TWI412631B - Copper plating solution for embedding ULSI (Ultra Large-Scale Integration) micro copper wiring - Google Patents

Abstract

An object of the present invention is to provide an electrolytic copper plating solution which can suppress, upon electrolytic copper plating on a copper seed layer during fabrication of ULSI copper microwiring (damascene copper wiring) having trends to further miniaturization, dissolution of the copper seed layer and accordingly can suppress occurrence of voids on the inner wall of vias/trenches. The present invention provides an electrolytic copper plating solution for filling for forming microwiring for ULSI, characterized in that it has a pH of 1.8 or higher and 3.0 or lower. The electrolytic copper plating solution preferably comprises a saturated carboxylic acid having 1 or more and 4 or less carbon atoms at 0.01 mol/L or more and 2.0 mol/L or less.

Description

Copper plating solution for embedding ULSI (Ultra Large-Scale Integration) micro copper wiring

The present invention relates to a copper plating solution for embedding ULSI fine copper wiring.

The copper plating solution for embedding the ULSI fine wiring is usually plated using a strong acid plating solution (pH of 1.2 or less) using sulfuric acid as a base material. In this case, a sputtered copper film is used as a seed layer, but the sputtered copper film in the trench/via is extremely thinned by the miniaturization of the wiring. The outermost surface of the seed layer is incapable of avoiding oxidation because it is exposed to the atmosphere. However, since the plating solution is strongly acidic, the oxidized portion of the seed layer is easily dissolved when immersed in the acidic plating solution. A defect occurs in a thin seed layer, and when a copper wiring layer is formed by subsequent copper plating, there is a problem that copper plating is peeled off everywhere. In particular, in the inner wall of the groove/hole, the problem of voids easily occurs.

An object of the present invention is to provide a copper plating solution for suppressing copper species during copper plating on a copper seed layer in the formation of a USI fine copper wiring (damascene copper wiring) which is increasingly refined and refined. The dissolution of the crystal layer, as a result, can suppress the occurrence of voids in the inner walls of the holes/trench.

The inventors of the present invention used a carboxylic acid or the like to replace the sulfuric acid used in the strong acid copper plating solution of a general sulfuric acid substrate, and tried to suppress the plating solution immersion when the pH of the plating solution was weakly acidic by the general strong acidity. The copper seed layer is easily soluble. As a result, the void of the sidewall of the trench which occurs when the strongly acidic plating solution of the sulfuric acid substrate is used is formed by the use of the plating solution of the carboxylic acid substrate, and it is found that the above problem can be solved. The present invention has been completed.

That is, the present invention is as follows.

(1) A copper plating solution for embedding ULSI fine wiring, characterized in that the pH is 1.8 or more and 3.0 or less.

(2) A copper plating solution for embedding ULSI fine wiring as in (1), wherein the pH is 2.0 or more and 2.2 or less.

(3) The copper plating solution for embedding ULSI fine wiring according to (1) or (2), which contains a saturated carboxylic acid having a carbon number of from 0.01 mol/L to 2.0 mol/L of 1 or more and 4 or less.

(4) The copper plating solution for embedding ULSI fine wiring as in (3), wherein the carboxylic acid is acetic acid.

(5) A method of copper plating for ULSI fine wiring, which is characterized by using a copper plating solution for embedding ULSI fine wiring as in any one of (1) to (4).

(6) A ULSI fine wiring board characterized in that a ULSI fine wiring is formed by a copper plating method for ULSI fine wiring as in (5).

In the formation of the ULSI fine copper wiring (inlaid copper wiring), the copper wiring layer is formed on the copper seed layer by using the copper plating solution of the present invention, whereby dissolution of the copper seed layer can be suppressed, and as a result, voids can be suppressed. / The occurrence of a void in the inner wall of the trench.

(Best form of implementing the invention)

The pH of the copper plating solution for embedding the ULSI fine wiring of the present invention is 1.8 or more and 3.0 or less. In general, the pH of the copper plating solution of the sulfuric acid base material is 1.2 or less, but the pH of the plating solution using a carboxylic acid such as acetic acid instead of sulfuric acid can be 1.8 or more and 3.0 or less. By setting the pH to 1.8 or more and 3.0 or less, the dissolution of the copper seed layer can be suppressed, and as a result, the occurrence of voids in the inner wall of the hole/trench can be suppressed. Preferably, the pH is 2.0 or more and 2.2 or less.

When the pH is less than 1.8, since the pH is low, the copper seed layer is easily dissolved, and as a result, voids are likely to occur. Further, when the pH is more than 3.0, the copper ions in the plating solution become oxides or hydroxides, and precipitation may occur.

As the carboxylic acid, any carboxylic acid which is dissolved in the plating solution and has a pH within the above range may be used, and a saturated carboxylic acid having 1 or more and 4 or less carbon atoms such as formic acid, acetic acid, propionic acid, butyric acid or oxalic acid may be used. For better, acetic acid is especially good.

The carboxylic acid is preferably contained in the plating solution in an amount of from 0.01 to 2.0 mol/L, more preferably from 0.2 to 1.0 mol/L. The concentration of the carboxylic acid in the plating solution has an effect on the embedding property and the pH. When the carboxylic acid concentration exceeds 2.0 mol/L, the pH of the plating solution drops to less than 1.8, and voids are likely to occur. Further, when the concentration in the plating solution of the carboxylic acid is less than 0.01 mol/L, the pH of the plating solution may exceed 3.0, and the precipitation phenomenon as described above may occur.

The copper plating solution of the present invention is an aqueous solution, and examples of the other components include a copper salt, a chloride ion, a trace additive, and the like, and each of them may be a conventional one without particular limitation.

Examples of the copper salt include copper sulfate, copper nitrate, copper chloride, and the like, and copper sulfate is preferred. The copper salt is preferably contained in the plating solution in an amount of from 0.05 to 1.5 mol/L, more preferably from 0.2 to 0.8 mol/L.

The chloride ion concentration is preferably 0.3 to 3.0 mol/L, more preferably 1.0 to 2.0 mol/L in the plating solution.

As a trace additive, a promoter, an inhibitor, a leveling agent, etc. are mentioned, for example.

Examples of the accelerator include bis(3-sulfopropyl) disodium disulfide and 3-hydrothiopropane sulfonic acid, and the plating solution preferably contains 1 to 30 mol/L.

Examples of the inhibitor include polyethylene glycol, polypropylene glycol, and the like, and the plating solution preferably contains 10 to 500 mg/L.

As the leveling agent, for example, Janus green B, polyethyleneimine, polyvinylpyrrolidone or the like may be mentioned, and the plating solution preferably contains 0.1 to 50 mg/L.

Further, the plating using the copper plating solution of the present invention is preferably carried out at a bath temperature of 20 to 30 ° C from the viewpoint of the stability of the plating bath and the deposition rate of copper, and the cathode current density is 0.1 to 5 A/dm ² is preferred.

It is preferable that a person who is a plated material for copper plating is a fine wiring board such as a semiconductor wafer, and a copper seed layer is provided on the surface of the substrate having the ULSI fine wiring such as a groove/hole.

The copper seed layer is preferably formed by a conventional method such as a sputtering method or an electroless plating method.

By performing electroplating using the copper plating solution of the present invention, even if the thickness of the copper seed layer in the trench/hole is 2 nm or 2 nm or less, plating without voids can be performed.

Example

Example 1

Copper plating was performed on the substrate with the ULSI fine wiring using the plating solution shown below. A fine groove pattern (line width: 180 nm, depth: 500 nm) is attached to the substrate of the material to be plated, and a Cu seed layer is formed on the outermost surface by sputtering. The thinnest portion of the trench is the 2 nm thickness of the Cu seed layer film.

Plating solution composition:

Copper (copper sulfate) 0.63 mol/L

Acetic acid 0.5 mol/L

HCl 1.4 mmol/L

Bis(3-sulfopropyl) disodium disulfide 10 mg/L

Polypropylene glycol 80 mg/L

Polyvinylpyrrolidone 10 mg/L

pH 2.1

Electroplating was carried out for 30 seconds at 25 ° C and 1 A/dm ² .

The results of cross-sectional SEM observation are shown in Fig. 1. There is no gap at all in the groove side wall portion.

Example 2

Copper plating was performed on the substrate with the ULSI fine wiring using the plating solution shown below. The tantalum substrate of the material to be plated was the same as in Example 1, and the thickness of the Cu seed layer film was 2 nm in the thinnest portion in the trench.

Plating solution composition:

Copper (copper sulfate) 0.63 mol/L

Formic acid 1.0 mol/L

HCl 1.4 mmol/L

Bis(3-sulfopropyl) disodium disulfide 10 mg/L

Polypropylene glycol 80 mg/L

Polyvinylpyrrolidone 10 mg/L

pH 1.9

Electroplating was carried out for 30 seconds at 25 ° C and 1 A/dm ² .

The results of the cross-sectional SEM observation, including the sidewall portion of the trench, were also completely free of voids.

Example 3

Copper plating was performed on the substrate with the ULSI fine wiring using the plating solution shown below. The film thickness of the Cu seed layer on the substrate of the material to be plated was the same as in Example 1 except that the thinnest portion in the trench was 1.8 nm.

Plating solution composition:

Copper (copper sulfate) 0.63 mol/L

Oxalic acid 0.1 mol/L

HCl 1.4 mmol/L

Bis(3-sulfopropyl) disodium disulfide 10 mg/L

Polypropylene glycol 80 mg/L

Polyvinylpyrrolidone 10mg/L

pH 2.5

Electroplating was carried out for 30 seconds at 25 ° C and 1 A/dm ² .

As a result of cross-sectional SEM observation, there was also no occurrence of voids in the sidewall portion of the trench.

Comparative example 1

Electroplating was carried out in the same manner as in Example 1 except that the composition of the plating solution was changed to the following.

Plating solution composition:

Copper (copper sulfate) 0.63 mol/L

Sulfuric acid 0.5 mol/L

HCl 1.4 mmol/L

Bis(3-sulfopropyl) disodium disulfide 10 mg/L

Polypropylene glycol 80 mg/L

Polyvinylpyrrolidone 10 mg/L

<pH 1.0

The result of SEM observation of the cross section is shown in Fig. 2, and at least a part of the side wall portion of the groove was observed to have a void (black shadow portion in the circle).

Fig. 1 is a cross-sectional SEM photograph of the plating material obtained in Example 1.

Fig. 2 is a cross-sectional SEM photograph of the electroplated article obtained in Comparative Example 1.

No component symbol description

Claims (5)

A copper plating solution for embedding ULSI (Ultra Large-Scale Integration) fine wiring, characterized in that the pH is 1.8 or more and 3.0 or less, and the carbon number is 0.01 mol/L or more and 2.0 mol/L or less. It is a saturated carboxylic acid of 1 or more and 4 or less. A copper plating solution for embedding ULSI fine wiring according to the first aspect of the invention, wherein the pH is 2.0 or more and 2.2 or less. A copper plating solution for embedding ULSI fine wiring according to the first aspect of the invention, wherein the carboxylic acid is acetic acid. The use of a copper plating solution for embedding ULSI fine wiring according to any one of claims 1 to 3, which is used for copper plating for ULSI fine wiring. A ULSI fine wiring board characterized in that ULSI fine wiring is formed by the use of a copper plating solution for embedding ULSI fine wiring as described in claim 4 of the patent application.