JP2007246981A - Electroless plating liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless plating liquid which can form a cobalt based alloy on wiring of copper or the like as a protective film at high selectivity, can prevent the surface contamination of the exposed wiring and electromigration to an interlayer insulation film, can evade anxieties about the increase of wiring resistance and the deposition of plating metal to the part other than the wiring, further does not include components as environmental hormones, and can suppress adverse influence on the using environment. <P>SOLUTION: The electroless plating liquid is used for selectively forming a protective film on the surface of exposed wiring upon the fabrication of a semiconductor device having a wiring structure, and comprises: cobalt ions; the ions of a second metal different from cobalt; a chelating agent; a reducing agent; polyoxyalkylene monoalkyl ether; and alkylammonium hydroxide expressed by formula (1); wherein R<SP>1</SP>, R<SP>2</SP>, R<SP>3</SP>, and R<SP>4</SP>are each a group selected from alkyl groups and hydroxyalkyl groups. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electroless plating solution used for selectively forming a protective film on the exposed surface of a wiring in the manufacture of a semiconductor device having a wiring structure using copper or a copper alloy as a wiring material. is there.

  Conventionally, an aluminum alloy has been mainly used for fine wiring of a high-density integrated circuit formed on a semiconductor substrate. However, in order to further increase the speed of the semiconductor device, it has become necessary to use copper or a copper alloy having a specific resistance lower than that of an aluminum-based alloy as a wiring material. Furthermore, copper is expected as a wiring material for next-generation semiconductor devices because it has an electromigration resistance that is about an order of magnitude higher than that of aluminum-based alloys.

  As a copper wiring forming process of a semiconductor device, a process (damascene process) of embedding metal in wiring trenches and contact holes is employed. In this damascene process, a metal such as copper or a copper alloy is embedded in a wiring groove or contact hole previously formed in an interlayer insulating film, and then the excess metal is removed by chemical mechanical polishing (CMP) and planarized. Is a process.

  In this type of wiring, after planarization, the surface of the wiring is exposed to the outside, and when an embedded wiring is further formed thereon, an interlayer insulating film is further formed on the wiring. Although grooves are formed, there are concerns about surface contamination of the exposed wiring and electromigration to the laminated interlayer insulating film. Therefore, conventionally, a wiring protective film such as silicon nitride is formed on the entire surface of the semiconductor substrate as well as the wiring forming portion whose surface is exposed.

  However, since the electromigration resistance at the interface between the silicon nitride film and copper is weak, and the silicon nitride film itself has a high dielectric constant, the wiring delay (RC delay due to the resistor R and the capacitor C) increases. Arise. It has been proposed to use cobalt tungsten phosphorus (CoWP) as a material that improves the RC delay and is excellent in electromigration resistance and is effective in preventing copper diffusion (US Pat. No. 5,958,810). 1)).

This CoWP has the advantage that it can be selectively deposited only on the copper wiring by electroless plating.
When performing CoWP electroless plating, sodium hypophosphite is generally used as a reducing agent. However, it is known that sodium hypophosphite is an inactive reducing agent that does not proceed on copper and cannot be plated directly on copper (eg, GOMallory, JB Hajdu, “Electroless Plating-Fundamentals & Applications -", American Electroplaters And Surface Finishers Society, Florida, page 318,1990) (Non-Patent Document 1)
.

Therefore, it is necessary to form the CoWP film by electroless plating after providing a seed layer such as palladium on the copper wiring. However, the palladium that forms the seed layer in this way may react with the copper that forms the wiring layer to increase the resistance of the copper. In addition, palladium may adhere to the surface of the insulator other than the wiring, and the CoWP film may be formed on the surface of the insulator other than the wiring. For this reason, there exists a problem that the insulation between wiring requested | required when forming fine wiring is reduced.

  Thus, in order to avoid the influence on the copper wiring due to the reaction of palladium with copper, it is necessary to use a reducing agent that does not use palladium as a catalyst, and dimethylamine borane (DMAB) is used as such a reducing agent. CoWB electroless plating methods have also been proposed (US Pat. No. 5,169,680 (Patent Document 2), JP-A-2003-49280 (Patent Document 3)). However, since dimethylamine borane (DMAB) has a strong reducing power, the stability of the electroless plating solution is inferior, and there is a problem that cobalt may be deposited in places other than copper wiring.

In addition, an anionic, cationic or nonionic surfactant is generally added to the electroless plating solution for the purpose of adjusting the stability of the plating bath and the deposition rate. Polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and their sulfates and phosphates may be used as an effective component for good plating bath stability and deposition rate optimization. These compound substances are considered to be endocrine disruptors (environmental hormones) or suspected, and there is a concern about the influence on electroless plating workers and the surrounding environment.
US Pat. No. 5,695,810 US Pat. No. 5,169,680 JP 2003-49280 A GOMallory, JBHajdu, "Electroless Plating-Fundamentals &Applications-", American Electroplaters And Surface Finishers Society, Florida, page 318,1990

  An object of the present invention is to solve the above-described problems of the prior art, more specifically, to prevent deterioration of the reliability of a semiconductor device due to contamination of copper and copper alloy wiring and copper diffusion, An object of the present invention is to provide an electroless plating solution capable of selectively forming a protective film having a diffusion preventing ability uniformly only on the wiring.

  The electroless plating solution of the present invention is an electroless plating solution used to selectively form a protective film on the surface of the wiring exposed during the manufacture of a semiconductor device having a wiring structure. It contains a second metal ion different from the above, a chelating agent, a reducing agent, a polyoxyalkylene monoalkyl ether and an alkylammonium hydroxide represented by the following formula (1).

In the above formula (1), R ¹ , R ² , R ³ and R ⁴ are each independently at least one group selected from the group consisting of an alkyl group and a hydroxyalkyl group.

  In the electroless plating solution of the present invention, by using polyoxyalkylene monoalkyl ether, the stability of the plating solution is good without using palladium, and the ability to selectively prevent diffusion uniformly only on the wiring. It can be set as the electroless-plating liquid which can form the protective film which has.

  Furthermore, by using the alkylammonium hydroxide represented by the above formula (1) as a pH adjuster not containing an alkali metal, an alkali metal is contained in the plating film and the protective film formed by electroless plating. Can be prevented.

Hereinafter, the electroless plating solution of the present invention will be specifically described.
The electroless plating solution of the present invention is an electroless plating solution suitably used to form a protective film containing cobalt on the surface of metallic copper or copper alloy and having a uniform diffusion preventing ability.

  As a source of cobalt ions contained in the electroless plating solution of the present invention, a water-soluble cobalt (II) salt is blended. The salt is not particularly limited, and examples thereof include cobalt sulfate, cobalt chloride, cobalt bromide, cobalt acetate, cobalt oxalate, cobalt nitrate, and cobalt hydroxide.

These can be used alone or in combination.
In the present invention, among these exemplified cobalt salts, cobalt sulfate, cobalt nitrate, and cobalt hydroxide are preferable. The amount of the cobalt salt to be blended is appropriately determined depending on the type of cobalt salt to be used, but is preferably 0.001 to 1 mol / liter, preferably 0.01 to 1 mol / liter, as cobalt ions. .

The electroless plating solution of the present invention contains second metal ions in addition to cobalt ions.
In the present invention, the second metal ion different from cobalt is selected from the ions of the fourth periodic metal, the fifth periodic metal and the sixth periodic metal in the periodic table other than cobalt, and the atomic group ion containing the metal. Is done. As specific elements,
4th period chromium, nickel, copper, zinc,
5th period molybdenum, technetium, ruthenium, rhodium, palladium, silver,
Examples of the sixth period include tungsten, rhenium, osmium, iridium, platinum, and gold. In the present invention, among these second metals, tungsten and / or molybdenum is preferable.

In the present invention, as the source of these second metal ions, for example,
Metal oxides, such as tungsten dioxide, tungsten trioxide, molybdenum dioxide and molybdenum trioxide etc.
Metal salts such as tungsten pentachloride, tungsten hexachloride,
Tungstic acid, molybdic acid tungstate, molybdate,
Mention may be made of heteropolyacids such as tungstophosphoric acid and their salts.

  In the electroless plating solution of the present invention, the amount of the second metal as described above is usually 0.001 to 1 mol / liter, preferably 0.01 to 1 mol / liter in terms of zero-valent metal. Used in.

A chelating agent is blended in the electroless plating solution of the present invention in order to stabilize metal ions such as cobalt.
Examples of chelating agents that can be used in the present invention include general chelating agents such as carboxylic acids and salts thereof, aminocarboxylic acids and salts thereof, and oxycarboxylic acids and salts thereof. Although not particularly limited, preferred examples include acetic acid, glycine, citric acid, tartaric acid, ethylenediaminetetraacetic acid, and salts thereof, pyrophosphoric acid and salts thereof, and citric acid is more preferred. These chelating agents may be used alone or in combination of two or more.

  The mixing amount of the chelating agent in the electroless plating solution of the present invention is usually 0.001 mol / liter to 2 mol / liter, preferably 0.01 mol / liter to 1.5 mol / liter.

A reduction reaction is used to deposit metal ions such as cobalt ions and second metal ions contained in the electroless plating solution of the present invention on the exposed wiring surface (surface to be plated) as metal. The reducing agent for advancing the reduction reaction in the electroless plating solution of the present invention preferably does not contain an alkali metal such as sodium.

  By using a reducing agent that does not contain an alkali metal as described above, the coating film formed from the electroless plating solution of the present invention contains no alkali metal and forms a coating film having good film characteristics. can do.

  Examples of such reducing agents include monoalkylamine boranes, dialkylamine boranes and trialkylamine boranes that do not contain alkali metals such as sodium, and specific examples include dimethylamine borane (Boran- dimethylamine complex, or dimethylamineborane, hereinafter referred to as DMAB).

A reducing agent such as dimethylalkylborane blended in the electroless plating solution of the present invention not only serves as a reducing agent for precipitating cobalt ions and second metal ions, but also deposits and forms an electroless plating layer. It also acts as a source of boron (B) in the constituent cobalt-based alloy (for example, CoWB).

Moreover, hypophosphorous acid and hypophosphite can be mentioned as a suitable reducing agent in this invention. In this case as well, hypophosphorous acid and hypophosphite, which are reducing agents, also act as a source of phosphorus (P) in a cobalt-based alloy (for example, CoWP) constituting the electroless plating layer to be deposited. To do.

The reducing agent as described above is usually blended in the electroless plating solution of the present invention in an amount of 0.001 mol / liter to 1 mol / liter, preferably 0.01 mol / liter to 1 mol / liter.
In general, an electroless plating solution is blended with a surfactant in order to ensure the stability of the plating bath and further to adjust the deposition rate of the metal. Examples of the surfactant blended in the electroless plating solution for such a purpose include an anionic surfactant, a cationic surfactant, and a nonionic surfactant. In particular, as an effective surfactant for ensuring the stability of the electroless plating solution and optimizing the deposition rate of metal, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, and their sulfate esters or Phosphate esters are used.

  Such a surfactant is necessary for smooth electroless plating. On the other hand, the above-mentioned compound used for electroless plating solution is an endocrine disrupting substance (environmental hormone). Considering the effects on electroless plating workers and the surrounding environment, it is desirable to use surfactants that do not have endocrine disrupting effects.

  In the present invention, in consideration of such effects on workers and the surrounding environment, a polyoxyalkylene monoalkyl ether type nonionic surfactant having no endocrine disrupting action is used as the surfactant.

  The polyoxyalkylene monoalkyl ether used in the present invention is a nonionic surfactant. This polyoxyalkylene monoalkyl ether can be represented by the following formula (2).

In the above formula (2), R ⁵ is an alkyl group having 10 or more carbon atoms, R ⁶ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 5 or more and less than 30. In the above formula (2), examples of R ⁵ which is an alkyl group having 10 or more carbon atoms include a decyl group, an isodecyl group,
A lauryl group, a tridecyl group, a cetyl group, an oleyl group, and a stearyl group can be exemplified. The above alkyl groups as R ⁵ may be the same or different.

R ⁶ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and specific examples include a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, and an iso-propyl group.
These may be used alone or in combination. Furthermore, in Formula (2), n is an integer of 5 or more and less than 30, and is particularly preferably an integer of 5 to 20.

The molecular weight of such polyoxyalkylene monoalkyl ether is usually 400 or more.
Moreover, about such polyoxyalkylene monoalkyl ether, it is preferable that the HLB value (Hydrophile-lipophile balance) measured by the Griffin method is 12 or more.

  Specific examples of such polyoxyalkylene monoalkyl ether include polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxypropylene decyl ether, Examples thereof include oxypropylene lauryl ether and polyoxypropylene tridecyl ether. Such polyoxyalkylene monoalkyl ethers can be used alone or in combination.

  The amount of the polyoxyalkylene monoalkyl ether blended in the electroless plating solution of the present invention is usually within the range of 0.0001% by mass to 1% by mass, preferably 0.001% by mass to 0.5% by mass. is there. In the present invention, the surfactants can be used alone or in combination.

In the electroless plating solution of the present invention, tetraalkylammonium hydroxide is blended in order to adjust the pH value. This tetraalkylammonium hydroxide can be represented by the following formula (1).

In the above formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent any group selected from the group consisting of an alkyl group and a hydroxyalkyl group.
This compound is a pH adjuster that does not contain an alkali metal.

In the present invention, examples of the compound represented by the formula (1) used as a pH regulator include tetramethylammonium hydroxide (hereinafter referred to as “TMAH”), tetraethylammonium hydroxide, tetrabutyl hydroxide. Examples include ammonium, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, 2-hydroxyethyltrimethylammonium hydroxide, and 2-hydroxyethyltriethylammonium hydroxide.

The compound represented by the formula (1) as described above is used in an amount capable of adjusting the pH value of the electroless plating solution of the present invention to a range of usually 5 to 14, preferably 7 to 11.
In the electroless plating solution of the present invention, known additives such as a buffer, a corrosion inhibitor, and an accelerator can be blended as necessary in addition to the above components. For example, boric acid is mentioned as an additive that acts as a buffer / accelerator.

As a method of forming a cobalt alloy plating film using the electroless plating solution of the present invention, a liquid temperature of 20 to 1 is applied to a semiconductor substrate that has been subjected to necessary pretreatments such as cleaning of the surface to be plated according to a conventional method.
A method of dipping until a plating film having a film thickness necessary for an electroless plating solution at 00 ° C., preferably 35 to 90 ° C., can be employed.

  As a wiring material constituting the wiring structure formed on the semiconductor substrate, copper is generally used. This copper film is not limited to pure copper, and the content ratio of copper such as copper-silicon and copper-aluminum is 95, for example. You may consist of a copper alloy which is the mass% or more. In this wiring, the interlayer insulating film in which the wiring groove is formed is covered with a hard metal such as tantalum or titanium and / or a barrier metal such as a nitride or oxide thereof, and the wiring metal is electroplated. The semiconductor substrate is deposited by a damascene method of chemical mechanical polishing (CMP).

  Here, the metal forming the barrier metal film is not limited to a pure product, and may be an alloy such as tantalum-niobium. In addition, when the barrier metal film is formed of nitride, tantalum nitride, titanium nitride, or the like is not necessarily pure. The material of the barrier metal film is particularly preferably tantalum and / or tantalum nitride. The barrier metal film is often formed of one of tantalum, titanium, and the like, but different materials such as a tantalum film and a tantalum nitride film may be formed on the same substrate as the barrier metal film. Good.

In addition, the interlayer insulating film is obtained by a silicon oxide film (PETOS film (Plasma Enhanced-TEOS film), HDP film (High Density Plasma Enhanced-TEOS film)) formed by a vacuum process such as chemical vapor deposition, or thermal CVD. is a silicon oxide film, etc.), a small amount of boron and phosphorus added boron phosphorus silicate film (BPSG film), FSG fluorine-doped _{SiO 2 (fluorine-doped silicate glass} ) and an insulating film called the SiO _2, SiON (silicon Examples thereof include an insulating film called oxynitride) and silicon nitride.

Furthermore, as a low dielectric constant interlayer insulating film, alkoxysilane, silane, alkylsilane, arylsilane, siloxane in the presence of oxygen, carbon monoxide, carbon dioxide, nitrogen, argon, H ₂ O, ozone, ammonia, etc. An interlayer insulating film made of a polymer obtained by plasma polymerization of a silicon-containing compound such as alkylsiloxane, and further an interlayer insulating film made of polysiloxane, polysilazane, polyarylene ether, polybenzoxazole, polyimide, silsesquioxane, etc. Can also be used.

Further, the low dielectric constant silicon oxide insulating film can be obtained by applying a raw material on a substrate by, for example, a spin coating method and then heating in an oxidizing atmosphere. Examples of the low dielectric constant silicon oxide insulating film thus obtained include an HSQ film (Hydrogen Silsesquioxane film) using triethoxysilane as a raw material, and an MSQ film using tetraethoxysilane and a small amount of methyltrimethoxysilane as a raw material ( Methyl Silsesquioxane film) and other low dielectric constant insulating films made from silane compounds. By mixing suitable organic polymer particles, etc. with a low dielectric constant insulating film made of such a material, the organic polymer particles are burned out in the heating process to form vacancies. As a result, the dielectric constant of the insulating film is further reduced.

  The insulating film having a low dielectric constant can also be formed using an organic polymer such as a polyarylene polymer, a polyarylene ether polymer, a polyimide polymer, or a benzocyclobutene polymer as a raw material.

  The electroless plating solution of the present invention forms a seed layer made of a cobalt-based alloy, which is a diffusion prevention film material, on the copper wiring with a very high selectivity with respect to the semiconductor substrate on which such copper wiring is exposed. Suitable for

Next, the electroless plating solution of the present invention will be described with reference to examples, but the present invention is not limited thereto.
[Example 1]
(1) Preparation of electroless plating solution A glass beaker having a capacity of 5000 ml was charged with 2000 ml of 25% by mass TMAH aqueous solution heated to 80 ° C., and 150 g of tungsten trioxide was added to the TMAH aqueous solution and dissolved.

  Next, in a glass beaker having a volume of 5000 ml, 2500 ml of 25% by mass of TMAH aqueous solution was put, and 850 g of citric acid, 150 g of boric acid, and 180 g of cobalt sulfate heptahydrate were put into this TMAH aqueous solution. Added and dissolved.

  Next, after mixing the two solutions prepared as described above, polyoxyethylene tridecyl ether having a HLB value of 13.3 (product name; Neugen TDS-, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to this mixed solution. 80) 3 g was added and dissolved.

Furthermore, deionized water and 25% by mass TMAH aqueous solution were added to the solution thus obtained to adjust the pH value of the mixed solution to 9.0 and the total volume to 10 liters.
20 g of DMAB was dissolved in the plating solution thus prepared to prepare a plating solution-1. (2) Stability evaluation of electroless plating solution 25 ml of the plating solution-1 prepared in a clean glass test tube is weighed, and this is palladium chloride having a concentration of 0.02 g / liter which serves as an initiation catalyst for the electroless plating reaction. After adding 0.2 ml of an aqueous solution to obtain a uniform solution, it was heated to 80 ° C., and the change in the state of the plating solution was observed. When the stability of the prepared plating solution is insufficient, the reduction reaction is started by heating in the presence of palladium chloride, and the metal is deposited.

However, it was found that the plating solution-1 had sufficient stability without the occurrence of turbidity due to metal deposition for 20 minutes or more after heating at 80 ° C.
(3) Evaluation of plating performance A commercially available silicon substrate on which a copper foil layer is formed by plating is cut into a 5 cm square test piece, washed with deionized water, and its mass (W1) is measured with a precision balance. did.

Subsequently, this test piece was immersed in 100 ml of plating solution-1 heated to 80 ° C. for 20 minutes.
When the test piece was taken out after 20 minutes and washed with deionized water, the surface of the test piece was changed to a silver mirror surface, and it was found that the cobalt-based alloy was plated on the copper surface.

  Measure the weight (W2) of the test piece after washing with a precision balance, calculate the amount of plated metal from the change in mass before and after plating (W2-W1), and calculate the plating rate from the plating time and the area of the test piece did.

The plating rate of the plating solution-1 was 0.5 nm / sec.
Next, it is polished using a copper CMP slurry (product name; CMS7401 and CMS7452) and barrier metal CMP slurry (product name; CMS8401 and CMS8452) manufactured by JSR Corporation, and patterned silicon with copper wiring exposed on the insulating film. A substrate (a substrate with ATDF copper damascene wiring, 854CMP001) was prepared and cut into a 3 cm square test piece. This test piece was washed with deionized water and then immersed in 100 ml of plating solution-1 heated to 80 ° C. for 1 minute. After washing again with deionized water, the plated specimen was observed with a scanning electron microscope, and it was confirmed that no metal was deposited on the insulating film that should not be plated.

[Example 2]
(1) Preparation of electroless plating solution A glass beaker having a capacity of 5000 ml was charged with 150 g of tungsten trioxide and 2000 ml of 25 mass% TMAH aqueous solution, and the TMAH aqueous solution was heated to 80 ° C. to dissolve tungsten trioxide. .

Next, another glass beaker with a capacity of 5000 ml was charged with 800 g of citric acid and 60 g of cobalt hydroxide, and 2000 ml of deionized water was added and dissolved.
After mixing the two solutions thus obtained, 3000 ml of 25 wt% TMAH aqueous solution, 300 ml of 50 wt% hypophosphorous acid aqueous solution and 150 g of boric acid were added and dissolved in this mixed solution.

  Further, 30 g of DMAB and 1 g of polyoxyalkylene isodecyl ether (product name: Neugen XL-100, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) having an HLB value of 14.7 were added and dissolved.

Thereafter, the pH value of the mixed solution was 9 using deionized water and 25% by mass TMAH aqueous solution.
. The plating solution-2 was prepared by adjusting 0 and the total volume to 10 liters.
For the plating solution-2 thus obtained, the stability and plating performance of the electroless plating solution were evaluated in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Example 3
(1) Preparation of electroless plating solution A glass beaker having a capacity of 5000 ml was charged with 2000 ml of 25 mass% TMAH aqueous solution heated to 80 ° C., and 150 g of tungsten trioxide was added to the TMAH aqueous solution and dissolved.

  Next, 3500 ml of 25% by weight TMAH aqueous solution, 850 g of citric acid, 150 g of boric acid, and 180 g of cobalt sulfate heptahydrate were put into another glass beaker having a volume of 5000 ml, and these were mixed and dissolved. .

After mixing the two solutions prepared as described above, 150 ml of a 50% by mass hypophosphorous acid aqueous solution, 10 g of N- (2-hydroxyethyl) ethylenediamine-
N, N ′, N′-triacetic acid, 0.1 g of polyoxyalkylene lauryl ether (product name: DKS NL-Dash410) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. having an HLB value of 12.5 is added and dissolved. It was.

Further, add 10 g of DMAB, and then adjust the pH of the mixed solution to 9.0 and the total volume to 10 liters using deionized water and 25% by mass TMAH aqueous solution to prepare plating solution-3 did.

For the plating solution-3 thus prepared, the stability and plating performance of the electroless plating solution were evaluated in the same manner as in Example 1, and the results shown in Table 1 were obtained.
Example 4
(1) Preparation of electroless plating solution In a glass beaker having a capacity of 5000 ml, 150 g of tungsten trioxide and 2000 ml of 25 mass% TMAH aqueous solution were placed and heated to 80 ° C. to dissolve the tungsten trioxide.

Next, another glass beaker with a capacity of 5000 ml was charged with 800 g of citric acid and 60 g of cobalt hydroxide, and 2000 ml of deionized water was added and dissolved.
Next, after mixing the two solutions prepared as described above, 3000 ml of 25% by weight TMAH aqueous solution, 300 ml of 50% by weight hypophosphorous acid aqueous solution, 150 g
Of boric acid was added and dissolved.

  Furthermore, 30 g of DMAB and 0.5 g of polyoxyethylene isodecyl ether (product name: Neugen SD-70, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) having an HLB value of 13.2 were added and dissolved.

Thereafter, deionized water and 25% by mass TMAH aqueous solution were used for this solution to adjust the pH value of the mixed solution to 9.0 and the total volume to 10 liters, thereby preparing a plating solution-4.

For the plating solution-4 thus obtained, the stability and plating performance of the electroless plating solution were evaluated in the same manner as in Example 1, and the results shown in Table 1 were obtained.
Example 5
(1) Preparation of electroless plating solution A glass beaker having a capacity of 5000 ml was charged with 2000 ml of 25 mass% TMAH aqueous solution heated to 80 ° C., and 150 g of tungsten trioxide was added to the TMAH aqueous solution and dissolved.

  Next, in another glass beaker with a capacity of 5000 ml, 2500 ml of 25% by mass of aqueous TMAH hydroxide solution, 850 g of citric acid, 150 g of boric acid, and 180 g of cobalt sulfate heptahydrate were added and dissolved. .

  Next, after mixing the two solutions prepared as described above, polyoxyalkylene tridecyl ether having a HLB value of 13.1 (product name; Neugen TDX-, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to this mixed solution. 80D) 2 g was added and dissolved.

Furthermore, deionized water and a mass% aqueous 2-hydroxyethyltrimethylammonium hydroxide solution were used for the mixed solution so that the mixed solution had a pH value of 9.0 and a total volume of 10 liters.

To the solution thus obtained, 20 g of DMAB was added and dissolved to prepare a plating solution-5.
For the obtained plating solution-5, the stability and plating performance of the electroless plating solution were evaluated in the same manner as in Example 1, and the results shown in Table 1 were obtained.

[Comparative Example 1]
The same procedure except that polyoxyalkylene isodecyl ether having a HLB value of 14.7 (product name; Neugen XL-100, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was not used in the procedure for preparing the plating solution described in Example 2. Plating solution-6 was prepared by blending.

[Comparative Example 2]
Among the preparation procedures of the plating solution described in Example 1, instead of polyoxyethylene tridecyl ether (product name: Neugen TDS-80, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) having an HLB value of 13.3, an HLB value of 13.5 A plating solution-7 was prepared with the same composition except that polyoxyethylene octylphenyl ether (manufactured by Dow Chemical Co., Ltd., product name Triton X-100) was used.

  The evaluation results for Comparative Examples 1 and 2 are also shown in Table 1.

  From the above results, Examples 1 to 5 have sufficient stability to stably perform the plating treatment while having a sufficient plating speed, as compared with Comparative Example 1, and moreover, It has the ability to selectively form a protective film having a copper diffusion preventing ability only on the exposed surface of the wiring on the semiconductor substrate having a wiring structure using copper or a copper alloy as a wiring material. I know that.

Further, from comparison with Comparative Example 2, it is found that the plating solution has a stability equal to or higher than that of a conventional plating solution using a surfactant, and further, plating is performed only on the exposed copper wiring. It can be seen that the selectivity is improved.

In manufacturing a semiconductor device having a wiring structure using copper or a copper alloy as a wiring material, a protective film by electroless plating is used to selectively form a protective film having a copper diffusion preventing function on the exposed surface of the wiring. Formation has been proposed as an effective means. The electroless plating solution of the present invention comprises cobalt ions, ions of a second metal different from cobalt, chelating agents, reducing agents, polyoxyalkylene monoalkyl ethers, and R ¹ R ² R ³ R ⁴ NOH (wherein , R ¹ , R ² , R ³ , and R ⁴ are as defined above), and a protective film is formed on the cobalt alloy only on the wiring such as copper with excellent selectivity. It is possible to prevent the surface contamination of the exposed wiring and the electromigration to the laminated interlayer insulating film. Moreover, since a seed layer of palladium or the like is not required, it is possible to avoid the possibility of increasing the wiring resistance and the possibility of plating metal being deposited on the wiring other than the wiring due to the adhesion of palladium on the insulating material other than the wiring. Furthermore, since these performances can be achieved without using endocrine disrupting substances (environmental hormones) such as conventional polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether, electroless plating workers and The influence on the surrounding environment can be suppressed.

Claims (4)

An electroless plating solution used for selectively forming a protective film on a surface of a wiring exposed in the manufacture of a semiconductor device having a wiring structure, wherein the ion of a second metal different from cobalt ion and cobalt An electroless plating solution comprising a chelating agent, a reducing agent, a polyoxyalkylene monoalkyl ether, and an alkylammonium hydroxide represented by the following formula (1):

(In the above formula (1), R ¹ , R ² , R ³ and R ⁴ are each independently at least one group selected from the group consisting of an alkyl group and a hydroxyalkyl group).   2. The electroless plating solution according to claim 1, wherein the second metal different from cobalt is a fourth periodic metal, a fifth periodic metal, or a sixth periodic metal in the periodic table of elements other than cobalt. The second metal different from cobalt is tungsten and / or molybdenum, and the source of ions of these second metals is:
Metal oxides consisting of tungsten dioxide, tungsten trioxide, molybdenum dioxide and molybdenum trioxide,
A metal salt comprising tungsten pentachloride and tungsten hexachloride,
3. A compound comprising at least one compound selected from the group consisting of tungstic acid, molybdic acid, tungstate, molybdate, tungstophosphoric acid heteropolyacid and tungstophosphoric acid heteropolyacid salt. The electroless plating solution described.   The electroless plating solution according to claim 1, wherein the reducing agent is an alkylamine borane.