JPH11131093A - Cleaning liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cleaning liquid capable of efficiently removing metal impurities on the surfaces of substrates without causing the problems of metal corrosion, storability, environmental loads and the like, and useful for cleaning chemically and mechanically polished wafers or the like by including a specific chelating agent without including hydrogen fluoride. SOLUTION: This cleaning liquid free from hydrogen fluoride and used for cleaning substrates to which metal wirings are applied contains (A) oxalic acid (ammonium) or (B) a polyaminocarboxylic acid such as ethylene diamine tetraacetate (ammonium). The cleaning liquid preferably contains both the components A and B, and can react with Fe of metal impurity to form a ternary complex having good solubility, thereby capable of enhancing cleanability. The cleaning liquid well forms complexes not only with Fe but also with metal impurities such as Mn, Al and Ce, and is thereby effective for cleaning and removing the metal impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning liquid, and more particularly to a cleaning liquid for removing metal contamination on a substrate after metal wiring has been provided. In addition, the present invention is particularly applicable to a semiconductor manufacturing process in which chemical mechanical polishing (CMP) is performed.
The present invention relates to a cleaning liquid for a substrate having a metal wiring to be used later.

[0002]

2. Description of the Related Art With the high integration of ICs, strict contamination control is required because a trace amount of impurities greatly affects device performance and yield. That is, the metal impurity concentration on the substrate surface is set to 10 ¹⁰ at
It is required to control it to oms / cm ² or less, and therefore, various cleaning liquids are used in each step of semiconductor manufacturing. Generally, sulfuric acid-
Hydrogen peroxide water, ammonia water-hydrogen peroxide water-water (SC
-1), hydrochloric acid-hydrogen peroxide water-water (SC-2), dilute hydrofluoric acid, etc., and each cleaning solution is used alone or in combination depending on the purpose. On the other hand, in recent years, flattening of insulating films,
Chemical mechanical polishing (C
MP) technology has been introduced into the semiconductor manufacturing process.
As cleaning of metal impurities adsorbed on the substrate surface after P, see, for example, Monthly Semiconductor World, p. 92, 3, 1
997 describes that an aqueous solution of citric acid is used, and International Publication WO96 / 26538 describes that an aqueous solution of citric acid or ethylenediaminetetraacetic acid (EDTA) is used together with hydrogen fluoride. I have. In addition, Japanese Patent Application Laid-Open No. HEI 1 (1995) published after the priority date in connection with the application before the priority date of the present application
0-72594 (EP-A-812011) describes a cleaning solution containing an organic acid such as citric acid and a complexing agent.

[0003]

The liquid properties of the above-mentioned general cleaning liquid are oxidizing and strong acid or strong alkaline. Therefore, when cleaning the substrate after metal wiring is applied, In addition, the metal exposed on the surface of the substrate is corroded (etched), and the metal is corroded by the permeation of the cleaning liquid even when the metal is covered by an insulating layer or the like. Therefore, it may not be used in a semiconductor manufacturing process. For example, CMP
It is impossible to use such a cleaning liquid in a technique such as an interlayer connection called W (tungsten) -plug, which is currently receiving the most attention as an applied technique.
In general, CMP of metal presses a wafer on a cloth called a buff while supplying a slurry, which is a mixture of abrasive particles and chemicals, and rotates the wafer by using both chemical and physical actions to provide interlayer insulation. Although this is a technique for polishing a film or a metal material to flatten the film, there is a problem that a large amount of metal impurities are adsorbed on a silicon oxide film surface after polishing. Accordingly, there is a need for a cleaning solution that can efficiently remove such metal impurities.

[0004] In particular, in W (tungsten) CMP,
Polishing rate, alumina-ferric nitrate slurry which is excellent in terms of processing accuracy is generally used, but since ferric nitrate is used as an oxidizing agent, after the blanket W is removed, There is a large problem that a large amount of Fe is adsorbed on the exposed silicon oxide film surface. Since the concentration of ferric nitrate used here is high, the surface concentration of Fe adsorbed on the surface of the silicon oxide film is extremely high at 10 ¹⁴ atoms / cm ² or more, and secondary contamination of not only the wafer but also the production line is a problem. Becomes Therefore, it is desired to remove Fe adsorbed on the substrate to 10 ¹⁰ atoms / cm ² by CMP before starting the next step. Although the cleaning solution containing hydrogen fluoride according to the conventional technique can be expected to remove metal impurities, it cannot solve the problems of corrosion of metal and etching of the interlayer insulating film. On the other hand, in order to solve the problem of corrosion to metal, in the method using an aqueous solution of citric acid in the above-described conventional technology as a cleaning solution used after CMP of a W-plug, although corrosion to metal is eliminated,
The concentration of Fe on the surface of the substrate after washing with an aqueous citric acid solution is about 10 ¹³ atoms / cm ^2, which is far from sufficient.

[0005] Furthermore, a cleaning solution using citric acid requires a high concentration of 20 to 30% in order to obtain a sufficient cleaning effect, which imposes a heavy burden on the environment such as waste liquid treatment and tends to cause mold. However, there is also a problem with storage stability. As described above, means for comprehensively solving the above-mentioned problems has not been known at present. Therefore, an object of the present invention is to provide a cleaning solution capable of easily and efficiently removing metal impurities on the surface of a substrate without corroding the metal. An object of the present invention is to provide a cleaning liquid for cleaning a substrate after wiring has been performed.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that at least one of oxalic acid, ammonium oxalate and polyaminocarboxylic acids is contained and hydrogen fluoride is contained. It has been found that a cleaning solution containing no is good for cleaning a semiconductor substrate, and in particular, can clean metal impurities adsorbed on a wafer after CMP. That is, the present invention provides a cleaning solution for cleaning a substrate after metal wiring, which is characterized by containing at least one of oxalic acid, ammonium oxalate, and polyaminocarboxylic acids, and not containing hydrogen fluoride. is there. Oxalic acid, ammonium oxalate or polyaminocarboxylic acids in the present invention can form a complex with Fe and have a large stability constant, and thus can be used for washing Fe. Particularly, oxalic acid or ammonium oxalate is used in combination with polyaminocarboxylic acids. By doing so, a high detergency can be obtained. This is presumably because Fe and oxalic acid and polyaminocarboxylic acid form a more soluble ternary complex, so that the detergency is further improved.

Further, the cleaning liquid of the present invention is also effective for cleaning metal impurities such as Mn, Al, Ce and the like caused by other slurries. The reason is considered as follows. -The stability constant of the complex of Mn and oxalic acid is large, and its salt is highly soluble in an aqueous oxalic acid solution. -The stability constant of the complex of Al and oxalic acid is much larger than that of citric acid. -Ce forms a stable complex with ethylenediaminetetraacetic acid (EDTA), and the oxalate of Ce dissolves well in an alkaline solution of EDTA. From the above, a sufficient effect is exhibited not only for Fe but also for metal impurities and the like caused by the slurry.

The cleaning solution of the present invention has a preferable property that it does not corrode metals such as aluminum, aluminum alloys, copper, tungsten, titanium, titanium nitride, etc., even if the cleaning solution is acidic. Therefore, the present invention relates to a substrate on which metal wiring has been applied, whether or not the metal is exposed on the surface thereof, even if the metal is not exposed. This is effective for cleaning metal impurities adsorbed on the substrate surface after CMP, and also in the case of a printed circuit board constituting an electronic component or a metal wiring having a damascene structure, without etching the metal wiring portion. This is effective for removing metal contaminants remaining on the substrate. In addition, the cleaning solution of the present invention exhibits a sufficient cleaning effect at a concentration of 1/10 of that of the citric acid cleaning solution, does not cause mold, and can significantly reduce the burden on the environment. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The cleaning solution for cleaning the substrate after the metal wiring of the present invention has been formed has a concentration of oxalic acid or ammonium oxalate in the cleaning solution of 0.1 to 10% by weight, particularly preferably 1.0 to 10% by weight. 6 wt%. If the concentration of oxalic acid is too low, the cleaning effect is not sufficiently exerted, and if the concentration is high, an effect commensurate with the concentration cannot be expected, and crystals may further precipitate.

The polyaminocarboxylic acids include:
Ethylenediaminetetraacetic acid (EDTA), trans-1,
2-cyclohexanediaminetetraacetic acid (CyDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), N- (2-hydroxyethyl) ethylenediamine-N, N ', N'-triacetic acid (EDTA
-OH) and ammonium salts thereof are preferred. Generally, these compounds are used in the form of a free acid or a salt, but the free acid has low solubility in water or an acid, and is not suitable for preparing a highly concentrated solution. Therefore, it is necessary to use a water-soluble salt in order to prepare a high-concentration solution, and a metal-free salt such as an ammonium salt which does not adversely affect the properties is most preferable for semiconductor production.

The concentration of the polyaminocarboxylic acid is as follows:
0.0001 to 5 wt%, particularly preferably 0.001 to 5 wt%
01 wt%. If the concentration is low, the cleaning effect is not sufficient, and if it is too high, the effect corresponding to it cannot be expected. The pH of the washing solution is 3 to 5. EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples of the present invention and Comparative Examples, but the present invention is not limited to these Examples.

[0012]

[Comparative example]

Comparative Example 1 A silicon wafer with an oxide film, which was immersed in an aqueous ferric nitrate solution and contaminated in advance, was subjected to a total reflection X-ray fluorescence apparatus (TRENO made by Technos)
X-610T) was used to measure the concentration of Fe on the wafer surface. Next, 200 g of citric acid was dissolved in 800 g of water,
After washing at 40 ° C. for 3 minutes as a 20% by weight aqueous solution, washing with water and drying, the concentration of Fe on the wafer surface was measured again to evaluate the ability to remove Fe (Table 4).

[0013]

【Example】

Example 1 (Oxalic acid concentration and removal ability) Oxalic acid was dissolved in water as a cleaning solution to obtain 0.1, 1.0,
Each aqueous solution of 3.4% by weight was prepared. Using each cleaning solution, the ability to remove Fe was evaluated at a liquid temperature of 40 ° C. for 3 minutes in the same manner as in Comparative Example 1 (Table 1).

[Table 1] Table 1

Example 2 (Treatment temperature and removal capacity) A 3.4% by weight aqueous solution prepared by dissolving 34 g of oxalic acid in 966 g of water was used as a cleaning solution.
The temperature was changed to 3, 30, and 40 ° C., and 3 mi as in Comparative Example 1.
The ability to remove Fe was evaluated using n (Table 2).

[Table 2] Table 2

Example 3 (pH and removal capacity) Ammonia was added to a 3.4% by weight aqueous solution of oxalic acid, and p
H3.0, 4.0, 5.0, and 6.5 washing solutions were prepared. Using each of the cleaning liquids, a liquid temperature of 40 ° C.
In minutes, the ability to remove Fe was evaluated (Table 3).

[Table 3] Table 3

Example 4 A 3.4% by weight aqueous solution of ammonium oxalate was prepared as a washing solution, and the solution was heated at 40 ° C. for 3 minutes in the same manner as in Comparative Example 1.
The removal ability of e was evaluated (Table 4). Example 5 As a cleaning solution, a mixed solution of oxalic acid and ammonium oxalate prepared by dissolving 5.0 g of oxalic acid and 29 g of ammonium oxalate in 966 g of water was used at a liquid temperature of 40 ° C. for 3 minutes as in Comparative Example 1. The ability to remove Fe was evaluated (Table 4). Example 6 An aqueous solution prepared by dissolving 34 g of oxalic acid and 0.1 g of ethylenediaminetetraacetic acid in 965.9 g of water was used as a washing solution, and the ability to remove Fe was evaluated at a liquid temperature of 40 ° C. for 3 minutes as in Comparative Example 1 ( Table 4).

Example 7 An aqueous solution prepared by dissolving 34 g of oxalic acid and 0.1 g of trans-1,2-cyclohexanediaminetetraacetic acid in 965.9 g of water was used as a washing solution, and a solution temperature of 40 as in Comparative Example 1.
The ability to remove Fe was evaluated at 3 ° C. for 3 minutes (Table 4). Example 8 0.1 g of ethylenediaminetetraacetic acid was used as a cleaning solution in water 99
Comparative Example 1 using an aqueous solution prepared by dissolving in 9.9 g
In the same manner as described above, the ability to remove Fe was evaluated at a liquid temperature of 40 ° C. for 3 minutes (Table 4). Table 4 shows the results of Comparative Example 1 and Examples 4 to 8.

[Table 4] Table 4

Example 9 (Etching property for various metals) A substrate with each metal film was immersed in a 3.4% aqueous solution of oxalic acid or a 10% aqueous solution of citric acid at 40 ° C. for 60 minutes, washed with water, and spin-dried. The film thickness was measured with a fluorescent X-ray film thickness meter to determine the amount of film reduction (Table 5).

[Table 5] Table 5

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/304 622 H01L 21/304 622Q 647 647A H05K 3/26 H05K 3/26 E (72) Inventor Hidemitsu Aoki Port of Tokyo 5-7-1, Shiba-ku, NEC Corporation

Claims (8)

[Claims] 1. A cleaning solution for cleaning a substrate after metal wiring is provided, wherein the cleaning solution contains at least one of oxalic acid, ammonium oxalate, and polyaminocarboxylic acids and does not contain hydrogen fluoride. The cleaning solution, characterized in that: 2. The method according to claim 1, wherein the composition contains any one of a combination of oxalic acid and polyaminocarboxylic acids, a combination of ammonium oxalate and polyaminocarboxylic acids, or a combination of oxalic acid and ammonium oxalate and polyaminocarboxylic acids. Cleaning solution. 3. The cleaning solution according to claim 2, wherein the cleaning solution is used at room temperature. 4. A composition containing a polyaminocarboxylic acid and having a pH of 3
The cleaning solution according to claim 1, wherein 5. The cleaning solution according to claim 1, which is used after chemical mechanical polishing. 6. The cleaning solution according to claim 5, wherein the cleaning solution is used for a substrate having a metal exposed on the surface after chemical mechanical polishing. 7. The method according to claim 5, wherein the substrate is not exposed to metal after chemical mechanical polishing.
The washing solution described in the above. 8. The cleaning solution according to claim 5, which is used after chemical mechanical polishing of the metal plug.