Electroless plating solution and method for manufacturing wiring board

Abstract

This electroless plating solution comprises a ruthenium salt, a complexing agent, a reducing agent and a pH regulator. The reducing agent comprises hydrazine hydrate. The complexing agent comprises tartaric acid and ammonium chloride.

Description

[Technical Field]

[0001] The present disclosure relates to an electroless plating solution and a method for manufacturing a wiring substrate. [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 Summary of the Invention

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

[0005] Ruthenium films can be formed using CVD (Chemical Vapor Deposition), but they can also be formed by electroless plating. Electroless plating, in particular, is highly productive and can form metal films of various shapes, making it suitable for manufacturing microstructures such as wiring on semiconductor substrates.

[0006] The present disclosure provides an advantageous technique for stably depositing ruthenium on a material by electroless plating.

[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 includes hydrazine hydrate, and the complexing agent includes tartaric acid and ammonium chloride.

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

[0009] [Figure 1A] FIG. 1A is an enlarged cross-sectional view of a substrate illustrating an example of a first method for manufacturing a wiring substrate. [Figure 1B] FIG. 1B is an enlarged cross-sectional view of a substrate illustrating an example of a first method for manufacturing a wiring substrate. [Figure 1C] FIG. 1C is an enlarged cross-sectional view of a substrate illustrating an example of a first method for manufacturing a wiring substrate. [Figure 2A] FIG. 2A is an enlarged cross-sectional view of a substrate illustrating an example of a second method for manufacturing a wiring substrate. [Figure 2B] FIG. 2B is an enlarged cross-sectional view of a substrate illustrating an example of a second method for manufacturing a wiring substrate. [Figure 2C] FIG. 2C is an enlarged cross-sectional view of a substrate illustrating an example of a second method for manufacturing a wiring substrate. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a substrate illustrating an example of a third method for manufacturing a wiring substrate. DETAILED DESCRIPTION OF THE INVENTION

[0010] Exemplary embodiments of the present disclosure will now be described.

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

[0012] Therefore, the plating solution used in the electroless plating of this 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, and ruthenium is typically present 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, ruthenium in general (including ruthenium ions and ruthenium hydrates) contained in the electroless plating solution may also be simply referred to as a ruthenium salt.

[0013] The electroless plating solution used in this embodiment further contains a complexing agent, a reducing agent, and a pH adjuster in addition to a ruthenium salt. The reducing agent includes hydrazine hydrate. The complexing agent includes tartaric acid and ammonium chloride.

[0014] As a result of extensive research, the present inventors have come to the knowledge that using the above-described electroless plating solution to perform electroless plating is advantageous for stably depositing ruthenium as a plating metal on a substrate.

[0015] The present inventors varied the molar concentrations of ruthenium salt (ruthenium(III) chloride-n hydrate: RuCl3·n(HO)), tartaric acid, and ammonium chloride in the electroless plating solution, deposited ruthenium on a substrate as a plating body, and evaluated the deposition rate and surface electrical resistivity of the ruthenium.

[0016] [Table 1]

[0017] [Table 2]

[0018] Table 1 above shows the evaluation conditions and evaluation results of ruthenium actually deposited on a substrate (i.e., Sample 1 and Sample 2). Table 2 above shows the evaluation conditions common to Sample 1 and Sample 2 shown in Table 1.

[0019] In Table 1, "RuCl3·n(H2O)" represents ruthenium(III) chloride n-hydrate, "L(+)-tartaric acid" represents tartaric acid, and "NH4Cl" represents ammonium chloride. Table 1 also shows the molar concentrations (mol / m) of ruthenium(III) chloride n-hydrate, tartaric acid, and ammonium chloride in the electroless plating solutions actually used for Sample 1 and Sample 2. 3 ) is shown.

[0020] In Table 1, "Ru deposition rate (nm / min)" indicates the deposition rate of ruthenium on the substrate, and is expressed as the increase in the length of ruthenium in the thickness direction (nanometers) per minute.

[0021] In Table 1, "As-depo. Ru surface electrical resistivity (μΩ·cm)" indicates the surface electrical resistivity of ruthenium measured immediately after the ruthenium film was formed on the substrate. "Ru surface electrical resistivity after forming gas heat treatment (μΩ·cm)" indicates the surface electrical resistivity of ruthenium measured after the ruthenium deposited on the substrate was heat-treated (annealed) using forming gas. In this heat treatment, a mixture of nitrogen and hydrogen gas was used as the forming gas, and the ruthenium deposited on the substrate was heated for 30 minutes using forming gas at 400°C.

[0022] In Table 2, "pH" indicates the pH of the electroless plating solution actually used. "Bath temperature" indicates the temperature of the electroless plating solution actually used (particularly the measured temperature of the electroless plating solution on the substrate).

[0023] The inventors prepared an electroless plating solution by adding a ruthenium salt to a solution containing a complexing agent (tartaric acid and ammonium chloride), a reducing agent (hydrazine hydrate), and a pH adjuster (potassium hydroxide), and then leaving it for two days or more.

[0024] Specifically, the molar concentration of tartaric acid (L(+)-tartaric acid) in the electroless plating solution is 10 mol / m 3~60mol / m 3 Several samples were prepared with the molar concentration of ammonium chloride in the electroless plating solution changed in the range of 10 mol / m 3 ~480mol / m 3 Several samples were prepared with the molar concentration of ruthenium(III) chloride n-hydrate in the electroless plating solution changed in the range of 10 mol / m 3 Although not shown in Tables 1 and 2, samples were also prepared using tetramethylammonium hydroxide (TMAH) or sodium hydroxide as a pH adjuster instead of potassium hydroxide.

[0025] In this way, the present inventors have actually performed electroless plating using various electroless ruthenium plating solutions prepared under various conditions and evaluated them. Samples 1 and 2 shown in Table 1 are a part of the many samples that the present inventors have actually evaluated.

[0026] The deposition rate of ruthenium was relatively fast in Samples 1 and 2 shown in Table 1. Furthermore, the surface electrical resistivity of ruthenium on the substrate after the forming gas heat treatment in Samples 1 and 2 was relatively low, and the resistivity was sufficient for wiring embedded in recesses in a semiconductor substrate.

[0027] Although not shown in Tables 1 and 2, the inventors of the present invention measured the surface electrical resistivity of several samples made under the same conditions by subjecting the ruthenium (plated body) to heat treatment (annealing treatment) at different heating temperatures in the range of 0°C to 600°C. Specifically, for several samples, the surface electrical resistivity was measured at an atmospheric pressure of 1×10 -3Heat treatment of ruthenium was performed in a vacuum of 100 Pa without using forming gas. Furthermore, heat treatment of ruthenium using forming gas was also performed on several other samples. As a result, in both cases where forming gas was used and where no forming gas was used, the higher the heating temperature, the lower the surface electrical resistivity of the ruthenium (plated body). In particular, the degree of decrease in the surface electrical resistivity of the ruthenium (plated body) tended to be greater in the heating temperature range of 200°C to 400°C. Furthermore, compared to heat treatment without forming gas, heat treatment with forming gas tended to result in a greater decrease in the surface electrical resistivity of the ruthenium (plated body) in the heating temperature range of 0°C to 400°C.

[0028] In all samples where ruthenium salt was added to a solution containing a complexing agent (tartaric acid and ammonium chloride), a reducing agent (hydrazine hydrate), and a pH adjuster, the ruthenium salt dissolved sufficiently in the solution, and no metal precipitates were observed in the electroless plating solution. Furthermore, in samples where an electroless plating solution containing a ruthenium salt, a complexing agent (tartaric acid and ammonium chloride), a reducing agent (hydrazine hydrate), and a pH adjuster was used, ruthenium deposits were stably deposited in the recesses of the substrate without forming voids. Furthermore, in samples where an electroless plating solution containing a ruthenium salt, a complexing agent (tartaric acid and ammonium chloride), a reducing agent (hydrazine hydrate), and a pH adjuster was used, the ruthenium deposition rate and surface electrical resistivity were within acceptable ranges.

[0029] In particular, the molar concentration of hydrazine hydrate (reducing agent) is 5 mol / m 3 ~40 mol / m 3 In the sample with a molar concentration of tartaric acid of 10 to 100 mol / m, the evaluation results of the solubility of ammonium chloride, the deposition property of ruthenium, the deposition rate of ruthenium, and the surface electrical resistivity were good from an overall viewpoint. 3 and the molar concentration of ammonium chloride is 10 to 1000 mol / m 3In the samples, the evaluation results of the ruthenium deposition rate and surface electrical resistivity were good. Furthermore, when the electroless plating solution after adjustment with a pH adjuster was alkaline, especially when the pH was 11 or higher (e.g., 13 or lower), ruthenium could be deposited on the substrate particularly stably.

[0030] The inventors of the present invention have also added ruthenium salt to pure water, but the ruthenium salt did not dissolve in the pure water.Furthermore, the inventors of the present invention have added ruthenium salt to a solution containing only ammonium chloride, but the ruthenium salt did not dissolve in the solution.

[0031] The present inventors also 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.The present inventors also performed electroless plating using an electroless ruthenium plating solution containing only tartaric acid as a complexing agent, but no ruthenium was deposited on the substrate.

[0032] The present inventors further evaluated the deposition rate of ruthenium by changing the base (material) on which ruthenium is deposited.

[0033] [Table 3]

[0034] [Table 4]

[0035] [Table 5]

[0036] [Table 6]

[0037] Table 3 above shows the evaluation conditions common to Samples 3 to 5 shown in Table 4. Table 4 above shows the evaluation results of the deposition rates of Samples 3 to 5. Table 5 shows the evaluation conditions for Sample 6 shown in Table 6. Table 6 shows the evaluation results of the deposition rate of Sample 6.

[0038] Tables 3 and 5 show the molar concentrations (mol / m) of "ruthenium chloride (III)-n hydrate," "tartaric acid," "ammonium chloride," and "reducing agent" contained in the electroless plating solutions actually used for Samples 3 to 6. 3 ) are shown. Tables 3 and 5 also show the pH (=12.3) and bath temperature (=60°C) of the electroless plating solution actually used for Samples 3 to 6. Potassium hydroxide was used as the pH adjuster for Samples 3 to 5, and TMAH was used as the pH adjuster for Sample 6.

[0039] In Sample 3, a cobalt (Co) film deposited on a substrate by CVD was used as a substrate on which ruthenium was deposited by electroless plating (see "CVD-Co" in Table 4). In Sample 4, a copper (Cu) film deposited on a substrate by physical vapor deposition (PVD) was used as a substrate on which ruthenium was deposited by electroless plating (see "PVD-Cu" in Table 4). In Sample 5, a substrate surface coated with palladium (Pd) nanoparticles was used as a substrate on which ruthenium was deposited by electroless plating (see "Pd nanoparticles" in Table 4). In Sample 6, a ruthenium (Ru) film deposited on a substrate by CVD was used as a substrate on which ruthenium was deposited by electroless plating (see "CVD-Ru" in Table 6).

[0040] The actual deposition rates of ruthenium by electroless plating for Samples 3 to 6 are shown in Tables 4 and 6, and all showed sufficient deposition rate performance from the viewpoint of manufacturing wiring boards. In particular, when palladium nanoparticles were applied to the base (see Sample 5 in Table 4), the deposition rate of ruthenium was relatively fast.

[0041] The present inventors further evaluated the element ratio (at %) of ruthenium and oxygen in the plated body by changing the composition ratio of the electroless ruthenium plating solution.

[0042] [Table 7]

[0043] [Table 8]

[0044] Table 7 above shows the evaluation conditions for Samples 7 to 9. Table 8 above shows the evaluation results for Samples 7 to 9 regarding the element ratio (at %) of ruthenium and oxygen in the plated body.

[0045] In Table 8, the rows marked "As depo." show the evaluation results for ruthenium immediately after film formation on the substrate. On the other hand, the rows marked "After forming gas heat treatment" show the evaluation results for ruthenium deposited on the substrate after heat treatment with forming gas (at 400°C for 30 minutes).

[0046] As is clear from Table 8, the plated bodies of Samples 7 to 9 all had a ruthenium element ratio of 80 (at%) or more and an oxygen element ratio of 20 (at%) or less. In particular, the plated bodies after forming gas treatment of Samples 7 to 9 all had a ruthenium element ratio of 90 (at%) or more and an oxygen element ratio of 10 (at%) or less.

[0047] As is clear from the above, the electroless ruthenium plating solution of this embodiment was able to deposit a high-quality ruthenium plated body on a substrate.

[0048] [Method of manufacturing wiring board] Next, a typical example of a method for manufacturing a wiring board using the above-mentioned electroless plating solution will be described.

[0049] First, a first method for manufacturing a wiring board will be described. Figures 1A to 1C are enlarged cross-sectional views of a substrate 10 illustrating an example of the first method for manufacturing a wiring board.

[0050] First, as shown in Fig. 1A, a substrate 10 having a recess 11 for wiring is prepared. Although only one recess 11 is shown in Figs. 1A to 1C, the substrate 10 may have multiple recesses 11.

[0051] 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) can be included in the concept of the recess 11.

[0052] The recess 11 is defined by a recess partition surface 12, which includes a partition bottom surface 12a and partition side surfaces 12b. In this example, the partition bottom surface 12a includes a metal surface that serves as a base on which ruthenium is deposited by electroless plating. In the example shown in FIGS. 1A to 1C, the partition bottom surface 12a is formed by a lower wiring layer 22 containing ruthenium, but the lower wiring layer 22 may contain a material other than ruthenium.

[0053] On the other hand, the compartment 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 ruthenium embedded in the recess 11 from diffusing into the insulating film 20, and can be made of, for example, any metal (e.g., Ta (tantalum) or TaN (tantalum nitride)).

[0054] Thereafter, electroless plating solution 50 is applied onto substrate 10 to form a puddle of electroless plating solution 50, and the entire recess 11 is filled with electroless plating solution 50, as shown in FIG. 1B. This ensures that electroless plating solution 50 is in contact with the entire recess compartment surface 12 (particularly compartment bottom surface 12a). The electroless plating solution 50 used here is the electroless ruthenium plating solution described above (see Samples 1 to 9 in Tables 1 to 8).

[0055] Thereafter, while maintaining the state in which the recess 11 is filled with the electroless plating solution 50, electroless plating is performed with the electroless plating solution 50 in contact with the recess compartment surface 12 (particularly the compartment bottom surface 12a). As a result, a plated body 40 containing ruthenium is deposited in the recess 11, and eventually, the entire recess 11 is filled with ruthenium as the plated body 40 (see FIG. 1C).

[0056] In particular, the electroless plating of this example employs a bottom-up deposition process in which ruthenium (plated body 40) is selectively deposited on the compartment bottom surface 12a, with no or almost no ruthenium (plated body 40) being deposited on the compartment side surface 12b. Therefore, this example makes it possible to fill the entire recess 11 with ruthenium (plated body 40) while effectively preventing voids from remaining in the recess 11.

[0057] The ruthenium plated body 40 thus embedded in the recess 11 can be used as wiring.

[0058] The element ratio of oxygen in plated body 40 deposited in recess 11 using the above-mentioned electroless ruthenium plating solution (see Samples 1 to 9 in Tables 1 to 8) is 20% or less, and the element ratio of ruthenium is 80% or more.

[0059] Furthermore, a forming gas consisting of a mixed gas of nitrogen and hydrogen may be used to further heat-treat the plated body 40 in the recess 11. In this case, it is possible to make the elemental ratio of oxygen in the plated body 40 deposited in the recess 11 10% or less and the elemental ratio of ruthenium 90% or more, thereby improving the purity of ruthenium in the plated body 40 embedded in the recess 11.

[0060] Substrate 10 can then undergo any processing to achieve the desired semiconductor substrate configuration.

[0061] Next, a second method for manufacturing a wiring board will be described.

[0062] 2A to 2C are enlarged cross-sectional views of substrate 10 illustrating an example of a second manufacturing method for a wiring board. In the second manufacturing method illustrated in FIGS. 2A to 2C, elements that are the same as or correspond to those in the first manufacturing method illustrated in FIGS. 1A to 1C described above are denoted by the same reference numerals, and detailed descriptions of matters similar to those in the first manufacturing method will be omitted.

[0063] In this example, as shown in FIG. 2A, a substrate 10 having a seed layer 25 provided on an insulating film 20 is prepared.

[0064] The seed layer 25 promotes the deposition of a plating metal (ruthenium) during electroless plating, and the plating metal is deposited. The seed layer 25 may have any composition that can promote the deposition of ruthenium as a plating metal. As an example, a thin film of ruthenium formed on the insulating film 20 by CVD can be used as the seed layer 25.

[0065] The recessed portion surface 12 (i.e., the bottom surface 12a and the side surface 12b) defining the recessed portion 11 is formed by the seed layer 25. In this example, the recessed portion surface 12 includes the seed layer 25 over its entirety, but only a portion of the recessed portion surface 12 may include the seed layer 25.

[0066] Thereafter, electroless plating solution 50 is applied onto substrate 10 to form a puddle of electroless plating solution 50, and the entire recess 11 is filled with electroless plating solution 50 as shown in FIG. 2B. This ensures that electroless plating solution 50 is in contact with recess section surface 12 (i.e., seed layer 25). The electroless plating solution 50 used here is the electroless ruthenium plating solution described above (see Samples 1 to 9 in Tables 1 to 8).

[0067] Thereafter, while maintaining the state in which the recess 11 is filled with the electroless plating solution 50, electroless plating is performed with the electroless plating solution 50 in contact with the recess section surface 12 (i.e., the 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 a plated body 40 (see FIG. 2C).

[0068] Next, a third method for manufacturing a wiring board will be described.

[0069] 3 is an enlarged cross-sectional view of substrate 10 illustrating an example of a third manufacturing method for a wiring board. In the third manufacturing method illustrated in FIG. 3, elements that are the same as or correspond to those in the first and second manufacturing methods described above are denoted by the same reference numerals, and detailed descriptions of matters similar to those in the first and second manufacturing methods will be omitted.

[0070] In this example, as shown in Figure 3, a substrate 10 is prepared in which a barrier film 21 is provided on an insulating film 20, and the recess partition surfaces 12 (i.e., the partition bottom surface 12a and the partition side surface 12b) that define the recess 11 are formed by the barrier film 21.

[0071] Catalyst particles 29 are attached to the barrier film 21 (particularly the surface area including the recessed area 12).

[0072] The catalyst particles 29 are catalytic nuclei that promote the deposition of a 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 a plating metal. As an example, a liquid (metal ion-containing liquid) in which metal ions that form the catalyst particles 29 are dispersed may be applied onto the substrate 10 (barrier film 21), and the metal ion-containing liquid may be removed from the barrier film 21 using a rinse liquid or the like, thereby adhering the catalyst particles 29 to the barrier film 21.

[0073] Thereafter, an electroless plating solution is applied onto substrate 10 to form a puddle of electroless plating solution, and the entire recess 11 is filled with electroless plating solution 50. Then, while maintaining the state in which recess 11 is filled with the electroless plating solution, electroless plating is performed with the electroless plating solution in contact with the recess section surface 12 to which catalyst particles 29 are attached. As a result, the catalyst particles 29 promote the deposition of ruthenium, and ultimately ruthenium is embedded in the entire recess 11 as plated body 40.

[0074] As described above, according to this embodiment, the electroless ruthenium plating solution is brought into contact with the recess partition surface 12 that defines the wiring recess 11 of the substrate 10, and a plated body 40 containing ruthenium can be deposited in the recess 11 by electroless plating. This allows ruthenium to be stably deposited on the material by electroless plating.

[0075] It should be noted that the embodiments and modifications disclosed in this specification are merely examples in all respects and should not be construed as limiting. The above-described embodiments and modifications can be omitted, substituted, and modified in various forms without departing from the scope and spirit of the appended claims. For example, the above-described embodiments and modifications may be combined in part or in whole, and embodiments other than those described above may be combined in part or in whole with the above-described embodiments or modifications.

[0076] Furthermore, the technical category embodying the above technical idea is not limited. For example, the above device may be applied to another device. The above technical idea may also be embodied by a computer program for causing a computer to execute one or more procedures (steps) included in the above method. The above technical idea may also be embodied by a computer-readable non-transitory recording medium on which such a computer program is recorded.

Claims

1. Contains a ruthenium salt, a complexing agent, a reducing agent, and a pH adjuster; the reducing agent comprises hydrazine hydrate; The electroless plating solution, wherein the complexing agent comprises tartaric acid and ammonium chloride.

2. The concentration of the tartaric acid is 10 to 100 mol / m ３ and The concentration of the ammonium chloride is 10 to 1000 mol / m ３ 2. The electroless plating solution according to claim 1, wherein

3. The concentration of the hydrazine hydrate is 5 mol / m ３ ~40 mol / m ３ 3. The electroless plating solution according to claim 1 or 2,

4. 3. The electroless plating solution according to claim 1, having a pH of 11 or more.

5. 3. A method for manufacturing a wiring substrate, comprising a step of depositing a plating body containing ruthenium in a recess by electroless plating while bringing the electroless plating solution according to claim 1 or 2 into contact with a recess partition surface that defines a recess for wiring of a substrate.

6. The method for manufacturing a wiring board according to claim 5 , wherein the recess includes at least one of a via and a trench.

7. The recessed section surface includes a compartment bottom surface and a compartment side surface; The method for manufacturing a wiring substrate according to claim 5 , wherein the compartment bottom surface includes a metal surface on which ruthenium is deposited by the electroless plating.

8. The method for manufacturing a wiring substrate according to claim 5 , wherein the recessed area includes a seed layer, and the electroless plating is performed with the electroless plating solution in contact with the seed layer, thereby depositing ruthenium on the seed layer.

9. The method for manufacturing a wiring substrate according to claim 5 , wherein the electroless plating is carried out in a state where the electroless plating solution is in contact with the recessed section surface to which a catalyst for accelerating the electroless plating is attached.

10. The method for manufacturing a wiring substrate according to claim 5 , wherein the element ratio of oxygen in the plating body deposited in the recess is 20% or less.

11. The method for manufacturing a wiring substrate according to claim 5, further comprising the step of heat treating the plated body using a mixed gas of nitrogen and hydrogen.

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