JP2002161389A - Method for improving adhesion between metal films - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving an adhesion between a metal thin film formed on a substrate and a metal film electroplated later thereon, even when the metal thin film is very thin. SOLUTION: The method for improving the adhesion between the metal thin film of a conducting layer and the electroplated film, comprises immersing the substrate provided with the metal thin film of the conducting layer, into a liquid of pH 2 or lower, which includes a predetermined concentration of a coupling agent having metal scavenging ability, before electroplating metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal thin film which becomes a conductive layer by subjecting a substrate having a metal thin film which becomes a conductive layer to a dipping treatment in a liquid containing a coupling agent having a metal-capturing ability. And a pretreatment method for improving adhesion to an electrometal plating film performed thereafter. Note that a substrate described in this specification refers to a semiconductor wafer, a glass substrate, a printed substrate, a build-up substrate, or the like.

[0002]

2. Description of the Related Art Conventionally, a conductive metal thin film is formed on a substrate, and a metal thin film of copper, nickel or the like is further formed thereon by electroplating. Generally, it is difficult to obtain sufficient adhesion when an electrometal plating film is applied to a thickness of about several μm on a metal thin film formed on a substrate. In this case, as a method of improving the adhesion, a method of improving the adhesion by roughening the surface of the conductive layer by etching or the like can be considered. However, conventionally, when electrometal plating is performed on a metal thin film to be a conductive layer, there has been a problem that when the thickness is about several μm, sufficient adhesion cannot be obtained. This is because the thickness of the metal thin film serving as the conductive layer is extremely small (1 μm
In the case of (less than or equal to), roughening of the surface is difficult, so that plating is difficult to attach. That is, when the thickness of the metal thin film formed on the substrate is very thin (about 1 μm or less), the metal thin film itself is lost by the above-described roughening treatment, and the next electroplating cannot be performed properly. This is because uneven plating or spots (mottle) may occur and effective plating cannot be performed.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a method for improving the adhesion to an electrometal plating film to be performed later, even if the thickness of the metal thin film formed on the substrate is very small. The task is to obtain

[0004]

In view of the above problems, a surface treatment using a specific compound having the function of capturing metal ions and the function of immobilizing it on a metal thin film in the same molecule is carried out. We have found that it is possible to improve the adhesion to the electroplating film. The present invention provides the following based on such knowledge. 1. 1. A substrate containing a metal thin film to be a conductive layer, containing a coupling agent having a metal-capturing ability at the following concentration and having a pH of 2.
A method of improving adhesion between metal films for improving adhesion between a metal thin film to be a conductive layer and an electroplating film, characterized by performing immersion treatment in a solution of 0 or less, and then performing electrometal plating. Coupling agent concentration : 0.001 to 10% by weight 2. The method for improving adhesion between metal films as described in 1 above, wherein the substrate provided with the metal thin film serving as the conductive layer is pickled with 1 to 10% acid before being immersed in a solution containing a coupling agent. 3. 3. The method for improving adhesion between metal films as described in 2 above, wherein the acid used for pickling is any one of hydrochloric acid, sulfuric acid, and nitric acid, or a mixed acid thereof. 4. The method for improving adhesion between metal films according to any one of the above items 1 to 3, wherein the material of the metal thin film serving as the conductive layer is nickel.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that a coupling agent (for example, a silane coupling agent, a titanium coupling agent, etc.) is used. That is, by using a coupling agent in which a functional group having a metal-capturing ability is adsorbed on a metal thin film and present in a molecule, metal ions in the plating solution are captured by the functional group, and as a result, electroplating is performed. In this case, the adhesiveness can be expressed.

[0006] Examples of the functional group having a metal-capturing ability include an amino group, a carboxyl group, an azole group, a hydroxyl group and a mercapto group. However, it is not limited to these groups, and may have another functional group. Among these, an azole group is preferred. As the azole group, imidazole, oxazole, thiazole, selenazole,
Pyrazole, isoxazole, isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, oxatriazole, thiatriazole, bendazole, indazole, benzimidazole, benzotriazole and the like. Among them, an imidazole group is particularly preferred.

Further, the silane coupling agent is -S
a compound having iX ₁ X ₂ X ₃ groups, wherein X _1, X _2,
X ₃ means an alkyl group, a halogen and an alkoxy group may be a functional group capable of fixing to be plated.
X _1, X _{2 and} X ₃ may be the same or different.
For example, a silane coupling agent obtained by a reaction between an azole compound and an epoxysilane compound can be exemplified (see JP-A-6-256358).

Other examples of the silane coupling agent having a metal-capturing ability used in the present invention include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropyl Trimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane and the like can be mentioned.

Further, the titanium coupling agent is -T
iX₁X₂X₃Group or TiX₁X ₂X₃X₄X₅Base
A compound having₁, X₂, X₃, X₄, X₅Is
Alkyl group, halogen, alkoxy group, etc.
Any functional group that can be fixed to a plating object may be used. X_1,
X_2,X₃, X₄, X₅Are the same or different
good. For example, isopropyl tris (dioctyl pyro
(Phosphate) titanate, tetraisopropylbis
(Dioctyl phosphite) titanate, tetraoctyl
Rubis (ditridecyl phosphite) titanate, tet
La (2,2-diallyloxymethyl-1-butyl) bis
(Di-tridecyl) phosphite titanate, bis (di
Octyl pyrophosphate) oxyacetate rape
Bis (dioctyl pyrophosphate) ethylene
Titanate, isopropyl tri (N-amidoethyl
(Minoethyl) titanate and the like.

The material of the metal thin film serving as the conductive layer is not particularly limited, and examples thereof include nickel and copper. Among them, nickel has an appropriate corrosion resistance, and thus is easily captured by a functional group having a metal capturing ability of a coupling agent, and is particularly preferable as a conductive layer. Further, before the substrate having the metal thin film to be a conductive layer is treated with the coupling agent, the substrate is pickled with an acid such as hydrochloric acid, sulfuric acid, or nitric acid of about 1 to 10%, so that the effect of the coupling agent is reduced. Can be bigger. If the acid concentration at the time of pickling is less than 1%, there is no effect of pickling, and if it exceeds 10%, the effect is saturated,
It is preferable to use about 1 to 10% of an acid since it becomes useless.

When the surface is treated with a liquid containing a coupling agent, the liquid is treated with a suitable solvent such as water, methyl alcohol, ethyl alcohol, 2-propanol, acetone,
It can be used as a solution prepared by dissolving toluene, ethylene glycol, polyethylene glycol, dimethylformamide, dimethylsulfoxide, dioxane, or the like, or a mixed solution thereof.

For a metal film, a method is generally used in which a solvent is volatilized after the surface is coated by immersion treatment, but the method is not necessarily limited thereto, and a method in which a coupling agent is uniformly adhered to the surface. Should be fine. Depending on the state of adhesion, the drying step may be omitted only by washing with water. The concentration of the coupling agent is not limited to this, but 0.001 to 10% by weight is suitable for use. 0.
If the amount is less than 001% by weight, the amount of the compound adhering to the surface of the base material tends to be low, and it is difficult to obtain the effect. On the other hand, if it exceeds 10% by weight, the amount of adhesion may be too large to be dried, or the coating may be too thick to lower the adhesion. Particularly when the pH of the solution containing the coupling agent is 2.0 or less, the effect of the coupling agent can be enhanced.

In order to volatilize the solvent used after the surface treatment, it is sufficient to heat the solvent to a temperature equal to or higher than the volatilization temperature and to dry the surface. preferable. When water is used as the solvent, the drying step can be omitted, and plating can be performed only by washing with water after the surface treatment. Although the temperature at which the pretreatment is performed is sufficient even at room temperature, the heating can increase the adhesion speed and the amount of adhesion. The temperature when heating is 30-8
0 ° C is good. The electroplating metal performed on the metal thin film is not particularly limited, and examples thereof include nickel, copper, gold, and alloys thereof.

[0014]

Examples and Comparative Examples Next, examples and comparative examples of the present invention will be described. The present embodiment is a preferred example, and does not limit the present invention. The present invention naturally includes modifications and other examples included in the scope of the technical idea. (Examples and Comparative Examples) As a material to be plated, a material obtained by sputtering nickel (200 nm) on the outermost surface of a silicon wafer was used. The adhesion of the plating film was confirmed by SEM observation of a cleavage cross section of the interface between the sputtered nickel film and the film.

(Example 1) 1% of the silicon wafer
-Immersion washing in hydrochloric acid solution for 1 minute, washing thoroughly with running water,
An aqueous solution (pH 1.5) containing 0.01% by weight of a silane coupling agent which is an equimolar reaction product of imidazole and γ-glycidoxypropyltrimethoxysilane has a concentration of 50%.
It was immersed at 5 ° C. for 5 minutes, washed sufficiently with running water, and plated with a thickness of 5 μm using an electric nickel plating solution (nickel sulfamate plating solution manufactured by Nikko Metal Plating Co., Ltd.). The conditions for the electro-nickel plating are as follows. Bath temperature: 50 ° C pH: 4.0 Cathode current density: 3 A / dm ² Plating time: 500 sec Stirring: Air stirring As a result of observing the cross section of the plating film interface, no gap was seen at all, and nickel adhered to the entire surface of the silicon wafer Plating was good. (See Fig. 1)

Example 2 1% of the silicon wafer
-Immersion washing in hydrochloric acid solution for 1 minute, washing thoroughly with running water,
An aqueous solution containing 0.02% by weight of γ-aminopropyltriethoxysilane (manufactured by Kanto Chemical Co., Ltd.) (pH 1.
2) Immerse in 50 ° C for 5 minutes, rinse thoroughly with running water,
Using an electric nickel plating solution (nickel sulfamate plating solution manufactured by Nikko Metal Plating Co., Ltd.)
Plating corresponding to a thickness of 5 μm was performed. Nickel plating was performed under the same conditions as in Example 1. As a result of observing the cross section of the plating film interface, no gap was observed at all, and nickel was plated with good adhesion over the entire surface of the silicon wafer.

Example 3 5% of the silicon wafer
-Immerse and wash in sulfuric acid solution for 1 minute, wash thoroughly with running water,
It was immersed in an aqueous solution (pH 1.0) containing 0.05% by weight of the silane coupling agent prepared in Example 1 at 50 ° C. for 5 minutes, thoroughly washed with running water, and then subjected to an electric nickel plating solution (Nikko Metal Plating). Using a nickel sulfamate plating solution (manufactured by Co., Ltd.), plating equivalent to a thickness of 5 μm was performed. Nickel plating was performed under the same conditions as in Example 1. As a result of observing the cross section of the plating film interface, no gap was observed at all, and nickel was plated with good adhesion over the entire surface of the silicon wafer.

(Embodiment 4) The above-mentioned silicon wafer is
% -Nitric acid solution for 1 minute, washed thoroughly with running water, and then 0.1% of the silane coupling agent prepared in Example 1 was added.
Immersed in an aqueous solution (pH 1.7) containing 5% by weight at 50 ° C. for 5 minutes, thoroughly washed with running water, and then, using an electric nickel plating solution (Nikko Metal Plating Co., Ltd. nickel sulfamate plating solution), Plating corresponding to a thickness of 5 μm was performed. Nickel plating was performed under the same conditions as in Example 1. As a result of observing the cross section of the plating film interface, no gap was observed at all, and nickel was plated with good adhesion over the entire surface of the silicon wafer.

Comparative Example 1 1% of the silicon wafer
-Immersion washing in hydrochloric acid solution for 1 minute, washing thoroughly with running water,
Using an electric nickel plating solution (nickel sulfamate plating solution manufactured by Nikko Metal Plating Co., Ltd.)
Plating corresponding to a thickness of 5 μm was performed. Nickel plating was performed under the same conditions as in Example 1. As a result of observing the cross section of the plating film interface, a gap was found throughout the interface (see FIG. 2).
As shown in this example, when the immersion treatment was not performed in the liquid containing the coupling agent of the present invention, the adhesion of the electronickel plating film was poor.

(Comparative Example 2) 5% of the silicon wafer
-Immersion washing in hydrochloric acid solution for 1 minute, washing thoroughly with running water,
It was immersed in an aqueous solution (pH 5.0) containing 0.1% by weight of the silane coupling agent prepared in Example 1 at 50 ° C. for 5 minutes, washed sufficiently with running water, and then subjected to an electric nickel plating solution (Nikko Metal Plating). Using a nickel sulfamate plating solution (manufactured by Co., Ltd.), plating equivalent to a thickness of 5 μm was performed. Nickel plating was performed under the same conditions as in Example 1. As a result of observing the cross section of the plating film interface, a gap was found in a part of the interface (see FIG. 3). It has been found that if the pH is high, plating may not be performed properly even when the same silane coupling agent as in the examples is used.

In the above embodiment, γ-aminopropyltriethoxysilane was used. However, other results, that is, when various coupling agents shown in the above-mentioned examples were used, similar results were obtained. In addition, an example of comparison (comparative example) is not particularly shown, but before the treatment with the coupling agent,
It was confirmed that the effect of the coupling agent was increased by pickling with about 1 to 10% of an acid such as hydrochloric acid, sulfuric acid or nitric acid. Further, when the pH of the liquid containing the coupling agent is 2.0 or less, there is an effect of particularly improving the adhesion.

[0022]

According to the present invention, when electroplating a substrate having a metal thin film as a conductive layer, a surface treatment using a coupling agent having a function of capturing metal ions and a function of fixing the same on the metal thin film in the same molecule. This has an excellent effect that the adhesion to the subsequent electroplating film can be remarkably improved by the relatively simple treatment.

[Brief description of the drawings]

FIG. 1 is a cross-sectional micrograph of a plating film interface in Example 1.

FIG. 2 is a cross-sectional micrograph of a plating film interface in Comparative Example 1.

FIG. 3 is a cross-sectional micrograph of a plating film interface in Comparative Example 2.

Continued on front page F term (reference) 4K024 AA03 AB01 BA01 BA15 BB11 BB12 DA03 DA10 GA01 4K044 AA06 AA11 AA12 BA06 BB03 BC05 CA04 CA13 CA18

Claims (4)

[Claims] 1. A substrate provided with a metal thin film serving as a conductive layer is subjected to immersion treatment in a solution containing a coupling agent having the following concentration of a metal and having a pH of 2.0 or less, followed by electrometal plating. A method for improving adhesion between metal films, which improves the adhesion between a metal thin film serving as a conductive layer and an electroplating film. Coupling agent concentration: 0.001 to 10% by weight 2. The method according to claim 1, further comprising:
1-10% before immersion treatment in liquid containing coupling agent
2. The method for improving the adhesion between metal films according to claim 1, wherein the substrate is pickled with an acid. 3. The method for improving adhesion between metal films according to claim 2, wherein the acid used for pickling is any one of hydrochloric acid, sulfuric acid and nitric acid, or a mixed acid thereof. 4. The method for improving adhesion between metal films according to claim 1, wherein the material of the metal thin film to be the conductive layer is nickel.