KR100826480B1 - Barrier film for flexible copper substrate and sputtering target for forming barrier film - Google Patents

Abstract

Flexible copper containing 5 to 30 wt% of Cr, the balance being made of Co-Cr alloy film composed of inevitable impurities and Co, having a film thickness of 3 to 150 nm and a film thickness uniformity of 1? A sputtering target for barrier film formation, comprising a substrate barrier film and 5 to 30 wt% of Cr, the remainder being an inevitable impurity and a Co-Cr alloy comprising Co, wherein the specific transmittance in the in-plane direction of the sputter surface is 100 or less. When suppressing diffusion of copper into a resin film such as polyimide, the film is thin enough not to cause film peeling, and a sufficient barrier effect can be obtained even with a thin wiring pitch, and a temperature increase is caused by heat treatment or the like. A barrier film for flexible copper substrates and a sputtering target for barrier film formation are obtained even if there is no barrier property change.

Description

Barrier film for flexible copper substrate and sputtering target for barrier film formation {BARRIER FILM FOR FLEXIBLE COPPER SUBSTRATE AND SPUTTERING TARGET FOR FORMING BARRIER FILM}

The present invention relates to a barrier film for flexible copper substrate and a sputtering target for barrier film formation, which can effectively suppress diffusion of copper into resin films such as polyimide.

Conventionally, at the time of manufacture of a flexible copper substrate, forming a copper layer on resin films, such as polyimide used as a base film, is performed. Specifically, forming a sheet layer of copper on a polyimide film by the sputtering method or an electroless plating method, and forming a thick plating layer of copper thereon is performed. Thereafter, a copper wiring circuit pattern is formed through a copper etching process.

The problem here is that the copper formed on the polyimide film is easily diffused (migrated) in the polyimide film, causing a problem that the wiring on the circuit board is short-circuited.

In order to suppress diffusion of such Cu into a polyimide film, it is proposed to form a barrier layer for preventing the diffusion of Cu on the polyimide film in advance, and to form a sheet layer of Cu and a thick plating layer of Cu thereon. have.

As the representative one, a barrier layer of Ni-Cr alloy is formed (see Patent Document 1).

However, if there is a temperature rise of about 200 to 300 ° C, diffusion of Cu into the polyimide film is still recognized. Moreover, especially when wiring pitch became narrower than 30 micrometers, in the conventional barrier layer, it cannot be prevented from spreading to a polyimide layer, and it turned out that it is not necessarily effective.

As a means of preventing this, it is also conceivable to improve the barrier properties by increasing the thickness of the conventional barrier layer. However, when thickness was thickened more than a fixed value, the problem that a barrier film peeled from a polyimide film generate | occur | produced. Therefore, this was not a fundamental solution.

As another proposal, a thermoplastic polyimide layer is formed on a thermosetting polyimide base film, and further, a barrier metal made of at least one metal selected from Ni, Cr, Co, and Mo is coated, and the thermoplastic resin is heated and fluidized. There is also a proposal to increase the bonding force between the thermoplastic polyimide and the barrier metal (see Patent Document 2).

However, in this case, the problem remains because it does not solve the fundamental problem of diffusion of the barrier metal.

Patent Document 1: Japanese Unexamined Patent Publication No. 2002-252257

Patent Document 2: Japanese Unexamined Patent Publication No. 2002-280684

Disclosure of the Invention

Problems to be Solved by the Invention

From the above problems of the prior art, when suppressing diffusion of copper into a resin film such as polyimide, a sufficient barrier effect can be obtained even with a thin film thickness and thin wiring pitch that do not cause film peeling, and furthermore, heat treatment. It is a problem to obtain a barrier film for a flexible copper substrate and a sputtering target for barrier film formation without a change in barrier properties even if the temperature rises due to the above.

Means to solve the problem

As a result of earnest research, the present inventors have found that the above problems can be solved by making the barrier film as thin as possible using an alloy having effective barrier properties to prevent peeling and increasing the uniformity of the film formed film.

Based on this fact,

(1) 5 to 30 wt% of Cr, the remainder being a Co-Cr alloy film composed of inevitable impurities and Co, having a film thickness of 3 to 150 nm and a film thickness uniformity of 1? Barrier Film for Flexible Copper Substrate

(2) A sputtering barrier film forming sputtering comprising 5 to 30 wt% of Cr and comprising a Co-Cr alloy composed of inevitable impurities and Co, in which the specific permeability in the in-plane direction of the sputtering surface is 100 or less. Provide the target.

Effects of the Invention

The barrier film for flexible copper substrates of the present invention has a thin film thickness that does not cause film peeling, and a sufficient barrier effect can be obtained even at a thin wiring pitch, and even if the temperature rises due to heat treatment or the like, It has an excellent feature of no change. This invention has the outstanding characteristic which effectively suppresses copper spreading to resin films, such as a polyimide.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the analysis (AES) result of Cu diffusion, when the barrier film of Co-Cr alloy of Example 1 is used.

It is a figure which shows the analysis (AES) result of Cu diffusion, when the barrier film of Ni-Cr alloy of the comparative example 1 is used.

Implement the invention  Best form for

The barrier film for flexible copper substrates of this invention contains 5-30 wt% of Cr, and is a Co-Cr alloy film which consists of an unavoidable impurity and Co.

In the film composition, when Cr does not reach 5wt%, barrier property is not enough and there is no advantage compared with the conventional barrier film. In addition, when Cr exceeds 30 wt%, when the Cu layer is etched to form a circuit, the barrier film inhibits etching, so it takes too long to remove and is not practical. Therefore, it is set as the range of said Cr.

The film thickness of the barrier film for flexible copper substrates of this invention shall be 3-150 nm. When film thickness is less than 3 nm: It does not have sufficient barrier property. In addition, when the film thickness exceeds 150 nm, film peeling is likely to occur.

The film thickness of the barrier film for flexible copper substrates of this invention makes film thickness uniformity 10% or less at 1 (sigma). When the film thickness uniformity (1 sigma) exceeds 10%, when etching until the thick portion of the barrier film is removed at the time of etching during patterning, the portion where the barrier film is thin is etched wider than the portion to be removed. There is a problem that the wiring width of the portion is narrowed. This lowers the durability of the actual device. Therefore, said film thickness uniformity (1σ) is made into 10% or less.

As for the sputtering target for barrier film formation of this invention, 5-30 wt% of Cr is used, and the Co-Cr alloy target which consists of impurities and Co which remain unavoidable is used. The composition of the Co—Cr alloy target of the present invention is directly reflected in the composition of the barrier film. That is, when Cr of the target composition does not reach 5 wt%, a Co alloy film of 5 wt% Cr or more cannot be formed.

On the other hand, when Cr exceeds 30 wt%, a film of Co alloy of Cr 30% or less cannot be formed. Therefore, the composition of the Co-Cr alloy target is in the above range.

Moreover, the specific permeability of the sputtering surface for forming a barrier film of the present invention in the in-plane direction of the sputtering surface is set to 100 or less. This is because when the specific permeability exceeds 100, the film thickness uniformity of the sputtered film exceeds 10% at 1 sigma.

As for the Co-Cr alloy target of this invention, 500 micrometers or less of an average crystal grain diameter are preferable, and 100 micrometers or less are especially preferable. This is because when the average crystal grain size exceeds 500 µm, the amount of particles generated increases, the film defect called pinhole increases, and the product yield decreases.

Moreover, in the Co-Cr alloy target of this invention, it is preferable that the variation of the average crystal grain diameter in a target is 30% or less. It is because there exists a possibility that the film thickness uniformity which sputtered film formation formed may exceed 10% at 1 (sigma) when the deviation of an average particle diameter exceeds 30%.

When manufacturing the target of this invention, it is preferable to process into a target board by the combination of forging in hot at 800-1370 degreeC, and rolling.

Further, after the above hot forging and rolling, it is preferable to perform a heat treatment at a holding temperature of 300 to 960 ° C. in an air, a vacuum or an inert gas atmosphere.

The heat treatment plate thus obtained is processed into a target shape, and the average roughness Ra of the sputtered surface is set to 0.01 to 5 µm.

In addition, the average roughness (Ra) of the surface of the non-sputter surface such as the side of the target or the backing plate, i.e., the portion to which the sputtered material adheres, by sandblasting treatment, etching treatment or formation of a spray coating layer. It is preferable to surface roughen to 1-50 micrometers, and to prevent the peeling of the adhered film from re-peeling. This is because re-peeled and suspended in the sputtering atmosphere causes particles to be generated in the substrate.

The target of the present invention is preferably bonded to a backing plate of Al alloy, Cu, Cu alloy, Ti, Ti alloy or the like by metal bonding such as soldering or diffusion bonding method or friction welding method so as to withstand high output sputtering.

As impurities contained in the target, the concentrations of Na and K are 5 ppm or less (hereinafter, ppm represents wtppm), and the concentrations of U and Th are respectively 0.05 ppm or less, and the sum of the metal elements other than the main element and the additive element. It is preferable that this is 0.5 wt% or less, and the oxygen concentration is 0.5% or less.

The present invention will be described based on examples. The examples shown below are for ease of understanding and do not limit the present invention by these examples. That is, modifications and other embodiments based on the technical idea of the present invention are naturally included in the present invention.

(Example 1)

A Co-Cr ingot was produced by dissolving and casting the composition of Co-20wt% Cr. This was hot forged and hot rolled at 1100 ° C, heat-treated at 500 ° C for 2 hours after cooling, and processed into a target. The crystal grain diameter of this target was 280 µm. Furthermore, the said target was finished so that average surface roughness Ra might be 0.14 micrometer.

The concentration of Cr in the target was 19.1 wt%, the impurity components were Na: 0.2 ppm, K: 0.1 ppm, U: 0.02 ppm, Th: 0.03 ppm, and the total metal component was 470 ppm and oxygen was 10 ppm.

The target was bonded to the backing plate with indium, and the backing plate portion near the target side and the target was roughened with sandblasting Ra = 7.5 mu m.

Using this target, a barrier layer with a film thickness of 140 nm was produced. As a result of analyzing the composition of each additive component of this barrier layer, it was consistent with the composition of Cr: 18.3 wt% and a little Cr. The film thickness of this barrier layer was measured at 49 points, and the film thickness uniformity thereof was examined. As a result, it was 7.2% at 1σ.

200 nm Cu was formed into a film by sputtering on this barrier layer.

A sample in the form of a film formed on the Cu / Co-Cr laminated film and a sample subjected to a heat treatment at 300 ° C for 2 hours in a vacuum were profiled in the depth direction by AES (Auger electron spectroscopy). Was obtained, and the diffusion of Cu into the barrier layer was evaluated.

1 shows the results of AES. In the case where Co-Cr was used as the barrier film, even if heat-treated at 300 ° C., the profile of Cu exhibited the same profile as that which was not subjected to heat treatment, and diffusion into the barrier layer was not recognized.

(Comparative Example 1)

A material having a composition of Ni-20 wt% Cr, which is a conventional barrier material, was dissolved and cast to produce a Ni-Cr ingot. This was hot forged and hot rolled at 1100 degreeC, heat-processed at 500 degreeC for 2 hours after cooling, and it processed into the target.

The crystal grain diameter of this target was 300 micrometers, and it finished to 0.15 micrometer with surface roughness Ra. The Cr concentration in the target was 19.7 wt%, the impurity component was Na: 0.1 ppm, K: 0.3 ppm, U: 0.02 ppm, Th: 0.04 ppm, and the total of impurity metal components was 510 ppm and oxygen was 10 ppm.

The target was bonded to the backing plate with indium, and the backing plate portion near the target side and the target was roughened with sandblasting at Ra = 7.0 µm. The specific permeability in the in-plane direction of the target was 130.

Using this target, a barrier layer with a film thickness of 140 nm was formed thereon using a SiO ₂ substrate so that the barrier film did not peel off.

As a result of analyzing the composition of each additive component of this barrier layer, Cr: 18.5 wt% resulted in a composition with a little Cr. The film thickness of this barrier layer was measured at 49 points, and the film thickness uniformity thereof was examined. As a result, it was 7.4% at 1σ.

The Cu film | membrane was formed into 200 nm film by the sputtering method on this barrier layer. The Cu / Ni-Cr film was subjected to a film formed as it was, and a sample subjected to a heat treatment at 300 ° C. for 2 hours in a vacuum to obtain a profile in the depth direction by AES (Auger Electron Spectroscopy) to obtain a copper profile. Diffusion to the barrier layer was evaluated. The result of AES is shown in FIG.

The copper profile heat-treated at 300 degreeC is contained in the barrier layer rather than the heat-processed. That is, it turned out that the function as a barrier layer is low.

(Examples 2 to 8)

A target was prepared using the same production method as in Example 1, and the film thickness was 10 nm on the polyimide sheet having a thickness of 38 µm using a target having an alloy composition and specific permeability in the range of the present invention shown in Table 1 below. Barrier layer was formed.

In addition, the composition (wt%) of each additive component of the barrier layer, the thickness of the barrier layer (nm) and the thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the thickness was examined. And the result (time) of an endurance test are shown in Table 1 similarly. The film composition (wt%), film thickness (nm), and film uniformity (%) of the barrier films of Examples 2 to 8 all fall within the scope of the present invention.

Further, after forming a 20 nm film of a Cu sheet layer on the barrier layer by the sputtering method, an 8 µm Cu layer was formed by electroplating. And the wiring pattern which produced these in 30 micrometer pitch (15 micrometers of wiring width, 15 micrometers of wiring distance) was subjected to the endurance test which adds a voltage of + 60V and maintains it in 85 degreeC and 85% of humidity conditions. It was. These results are shown in Table 1 similarly.

As a result, the short circuit of each wiring was not seen in Examples 2-8.

(Comparative Example 2)

The Ni-Cr barrier layer with a film thickness of 10 nm was formed on the 38-micrometer-thick polyimide sheet using the target similar to the said Comparative example 1 shown in Table 1.

Furthermore, the composition (wt%) of each additive component of this barrier layer, the film thickness (nm) of the barrier layer, and the film thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the film thickness was examined. And the result (time) of an endurance test are shown in Table 1 similarly.

The alloy component (Ni-Cr) of the barrier film of Comparative Example 2 is different from the present invention.

Furthermore, after forming a 20 nm film of a Cu sheet layer on this barrier layer, the 8 micrometers Cu layer was formed by electroplating. And the wiring pattern which produced these in 30 micrometer pitch (15 micrometers of wiring width, 15 micrometers of wiring distance) was subjected to the endurance test which adds a voltage of + 60V and maintains it in 85 degreeC and 85% of humidity conditions. It was. These results are shown in Table 1 similarly.

As a result of the endurance test above, Comparative Example 2 lasted 350 hours, but a short circuit of the wiring occurred thereafter.

(Comparative Example 3)

The target was manufactured using the manufacturing method similar to the said Example 1, and the polyimide of 38 micrometers thickness was used using the target of the alloy composition (Cr amount is less than this invention) in the range outside the present invention shown in following Table 1. On the sheet, a Co-Cr barrier layer having a film thickness of 10 nm was formed.

In addition, the composition (Cr 3.5wt%) of each additive component of this barrier layer, the film thickness (nm) of the barrier layer, and the film thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the film thickness was investigated. A result and the result (time) of an endurance test are shown in Table 1 similarly.

The film composition (Cr 3.5 wt%) of the barrier film of Comparative Example 3 is less than the Cr content (5 to 30 wt%) of the film of the present invention.

Furthermore, after forming a 20 nm film of a Cu sheet layer on this barrier layer, the copper layer of 8 micrometers was formed by electroplating. And the endurance test which hold | maintained in the atmosphere of 85 degreeC and 85% of humidity by applying voltage of + 60V to this wiring pattern which produced these in 30 micrometer pitch (15 micrometers of wiring width, 15 micrometers of wiring distance) was carried out. . These results are shown in Table 1 similarly.

As a result of the endurance test above, Comparative Example 3 lasted 210 hours, but a wiring short circuit thereafter occurred.

(Comparative Example 4)

A target was produced using the same production method as in Example 1, and a polyimide having a thickness of 38 μm was obtained using a target having an alloy composition (the amount of Cr is greater than the present invention) in the range outside the present invention shown in Table 1 below. On the sheet, a Co-Cr barrier layer having a film thickness of 10 nm was formed.

In addition, the composition (Cr 33.1wt%) of each additive component of this barrier layer, the film thickness (nm) of the barrier layer, and the film thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the film thickness was investigated. A result and the result (time) of an endurance test are shown in Table 1 similarly.

The film composition (Cr 33.1 wt%) of the barrier film of Comparative Example 3 is higher than the Cr content (5 to 30 wt%) of the film of the present invention.

Furthermore, after forming a 20 nm film of a Cu sheet layer on this barrier layer, the 8 micrometers Cu layer was formed by electroplating. And they tried to produce wiring patterns in 30 micrometer pitch (wire width 15 micrometers, distance between wirings 15 micrometers), but the Co-Cr layer remained unetched and the pattern could not be formed.

(Comparative Example 5)

The target was manufactured using the manufacturing method similar to the said Example 1, and as shown in following Table 1, using the target whose specific permeability is outside this invention, the film thickness 10 on a 38-micrometer-thick polyimide sheet. A Co-Cr barrier layer of nm was formed.

In addition, the composition of each additive component of this barrier layer, the film thickness of the barrier layer (nm), and the film thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the film thickness was examined. The result (time) is shown in Table 1 similarly.

Furthermore, after forming a 20 nm film of a Cu sheet layer on this barrier layer, the 8 micrometers Cu layer was formed by electroplating. And the endurance test which hold | maintained in the atmosphere of 85 degreeC and 85% of humidity by applying voltage of + 60V to this wiring pattern which produced these in 30 micrometer pitch (15 micrometers of wiring width, 15 micrometers of wiring distance) was carried out. . These results are shown in Table 1 similarly.

As a result of the endurance test above, Comparative Example 5 lasted 470 hours, but a wiring short circuit thereafter occurred. Moreover, the uniformity of film thickness also fell very much.

(Comparative Example 6)

The target was manufactured using the manufacturing method similar to the said Example 1, sputtered using the target shown in following Table 1, and on a polyimide sheet of 38 micrometer thickness, 2.5 nm of film thickness outside this invention (than this invention) Thin) to form a Co—Cr barrier layer.

The composition of each additive component of the barrier layer, the specific permeability of the target, the film composition, and the film thickness of the barrier layer were measured at 49 points, and the uniformity (%) of the film thickness was examined, and the results of the durability test. (Time) is shown in Table 1 similarly.

And the endurance test which hold | maintained in the atmosphere of 85 degreeC and 85% of humidity by applying voltage of + 60V to this wiring pattern which produced these in 30 micrometer pitch (15 micrometers of wiring width, 15 micrometers of wiring distance) was carried out. . These results are shown in Table 1 similarly.

As a result of the endurance test above, Comparative Example 6 lasted 390 hours, but a wiring short thereafter occurred. When the film thickness of the barrier layer was not sufficient, it was found that diffusion of Cu into the polyimide sheet occurred, resulting in no durability.

(Comparative Example 7)

The target shown in Table 1 was manufactured using the manufacturing method similar to the said Example 1, and as shown in following Table 1, on the 38-micrometer-thick polyimide sheet on the conditions which the film thickness of a barrier layer is outside this invention, The 180-nm (thicker than this invention) Co-Cr barrier layer whose film thickness is outside this invention was formed.

In addition, the composition of each additive component of this barrier layer and the film thickness (nm) of a barrier layer are shown in Table 1 similarly. However, since this barrier layer peeled, subsequent measurement was impossible. As mentioned above, it turned out that the excess film thickness of a barrier layer is not suitable.

The present invention has an excellent feature that a sufficient barrier effect can be obtained even with a thin wiring pitch, and that there is no change in barrier properties even if the temperature rises due to heat treatment or the like. Thus, since it has the outstanding characteristic which effectively suppresses copper spreading to resin films, such as a polyimide, it is useful as a barrier film for flexible copper substrates.

Claims (2)

Flexible copper containing 5 to 30 wt% of Cr, the balance being made of Co-Cr alloy film composed of inevitable impurities and Co, having a film thickness of 3 to 150 nm and a film thickness uniformity of 1? Barrier film for substrate. A sputtering target for forming a barrier film, wherein the Co-Cr alloy contains 5 to 30 wt% of Cr, and the remainder is an inevitable impurity and Co, and the specific permeability in the in-plane direction of the sputter surface is 100 or less.

Images