Glass via direct current electroplating super-conformal fill method

Abstract

The application discloses a glass via direct current electroplating super-conformal filling method, and belongs to the technical field of microelectronic packaging and electrochemical deposition. First, a target area of a glass substrate is modified by laser processing, and then wet etching is performed to form a glass via structure; a seed layer is deposited on the inner wall of the glass via and the glass surface to provide a conductive path required by electroplating; an acidic copper sulfate system plating solution is prepared; the plating solution is sprayed to the surface of the glass substrate through a jet vacuum pump on one side of the glass substrate to accelerate directional flow of the plating solution at the entrance area of the via; air is introduced into the plating solution through a bubbling device at the bottom of the electroplating tank to continuously disturb the bubbles in the plating solution; and electroplating is started. The application significantly enhances the convection of the plating solution through the synergistic effect of the jet and the bubbling device, improves the mass transfer efficiency in the plating solution, and accelerates the diffusion of components of the plating solution, especially copper ions, to the central area of the via with the lowest concentration.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic packaging and electrochemical deposition technology, specifically relating to an electroplating filling method for high aspect ratio glass via structures, and more particularly to a DC electroplating method for achieving ultra-conformal filling of glass vias by enhancing mass transfer of the electroplating solution and controlling the electrochemical deposition rate. Background Technology

[0002] As integrated circuit technology continues to evolve towards higher performance, higher integration, and miniaturization, traditional two-dimensional packaging structures are increasingly unable to meet the demands of modern electronic systems in terms of interconnect density, transmission rate, and system power consumption. In recent years, 2.5D and 3D advanced packaging technologies have gradually become important technological routes for improving system performance. By constructing vertical interconnect structures between multiple chips, signal transmission paths can be significantly shortened, interconnect delays reduced, and system bandwidth increased.

[0003] In 3D packaging technology, vertical interconnect structures are typically achieved by constructing through-hole structures in the interposer and filling them with metal conductors. Glass substrates are considered a crucial material for next-generation advanced packaging interposers due to their low dielectric loss, excellent electrical insulation properties, and good dimensional stability. Glass substrates also offer advantages such as low cost, the ability to process large-size panels, and good thermal expansion matching capabilities, thus showing broad application prospects in high-frequency communication modules, RF devices, and multi-chip packaging.

[0004] Forming through-hole structures in a glass substrate and filling them with conductors enables vertical electrical connections between different chips; this structure is called a glass via (TGV). Currently, copper is typically used as the filler metal in TGV structures, primarily because copper has excellent electrical conductivity, good thermal conductivity, and low material cost.

[0005] Currently, the most common method for metallizing glass through-holes is electrochemical deposition (electroplating). This method involves depositing a metal seed layer on the inner wall of the glass through-hole and then electrodepositing it in an electroplating solution. This allows copper ions to be reduced and gradually grow on the cathode surface, thus achieving metal filling inside the through-hole. However, in actual electroplating processes, the high aspect ratio of glass through-holes significantly limits the mass transfer process of the electroplating solution within the through-hole. When the electroplating reaction occurs, copper ions are initially consumed in large quantities at the orifice region. If the electroplating solution cannot enter the hole in time to replenish the reactants, the copper ion concentration inside the hole will rapidly decrease. In this case, the copper deposition rate at the orifice region is often significantly higher than that inside the hole. When the orifice deposition rate is too fast, a metal bridging structure will prematurely form at the top of the through-hole, hindering the electroplating solution from entering the hole region and ultimately creating void defects inside the through-hole. These defects significantly reduce the mechanical strength and electrical reliability of the conductive structure, severely affecting the stability of the packaging structure.

[0006] Furthermore, organic additives such as inhibitors, accelerators, and leveling agents are typically added during the electroplating process to regulate copper deposition behavior. The adsorption behavior of these additives at different locations also significantly affects the deposition rate. For example, inhibitors usually preferentially adsorb onto the copper surface, thereby reducing the deposition rate, while accelerators can promote the reduction reaction of copper ions. When additives form a concentration gradient inside and outside the pores, it further exacerbates the unevenness of the deposition rate, leading to filling defects.

[0007] For through-hole structures with large aspect ratios, traditional conformal filling methods are insufficient to achieve complete filling. When the aspect ratio reaches 8:1 or even 10:1 or higher, mass transfer within the hole becomes more difficult, leading to more severe void defects. Therefore, enhancing the mass transfer capability of the electroplating solution inside the through-hole and rationally controlling the electrochemical deposition rate to ensure that the deposition rate inside the hole is higher than that at the hole opening, thereby achieving void-free filling of high aspect ratio glass through-holes, has become a key research issue in current glass through-hole electroplating technology. Summary of the Invention

[0008] The purpose of this invention is to address the problem of central voids caused by limited mass transfer within the glass through-hole during the existing glass through-hole electroplating filling process. A super conformal filling method for glass through-hole DC electroplating is proposed, which achieves void-free filling of high aspect ratio glass through-holes by enhancing the convection of the electroplating solution and controlling the electrodeposition rate.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for conformal filling of glass through-holes by DC electroplating includes the following steps:

[0011] Step 1. Preparation of glass through-holes:

[0012] The target area of ​​the glass substrate is modified by laser processing and then wet etched to form a glass through-hole structure.

[0013] Step 2. Preparation of the seed layer:

[0014] A seed layer is deposited on the inner wall of the glass through-hole and on the glass surface to provide the conductive path required for electroplating;

[0015] Step 3. Preparation of electroplating solution:

[0016] Preparation of an acidic copper sulfate system for electroplating;

[0017] Step 4. Jetting and bubbling enhance convection and mass transfer in the electroplating solution:

[0018] Electroplating solution is sprayed onto the surface of the glass substrate by a jet vacuum pump on one side, which accelerates the directional flow of the electroplating solution in the inlet area of ​​the through hole, with a flow rate of 0.2 to 1 m / s.

[0019] Air is introduced into the electroplating solution through a bubbling device at the bottom of the electroplating tank, causing the bubbles to continuously turbulently in the electroplating solution. The bubbling flow rate is 0.5 to 1 L / min.

[0020] Step 5. Electroplating;

[0021] Electroplating begins with a current density of 0.1 ASD to 0.15 ASD.

[0022] Furthermore, in step 1, the target area is first modified by laser processing, and then wet etching is performed using hydrofluoric acid solution to form a glass via with a thickness of 500 μm, a via diameter of 50 μm, and a via depth-to-width ratio of 10:1.

[0023] Furthermore, the seed layer described in step 2 is a Ti / Cu bilayer structure deposited by magnetron sputtering, wherein the thickness of the Ti adhesion layer is 20-50 nm, which mainly serves as an adhesion layer to compensate for the poor adhesion between copper and glass, and the thickness of the copper seed layer is 200-500 nm.

[0024] Furthermore, the electroplating solution described in step 3 includes copper sulfate pentahydrate, sulfuric acid, chloride ions, inhibitors, leveling agents, and accelerators.

[0025] Furthermore, the concentrations of the inhibitor, leveling agent, and accelerator are: accelerator 3~5 ml / L, inhibitor 5~6 ml / L, and leveling agent 6~10 ml / L.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The synergistic effect of jetting and bubbling devices significantly enhances the convection of the electroplating solution, improves the mass transfer efficiency in the electroplating solution, and accelerates the diffusion of electroplating solution components, especially copper ions, to the central region of the pore where their concentration is lowest.

[0028] 2. By controlling the application of a lower current density and a suitable additive concentration, the consumption rate of copper ions is slowed down, and the copper ion concentration in the hole, especially in the central region of the hole, is maintained at a high level. At the same time, a certain concentration gradient is formed in the through hole by using a suitable inhibitor concentration, which effectively inhibits the copper deposition rate on both sides of the hole.

[0029] 3. By using a conformal filling method, more copper is deposited in the center area of ​​the hole, effectively avoiding the central void defect that is easily generated in the traditional conformal filling process.

[0030] 4. It can achieve complete filling of glass through holes with a depth-to-width ratio of 10:1, improving the reliability of conductive structures. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the glass through-hole structure of the present invention;

[0032] Figure 2 Schematic diagram of a jetting and bubbling enhanced mass transfer electroplating device;

[0033] Figure 3 This is a schematic diagram of copper deposition defects that occur during the electroplating filling process.

[0034] Figure 4 This is a schematic diagram illustrating the changes in copper deposition morphology during the electroplating filling process;

[0035] Figure 5 To finally achieve the X-ray image of the fully filled glass via;

[0036] Figure 6 This is a cross-sectional view of the glass through-hole after it is fully filled. Detailed Implementation

[0037] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0038] A method for conformal filling of glass through-holes by DC electroplating includes the following steps:

[0039] Step 1. Preparation of glass through-holes:

[0040] First, the target area was modified using laser processing, and then wet etching was performed using hydrofluoric acid solution to form a glass via with a thickness of 500 μm, a via diameter of 50 μm, and a via depth-to-width ratio of 10:1. The resulting two-dimensional planar structure of the glass via is shown below. Figure 1 As shown, the blue area is glass, and the yellow parts on its surface and the inner wall of the hole are copper seed layers.

[0041] Step 2. Preparation of the seed layer:

[0042] Seed layers are deposited on the inner wall of the glass through-hole and on the glass surface to provide the conductive path required for electroplating. The seed layer is a Ti / Cu bilayer structure deposited by magnetron sputtering, wherein the thickness of the Ti adhesion layer is 20-50 nm, which mainly serves as an adhesion layer to compensate for the poor adhesion between copper and glass, and the thickness of the copper seed layer is 200-500 nm.

[0043] Step 3. Preparation of electroplating solution:

[0044] The electroplating solution is an acidic copper sulfate system, whose main components include: copper sulfate pentahydrate (CuSO4·5H2O): 220 g / L; sulfuric acid (H2SO4): 50 g / L; chloride ions (Cl... - ): 50 ppm; An organic additive system is also added, including: inhibitors such as PEG, leveling agents such as JGB, and accelerators such as SPS. Copper sulfate pentahydrate is primarily responsible for providing copper ions (Cu). 2+ Sulfuric acid primarily provides an acidic environment, adjusting the pH of the solution to ensure the normal operation of the electroplating process. Chloride ions not only activate the anode and prevent passivation but also interact with organic additives to improve the efficiency of through-hole filling. Inhibitors adsorb onto the copper layer surface during electroplating and combine with chloride and copper ions to form a PEG-Cu-Cl complex, thus inhibiting copper deposition. Accelerators adsorb onto the copper layer surface to accelerate the electroplating rate. There is competition between accelerators and inhibitors; since accelerators are mostly small molecules while inhibitors are mostly large molecules, accelerators are generally distributed inside the holes, while inhibitors are distributed on the surface and near the hole opening. Leveling agents inhibit the growth of copper layers on protrusions with higher current densities, while their inhibitory effect weakens at lower current densities, ensuring uniform copper layer growth.

[0045] Step 4. Enhancing convection and mass transfer of the plating solution through jetting and bubbling.

[0046] During electroplating, due to the high aspect ratio and small aperture of the through-hole structure, the consumption of copper ions within the holes cannot be replenished solely through diffusion caused by the concentration gradient. This easily leads to defects such as voids and gaps due to insufficient copper ion concentration at the hole center. Therefore, this invention uses a jetting device and a bubbling device to enhance the convection of the plating solution and further accelerate the mass transfer process, thereby increasing the copper ion concentration within the through-holes, especially at the hole center, to reduce the generation of defects. A schematic diagram of the electroplating apparatus is shown below. Figure 2 As shown, an electroplating solution is sprayed onto the surface of the glass substrate using a jet vacuum pump on one side, accelerating the directional flow of the solution in the through-hole inlet region. Utilizing the Venturi principle—that when fluid passes through a pipe with a suddenly narrowed cross-sectional area, the flow velocity increases, the pressure decreases, and adsorption occurs—the flow velocity is approximately 0.2–1 m / s. Simultaneously, air is introduced into the electroplating solution at the bottom of the electroplating tank via a bubbling device, causing continuous turbulence in the solution. The bubbling flow rate is approximately 0.5–1 L / min. The synergistic effect of the jet and bubbling significantly enhances the convection of the electroplating solution, thereby improving the transport capacity of copper ions into the through-hole.

[0047] Step 5. Deposition rate regulation:

[0048] During electroplating, the main factors affecting copper ion deposition inside the holes, especially in the central region, are current density and inhibitor concentration. First, current density determines the rate of copper ion consumption; higher current densities correspond to faster copper ion consumption. At a fixed current density, the copper ion concentration within the hole will eventually form a stable concentration gradient, decreasing towards the hole center. If, at a high current density, the copper ion concentration is rapidly consumed and stabilizes at a low level, defects will inevitably occur inside the hole due to insufficient copper ion concentration. Second, while inhibitors can suppress copper ion deposition, like copper ions, they also exhibit a certain concentration distribution within the via. Similarly, as the current density increases, the rate at which inhibitors combine with chloride and copper ions to form complexes also increases. The inhibitor's inhibitory effect weakens due to insufficient concentration within the hole, resulting in faster deposition at the sides of the hole center, thus leaving pores inside the hole, as illustrated in the diagram. Figure 3 As shown in the diagram. Therefore, a lower current density and a suitable additive concentration are required to achieve the super-conformal filling effect. The current density is controlled between 0.1 ASD and 0.15 ASD, and the volume ratio of inhibitor, leveling agent, and accelerator is 3:5:1. A schematic diagram of the filling process is shown in the diagram. Figure 4 As shown.

[0049] Example

[0050] A method for conformal filling of glass through-holes by DC electroplating specifically includes the following steps:

[0051] Step 1. Clean the surface of the glass substrate with sodium hydroxide, and then rinse the surface of the cleaning solution with deionized water to prevent contaminants on the glass substrate surface from interfering with laser processing.

[0052] Step 2. Perform laser modification on the cleaned glass substrate. Import the pre-designed through-hole array pattern into the laser equipment. Simultaneously, place the glass substrate on the micromachining platform of the femtosecond laser, turn on vacuum adsorption to fix it and prevent the glass from sliding during the modification process, and then select 4 mark points for locking the position. At the same time, adjust the laser parameters such as focal length, pulse frequency, pulse width, pulse energy and other parameters to the required values. After the modification is completed, turn off vacuum adsorption and remove the glass substrate.

[0053] Step 3. Clean the laser-modified glass substrate with a cleaning solution to remove the powder generated during the laser processing and avoid affecting the subsequent wet etching. Then, use deionized water to remove the cleaning solution from the surface.

[0054] Step 4. Perform wet etching on the laser-modified glass substrate. The etching solution mainly consists of hydrofluoric acid solution, with a small amount of additives to accelerate etching and reduce the roughness of the inner wall of the glass vias. Because hydrofluoric acid is extremely corrosive and harmful to the human body, the laser-modified glass substrate must be placed in a fixed fixture, which then places it in the etching solution. Using ultrasound at a certain frequency can also accelerate etching and improve its uniformity. During the etching process, the container should be kept sealed to prevent hydrofluoric acid evaporation. The substrate can be removed after the set etching time.

[0055] Step 5. Use a cleaning solution to clean the etching solution from the surface of the glass substrate and inside the holes that have been etched. Then, use deionized water to remove the cleaning solution completely. During the cleaning process, use an appropriate frequency of ultrasound to ensure that the inside of the holes is cleaned more thoroughly. Finally, put the cleaned glass substrate into an oven to dry it completely.

[0056] Step 6. Prepare a seed layer on the surface and inside the holes of the glass substrate that has already been perforated. The seed layer consists of two metal thin films: titanium (Ti) and copper (Cu). Since the adhesion between copper and glass is poor, the main function of the titanium layer is to improve the adhesion. Place the dried glass substrate into the corresponding fixture and fix it. Wear gloves to prevent leaving contaminants on the glass surface, which would affect the adhesion of the metal thin film. Then, set the power supply, the target material used, and the corresponding sputtering time, and close the equipment door to start operation. First, evacuate the vacuum and then start sputtering. Sputter titanium and copper onto both sides of the glass substrate simultaneously. After that, release the vacuum, take it out, and obtain the experimental sample required for electroplating. Place it in a vacuum chamber to prevent the copper layer on the surface from oxidizing.

[0057] Step 7. Prepare the electroplating solution. The main components of the electroplating solution include 220 g / L copper sulfate pentahydrate (CuSO4·5H2O), 50 g / L sulfuric acid (H2SO4), and 50 ppm chloride ions (Cl). -This involves adding DC electroplating additives, including inhibitors, leveling agents, and accelerators. The preparation process begins by adding 1.5 L of deionized water to a 2 L beaker, followed by weighing 330 g of copper sulfate pentahydrate and stirring at a constant speed using a magnetic stirrer until fully dissolved. Then, sulfuric acid and chloride ions are added. The 98% concentrated sulfuric acid used has a density of 1.84 g / mL, requiring approximately 40.76 mL of concentrated sulfuric acid in the 1.5 L solution. The corresponding volume is measured using a graduated cylinder, and the concentrated sulfuric acid is slowly added to the solution along the inner wall of the beaker to avoid splashing due to localized temperature increases. Simultaneously, to obtain a chloride ion concentration of 50 ppm, 0.125 mL of concentrated hydrochloric acid is added, measured using a pipette and added to the solution. Because concentrated sulfuric acid is highly corrosive and concentrated hydrochloric acid is highly volatile, the entire solution preparation process was carried out in a fume hood, with protective face shields, masks, and chemical-resistant gloves worn to ensure experimental safety. Then, DC electroplating additives were added, with the ratio of the three additives being inhibitor: leveling agent: accelerator = 3:5:1. After adding the additives, stirring was continued for a period of time to ensure thorough mixing. The electroplating solution was then prepared and transferred to the electroplating tank for later use.

[0058] Step 8. Before the formal electroplating, the newly prepared electroplating solution needs to be activated. The specific method is as follows: Select a conductive glass substrate, immerse it in the electroplating solution, and perform pre-electroplating for about 1 hour at a current density of approximately 0.1 ASD to stabilize the distribution of additives in the solution and bring the electroplating solution into a stable working state. After activation, remove the glass substrate, and the formal electroplating can begin. Before electroplating, perform a simple pretreatment on the sample surface by immersing it in a low-concentration sulfuric acid solution for about 15 seconds to remove any oxide layer that may form on the surface, preventing the presence of copper oxide from affecting conductivity. Then, place the sample in a vacuum water bath for vacuum treatment, evacuating the vacuum to -85.8 kPa. The main purpose of this step is to remove air from the glass vias and fully wet the inner walls of the vias, thereby preventing residual air from preventing the electroplating solution from entering the vias during the electroplating process, resulting in only a copper layer being deposited on the surface. After vacuum treatment, the sample was fixed in an electroplating fixture. A multimeter was used to measure the resistance between the glass substrate and the fixture to confirm its conductivity. Once confirmed, the fixture and sample were placed into the electroplating tank. The electroplating system employed a double-sided simultaneous electroplating method, with copper plates on both sides serving as soluble anodes. During electroplating, continuous jetting occurred on both sides of the cathode, while bubbling occurred at the bottom of the electroplating tank to accelerate the ion exchange rate within the vias. The electrode spacing was set to 12 cm, and the electroplating voltage was 5 V. A constant current density of 0.1 ASD was used during electroplating, with a plating time of 28 hours, ultimately achieving complete filling of the glass vias with an aspect ratio of 10:1. The X-ray image after filling is shown below. Figure 5 As shown, the black shaded area represents the filled copper. The absence of obvious white within the shaded area indicates that the filling is relatively uniform and without significant defects. After metallographic sample preparation, its cross-section was observed using an optical microscope as shown. Figure 6 As shown, it can be seen that when the sample is ground to a cross-sectional width of about 50 μm, it is still a uniform and dense coating, achieving complete filling of glass through holes with a depth-to-width ratio of 10:1 and a pore size of 50 μm.

Claims

1. A method for super-conformal filling of glass through-holes by DC electroplating, characterized in that, Includes the following steps: Step 1. Preparation of glass through-holes: The target area of ​​the glass substrate is modified by laser processing and wet etching to form a glass through-hole structure; Step 2. Preparation of the seed layer: A seed layer is deposited on the inner wall of the glass through-hole and on the glass surface to provide the conductive path required for electroplating; Step 3. Preparation of electroplating solution: Preparation of an acidic copper sulfate system for electroplating; Step 4. Jetting and bubbling enhance convection and mass transfer in the electroplating solution: Electroplating solution is sprayed onto the surface of the glass substrate by a jet vacuum pump on one side, which accelerates the directional flow of the electroplating solution in the inlet area of ​​the through hole, with a flow rate of 0.2 to 1 m / s. Air is introduced into the electroplating solution through a bubbling device at the bottom of the electroplating tank, causing the bubbles to continuously turbulently in the electroplating solution. The bubbling flow rate is 0.5 to 1 L / min. Step 5. Electroplating; Electroplating begins with a current density of 0.1 ASD to 0.15 ASD.

2. The method for super-conformal filling of glass through-hole DC electroplating according to claim 1, characterized in that, In step 1, the target area is first modified by laser processing, and then wet etching is performed using hydrofluoric acid solution to form glass through holes.

3. The method for super-conformal filling of glass through-hole DC electroplating according to claim 1, characterized in that, The seed layer described in step 2 is a Ti / Cu bilayer structure deposited by magnetron sputtering, wherein the thickness of the Ti adhesion layer is 20–50 nm and the thickness of the copper seed layer is 200–500 nm.

4. The method for super-conformal filling of glass through-hole DC electroplating according to claim 1, characterized in that, The electroplating solution described in step 3 includes copper sulfate pentahydrate, sulfuric acid, chloride ions, inhibitors, leveling agents, and accelerators.

5. The method for super-conformal filling of glass through-hole DC electroplating according to claim 1, characterized in that, The concentration of the inhibitor is 5-6 ml / L, the concentration of the accelerator is 3-5 ml / L, and the concentration of the leveling agent is 6-10 ml / L.

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