of copper sulfate before and after and around 150 g. Note that the “before and after” means about ± 5%.

Examples of the chloride ion source include hydrochloric acid, sodium chloride, potassium chloride, and ammonium chloride. These may be used alone or in combination. The amount of chlorine ion added can be used in the range of 10 to 200 mgZl as chloride ion, but is preferably around 3 SmgZ1.

The sulfur compound is not particularly limited. However, 3-mercapto-1 sodium monopropanesulfonate or 2-sodium sodium mercaptoethanesulfonate, bis- (3-sulfopropyl) disulfido disodium Sulfur compounds such as chromium can be used alone or in combination.

The effect of adding these sulfur compounds is as small as about lmg / 1.

Although the surfactant is not particularly limited, a surfactant such as polyethylene glycol and polypropylene glycol can be used alone or in combination.

The addition amount of the surfactant can be used in the range of several mgZ1 to 1 OgZ1.

Surfactants, when present with chlorine, increase the polarization resistance at the cathode.

On the other hand, a sulfur compound functions as a promoter by lowering the polarization resistance at the cathode.

When surfactants, chloride ions, and sulfur compounds are contained in the copper sulfate plating solution, the polarization resistance of the cathode surface depends on the balance between the amounts of these additives adsorbed. In particular, sulfur compounds are adsorbed on the surface of the adherend, and have a strong effect of lowering the polarization resistance of the adsorbed surface. Therefore, controlling the amount of sulfur compound adsorbed leads to control of polarization resistance.

According to the present invention, during positive electrolysis, the surface of By controlling the polarization resistance on the inlet side of the large-diameter hole to be high and the polarization resistance in the small-diameter hole to be low, a plating film with a uniform thickness is formed as a whole.

For this purpose, reverse electrolysis is performed to remove the sulfur compounds adsorbed on the surface side of the adherend and near the entrance of the small-diameter hole, thereby causing a difference in polarization resistance during positive electrolysis as described above. So that you can hold it.

The electrical resistance of the plating system is defined as the sum of the polarization resistance and the electrical resistance of the plating solution.

Therefore, if the electric resistance of the plating solution is made sufficiently smaller than the polarization resistance, the electric resistance of the plating system, and hence the current value inversely proportional thereto, depends on the magnitude of the polarization resistance. As described above, by increasing the sulfuric acid concentration in the copper plating solution, the electric resistance of the plating solution is suppressed to make it easier to control the polarization resistance.

The polarization resistance R c is

R c = IV _SCE- V. | 1 (V is the equilibrium potential), and the polarization resistance was measured by the potential and the current value.

FIG. 3 is a graph showing the magnitude of the polarization resistance when reverse electrolysis was performed on the wiring substrate at various potentials for 10 seconds and then positive electrolysis was performed. The polarization resistance indicates the polarization resistance on the surface of the object (wiring board). The polarization resistance in the small hole is naturally lower than the polarization resistance of the surface.

As shown in Fig. 3, when the electrolysis potential during reverse electrolysis is in the range of 0.10 to 0.16 V (Vs SCE), the polarization resistance during positive electrolysis changes, and the electrolysis potential during reverse electrolysis changes. It can be seen that the polarization resistance during positive electrolysis can be controlled. The higher the electrolytic potential, the higher the polarization resistance. In other words, the higher the electrode potential, the more the sulfur compound peels off, and the higher the polarization resistance during positive electrolysis. In addition, it is noteworthy that the potential range in which the polarization resistance during positive electrolysis can be controlled was obtained when the reverse electrolysis time was set as long as 10 seconds. This suggests that long-period PPR plating can be performed.

The results of the experiment, the time of reverse electrolysis, well done this and the force ^s' s power in the range of 1 second to a few tens of seconds, ivy.

If the reverse electrolysis is controlled by the potential, the current density may run away. Therefore, it is preferable to control the reverse current by the current density. Current density corresponding to the conductive position becomes 0. l A~ l / dm ^2.

In the case of larger current density than 0. 5 ΑΖ η ² are as they may go rough surface of the object to be plated was controlled by current density in the range of 0. 1~ 0. 5 A / dm ² Is preferred. However, in the case of an adherend whose roughness is not so problematic, it may be controlled at a current density higher than the above. Thus, the degree of peeling of the sulfur compound depends on the current density during reverse electrolysis. Can be controlled, and as a result, the polarization resistance during positive electrolysis can be controlled.

The magnitude of the polarization resistance cannot be measured in the small-diameter hole of the object, but the effect of reverse electrolysis is almost ineffective in the small-diameter hole. Except that it hardly occurs. Therefore, the polarization resistance during the positive electrolysis in the small-diameter hole is maintained at a low level, and accordingly, the current flows into the small-diameter hole, and even in the small-diameter hole, the plating positive rotation is improved. . The setting of the current density during reverse electrolysis, the reverse electrolysis time, the current density during positive electrolysis, and the electrolysis time may be performed while measuring the plating thickness according to the target adherend.

FIG. 4 schematically shows a current waveform of PPR plating in the present embodiment. Current density during optimal reverse electrolysis 0. 1~0. 5 AZ dm ^2, the optimal electrolysis time is 1 to about 1 0 seconds.

In addition, as a result of the experiment, it is more effective to perform two-stage reverse electrolysis in which the reverse electrolysis in the first half is performed at a higher current density and the reverse electrolysis in the latter half is performed at a lower current density than in the first half. It turned out to be a target.

It is considered that the effect is improved by performing the reverse electrolysis in two stages for the following reasons. That is, in the reverse electrolysis in the first half (first stage), the peeling action on the outside of the through hole is strong, and the peeling action on the inside of the through hole is weak. In the reverse electrolysis in the second half (second stage), the potential for peeling is extremely weak, so that peeling occurs slightly outside the through-hole, but there is almost no peeling action inside, and rather adsorption of sulfur compounds occurs. It is thought to proceed.

Therefore, in the first-stage reverse electrolysis, the sulfur compound outside the through-hole is reliably peeled off, and in the second-stage reverse electrolysis, the through-hole is maintained while the peeled state outside the through-hole is maintained by a weak peeling action. Adsorption of sulfur compounds inside occurs. As a result, the difference in the adsorption concentration of the sulfur compound between the outside and the inside of the through hole is larger than in the case where the reverse electrolysis is performed in a single step, and a larger polarization resistance difference is generated.

Also, in reverse electrolysis with only one stage, depending on the shape of the through-hole, the inside of the through-hole may be excessively peeled off, and a sufficient polarization resistance difference between the outside and the inside of the through-hole may not be obtained. Even in such a case, the polarization resistance difference can be reliably obtained by performing the second-stage weak reverse electrolysis.

The current density during positive electrolysis is about 1.5 AZ dm ² (this is not particularly limited; it may be determined by considering the throwing power of the plating), and the electrolysis time is preferably about 50 to 200 seconds. . Example

Copper sulfate plating solution with the following composition was used in common

Copper sulfate pentahydrate 1 500 g / 1

Sulfuric acid 200 g / 1

Polyethylene glycol 4 0 0 3 g / 1

S P S 1 mg / 1

Chlorine 3 5 mg / 1

In addition, SPS refers to bis- (3-sulfopropyl) disodium disodium.

Example 1

A 0.8 mm thick wiring board having a through hole with an opening diameter of 0.1 mm was subjected to PPR plating under the following conditions.

Positive electrolysis: current density 1.5 A / dm ² , electrolysis time 120 seconds

Reverse electrolysis: current density 0.5 A // dm ² , electrolysis time 10 seconds

Plating time 7 6 minutes

As a result, the ratio of film thickness: (film thickness at the center of the through hole / film thickness on the substrate surface) X100 was 91.3%.

Example 2

A 0.8 mm thick wiring board having a through hole with an opening diameter of 0.15 mm was subjected to PPR plating under the following conditions.

Reverse electrolysis: current density 0. δ ΑΖ η ² , electrolysis time 10 seconds

Plating time 7 6 minutes

As a result, the film thickness ratio was 101.4%.

Example 3

PPR plating was performed on a 0.8 mm thick wiring board having a through horn with an opening diameter of 0.1 mm under the following conditions. Positive electrolysis: current density 1.5 AZdm ² , electrolysis time 120 seconds

Reverse electrolysis 1: current density 0.5 A / dm ² , electrolysis time 5 seconds

Reverse electrolysis 2: current density 0.1 A / dm ² , electrolysis time 5 seconds

Plating time 7 6 minutes

As a result, the film thickness ratio was 109.8%.

Example 4

A PPR plating was performed on a 0.8 mm thick wiring board having a through hole with an opening diameter of 0.15 mm under the following conditions.

Positive electrolysis: current density 1.5 AZdm ² , electrolysis time 120 seconds

Reverse electrolysis 1: current density 0. S AZdm ² , electrolysis time 5 seconds

Reverse electrolysis 2: current density 0.1 AZdm ² , electrolysis time 5 seconds

Installation time 7 6 minutes

As a result, the film thickness ratio was 10.8%.

Comparative Example 1

Using the above copper sulfate plating solution, DC plating was performed on a wiring board having a through hole with an opening diameter of 0.1 mm and a thickness of 0.8 mm under the following conditions.

Current density 1.35 AZdm ² ,

Plating time 7 6 minutes

As a result, the film thickness ratio was 53.9%.

Comparative Example 2

Using the above copper sulfate plating solution, DC plating was performed on a wiring board having a through hole with an opening diameter of 0.15 mm and a thickness of 0.8 mm under the following conditions.

Current density 1.35 A / dm ² ,

Plating time 7 6 minutes

As a result, the film thickness ratio was 54.8%. FIGS. 5 to 10 are cross-sectional photographs (75 × magnification) of the through holes. FIGS. 5, 6, 7, and 8 show the through holes of Examples 1, 2, 3, and 4, respectively, and FIGS. Indicates through holes of Comparative Examples 1 and 2, respectively. As described above, in Examples 1 to 4, the film thickness ratio (slowing power) was approximately 100%, and a copper-coated film having a uniform thickness was formed on the surface and in the small-diameter holes. Can be.

In particular, when the reverse electrolysis was performed in two stages, the plating thickness inside the small-diameter hole became thicker than the plating thickness on the surface. In this case, if the plating time is extended, the inside of the small-diameter hole can be filled by plating.

Further, in the above embodiment, plating of through holes has been described as an example, but plating in micro blind vias can be performed in the same manner. Industrial applicability

As described above, according to the method of the present invention, a long-period PPR plating method can be performed in a unit of second, and a high-precision, large-capacity pulse current is not required, so that equipment cost can be reduced. .

In addition, the current for plating on the front and back of the substrate can be easily synchronized, and wiring that takes into account the loss due to inductance becomes unnecessary.

Further, it is possible to form a plating film having a substantially uniform film thickness on the surface, the opening, and the inside of the small-diameter hole.

Claims

The scope of the claims

1. Copper plating using a copper sulfate plating solution containing copper sulfate, sulfuric acid, chlorine ions, sulfur compounds, and surfactants, in a small-diameter hole of an object with small-diameter holes, using the PPR method. In the method of attaching copper to a small diameter hole,

The reverse electrolysis performed at a current density range of 0. l~ l AZdm ^2, the sulfur compounds which are adsorbed on the plated material, Ri particular good performing separation of sulfur of compounds near the entrance of the small-diameter hole, Copper plating in small holes characterized by maintaining a polarization resistance in small holes during positive electrolysis lower than near the entrance of small holes and forming a copper-plated film of uniform thickness in small holes. Method.

2. The two-stage reverse electrolysis in which the reverse electrolysis in the first half is performed at a high current density and the reverse electrolysis in the second half is performed at a lower current density than that in the first half, wherein the reverse electrolysis is performed. Copper plating method for small diameter holes.

3. The method of claim 1 or 2, wherein the positive electrolysis is performed for several tens to several hundred seconds, and the reverse electrolysis is performed for several seconds to several tens of seconds.

4. The method of claim 1, 2, or 3, wherein the positive electrolysis is performed in a current density range of l to ² AZdm2.

5. Use a copper sulfate plating solution with low electrical resistance and high copper concentration, with sulfuric acid concentration of 150-250 g / l and copper sulfate concentration of 130-200 g Zl. The method of claim 1, 2, 3 or 4, wherein the small diameter hole is copper-plated.

6. The copper plating method for a small diameter hole according to claim 1, wherein the inside of the small diameter hole is filled with copper plating.