Wiring board and manufacturing method thereof

A wiring board includes a substrate having a surface made of an insulating resin. An adhesion layer is formed on the substrate. A wiring layer is formed on the adhesion layer. The adhesion layer is formed by a nitrided NiCu alloy containing nitrogen therein. A nitrogen content of the nitrided NiCu alloy is within a range from 1 atoms % to 5 atoms %.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-211368, filed on Sep. 14, 2009, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a wiring board and, more particularly, to a wiring board provided with an adhesion layer between a wiring layer and an insulating layer.

BACKGROUND

In many conventional Cu wiring boards, an adhesion layer is provided between an insulating layer formed on a substrate and a Cu wiring layer formed on the insulating layer (for example, refer to Japanese Laid-Open Patent Application No. 2003-218516). The adhesion layer is provided to fix the Cu wiring layer so that the Cu wiring layer is not separated from the substrate.

A resin material is used as an insulating layer formed on a substrate in many cases. According to a type of a resin to be used, even an adhesion layer formed of CuN does not provide sufficient adhesion strength. If adhesion strength of the adhesion layer is insufficient, a separation may occur between the CuN adhesion layer and the resin insulating layer, which may result in separation of a Cu wiring layer together with the resin insulating layer. Thus, it is suggested to improve adhesiveness between the resin insulating layer and the adhesion layer by forming the adhesion layer by an NiCu alloy (for example, refer to Japanese Laid-Open Application No. 2009-188324).

However, even if an adhesion layer is formed by an NiCu alloy to improve adhesiveness between an insulating layer and an adhesion layer as suggested in the above-mentioned patent document, sufficient adhesiveness may not be obtained depending on a type of resin forming the insulating layer.

SUMMARY

It is a general object of the present invention to provide a wiring substrate and a manufacturing method thereof, in which the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide a wiring board and a manufacturing method thereof, in which adhesion strength of an adhesion layer to an insulating layer is improved.

According to an aspect of the invention, a wiring board includes a substrate; an adhesion layer formed on the substrate; and a wiring layer formed on the adhesion layer, wherein the adhesion layer is formed by a nitrided NiCu alloy.

According to another aspect of the invention, a manufacturing method of a wiring board includes: preparing a substrate having a surface made of an insulating resin; forming an adhesion layer on the substrate by a nitrided NiCu alloy; and forming a wiring layer on the adhesion layer.

According to the above-mentioned invention, the adhesion layer, which is provided between the substrate and the wiring layer, is prevented from being exfoliated or separated from the substrate.

The object and advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary explanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION OF EMBODIMENT(S)

Preferred embodiment of the present invention will be explained with reference to the accompanying drawings.

FIG. 1is a cross-sectional view of a part of a wiring board according to an embodiment of the present invention. The wiring board10according to the embodiment of the present invention includes a substrate body11, a pad12, an insulating layer13, an adhesion layer15, a seed layer16, a circuit pattern18, and wiring19. The seed layer16, the circuit pattern18, and the wiring19together correspond to a wiring layer.

The pad12and the insulating layer13are formed on the substrate main part11. As the substrate body11, for example, a build-up substrate or a coreless substrate is used. The pad12is formed on a top surface11A of the substrate body11. The pad12is electrically connected with wiring and vias (not illustrated in the figure) provided in the substrate body11.

The insulating layer13is formed on a top face11A of the substrate body11. A via hole21(opening) is formed in the insulating layer13so that an upper surface of the pad12is exposed on the bottom of the via hole21. The via hole21is an opening provided to form a via23, which is a part of the wiring pattern18. As the insulating layer13, for example, an insulated resin material such as an epoxy resin or a polyimide resin is used.

If the substrate body11is formed of an insulating resin material such as, for example, an epoxy resin or a polyimide resin, it is not necessary to form the insulating layer13. In such a case, it can be interpreted that the insulating layer13is contained in the substrate body11. Therefore, if the substrate body11is formed of an insulating resin material, the substrate body11corresponds to the substrate, and if the insulating layer13is formed on the substrate body11, the combination of the substrate body and the insulating layer13corresponds to the substrate. The adhesion layer15is formed on the thus-formed substrate.

In the present embodiment, the adhesion layer15is formed on an upper surface13A of the insulating layer13in an area where the wiring pattern18and the wiring19are formed. The adhesion layer15is also formed on a surface of the insulating layer, which corresponds to an inner surface of the via hole21. Further, the adhesion layer15is formed on an upper surface of the pad12, which surface is exposed in a bottom part of the via hole21. The adhesion layer15is arranged between the insulating layer13and the seed layer16. The adhesion layer15is formed of a material having excellent adhesiveness to the seed layer16and also to the insulating layer13. If, for example, an epoxy resin substrate is used for the substrate body11as mentioned above, the insulating layer13is not formed but the adhesion layer15is formed directly on the substrate body11.

In the present embodiment, the adhesion layer15is formed by a nitrided NiCu alloy. That is, the adhesion layer15is a thin film formed of a material which is made of an NiCu alloy containing nitrogen. The content of nickel in the adhesion layer15formed of a nitrided NiCu alloy is preferably set to 20 wt % or more. This can improve the adhesiveness between the adhesion layer15and the insulating layer13. Because the adhesiveness between the insulating layer13and the adhesion layer15is improved by using a nitrided NiCu alloy having an Ni content of 20 wt % or more, the adhesion layer15is hardly separated from the insulating layer13.

It is preferable to set a content of Ni in the nitrided NiCu alloy in a range, for example, from 20 wt % to 75 wt %. By setting the content of Ni in the nitrided NiCu alloy in a range from 20 wt % to 75 wt %, the adhesion layer15becomes hardly separable from the insulating layer13. If, for example, a Cu layer is used for the seed layer16, the adhesion layer15can be removed by etching using a Cu etchant (for example, a solution of sulfuric acid system), which is used for removing an unnecessary portion of the seed layer16.

If the content of nickel in the nitrided NiCu alloy exceeds 75 wt %, it is difficult to remove the Ni—Cu alloy layer (the adhesion layer15) by using the Cu etchant. If the content of Ni in the nitrided NiCu alloy is set within the range from 20 wt % to 75 wt %, a thickness of the adhesion layer15formed of the nitrided NiCu alloy, is preferably set to, for example, 30 nm to 100 nm.

In the present embodiment, the adhesion layer15is formed by a nitrided NiCu alloy, and, thus, the adhesion layer15contains nitrogen. The present inventor newly found that adhesion strength between the adhesion layer15and the resin layer13can be further improved by adding nitrogen to an NiCu alloy used as a material of the adhesion layer15. It is preferable that the content of nitrogen in the NiCu alloy is set in a range from 0.5 to 5.0 atoms %. It is also preferable to set a weight ratio of Ni and Cu other than nitrogen to 1:2 (Ni:Cu-1:2).

The seed layer16is arranged to cover an upper surface of the adhesion layer15. The seed layer16serves a power supply layer when forming the wiring pattern18and the wiring19according to an electroplating method. For example, a Cu layer is used for the seed layer16. If a Cu layer is used as the seed layer16, a thickness of the seed layer16is preferably set in a range, for example, from 300 nm to 500 nm.

If the circuit pattern18and the wiring19are formed according to a film-deposition method other than an electroplating method, the seed layer16serving as a power supply layer is unnecessary. Thus, a wiring layer forming the circuit pattern18and the wiring19may be formed directly on the adhesion layer15.

The circuit pattern18includes a via23and a wiring24integrally formed with an upper portion of the via23. The via23is provided on the seed layer16formed in the via hole21. Cu may be used as a material of the circuit pattern18. The circuit pattern18is electrically connected to the pad21through the adhesion layer15and the seed layer16.

The wiring19is provided on an upper surface of the seed layer16, which is arranged at a position separate from the wiring pattern18. For example, Cu may be used as a material of the wiring19.

According to the wiring board of the present embodiment, the adhesion layer15is hardly separated from the insulating layer13because the adhesiveness between the insulating layer13and the adhesion layer15is improved by using an NiCU alloy having a nitrogen content of 0.5 atoms % to 5.0 atoms % (0.5-5.0 atoms %) as a material of forming the adhesion layer15, which is arranged between the insulating layer13and the seed layer16.

Moreover, the adhesion layer15is hardly separated from the insulating layer13by setting the Ni content in the adhesion layer15within a range of 20 wt % to 75 wt %. Further, the adhesion layer15can be removed by etching using, for example, a Cu etchant (for example, a solution of sulfuric acid system).

A description will be given below, with reference toFIG. 2throughFIG. 8, of a manufacturing method of the above-mentioned wiring board.FIG. 2throughFIG. 8are cross-sectional views illustrating a manufacturing process of the wiring board10illustrated inFIG. 1. In this manufacturing process, Cu wiring is formed according to an additive method.

First, in an insulating layer forming process illustrated inFIG. 2, the pad12and the insulating layer13having the opening part21are formed sequentially on the upper surface11A of the substrate body11according to a known method. Thereafter, the upper surface of the insulating layer13and a surface of the insulating layer13to form the opening part21are cleaned (removing a water component, etc.).

As the substrate body11, a substrate such as, for example, a build up substrate with a core or a careless substrate may be used. The pad12can be formed by, for example, a subtractive method, a semi additive method, etc. Cu may be used as a material of the pad12. The insulating layer13is formed by sticking a half-cured insulating resin sheet made of an epoxy resin, a polyimide resin, etc., onto the upper surface11A of the substrate body11on which the pad12is formed, and curing the half-cured insulating resin sheet.

Then, in an adhesion layer forming process illustrated inFIG. 3, the adhesion layer is formed by a nitrided NiCu alloy to cover the upper surface13A of the insulating layer13, the surface of the insulating layer13to form the via hole21, and the upper surface of the pad12.

By forming the adhesion layer15by the NiCu alloy having the nitrogen content of 0.5 to 5.0 atoms %, the adhesiveness between the insulating layer13and the adhesion layer15is improved. Specifically, because peel strength of the adhesive layer15to the insulating layer13becomes 0.5 kgf/cm or more, the adhesion layer15can be prevented from being separated or exfoliated from the insulating layer13.

It is preferable that the Ni content of the nitrided NiCu alloy of the adhesion layer15is set within a range, for example, from 20 wt % to 75 wt %. By setting a content of Ni in the nitrided NiCu alloy in the range from 20 wt % to 75 wt %, the adhesion layer15becomes hardly separable from the insulating layer13, and an unnecessary portion of the adhesion layer15can be removed by using an etchant (for example, a solution of sulfuric acid system), which is used for removing an unnecessary portion of the seed layer16. Thus, there is no need to remove an unnecessary portion of the seed layer16and an unnecessary portion of the adhesion layer15by using different etchants, thereby suppressing an increase in the manufacturing cost of the wiring board10.

If the content of Ni in the nitrided NiCu alloy is set within the range from 20 wt % to 75 wt %, a thickness of the adhesion layer15formed of the nitrided NiCu alloy may be set to, for example, 30 nm to 100 nm.

The adhesion layer15is preferably formed by, for example, a sputtering method. By forming the adhesion layer15by using a sputtering method, the nitrogen content and the Ni content of the adhesion layer15(nitrided NiCu alloy) can be set to a desired ratio with high accuracy. For example, the above-mentioned ratio Ni:Cu=1:2 can be attained by setting the Ni content of an NiCu alloy target used in a sputtering method to 33 wt %.

Subsequently, in a seed layer forming process illustrated inFIG. 4, the seed layer16is formed to cover the upper surface of the adhesion layer15. It is preferable to form the seed layer16by using a sputtering method. By forming the seed layer16using the sputtering method, the seed layer16can be formed using a sputtering apparatus, which is used to form the adhesion layer15. For example, Cu may be used as a material of the seed layer16. If the seed layer16is formed of Cu, a thickness of the seed layer16is preferably set within a range from 300 nm to 500 nm.

Subsequently, in a resist film forming process illustrated inFIG. 5, a resist film27having opening parts27A and273is formed on the top surface of the seed layer16. The opening part27A is formed so that a portion of the seed layer16corresponding to an area where the circuit pattern18is formed is exposed. The opening part27B is formed so that a portion of the seed layer16corresponding to an area where the wiring19is formed is exposed. For example, it is preferable to set L/S of the resist film27to 12/12 μm, and set a thickness of the resist film27to 25 μm.

Subsequently, in a wiring and circuit pattern forming process illustrated inFIG. 6, the wiring19and the circuit pattern18having the via23and the wiring24are simultaneously formed by forming a plating film (for example, a Cu plating film) on the seed layer16exposed by the openings27A and27B. At this stage, the circuit pattern18is electrically connected to the wiring19through the adhesion layer15and the seed layer16. The thickness of the wiring19and the wiring24is preferably set to 20 μm.

Subsequently, in a resist film removing process illustrated inFIG. 7, the resist film illustrated inFIG. 6is removed. Then, in a seed layer and adhesion layer removing process illustrated inFIG. 8, portions of the seed layer16and the adhesion layer15formed in areas other than the area where the circuit pattern18and the wiring19are formed are removed. That is, an unnecessary portion of the seed layer16and an unnecessary portion of the adhesion layer15are removed.

Specifically, when a Cu layer is used as the seed layer16and the Ni content of the adhesion layer15is set within a range from 20 wt % to 75 wt %, an unnecessary portion of the seed layer16and an unnecessary portion of the adhesion layer15are removed simultaneously by using a Cu etchant (for example, a solution of sulfuric acid system).

The wiring board10according to the present embodiment can be formed by performing the above-mentioned processes.

A description will be given below of results of experiments to check adhesiveness of the adhesion layer15. The inventor formed the adhesion layer15on the insulating layer13by the above-mentioned manufacturing method, and carried out peel tests of the adhesion layer15. Nitrogen gas was added to an Ar gas atmosphere when forming the adhesion layer15by a sputtering method in order to cause an NiCu alloy to contain nitrogen. Samples were fabricated while varying an amount of the nitrogen gas added to the Ar gas atmosphere from 0% to 20%, the thus-fabricated samples were subjected to the peel test. The peel strength was represented by a force (kgf/cm) necessary to peel or separate the adhesion layer15of a width of 1 cm from the insulating layer13.FIG. 9is a graph indicating the peel strength of the adhesion layer15.

As interpreted fromFIG. 9, the peel strength of the adhesion layer15when nitrogen gas was not added (0%) was 0.24 kgf/cm, which is a low value. When nitrogen gas was added to the Ar gas atmosphere, the peel strength increased, and the peel strength when nitrogen gas was added by 5% was raised to 0.76 kgf/cm. When nitrogen gas was added by 7.7%, the peel strength was 9.1 kgf/cm, which is the maximum peak value. When an amount of nitrogen gas was increased further, the peel strength decreased. When an amount of nitrogen gas added to the Ar gas atmosphere was increased to 15%, the peel strength was decreased to 0.28 kgf/cm.

As a result of investigation of the peel strength at which a separation of the adhesion layer does not occur in actual products, it was found that separation of the adhesion layer hardly occurs if the peel strength is 0.5 kgf/cm or more, which provides no problem in practice. From the graph ofFIG. 9, it was found that the peel strength is 0.5 kgf/cm or more if an amount of nitrogen gas added to the Ar gas atmosphere is in a range from 2.5% to 12.5%. Thus, the inventor investigated a nitrogen content of the nitrided NiCu alloy formed as the adhesion layer15when the amount of nitrogen gas added to the Ar gas atmosphere was varied from 2.5% to 12.5%.

FIG. 10is a graph indicating a composition of a nitrided NiCu alloy when the nitrided NiCu alloy was formed by a sputtering method while varying an amount of nitrogen gas added to the Ar gas atmosphere. When the amount of nitrogen gas added to the Ar gas atmosphere was 0% (that is, nitrogen gas is not added), an amount of Ni in the NiCu alloy was 32 atoms % and an amount of Cu was 68 atoms %. When nitrogen gas was added to the Ar gas atmosphere, an NiCu alloy containing nitrogen, that is, a nitrided NiCu alloy was formed. When an amount of nitrogen gas was increased, an amount of nitrogen contained in the nitrided NiCu alloy was also increase.

FIG. 11is a graph indicating a change in the nitrogen content ofFIG. 10with an enlarged scale of the vertical axis.FIG. 11clearly indicates a change in the nitrogen content. That is,FIG. 11is a graph indicating the nitrogen content in the nitrided NiCu alloy when the nitrided NiCu alloy was formed by a sputtering method while varying an amount of nitrogen gas added to the Ar gas atmosphere. It was found from the graph ofFIG. 11that the nitrogen content of the nitrided NiCu alloy when an amount of nitrogen gas added to the Ar gas atmosphere was varied from 2.5% to 12.5% was equal to or greater than 1 atoms % and equal to or less than 5 atoms % (from 1 atoms % to 5 atoms %). Accordingly, it was found that if the nitrogen content of the nitrided NiCu alloy is in the range from 1 atoms % to 5 atoms %, the peel strength of the adhesion layer15formed of a nitrided NiCu alloy is 0.5 kgf/cm or more. That is, by setting the nitrogen content of the nitrided NiCu alloy to a value within the range from 1 atoms % to 5 atoms %, the peel strength of the adhesion layer15can be 0.5 kgf/cm or more, thereby surely preventing separation or exfoliation of the adhesion layer15.

Although the Cu wiring is formed by an additive method in the above-mentioned manufacturing method of the wiring board10, the Cu wiring may be formed by using a subtractive method or a damascene method.

FIG. 12throughFIG. 17are cross-sectional views illustrating a process of forming a Cu wiring on the substrate via the adhesion layer by a subtractive method. InFIG. 12throughFIG. 17, parts that are the same as the parts illustrated inFIG. 2throughFIG. 8are given the same reference numerals.

In a process illustrated inFIGS. 12 and 13, a process of forming the adhesion layer15and the seed layer16on the insulating layer13is the same as that illustrated inFIGS. 2 through 4, and descriptions thereof will be omitted. The adhesion layer15is formed by a nitrided NiCu alloy as mentioned above. In a subtractive method, a Cu plating layer30is formed on an entire surface of the seed layer16by an electroplating method after forming the adhesion layer15and the seed layer16on the insulating layer13. A part of the Cu plating layer30serves as the circuit pattern18and the wiring19.

After forming the Cu plating layer30, a resist27is formed on the Cu plating layer30in a resist pattering process illustrated inFIG. 15and an opening27C is formed in the resist27. The opening27C is formed so that the Cu plating layer30is exposed in an area other than the area where the circuit pattern18and the wiring19are formed.

Then, in a plating layer removing process illustrated inFIG. 16, the Cu plating layer30exposed in the opening27C is removed by etching. For example, a copper chloride solution is used as an etchant. In this etching, the seed layer16and the adhesion layer15located under the Cu plating layer30can be removed simultaneously by the etching. A portion of the Cu plating layer30covered by the resist27remains, which portion serves as the circuit pattern18and the wiring19. Then, the resist27is removed in a resist removing process illustrated inFIG. 17, and the wiring board10having the circuit pattern18and the wiring19is completed.

FIG. 18throughFIG. 21are cross-sectional views illustrating a process of forming a Cu wiring on a substrate via an adhesion layer by a dual damascene method. InFIG. 18throughFIG. 21, parts that are the same as the parts illustrated inFIG. 2throughFIG. 8are given the same reference numerals.

InFIG. 18, a process of forming the adhesion layer15and the seed layer16on the insulating layer13is the same as that illustrated inFIG. 2throughFIG. 4, and descriptions thereof will be omitted. According to the dual damascene method, wiring grooves13A and13B are formed in an area of the insulating layer13where the circuit pattern18and the wiring19are to be formed. The wiring groove13A corresponds to an area where the circuit pattern18is formed, and the wiring groove13B corresponds to an area where the wiring19is formed.

Then, as illustrated inFIG. 19, the adhesion layer15made of a nitrided NiCu alloy film and the seed layer16are formed on the surface of the insulating layer13including inner surfaces of the wiring grooves13A and13B. Then, as illustrated inFIG. 20, a Cu plating layer40is formed on the seed layer16by an electroplating method to fill the Cu plating layer40in the wiring grooves13A and13B. Then, as illustrated inFIG. 21, the Cu plating layer40formed on the surface of the insulating layer13is removed by chemical mechanical polishing (CMP), and the seed layer16and the adhesion layer15are removed. Thereby, the Cu plating layer40remains in the wiring grooves13A and13B, and the Cu plating layer40in the wiring grooves13A and13B serves as the circuit pattern18and the wiring19.

According to the wiring board and the manufacturing method according to the present embodiment, the peel strength of the adhesion layer15to the insulating layer13can be made larger than that of an adhesion layer formed of an NiCu alloy containing no nitrogen, by forming the NiCu alloy layer containing nitrogen as the adhesion layer15arranged between the insulating layer13and the seed layer16. For example, in a case where a Cu layer is used as the seed layer16, an unnecessary portion of the seed layer16and an unnecessary portion of the adhesion layer15can be removed in the same etching process using a Cu etchant (for example, a liquid for etching Cu) by setting the nitrogen content of the adhesion layer15within the range from 20 wt % to 75 wt %. Thereby, an increase in the manufacturing cost of the wiring board10can be suppressed.