Electro-coppering solution applied to wafer-level packaging and electroplating process thereof
Technical Field
The invention relates to the technical field of surface treatment, in particular to an electroplating copper solution applied to wafer-level packaging and an electroplating process thereof.
Background
Traditionally, electrical connections between IC chips and the outside have been made by wire bonding I/O on the chip to a package carrier to form a leaded package. However, with I/O pitches shrinking below 70 μm, wire bonding techniques have not met the era. Wafer Level Packaging (WLP) technology is developed due to its advantages of small size, low cost, etc., and is currently used in many fields such as mobile phones, GPS, bluetooth devices, etc., and the production range is very wide.
In flip-chip interconnect, an Under Bump Metallization (UBM) is a critical interface layer between the metal pads and the gold bumps on the IC. UBM requires sufficiently good adhesion to the metal pads and the wafer passivation layer, which is typically achieved by depositing multiple layers of metal across the wafer surface. The most common metal deposition in wafer fabrication is typically accomplished by electroplating processes, since electroplating processes can achieve very narrow bump pitches and maintain high yields, and can achieve electroplating on a different size, pitch, and geometry basis. The electroplating technology is most widely applied due to the advantages of low cost, mature technology and the like. However, the current wafer level package electro-coppering technology still faces many important problems, such as the generation of voids due to scorching under high current density, non-uniform high and low current density of the plating layer, wall growth of blind holes, etc., and the like.
As a wafer level packaging technique in the modern technology, the copper electroplating solution can be cited in patent CN103290438B, wherein the wafer level packaging electroplating solution and the electroplating process described therein comprise copper salt 120-300 g/L; acid 10-200 g/L; 30-80mg/L of chloride ions; 0.001-0.3g/L of sulfide; polyoxyether compounds 0.5-10 g/L; 0.05-5g/L of polyethylene glycol; 0.001-0.2g/L of quaternary ammonium salt; the temperature is 10-50 ℃, the current density is 0.2-20A/dm2, the formula inhibits the growth of copper in a high current density area to a certain extent, and the uniformity of a plating layer is improved to a certain extent, but the phenomenon of void caused by equal wall growth exists in blind hole electroplating.
Patent CN110541179B, Yaojihao, etc. discloses a wafer level packaging super TSV copper interconnection material electroplating solution formula, copper sulfate pentahydrate 100-; concentrated sulfuric acid 40-80 g/L; 30-50mg/L of chloride ions; 1-5mg/L of 3-sulfur-isothiourea propanesulfonic acid inner salt; nonylphenol polyoxyethylene ether; 50-100 mg/L; the phenazine dye is 40-80mg/L, and the nonylphenol polyoxyethylene ether is an organic surfactant, so that a large amount of foam is easily generated, and the actual production is not facilitated.
Patent CNl111074306B, Sunyu et al, discloses a copper column electroplating solution with super-high current density and an electroplating process, wherein the formula is 150-; 40-70g/L of methanesulfonic acid; 30-50mg/L of chloride ions; 40-80mg/L of Tuolu green; sodium polydithio-dipropane sulfonate: 2-5 mg/L; 40-100mg/L of polyethylene glycol. The copper methylsulfonate is used as the copper salt in the formula, so that the cost is high, and the production and the use are greatly limited.
Disclosure of Invention
Aiming at the defects in the technology, the invention provides the electrolytic copper plating solution applied to wafer level packaging and the electroplating process thereof, and the solution has the effect of filling without holes and gaps; and the electroplating uniformity effect is good, and the arch rate is low.
In order to achieve the purpose, the invention provides an electrolytic copper plating solution applied to wafer level packaging, which comprises the following components in percentage by mass:
the reaction antifouling agent is a compound of ethylene glycol tertiary butyl ether and phosphate ester, and the mass concentration ratio of the ethylene glycol tertiary butyl ether to the phosphate ester is 1:1 when the reaction antifouling agent is used;
the carrier is a compound of chloride ions and alum ions, and the mass concentration ratio is 1: (1-5), mixing, wherein the concentration of chloride ions is controlled to be 60-80ppm/L and the concentration of alum ions is controlled to be 60-400ppm/L when in use;
the components are uniformly mixed according to the proportion, the balance is water, and the operation temperature is 15-40 ℃ to form the copper electroplating solution.
Wherein the brightener is a compound consisting of organic propane betaine with the mass concentration of 30-45ppm/L, sodium cumene sulfonate with the mass concentration of 15-20ppm/L and hydroxylamine sulfate with the mass concentration of 15-25 ppm/L.
Wherein the mass concentration ratio of the antioxidant to the inhibitor in use is 3: 1, the antioxidant and the inhibitor form a compound with a conjugated transmission bridge function when in use, and the rapid deposition of pit parts is accelerated.
Wherein the mass concentration ratio of the antioxidant to the reactive antifouling agent in use is 1:1, the antioxidant is matched with the reaction antifouling agent, so that not only can an oil pollution source be prevented, but also the corrosion of chemical trace ions can be prevented.
Wherein the antioxidant is 1,2, 4-triazole.
Wherein the leveling agent is a nitrogen-containing aromatic compound methotrexate.
Wherein the inhibitor is aryl polyoxyethylene ether sulfate, the copper salt is copper sulfate pentahydrate, the chloride ions are provided by hydrochloric acid, and the alum ions are provided by alum sulfate.
In order to achieve the above object, the present invention further provides an electro-coppering process of the electro-coppering solution applied to wafer-level packaging, comprising the following steps:
step 1, performing vacuum treatment on a plating piece by using a pretreatment solution before electroplating, and removing air in a hole by using DI pure water under vacuum negative pressure;
step 2, stirring and circularly swinging the vacuumized plated part in an electroplating solution to accelerate proton transmission and ensure that copper ions and additives enter the holes;
step 3, adjusting the current density to 25ASD, electroplating according to the height adjustment time required by the electroplated copper column, and simultaneously adjusting the flow by using a variable frequency regulator; the flow rate of the plating solution introduced into the bath solution is changed through the variable frequency regulator, and the balance force applied to the interior of the plating solution is broken.
Wherein the specific time of the copper plating pretreatment in the step 1 is 4-8 min.
Wherein, the specific conditions of the copper plating treatment in the step 2 are as follows: the temperature of the plating solution is 15-40 ℃, the stirring speed is between 100 and 200r/min, and the current density is between 0.5 and 45 ASD; and 3, adjusting the flow rate of copper plating to 10-30L/min by using a variable frequency regulator.
The invention has the beneficial effects that: compared with the prior art, the electro-coppering solution applied to wafer level packaging and the electro-coppering process thereof provided by the invention have the following advantages:
1) the carrier is added into the copper electroplating solution, and the alum ions and the chloride ions of the carrier are matched according to the proportion of 1: (1-5) mixing in a ratio range to allow deposition of copperThe effect is better, and the effect is better,the reduction rate is accelerated, and the continuous nucleation rate is improved, so that the compactness of the whole copper layer is greatly improved.
2) The electro-coppering solution is added with a mixture of ethylene glycol tertiary butyl ether and phosphate ester as a reaction antifouling agent, and the mass concentration ratio of the ethylene glycol tertiary butyl ether to the phosphate ester is 1: 1. In the production process, the material numbers enter the cylinder and exit the plate cylinder, and are different, so that impurities are easily polluted, the phenomenon of uneven electroplating effect and the like is caused, and the microscopic observation is difficult because the wafer-level size is too small. Therefore, a reactive stain-proofing agent is added to the copper plating solution to maintain the surface cleanliness of the plated article during the plating process.
3) The copper electroplating solution is added with an antioxidant, and the mass concentration ratio of the antioxidant to the reaction antifouling agent is 1: the purpose of the antioxidant is to prevent oxidation of copper and protect the copper, while some substances contained in impurities, such as introduced trace iron, tin and other compounds, may corrode and oxidize the copper surface, resulting in the unevenness of the copper layer. The antioxidant is matched with the reaction antifouling agent, so that not only can an oil pollution source be prevented, but also the corrosion of chemical trace ions can be prevented, and the optimal effect can be achieved by the proportion.
4) The electrolytic copper plating solution is added with an inhibitor, and the mass concentration ratio of the antioxidant to the inhibitor is 3: 1, the purpose of the inhibitor is to inhibit the salient points on the surface of the substrate and accelerate the rapid deposition of the concave points, but the common single inhibitor has larger molecular compound and is difficult to be adsorbed to the salient points firstly, so that a compound with the function of conjugate transmission bridges is needed as connection, and the selected antioxidant has the effect and has the optimal effect according to the proportion;
5) in the copper electroplating process, a variable frequency regulator is adopted to regulate the flow, although operations such as stirring, circular swinging and the like are carried out in advance in the step 2, the proton transmission of the solution in the electroplating process still cannot ensure that subsequent copper ions and additives continuously enter holes, and meanwhile, bubbles generated in the electroplating process easily form concave holes on a plating layer.
6) The coating obtained by the invention not only achieves the effect of filling the wafer packaging micropores without holes and gaps; and the electroplating uniformity effect is good, and the arch rate is low.
Drawings
FIG. 1 is an external view of an electrolytic copper plating product obtained by the present invention;
FIG. 2 is a top view of a wafer obtained by the method of example 1;
FIG. 3 is a drawing of a wafer plating slice obtained in example 1 of the present invention;
FIG. 4 is a top view of a wafer obtained by the electroplating method of example 2 of the present invention;
FIG. 5 is a drawing of a wafer plating slice obtained in example 2 of the present invention;
FIG. 6 is a top view of a wafer obtained by the method of example 3;
FIG. 7 is a drawing of a wafer plating slice obtained in example 3 of the present invention;
FIG. 8 is a top view of the wafer plating from the comparative example;
fig. 9 is a drawing of a wafer plating slice obtained in the comparative example.
Detailed Description
In order to make the invention more clear, the invention is further described below with reference to the text and the accompanying drawings.
The invention provides an electro-coppering solution applied to wafer-level packaging and an electro-coppering process thereof, which comprises the following components in mass concentration:
the reaction antifouling agent is a compound of ethylene glycol tertiary butyl ether and phosphate ester, and the mass concentration ratio of the ethylene glycol tertiary butyl ether to the phosphate ester is 1: 1;
the carrier is a compound of chloride ions and alum ions, and the mass concentration ratio is 1: (1-5) mixing, wherein the concentration of chloride ions is controlled to be 60-80ppm/L, and the concentration of alum ions is controlled to be 60-400 ppm/L;
the components are uniformly mixed according to the proportion, the balance is water, and the operation temperature is 15-40 ℃ to form the copper electroplating solution.
In this example, the brightener is a complex composed of organic propane betaine with a mass concentration of 30-45ppm/L, sodium cumene sulfonate with a mass concentration of 15-20ppm/L and hydroxylamine sulfate with a mass concentration of 15-25 ppm/L. The organic propane betaine is positively charged, under the action of current, the adsorption of the organic propane betaine is caused in the double electric layer electron exchange process, and the hydroxylamine sulfate can improve the electron transfer and promote the electrolytic reduction of the brightener, so that the ordered deposition of metal is accelerated. Sodium cumene sulfonate can reduce surface tension, resulting in accelerated and reabsorption of organic betaines. Because the difference of height on substrate surface leads to unsmooth inconsistency, organic propane betaine's absorption is many and the low point is few at the high point to lead to the metal deposition rate low at the high point, and the phenomenon that the low point is high, thereby make the plane level, brightener can take place the loss in the current condition effect, after organic propane betaine desorption, sodium cumene sulfonate adsorbs once more, thereby it attracts organic propane betaine effect to reduce surface tension, so circulation, can greatly improve the microscopic effect, reach the effect that single brightener can not reach. The mass concentration of the brightener during use is not lower than 60mg/L, otherwise, the possibility of heavy-current scorching can be caused, and meanwhile, the mass concentration of the antifouling agent is not higher than 2 times of the mass concentration of the brightener, otherwise, the effect of the brightener can be shielded due to too high mass concentration. Therefore, the mass concentration range of the brightener in use is set to be 60-90mg/L, and the mass concentration range of the antifouling agent matched with the brightener is set to be 60-120 ppm/L.
In this embodiment, the mass concentration ratio of the antioxidant to the inhibitor when in use is 3: 1. the purpose of the inhibitor is to inhibit the salient points on the surface of the substrate and accelerate the rapid deposition of the concave points, but the common single inhibitor has larger molecular compound and is difficult to be adsorbed to the salient points firstly, so that a compound with the function of conjugate transmission bridges is needed as connection, and the selected antioxidant has the effect, and the effect is optimal according to the proportion.
In this embodiment, the mass concentration ratio of the antioxidant to the reactive antifouling agent when used is 1: 1. the antioxidant is mainly 1,2, 4-triazole, and the antioxidant is matched with the antifouling agent, so that not only can an oil pollution source be prevented, but also the corrosion of chemical trace ions can be prevented, and the optimal effect can be achieved by the proportion.
In this embodiment, the leveling agent is a nitrogen-containing aromatic compound methotrexate, and the mass concentration is 10-30ppm/L when in use. The leveling agent has the functions of deep plating of the through holes and filling plating of the blind holes. The inhibitor is aryl polyoxyethylene ether sulfate.
In order to achieve the above object, the present invention further provides a process for electroplating copper for wafer level packaging, comprising the following steps:
step 1, performing vacuum treatment on a plating piece by using a pretreatment solution before electroplating, and removing air in a hole by using DI pure water under vacuum negative pressure;
step 2, stirring and circularly swinging the vacuumized plated part in an electroplating solution to accelerate proton transmission and ensure that copper ions and additives enter the holes;
and 3, adjusting the current density to 25ASD, electroplating according to the height adjustment time required by the electroplated copper column, and adjusting the flow by using a variable frequency regulator. Although operations such as stirring, circular swinging and the like are carried out in advance in the step 2, the proton transmission of the solution is still difficult to ensure that subsequent copper ions and additives continuously enter the holes in the electroplating process, and meanwhile, bubbles generated in the electroplating process easily form concave holes on the coating.
In this embodiment, the specific time of the copper plating pretreatment in step 1 is 4-8 min. The temperature of the plating solution in the step 2 is 15-40 ℃, the stirring speed is between 100 and 200r/min, and the current density is between 0.5 and 45 ASD. And the flow rate of the copper plating in the step 3 is adjusted to 10-30L/min.
The invention has the beneficial effects that: compared with the prior art, the electro-coppering solution applied to wafer level packaging and the electro-coppering process thereof provided by the invention have the following advantages:
1) the reaction carrying agent alum ions are added into the copper electroplating solution, and the reaction carrying agent and chloride ions are matched and mixed according to the proportion range of 1:1-5:1, so that the deposition of copper is accelerated, the reduction rate is increased, the continuous nucleation rate is increased, the compactness of the whole copper layer is greatly improved, and the carrying agent adopts a composite mode, so that the defect that the compactness is not improved due to acceleration of a single reaction carrying agent is overcome.
2) The electro-coppering solution is added with a mixture of ethylene glycol tertiary butyl ether and phosphate ester as an anti-fouling agent, and the mass concentration ratio of the ethylene glycol tertiary butyl ether to the phosphate ester is 1: 1. In the production process, the material numbers enter the cylinder and exit the plate cylinder, and are different, so that impurities are easily polluted, the phenomenon of uneven electroplating effect and the like is caused, and the microscopic observation is difficult because the wafer-level size is too small. Therefore, an antifouling agent is added to the copper plating solution to maintain the cleanliness of the surface of the plated article during the plating process. 3) The copper electroplating solution is added with an antioxidant, and the mass concentration ratio of the antioxidant to the reaction antifouling agent is 1: the purpose of the antioxidant is to prevent oxidation of copper and protect the copper, while some substances contained in impurities such as introduced trace iron, tin and other compounds may corrode and oxidize the copper surface, so that the copper surface is easy to be short-circuited to cause scorching and unevenness of the copper layer. The antioxidant is matched with the reaction antifouling agent, so that not only can an oil pollution source be prevented, but also the phenomena of corrosion, scorching and the like of chemical trace ions can be prevented, and the optimal effect can be achieved by the proportion.
4) The electrolytic copper plating solution is added with an inhibitor, and the mass concentration ratio of the antioxidant to the inhibitor is 3: the purpose of the inhibitor is to inhibit the salient points on the surface of the substrate and accelerate the rapid deposition of the concave points, but the common single inhibitor has larger molecular compound and is difficult to be adsorbed to the salient points firstly, so that a compound with the function of conjugate transmission bridges is needed as connection, the arch rate is less than 5%, and the selected antioxidant has the effect and has the optimal effect according to the proportion.
5) In the copper electroplating process, a variable frequency regulator is adopted to regulate the flow, although operations such as stirring, circular swinging and the like are carried out in advance in the step 2, the proton transmission of the solution in the electroplating process still cannot ensure that subsequent copper ions and additives continuously enter holes, and meanwhile, bubbles generated in the electroplating process easily form concave holes on a plating layer.
The following are several embodiments of the invention in which the brightener includes components.
Example 1
An electrolytic copper plating solution comprising the following composition per 1 liter:
the other parameters of the plating solution operation also comprise vacuumizing time of 5min, stirring speed of 100r/min, electroplating time of 12min and flow rate regulation of 10-30L/min.
The copper plating solution prepared by the components is adopted, and after a wafer packaging product is electroplated by the copper plating method, the diameter of the product is 80.95 microns, the height of the product is 40.47 microns, the crystal sizes of the plating layers are consistent, and no cavity or crack exists; the surface was smooth with 0% camber as shown in FIGS. 1-3.
Example 2
An electrolytic copper plating solution comprising the following composition per 1 liter:
the other parameters of the plating solution operation also comprise vacuumizing time of 5min, stirring speed of 100r/min, electroplating time of 12min and flow rate regulation of 10-30L/min.
The copper plating solution prepared by the components is adopted, and after a wafer packaging product is electroplated by the copper plating method, the diameter of 81.09 micrometers, the height of 53.10 micrometers, the sizes of the crystals of the plating layer are consistent, and no holes or cracks are formed; the surface was smooth with 0% camber as shown in FIGS. 4-5.
Example 3
An electrolytic copper plating solution comprising the following composition per 1 liter:
the other parameters of the plating solution operation also comprise vacuumizing time of 5min, stirring speed of 100r/min, electroplating time of 12min and flow rate regulation of 10-30L/min.
The copper plating solution prepared by the components is adopted, and after a wafer packaging product is electroplated by the copper plating method, the diameter of 81.37 micrometers, the height of 49.32 micrometers, the crystal size of a plating layer are consistent, and no cavity or crack exists; the surface was smooth with 0% camber as shown in FIGS. 6-7.
Comparative examples
The other parameters of the plating solution operation also comprise vacuumizing time of 5min, stirring speed of 100r/min, electroplating time of 12min and flow rate regulation of 10-30L/min.
The components do not contain reaction carrying agents such as alum ions, inhibitors and antifouling agents; the copper plating solution prepared by the components is adopted to obtain a copper plating solution with the diameter of 80.81 mu m, the height of 47.82 mu m and the arch height of 3.40 mu m, and after the wafer packaging product is plated with copper by electroplating, the obtained copper plating layer has a slight cavity and crack, and the arch rate is 7.2%; as shown in fig. 8-9.
As can be seen by comparing the three implementation examples and the comparative examples, the coating obtained by the invention not only achieves the effect of filling the wafer packaging micropores without holes and gaps; and the electroplating uniformity effect is good, and the arch rate is low.
The above disclosure is only an example of the present invention, but the present invention is not limited thereto, and any variations that can be made by those skilled in the art should fall within the scope of the present invention.