JP7126681B2 - METHOD FOR MANUFACTURING METAL FILM - Google Patents

Description

The present disclosure relates to a method for manufacturing a metal film. In particular, it relates to a method for improving the adhesion of a metal film to a substrate.

Metal films are widely used for wiring of electronic devices and plating of ornaments. Adhesion to the substrate is important in the formation of the metal film. If the adhesion is weak, peeling of the metal film from the base material is likely to occur. As a result, defective wiring of the electronic device may occur, or the appearance of the decorative article may be deteriorated, thereby lowering the ornamental value.

In addition, as the electronic devices become finer, the width of the wiring becomes finer, and the increase in current density and resistance in the wiring becomes serious. In particular, the increase in power consumption due to the recent development of power semiconductors has made this even more remarkable. An increase in current density and resistance causes thermal stress and electromigration, which can lead to peeling and damage of wiring. Therefore, improving the adhesion of wiring is an important issue.

In general, the adhesion strength of a metal film varies greatly depending on the film formation method, and the physical vapor deposition (PVD) method is considered effective for increasing the adhesion. Also when wiring is formed, a film is formed by the PVD method, which is excellent in adhesion and film quality.

In order to improve film quality and adhesion in the PVD method, it is necessary to increase the degree of vacuum during film formation to avoid inclusion of impurities and voids. For that purpose, a high-vacuum and clean chamber is essential. For example, the sputtering method classified as PVD requires an expensive vacuum pump because it requires a high degree of vacuum. Also, in order to improve adhesion, it is necessary to sufficiently increase the energy during film formation.

Furthermore, compatibility between the material of the base material to be film-formed and the material of the metal film is also an important factor, which greatly affects the adhesion. Specifically, the mismatch strain caused by the difference in lattice constant between materials greatly affects the adhesion.

An intermediate film may be formed between the base material and the base material in order to alleviate this mismatch strain. For example, when forming an Au thin film on a Si substrate, an intermediate film made of Cr or Ti is formed between Si and Au, thereby relaxing mismatch strain between Si and Au and improving adhesion. are improving. However, Ti and Au may react to form brittle metal phases such as TiAu ₂ and Ti ₃ Au. Therefore, a barrier metal layer such as Pt is sometimes provided between Ti and Au.

Patent Document 1 describes forming an intermediate film by vapor deposition polymerization of a polyimide resin on a resin base material, and forming a metal film on the intermediate film, thereby improving the adhesion of the metal film. is stated.

Non-Patent Document 1 describes that by applying a high-density current to a metal material, the crystal structure and crystal grain size are changed to repair fatigue cracks.

JP-A-2003-34883

X. N. Du, et al., Journal of Materials Research, pp.1948-1951

However, in the conventional method, the number of laminations on the base material is increased, and there are problems such as an increase in the number of steps and an increase in the thickness of the wiring, which causes an increase in cost. Therefore, there has been a demand for a technique for improving the adhesion of metal films without increasing the number of layers.

Accordingly, an object of the present disclosure is to improve adhesion of a metal film formed on a substrate in a method for producing a metal film.

The present disclosure includes a step of forming a metal film made of Au, Cu, Al, and Ag on a substrate, and applying an alternating current having a current density of 100 A/mm ² or more and 10 kA/mm ² or less and a frequency of 5 MHz or more to the metal film. and a step of repairing defects in the metal film by applying for 10 to 30 minutes and increasing the contact area between the base material and the metal film, thereby improving the adhesion between the base material and the metal film. It is a manufacturing method of the metal film which does.

According to the method for producing a metal film of the present disclosure, it is possible to improve the adhesion of the metal film to the substrate.

4 is a flow chart showing steps of a method for manufacturing a metal film according to the present disclosure; FIG. 4 is a schematic diagram showing a manufacturing process of the metal film of the present disclosure; The figure which showed the peel-off test method. The graph which showed the frequency of alternating current, and the relationship of adhesion force. The graph which showed the relationship between the application time of an alternating current, and adhesive strength. 4 is a graph showing the relationship between the application time of an alternating current and the crystal grain size of a metal film. The graph which showed the relationship between the crystal grain size of a metal film, and adhesive strength. The graph which showed the application time of an alternating current, and the ratio of a crystal face.

FIG. 1 is a flow chart showing the steps of the method for manufacturing a metal film of the present disclosure. Hereinafter, the manufacturing process of the metal film of the present disclosure will be described along this flow chart.

(Step S1)
First, a metal film 2 is formed on a substrate 1 by sputtering (see FIG. 2). In the sputtering method, inert gas ions having high kinetic energy collide with a target to repel target atoms (atoms forming the metal film 2). Then, a film is formed when the target atoms that have been flipped off reach the surface of the substrate 1 . The target atoms that have reached the surface of the base material 1 do not immediately settle on the surface of the base material 1, but diffuse in the plane direction and then settle on the surface of the base material 1 in order from the target atoms that have lost their kinetic energy. It continues to form a thin film. At this time, atoms are basically arranged and fixed so as to be lattice-matched to the base material 1, but if the atoms are arranged irregularly or impurities remaining in the vacuum chamber are mixed in the thin film, I have something to do. As a result, defects such as voids and dislocations occur in the thin film. In particular, the atomic arrangement in the vicinity of the interface between the metal film 2 and the base material 1 is in the initial stage of film formation, so there are many crystal variations and many defects. Due to this defect, there is a region where the base material 1 and the metal film 2 are not in contact with each other, which is a factor in reducing the adhesion between the base material 1 and the metal film 2 .

Although a method other than the sputtering method can be used as the method for forming the metal film 2, it is preferable to use the PVD method because of its high adhesion. In particular, the sputtering method and vacuum deposition are suitable because of their high adhesion.

Substrate 1 can be any material. A material having low adhesion to the substrate 1 can also be used. For example, glass, ceramic, plastic, or the like can be used as the material of the base material 1 .

Metal film 2 may be of any material. A material having low adhesion to the substrate 1 can also be used. Also, the metal film 2 can be a material that is used as an electrode material or a plating material for ornaments. The material of the metal film 2 is, for example, Au, Cu, Pt, Al, Ag, or the like.

Although the thickness of the metal film 2 may be arbitrary, it is preferably 10 nm to 10 μm so that an alternating current with a high current density can be easily applied. It is more preferably 50 nm to 1 μm.

The shape of the substrate 1 is not limited to a flat plate, and may be any curved shape. Moreover, the shape of the metal film 2 is also arbitrary as long as it is formed in the shape of a film having a substantially uniform thickness along the surface shape of the substrate 1 . Moreover, the metal film 2 does not need to be provided on the entire surface of the substrate 1, and may be formed in an arbitrary planar pattern.

(Step S2)
Next, an AC power source is connected to both ends of the metal film 2 to apply an AC voltage, and an AC current with a current density of 100 A/mm ² or more is applied in the plane of the metal film 2 . The application of this alternating current improves the adhesion of the metal film 2 to the substrate 1 . The reason is as follows.

When an alternating current with a high current density is applied to the metal film 2, the atoms in the metal film 2 are induced to diffuse by the electron force. That is, electrons collide with atoms in the metal film 2 to exchange momentum, thereby diffusing the atoms. Atomic diffusion due to electron wind power becomes more pronounced as the current density increases. Also, since the alternating current is used, atoms are not diffused in one direction, but isotropic diffusion is induced. This atomic diffusion causes rearrangement of atoms. Due to this rearrangement, defects such as voids generated during the deposition of the metal film 2 are repaired. As a result, the contact area between the substrate 1 and the metal film 2 is increased, and the adhesion between the substrate 1 and the metal film 2 is improved.

In addition, the rearrangement of atoms increases the crystal grain size. The crystal grain size of the metal film 2 formed by the sputtering method is about 10 to 25 nm, but the crystal grain size becomes larger than 25 nm by applying the alternating current in step S2. When the crystal grain size is 40 nm or less, sliding at the crystal grain boundary is dominant, and an inverse Hall Petch phenomenon is known in which the hardness of the metal film 2 increases as the crystal grain size increases. Therefore, the reason why the adhesion between the base material 1 and the metal film 2 is improved is that the crystal grain size is increased, the crystal grain boundary is decreased, and the hardness of the metal film 2 is increased.

For the above reason, the crystal grain size at the interface of the metal film 2 on the substrate 1 side is preferably 30 nm or more and 40 nm or less. It is more preferably 32 nm or more and 40 nm or less.

The current density of alternating current is 100 A/mm ² or more. Here, the current density is a value near the interface between the metal film 2 and the substrate 1 . If the density is less than 100 A/mm ² , the rearrangement of atoms due to the electron wind force does not proceed sufficiently, and the adhesion is not improved. On the other hand, if the density is 100 A/mm ² or more, the rearrangement of atoms caused by the electron wind force proceeds remarkably, and repair of defects in the metal film 2 proceeds further, so that the adhesion is improved. More preferably, the current density is 120 A/mm ² or higher, more preferably 150 A/mm ² or higher. Moreover, the upper limit of the current density is preferably set to a value at which the Joule heat generated in the metal film 2 is equal to or lower than the creep temperature of the metal film 2 . For example, when the metal film 2 is Au, the accelerated electromigration test conditions already demonstrated in previous research (A. Blech and E. Kinsbron, Thin Solid Films, 25 (1975) 327-334), namely 10 kA/mm ² or less is preferable.

The frequency of the alternating current is preferably 5 MHz or higher. When the frequency is high, current concentrates at the interface of the metal film 2 due to the skin effect, so defects near the interface between the metal film 2 and the substrate 1 are repaired more efficiently, improving adhesion. More preferably, it is 10 MHz or higher. Although there is no particular upper limit to the frequency, it is preferable to set it to 1 GHz or less in consideration of power supply costs and the like.

The application time of alternating current is 10 to 30 minutes. If it is less than 10 minutes, rearrangement of atoms does not proceed sufficiently, and defects such as voids are not repaired, so adhesion is not improved. On the other hand, if it exceeds 30 minutes, the adhesion will deteriorate. This is considered to be due to the expansion of voids such as grain boundary triple junctions due to the mismatch of vacancy flux. A more preferable alternating current application time is 20 to 30 minutes.

It is desirable that the current density of the alternating current be distributed as evenly as possible in the in-plane direction of the metal film 2 . Therefore, when connecting the AC power supply to the metal film 2, it is preferable to set the connection position so that the current density distribution is uniform. For example, if the metal film 2 has a rectangular planar pattern, it is preferable to connect an AC power source near both short sides.

The temperature of the metal film 2 may be room temperature when the alternating current is applied, but the application may be performed by heating. Heating promotes the rearrangement of atoms, making it easier to improve adhesion.

As described above, according to the method for manufacturing a metal film of the present disclosure, the adhesion between the substrate 1 and the metal film 2 can be improved.

Specific examples of the method for producing a metal film according to the present disclosure will be described below with reference to the drawings, but the method for producing a metal film according to the present disclosure is not limited to the examples.

A metal film of Au having a thickness of 150 nm was formed on a substrate of SiO ₂ by DC sputtering. The planar pattern of the metal film was rectangular with a short side of 4 mm and a long side of 30 mm.

Next, terminals of a power source were brought into contact with the respective short sides of the metal film, and an alternating current was applied. The current density was 150 A/mm ² , the waveform was a sine wave, the substrate temperature was room temperature, and the application time was 30 minutes. Also, the frequency of the alternating current was set to 3 types of 0.1 MHz, 1.0 MHz, and 10 MHz. The temperature of the metal film was measured using an infrared thermometer, and it was confirmed that the temperature did not change due to the application of the alternating current.

A peeling test was performed on a total of four samples, ie, the three samples prepared as described above and a sample to which no alternating current was applied, and the adhesion of the metal film was evaluated. A peel test is performed as shown in FIG. First, the back surface of one end of a rectangular cantilever is adhered to a metal film with an adhesive. Next, a force gauge is applied perpendicularly to the surface of the other end of the cantilever (at a position 31.5 mm from the one end), and the load when the metal film 2 is peeled off is measured. Then, the value obtained by dividing the load by the adhesion area between the cantilever and the metal film was defined as adhesion strength (unit: N/cm ² ), and adhesion was evaluated.

FIG. 4 is a graph showing the measurement results of adhesion. As shown in FIG. 4, it was found that the higher the frequency, the better the adhesion. In particular, at a frequency of 10 MHz, the adhesion was greatly improved compared to the frequencies of 0.1 MHz and 1.0 MHz, and the adhesion was improved by 27% compared to the case where no AC current was applied. Also, from this result, it is inferred that the higher the frequency, the better the adhesion.

The frequency of the alternating current was 10 MHz, and the application time of the alternating current was 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 600 minutes, and 1200 minutes. was prepared, and the adhesion was evaluated in the same manner as in Example 1. Also, the metal film of each sample was subjected to X-ray diffraction to determine the crystal grain size. The crystal grain size was calculated by Scherrer's formula (D=Kλ/(b cos θ), where D is the crystal grain size, K is the Scherrer constant, λ is the X-ray wavelength, b is the half width, and θ is the Bragg angle). . The Scherrer constant was set to 0.9 rad.

FIG. 5 is a graph showing the measurement results of adhesion. As shown in FIG. 5, the adhesion increases until the application time is 20 minutes, but when the application time exceeds 20 minutes and reaches 30 minutes, the adhesion decreases slightly, and when the application time exceeds 30 minutes, the adhesion decreases. It gradually decreased and became equal to or less than the case where no alternating current was applied. From this result, it was found that the application time should be 10 to 30 minutes.

FIG. 6 is a graph showing the calculation results of the crystal grain size. As shown in FIG. 6, the crystal grain size increases until the application time is 20 minutes. The grain size became smaller than when no alternating current was applied.

FIG. 7 is a graph showing the relationship between crystal grain size and adhesion. As shown in FIG. 7, it was found that the crystal grain size and the adhesion strength had a high correlation, and the correlation coefficient was 0.85. Moreover, from this result, it is inferred that the crystal grain size must be 27 nm or more in order to increase the adhesion force compared to the case where the alternating current is not applied.

As a result of X-ray analysis, it was found that the metal film had a face-centered cubic structure, and its surface was mainly composed of (111) planes. FIG. 8(a) is a graph showing the ratio of (111) planes of the metal film 2, and FIG. 8(b) is a graph showing the ratio of (200) planes. As shown in FIG. 8A, when the alternating current is applied for 10, 20, 30, and 50 minutes, the proportion of the (111) plane increases compared to when the alternating current is not applied. The ratio of the (111) face decreased in . In addition, as shown in FIG. 8(b), the ratio of the (200) plane decreases when the alternating current is applied for 10, 20, 30, and 40 minutes, and the (200) plane increases with other application times. Was. The (111) plane increased and the (200) plane decreased when the application time was 10, 20, and 30 minutes. From this, it can be seen that by applying an alternating current for 10 to 30 minutes, the rearrangement of atoms in the metal film 2 occurs, and the ratio of the (111) plane increases and the ratio of the other crystal planes decreases. It was found that the adhesion of 2 was improved.

INDUSTRIAL APPLICABILITY According to the present disclosure, it can be used to improve the adhesion of metal wiring on a substrate, prevent peeling of metal plating on ornaments, and the like.

1: base material 2: metal film

Claims (7)

A step of forming a metal film made of Au, Cu, Al, and Ag on a substrate;
An alternating current having a current density of 100 A/mm ² or more and 10 kA/mm ² or less and a frequency of 5 MHz or more is applied to the metal film for 10 to 30 minutes to repair defects in the metal film, and the base material and the metal improving adhesion between the substrate and the metal film by increasing the contact area of the film;
A method for producing a metal film, comprising: 2. The method for producing a metal film according to claim 1, wherein the current density is an alternating current of 150 A/mm< ² > or more. 3. The method for producing a metal film according to claim 1, wherein the alternating current is applied for 20 to 30 minutes. 4. The method for producing a metal film according to claim 1 , wherein the metal film has a crystal grain size of 30 nm or more at an interface with the substrate. 5. The method of manufacturing a metal film according to claim 1 , wherein the metal film is formed by a PVD method. 6. The method of manufacturing a metal film according to claim 1 , wherein the metal film is made of Au. 7. The method for producing a metal film according to any one of claims 1 to 6 , wherein the base material is made of glass, ceramic, or plastic.

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