A plating method for wafer-level copper pillars

Abstract

The present invention belongs to the field of semiconductors, and specifically discloses a method for electroplating wafer-level copper pillars. During the process of electroplating copper pillars in the present invention, polyvinylpyrrolidone and alkylbenzene sulfonate in the electroplating solution cooperate with each other, which can significantly reduce the number of defects such as holes and cracks in the copper pillars, improve the adhesion of the copper pillars, and improve the mechanical properties of the copper pillars.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductors, and particularly relates to a method for electroplating wafer-level copper pillars. Background Art

[0002] The copper pillar bump interconnection technology is one of the key technologies for advanced packaging flip chips and has received extensive attention. The preparation process of copper pillar bumps mainly includes spin-coating photoresist (such as polyimide) on a wafer silicon wafer and patterning the photoresist by etching, sputtering a seed layer (including an adhesion layer of Ti or TiW and a Cu electroplating seed layer, UBM) on the adhesion layer, coating photoresist (PR) and lithographing the pattern to be electroplated, electroplating the copper pillar bumps, electroplating solder, removing PR and UBM, and solder reflow. If it is applied to the chip packaging process of copper-copper bonding, after electroplating the copper pillars, the electroplating of solder is omitted, and the PR and UBM are directly removed and then the thermocompression bonding process is carried out. In the copper pillar bump interconnection process, electroplating copper pillars is one of the most challenging steps. For the reliability of subsequent interconnections, the copper pillars generally require a certain mechanical strength to avoid short circuits caused by defects such as the shedding, fracture, and deformation of the copper pillars. However, due to the complexity of the electrochemical reaction and microscopic reaction in the electroplating system during the preparation of electroplated copper pillars, there are often defects such as holes, cracks, and grain coarsening in the deposited copper coating, resulting in poor mechanical properties of the obtained copper pillars and affecting the reliability of the copper pillar bumps.

[0003] Therefore, there is still a need to continue developing a technology to improve the mechanical properties of copper pillars. Summary of the Invention

[0004] Aiming at the problem of poor mechanical properties of electroplated copper pillars involved in the above-mentioned prior art, the present invention will provide a method for electroplating wafer-level copper pillars.

[0005] To achieve the above object, the specific technical solutions include the following:

[0006] A method for electroplating wafer-level copper pillars includes the following steps:

[0007] (1) Providing a chip wafer metal pad to be electroplated;

[0008] (2) Sequentially passing the chip wafer metal pad to be electroplated through air plasma cleaning and acid dipping;

[0009] (3) Electroplating the chip wafer metal pad to be electroplated after acid dipping in step (2) in an electroplating solution, and then through cleaning and degumming to obtain the copper pillar;

[0010] The electroplating solution includes the following components: copper sulfate 100 - 300 g / L, sulfuric acid 40 - 100 g / L, Cl -30 - 60 mg / L, accelerator 25 - 60 mg / L, polyethylene glycol 10 - 80 mg / L, polyvinylpyrrolidone 10 - 70 mg / L, alkylbenzene sulfonate 10 - 50 mg / L, with the balance being water.

[0011] During the electroplating of copper pillars in the present invention, polyvinylpyrrolidone and alkylbenzene sulfonate in the electroplating solution synergistically act with each other, which can significantly reduce the number of defects such as holes and cracks in the copper pillars, improve the adhesion of the copper pillars, and enhance the mechanical properties of the copper pillars.

[0012] Preferably, the mass ratio of polyvinylpyrrolidone to alkylbenzene sulfonate is (0.5 - 6):1.

[0013] More preferably, the mass ratio of polyvinylpyrrolidone to alkylbenzene sulfonate is (1 - 3):1.

[0014] Polyvinylpyrrolidone is a type of N-vinylamide polymer, which has the functions of adsorption, complexation or polarization. The sulfonic group in alkylbenzene sulfonate has a complexation effect, and the alkylbenzene sulfonate anion with strong adsorption can act as a surfactant. In the electroplating solution system of the present invention, polyvinylpyrrolidone and alkylbenzene sulfonate may have a regulatory effect on copper deposition, jointly regulating copper deposition with inhibitors and accelerators in the electroplating solution, reducing copper grain defects and internal stress, making the grains in the copper pillars fine, with fewer defects such as holes and cracks, thereby improving the mechanical properties of the copper pillars. The mass ratio of polyvinylpyrrolidone to alkylbenzene sulfonate affects the mechanical properties of the finally electroplated copper pillars. Below the above mass ratio range, the mechanical properties of the copper pillars are better and the defects are fewer.

[0015] Preferably, the alkylbenzene sulfonate includes at least one of undecylbenzene sulfonate, dodecylbenzene sulfonate, tridecylbenzene sulfonate, tetradecylbenzene sulfonate, pentadecylbenzene sulfonate, hexadecylbenzene sulfonate, heptadecylbenzene sulfonate, octadecylbenzene sulfonate, nonadecylbenzene sulfonate. The number of carbon atoms in the alkyl group of alkylbenzene sulfonate is different, and the molecular structure is different. Preferably, the number of carbon atoms in the alkyl group of alkylbenzene sulfonate ≥ 12, and more preferably, the number of carbon atoms in the alkyl group of alkylbenzene sulfonate is 12 - 18.

[0016] Preferably, the number-average molecular weight of polyvinylpyrrolidone is 3500 - 40000, and more preferably, 10000 - 24000.

[0017] Preferably, the polyethylene glycol includes at least one of PEG-200, PEG-400, PEG-600, PEG-800, PEG-1000, PEG-2000, PEG-3000, PEG-4000, PEG-6000, PEG-8000, PEG-10000, and PEG-20000.

[0018] As an inhibitor of the electroplating solution, polyethylene glycol is easily adsorbed on the copper surface during electroplating, has a polarization effect on the copper deposition potential, can inhibit the deposition of copper, and also has a wetting effect, improving the electroplating quality and mechanical properties of copper pillars.

[0019] Preferably, the accelerator includes at least one of 3-mercapto-1-propanesulfonate, polydisulfide dipropanesulfonate, 3-mercapto-ethylsulfonate, and 3-mercapto-1-ethanesulfonic acid potassium salt.

[0020] The accelerator can accelerate the deposition rate of copper ions in the micropores, reduce the missing plating and defects in the micropore plating; compete for adsorption with the inhibitor and other substances to improve the electroplating quality of copper pillars.

[0021] Preferably, the metal pad of the chip wafer to be electroplated sequentially includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, and a photoresist from bottom to top; the metallization layer includes an adhesion layer and a copper seed layer, and the thickness of the copper seed layer is 100-500 nm; there are micropores on the photoresist, the micropores are located at the metallization layer, the diameter of the micropores is 50-150 μm, the pore spacing between the micropores is 80-200 μm, and the thickness of the photoresist is 10-150 μm.

[0022] Preferably, the current density of the electroplating is 3-40 A / dm 2 , and the electroplating time is 10-60 min.

[0023] More preferably, the current density of the electroplating is 5-20 A / dm 2 .

[0024] Preferably, the acid used in the acid pickling is a sulfuric acid aqueous solution with a concentration of 20-80 g / L.

[0025] Preferably, the solvents used in the photoresist removal are tetramethylammonium hydroxide (TMAH) and dimethyl sulfoxide (DMSO).

[0026] A wafer sequentially includes a wafer substrate, a metal pad, an insulating layer, and a metallization layer, and copper pillars prepared by the above-described wafer-level copper pillar electroplating method on the metallization layer.

[0027] Compared with the prior art, the present invention has the following beneficial effects: During the electroplating of copper pillars, polyvinylpyrrolidone and alkylbenzenesulfonate in the electroplating solution cooperate with each other, which can significantly reduce the number of defects such as holes and cracks in the copper pillars, improve the adhesion of the copper pillars, and improve the mechanical properties of the copper pillars. Detailed implementation manners

[0028] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0029] Example 1

[0030] A method for electroplating copper pillars includes the following steps:

[0031] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd.). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0032] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores thereon is 80 μm, and the pitch between the micropores is 150 μm;

[0033] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peeled off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0034] (2) Clean the chip wafer metal pad with air plasma for 20 s, then acid-immerse it in a 50 g / L sulfuric acid solution, and remove the bubbles by shaking, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0035] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0036] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate 20 mg / L, solvent water;

[0037] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0038] Example 2

[0039] The difference between this example and Example 1 is that the polyvinylpyrrolidone in this example is PVP-3500, and the specific steps are as follows:

[0040] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf of others). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0041] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0042] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0043] (2) Use air plasma to clean the chip wafer metal pad for 200 min, then perform acid pickling with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0044] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0045] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, PVP-3500 (average molecular weight of 3500, purchased from Gongbik New Materials Technology (Shanghai) Co., Ltd.) 50 mg / L, sodium dodecylbenzenesulfonate 20 mg / L, solvent water;

[0046] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0047] Example 3

[0048] The difference between this example and Example 1 is that the polyvinylpyrrolidone in this example is PVP-10100, and the specific steps are as follows:

[0049] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0050] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores thereon is 80 μm, and the pitch between the micropores is 150 μm;

[0051] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0052] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid pickling with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0053] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 )), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0054] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, PVP-10100 (average molecular weight of 10,100, purchased from Gongbik New Materials Technology (Shanghai) Co., Ltd.) 50 mg / L, sodium dodecylbenzenesulfonate 20 mg / L, solvent water;

[0055] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio of 1:1) to remove the photoresist to expose the deposited copper pillars.

[0056] Example 4

[0057] The difference between this example and Example 1 is that the polyvinylpyrrolidone in this example is PVP-37900, and the specific steps are as follows:

[0058] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0059] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pore spacing between the micropores is 150 μm;

[0060] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peeled off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0061] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0062] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 10 ASD (1 ASD = A / dm 2 )), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0063] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, PVP-37900 (average molecular weight of 37900, purchased from Gongbik New Materials Technology (Shanghai) Co., Ltd.) 50 mg / L, sodium dodecylbenzenesulfonate 20 mg / L, solvent water;

[0064] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0065] Example 5

[0066] The difference between this example and Example 1 is that the alkylbenzenesulfonate in this example is sodium undecylbenzenesulfonate, and the specific steps are as follows:

[0067] (1) Provide a chip wafer metal pad (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf) for electroplating copper pillars. The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0068] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0069] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peeled off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0070] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0071] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0072] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate (purchased from Seebio Technology Co., Ltd. (Shanghai)) 20 mg / L, solvent water;

[0073] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0074] Example 6

[0075] The difference between this example and Example 1 is that the alkylbenzenesulfonate in this example is sodium octadecylbenzenesulfonate, and the specific steps are as follows:

[0076] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0077] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0078] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0079] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0080] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0081] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight of 24000, purchased from Aladdin) 50 mg / L, sodium octadecylbenzenesulfonate (purchased from Hubei Wande Chemical Co., Ltd.) 20 mg / L, solvent water;

[0082] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0083] Example 7

[0084] The difference between this example and Example 1 is that in this example, the mass ratio of PVP to alkylbenzenesulfonate is 0.5, and the specific steps are as follows:

[0085] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top, so as to expose the metallization layer to facilitate the subsequent realization of electroplating copper pillars;

[0086] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0087] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easy to peel off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0088] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid pickling with a 50 g / L sulfuric acid solution, and use a swinging method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0089] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0090] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 23.3 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 46.7 mg / L, solvent water;

[0091] (4)After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0092] Example 8

[0093] The difference between this example and Example 1 is that in this example, the mass ratio of PVP to alkylbenzenesulfonate is 1, and the specific steps are as follows:

[0094] (1)Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0095] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0096] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0097] (2)Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0098] (3)Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0099] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight of 24000, purchased from Aladdin) 35 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 35 mg / L, solvent water;

[0100] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0101] Example 9

[0102] The difference between this example and Example 1 is that in this example, the mass ratio of PVP to alkylbenzenesulfonate is 3, and the specific steps are as follows:

[0103] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0104] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0105] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0106] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0107] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 10 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0108] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 52.5 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 17.5 mg / L, solvent water;

[0109] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0110] Example 10

[0111] The difference between this example and Example 1 is that in this example, the mass ratio of PVP to alkylbenzenesulfonate is 6, and the specific steps are as follows:

[0112] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence, to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0113] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0114] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peeled off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0115] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid pickling with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0116] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 10 ASD (1 ASD = A / dm 2 )), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0117] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 60 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 10 mg / L, solvent water;

[0118] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0119] Example 11

[0120] The difference between this example and Example 1 is that the current density in this example is 3 A / dm 2 , and the specific steps are as follows:

[0121] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top, so as to expose the metallization layer to facilitate the subsequent realization of electroplating copper pillars;

[0122] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0123] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0124] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid pickling with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0125] (3) Place it in a copper pillar electroplating solution for electroplating. The electroplating current density is 3 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0126] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight of 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yongli New Materials Technology Co., Ltd.) 20 mg / L, solvent water;

[0127] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0128] Example 12

[0129] The difference between this example and Example 1 is that the current density in this example is 5 A / dm 2 , and the specific steps are as follows:

[0130] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes, from bottom to top in sequence, a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist to expose the metallization layer, facilitating the subsequent realization of electroplating copper pillars;

[0131] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0132] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100 nm Ti barrier layer and a 300 nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0133] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0134] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 5 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0135] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Materials Technology Co., Ltd.) 20 mg / L, solvent water;

[0136] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0137] Example 13

[0138] The difference between this example and Example 1 is that the current density in this example is 20 A / dm 2 , and the specific steps are as follows:

[0139] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence. The micropores expose the metallization layer to facilitate subsequent electroplating;

[0140] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0141] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peeled off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0142] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid pickling in a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0143] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 20 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0144] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight of 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 20 mg / L, solvent water;

[0145] (4) After electroplating, perform water washing, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0146] Example 14

[0147] The difference between this example and Example 1 is that the current density in this example is 40 A / dm 2 , and the specific steps are as follows:

[0148] (1) Provide a chip wafer metal pad for electroplating copper pillars (commercially available, manufactured by Guangdong Fozhixin Microelectronics Technology Research Co., Ltd. on behalf). The chip wafer metal pad includes a wafer substrate, a metal pad, an insulating layer, a metallization layer, a photoresist, and micropores on the photoresist from bottom to top in sequence. The micropores expose the metallization layer to facilitate subsequent electroplating;

[0149] Among them, the thickness of the photoresist is 50 μm, the diameter of the micropores on it is 80 μm, and the pitch between the micropores is 150 μm;

[0150] The metallization layer includes an adhesion layer and a Cu seed layer sputtered on the surface of the adhesion layer; among them, the adhesion layer can enhance the adhesion between metals, making the upper and lower layers adhere firmly and not easily peel off. The Cu seed layer is composed of a 100-nm Ti barrier layer and a 300-nm copper seed layer sputtered by PVD technology, enabling the subsequent copper electroplating process to be realized;

[0151] (2) Use air plasma to clean the chip wafer metal pad for 20 s, then perform acid leaching with a 50 g / L sulfuric acid solution, and use a rocking method to remove bubbles, which can remove impurities and bubbles at the bottom of the micropores and increase the wettability of subsequent electroplating;

[0152] (3) Place it in a copper pillar electroplating solution for electroplating. The current density of electroplating is 40 ASD (1 ASD = A / dm 2 ), the electroplating time is 40 min, the electroplating temperature is 30 °C, and the stirring rate during electroplating is 30 rpm;

[0153] The components of the electroplating solution are: copper sulfate pentahydrate 200 g / L, sulfuric acid 80 g / L, Cl -40 mg / L, 3-mercapto-1-propanesulfonic acid (sodium) salt (MPS) 30 mg / L, polyethylene glycol 1000 (PEG-1000) 40 mg / L, polyvinylpyrrolidone (PVP-24000, average molecular weight 24000, purchased from Aladdin) 50 mg / L, sodium dodecylbenzenesulfonate (purchased from Shandong Yonglida New Material Technology Co., Ltd.) 20 mg / L, solvent water;

[0154] After electroplating, wash with water, and then use a mixed solution of TMAH and DMSO (mass ratio 1:1) to remove the photoresist to expose the deposited copper pillars.

[0155] Comparative Example 1

[0156] The difference between this comparative example and Example 1 is that there is no PVP-24000 in the electroplating solution of this comparative example.

[0157] Comparative Example 2

[0158] The difference between this comparative example and Example 1 is that there is no sodium dodecylbenzenesulfonate in the electroplating solution of this comparative example.

[0159] Comparative Example 3

[0160] The difference between this comparative example and Example 1 is that there is no PVP-24000 and sodium dodecylbenzenesulfonate in the electroplating solution of this comparative example.

[0161] Comparative Example 4

[0162] The difference between this comparative example and Example 1 is that the sodium dodecylbenzenesulfonate in the electroplating solution of this comparative example is replaced with sodium dodecylbenzenesulfonate of the same mass concentration.

[0163] Comparative Example 5

[0164] The difference between this comparative example and Example 1 is that the concentration of PVP-24000 in the electroplating solution of this comparative example is 5 mg / L.

[0165] Comparative Example 6

[0166] The difference between this comparative example and Example 1 is that the concentration of PVP-24000 in the electroplating solution of this comparative example is 80 mg / L.

[0167] Comparative Example 7

[0168] The difference between this comparative example and Example 1 is that the concentration of sodium dodecylbenzenesulfonate in the electroplating solution of this comparative example is 5 mg / L.

[0169] Comparative Example 8

[0170] The difference between this comparative example and Example 1 is that the concentration of sodium dodecylbenzenesulfonate in the electroplating solution of this comparative example is 60 mg / L.

[0171] Use AOI (Automated Optical Inspection), assisted with a scanning electron microscope, to detect the obtained copper pillars. The detection index is the detection of defects such as holes and gaps in the cross-section of the copper pillars. Calculate the proportion of copper pillars without defects among 100 copper pillars to investigate the defect-free situation of the electroplated copper pillars, that is, the qualification rate (in percentage: %).

[0172] Conduct mechanical property tests on the above-prepared copper pillars. The test equipment is a bonding strength tester (PTR-1102). During the shear experiment, fix the electroplated chip on the testing machine. Since the tool head is large, during the test, shear tests are performed on 4 copper pillars in a row on the chip. The distance between the shear tool head and the sample seed layer is 2 μm, and the shear speed is 6 mm / min. After multiple measurements and taking the average, 1 / 4 of this average value is the mechanical property of a single copper pillar.

[0173] Table 1

[0174]

[0175] As can be seen from the above embodiments, the method for electroplating and preparing copper pillars of the present invention can prepare copper pillars with good mechanical properties and fewer defects, which can improve the reliability of subsequent copper pillar interconnection. Among them, the shear force of the copper pillars ≥ 150 MPa, and the probability of copper pillars without defects on the wafer is greater than 85%.

[0176] As can be seen from Example 1 and Comparative Examples 1-8, polyvinylpyrrolidone and alkylbenzene sulfonate in the electroplating solution of the present invention have the effect of synergistically improving the shear force of the obtained copper pillars and reducing the number of defects of the copper pillars, and the dosages of polyvinylpyrrolidone and alkylbenzene sulfonate also have a significant impact on the electroplating quality of the copper pillars. Therefore, when the concentration of polyvinylpyrrolidone is 10-70 mg / L and the concentration of alkylbenzene sulfonate is 10-50 mg / L in the electroplating process of the present invention, the obtained copper pillars meet the requirements.

[0177] As can be seen from Examples 1-4, the molecular weight of polyvinylpyrrolidone has a certain impact on the shear force and the number of defects of copper pillars. It is preferred that the number-average molecular weight of the polyvinylpyrrolidone is 3500-40000, and more preferably 10000-24000.

[0178] As can be seen from Examples 1, 5-6, the number of carbon atoms on the alkyl group of alkylbenzene sulfonate has a certain impact on the shear force and the number of defects of copper pillars. It is preferred that the number of carbon atoms on the alkyl group of alkylbenzene sulfonate is 11-19, and more preferably 12-18.

[0179] As can be seen from Examples 1, 7 - 10, the mass ratio of polyvinylpyrrolidone to alkylbenzenesulfonate affects the shear force and defects of the copper pillar. When the mass ratio of polyvinylpyrrolidone to alkylbenzenesulfonate is (0.5 - 6):1, and further preferably (1 - 3):1, the copper pillar of the present invention has good shear force and fewer defects.

[0180] As can be seen from Examples 1, 11 - 14, the current density in the electroplating process affects the copper deposition rate. In combination with the specific electroplating solution of the present invention, the electroplating system of the present invention is suitable for a relatively wide range of current densities. The appropriate current density and the specific electroplating solution cooperate with each other, and electroplating can be carried out at a current density of 3 - 40 A / dm 2 Moreover, the mechanical properties of the copper pillar are relatively good and the defects of the copper pillar are fewer.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A plating method for wafer-level copper pillars, characterized in that, It includes the following steps: (1) Provide the metal pads of the chip wafer to be electroplated; (2) Sequentially pass the metal pads of the chip wafer to be electroplated through air plasma cleaning and acid pickling; (3) Electroplate the metal pads of the chip wafer to be electroplated after acid pickling in step (2) in an electroplating solution, and then through cleaning and degumming to obtain the copper pillars; The electroplating solution consists of the following components Composition: copper sulfate 100 - 300 g / L, sulfuric acid 40 - 100 g / L, Cl - 30 - 60 mg / L, accelerator 25 - 60 mg / L, polyethylene glycol 10 - 80 mg / L, polyvinylpyrrolidone 10 - 70 mg / L, dodecylbenzenesulfonate 10 - 50 mg / L, the balance being water; The mass ratio of the polyvinylpyrrolidone to the dodecylbenzenesulfonate is (1 - 3):1; The number-average molecular weight of the polyvinylpyrrolidone is 10100 - 40000.

2. The electroplating method of the wafer-level copper pillar according to claim 1, characterized in that, The polyethylene glycol includes at least one of PEG-2000, PEG-3000, PEG-4000, PEG-6000, PEG-8000, PEG-10000, and PEG-20000.

3. The electroplating method of the wafer-level copper pillar according to claim 1, wherein The accelerator includes at least one of 3-mercapto-1-propanesulfonate, polydithiodipropanesulfonate, 3-mercapto-ethylsulfonate, and 3-mercapto-1-ethanesulfonate potassium salt.

4. The electroplating method of the wafer-level copper pillar according to claim 1, characterized in that, The current density of the electroplating is 3 - 40 A / dm 2 , and the time of the electroplating is 10 - 60 min.

5. The electroplating method of the wafer-level copper pillar according to claim 1, wherein The acid used in the acid pickling is a 20 - 80 g / L sulfuric acid aqueous solution, and the solvents used in the degumming are tetramethylammonium hydroxide and dimethyl sulfoxide.

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