Patent Application
20250075330
The invention relates to an electroless copper plating solution. More specifically the present invention relates to high rate electroless copper plating solution usable for formation of electro-conductive copper layers on the surface of insulators (polymeric articles, ceramic articles, or the like) semiconductors (silicon, solar cells or the like).
Electroless copper deposition is an autocatalytic process, where electrons appearing during the anodic oxidation of the reducing agent reduce copper (II) ions to metallic copper on the surface to be plated. Most popular used reducing agent for such system is formaldehyde. Since formaldehyde reduces copper(II) to metallic state only in alkaline solutions, complexing agents forming stable copper(II) complexes are needed with the aim to prevent precipitation of copper(II) hydroxide. The electroless copper deposition process is highly dependent on various parameters of the plating solution, e. g. temperature, pH, nature and concentration of electroless plating solution components.
The literature survey suggest that the electroless copper deposition rate to a great extent depends on the nature of the ligand used. When investigating the electroless copper deposition process at ambient temperature, it was found that the comparatively highest plating rates up to 9 μm/h were obtained using Quadrol as copper(II) ligand (E. Norkus, J. Solid State Electrochem. 2000), wheras in the case of DL-tartrate the plating rate is lover and do not exceed 8 μm/h (E. Norkus, J. Solid State Electrochem. 2000; A. Vaskelis, Electrochim. Acta 2004; E. Norkus, Chemija 2012). Using EDTA (ethylenediamine tetraacetic acid), probably, the most usable ligand for electroless copper deposition processes, copper plating rate was found to be lower and equal to 3-5 μm/h (A. Vaskelis, J. Electroanal. Chem. 2007). Application of the environmentally friendly polyhydroxylic copper(II) ligands results in lower copper plating rates comparing to above-mentioned. The following electroless copper plating rates were obtained: 1.5 μm/h, 2 μm/h and 2.5 μm/h, when using D-sorbitol, D-mannitol and xylitol, respectively (E. Norkus, J. Appl. Electrochem. 2005). When using pyridine-2,6-dicarboxylic acid and 4-hydropyridine-2,6-dicarboxylic, the plating rates were also not high enough, i. e. 2.5 μm/h and 3.5 μm/h, respectively (E. Norkus, Electrochim. Acta 2006). U.S. Pat. No. 9,869,026B2 describes electroless copper plating compositions using different reducing agents. The use of different reducing agents and copper(II) ligands result room temperature plating rates lower than 10 μm/h, therefore the electroless copper plating rate to low for high rate technological processes. The other disadvantage of the known method is that the compositions contain an additional additives, that make electroless copper deposition process more complicated.
The closest prior art document CN109457238A discloses the use of potassium sodium tartrate as copper(II) ligand in electroless copper plating solutions. The plating rate of ca. 10 μm/h was reached. The known method has several disadvantages: 1) the electroless copper plating rate to low for high rate technological processes; 2) the electroless copper plating solutions contain an additional additives, that make electroless copper deposition process more complicated.
In our invention a new type copper(II) ligand is suggested, namely, diisopropanolamine. Using this copper(II) ligand, for the first, the proposed solution for electroless copper deposition enables to deposit at least 30 μm thick (or more) copper coatings in one hour at ambient temperature (favourable for technological processes). Second, the solution is stable and exhibit high copper plating rate without the use of any additional additives (no accelerating and stabilizing additives are needed).
At ambient temperature the copper deposition rate of known electroless copper solutions do not exceed ca. 2-10 μm/h. For the technical purposes such plating rate is to low, especially when thicker coatings are required. Therefore the aim of the invention is to create composition of electroless copper plating solution, which allows to obtain higher electroless copper plating rates.
To achieve the foregoing and in accordance with the purpose of the present invention, a solution for electroless deposition of copper is provided. A new type of copper(II) ligand is suggested, namely, diisopropanolamine. Using this copper(II) ligand, for the first, the proposed solution enables to deposit at least 30 μm thick (or more) copper coatings in one hour at ambient temperature (favourable for technological processes). Second, the solution is stable without the use of any addition additives (no accelerating and stabilizing additives are needed). Third, using proposed solution more than 98% of initial copper(II) content can be reduced to metallic copper coating in 1.5 hours (environmental advantage). Fourth, the solution can be replenished and repeatedly used manyfold (favourable for technological processes and environment).
The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements and in which:
An invention is described for providing improved formulations of high plating rate electroless copper deposition solutions. The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
It is generally agreed, that electroless metal deposition processes are based upon simple electron transfer concepts. The processes involve placing of the article to be plated into an electroless metal plating bath, then inducing the metal ions in the solution to accept electrons from the reducing agent resulting in the deposition of the reduced metal onto the surface to be plated. The success of the of the electroless metal deposition process is highly dependent upon the various physical (e. g., temperature, etc.) and chemical (e. g. pH, reagents, etc.) parameters of the plating solution.
As used herein, a reducing agent is a compound in an oxidation-reduction reaction that reduces an other compound. In doing so, the reducing agent becomes oxidized. That is, the reducing agent is an electron donor that donates electrons to the compound to be reduced.
A complexing agent (i. e. chelator or chelating agent) is any chemical compound that can be utilized to reversibly bind to compounds to form a complex. Such kind of complexing agents forming complexes are necessary in the case of alkaline electroless copper plating solutions and they prevent precipitation of copper(II) hydroxide (Cu(OH)2).
A copper plating solution for use in electroless copper deposition applications is disclosed below. The components of the solution are a copper source—copper(II) salt, a secondary amine complexing agent, a reducing agent and pH modifying substance.
In one embodiment, the copper(II)salt is a simple salt, e. g. copper(II) sulphate (CuSO4). It should be appreciated that essentially any simple salt of copper(II) can be used in solution so long as the salt can be effectively solubilized into solution, be complexed by complexing agent, and reduced by a reducing agent in an alkaline environment to result in deposition of the reduced copper onto the surface to be plated. Preferably, the concentration of copper sulphate (CuSO4) is between about 0.005 mol/L to a solubility limit of the aqueous copper sulphate (CuSO4) component. More preferably, the concentration of copper sulphate (CuSO4) is between about 0.05 mol/L to about 0.5 mol/L. Most preferably, the concentration of copper sulphate (CuSO4) is between about 0.1 mol/L to about 0.15 mol/L.
In one embodiment a secondary amine complexing agent is diisopropanolamine ((CH3CH(OH)CH2)2NH). Preferably, the concentration of complexing agent diisopropanolamine ((CH3CH(OH)CH2)2NH) is from about 0.1 mol/L to about 3 mol/L. More preferably, the concentration of complexing agent diisopropanolamine ((CH3CH(OH)CH2)2NH) is from about 0.15 mol/L to about 2 mol/L. Most preferably, the concentration of complexing agent diisopropanolamine ((CH3CH(OH)CH2)2NH) is from about 0.2 mol/L to about 1 mol/L.
In one embodiment the reducing agent is formaldehyde (CH2O). Preferably, the concentration of reducing agent formaldehyde (CH2O) is from about 0.1 mol/L to about 4 mol/L. More preferably, the concentration of reducing agent formaldehyde (CH2O) is from about 0.15 mol/L to about 3 mol/L. Most preferably, the concentration of reducing agent formaldehyde (CH2O) is from about 0.3 mol/L to about 2 mol/L.
In one embodiment the pH modifying substance is a mixture of disodium carbonate (Na2CO3) and sodium hydroxide (NaOH). Preferable the concentrations of pH modifying substances are from about 0.05 mol/L to about 1.0 mol/L for disodium carbonate (Na2CO3) and from about 0.1 mol/L to about 3.0 mol/L for sodium hydroxide (NaOH). More preferable, the concentrations of pH modifying substances are from about 0.1 mol/L to about 0.8 mol/L for disodium carbonate (Na2CO3) and from about 0.2 mol/L to about 2.0 mol/L for sodium hydroxide (NaOH). Most preferable, the concentrations of pH modifying substances are from about 0.2 mol/L to about 0.5 mol/L for disodium carbonate (Na2CO3) and from about 0.3 mol/L to about 1.0 mol/L for sodium hydroxide (NaOH).
In one embodiment the electroless copper plating solution is prepared by sequentially combining the aqueous copper sulphate (CuSO4) salt component to a volume of water, then adding the complexing agent diisopropanolamine ((CH3CH(OH)CH2)2NH) to the aqueous copper sulphate (CuSO4) salt component/water combination, thereafter adding the pH modifying substance (NaOH and Na2CO3), and lastly adding the aqueous reducing agent component (CH2O). A pH of electroless copper plating solution is over 13.
In one embodiment the electroless copper plating solution is operated without additional stabilizing additives, whereas the stabilization of the electroless copper plating solution is obtainable by means of the bubbling of air through the solution.
This embodiment of the invention provides the preparation procedure of the roughed glass sheet surface before the electroless copper plating. For the first, the roughed glass sample was degreased in an 50-90% solution of C2H5OH in ultrasound bath for 10 min. A 1 g/L SnCl2 solution was used for sensitization, to which a roughed glass sheet was immersed for one minute. After that, the roughed glass sheet was immersed into deionized water, where Sn(II) hydrolysis was carried out for 3 min. The glass was washed with deionized water and for activation purpose maintained for 1 min in a PdCl2 solution with a concentration of 1 g/L, then thoroughly twice washed with deionized water. This sensitization and activation procedure can be performed several (two, three) times. Finally, the prepared roughed glass sheet was immersed into the electroless copper deposition solution.
Although a few embodiments of the present invention have been described in detail herein, it should be understood, by those of original skill, that the present invention may by embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative but not restrictive, and the invention is not to be limited to the details provided herein, but may be modified and practiced within the scope of the appended claims.
The following numbered clauses present some embodiments and combinations thereof. Further features from the specification may be combined with one or more of the items.
Clause 1. An electroless copper plating solution, comprising:
Clause 2. The electroless copper plating solution, according to clause 1, wherein, the copper source is copper sulphate (CuSO4).
Clause 3. The electroless copper plating solution, according to clauses 1-2, wherein, the secondary amine complexing agent is diisopropanolamine ((CH3CH(OH)CH2)2NH).
Clause 4. The electroless copper plating solution, according to clauses 1-3, wherein, the reducing agent is formaldehyde (CH2O).
Clause 5. The electroless copper plating solution, according to clauses 1-4, wherein, the pH modifying substance is a mixture of disodium carbonate (Na2CO3) and sodium hydroxide (NaOH).
Clause 6. The electroless copper plating solution, according to clauses 1-5, wherein, a pH of electroless copper plating solution is more than 13.
Clause 7. The electroless copper plating solution, according to clause 2, wherein, the concentration of sulphate (CuSO4) is between about 0.05 mol/L to a solubility limit of the aqueous copper sulphate (CuSO4) component.
Clause 8. The electroless copper plating solution, according to clause 3, wherein, the concentration of secondary amine complexing agent diisopropanolamine ((CH3CH(OH)CH2)2NH) is from about 0.1 mol/L to about 3 mol/L.
Clause 9. The electroless copper plating solution, according to clause 4, wherein, the concentration of reducing agent formaldehyde (CH2O) is from about 0.1 mol/L to about 4 mol/L.
Clause 10. The electroless copper plating solution, according to clause 5, wherein, the concentrations of pH modifying substances are from 0.05 mol/L to 1.0 mol/L for disodium carbonate (Na2CO3) and from 0.1 mol/L to 3.0 mol/L for sodium hydroxide (NaOH).
Clause 11. The electroless copper plating solution, according to clause 1, wherein, the electroless copper plating solution is prepared by sequentially combining the copper source component to a volume of water, then adding the complexing agent to the aqueous copper source component/water combination, thereafter adding the pH modifying substance, and lastly adding the aqueous reducing agent component.
Clause 12. The electroless copper plating solution, according to clause 11, wherein, the electroless copper plating solution is prepared by sequentially combining the aqueous copper sulphate (CuSO4) salt as copper source component to a volume of water, then adding diisopropanolamine ((CH3CH(OH)CH2)2NH) as complexing agent to the aqueous copper sulphate (CuSO4) salt component/water combination, thereafter adding NaOH and Na2CO3 as the pH modifying substances, and lastly adding the CH2O as aqueous reducing agent component.
Clause 13. The electroless copper plating solution, according to clauses 1-11, wherein, the electroless copper plating solution is operated without additional stabilizing additives.
Clause 14. The electroless copper plating solution, according to clause 13, wherein the stabilization of the electroless copper plating solution is obtainable by means of the bubbling of air through the solution.
Clause 15. The electroless copper plating solution, according to clauses 1-14, wherein, the electroless copper plating solution is operated at ambient temperature.
Clause 16. The electroless copper plating solution, according to clauses 1-15, wherein, the composition of electroless copper plating solution comprises as follows: copper source is CuSO4 and is provided at concentration 0.11 mol/L, complexing agent is diisopropanolamine and is provided at concentration 0.2 mol/L, reducing agent is formaldehyde and is provided at concentration 0.38 mol/L, pH modifying substances (Na2CO3 and NaOH)-0.26 mol/L and 0.5 mol/L, respectively.
Clause 17. The electroless copper plating solution, according to clauses 1-15, wherein, the electroless copper plating solution enables depositing at least 30 μm thick (or more) copper coatings per one hour.
Clause 18. The electroless copper plating solution, according to clauses 1-16, wherein, the electroless copper plating solution enables reducing more than 98% of the initial copper(II) content to metallic copper coating in 1.5 hours.
Clause 19. The electroless copper plating solution, according to clauses 1-18, wherein, the electroless copper plating solution after electroless copper deposition can be replenished and repeatedly used.
E. Norkus, V. Kepeniene, I. Stalnioniene. “Application of environment-friendly ligands for alkaline electroless copper plating systems: A comparative study of electroless copper deposition using D-,L- and DL-tartrate as Cu(II) ligands.” Chemija 2012, vol. 23, N 3, pp. 155-170.
