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CN-122013274-A - Direct copper electroplating process without silver paste priming

CN122013274ACN 122013274 ACN122013274 ACN 122013274ACN-122013274-A

Abstract

The invention relates to the technical field of electroplating, in particular to a direct copper electroplating process without silver paste priming. The preparation method comprises the steps of pre-treating a crystalline silicon substrate to remove an oxide layer and activate the oxide layer, covalently grafting a directional modifier containing benzothiazole mercapto groups and hydrolyzable silane end groups on the surface of the substrate in an alcohol/water-containing grafting solution, thermally curing to form a localized coordination interface layer, preparing an electroplating solution containing complexing agent, copper salt, chloride salt and free benzothiazole mercapto groups, adopting a specific feeding sequence to ensure the stability of the solution, and carrying out pulse plating and constant-current growth electroplating by taking the modified substrate as a cathode. The invention promotes copper to be uniformly and densely nucleated through the molecular interface layer, replaces silver paste priming, obviously reduces the cost, has strong plating binding force, low resistance and good damp-heat reliability, and is suitable for metallization of bare silicon areas such as fine grids of crystalline silicon solar cells.

Inventors

  • YANG ZIYUAN
  • WANG LINJIE

Assignees

  • 三合镁(深圳)科技有限公司

Dates

Publication Date
20260512
Application Date
20260311

Claims (10)

  1. 1. A direct copper electroplating process without silver paste priming is characterized by comprising the following steps: (1) The substrate pretreatment, namely cleaning a crystal silicon substrate with an open bare silicon area, removing an intrinsic oxide layer by adopting a fluorine-containing system, and then activating by adopting an oxidant; (2) Constructing a directional modification interface layer, namely covalent grafting is carried out on a directional modifier A containing benzothiazole-mercapto sites and having hydrolyzable silane end groups and a pretreated crystalline silicon substrate in a grafting liquid containing alcohol/water, and thermal curing is carried out, so as to obtain a crystalline silicon substrate with localized benzothiazole-mercapto site interface layers; (3) Preparing an electrolytic copper plating electrolyte, namely dissolving a complexing agent in water, adding an alkali source to pre-form salt of the complexing agent, adding free 2-mercaptobenzothiazole, stirring until the solution is clear, adding copper salt in batches, stirring until the complexing is stable, and finally adding chloride salt to obtain the electrolytic copper plating electrolyte; (4) And (3) copper electroplating, namely electroplating copper in an electrolytic solution of copper electroplating by taking a crystalline silicon substrate with a localized benzothiazole-sulfhydryl site interface layer as a cathode, wherein a silver paste priming layer is not formed in the whole process.
  2. 2. The direct copper electroplating process without silver paste priming according to claim 1, wherein in the step (1), the fluorine-containing system is hydrofluoric acid or a buffer ammonium fluoride system, the concentration of the fluorine-containing system is 0.2-5wt%, the treatment time is 10-120 s, the treatment temperature is 15-35 ℃, the oxidant is one or more of hydrogen peroxide, ozone water or a persulfate system, the concentration of the oxidant is 0.01-1wt%, the treatment temperature is 20-60 ℃, and the treatment time is 0.5-10 min.
  3. 3. The direct electrolytic copper plating process without silver paste priming according to claim 1, wherein said orientation modifier a is obtained by reacting 6-amino-2-mercaptobenzothiazole with 3- (triethoxysilylpropyl) isocyanate.
  4. 4. The direct copper plating process without silver paste priming according to claim 1, wherein in the step (2), the alcohol/water volume ratio or the mass ratio of the grafting liquid is 85/15-97/3, the concentration of the orientation modifier A in the grafting liquid is 0.1-1wt%, the grafting temperature is 30-45 ℃, the grafting time is 5-15 min, the heat curing temperature is 100-130 ℃ and the heat curing time is 10-30 min.
  5. 5. The direct electrolytic copper plating process without silver paste priming according to claim 1, wherein said complexing agent in step (3) is one or more of amino acid, amino carboxylate or hydroxycarboxylic acid salt.
  6. 6. The direct copper electroplating process without silver paste priming according to claim 1, wherein the pH of the copper electroplating electrolyte in the step (3) is 8.5-10.5, and the concentration of free 2-mercaptobenzothiazole in the copper electroplating electrolyte is 5-200 mg/L.
  7. 7. The direct copper plating process without silver paste priming according to claim 1, wherein the concentration of the complexing agent in the step (3) is 0.6 to 1.8mol/L, and the concentration of the copper salt is 0.1 to 0.4mol/L.
  8. 8. The direct copper electroplating process without silver paste priming according to claim 1, wherein in the step (3), the chloride salt is NaCl or KCl, and the concentration of the chloride salt in the copper electroplating electrolyte is 20-120 g/L.
  9. 9. The direct copper electroplating process without silver paste priming according to claim 1, wherein the electroplating in the step (4) comprises a plating starting pulse stage and a growing stage, wherein the pulse current density of the plating starting pulse stage is 20-40 mA/cm 2 , the power-on time is 100-1000 ms, the power-off time is 300-3000 ms, the cycle number is 20-200, the growing stage adopts constant current or weak pulse growth, the current density is 8-15 mA/cm 2 , and the electroplating time is 5-20 min.
  10. 10. The direct copper electroplating process without silver paste priming according to claim 1, further comprising post-treatment after copper electroplating in the step (4), wherein a purifying liquid is adopted to treat the electroplated crystal silicon substrate, the purifying liquid comprises an oxidant and an organic acid, the concentration of the oxidant is 0.01-0.5wt%, the concentration of the organic acid is 0.05-2wt%, the treatment temperature is 20-60 ℃, the treatment time is 0.5-10 min, and then annealing is performed under an inert atmosphere, the annealing temperature is 150-250 ℃, and the annealing time is 1-30 min.

Description

Direct copper electroplating process without silver paste priming Technical Field The invention relates to the technical field of electroplating, in particular to a direct copper electroplating process without silver paste priming. Background The metallization of the crystalline silicon solar cell is a key link for improving the photoelectric conversion efficiency, and the core of the metallization is that a high conductive path is formed on the surface of a cell so as to collect and transmit photo-generated charges. Silver paste priming is widely adopted as a pretreatment layer of electroplated copper in the traditional process, and low-resistance connection is realized by utilizing excellent conductivity of silver and ohmic contact characteristics of silver and silicon. However, silver paste priming processes suffer from a number of inherent drawbacks, particularly with respect to cost, interfacial stability and environmental compatibility. Silver is used as noble metal, resources are scarce, price fluctuation is severe, production cost of the solar cell is high, and the requirement of continuous cost reduction of the photovoltaic industry is difficult to meet. The preparation of silver paste involves complex powder dispersion, organic carrier allocation and printing sintering processes, not only increases the process complexity, but also introduces organic residue risks, and influences the interface cleanliness. More critical, the combination of silver paste and the silicon surface mainly depends on physical adsorption and low-temperature eutectic reaction, the interfacial adhesion is weak, stripping is easy to occur under thermal stress or mechanical stress, and the long-term reliability of the electroplated copper layer is limited. During the electrolytic copper plating process, the silver paste primer layer provides initial conductivity, but lattice mismatch and potential difference between silver and copper are easy to cause galvanic corrosion tendency. In the migration and reduction process of copper ions on the silver surface, nucleation sites are unevenly distributed, and an island growth mode tends to be formed, so that the plating layer is insufficient in compactness and coarsening of crystal grains is caused. Such microstructural defects increase contact resistance and become a starting point for current crowding, reducing battery fill factor and maximum output power. In addition, the glass phase component in the silver paste may migrate to the interface, forming an insulating layer, further impeding charge transport. Reliability in hot and humid environments is another serious challenge. Microscopic pores exist at the interface between the silver paste priming layer and silicon, moisture and oxygen are easy to penetrate and cause electrochemical corrosion, and the contact resistance is caused to drift remarkably along with time. The heterogeneous interface of silver and copper is more easy to generate ion migration under high temperature and high humidity to form conductive filaments or cavities, and the accelerated performance is attenuated. The existing technology improves the adhesive force by increasing the thickness of the silver layer or adding alloy elements, but the conductivity is often sacrificed, and the problem of unstable interface cannot be fundamentally solved. In addition, the environmental protection pressure of silver paste priming technology is increasing. The exploitation of silver and the preparation process of sizing agent involve the emission of harmful substances, and the treatment of silver ions in the electroplating waste liquid is complex, thus increasing the environmental burden. The industry tries to adopt a silver-free or silver-reduced scheme, such as directly electroplating copper on the surface of bare silicon, but the inherent oxide layer and hydrophobicity of the bare silicon area make copper nucleation difficult, and the problems of discontinuous plating layer, poor adhesive force and the like are easy to occur. On the premise of not depending on silver paste, stable and low-resistance connection of copper and silicon is realized, and the method becomes a technical bottleneck for solar cell metallization. Disclosure of Invention In view of the above, the present invention aims to provide a direct copper electroplating process without silver paste priming, so as to realize stable and low-resistance connection between copper and silicon on the premise of not depending on silver paste. Based on the above object, the invention provides a direct copper electroplating process without silver paste priming, comprising the following steps: (1) The substrate pretreatment, namely cleaning a crystal silicon substrate with an open bare silicon area, removing an intrinsic oxide layer by adopting a fluorine-containing system, and then activating by adopting an oxidant; (2) Constructing a directional modification interface layer, namely covalent grafting is carried out on a