A nanotwinned copper electroplating solution for filling high-density packaging structures, a plated layer and a preparation method and application thereof
By adding specific additives and controlling the plating parameters to the nanotwinned copper plating solution, the problem of patterned filling of the nanotwinned copper plating solution in high-density packaging structures was solved, and a high-strength, high-elongation plating layer was achieved, which is suitable for uniform filling of high-density electronic packaging.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN INST OF ADVANCED TECH CHINESE ACAD OF SCI
- Filing Date
- 2021-12-15
- Publication Date
- 2026-06-05
AI Technical Summary
Existing commercially available nanotwin copper plating solutions are difficult to achieve patterned and uniform filling in high-density packaging structures, and the addition of additives can cause the disappearance of nanotwin structures, affecting their application in electronic packaging.
A mixture containing sodium thiazolinyl dithiopropane sulfonate or sodium 3-mercapto-1-propanesulfonate and tetrahydrothiazothione is used as a key patterning additive, combined with gelatin as a twinning promoter, to form a high-performance nanotwinned copper plating. Copper is deposited on the substrate by electrochemical methods, and the current density and temperature are controlled to ensure the uniformity and smoothness of the plating.
It improves the strength and elongation of nanotwinned copper plating, enables uniform filling of fine interconnect structures such as wiring, rewiring, and pads in high-density packaging structures, reduces the thickness of the transition layer, and enhances the filling capacity of the plating solution and the toughness of the plating layer.
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Figure CN116262982B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of integrated circuit packaging and printed circuit board manufacturing technology, specifically relating to a nano-twin copper electroplating solution for filling high-density packaging structures, the plating layer, its preparation method, and its application. Background Technology
[0002] Currently, commercially available wafer-level packaging copper plating solutions mainly consist of copper chloride and additives. (Copper refers to the main salt that provides copper ions, generally copper sulfate, copper methanesulfonate, etc.; acids are generally concentrated sulfuric acid, hydrochloric acid, methanesulfonic acid, etc.; chloride is generally sodium chloride or hydrochloric acid, etc.) The fine and uniform filling of patterns on 8-inch or 12-inch wafers is primarily achieved through additives. Additives are mainly divided into accelerators, inhibitors, and leveling agents. These three additives work together to ensure good pattern filling capability. Specifically, inhibitors are generally high-molecular-weight polyether organic compounds, such as PEG; accelerators are mainly sulfur-containing organic compounds, which lower the potential and accelerate the copper deposition rate during copper plating, such as SPS; leveling agents are mainly quaternary ammonium organic compounds, which easily adsorb at positions with high current density on the cathode surface, competing with copper ions for adsorption and playing a leveling role, such as JGB. The plating structure corresponding to commercially available wafer-level packaging copper plating solutions, from a microscopic perspective, is generally dominated by equiaxed grains. As the density of electronic packaging increases, the size of copper interconnects continues to decrease, and feature dimensions become increasingly smaller. For example, the linewidth of wiring and rewiring layers has been further reduced from tens to hundreds of micrometers to just a few micrometers; the diameter of copper pads, blind vias, grooves, bumps, copper pillars, and other patterns has decreased from hundreds of micrometers to just a few micrometers. Traditional metallic copper cannot meet the requirements for strength and toughness, and problems such as broken wires and torn pads often occur in reliability testing.
[0003] The microstructure of a material is the essential factor determining its properties. Patent application CN200510047555.2, filed by Academician Lu Ke's team at the Institute of Metal Research, Chinese Academy of Sciences, discloses a special high-strength, high-tensile-plasticity nanotwinned pure copper material. This nanotwinned copper structure is obtained by pulse electrodeposition, and its microstructure consists of equiaxed crystals with isotropic lamellar spacing at the nanoscale twin boundaries. Controlled solely by microstructure (grain boundaries, twin boundaries), without any doping, the nanotwinned pure copper exhibits a strength 10 times higher than coarse-grained copper and conductivity comparable to oxygen-free copper. The nanotwinned copper material balances high toughness and high conductivity, solving the bottleneck problems of "strength-toughness inversion" and "incompatibility between strength and conductivity" that have plagued the materials science community for many years. Professor Chen Zhi's team at National Chiao Tung University in Taiwan has disclosed a highly (111)-preferred-orientation nanotwinned copper structure, which, as a metal layer under bumps, can annihilate Kirkendal pores at the interface and control the morphology of interface compounds, improving welding reliability. However, as can be seen from the above-mentioned publicly available information, nanotwinned copper plating solutions lack additives that can achieve patterning compared to commercial copper plating solutions for wafer packaging. To achieve large-area uniform filling of fine patterns such as trenches and blind vias on 8-inch or 12-inch wafers, existing nanotwinned copper plating solutions need further improvement. However, the biggest problem currently is that the addition of most commercially available additives such as accelerators, leveling agents, and inhibitors leads to the inactivation of the twinning promoter gelatin due to the interaction of these additives, further resulting in the disappearance of the nanotwin structure. Moreover, the electroplating process also needs to be adjusted after adding additives. Therefore, finding effective additives that can improve the filling capacity of nanotwinned copper plating solutions without affecting its twinning characteristics is crucial and represents a bottleneck affecting the application of nanotwinned copper packaging interconnects. Summary of the Invention
[0004] To address the problems existing in the prior art, the present invention aims to provide a nanotwinned copper electroplating solution, a plating layer, a preparation method thereof, and applications for filling high-density packaging structures. The nanotwinned copper plating layer of the present invention exhibits increased strength and elongation, and the filling capacity (uniformity and flatness) of the nanotwinned copper electroplating solution is significantly improved, making it suitable for filling fine interconnect structures such as wiring, rewiring, pads, and trenches in electronic packaging.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A nanotwinned copper electroplating solution for filling high-density encapsulation structures comprises the following components: 30-50 g / L copper ions, 100-150 g / L sulfuric acid, 50-100 ppm chloride ions, 5-200 ppm key patterning additives, 20-200 ppm twinning promoters, and the balance being pure water.
[0007] Other additives can be added to the components of the aforementioned nanotwinned copper electroplating solution, such as one or more of accelerators, inhibitors, leveling agents, stabilizers, and lubricants. The accelerators, inhibitors, and leveling agents include sodium polydithiopropane sulfonate, thiourea, Janus Green, and polyethylene glycol. The stabilizers and lubricants include sodium N,N-dimethyl-dithiocarbonylpropane sulfonate or sodium dodecyl sulfate. The accelerators, inhibitors, and leveling agents not only produce high-performance twinned structures but also further improve the uniformity and flatness of the pattern.
[0008] The nanotwinned copper electroplating solution contains a key patterning additive comprising sodium thiazolinyl dithiopropane sulfonate or a mixture of sodium 3-mercapto-1-propanesulfonate and tetrahydrothiazothione, which have similar functional groups. This key patterning additive decomposes into two products in the plating solution and adsorbs to different sites, improving filling capacity. Simultaneously, it synergistically works with twinning promoters without affecting gelatin adsorption or the formation of nanotwinned structures.
[0009] The nano-twinned copper electroplating solution comprises copper ions including copper sulfate pentahydrate, sulfuric acid including a diluted solution of 96%–98% concentrated sulfuric acid, chloride ions including a diluted solution of 36%–38% concentrated hydrochloric acid, sodium chloride, or potassium chloride, and a twinning promoter including gelatin. Electrochemical testing shows that gelatin adsorbs onto the copper film surface during electroplating, inhibiting copper deposition.
[0010] A nanotwinned copper plating layer for filling high-density packaging structures is prepared by electroplating using the nanotwinned copper plating solution as described above.
[0011] The method for preparing a nanotwinned copper plating layer for filling high-density packaging structures includes the following steps:
[0012] (1) The electroplating solution is prepared with the following components: copper ions 30~50 g / L, sulfuric acid 100~150 g / L, chloride ions 50~100 ppm, key patterning additives 5~200 ppm, twinning promoters 20~200 ppm, other additives 0~500 ppm, and the balance is pure water;
[0013] (2) Take a cathode substrate and attach a seed layer on the cathode substrate;
[0014] (3) Spin-coating photoresist and using exposure and development methods to create patterns;
[0015] (4) After pretreatment, the cathode substrate with seed layer obtained by the pattern windowing in step (3) is immersed together with the phosphorus copper anode in the electroplating solution prepared in step (1). The flow rate of the plating solution is controlled by stirring, the temperature of the plating solution is controlled, and the plating solution is pre-deposited for 0.5~1 h with a constant current density to activate the plating solution.
[0016] (5) Replace the new cathode substrate and repeat step (4) for electroplating. After taking it out, rinse it repeatedly with pure water to remove the plating solution from the surface of the plating layer, and dry it to obtain the plating layer.
[0017] In the preparation method described above, the cathode substrate in step (2) includes one or more of silicon-based, carbon-based, gallium arsenide, gallium nitride, and glass; the seed layer includes one or more of copper, titanium, gold, nickel, and their alloys; the thickness of the seed layer is 100~500 nm; and the attachment method includes electroplating, chemical plating, sputtering, or evaporation. In step (3), the pattern windowing includes wiring, rewiring, pads, deep holes, and trenches; the linewidth and depth of the wiring and rewiring are 1.5-200 μm; and the aperture of the pads, deep holes, and trenches are 5-500 μm and the depth is 3-100 μm.
[0018] The preparation method described herein, wherein the pretreatment method in step (4) is as follows: the cathode substrate is sequentially subjected to pre-wetting, acid washing, water washing, and plasma cleaning to completely remove surface oil and oxides, resulting in a fresh and clean cathode substrate surface. Preferably, the acid washing method includes immersion and stirring in a 5% sulfuric acid solution or deoxidation. Preferably, the plasma cleaning method includes cleaning in an oxygen atmosphere for 100-500 s with a power of 100-800W. The phosphorus content in the phosphorus-copper anode is 0.03-0.075 wt.%. The stirring includes one or more of the following: circulating jet, ultrasonic dispersion, air stirring, magnetic stirring, mechanical stirring, cathode rotation, and cathode movement. The temperature of the plating solution is constant at 20-50 ℃, and the current density is 2-8 A / dm³. 2 .
[0019] In the preparation method described above, the electroplating time in step (5) is 20~1200 min.
[0020] The nanotwinned copper electroplating solution and the nanotwinned copper plating layer are used for uniform filling of patterns at different positions on large-area substrates of 8 inches or 12 inches involved in wafer-level electroplating, as well as for filling of fine patterns with small feature sizes involved in wafer-level electroplating.
[0021] In the aforementioned application, the nanotwinned copper has an equiaxed or columnar crystal structure, and the average transition layer thickness is less than 1 μm. In some locations near the matrix, smaller columnar crystals without a transition layer are present.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] 1. The electroplating solution of the present invention contains sodium thiazolinyl dithiopropane sulfonate (SH110) or a mixture of sodium 3-mercapto-1-propanesulfonate (H1) and tetrahydrothiazothione (MPS) with similar functional groups. The resulting coating has two types of crystals: equiaxed crystals and columnar crystals. It has a nanotwinned structure, and the coating has good toughness. The coating strength and elongation are both increased.
[0024] 2. The plating solution of this invention has significantly improved filling capacity (uniformity and flatness) compared with traditional nano-twin copper electroplating solutions. It can achieve uniform filling of patterns such as narrow-pitch wiring, with a thickness uniformity difference of less than 6% and a flatness difference of less than 6% across the entire wafer. It solves the difficulty of filling patterns in nano-twin copper and can be used for large-area uniform filling of 8-inch or 12-inch wafers.
[0025] 3. The average thickness of the nanotwinned transition layer obtained by the electroplating solution of the present invention is less than 1 micrometer, and the thickness of the transition layer is significantly reduced. It is suitable for fine patterns with small feature sizes, such as wiring, rewiring, pads, trenches and other interconnection structures in high-density electronic packaging.
[0026] 4. The present invention relates to a preparation method that is simple to operate, low in cost, and highly practical. It can be widely applied to fields related to electroplating copper technology, such as advanced integrated circuit packaging and printed circuit board manufacturing, and comprehensively improves the mechanical properties of metallic copper. Attached Figure Description
[0027] Figure 1 The cross-sectional morphology of the coating obtained in Example 1;
[0028] Figure 2 The cross-sectional morphology (grain refinement) of the coating obtained in Example 2 is shown.
[0029] Figure 3 This is an enlarged view of the cross-sectional morphology of the coating obtained in Example 2;
[0030] Figure 4 The cross-sectional morphology of the coating obtained in Comparative Example 1;
[0031] Figure 5 The cross-sectional morphology of the coating obtained in Comparative Example 2 is shown.
[0032] Figure 6 This is a comparison graph of the mechanical properties of Example 1 and Comparative Examples 1-2;
[0033] Figure 7 This is a cross-sectional view along the width direction of the RDL with a linewidth of 15 μm obtained from the formulation of Example 1;
[0034] Figure 8 The uniformity and smoothness of the filling effect in Example 1 are statistically analyzed, where (a) represents uniformity and (b) represents smoothness.
[0035] Figure 9 This is a process flow diagram of the present invention. Detailed Implementation
[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0037] Example 1:
[0038] 1. Plating solution preparation: Prepare the plating solution using the following component ratio and ensure thorough mixing: copper ions 30~50 g / L, sulfuric acid 100~150 g / L, chloride ions 50~100 ppm, SH110 5 ppm, gelatin 20~200 ppm, with the balance being pure water.
[0039] 2. Substrate preparation: Prepare a silicon-based wafer and magnetron sputter 100 nm Ti and 400 nm Cu as seed layers on the surface. The magnetron sputtering power is 10~90 KW, and the magnetron sputtering time is 2~15 min.
[0040] 3. Patterning: Photoresist is spin-coated onto a wafer with a seed layer, and patterns such as circuits, pads, and grooves are formed through processes such as exposure and development.
[0041] 4. Substrate pretreatment: First, clean the wafer with deionized water, then use 5% sulfuric acid to remove the oxide layer, and finally rinse it clean with deionized water.
[0042] 5. DC Electroplating: The cathode substrate and phosphorus-copper anode (phosphorus content 0.03~0.075 wt.%) are immersed in the plating bath. During the electroplating process, the cathode rotates horizontally, accompanied by a circulating jet of the plating bath for stirring. The plating bath temperature is controlled at 30 ℃, and the current density is 2~5 A / dm³. 2 Electroplating at current density for 10 minutes.
[0043] 6. Post-plating treatment: Remove the plating and substrate, rinse repeatedly with pure water to remove residual plating solution from the plating surface, and finally dry the plating surface with compressed air.
[0044] The cross-sectional microstructure of the obtained coating is as follows Figure 1 As shown, the coating contains nanotwinned structures, and high-density nanotwinned structures can still be observed within the columnar crystals.
[0045] Example 2:
[0046] 1. Plating solution preparation: Prepare the plating solution using the following component ratio and ensure thorough mixing: copper ions 30~50 g / L, sulfuric acid 100~150 g / L, chloride ions 50~100 ppm, SH110 10 ppm, gelatin 20~200 ppm, with the balance being pure water.
[0047] 2. Substrate preparation: A wafer with a seed layer of 100 nm Ta and 400 nm Cu sputtered is used as the cathode substrate.
[0048] 3. Patterning: Photoresist is spin-coated onto a wafer with a seed layer, and patterns such as copper pillars are formed through processes such as exposure and development.
[0049] 4. DC Electroplating: The cathode substrate and phosphorus-copper anode (phosphorus content 0.03~0.075 wt.%) are immersed in the plating bath. During the electroplating process, the cathode rotates horizontally, accompanied by a stirring method involving circulating jets of plating bath. The plating bath temperature is controlled at 20 ℃, and the current density is 3~8 A / dm³. 2 Electroplating at current density for 10 minutes.
[0050] The remaining process is the same as in Example 1, and the resulting coating cross-sectional microstructure is as follows: Figure 2 As shown, the coating consists of equiaxed crystals, and a high-density nanotwin structure can be observed under magnification. Figure 3 The image shown is an enlarged view of the coating, which consists of equiaxed crystals with no transition layer and contains a high-density nanotwin structure within the grains.
[0051] Comparative Example 1:
[0052] 1. Plating solution preparation: Prepare the electroplating solution using the following component ratio and ensure thorough mixing: copper ions 30~50 g / L, sulfuric acid 100~150 g / L, chloride ions 50~100 ppm, H1 5~200 ppm, polyethylene glycol 0~200 ppm, gelatin 20~200 ppm, with the balance being pure water.
[0053] 2. The remaining process is the same as in Example 1.
[0054] The resulting coating cross-sectional microstructure is as follows Figure 4 As shown, the coating microstructure consists of two parts: the side near the substrate is composed of equiaxed fine grains without nanotwins (i.e., a transition layer with an average thickness of over 10 μm); the side near the plating bath is composed of columnar crystals containing nanotwins.
[0055] Comparative Example 2:
[0056] 1. Plating solution preparation: Prepare the electroplating solution using the following component ratios and ensure thorough mixing: copper ions 30~50 g / L, sulfuric acid 5~150 g / L, chloride ions 18~60 ppm, sodium polydisulfide dipropane sulfonate 5~20 ppm, methylene blue 1~100 ppm, gelatin 20~200 ppm, with the balance being pure water.
[0057] 2. The remaining process is the same as in Example 1.
[0058] The resulting coating cross-sectional microstructure is as follows Figure 5 As shown, the coating is primarily composed of equiaxed fine grains, without any nanotwinned structure.
[0059] Experimental comparison:
[0060] like Figure 6 The mechanical properties are compared as shown. The sample shape is dog bone-shaped, with a central width of 2.5 mm and a film thickness of 12 micrometers. Example 1: strength 413.8 MPa, elongation 3.162%; Comparative Example 1: strength 394.7 MPa, elongation 1.21%; Comparative Example 2: strength 250 MPa, elongation 0.63%. The tensile strength and elongation of the three coatings in Examples and Comparative Examples 1 and 2 are shown. According to the Hall-Page formula for grain size and strength, smaller grains result in higher strength. However, in the performance comparison of this invention, the grain size is Example 1 > Comparative Example 1 > Comparative Example 2, while the strength variation is Example 1 > Comparative Example 1 > Comparative Example 2. This shows that fine grain reinforcement has little effect on strength in Comparative Examples 1 and 2, and the reduced twin density leads to a corresponding decrease in strength. Example 1, due to its high-density twins, achieves higher strength and toughness mechanical properties than the other two samples. Mechanical property tests demonstrated that the electroplating solution formulation of this invention utilizes suitable patterning additives, and the resulting coating still retains the high strength and toughness advantages of nanotwinned copper while effectively eliminating the transition layer, resulting in a higher proportion of nanotwinned structure in the coating thickness direction. Although Comparative Example 1 contains nanotwinned structure, its transition layer thickness is relatively large, approximately 10 micrometers, leading to a low proportion of nanotwinned structure in the total coating thickness. Comparative Example 2 contains almost no nanotwinned structure.
[0061] like Figure 7 The image shows a cross-section along the width direction of the 15 μm linewidth RDL obtained from the formulation of Example 1. High-density twinned crystalline layers are visible within the columnar crystals, with an average transition layer thickness of less than 1 μm. Some locations lack a transition layer, and the nanotwinned structure grows from bottom to top. Figure 1 Compared to planar thin films, the plating solution system obtained by this formulation showed no difference in microstructure filling at narrow linewidths. Furthermore, reducing the transition layer thickness is significant for nanotwins in high-density packaging. Previously reported nanotwins have transition layers of a certain thickness, essentially forming a bilayer structure. However, in the miniaturization of packaging, where linewidths become narrower and thinner, a thinner transition layer is needed to fully leverage the strength and toughness advantages of nanotwins.
[0062] like Figure 8(a) shows the overall uniformity statistics. Overall uniformity reflects the difference in height between different patterns, which is the ratio of the difference between the highest and lowest thicknesses in each pattern to the highest thickness in each pattern. It can be seen that the overall uniformity of Example 1 is significantly reduced, with the overall uniformity being less than 3% in linewidths of 2 μm, 5 μm, and 15 μm. In contrast, the overall uniformity of Comparative Example 1 is below 11%. Figure 8 (b) Statistical analysis of the overall average flatness. Flatness reflects the macroscopic protrusions and depressions of the coating, and can be understood as the uniformity of a single pattern, i.e., the ratio of the difference between the highest and lowest thickness within a single pattern to the highest thickness within that pattern. It can be seen that the average flatness of the pattern in Example 1 is below 2%, while that in Comparative Example 1 is below 5%. In summary, using the formulation of this invention, the pattern filling ability is significantly improved, and both the overall uniformity and average flatness are significantly improved. General industry requirements dictate that both pattern flatness and uniformity should be within 8%.
Claims
1. A nanotwinned copper electroplating solution for filling high-density encapsulation structures, characterized in that... The product comprises the following components: copper ions 30-50 g / L, sulfuric acid 100-150 g / L, chloride ions 50-100 ppm, key patterning additive 5-200 ppm, twinning promoter 20-200 ppm, and the balance being pure water; the average transition layer thickness of the nanotwinned copper is less than 1 μm; the key patterning additive is sodium thiazolinyl dithiopropane sulfonate or a mixture of sodium 3-mercapto-1-propanesulfonate and tetrahydrothiazothione; and the twinning promoter is gelatin.
2. The nanotwinned copper electroplating solution as described in claim 1, characterized in that... The copper ions include copper sulfate pentahydrate, the sulfuric acid includes a diluted solution of 96% to 98% concentrated sulfuric acid, and the chloride ions include a diluted solution of 36% to 38% concentrated hydrochloric acid, sodium chloride, or potassium chloride.
3. A method for preparing a nanotwinned copper plating layer for filling high-density encapsulation structures, characterized in that... The nanotwinned copper plating solution described in any one of claims 1-2 is used to prepare the copper, comprising the following steps: (1) The electroplating solution is prepared with the following components: copper ions 30~50 g / L, sulfuric acid 100~150 g / L, chloride ions 50~100 ppm, key patterning additives 5~200 ppm, twinning promoters 20~200 ppm, and the balance is pure water; (2) Take a cathode substrate and attach a seed layer on the cathode substrate; (3) Spin-coating photoresist and using exposure and development methods to create patterns; (4) After pretreatment, the cathode substrate with seed layer obtained by the pattern windowing in step (3) is immersed together with the phosphorus copper anode in the electroplating solution prepared in step (1). The flow rate of the plating solution is controlled by stirring, the temperature of the plating solution is controlled, and the plating solution is pre-deposited for 0.5~1 h with a constant current density to activate the plating solution. (5) Replace the new cathode substrate and repeat step (4) for electroplating. After taking it out, rinse it repeatedly with pure water to remove the plating solution from the surface of the plating layer, and dry it to obtain the plating layer.
4. The preparation method according to claim 3, characterized in that... In step (2), the cathode substrate includes one or more of silicon-based, carbon-based, gallium arsenide, gallium nitride, and glass. The seed layer includes one or more of copper, titanium, gold, nickel, and their alloys. The thickness of the seed layer is 100-500 nm. The attachment method includes electroplating, chemical plating, sputtering, or evaporation. In step (3), the pattern windowing includes wiring, rewiring, pads, deep holes, and trenches. The linewidth and depth of the wiring and rewiring are 1.5-200 μm. The aperture of the pads, deep holes, and trenches is 5-500 μm, and the depth is 3-100 μm.
5. The preparation method according to claim 3, characterized in that... The pretreatment method in step (4) is as follows: the cathode substrate is sequentially subjected to pre-wetting, acid washing, water washing, and plasma cleaning to completely remove surface oil and oxides, resulting in a fresh and clean cathode substrate surface. The acid washing method includes immersion and stirring in a 5% sulfuric acid solution or deoxidation. The plasma cleaning method includes cleaning in an oxygen atmosphere for 100-500 s with a power of 100-800W. The phosphorus content in the phosphorus copper anode is 0.03~0.075wt.%. The stirring includes one or more of the following: circulating jet, ultrasonic dispersion, air stirring, magnetic stirring, cathode rotation, and cathode movement. The temperature of the plating solution is constant at 20-50 ℃, and the current density is 2~8 A / dm³. 2 .
6. The preparation method according to claim 3, characterized in that... The electroplating time in step (5) is 20~1200 min.