Tin-silver plating solution and method for forming tin-silver solder bump using the same

Abstract

The present invention provides a tin-silver plating solution, characterized by comprising a tin ion source, a silver ion (Ag + ) source, and an organic additive containing a silver (Ag) complexing agent, a tin carrier, and a grain refiner, whereby, in the case of high-speed plating using the above-described plating solution, whisker generation can be reduced, and, with the silver ion (Ag + ) component in the tin-silver plating solution being uniformly maintained, the silver component in the formed tin-silver solder bump can be uniformly formed.

Description

Technical Field

[0001] The present invention relates to tin-silver plating solutions, and more specifically, to tin-silver plating solutions for plating on substrates of electronic components including semiconductor devices. Background Technology

[0002] With the trends of miniaturization, ultra-thinning, high-capacity, and high-functionality of electronic components, the reduction in the area of ​​circuit boards and other core components of the aforementioned electronic products, or the increase in the mounting area of ​​semiconductor devices, will directly affect the competitiveness of the aforementioned electronic products. Research and development is underway to increase the mounting area of ​​semiconductor devices mounted on the aforementioned circuit boards.

[0003] Therefore, recently, in order to reduce the installation area, a method of directly mounting semiconductor devices in the form of bare chips has been used. As one type of bare chip mounting, the method of mounting flip chips is mainly used.

[0004] Flip chip packaging comes in various forms, and the flip chip packaging technology using solder bumps has the following advantages: solder bumps are directly bonded between circuit boards, and the number of input / output terminals per unit area is greatly increased by using an area array of the entire chip area, thereby enabling the production of products suitable for fine pitch, high speed, lightweight, high functionality, and high performance.

[0005] Previously, tin-lead solder bumps were commonly used due to their excellent soldering properties, low melting point, and ease of plating solution management. However, with the implementation of the RoHS regulation restricting the use of hazardous substances such as lead, the use of tin-lead solder bumps has been limited. Furthermore, whiskers frequently appear during reflow soldering of solder balls after plating solder bumps with tin plating solution, necessitating research to address this issue. Therefore, tin-based alloys such as tin-silver, tin-bismuth, tin-copper, and tin-zinc are being explored as alternatives to tin-lead alloys.

[0006] Tin-silver alloys have attracted much attention due to their low resistivity, stability, ability to achieve a wide melting point range, and ability to remove alpha particle release caused by pure tin (Sn) sources. However, during the preparation of tin-silver solder bumps, silver ions (Ag) in the electroplating solution... + Silver ions (Ag) tend to be deposited on specific under bump metal (UBM) layers or tin anodes, making it difficult to control their concentration in the plating solution. +The concentration of tin-silver solder bumps is important. Furthermore, if the tin-silver solder bumps do not have the appropriate alloy composition ratio, whiskers or nodules may appear, potentially leading to interconnect reliability issues within the flip chip.

[0007] Another problem in the preparation of the aforementioned tin-silver solder bumps is that the plating current density is limited. When plating, a high current density will accelerate the bump plating speed and have a positive impact on high throughput, but it is difficult to control the plating surface, and excessive hydrogen gas will be generated in the plating electrode, which may lead to adverse effects such as the formation of voids in the bump due to poor plating.

[0008] Therefore, it is necessary to develop a tin-silver electroplating solution that has a stable electroplating speed, stable silver content, and smooth electroplating surface under high-speed electroplating conditions.

[0009] Existing technical documents

[0010] Patent Document 1: Korean Patent Publication No. 10-1175062 Summary of the Invention

[0011] Technical issues

[0012] One problem with this invention is to provide a tin-silver plating solution that reduces whisker formation during high-speed electroplating and improves the inhomogeneity of silver composition during the soldering process.

[0013] The technical problems to be solved by this invention are not limited to those mentioned above. Those skilled in the art can clearly understand other technical problems not mentioned from the following description.

[0014] Problem Solving Methods

[0015] To address the aforementioned problems, one embodiment of the present invention provides a tin-silver electroplating solution, characterized in that it comprises a tin ion source and silver ions (Ag). + The source and organic additives, wherein the organic additives include: a silver (Ag) complexing agent represented by the following chemical formula 1; a tin carrier represented by the following chemical formula 2; and a grain refiner represented by the following chemical formula 3.

[0016] Chemical Formula 1:

[0017]

[0018] In this case, A1 is a straight-chain alkylene group having 1 to 10 carbon atoms, and R1 and R2 are each independently a functional group containing at least one of carbon, oxygen, nitrogen, sulfur, and silicon.

[0019] Chemical formula 2:

[0020]

[0021] In this case, A2 above refers to substituted or unsubstituted C6 to C. 30 An aryl group or a heteroaryl group having 6 to 30 ring atoms including heteroatoms, wherein one or more ring carbons are composed of at least one of nitrogen, oxygen, and sulfur.

[0022] The R3 mentioned above is hydrogen, substituted or unsubstituted C1 to C2. 30 Alkyl, substituted or unsubstituted C3 to C4 30 Cycloalkyl, substituted or unsubstituted C2 to C3 30 alkenyl, substituted or unsubstituted C2 to C 30 Alkyne group, substituted or unsubstituted C1 to C 30 The n1 to n4 are each one of the following: alkoxy group, hydroxyl group, sulfonic acid group that forms an ionic bond with an alkali metal cation, phosphonic acid group that forms an ionic bond with an alkali metal cation, nitrate group that forms an ionic bond with an alkali metal cation, and carboxylic acid group that forms an ionic bond with an alkali metal cation, wherein each of the above n1 to n4 is an independent integer from 0 to 26, and the sum of n1 to n4 is from 10 to 26.

[0023] Chemical formula 3:

[0024]

[0025] In this case, R4 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R5 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R6 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; R7 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; and X is selected from the group consisting of chlorine (Cl), bromine (Br), iodine (I), nitrate (NO3), sulfate (SO4), carbonate (CO3), and hydroxyl (OH).

[0026] In one embodiment of the present invention, the tin-silver electroplating solution is characterized in that the tin ion source may include at least one water-soluble tin compound selected from the group consisting of stannous sulfate, stannous hydrochloride, stannous aminosulfonate, stannous acetate, stannous phosphate, stannous methanesulfonate, stannous gluconate, and stannous carboxylate.

[0027] Furthermore, in one embodiment of the present invention, the tin-silver electroplating solution is characterized in that the aforementioned silver ions (Ag) +The source may contain at least one water-soluble silver (Ag) compound selected from the group consisting of silver sulfate, silver hydrochloride, silver sulfamate, silver acetate, silver phosphate, silver methanesulfonate, silver gluconate, and silver carboxylate.

[0028] Furthermore, in one embodiment of the present invention, the tin-silver electroplating solution is characterized in that, in the aforementioned tin-silver electroplating solution, tin ions and silver ions (Ag) + The weight ratio of () can be from 75:25 to 99.9:0.1.

[0029] Furthermore, in one embodiment of the present invention, the tin-silver electroplating solution is characterized in that the aforementioned silver ions (Ag) + The molar ratio of the source to the silver (Ag) complexing agent can be from 1:1 to 1:10.

[0030] Furthermore, in one embodiment of the present invention, the tin-silver electroplating solution is characterized in that it may also contain at least one of a conductive salt, an antioxidant, and a leveling agent.

[0031] In this case, the tin-silver plating solution is characterized in that the aforementioned conductive salt can be one of hydroxycarboxylic acid or alkyl sulfonic acid.

[0032] Furthermore, in this case, the tin-silver plating solution is characterized in that the antioxidant can be at least one selected from the group consisting of catechol, hydroquinone, resorcinol, cresol, phloroglucinol, hydroxyhydroquinone, and pyroglucinol.

[0033] Furthermore, in this case, the tin-silver plating solution is characterized in that the leveling agent can be at least one selected from the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, and synthetic polymers.

[0034] To address the aforementioned problems, another embodiment of the present invention provides a method for forming tin-silver solder bumps, comprising: exposing a lower bump metal structure to an electroplating bath containing a tin-silver electroplating solution, wherein the tin-silver electroplating solution contains a tin ion source, a silver ion source, and an organic additive, wherein the organic additive contains a silver complexing agent represented by the following chemical formula 1, a tin carrier represented by the following chemical formula 2, and a grain refiner represented by the following chemical formula 3; and electroplating a tin-silver alloy onto the lower bump metal structure by applying an electric current.

[0035] Chemical Formula 1:

[0036]

[0037] In this case, A1 is a straight-chain alkylene group having 1 to 10 carbon atoms, and R1 and R2 are each independently a functional group containing at least one of carbon, oxygen, nitrogen, sulfur, and silicon.

[0038] Chemical formula 2:

[0039]

[0040] In this case, A2 above refers to substituted or unsubstituted C6 to C. 30 The aryl group or a heteroaryl group having 6 to 30 ring atoms including heteroatoms, wherein one or more ring carbons are composed of at least one of nitrogen, oxygen, and sulfur, and R3 is hydrogen, substituted or unsubstituted C1 to C2. 30 Alkyl, substituted or unsubstituted C3 to C4 30 Cycloalkyl, substituted or unsubstituted C2 to C3 30 alkenyl, substituted or unsubstituted C2 to C 30 Alkyne group, substituted or unsubstituted C1 to C 30 The n1 to n4 are each one of the following: alkoxy group, hydroxyl group, sulfonic acid group that forms an ionic bond with an alkali metal cation, phosphonic acid group that forms an ionic bond with an alkali metal cation, nitrate group that forms an ionic bond with an alkali metal cation, and carboxylic acid group that forms an ionic bond with an alkali metal cation, wherein each of the above n1 to n4 is an independent integer from 0 to 26, and the sum of n1 to n4 is from 10 to 26.

[0041] Chemical formula 3:

[0042]

[0043] In this case, R4 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing a hydroxyl group and having 1 to 7 carbons; R5 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing a hydroxyl group and having 1 to 7 carbons; R6 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; R7 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; and X is selected from the group consisting of chlorine, bromine, iodine, nitrate, sulfate, carbonate, and hydroxyl groups.

[0044] In one embodiment of the present invention, the method for forming tin-silver solder bumps is characterized in that, in the step of electroplating the tin-silver alloy, the applied current may have a current density of 1 ASD to 10 ASD.

[0045] To address the aforementioned problems, another embodiment of the present invention provides a tin-silver solder bump formed by the above method.

[0046] The effects of the invention

[0047] When using the tin-silver plating solution of an embodiment of the present invention for high-speed electroplating, the formation of whiskers can also be reduced, and silver ions (Ag) are uniformly maintained in the tin-silver plating solution.+ The composition of the tin-silver solder bumps can be uniformly formed by the silver component.

[0048] Furthermore, the method for forming tin-silver solder bumps of the present invention can perform electroplating at high current density and high speed, thereby achieving high throughput.

[0049] Furthermore, the tin-silver solder bumps formed using the tin-silver solder bump formation method of the present invention can have uniform bump height, improved surface roughness and solderability, and uniform silver (Ag) content and distribution within the bump, reducing whisker formation and retaining good reflow characteristics. Consequently, it exhibits the effect of effectively maintaining the processability and reliability of ultra-fine bumps.

[0050] The effects of this invention are not limited to those described above, but include all effects that can be inferred from the structure of the invention as described in the detailed description of the invention or the claims. Attached Figure Description

[0051] Figure 1 This is a flowchart of the method for forming tin-silver solder bumps according to the present invention.

[0052] Figure 2 The images are scanning electron microscope images of the surface of tin-silver solder bumps in an embodiment and comparative example of the present invention.

[0053] Figure 3 These are scanning electron microscope images of the welded products of an embodiment and a comparative example of the present invention.

[0054] Figure 4 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 2a of the present invention.

[0055] Figure 5 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 2b of the present invention.

[0056] Figure 6 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 3a of the present invention.

[0057] Figure 7 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 3b of the present invention.

[0058] Figure 8 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 4a of the present invention.

[0059] Figure 9The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 4b of the present invention.

[0060] Figure 10 The images are scanning electron microscope images of the surface of the tin-silver solder bump and the soldering product of Embodiment 4c of the present invention. Detailed Implementation

[0061] The present invention will now be described with reference to the accompanying drawings. However, the present invention can be embodied in many different forms and is therefore not limited to the embodiments described herein.

[0062] The terminology used in this invention is for illustrative purposes only and is not intended to limit the invention. Unless explicitly stated in the context, singular expressions include plural expressions. In this specification, unless specifically stated to the contrary, terms such as "comprising" or "having" are used to specify the presence of features, numbers, steps, actions, structural elements, components, or combinations thereof described in the specification, and do not preclude the presence or additional possibilities of one or more other features, numbers, steps, actions, structural elements, components, or combinations thereof.

[0063] One embodiment of the present invention provides a tin-silver electroplating solution, characterized in that it comprises a tin ion source and silver ions (Ag). + Source and organic additives, wherein the organic additives include: a silver (Ag) complexing agent represented by the following chemical formula 1; a tin carrier represented by the following chemical formula 2; and a grain refiner represented by the following chemical formula 3.

[0064] Chemical Formula 1:

[0065]

[0066] In this case, A1 is a straight-chain alkylene group having 1 to 10 carbon atoms, and R1 and R2 are each independently a functional group containing at least one of carbon, oxygen, nitrogen, sulfur and silicon.

[0067] Chemical formula 2:

[0068]

[0069] In this case, A2 above refers to substituted or unsubstituted C6 to C. 30 The aryl group or a heteroaryl group having 6 to 30 ring atoms including heteroatoms, wherein one or more ring carbons are composed of at least one of nitrogen, oxygen, and sulfur, and R3 is hydrogen, substituted or unsubstituted C1 to C2. 30 Alkyl, substituted or unsubstituted C3 to C4 30 Cycloalkyl, substituted or unsubstituted C2 to C3 30alkenyl, substituted or unsubstituted C2 to C 30 Alkyne group, substituted or unsubstituted C1 to C 30 One of alkoxy, hydroxy, sulfonic acid group that forms an ionic bond with an alkali metal cation, phosphonic acid group that forms an ionic bond with an alkali metal cation, nitrate group that forms an ionic bond with an alkali metal cation, and carboxylic acid group that forms an ionic bond with an alkali metal cation, wherein each of n1 to n4 is an integer from 0 to 26, and the sum of n1 to n4 is from 10 to 26.

[0070] Chemical formula 3:

[0071]

[0072] In this case, R4 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R5 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R6 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; R7 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; and X is selected from the group consisting of chlorine, bromine, iodine, nitrate, sulfate, carbonate, and hydroxyl.

[0073] Recently, with increasingly stringent regulations regarding the environmental problems caused by lead, people have been paying more attention to lead-free solders, and pure tin, tin-copper, tin-silver and ternary tin alloys have been explored as potential alternatives to the previously used tin-lead alloys.

[0074] In particular, tin-silver alloys have advantages such as low resistivity, stability, and a wide melting point range. Compared with tin-lead alloys, they have excellent mechanical properties such as tensile strength, thermal fatigue and creep, and the joint strength is especially excellent.

[0075] The tin-silver electroplating solution of the present invention is used to prepare solder bumps containing the above-mentioned tin-silver alloy, which includes a tin ion source and a silver ion source.

[0076] In one embodiment of the present invention, the tin ion source is used to supply tin ions (Sn) to the tin-silver electroplating solution of the present invention. 2 + The substance can be a water-soluble tin compound. For example, the water-soluble tin compound can be at least one selected from the group consisting of stannous sulfate, stannous hydrochloride, stannous aminosulfonate, stannous acetate, stannous phosphate, stannous methanesulfonate, stannous gluconate and stannous carboxylate. For example, it can be stannous methanesulfonate, which has high solubility.

[0077] In one embodiment of the present invention, the silver ion source is a substance that supplies silver ions to the tin-silver electroplating solution of the present invention, and can be a water-soluble silver compound. For example, the water-soluble silver compound may contain at least one selected from the group consisting of silver sulfate, silver hydrochloride, silver aminosulfonate, silver acetate, silver phosphate, silver methanesulfonate, silver gluconate and silver carboxylate. For example, it may contain silver methanesulfonate.

[0078] In one embodiment of the present invention, in the tin-silver electroplating solution, the weight ratio of tin ions to silver ions can be from 75:25 to 99.9:0.1, and in the tin ion source and silver ion source, the weight ratio of tin ions to silver ions can be the aforementioned weight ratio.

[0079] When tin-silver plating solution with a tin-silver ion weight ratio within the aforementioned range is used to form tin-silver solder bumps, solderability is good. Conversely, when the tin-silver ion weight ratio exceeds the aforementioned range, problems such as increased whisker formation during the electroplating process and higher melting temperature during reflow soldering may occur when forming tin-silver solder bumps.

[0080] Next, the tin-silver plating solution of the present invention contains organic additives.

[0081] The aforementioned organic additives are used to reduce the formation of whiskers in tin-silver solder bumps prepared using the tin-silver electroplating solution of the present invention and to improve the non-uniformity of the silver composition. They include a silver complexing agent, a tin carrier, and a grain refiner.

[0082] In one embodiment of the present invention, the silver complexing agent contained in the above-mentioned organic additive may be a compound represented by the following chemical formula 1.

[0083] Chemical Formula 1:

[0084]

[0085] In this case, A1 is a straight-chain alkylene group having 1 to 10 carbons, and R1 and R2 are each independently a functional group containing at least one of carbon, oxygen, nitrogen, sulfur and silicon.

[0086] Tin-silver plating solutions can form whisker structures that reduce solder bump characteristics depending on the silver composition, or Ag3Sn phases with high melting points, thus requiring precise control of the silver composition.

[0087] The silver content is difficult to control because the reduction potential difference between tin ions and silver ions is extremely large, and silver will precipitate out during long-term use, thus shortening the life of the electroplating solution.

[0088] The reduction potentials of silver ions and tin ions are shown in the following reaction formula 1.

[0089] Reaction 1:

[0090] Ag + +e→Ag E0=+0.8V

[0091] Sn2 + +2e→Sn E0=-0.14V

[0092] In one embodiment of the present invention, when electroplating is performed using a tin-silver plating solution, silver ions may spontaneously oxidize tin ions or the aforementioned lower bump metal when exposed to tin ions or the lower bump metal, and at the same time can be reduced to silver and precipitated.

[0093] The silver precipitated above can be transformed into finely separated silver metal suspended in the electroplating solution or spontaneously precipitated on the substrate, the wall of the electroplating tank, and the electrodes, which makes it difficult to control the concentration of silver ions in the electroplating solution.

[0094] Therefore, when using tin-silver plating solution for electroplating, it is necessary to improve stability by preventing silver precipitation and reducing the reduction potential difference between tin ions and silver ions in order to minimize the error range of silver composition in tin-silver solder. The aforementioned silver complexing agent can play a role in improving stability by preventing silver precipitation and reducing the reduction potential difference between tin ions and silver ions, thereby minimizing the error range of silver composition in tin-silver solder.

[0095] In one embodiment of the present invention, the molar ratio of the silver ion source to the silver complexing agent can be from 1:1 to 1:10.

[0096] In one embodiment of the present invention, R1 is one of aldehyde, hydroxyl, methyl, carboxyl, mercapto, amino, thiol, nitrile and pyridyl, for example, it can be pyridyl; R2 is one of aldehyde, hydroxyl, methyl, carboxyl, mercapto, amino, thiol, nitrile and pyridyl, for example, it can be pyridyl; and the compound of the above chemical formula 1 can be 3,6-dithia-1,8-octanediol.

[0097] In one embodiment of the present invention, the tin support contained in the above-mentioned organic additive may be a compound represented by the following chemical formula 2.

[0098] Chemical formula 2:

[0099]

[0100] In this case, A2 is either substituted or unsubstituted C6 to C. 30The aryl group or a heteroaryl group having 6 to 30 ring atoms including heteroatoms, wherein one or more ring carbons are composed of at least one of nitrogen, oxygen, and sulfur, and R3 is hydrogen, substituted or unsubstituted C1 to C2. 30 Alkyl, substituted or unsubstituted C3 to C4 30 Cycloalkyl, substituted or unsubstituted C2 to C3 30 alkenyl, substituted or unsubstituted C2 to C 30 Alkyne group, substituted or unsubstituted C1 to C 30 One of alkoxy, hydroxyl, sulfonic acid group that forms an ionic bond with an alkali metal cation, phosphonic acid group that forms an ionic bond with an alkali metal cation, nitrate group that forms an ionic bond with an alkali metal cation, and carboxylic acid group that forms an ionic bond with an alkali metal cation, wherein n1 to n4 are each independently an integer from 0 to 26, and the sum of n1 to n4 is from 10 to 26.

[0101] In one embodiment of the present invention, the grain refiner contained in the above-mentioned organic additive may be a compound represented by the following chemical formula 3.

[0102] Chemical formula 3:

[0103]

[0104] In this case, R4 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R5 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R6 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; R7 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; and X is selected from the group consisting of chlorine, bromine, iodine, nitrate, sulfate, carbonate, and hydroxyl.

[0105] In one embodiment of the present invention, when tin-silver electroplating is performed on the lower bump metal, for example, on copper, an intermetallic compound (IMC) is generated during heating after tin plating. This may lead to the formation of whiskers due to stress caused by thermal expansion. Specifically, whiskers may grow due to direct mechanical stress such as the formation of intermetallic compounds, stretching, and compression, thermomechanical stress caused by differences in thermal expansion coefficients, and stress generated by surface oxidation.

[0106] In one embodiment of the present invention, the grain refiner contained in the organic additive can reduce the internal stress of the tin plating layer and inhibit whisker growth by suppressing the growth of the intermetallic compounds of copper and tin.

[0107] In one embodiment of the present invention, R4 can be a straight-chain alkyl group having two carbons containing a hydroxyl group, R5 is a straight-chain alkyl group having two carbons containing a hydroxyl group, R6 is a straight-chain alkyl group having 12 carbons, R7 can contain hydrogen alone, and X can be a halide ion. For example, the grain refiner can be bis(2-hydroxyethyl)-methyl-tridecylazanium.

[0108] The tin-silver electroplating solution of the present invention may also contain at least one of conductive salt, antioxidant and leveling agent.

[0109] In one embodiment of the present invention, the conductive salt serves to maintain the pH of the tin-silver plating solution and impart conductivity. The conductive salt may be selected from at least one of the group consisting of hydroxycarboxylic acids and alkyl sulfonic acids, but is not limited thereto. For example, it may be selected from at least one of the group consisting of methanesulfonic acid, ethanesulfonic acid and propanesulfonic acid, for example, methanesulfonic acid.

[0110] The conductive salt can be contained in a 100% tin-silver plating solution from 5% to 30% by weight. When the conductive salt is less than 5% by weight, the conductivity of the plating solution is not adequately imparted, which may reduce the plating speed. When it is greater than 30% by weight, it may be difficult to control the plating shape.

[0111] In one embodiment of the present invention, the antioxidant is used to minimize or prevent divalent tin ions (Sn). 2+ ) oxidized to tetravalent tin ions (Sn) 4+ ), and help maintain divalent tin ions (Sn). 2+ The antioxidants mentioned above may be selected from one or more polyhydroxy aromatic compounds, but are not limited thereto. For example, they may be selected from at least one of the group consisting of catechol, hydroquinone, resorcinol, cresol, phloroglucinol, oxy hydroquinone, and pyrogallol.

[0112] The content of the aforementioned antioxidant can be from 0.01 g / L to 20 g / L. When the content of the aforementioned antioxidant is less than 0.01 g / L, the tetravalent tin ions (Sn) in the electroplating solution... 4+ The concentration of 20 g / L will increase, shortening the lifespan of the electroplating solution. When it exceeds 20 g / L, the uniformity and smoothness of the solder will decrease.

[0113] In one embodiment of the present invention, when electroplating is performed, the leveling agent improves the wettability of the solution to enhance its ability to wet fine patterns or narrow spaces and expand the working range. The leveling agent may be selected from at least one of the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants and synthetic polymers, but is not limited thereto. For example, it may be a nonionic surfactant, such as 2-naphthylethyl ether, polyoxyethylene ether, polyoxyethylene glycol, polyoxyethylene alkylphenyl ether, or polyoxyethylene alkylamino ether.

[0114] One embodiment of the present invention provides a method for forming tin-silver solder bumps.

[0115] Figure 1 This is a flowchart of the method for forming tin-silver solder bumps according to the present invention.

[0116] Reference Figure 1 The method for forming tin-silver solder bumps of the present invention includes: step S10, exposing a lower bump metal structure to an electroplating bath containing a tin-silver electroplating solution, wherein the tin-silver electroplating solution contains a tin ion source, a silver ion source, and an organic additive, wherein the organic additive contains a silver complexing agent represented by the following chemical formula 1, a tin carrier represented by the following chemical formula 2, and a grain refiner represented by the following chemical formula 3; and step S20, electroplating a tin-silver alloy on the lower bump metal structure by applying an electric current.

[0117] Chemical Formula 1:

[0118]

[0119] In this case, A1 is a straight-chain alkylene group having 1 to 10 carbon atoms, and R1 and R2 are each independently a functional group containing at least one of carbon, oxygen, nitrogen, sulfur and silicon.

[0120] Chemical formula 2:

[0121]

[0122] In this case, A2 above refers to substituted or unsubstituted C6 to C. 30The aryl group or a heteroaryl group having 6 to 30 ring atoms including heteroatoms, wherein one or more ring carbons are composed of at least one of nitrogen, oxygen, and sulfur, and R3 is hydrogen, substituted or unsubstituted C1 to C2. 30 Alkyl, substituted or unsubstituted C3 to C4 30 Cycloalkyl, substituted or unsubstituted C2 to C3 30 alkenyl, substituted or unsubstituted C2 to C 30 Alkyne group, substituted or unsubstituted C1 to C 30 One of alkoxy, hydroxy, sulfonic acid group that forms an ionic bond with an alkali metal cation, phosphonic acid group that forms an ionic bond with an alkali metal cation, nitrate group that forms an ionic bond with an alkali metal cation, and carboxylic acid group that forms an ionic bond with an alkali metal cation, wherein each of n1 to n4 is an integer from 0 to 26, and the sum of n1 to n4 is from 10 to 26.

[0123] Chemical formula 3:

[0124]

[0125] In this case, R4 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R5 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, a branched alkyl group having 5 to 20 carbons, or a straight-chain alkyl group containing hydroxyl and having 1 to 7 carbons; R6 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; R7 is hydrogen, a straight-chain alkyl group having 1 to 20 carbons, or a branched alkyl group having 5 to 20 carbons; and X is selected from the group consisting of chlorine, bromine, iodine, nitrate, sulfate, carbonate, and hydroxyl.

[0126] The method for forming tin-silver solder bumps of the present invention includes step S10, which exposes a lower bump metal structure in an electroplating bath containing a tin-silver electroplating solution.

[0127] In one embodiment of the present invention, the tin-silver electroplating solution can be the tin-silver electroplating solution in the above embodiments, and the tin ion source, silver ion source and organic additive can be the tin ion source, silver source and organic additive in the above embodiments.

[0128] The above description of the tin ion source, silver ion source, and organic additives is used instead of the above-described embodiments.

[0129] The method for forming tin-silver solder bumps of the present invention includes step S20 of electroplating a tin-silver alloy onto a lower bump metal structure by applying an electric current.

[0130] In one embodiment of the present invention, step S20 of electroplating the tin-silver alloy can be performed by an electroplating method, for example, in an electroplating bath containing the tin-silver electroplating solution.

[0131] The method for forming tin-silver solder bumps of the present invention is not limited as long as it is a solder forming method using the electroplating method in the technical field of the present invention. The above method can be used to prepare microelectronic devices.

[0132] For example, a lower bump metal structure can be formed on a silicon wafer substrate with a pattern for fabricating microelectronic devices, and the silicon wafer substrate with the lower bump metal structure can be immersed in an electroplating bath containing the tin-silver electroplating solution to expose the lower bump metal structure.

[0133] In this case, the aforementioned lower bump metal structure can be formed sequentially on the silicon wafer substrate with titanium (Ti) and copper (Cu), titanium and nickel (Ni), chromium (Cr) and copper, chromium and nickel, titanium tungsten (TiW) and copper, or titanium tungsten and nickel, etc., according to a specified thickness, but is not limited to this. For example, copper can be formed on the aforementioned silicon wafer substrate.

[0134] In one embodiment of the present invention, the current applied in the step of electroplating the tin-silver alloy can be 1 ASD (Amp / dm). 2 ) to 20ASD (Amp / dm 2 For example, it can be from 1ASD to 10ASD.

[0135] The method for forming tin-silver solder bumps of the present invention can perform electroplating at high current density and high speed, thereby achieving high throughput.

[0136] Furthermore, the tin-silver solder bumps formed using the tin-silver solder bump formation method of the present invention can have uniform bump height, improved surface roughness and solderability, and uniform silver (Ag) content and distribution within the bump, while reducing whisker formation and retaining good reflow characteristics. Consequently, it exhibits the effect of effectively maintaining the processability and reliability of ultra-fine bumps.

[0137] The present invention will now be described in more detail through preparation examples, comparative examples, and experimental examples. However, the present invention is not limited to the preparation examples, comparative examples, and experimental examples.

[0138] Preparation Example 1

[0139] In this preparation example 1, a lower bump metal structure was formed by electroplating on a patterned silicon wafer with a thickness of 10 μm using a copper plating solution.

[0140] In this case, the copper plating solution is prepared by adding 50g of copper ions, 150g of sulfate ions, 50mg of chloride ions, a polyethylene oxide derivative containing aromatic hydrocarbons as inhibitors, an organic compound containing mercapto groups as promoters, and a saturated heterocyclic compound containing nitrogen as a leveling agent to each 1L of the plating solution. The electroplating is carried out by applying a current at a current density of 5ASD for 10 minutes.

[0141] Example 1

[0142] In this Example 1, a tin-silver electroplating solution containing a grain refiner was prepared.

[0143] Specifically, an electroplating solution containing 50.0 g / L tin ions, 0.5 g / L silver ions, and 120 g / L methanesulfonate ions was prepared by mixing tin methanesulfonate and silver methanesulfonate. 2 g / L of a silver complexing agent (represented by Chemical Formula 1) and 20 g / L of a tin carrier (represented by Chemical Formula 2) were added as organic additives, along with 1 g / L of catechol as an antioxidant and 10 g / L of a grain refiner (represented by Chemical Formula 3) to prepare the tin-silver electroplating solution.

[0144] Chemical Formula 1:

[0145]

[0146] In this case, A1 is ethylene, and R1 and R2 are pyridyl groups, respectively.

[0147] Chemical formula 2:

[0148]

[0149] In this case, A2 is phenyl, R3 is hydroxyl, n1 to n3 are 0, n4 is 12, and the sum of the above is 12.

[0150] Chemical formula 3:

[0151]

[0152] In this case, R4 is a straight-chain alkyl group having two carbons containing a hydroxyl group at the end, R5 is a straight-chain alkyl group having two carbons containing a hydroxyl group at the end, R6 is a straight-chain alkyl group having 12 carbons, R7 is a straight-chain alkyl group having one carbon, and X is chlorine (Cl).

[0153] Comparative Example 1

[0154] In Comparative Example 1, a tin-silver plating solution without grain refiner was prepared.

[0155] As a specific preparation method, except for adding a grain refiner in Example 1 above, the same method as in Example 1 above was used to prepare the tin-silver electroplating solution.

[0156] Experimental Example 1

[0157] In this Experimental Example 1, tin-silver electroplating was carried out using the tin-silver electroplating solution prepared in Example 1 and Comparative Example 1 above, and experiments were conducted on the performance of the electroplating solution.

[0158] The silicon wafer with the lower bump metal structure formed in Preparation Example 1 was immersed in the tin-silver plating solution prepared in Example 1 and Comparative Example 1, respectively, and a current was applied in the range of 1 ASD to 10 ASD to perform tin-silver plating.

[0159] exist Figure 2 The image shows a surface scanning electron microscope (SEM) image of tin-silver solder bumps formed by the tin-silver plating solutions of Comparative Example 1 and Example 1.

[0160] exist Figure 3 The image shows a scanning electron microscope image of the solder product formed by performing a reflow soldering process on the tin-silver solder bumps formed by the tin-silver electroplating solution of Comparative Example 1 and Example 1. The surface roughness and silver content are shown in Table 1 below.

[0161] Table 1

[0162] Surface roughness (nm) Silver content (by weight) Comparative Example 1 168.05 1.99 Example 1 89.71 2.07

[0163] Referring to the above Figure 2 , Figure 3 As shown in Table 1, compared with Comparative Example 1, it can be confirmed that the surface roughness and weldability of the pattern were improved in Example 1.

[0164] Example 2

[0165] In this Example 2, a tin-silver electroplating solution was prepared using a variety of silver complexing agents.

[0166] In this Example 2, only the silver complexing agent in Example 1 was changed for preparation. In this case, as will be described later, only A1, R1, and R2 in Chemical Formula 1 were changed in the silver complexing agent.

[0167] The above A1, R1 and R2 are shown in Table 2 below.

[0168] Chemical Formula 1:

[0169]

[0170] Table 2

[0171] Entry <![CDATA[A1]]> <![CDATA[R1]]> <![CDATA[R2]]> Example 2a Methylene carboxyl carboxyl Example 2b Methylene Diethylamine Diethylamine

[0172] Example 3

[0173] In this Example 3, a tin-silver electroplating solution was prepared using a variety of tin carriers.

[0174] In this Example 3, only the tin support in Example 1 was changed for preparation. In this case, as will be described later, only A2, R3, and n1 to n4 in Chemical Formula 2 were changed in the tin support.

[0175] The above A2, R3, and n1 to n4 are shown in Table 3 below.

[0176] Chemical formula 2:

[0177]

[0178] Table 3

[0179] entry <![CDATA[A2]]> <![CDATA[R3]]> <![CDATA[n1]]> <![CDATA[n2]]> <![CDATA[n3]]> <![CDATA[n4]]> Example 3a Naphthol Sodium sulfonate 0 0 0 12 Example 3b Nonylphenol hydroxyl 0 0 0 15

[0180] Example 4

[0181] In this Example 4, a tin-silver electroplating solution was prepared using a variety of grain refiners.

[0182] In this Example 4, only the grain refiner in Example 1 was changed for preparation. In this case, as will be described later, only R4, R5, R6, R7 and X in Chemical Formula 3 were changed, and R4, R5, R6, R7 and X are shown in Table 4 below.

[0183] Chemical formula 3:

[0184]

[0185] Table 4

[0186]

[0187] Experiment Example 2

[0188] In this Experiment Example 2, experiments were conducted using various tin-silver plating solutions prepared in Examples 2 to 4 above for electroplating.

[0189] The specific experimental method of this Example 2 is the same as that used in Example 1 above, except that the tin-silver electroplating solution used is changed to that used in Examples 2 to 4 above.

[0190] The silicon wafers with the lower bump metal structure formed in Preparation Example 1 were immersed in the tin-silver plating solutions prepared in Examples 2 to 4, and tin-silver plating was performed by applying a current in the range of 1 ASD to 10 ASD.

[0191] Scanning electron microscope images of the solder products formed by performing a reflow soldering process on tin-silver solder bumps formed by the tin-silver electroplating solutions of Examples 2 to 4 are shown respectively. The surface roughness and silver content are shown in Table 5 below.

[0192] Table 5

[0193] picture Surface roughness (nm) Silver content (by weight) Example 2a Figure 4 86.21 1.99 Example 2b Figure 5 73.16 2.07 Example 3a Figure 6 65.22 2.23 Example 3b Figure 7 55.38 1.95 Example 4a Figure 8 78.59 2.11 Example 4b Figure 9 49.36 1.86 Example 4c Figure 10 68.18 2.03

[0194] The results of the above experiments show that by controlling various silver complexing agents, tin carriers and grain refiners, the surface roughness or solderability of the pattern becomes excellent.

[0195] Experimental Example 3

[0196] In Experiment 3, an experiment was conducted to confirm the effect of the weight ratio based on the above-mentioned weight ratio by changing the weight ratio of tin ions and silver ions in the above-mentioned tin-silver electroplating solution.

[0197] The silver content and solution state based on the specific weight ratio of tin ions and silver ions are shown in Table 6 below.

[0198] When the weight ratio is greater than 99.9:0.1, there are too few silver ions, and the amount that enters the electroplating film is negligible. Therefore, the silver content converges to 0. When the weight ratio is less than 75:25, the excessive silver ions react with tin ions and produce precipitates.

[0199] Table 6

[0200]

[0201] Experiment Example 4

[0202] In Experiment 4 of this experiment, an experiment was conducted to confirm the effect of changing the molar ratio of silver ions to silver complexing agent.

[0203] The molar ratio of silver ions to silver complexing agent was varied, and the silver content and solution state based on the above molar ratio are shown in Table 7 below.

[0204] When the weight ratio is less than 1:1, silver ions are not sufficiently complexed, resulting in precipitates.

[0205] Conversely, when the weight ratio is greater than 1:1, the silver ions are fully complexed, thus the solution is in a stable state and the silver content can be maintained uniformly.

[0206] Table 7

[0207]

[0208] The above description of the present invention is for illustrative purposes only. Those skilled in the art will understand that the present invention can be easily modified into other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above are illustrative in all respects and are not intended to limit the present invention. For example, the various structural elements described as a single type can also be implemented separately; similarly, multiple structural elements described separately can also be implemented in a combined form.

[0209] The scope of this invention is presented by the scope of protection described below, and all modifications or variations derived from the meaning, scope and equivalent concepts of the scope of protection are within the scope of this invention.

Claims

1. A tin-silver electroplating solution, characterized in that, It contains tin ion source, silver ion source and organic additives. The aforementioned organic additives include: a silver complexing agent represented by the following chemical formula 1; a tin carrier represented by the following chemical formula 2; and a grain refiner represented by the following chemical formula 3. Chemical Formula 1: In this case, A1 is methylene or ethylene. Chemical formula 2: R1 and R2 are one of the following groups: aldehyde, hydroxyl, carboxyl, mercapto, amino, thiol, nitrile, and pyridyl. In this case, A2 is phenyl, naphthyl, or nonylphenyl. R3 is one of hydrogen, hydroxyl, sulfonic acid group forming an ionic bond with an alkali metal cation, phosphonic acid group forming an ionic bond with an alkali metal cation, nitrate group forming an ionic bond with an alkali metal cation, and carboxylic acid group forming an ionic bond with an alkali metal cation. n1 to n4 are each independently an integer from 0 to 26, and the sum of n1 to n4 is 10 to 15. Chemical formula 3: In this case, R4 is a straight-chain alkyl group having 4 to 20 carbons or a straight-chain alkyl group containing a hydroxyl group and having 1 to 7 carbons. The aforementioned R5 is a straight-chain alkyl group having 4 to 20 carbons, including a hydroxyl group, and having 1 to 7 carbons. The aforementioned R6 is a straight-chain alkyl group having 2 to 20 carbons. The aforementioned R7 is a straight-chain alkyl group having 4 to 20 carbons. X is selected from the group of ions composed of chlorine, bromine, iodine and hydroxyl.

2. The tin-silver electroplating solution according to claim 1, characterized in that, The aforementioned tin ion source comprises at least one water-soluble tin compound selected from the group consisting of stannous sulfate, stannous hydrochloride, stannous aminosulfonate, stannous acetate, stannous phosphate, stannous methanesulfonate, stannous gluconate, and stannous carboxylate.

3. The tin-silver electroplating solution according to claim 1, characterized in that, The aforementioned silver ion source comprises at least one water-soluble silver compound selected from the group consisting of silver sulfate, silver hydrochloride, silver sulfamate, silver acetate, silver phosphate, silver methanesulfonate, silver gluconate, and silver carboxylate.

4. The tin-silver electroplating solution according to claim 1, characterized in that, In the above tin-silver electroplating solution, the weight ratio of tin ions to silver ions is 75:25 to 99.9:0.

1.

5. The tin-silver electroplating solution according to claim 1, characterized in that, The molar ratio of the silver ion source to the silver complexing agent is 1:1 to 1:

10.

6. The tin-silver electroplating solution according to claim 1, characterized in that, It also contains at least one of conductive salts, antioxidants, and leveling agents.

7. The tin-silver electroplating solution according to claim 6, characterized in that, The aforementioned conductive salt is one of hydroxycarboxylic acid or alkyl sulfonic acid.

8. The tin-silver electroplating solution according to claim 6, characterized in that, The antioxidants mentioned above are selected from at least one of the following groups: catechol, hydroquinone, resorcinol, cresol, phloroglucinol, hydroxyhydroquinone, and pyroglucinol.

9. The tin-silver electroplating solution according to claim 6, characterized in that, The leveling agent mentioned above is selected from at least one of the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, and synthetic polymers.

10. A method for forming tin-silver solder bumps, characterized in that, include: The lower bump metal structure is exposed in an electroplating bath containing a tin-silver plating solution, the tin-silver plating solution comprising a tin ion source, a silver ion source, and an organic additive, the organic additive comprising a silver complexing agent represented by chemical formula 1, a tin carrier represented by chemical formula 2, and a grain refiner represented by chemical formula 3; and A tin-silver alloy is electroplated onto the aforementioned lower bump metal structure by applying an electric current. Chemical Formula 1: In this case, A1 is methylene or ethylene. Chemical formula 2: R1 and R2 are one of the following groups: aldehyde, hydroxyl, carboxyl, mercapto, amino, thiol, nitrile, and pyridyl. In this case, A2 is phenyl, naphthyl, or nonylphenyl. R3 is one of hydrogen, hydroxyl, sulfonic acid group forming an ionic bond with an alkali metal cation, phosphonic acid group forming an ionic bond with an alkali metal cation, nitrate group forming an ionic bond with an alkali metal cation, and carboxylic acid group forming an ionic bond with an alkali metal cation. n1 to n4 are each independently an integer from 0 to 26, and the sum of n1 to n4 is 10 to 15. Chemical formula 3: In this case, R4 is a straight-chain alkyl group having 4 to 20 carbons or a straight-chain alkyl group containing a hydroxyl group and having 1 to 7 carbons. The aforementioned R5 is a straight-chain alkyl group having 4 to 20 carbons or a straight-chain alkyl group containing a hydroxyl group and having 1 to 7 carbons. The aforementioned R6 is a straight-chain alkyl group having 2 to 20 carbons. The aforementioned R7 is a straight-chain alkyl group having 4 to 20 carbons. X is selected from the group of ions composed of chlorine, bromine, iodine and hydroxyl.

11. The method for forming tin-silver solder bumps according to claim 10, characterized in that, In the electroplating step of the above-mentioned tin-silver alloy, the applied current has a current density of 1 ASD to 10 ASD.

12. A tin-silver solder bump, characterized in that, Formed by the method of claim 10.

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