Electroless plating solution and method for manufacturing a wiring board

Abstract

To provide a technology that is advantageous for stably precipitating ruthenium on a raw material with electroless plating.SOLUTION: An electroless plating solution includes ruthenium salt, a complexing agent, a reductant and a pH adjuster, where the reductant includes a hydrazine-hydrate and the complexing agent includes carboxylic acid having one or two carboxyl groups.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] This disclosure relates to an electroless plating solution and a method for manufacturing a wiring board. [Background technology]

[0002] Electroless plating is used as a method for forming a metal film on a substrate. For example, Patent Document 1 discloses a method for depositing copper in wiring grooves and wiring holes of a substrate by electroless copper plating. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2005 / 038088 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] With the recent advancements in miniaturization of semiconductor wiring, ruthenium (Ru) has attracted attention as a wiring material.

[0005] Ruthenium films can be deposited using CVD (Chemical Vapor Deposition), but they can also be deposited by electroless plating. In particular, electroless plating offers excellent productivity and can form metal films of various shapes, making it suitable for manufacturing microstructures such as wiring on semiconductor substrates.

[0006] This disclosure provides a technology that is advantageous for stably depositing ruthenium onto a material by electroless plating. [Means for solving the problem]

[0007] One aspect of the present disclosure relates to an electroless plating solution containing a ruthenium salt, a complexing agent, a reducing agent, and a pH adjuster, wherein the reducing agent contains hydrazine hydrate and the complexing agent contains a carboxylic acid having one or two carboxyl groups.

Advantages of the Invention

[0008] According to the present disclosure, it is advantageous to stably deposit ruthenium on a material by electroless plating.

Brief Description of the Drawings

[0009] [Figure 1A] FIG. 1A is an enlarged cross-sectional view of a substrate showing an example of a first manufacturing method of a wiring substrate. [Figure 1B] FIG. 1B is an enlarged cross-sectional view of a substrate showing an example of a first manufacturing method of a wiring substrate. [Figure 1C] FIG. 1C is an enlarged cross-sectional view of a substrate showing an example of a first manufacturing method of a wiring substrate. [Figure 2A] FIG. 2A is an enlarged cross-sectional view of a substrate showing an example of a second manufacturing method of a wiring substrate. [Figure 2B] FIG. 2B is an enlarged cross-sectional view of a substrate showing an example of a second manufacturing method of a wiring substrate. [Figure 2C] FIG. 2C is an enlarged cross-sectional view of a substrate showing an example of a second manufacturing method of a wiring substrate. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a substrate showing an example of a third manufacturing method of a wiring substrate.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, typical embodiments of the present disclosure will be described.

[0011] [Electroless Plating Solution] In this embodiment, ruthenium (Ru) is embedded as wiring in recesses (such as wiring grooves like trenches and wiring holes like vias) of a semiconductor substrate (wafer) by electroless plating.

[0012] Therefore, the plating solution used in the electroless plating of the present embodiment is an electroless plating solution containing a ruthenium salt (i.e., an electroless ruthenium plating solution). The form of the ruthenium salt in the electroless ruthenium plating solution is not limited. Typically, ruthenium exists in the electroless plating solution in the form of ions or hydrates, and the ruthenium salt may be in an equilibrium state in the electroless ruthenium plating solution. In the following description, all ruthenium contained in the electroless plating solution (including ruthenium ions and ruthenium hydrates) may be simply referred to as a ruthenium salt.

[0013] The electroless plating solution used in the present embodiment further contains a complexing agent, a reducing agent, and a pH adjuster in addition to the ruthenium salt. The reducing agent includes hydrazine-hydrate. The complexing agent includes a carboxylic acid having one or two carboxyl groups.

[0014] As a result of intensive research, the inventor of the present invention has obtained the finding that performing electroless plating using the above electroless plating solution is advantageous for stably depositing ruthenium as a plating metal on a material.

[0015] Typical examples of the "carboxylic acid having one carboxyl group (i.e., monocarboxylic acid)" that the complexing agent can contain include lactic acid, acetic acid, and formic acid. Also, typical examples of the "carboxylic acid having two carboxyl groups (i.e., dicarboxylic acid)" that the complexing agent can contain include tartaric acid, succinic acid, oxalic acid, malonic acid, malic acid, glutaric acid, adipic acid, and pimelic acid.

[0016] The inventor of the present invention prepared a plurality of types of electroless plating solutions (especially a plurality of types of electroless plating solutions having different compositions and / or concentrations of carboxylic acids as complexing agents), performed electroless plating for each electroless plating solution, and evaluated the deposition of the plating metal (i.e., ruthenium).

[0017] As a result, it has been found that an electroless plating solution containing a monocarboxylic acid as a complexing agent is particularly advantageous for stably depositing ruthenium on a material by electroless plating. In particular, the complexing agent contains lactic acid as a monocarboxylic acid, and the concentration of the lactic acid is 10 mol / m 3 ~100 mol / m 3 In this case, ruthenium could be stably deposited on the material with good quality by electroless plating.

[0018] Also, it has been found that an electroless plating solution containing a dicarboxylic acid as a complexing agent is particularly advantageous for stably depositing ruthenium on a material by electroless plating. In particular, the complexing agent contains succinic acid as a dicarboxylic acid, and the concentration of the succinic acid is 10 mol / m 3 ~150 mol / m 3 In this case, ruthenium could be stably deposited on the material with good quality by electroless plating.

[0019] The inventors of the present invention prepared a plurality of types of electroless plating solutions containing succinic acid as a complexing agent at concentrations of 10 mol / m 3 ~150 mol / m 3 (for example, 30 mol / m 3 , 60 mol / m 3 and 120 mol / m 3 ). These electroless plating solutions were basically common in conditions other than the concentration of succinic acid (complexing agent), and contained ruthenium salts, reducing agents, and pH adjusters with the same composition and the same concentration.

[0020] The inventors of the present invention performed electroless plating under common conditions using these electroless plating solutions, and observed and evaluated the deposition mode of ruthenium on the material based on an image (SEM image) obtained by a scanning electron microscope (SEM). Specifically, electroless plating was performed in a state where a liquid film (paddle) of the electroless plating solution adjusted to 60°C was formed on the treatment surface (upper surface) of the substrate (material), and the deposition state (thickness) of ruthenium on the treatment surface 30 minutes after forming the liquid film on the treatment surface was confirmed.

[0021] As a result, it was confirmed that, 30 minutes after forming a liquid film of electroless plating solution on the treated surface of the substrate, the rate of ruthenium deposition (deposition) increased as the concentration of succinic acid (complexing agent) increased. In particular, the concentration of succinic acid (complexing agent) (mol / m³) 3 A substantial proportional relationship was observed between the concentration of succinic acid (complexing agent) and the ruthenium deposition rate (nm / min), and the ruthenium deposition rate increased roughly linearly with increasing succinic acid concentration.

[0022] Furthermore, the inventors of this invention have provided, for example, a solution containing lactic acid as a complexing agent in an electroless plating solution, with a concentration of 10 mol / m². 3 ~100 mol / m 3 (For example, 30 mol / m³ 3 , 60 mol / m³ 3 and 100 mol / m³ 3 Several types of electroless plating solutions containing lactic acid at a concentration of ) were prepared. These electroless plating solutions were basically the same in all conditions except for the concentration of lactic acid (complexing agent), and contained the same composition and the same concentration of ruthenium salt, reducing agent, and pH adjuster.

[0023] The inventors performed electroless plating under common conditions using these electroless plating solutions and observed and evaluated the ruthenium deposition pattern on the substrate based on SEM images. Specifically, electroless plating was performed with a liquid film of the electroless plating solution adjusted to 60°C to 70°C formed on the treatment surface of the substrate, and the ruthenium deposition state (thickness) on the treatment surface was confirmed 15 minutes, 30 minutes, and 50 minutes after the liquid film was formed on the treatment surface.

[0024] As a result, at 15 minutes, 30 minutes, and 50 minutes after the formation of a liquid film on the treated surface, the rate of ruthenium deposition (deposition) increased as the concentration of lactic acid (complexing agent) increased. It was also confirmed that the amount of ruthenium deposited (thickness on the substrate) increased as the electroless plating time increased. Furthermore, a tendency was observed for the rate of ruthenium deposition to be higher with electroless plating solutions at relatively higher temperatures (e.g., 70°C) compared with electroless plating solutions at relatively lower temperatures (e.g., 60°C).

[0025] Furthermore, ruthenium deposited using an electroless plating solution containing succinic acid as a complexing agent exhibited less surface roughness and was more stably deposited on the substrate compared to ruthenium deposited using an electroless plating solution containing lactic acid as a complexing agent.

[0026] Furthermore, the inventors performed electroless plating using an electroless plating solution containing citric acid (tricarboxylic acid) having three carboxyl groups as a complexing agent, and observed and evaluated the deposition pattern of ruthenium. In this case, the other conditions for electroless plating were set to be basically the same as those when using an electroless plating solution containing monocarboxylic acid (lactic acid) or dicarboxylic acid (succinic acid) as a complexing agent. As a result, ruthenium deposition could not be confirmed with the electroless plating solution containing citric acid as a complexing agent.

[0027] Furthermore, when an electroless plating solution containing a "complexing agent additionally containing ammonium chloride" was used, an improvement in the deposition rate (e.g., deposition rate) of ruthenium in electroless plating was observed. Specifically, the "complexing agent additionally containing ammonium chloride" refers to a complexing agent containing a monocarboxylic acid (such as lactic acid) and ammonium chloride, and a complexing agent containing a dicarboxylic acid (such as succinic acid) and ammonium chloride. It should be noted that even when an electroless plating solution containing only lactic acid (monocarboxylic acid) or succinic acid (dicarboxylic acid) as a complexing agent (i.e., an electroless plating solution that does not contain ammonium chloride) was used, ruthenium could be appropriately deposited by electroless plating.

[0028] The inventors measured the surface electrical resistivity of ruthenium deposited by electroless plating using samples of multiple types of electroless plating solutions with different complexing agent compositions and / or concentrations, by performing heat treatment (annealing) at heating temperatures ranging from 0°C to 600°C. Specifically, for some samples, the ambient pressure was 1 × 10⁻⁶ -3 Ruthenium was heat-treated in a vacuum of (Pa) without the use of a forming gas. For several other samples, the ruthenium was heat-treated using a forming gas composed of a nitrogen and hydrogen mixture. The results showed that, in both cases (without and with the forming gas), the surface electrical resistivity of the ruthenium (plated material) tended to decrease as the heating temperature increased. In particular, the decrease in surface electrical resistivity of the ruthenium (plated material) tended to be greater in the heating temperature range of 200°C to 400°C. Furthermore, compared to heat treatment without the forming gas, the decrease in surface electrical resistivity of the ruthenium (plated material) tended to be greater when heat treatment was performed with the forming gas in the heating temperature range of 0°C to 400°C.

[0029] In all samples in which ruthenium salt was added to a solution containing a complexing agent (including monocarboxylic acid or dicarboxylic acid), a reducing agent (hydrazine hydrate), and a pH adjuster, the ruthenium salt dissolved in the solution at room temperature (5°C to 35°C), and no metal precipitate was observed in the electroless plating solution. However, when the electroless plating solution was heated to 60°C to 70°C, no precipitate was observed in the electroless plating solutions using lactic acid, tartaric acid, and succinic acid as complexing agents, but precipitate was visually observed in the electroless plating solution containing citric acid as a complexing agent. Furthermore, in the electroless plating solution samples containing ruthenium salt, a complexing agent (e.g., lactic acid or succinic acid), a reducing agent (hydrazine hydrate), and a pH adjuster, ruthenium as a plated body was stably deposited in the recesses of the substrate without creating voids. Furthermore, in electroless plating using samples of electroless plating solutions containing ruthenium salt, complexing agent (e.g., lactic acid or succinic acid), reducing agent (hydrazine hydrate), and pH adjuster, the ruthenium deposition rate and surface electrical resistivity were within acceptable limits.

[0030] In particular, the molar concentration of hydrazine hydrate (reducing agent) is 5 mol / m³. 3 ~40 mol / m² 3 In the sample, the solubility of ammonium chloride, the deposition properties of ruthenium, and the deposition rate and surface electrical resistivity of ruthenium were all good from an overall perspective. For electroless plating solutions containing ammonium chloride as a complexing agent in addition to monocarboxylic acid or dicarboxylic acid, the molar concentration of ammonium chloride was 10 to 1000 mol / m³. 3 In the sample, the evaluation results for ruthenium deposition rate and surface electrical resistivity were favorable. Furthermore, when the electroless plating solution adjusted with a pH adjuster was alkaline, especially when the pH was 11 or higher (for example, 13 or lower), ruthenium could be stably deposited on the substrate.

[0031] The inventors in this case added ruthenium salt to pure water, but the ruthenium salt did not dissolve in the pure water. Furthermore, the inventors added ruthenium salt to a solution containing only ammonium chloride, but the ruthenium salt did not dissolve in the solution.

[0032] Furthermore, the inventor performed electroless plating using an electroless ruthenium plating solution containing only ammonium chloride as a complexing agent, but no ruthenium was deposited on the substrate.

[0033] [Manufacturing method for wiring boards] Next, we will describe a typical example of a method for manufacturing a wiring board using the electroless plating solution described above.

[0034] First, we will explain the first manufacturing method of the wiring board. Figures 1A to 1C are enlarged cross-sectional views of a substrate 10 showing an example of the first manufacturing method of the wiring board.

[0035] First, as shown in Figure 1A, a substrate 10 having recesses 11 for wiring is prepared. Although only one recess 11 is shown in Figures 1A to 1C, the substrate 10 may have multiple recesses 11.

[0036] The specific shape and size of the recess 11 are not limited, and typically, at least one of a trench (wiring groove) and a via (wiring hole) may be included in the concept of the recess 11.

[0037] The recessed area screen 12 that demarcates the recess 11 includes a bottom surface 12a and a side surface 12b. In this example, the bottom surface 12a of the recess includes a metal surface that acts as a base for the deposition of ruthenium by electroless plating. In the example shown in Figures 1A to 1C, the bottom surface 12a of the recess is composed of a lower layer wiring 22 containing ruthenium, but the lower layer wiring 22 may contain materials other than ruthenium.

[0038] On the other hand, the partition side surface 12b in this example is formed by a barrier film 21 that covers the insulating film 20. The barrier film 21 is a film that prevents the ruthenium embedded in the recess 11 from diffusing into the insulating film 20, and can be made of any metal (for example, Ta (tantalum) or TaN (tantalum nitride)).

[0039] Subsequently, the electroless plating solution 50 is applied to the substrate 10 to form paddles of the electroless plating solution 50, and as shown in Figure 1B, the entire recess 11 is filled with the electroless plating solution 50. This ensures that the electroless plating solution 50 is in contact with the entire surface of the recess 12 (especially the bottom surface 12a of the recess). The electroless plating solution 50 used here is the electroless ruthenium plating solution described above.

[0040] Subsequently, the state in which the recess 11 is filled with the electroless plating solution 50 is maintained, and electroless plating is performed with the electroless plating solution 50 in contact with the recess area surface 12 (especially the bottom surface 12a of the area). As a result, a plating body 40 containing ruthenium is deposited in the recess 11, and ultimately the entire recess 11 is filled with ruthenium as the plating body 40 (see Figure 1C).

[0041] In particular, in the electroless plating method of this example, ruthenium (plated body 40) is deposited selectively on the bottom surface 12a of the compartment, with little to no ruthenium (plated body 40) deposited on the side surface 12b of the compartment. Therefore, according to this example, it is possible to effectively avoid leaving voids in the recess 11 while filling the entire recess 11 with ruthenium (plated body 40).

[0042] The ruthenium plated body 40, thus embedded in the recess 11, can be used as wiring.

[0043] Furthermore, using the electroless ruthenium plating solution sample described above, the elemental ratio of oxygen in the plated body 40 deposited in the recess 11 was 20% or less, and the elemental ratio of ruthenium was 80% or more.

[0044] Furthermore, the plated body 40 in the recess 11 may be further heat-treated using a forming gas composed of a mixture of nitrogen and hydrogen. In this case, it is possible to reduce the elemental ratio of oxygen in the plated body 40 deposited in the recess 11 to 10% or less and the elemental ratio of ruthenium to 90% or more, thereby improving the purity of ruthenium in the plated body 40 embedded in the recess 11.

[0045] Subsequently, the substrate 10 can undergo any processing necessary to realize a desired semiconductor substrate configuration.

[0046] Next, we will explain the second manufacturing method for the wiring board.

[0047] Figures 2A to 2C are enlarged cross-sectional views of a substrate 10 showing an example of a second manufacturing method for a wiring board. In the second manufacturing method shown in Figures 2A to 2C, elements that are the same as or corresponding to those in the first manufacturing method shown in Figures 1A to 1C are denoted by the same reference numerals, and detailed explanations of matters similar to those in the first manufacturing method are omitted.

[0048] In this example, a substrate 10 is prepared in which a seed layer 25 is provided on an insulating film 20, as shown in Figure 2A.

[0049] The seed layer 25 promotes the deposition of the plating metal (ruthenium) in electroless plating, and the plating metal is deposited. The seed layer 25 can have any composition that can promote the deposition of ruthenium as the plating metal. For example, a thin film of ruthenium formed on the insulating film 20 by CVD can be used as the seed layer 25.

[0050] The recessed area screen 12 (i.e., the bottom surface 12a and side surface 12b of the recess) that demarcates the recess 11 is formed by the seed layer 25. In this example, the recessed area screen 12 includes the seed layer 25 throughout its entirety, but it is also possible that only a part of the recessed area screen 12 includes the seed layer 25.

[0051] Subsequently, the electroless plating solution 50 is applied to the substrate 10 to form paddles of the electroless plating solution 50, and as shown in Figure 2B, the entire recess 11 is filled with the electroless plating solution 50. This ensures that the electroless plating solution 50 is in contact with the recess area surface 12 (i.e., the seed layer 25). The electroless plating solution 50 used here is the electroless ruthenium plating solution described above.

[0052] Subsequently, the state in which the recess 11 is filled with the electroless plating solution 50 is maintained, and electroless plating is performed with the electroless plating solution 50 in contact with the recess area surface 12 (i.e., seed layer 25). As a result, ruthenium is gradually deposited on the seed layer 25, and eventually the entire recess 11 is filled with ruthenium as the plated body 40 (see Figure 2C).

[0053] Next, we will describe the third manufacturing method for the wiring board.

[0054] Figure 3 is an enlarged cross-sectional view of a substrate 10 showing an example of a third manufacturing method for a wiring board. In the third manufacturing method shown in Figure 3, elements that are the same as or corresponding to those in the first and second manufacturing methods described above are denoted by the same reference numerals, and detailed explanations of matters similar to those in the first and second manufacturing methods are omitted.

[0055] In this example, as shown in Figure 3, a barrier film 21 is provided on an insulating film 20, and a substrate 10 is prepared in which the recessed area screen 12 (i.e., the bottom surface 12a and the side surface 12b of the recessed area) that demarcates the recess 11 is formed by the barrier film 21.

[0056] Catalyst particles 29 are attached to the barrier film 21 (particularly the surface area including the recessed area screen 12).

[0057] The catalyst particles 29 are catalytic nuclei that promote the deposition of the plating metal (ruthenium) in electroless plating. The catalyst particles 29 may have any composition (e.g., palladium (Pd)) that promotes the deposition of ruthenium as the plating metal. As an example, the catalyst particles 29 can be attached to the barrier film 21 by applying a liquid in which metal ions that will become the catalyst particles 29 are dispersed (metal ion-containing liquid) onto the substrate 10 (barrier film 21), and then removing the metal ion-containing liquid from the barrier film 21 using a rinsing solution or the like.

[0058] Subsequently, an electroless plating solution is applied to the substrate 10 to form paddles of the electroless plating solution, and the entire recess 11 is filled with the electroless plating solution 50. The state in which the recess 11 is filled with the electroless plating solution is maintained, and electroless plating is performed with the electroless plating solution in contact with the recess area screen 12 to which the catalyst particles 29 are attached. As a result, the deposition of ruthenium is promoted by the catalyst particles 29, and ultimately, ruthenium as a plated body 40 is embedded throughout the entire recess 11.

[0059] As described above, according to this embodiment, the electroless ruthenium plating solution described above is brought into contact with the recess area screen 12 that defines the recess 11 for wiring on the substrate 10, and a ruthenium-containing plated body 40 can be deposited in the recess 11 by electroless plating.

[0060] In particular, by including a monocarboxylic acid (such as lactic acid) or dicarboxylic acid (such as succinic acid) as a complexing agent in the electroless plating solution, ruthenium salts can be stably dissolved in the electroless plating solution. On the other hand, by including hydrazine hydrate as a reducing agent in the electroless plating solution, ruthenium can be stably deposited on the material by electroless plating.

[0061] It should be noted that the embodiments and modifications disclosed herein are illustrative in all respects and should not be construed restrictively. The embodiments and modifications described above may be omitted, substituted, and modified in various ways without departing from the scope and spirit of the appended claims. For example, the embodiments and modifications described above may be combined in part or in whole, and other embodiments may be combined in part or in whole with the embodiments or modifications described above.

[0062] Furthermore, the technical categories that embody the above-described technical concept are not limited. For example, the above-described apparatus may be applied to other apparatuses. The above-described technical concept may also be embodied by a computer program that causes a computer to execute one or more steps included in the above-described method. The above-described technical concept may also be embodied by a computer-readable, non-transitory recording medium on which such a computer program is recorded. [Explanation of Symbols]

[0063] 10 circuit boards 11 recess 12 Recessed area screen 40 Plated body 50 Electroless plating solution

Claims

1. It contains a ruthenium salt, a complexing agent, a reducing agent, and a pH adjuster. The reducing agent comprises hydrazine hydrate, The complexing agent is an electroless plating solution containing a carboxylic acid having one or two carboxyl groups.

2. The complexing agent includes succinic acid as the carboxylic acid, The concentration of succinic acid is 10 to 150 mol / m³. ３ The electroless plating solution according to claim 1.

3. The complexing agent includes lactic acid as the carboxylic acid, The concentration of lactic acid is 10 to 100 mol / m³. ３ The electroless plating solution according to claim 1.

4. The concentration of the hydrazine hydrate is 5 mol / m³. ３ ~40 mol / m³ ３ The electroless plating solution according to claim 1.

5. The electroless plating solution according to claim 1, having a pH of 11 or higher.

6. A method for manufacturing a wiring substrate, comprising the step of depositing a ruthenium-containing plated body in recesses by electroless plating while the electroless plating solution according to any one of claims 1 to 5 is in contact with a recess partitioning surface that partitions recesses for wiring on the substrate.

7. The method for manufacturing a wiring board according to claim 6, wherein the recess includes at least one of a via and a trench.

8. The recessed area screen includes the bottom surface and the side surface of the area, The method for manufacturing a wiring board according to claim 6, wherein the bottom surface of the compartment includes a metal surface on which ruthenium is deposited by the electroless plating.

9. The recessed area screen includes a seed layer. The method for manufacturing a wiring substrate according to claim 6, wherein the electroless plating is performed with the electroless plating solution in contact with the seed layer, and ruthenium is deposited on the seed layer.

10. The method for manufacturing a wiring board according to claim 6, wherein the electroless plating is performed while the electroless plating solution is in contact with the recessed compartment surface to which the catalyst for promoting electroless plating is attached.

11. The method for manufacturing a wiring board according to claim 6, wherein the elemental ratio of oxygen in the plated body deposited in the recess is 20% or less.

12. A method for manufacturing a wiring board according to claim 6, comprising the step of performing heat treatment on the plated body using a mixed gas of nitrogen and hydrogen.

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