KR20090075571A - Autocatalytic-type electroless ni-p-co plating solution and method for producing thereof - Google Patents

Abstract

Autocatalytic-type electroless Ni-P-Co plating solution and a method for preparing the same are provided to perform selective plating directly on the copper surface, excluding a pre-treating process for activation of precious metal. Autocatalytic-type electroless Ni-P-Co plating solution comprises nickel sulfate as nickel chloride, sodium hypophosphite as reductant, cobalt sulfate as cobalt chloride, complexing agent selected from the group consisting of adipic acid, lactic acid and their compound, and ionized palladium.

Description

Autocatalytic-type electroless Ni-P-Co plating solution and method for producing etc.

The present invention relates to a self-catalyzed electroless plating solution, and more particularly, to a selective electroless nickel-in-cobalt (Ni-P-Co) tertiary alloy plating solution that can be plated by autocatalytic reaction without activation on a copper substrate. .

Due to the high integration of semiconductors and electronic components, the line width of metal wirings is becoming finer and the current density is rapidly increasing, which causes a problem of electromigration phenomenon.

In semiconductor wiring materials, this problem can be solved by forming a very thin capping layer using hard mask-type SiCN and SiN, but it prevents an increase in the interlayer electrical resistance due to the narrower line width in the future. The trend is to use an electroless metal cladding technology that can further reduce the low-k value of, while mechanically suppressing the occurrence of hillocks due to EM (stress migration) or stress migration (SM).

Nickel-borane alloys in the electroless alloy coating layer that can improve the characteristics of suppressing EM phenomena have strong reducing power of the alloys. Therefore, when nickel alloy plating on copper base is possible, plating is possible directly on copper base without activation treatment. This strong, poor stability and the plated coating has the property of breaking due to high stress. Therefore, in order to remedy these disadvantages, a plating solution using sodium hypophosphite as a reducing agent has been developed. Thus, when sodium hypophosphite is used, a pretreatment process for activating a copper material is required because the reducing power is lower than that of borane compounds. .

In other words, copper does not act as a catalyst for the electroless nickel reaction, so a chemical activation process must be preceded. Such a surface metal capping layer formation technique is a site other than wiring by a precious metal catalyst activation process in a pretreatment process. That is, the residue is left in the space to contaminate the surface, or may be locally coated to cause contamination problems.

Therefore, there is a need in the market for the development of an electroless alloy plating technique that eliminates the pretreatment process, which selectively forms a coating layer on a fine line width wiring. This technique is called self-aligned electroless plating, and it is possible to form a coating layer successfully even at a 45nm ultrafine structure.

Under this background, the present inventors use borane compounds having strong reduction reactions but problems in toxicity and stability as reducing agents in order to selectively form an electroless coating layer on a metal surface material for improving EM properties and decreasing resistance. Instead of nickel-boron-cobalt (Ni-B-Co) alloys, we developed nickel-in-cobalt (Ni-P-Co) ternary alloy plating solutions, and in case of using such plating solutions, the pretreatment process for noble metal catalyst activation such as palladium is omitted. The present invention was completed by confirming that a plated material of excellent quality could be obtained by selectively plating a copper surface directly.

It is an object of the present invention to provide an electroless nickel- phosphorus-cobalt plating solution which is capable of selectively plating a copper surface directly, omitting the precious metal catalyst activation pretreatment process.

Still another object of the present invention is to provide a method for plating using the plating solution.

As one aspect for achieving the above object, the present invention relates to an electroless nickel- phosphorus-cobalt plating solution containing nickel sulfate as the nickel salt, sodium hyposulfite as the reducing agent and cobalt sulfate as the cobalt salt.

Nickel sulfate used as the nickel salt is preferably used 22 to 30g / l. If the concentration of nickel sulfate is 22 g / l or less, the plating rate is lowered. If it is 30 g / l or more, the plating rate is increased but decomposition of the plating liquid is likely to occur.

In addition, the reducing agent is for reducing nickel ions, and generally, materials which may be used as reducing agents include sodium hypophosphite, sodium borohydride, dimethylamine borane, diethylamine borane and hydrazine, but in the present invention, sodium hypophosphite Use In a preferred embodiment, sodium hypophosphite is used at 20-50 g / l.

In the present invention, cobalt sulfate is used as the cobalt salt, and 5 to 10 g / l is preferably used.

In a preferred embodiment, the plating liquid of the present invention may further include a complexing agent. The complexing agent controls the plating speed and prevents spontaneous decomposition of the plating. In the present invention, a complexing agent includes a material selected from adipic acid, lactic acid, dried acid and a mixture of two or more thereof. The amount of these complexing agents used is 5-20 g / l for adipic acid and 5-25 g / l for lactic acid.

In another preferred embodiment, the plating liquid of the present invention may further include ionized palladium. The ionized palladium is preferably contained in 1g to 5g per 100ml of solvent. In addition, palladium chloride may be used when palladium is added as a catalyst in the present invention. In this case, when palladium chloride is directly added to the plating liquid, the plating liquid is liable to self-decompose, so that the palladium chloride is dissolved in a solvent and then added to the plating liquid in ionic form. Add. In one specific embodiment, the inventors dissolved 1 g of palladium chloride in 100 ml of distilled water and added it to the plating solution.

The nickel-phosphorus cobalt plating liquid according to the present invention exhibits a pH of about 5.5 to 6.5 when titrated with ammonia water, and functions at a temperature of 80 to 95 ° C. during plating, and is stable without self decomposition.

In addition, when plating using the plating solution according to the present invention, it can be plated directly without a palladium activation treatment to enable the formation of fine crystal grains on a copper base, etc., the nickel-in-cobalt plating solution of the present invention In addition to improving the disadvantage that a film having poor adhesion due to high stress, which is a disadvantage of a nickel-borane-cobalt plating solution using a borane having a high reducing power, was used, an activation treatment process using a precious metal such as palladium, which is required in the past, is required. Since it is possible to directly reduce the plating using the autocatalytic reaction without going through, it is possible to improve the contamination problem that may occur in the activation pretreatment process.

The nickel-phosphorus cobalt plating liquid of the present invention may include, in addition to the above components, additives such as a brightening agent and a pH adjusting agent for gloss of the plating film as necessary.

In another aspect, the present invention relates to a plating method using the plating liquid. The plating method according to the present invention may use a process of an electroless nickel plating bath using known sodium hypophosphite, but an activation pretreatment process using a noble metal such as palladium is removed from these processes.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited by these examples.

Example  : According to the present invention Electroless  Preparation of Nickel-In-Cobalt Plating Solution and Comparison of Plating Performance with Conventional Plating Solutions

(1) according to the present invention Electroless  Preparation of Nickel-In-Cobalt Plating Solution

The electroless nickel plating solution according to the present invention includes nickel sulfate 22-30 g / l as a nickel salt, 20-50 g / l sodium hypophosphite as a reducing agent, cobalt sulfate 5-10 g / l as a cobalt salt, and adipic acid 5-5 as a complexing agent. 20 g / l and 5 to 25 g / l lactic acid were mixed to prevent spontaneous decomposition of the electroless nickel plating solution and to control the reaction so that a reduction reaction occurred only on selective surfaces. In addition, a certain amount of additives (thallium in this embodiment) was mixed for the gloss and high roughness of the plating film. In addition, a plating solution was prepared by adding palladium as a catalyst for causing a self-catalytic reaction in the plating solution to a plating solution in the form of palladium chloride, and when palladium chloride was directly added to the plating solution, the plating solution was easily decomposed by 1 g of chloride. Palladium was dissolved in 100 ml of distilled water to make an ionic form and then added to the plating solution. At this time, the temperature of the plating liquid was adjusted to 75 to 90 ℃, the pH of the plating liquid was kept constant at 5.0 to 7.0. Table 1 shows the composition and process conditions of the electroless nickel-phosphorus-cobalt plating solution.

Plating amount Metal salt Nickel Sulfate (NiSO ₄ ) 22 ~ 30g / ℓ Cobalt Sulfate (CoSO ₄ ) 5 ~ 10g / ℓ reducing agent Sodium hypophosphite (NaH ₂ PO ₂ ) 25-50g / ℓ Complexing agent Adipic acid 5 ~ 20g / ℓ Lactic acid 5 ~ 25g / ℓ additive Tl 0.5 ~ 5ppm catalyst Pd 0.1 ~ 0.5ppm Temperature 75 ~ 90 ℃ pH 5.0 ~ 7.0

(2) Comparison of Plating Performance of Plating Solution and Existing Plating Solution According to the Present Invention

In order to examine the plating performance of the plating solution according to the present invention and various plating solutions including the conventional commercial plating solution, palladium activation treatment using the plating solution of the present invention and the existing commercially available nickel-borane plating solution or the like is excluded or the plating is performed as follows. The process was carried out.

1.Skim degreasing-40 to 50 ℃, 3 to 5 minutes

2. Soft etching-20-30 degreeC, 1-2 minutes

3. Degreasing-20 to 30 ℃, 30 to 60 seconds

4. Degreasing-25-35 ° C., 1-3 minutes

(Two washing processes were performed with distilled water (pure water) between each process.

The plating obtained by this plating process was evaluated as follows and shown in Table 2.

Table 1 shows the plating thickness obtained by using a commercially available Ni-B plating solution and the amount of borane deposited on the coating film, and the second time was 5-10 g / l cobalt sulfate as a cobalt salt in the commercial Ni-B plating solution. The plating thickness obtained using the added solution and the content of precipitated borane and cobalt are shown. In addition, No. 3 in Table 2 shows the results obtained by using a plating solution synthesized without adding cobalt sulfate added as a cobalt salt in the plating solution compositions shown in Table 1, and in case of No. 4 in Table 2, plating obtained using the plating solution composition in Table 1 It shows thickness and the amount of precipitated phosphorus and cobalt deposited on the plating film.

1. (Ni-B) 2. (Ni-B-Co) 3. (Ni-P) 4. (Ni-P-Co) Plating speed (㎛ / h) 8.3 10.7 27 32.8 P or B% (wt.%) 3.8 4.5 5.2 6.75 Co% (wt.%) 3.4 2.2

The deposited plating thickness was observed by FE-SEM (Field emission-scanning electomicroscope) and the plated film was also magnified × 5,000 times by FE-SEM. This is illustrated in FIGS. 1 to 8.

1 shows a plated film obtained by plating for 30 minutes using a commercially available nickel-borane plating solution. As a result of SEM measurement, it was observed that crystal particles of nickel-borane were formed on the plated film. A similar plating film was also observed in the nickel-borane-cobalt tertiary alloy plating film obtained by adding cobalt.

In the case of Figure 3 is a SEM image of the film obtained by using an electroless nickel-phosphorus (Ni-P) alloy liquid when the palladium ions are added directly to the plating solution without the palladium activation treatment, the crystal grains are different from the nickel-borane alloy liquid Almost no formation was observed, and even though the grains were formed, the size of the crystals was found to be fine.

FIG. 4 shows a SEM photograph of a plating film obtained from a three-alloy plating solution prepared by adding cobalt sulfate to an electroless nickel-phosphorus alloy solution. In this experiment, palladium ions were added directly to the plating solution without palladium activation. The nickel-phosphorus cobalt ternary alloy was selectively plated, and crystal grains were hardly formed in the plating film.

FIG. 5 shows that the electroless nickel-phosphorus plated specimens were subjected to nickel-phosphorus plating on the exposed portions of copper after palladium treatment.

6 shows that the electroless nickel-phosphorus plated specimens after palladium treatment should not be plated with no exposed copper. However, when palladium activation was performed, all palladium was not removed during the pretreatment process. .

FIG. 7 shows a case where electroless nickel plating was performed without a palladium activation treatment with a plating sample obtained by using the plating solution of the present invention, and it was observed that nickel-phosphorus plating was performed only on the copper exposed portion.

FIG. 8 is a view in which the copper is not exposed in the case where electroless nickel plating is performed without the palladium activation treatment, and the material part is not plated by a magnification of 10,000 ×.

In the case of plating various semiconductor materials such as copper wiring using the plating solution according to the present invention, a disadvantage in that a film having reduced adhesion due to high stress, which is a disadvantage of the nickel-borane-cobalt plating solution using borane having high reducing power as a reducing agent, is produced. In addition to the improvement, the plating can be directly reduced using autocatalytic reaction without the need for the activating treatment process using a precious metal such as palladium. It has an excellent advantage.

FIG. 1 is a view illustrating a film selectively plated on a substrate to be plated without a palladium activation process using a conventional commercial Ni-B plating solution.

FIG. 2 is a scanning electron microscope (SEM) photograph of a plating film obtained by adding 5-10 g / l of cobalt sulfate to a commercial Ni-B plating solution without a palladium activation treatment.

FIG. 3 is an SEM image of a coating plated on a copper substrate without a palladium activation treatment using the developed electroless nickel plating solution, that is, Ni-P plating solution.

FIG. 4 is a SEM photograph of the coating film without palladium activation by mixing 5-10 g / l cobalt sulfate with a cobalt salt in the developed electroless nickel plating solution.

5 is a SEM photograph obtained by plating after palladium activation using an electroless nickel plating solution.

FIG. 6 is an enlarged view of FIG. 5, where copper is not exposed.

7 is a SEM photograph obtained by plating without palladium treatment using the developed electroless nickel plating solution.

FIG. 8 is an enlarged view of FIG. 7 and is a portion where copper is not exposed.

Claims (6)

An electroless nickel-phosphorus-cobalt plating solution comprising nickel sulfate as the nickel salt, sodium hypophosphite as the reducing agent and cobalt sulfate as the cobalt salt. The electroless nickel-in-cobalt plating liquid according to claim 1, wherein the plating liquid further comprises a material selected from the group consisting of adipic acid, lactic acid, and mixtures thereof as a complexing agent. The electroless nickel-phosphorus-cobalt plating liquid according to claim 1, wherein the plating liquid further includes palladium in ionic form. The electroless nickel-phosphorus cobalt plating solution according to claim 1, wherein the plating solution contains 22 to 30 g / l of nickel sulfate, 20 to 50 g / l of sodium hypophosphite, and 5 to 10 g / l of cobalt sulfate. . The electroless nickel-in-cobalt plating solution of claim 2, wherein the adipic acid comprises 5 to 20 g / l and the lactic acid is 5 to 25 g / l. The plating method using the electroless nickel- phosphorus-cobalt plating liquid of Claim 1 thru | or 5, and there is no palladium activation process.

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