CN103668356B - Fe is added in copper-connection copper sulfate bath 2+and Fe 3+electro-plating method - Google Patents

Abstract

The invention relates to an electroplating method for adding Fe ²⁺ and Fe ³⁺ to copper interconnected copper sulfate plating solution, comprising the following steps: placing a silicon chip with a TSV through hole in the pretreatment solution for ultrasonic pretreatment; The silicon wafer is immersed in an acidic copper sulfate electroplating solution containing Cu ²⁺ , Cl ^- and sulfuric acid; the additives PEG, SPS, JGB and Fe ²⁺ /Fe ³⁺ redox couple are pre-mixed and allowed to stand to obtain Pre-mixed additive solution, inject the pre-mixed additive solution into the acidic copper sulfate electroplating solution, after stirring and mixing, electroplating is performed under a constant working current, and at the same time, the electroplating solution is passed through a high-purity Electrolyzer for copper pellets. In the present invention, Fe ²⁺ /Fe ³⁺ redox pair is combined with PEG and SPS in the plating solution, thereby accelerating the deposition rate of copper inside the through hole and effectively inhibiting the deposition of copper on the surface, thereby realizing defect-free filling and reducing The thickness of copper plating on the surface is convenient for subsequent processing.

Description

The electroplating method of adding Fe2+ and Fe3+ in the copper sulfate plating solution for copper interconnection

technical field

The invention belongs to the technical field of electronic packaging, and in particular relates to an electroplating method for adding Fe ²⁺ and Fe ³⁺ to a copper sulfate plating solution for copper interconnection.

Background technique

TSV three-dimensional stack packaging based on through-silicon vias is an inevitable trend in the development of packaging technology. At present, the research focus of TSV through-hole filling has shifted from non-porous filling to high-speed, high-quality, and low-cost filling. In the electroplating process, it faces a series of problems caused by the oxidation consumption of additives, inclusions and copper anodes. The Fe ²⁺ /Fe ³⁺ redox pair can control the electrode potential, prevent the oxidation and inclusion of additives, make the application of inert electrodes possible, reduce the phosphorus content in the plating solution, and reduce impurities; and through the control of Fe ³⁺ concentration, the use of through holes The difference in internal and external current efficiency can improve the overfilling ability of the plating solution and reduce the use of additives. However, the effect of redox on other organic additives in TSV through-hole plating, and the effect on through-hole filling and coating quality still need to be further studied. In the process of the present invention, by studying the influence of Fe ²⁺ /Fe ³⁺ on electrode process kinetics, additive action and coating performance, especially the stress, the relationship between coating stress and impurities is clarified, the superfilling ability of the plating solution is improved, and the Plating reliability, lower costs.

Contents of the invention

Aiming at the above-mentioned problems that existing copper plating filling technology exists, the present invention provides a kind of electroplating method that adds Fe ²⁺ and Fe ³⁺ in copper interconnect copper sulfate bath, the present invention has increased Fe ²⁺ in plating bath The /Fe ³⁺ redox pair is combined with PEG and SPS to accelerate the deposition rate of copper inside the through hole and effectively inhibit the deposition of copper on the surface, thereby achieving defect-free filling and reducing the thickness of copper plating on the surface to facilitate subsequent processing.

The present invention is achieved by the following technical scheme, a kind of electroplating method that adds Fe ²⁺ and Fe ³⁺ in copper interconnect copper sulfate bath, it is characterized in that, comprises the following steps:

Step (1) Place the silicon wafer with TSV through holes in the pretreatment solution for ultrasonic pretreatment;

Step (2) immersing the pretreated silicon wafer into an acidic copper sulfate electroplating solution containing Cu ²⁺ , Cl ^- and sulfuric acid, the pH of the acidic copper sulfate electroplating solution is 0-4;

Step (3) Premix the additives PEG, SPS, JGB and Fe ²⁺ /Fe ³⁺ redox pair, let stand to obtain a premixed additive solution, inject the premixed additive solution into the acidic copper sulfate In the electroplating solution, after stirring and mixing, electroplating is carried out under a constant working current, and at the same time, the electroplating solution is passed through an electrolytic cell filled with high-purity copper particles during the electroplating process.

Preferably, in step (1), the ultrasonic pretreatment time is 2 minutes.

Preferably, in step (2), the acidic copper sulfate electroplating solution has a Cu ²⁺ concentration of 35 g/L, a Cl ⁻ concentration of 50 ppm, and a sulfuric acid concentration of 0.6 mol/L.

Preferably, in step (3), the standing time after premixing the additives PEG, SPS, JGB and Fe ²⁺ /Fe ³⁺ redox pair is 3 hours.

Preferably, in step (3), the electroplating process is performed at a constant working current of 10mA/cm ² , which increases the Fe ²⁺ /Fe ³⁺ redox pair and reduces the copper ion deposition current on the surface of the cathode, thereby reducing Reduced deposition rate of copper ions around TSV via openings.

Preferably, in step (3), an insoluble inert electrode with a fixed size is used in the electroplating process, which avoids the introduction of impurities by using an electrolytic copper anode.

Preferably, during the electroplating process, the plating solution passes through an electrolytic cell equipped with high-purity copper particles to supplement the consumed copper ions and Fe ²⁺ ions to prolong the life of the electroplating solution.

More preferably, the impurities in the deposited copper are reduced, and the internal stress of the plating layer is reduced to below 10 MPa, so as to obtain a TSV interconnection device with more stable performance.

Compared with the prior art, the beneficial effects of the present invention are as follows: compared with the plating solution that does not contain Fe ²⁺ /Fe ³⁺ redox pair, because Cu ²⁺ is passed through the electrolytic cell that contains high-purity copper particle by plating solution Fe ³⁺ reacts with Cu to produce, so the insoluble anode with fixed size can be used in the method of the present invention, can prevent like this because soluble copper anode can introduce phosphorus-containing impurity in the dissolution process, simultaneously because Fe ²⁺ /Fe ³⁺ It can reduce the use of accelerators, thereby ensuring that the obtained deposited copper contains less impurities, which increases the stability of performance and reduces the stress of the coating, ensuring that the stress of the coating is below 10MPa; due to Fe The reduction of ³⁺ to Fe ²⁺ on the cathode surface consumes electrons, which reduces the copper ion deposition current on the silicon surface around the TSV through hole, which leads to a thinner copper film deposited on the surface around the through hole, and because of the transfer of Fe ³⁺ It is mainly controlled by diffusion, so the deposition rate inside the TSV through hole is not affected, which facilitates Cu ²⁺ and facilitates the subsequent chemical polishing process. The existence of Fe ²⁺ /Fe ³⁺ redox pair thins the surface copper film and enables defect-free filling of larger diameter via holes.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

This embodiment relates to a TSV electroplating method under the condition of a fixed electrode, comprising the following steps:

Step (1) Preparation of silicon wafers with TSV through holes: firstly, deep reactive ion etching (DeepReactiveIonEtch, DRIE) is used to make through holes of a certain size, and then plasma-enhanced chemical vapor deposition (PECVD) is used to deposit an insulating layer. The deposition material used is silicon nitride or silicon dioxide (SiNx or SiO ₂ ), followed by a barrier layer (TiN or TaN) deposited by metalorganic chemical vapor deposition (MOCVD) to prevent the diffusion of copper to the silicon substrate, and finally Deposit the seed layer (Cu) by chemical vapor deposition (CVD) or physical vapor deposition (PVD);

Step (2) Ultrasonic treatment of the silicon wafer with TSV through holes in the pretreatment solution for 2 minutes;

Step (3) Immerse the pretreated silicon wafer into the acidic copper sulfate electroplating solution containing Cu ²⁺ concentration of 35g/L, Cl ^- concentration of 50ppm, and sulfuric acid concentration of 0.6mol/L. The state of existence plays a vital role. When the pH value is between 0-4, the solution exists as divalent copper ions under positive potential;

Step (4) Pre-mix the following additives, including: 300ppm PEG (polyethyleneglycol), 3ppmSPS (bis-(3-sulfopropyl)disulfide), 20ppmJGB (leveler), 50ppmCl ^- , 0.5g/LFe ²⁺ and 0.024g/ LFe ³⁺ , where Fe ²⁺ and Fe ³⁺ are added through FeSO ₄ 7H ₂ O and Fe ₂ (SO ₄ ) ₃ to obtain a pre-mixed additive mixture; add the pre-mixed additive mixture to the electroplating In the solution, after sufficient stirring and mixing, under the condition of fixed electrodes, under the constant working current of 10mA/cm ² , the insoluble inert electrode with fixed size is used for electroplating, and the electrode potential is -150mV. During the electroplating process, let the plating solution Pass through an electrolytic cell filled with high-purity copper particles.

Example 2

This embodiment relates to a TSV electroplating method under the condition of a rotating disk electrode (RDE), comprising the following steps:

Step (1) Preparation of silicon wafers with TSV through holes: firstly, deep reactive ion etching (DeepReactiveIonEtch, DRIE) is used to make through holes of a certain size, and then plasma-enhanced chemical vapor deposition (PECVD) is used to deposit an insulating layer. The deposition material used is silicon nitride or silicon dioxide (SiNx or SiO ₂ ), followed by a barrier layer (TiN or TaN) deposited by metalorganic chemical vapor deposition (MOCVD) to prevent the diffusion of copper to the silicon substrate, and finally Deposit the seed layer (Cu) by chemical vapor deposition (CVD) or physical vapor deposition (PVD);

Step (2) Ultrasonic treatment of the silicon wafer with TSV through holes in the pretreatment solution for 2 minutes;

Step (3) Immerse the pretreated silicon wafer into the acidic copper sulfate electroplating solution containing Cu ²⁺ concentration of 35g/L, Cl ^- concentration of 50ppm, and sulfuric acid concentration of 0.6mol/L. The state of existence plays a vital role. When the pH value is between 0-4, the solution exists as divalent copper ions under positive potential;

Step (4) Pre-mix the following additives, including: 300ppm PEG (polyethyleneglycol), 3ppmSPS (bis-(3-sulfopropyl)disulfide), 20ppmJGB (leveler), 50ppmCl ^- , 12g/LFe ²⁺ and 0.5g/LFe ³⁺ , wherein Fe ²⁺ and Fe ³⁺ are added through FeSO ₄ 7H ₂ O and Fe ₂ (SO ₄ ) ₃ to obtain a pre-mixed additive mixture; adding the pre-mixed additive mixture to the electroplating In the solution, after sufficient stirring and mixing, under the condition of rotating disk electrode (RDE), electroplating is carried out with an insoluble inert electrode with fixed size at a constant working current of 10mA/ ^cm2 , and the rotating speed of the rotating disk electrode is 900rpm ( At this time, 9% of the working current is consumed by the reduction reaction of Fe ³⁺ into Fe ²⁺ ), and the electrode potential is -50mV. During the electroplating process, the electroplating solution is passed through the electrolytic cell filled with high-purity copper particles.

Implementation Effect

According to embodiment 1 and embodiment 2, this method requires additive to add in the electroplating solution after premixing for a period of time according to the ratio that needs to add, because there is following reaction between Fe ²⁺ and copper ion and SPS and Fe ²⁺ :

2MPS+2Cu ²⁺ →SPS+2H ⁺ +2Cu ⁺ (3)

$\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; MPS</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Right\; Arrow;</span>\mathrm{<span\; class="notranslate">\; SPS</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

The deposition rate of copper is accelerated by increasing the concentration of Cu ⁺ through reaction (1), because the mass transfer rate of Fe ²⁺ is controlled by diffusion, and the experimental acceleration has a maximum value. MPS produced by reaction (2) accelerates the effect faster than SPS. Reaction (2)-(4) can consume Fe ²⁺ to keep the amount of MPS in the solution constant, and at the same time, Fe ²⁺ can be continuously produced through the reaction of Fe ³⁺ with high-purity copper particles and there is a part of Fe ²⁺ in the cathode Therefore, the deposition rate of copper inside the via can be accelerated. Experimental research shows that Fe ²⁺ /Fe ³⁺ has basically no effect on the reaction of SPS at the deposition surface, mainly on the composition of the electrolyte, that is, the balance of MPS.

According to Embodiment 1 and Embodiment 2, under the condition of rotating electrode, the electrode overpotential is reduced, because the mass transfer effect of iron ion is accelerated under the condition of rotating electrode, the electrode overpotential is reduced, and the copper at the through hole can be better suppressed. ion deposition.

In the electroplating process of the method of the present invention, the electroplating solution is allowed to pass through the electrolytic tank equipped with high-purity copper particles, and in this process, Fe ³⁺ and copper particles undergo redox reactions to generate Fe ²⁺ and Cu ²⁺ , thereby realizing The balance between the generation and consumption of iron ions is achieved, and the generated copper ions can supplement the consumption of copper ions in the plating solution, thereby prolonging the service life of the plating solution.

Since the Fe ²⁺ /Fe ³⁺ redox pair can slow down the deposition of copper ions at the opening of the through hole, and at the same time accelerate the deposition rate of copper ions inside the through hole, the use of additives can be reduced.

In the method of the present invention, the disadvantage of introducing phosphorus-containing impurities by using anode copper is avoided by using an inert electrode and passing the plating solution through high-purity copper particles. Since the use of Fe ²⁺ /Fe ³⁺ can reduce the consumption of additives, the use of additives can also reduce the use of purer copper, which contains less impurities to obtain devices with more stable performance, and can also reduce the coating stress to below 10MPa .

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (6)

1. a kind of electroplating method that adds ^Fe and ^Fe in copper interconnect copper sulfate bath, it is characterized in that, may further comprise the steps: Step (1) placing the silicon wafer with the TSV through hole in the pretreatment liquid for ultrasonic pretreatment; Step (2) immersing the pretreated silicon wafer into an acidic copper sulfate electroplating solution containing Cu ²⁺ , Cl ⁻ and sulfuric acid, the pH of the acidic copper sulfate electroplating solution is 0-4; Step (3) Premix the additives PEG, SPS, JGB and Fe ²⁺ /Fe ³⁺ redox pair, let it stand to obtain a premixed additive solution, inject the premixed additive solution into the acidic copper sulfate In the electroplating solution, after stirring and mixing, electroplating is carried out under a constant working current, and at the same time, the electroplating solution is passed through the electrolytic cell filled with high-purity copper particles during the electroplating process; In the premixed additive solution, the concentration of the additive is 300ppmPEG, 3ppmSPS, 20ppmJGB, 0.5g/LFe ²⁺ and 0.024g/LFe ³⁺ ; In step (3), the standing time after premixing the additives PEG, SPS, JGB and Fe ²⁺ /Fe ³⁺ redox pair is 3 hours; In step (3), the electroplating process is performed under a constant working current of 10mA/cm ² , which increases the Fe ²⁺ /Fe ³⁺ redox pair and reduces the reduction reaction on the cathode surface to reduce the copper ion deposition current, thereby reducing the TSV Deposition rate of copper ions around via openings. 2. The electroplating method according to claim 1, characterized in that, in step (1), the time of the ultrasonic pretreatment is 2min. 3. electroplating method according to claim 1, is characterized in that, in step (2), the ^Cu of described acidic copper sulfate electroplating solutionConcentration is 35g/L, ^{ClConcentration} is 50ppm, sulfuric acid concentration is 0.6mol /L. 4. The electroplating method according to claim 1, characterized in that, in step (3), the electroplating process adopts an insoluble inert electrode with fixed size, which avoids the introduction of impurities by using electrolytic copper anodes. 5. electroplating method according to claim 1, is characterized in that, plating solution is by the electrolyzer that high-purity copper particle is housed in the electroplating process, supplements the copper ion of consumption and Fe ²⁺ ion, prolongs the electroplating solution life-span. 6. The electroplating method according to claim 5, characterized in that the impurities in the deposited copper are reduced, and the internal stress of the coating is reduced to below 10MPa, thereby obtaining a TSV interconnection device with more stable performance.