JPH07254604A - Method for forming copper thin film pattern - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a method for forming a copper thin film pattern, which aims to form a fine pattern without corrosion. [Structure] Copper or copper alloy thin film 3 on substrate 1 to be processed
After forming the thin film 3, the thin film 3 is dry-etched using a chlorine-based etchant to form a thin film pattern 5 made of copper or a copper alloy, and then the substrate 1 to be processed is immersed in aqueous ammonia to form the thin film pattern. A method of forming a copper thin film pattern is characterized in that the reaction product 7 adhering to the side wall 6 of 5 and the substrate and the chlorine gas adsorbed thereto are removed by dissolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a copper (Cu) or Cu alloy thin film pattern. Since it is necessary to process a large amount of information quickly, the semiconductor device that constitutes the main body of the information processing device is becoming more integrated due to the miniaturization of unit elements, and LSI and V
The LSI has been put to practical use, and the ULSI has been put to practical use as the size and capacity have been further increased.

Here, thin film forming technology, photolithography technology (photolithography), impurity ion implantation technology and the like are used for manufacturing such integrated circuits. 1/4 μm (Quarter-mic
ron) is required for practical use.

[0003]

2. Description of the Related Art In forming a wiring pattern forming a conventional integrated circuit such as an LSI or VLSI, aluminum (Al) has been used as a pattern forming material except for a special case such as high frequency.

However, as the degree of integration is improved, the width of the wiring pattern is reduced. On the other hand, the integrated circuit is multi-layered, and it is necessary to flatten the substrate surface to maintain the pattern accuracy. There is also a limit on the thickness of the pattern.

For these reasons, forming a 1/4 μm pattern using Al as in the prior art has a problem in terms of current capacity, and the use of Cu is being considered in place of this. Initially, a Cu thin film was formed on a semiconductor substrate (wafer) such as silicon (Si) through an oxide film (SiO ₂ ) using a vacuum deposition method or a sputtering method, and a photo-etching technique using a resist was used. Wet etching is used as a method for selectively etching Cu thin films to form fine patterns such as wiring.Sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), ammonium persulfate [(NH ₄ ) ₂ S ₂ O is used as a solute. ₈ ], various aqueous solutions of hydrochloric acid (HCl) containing iron chloride (FeCl ₂ ) have been used.

However, in the wet etching using these chemicals, the etching is isotropic, so that the side etching of the pattern side wall cannot be avoided, and therefore the wet etching cannot be applied to the formation of a fine pattern.

Therefore, ion milling using a reactive gas has been carried out. In this case, however, there is a problem that vertical etching is carried out and that the product adheres to the side wall of the pattern.

Therefore, for example, in Japanese Unexamined Patent Publication (Kokai) No. 2-83930, ion milling is performed using a mixed gas of carbon tetrachloride (CCl ₄ ) and argon (Ar) as a reactive gas (etchant), and then deposited on the side wall of the pattern. The method of removing the existing copper compound using ethyl alcohol is adopted.

The reaction products produced by the reaction between CCl ₄ gas and Cu include first copper chloride (CuCl) and second copper chloride (CuCl ₂ ), which are dissolved by washing with ethyl alcohol. being removed Te is only CuCl _2, remains CuCl in the side wall of the pattern, the chlorine ions contained in the residue ^- Cu wiring has a problem referred to be corroded by (Cl).

[0010]

A chlorine-based etchant is used to form a fine pattern by dry-etching a Cu thin film formed on a wafer, whereby a fine pattern having vertical sidewalls is formed. Can be formed.

However, in the cleaning with ethyl alcohol, there is a problem that a part of the reaction product remains and the reaction product containing Cl ⁻ corrodes Cu wiring and the like, and this solution is a problem.

[0012]

[Means for Solving the Problems]
After forming a thin film of Cu, this thin film is dry-etched using a chlorine-based etchant to form a thin film pattern of Cu, and then the wafer is immersed in aqueous ammonia to form a sidewall of the thin film pattern of Cu. A method of forming a Cu thin film pattern is characterized by dissolving and removing the reaction product adhering to the substrate and the Cl ₂ gas adsorbed thereto.

[0013]

[Function] The present invention applies not only CuCl ₂ but also CuCl to ammonia water.
It was made as a result of the finding that it dissolves in (NH ₃ aqueous solution).

The inventor has preferred a chlorine-based gas such as chlorine (Cl ₂ ) or CCl ₄ as an etchant for dry-etching a Cu thin film, but it is a reaction product of such a chlorine-based gas and Cu. It was found that among certain CuCl ₂ and CuCl, CuCl is less likely to react than CuCl ₂ but it dissolves by forming complex ions in ammonia water.

CuCl ₂ is prepared by dissolving ammonia water and copper aluminium chloride dihydrate (CuCl ₂ · 2NH ₄ Cl · 2H ₂ O). Thisゝa, aqueous ammonia is a solution dissolved the NH ₃ in water, commercially available concentrated aqueous ammonia is 28% solution, NH ₃
The solubility of water in water changes as follows depending on the temperature. That is, 40.6% by weight at 10 ° C, 34.6% by weight at 20 ° C, 2% at 30 ° C.
9.1% by weight, 24.0% by weight at 40 ° C, 19.0% by weight at 50 ° C, which decrease with increasing temperature.

Therefore, according to the present invention, after the Cu thin film is dry-etched by using a chlorine-based gas as an etchant, the Cu thin film is immersed in ammonia water whose liquid temperature is adjusted to react with the reaction product attached to the side wall of the Cu thin film pattern. However, Cl ₂ adsorbed on the side wall is easily removed by reacting with NH ₃ .

[0017]

【Example】

Embodiment 1 FIG. 1 shows that an oxide film 2 made of silicon dioxide (SiO ₂ ) is formed on a Si substrate 1 by a thermal oxidation method to a thickness of about 5000Å, and then is sputtered to a thickness of about 5000Å. After forming the Cu thin film 3, the Cu thin film 3 is dry-etched to form a fine thin film pattern 5.
As the mask 4, a SiO ₂ film having a thickness of about 3000 Å was formed by a vapor phase growth method (CVD method), and then formed by a photo-etching technique for coating a resist.

Next, the dry etching method for the Cu thin film 3 and
Then, the flow rate of Cl is used as an etchant. ₂: SiCl_Four: N₂: NH
₃= Use a mixed gas adjusted to 20: 20: 80: 10cc
To a reactive ion etching device (abbreviated as RIE device)
Supply, and operate the exhaust system to keep the pressure in the reaction chamber at 30 mtorr.
Dry etching was performed. (A in the figure above) A thin film made of a Cu thin film when dry etching is completed.
Pattern 5 is etched vertically, but this wall
6 and Cu on the oxide film 2 which has been dry-etched
Cl and CuCl₂The reaction product 7 consisting of
Cl₂Gas is adsorbed. (Above B in the same figure) Next, this substrate 1 is treated with ammonia water having a concentration of 28% by weight at room temperature.
As a result of soaking for 20 seconds, reaction product 7 was completely dissolved
I was there. (Above C in the same figure) Next, wash with pure water for 2 minutes and dry.
I dried it and formed a conductor line, but I observed it for a week
However, no occurrence of corrosion was observed. Example 2: Dry etching is performed in the same manner as in Example 1.
Was performed to form a thin film pattern 5 composed of a Cu thin film 3.
Then, the commercially available ammonia water with a concentration of 28% by weight was kept at 50 ° C.
The substrate 1 was soaked for 10 seconds. In this case NH₃The solubility of
It is 19% by weight, but the liquid temperature is high, so even in a short time
Reaction product 7 was completely dissolved.

Next, pure water was washed for 2 minutes and dried to form a conductor line, but no corrosion was observed even after observing for one week.

[0020]

The Cu thin film is dry-etched by using a chlorine-based etchant, and then the reaction product and the adsorbed Cl ₂ gas are dissolved by immersing it in ammonia water to form a Cu thin film. The pattern can be formed with high reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method for carrying out the present invention.

[Explanation of symbols]

 1 Si substrate (substrate to be processed) 2 Oxide film 3 Cu thin film 4 Mask 5 Thin film pattern 6 Wall surface 7 Reaction product

Claims (1)

[Claims] 1. A copper or copper alloy is formed by forming a thin film (3) of copper or a copper alloy on a substrate (1) to be processed and then dry etching the thin film (3) using a chlorine-based etchant. After the formation of the thin film pattern (5) consisting of the above, the substrate (1) is immersed in aqueous ammonia to adsorb the reaction product (7) attached to the side wall (6) of the thin film pattern (5). A method for forming a copper thin film pattern, which comprises dissolving and removing chlorine gas that is being formed.