KR20120063565A - Electroless silver plating solution for semiconductor interconnects, electroless plating method using the same and silver coating layer prepared by the same - Google Patents

Abstract

PURPOSE: Electroless silver plating solution for semiconductor wiring, an electroless plating method using the same, and a silver coating layer prepared by the same are provided to implement efficient and stable electroless plating at low temperatures. CONSTITUTION: Electroless silver plating solution for semiconductor wiring comprises silver nitrate as metal salt, formalin as reductant, and ammonia solution as complexing agent. The plating solution also includes one of ethylenediamine and ethylenediaminetetraacetic acid(EDTA) as complexing agent. In the plating solution, the concentration of silver nitrate is 0.5-5 g/l and the concentration of formalin is 5-30 ml/l.

Description

Electroless silver plating solution for semiconductor wiring, electroless plating process using the same and silver film produced thereby {Electroless silver plating solution for semiconductor interconnects, electroless plating method using the same and silver coating layer prepared by the same}

The present invention relates to an electroless silver plating solution for semiconductor wiring, an electroless plating process using the same, and a silver film prepared thereby. More specifically, the present invention relates to using silver nitrate as a metal source, formalin as a reducing agent, and ammonia water and ethylene as complexing agents. By adding diamine, 1) more stable, and 2) electroless silver plating solution for semiconductor wiring, which can effectively improve the resistivity of the coating film for semiconductor wiring as well as reduce pits or cracks and have a dense surface structure during plating. It relates to an electroless plating process and a silver film produced thereby.

The signal transfer speed of the semiconductor chip is generally lowered by the resistance-capacitance delay (RC delay) occurring in the metal wiring. That is, the resistance-capacitance delay caused by the resistance of the wiring and the capacitance of the interlayer insulating film has a negative effect on the speedup of the device. In the past 30 years, aluminum (Al) has been mainly used as a wiring material. However, recently, the use of copper (Cu), which has a greater resistance to electromigration than aluminum and has a specific resistance of about 1/2 of aluminum, has made it possible to increase the signal transmission speed even in a small fine wiring. .

Nevertheless, unlike aluminum, which has been used as a wiring material, copper has a low passivation effect due to its own surface oxide film, so that the surface is easily oxidized, and its reactivity with silicon is strong to form silicide. . In addition, since the diffusion coefficient of copper in silicon or silicon dioxide is about 100 times higher than that of general metals, there is a problem that the breakdown of the semiconductor element is high due to heat treatment. In addition, as CPU speed increases and the pattern size continues to decrease, development of next-generation metal wiring materials that can replace copper is required.

Recent research suggests the introduction of silver as the next generation of metal wiring material, which has lower resistivity, higher resistance to oxidation, and better resistance to silicide formation than copper. However, various and endless studies on electrolytic and electroless copper plating for forming copper wiring have been conducted, while research on silver plating for semiconductor wiring has not been actively conducted yet.

Electroless plating is a method of plating a plated body through a chemical reaction without using electricity, and the metal ions are generated by the reducing agents included in the plating solution oxidized on the metal surface. It is a spontaneous process of reducing to form a metal film. Thus, in electroless plating, the reducing agent used in the electroless plating solution is an important factor in determining the plating speed and the properties of the plated film.

Recently, studies have been made to use cobalt ions such as cobalt sulfate as a reducing agent of an electroless silver plating solution, but cobalt ion reducing liquids have a fatal problem that decomposition occurs within minutes after preparation. Therefore, the use as a reducing agent is restricted.

Under this background, the present inventors conducted formal electroless silver plating using formalin as a reducing agent in order to develop a basic electroless silver plating composition (VMS) for wiring that can replace a cobalt ion reduction plating solution. The present invention was completed by confirming the superiority of the film obtained here.

Accordingly, an object of the present invention is to provide an electroless silver plating solution for semiconductor wiring which can effectively improve the specific resistance of the semiconductor wiring film by using silver, which is a metal having a low specific resistance.

It is also an object of the present invention to provide an electroless silver plating solution for semiconductor wiring which can be stably present for a long time unlike the case of using a conventional cobalt ion reducing agent.

It is also an object of the present invention to provide an electroless silver plating solution for semiconductor wiring, which has a very dense surface structure without pits or cracks of the plating layer, thereby exhibiting a low specific resistance of the silver film to be plated, and very stable without decomposition for a long time. .

It is also an object of the present invention to provide a more efficient electroless plating process since the plating process can be performed in a low temperature range.

It is also an object of the present invention to provide an electroless plating process in which a plating process is performed at a low temperature range and an appropriate pH range, so that plating can be effectively performed while plating is effectively performed.

It is also an object of the present invention to provide a plating process that can significantly reduce the specific resistance of a plated silver film by performing heat treatment on the formed plating film.

It is also an object of the present invention to provide a silver film in which pits or cracks can be reduced and have a very dense surface texture, whereby defects in the material due to the pits or cracks can be reduced.

In order to achieve the above object, the present invention, as one embodiment, relates to an electroless silver plating solution comprising silver nitrate as a metal salt and formalin as a reducing agent.

This silver has the effect of providing a low resistivity of the silver wiring to be plated due to the low resistivity of the metal, and by using formalin, silver can be more easily precipitated.

At this time, the concentration of the silver nitrate is 0.5 to 5 g / l, the concentration of the formalin is preferably 5 to 30 ml / l.

This is because the plating rate is lowered when the concentration of silver nitrate is less than the above range, and the plating rate is increased when the silver nitrate concentration is below the above range, but decomposition of the plating solution is likely to occur. Similarly, if the concentration of formalin is less than 5 ml / l, the plating rate decreases and productivity decreases. If the concentration of formalin exceeds 30 ml / l, the plating rate increases, but the stability of the solution decreases, causing the plating solution to degrade. Because of this.

On the other hand, in the production of a plating solution, in order to stabilize and prevent decomposition of the plating solution, it is preferable to dissolve and mix the metal source and the reducing agent, respectively.

The electroless silver plating solution is characterized in that it further comprises ammonia water as a complexing agent. In addition, it is characterized in that it further comprises any one of ethylenediamine and ethylenediaminetetraacetic acid (EDTA) as a complexing agent.

Such a complexing agent controls the plating rate and prevents spontaneous decomposition of the plating to provide a composition having excellent solution stability. Particularly, ammonia water, which is stable in alkalinity and exhibits good stability of silver and good complexability, is provided as a basic complexing agent. It is preferred that, as an additional complexing agent, either ethylenediamine or ethylenediaminetetraacetic acid be provided. In order to maintain the performance as a complexing agent in the plating solution, the concentration of ammonia water is 50 to 400 ml / l, and the concentrations of ethylenediamine and ethylenediaminetetraacetic acid are preferably 1.0 to 10 g / l.

The pH of the plating liquid is controlled by sodium hydroxide, characterized in that about 9.0 to 11.0. When the pH range is 9.0 to 11.0, the plating can be effectively performed while the plating speed is high.

As another aspect of the present invention, the present invention relates to a plating process comprising the step of forming a plating layer for semiconductor wiring using an electroless silver plating solution.

At this time, the plating process is preferably carried out in a temperature range of 20 to 60 ℃ and a pH range of 9.0 to 11.0. These process conditions minimize the chemical influence on the metal surface on which the plating layer is formed, and are more easily set so that the plating layer is formed on the metal surface.

In particular, according to this process temperature range, a denser and finer plating layer can be formed at a lower temperature. In this case, when the temperature is lower than the above-mentioned temperature range, it has a low plating rate, and when the temperature is higher than the above-mentioned temperature range, it has a fast plating rate.

In addition, according to the process pH range, it is preferable that silver is more effectively precipitated, and plating is performed in the process pH range because the plating solution is unstable and easily decomposed outside the pH range.

In addition, the present invention is characterized in that it further comprises the step of heat-treating the plating layer formed in the step at 300 to 500 ℃. The reason for performing this heat treatment step is to further reduce the specific resistance of the plated film by heat treatment.

At this time, the heat treatment step is preferably performed for about 10 minutes to 60 minutes, more preferably 20 minutes to 40 minutes at about 500 ℃ under vacuum to nitrogen atmosphere conditions. This is because the silver film subjected to the heat treatment under the above conditions has a lower specific resistance value.

As another aspect of the present invention, the present invention relates to a silver coating plated on a metal (eg silver) surface by the electroless silver plating solution described above. Such a silver film has a very low resistivity value, thereby enabling an effective signal transfer speed of a semiconductor chip.

According to the present invention, by using silver, which is a metal having a low specific resistance, an electroless silver plating solution for semiconductor wiring capable of forming a more reliable and low specific resistance semiconductor wiring film can be provided.

In addition, according to the present invention, unlike the case of using a conventional cobalt ion reducing agent can provide an electroless silver plating solution for semiconductor wiring that can be stably present for a long time.

Further, according to the present invention, by having a very dense surface structure without pits or cracks of the plating layer, the silver film to be plated can have a low specific resistance.

In addition, according to the present invention, since the electroless plating process can be performed at a low temperature range, plating can be performed more efficiently.

In addition, according to the present invention, the silver film is densely grown without pits or cracks, thereby ensuring the reliability and low resistance of the microcircuits in the semiconductor, package, and printed circuit board.

In addition, according to the present invention, the effect that the specific resistance of the plated silver film can be further reduced by performing heat treatment on the formed plated film.

1 is a photograph of the surface of the silver film formed by the plating solution prepared in Preparation Example 1 using a scanning electron microscope (SEM),
2 is a photograph taken of the surface of the silver film formed by the plating solution prepared in Comparative Preparation Example 1 using a scanning electron microscope,
3 is an analysis result obtained by using an X-ray photoelectron spectroscopy (XPS) of the surface of the plating film formed using the electroless silver plating solution of Preparation Example 1,
4 is an analysis result obtained by using X-ray photoelectron spectroscopy on the surface of the plating film formed using the electroless silver plating solution of Comparative Preparation Example 1,
FIG. 5 is a graph showing a change in specific resistance value according to the heat treatment temperature of the plating film formed using the electroless silver plating solution of Preparation Example 1 and Comparative Preparation Example 1, wherein the time is fixed to 30 minutes.
FIG. 6 is a graph showing a change in the specific resistance value according to the heat treatment time (the temperature is fixed at 500 ° C.) of the plated film formed using the electroless silver plating solution of Preparation Example 1 and Comparative Preparation Example 1. FIG.

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following examples are merely provided to more easily understand the present invention, and the contents of the present invention are not limited by the examples.

Preparation Example 1

Silver nitrate was dissolved as the silver salt to prepare a silver salt solution having a concentration of 2.0 g / l of silver nitrate. Then, 120 mL / L and 5.2 g / L of aqueous ammonia and ethylenediamine were added to the silver salt solution as a complexing agent.

Formalin, a reducing agent, was dissolved to prepare a reducing agent solution having a concentration of 10 ml / l. Then, the sodium hydroxide solution for pH adjustment in the reducing agent solution was dissolved to stabilize the plating solution without self-decomposition when mixed.

The plating solution was prepared by mixing the prepared silver salt solution and reducing agent solution. Note that the silver salt solution and the reducing agent solution were dissolved and mixed to stabilize the plating solution.

At this time, the pH of the plating liquid was kept constant at pH 10.5 by sodium hydroxide, the temperature of the plating liquid was adjusted to room temperature.

Comparative Production Example 1

Silver nitrate was dissolved as the silver salt to prepare a silver salt solution having a concentration of 2.0 g / l of silver nitrate. Then, 120 ml / l and 5.2 g / l of aqueous ammonia and ethylenediamine were added to the silver salt solution as a complexing agent, and 59.5 g / l of ammonium sulfate was added to stabilize the pH.

A reducing agent solution having a concentration of 50 g / l of cobalt sulfate as a reducing agent was prepared. Then, the sodium hydroxide solution for pH adjustment in the reducing agent solution was dissolved to stabilize the plating solution without self-decomposition when mixed.

The plating solution was prepared by mixing the prepared silver salt solution and reducing agent solution. Note that the silver salt solution and the reducing agent solution were dissolved and mixed to stabilize the plating solution.

In addition, as in Preparation Example 1, the pH of the plating liquid was kept constant at pH 10.5 by sodium hydroxide, and the temperature of the plating liquid was adjusted to room temperature.

Experimental Example 1

In order to evaluate the stability of the electroless silver plating solution according to the present invention, the plating solutions prepared in Preparation Example 1 and Comparative Preparation Example 1 were left at room temperature for a long time (about 1 day or more), and the decomposition degree of each plating solution was observed.

As a result, the plating solution according to Comparative Preparation Example 1 was completely decomposed within a few minutes after the preparation, but the plating solution according to Preparation Example 1 was confirmed to exist stably after a long time.

Experimental Example 2

In order to compare the performance of the electroless silver plating solution according to the present invention, the following plating process was performed using the plating solutions prepared in Preparation Example 1 and Comparative Preparation Example 1.

1) pickling the wafer material on which a 20 nm thick copper seed layer is formed using a sulfuric acid solution of 10% for about 30 seconds to remove an oxide film of copper in a temperature range of 25 to 30 ° C .;

2) washing the wafer material with non-ionized water;

3) soft etching treatment and washing treatment for 30 seconds in the temperature range of 20 ~ 30 ℃ to improve the adhesion;

4) Plating process (Preparation Example 1 and Comparative Preparation Example 1; pH 10.5 maintenance, room temperature maintenance)

At this time, the impurities were removed from the surface in the previous step through two washing steps with pure water between the above steps.

The surface of the silver film obtained through this process was compared through FIGS. 1 and 2.

BRIEF DESCRIPTION OF THE DRAWINGS The photograph of the surface of the silver film formed of the plating liquid of the manufacture example 1 using the scanning electron microscope. FIG. 2 is a photograph of the surface of the silver film formed by the plating solution of Comparative Preparation Example 1 using a scanning electron microscope. FIG.

1 and 2, although both films have a dense structure without pits or cracks, it can be seen that the film of Preparation Example 1 has a more uniform and even surface structure than the film of Comparative Preparation Example 1.

Experimental Example 3

Plating was carried out in the same manner as in Experiment 2 using the silver plating solution prepared in Preparation Example 1 and Comparative Preparation Example 1. And the surface of the film obtained by each plating liquid was surface-analyzed using X-ray photoelectron spectroscopy.

As a result of analysis using a 15 keV Al Mono Gun Source, it can be seen that the silver film was formed in both Preparation Example 1 and Comparative Preparation Example 1 as shown in Figs.

Experimental Example 4

Plating was carried out in the same manner as in Experiment 2 using the silver plating solution prepared in Preparation Example 1 and Comparative Preparation Example 1. Then, the formed plating film was subjected to heat treatment at 300 ° C., 400 ° C. and 500 ° C. for about 30 minutes under vacuum to nitrogen atmosphere conditions to measure the resistivity of the plating film at each temperature. These results are shown in FIG.

FIG. 5 is a graph showing a specific resistance value according to a heat treatment temperature of a plating film obtained by using an electroless silver plating solution prepared in Preparation Example 1 and Comparative Preparation Example 1. FIG.

Referring to FIG. 5, both of the coating films obtained from the two plating solutions decreased as the heat treatment temperature was increased, and the silver coating film obtained using the plating solution prepared in Preparation Example 1 in the entire temperature range was used using the plating solution prepared in Comparative Preparation Example 1. It can be seen that the specific resistance value is lower than that obtained by the silver film.

Specifically, at 300 ° C. heat treatment temperature, the silver film obtained in Preparation Example 1 is 3.25 μΩcm, and the silver film obtained in Comparative Preparation Example 1 is 4.25 μΩcm, which shows that the specific resistance is lower in the case of Preparation Example 1. On the other hand, at 500 ° C. heat treatment temperature, it can be seen that the silver films obtained in Preparation Example 1 and Comparative Preparation Example 1 exhibited similar minimum resistivity values of 2.432 μΩcm and 2.435 μΩcm, respectively.

Experimental Example 5

Plating was carried out in the same manner as in Experiment 2 using the silver plating solution prepared in Preparation Example 1 and Comparative Preparation Example 1. Then, the formed coating film was subjected to heat treatment at about 500 ° C. for 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes under vacuum to nitrogen atmosphere conditions, so that the resistivity value of the plated film at each heat treatment time. Was measured. These results are shown in FIG.

FIG. 6 is a graph showing a specific resistance value according to a heat treatment time of a plating film obtained using the electroless silver plating solution prepared in Preparation Example 1 and Comparative Preparation Example 1. FIG.

Referring to FIG. 6, it can be seen that in the initial stage of the heat treatment, the resistivity decreases as the heat treatment time increases for both of the coating films, and the resistivity increases again after about 30 minutes. At this time, when the heat treatment for 30 minutes, it can be seen that the film obtained in Preparation Example 1 and Comparative Preparation Example 1 exhibited the lowest specific resistance value of 2.432μΩcm and 2.435μΩcm, respectively. That is, it can be seen that the specific resistance of the silver film is lowered when the heat treatment is performed for about 10 minutes to 60 minutes, more preferably 20 minutes to 40 minutes, at about 500 ° C. on the formed plating film.

Based on these results, the silver plated coating plated using the electroless silver plating solution according to the present invention is very stable without the use of an unstable cobalt ion reducing agent and exhibits the same or improved coating properties as the existing coating. Therefore, it can be seen that it has very excellent characteristics for use as a semiconductor wiring.

As mentioned above, although the present invention has been illustrated and described with reference to specific embodiments, the present invention is not limited thereto, and the following claims are not limited to the scope of the present invention without departing from the spirit and scope of the present invention. It can be easily understood by those skilled in the art that can be modified and modified.

Claims (10)

It characterized by containing silver nitrate as a metal salt, and formalin as a reducing agent,
Electroless silver plating solution.
The method of claim 1,
The plating liquid further comprises ammonia water as a complexing agent,
Electroless silver plating solution.
The method of claim 2,
The plating liquid further comprises any one of ethylenediamine and ethylenediaminetetraacetic acid (EDTA) as a complexing agent,
Electroless silver plating solution.
The method of claim 1,
The concentration of the silver nitrate is 0.5 to 5 g / l, the concentration of the formalin is characterized in that 5 to 30 ml / l,
Electroless silver plating solution.
The method of claim 2,
The concentration of the ammonia water is 50 to 400 ml / l,
The concentration of any one of the ethylenediamine and the ethylenediaminetetraacetic acid is characterized in that 1.0 to 10 g / L,
Electroless silver plating solution.
A method of forming a plating layer for semiconductor wiring by using the electroless silver plating solution according to any one of claims 1 to 5,
Plating process.
The method of claim 6,
The electroless plating process is characterized in that carried out in a temperature range of 20 to 60 ℃ and a pH range of 9.0 to 11.0,
Plating process.
The method of claim 6,
Further comprising the step of heat-treating the formed plating layer at 300 to 500 ℃,
Plating process.
The method of claim 8,
The heat treatment is characterized in that performed for 10 to 60 minutes,
Plating process.
It is plated on the metal surface by the electroless silver plating liquid as described in any one of Claims 1-5,
Silver film.

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