JPH04106930A - How to form copper wiring - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of forming copper wiring.

Steel has poor oxidation resistance and is difficult to use alone.

As a means to solve this problem, there is a need for a method of covering the entire wiring with a high-melting point metal.

[Conventional technology]

In the conventional method, titanium, zirconium, aluminum,
After forming a copper alloy wiring of boron, it is heated or exposed to plasma, and the substance forming the alloy diffused on the surface (top surface and side surfaces) forms nitride in a nitrogen atmosphere. It is argued that this nitride improves copper's oxidation resistance, making the copper alloy increasingly pure and approaching the resistance of pure copper.

In this method, the copper alloy is heat-treated to diffuse the alloying elements onto the surface, so the diffusion temperature also changes the characteristics of other semiconductor elements. Furthermore, copper has poor heat resistance and is oxidized by trace amounts of oxygen, so high-temperature processes must be avoided.

Therefore, copper oxide is formed on the copper surface in the above process, and a highly reliable nitride such as TiN is formed in the subsequent nitriding process.
etc. is difficult to form.

[Problem to be solved by the invention]

Since the above-mentioned conventional technology uses a high-temperature heat treatment process, there are problems such as oxidation of the copper surface (top surface and side surfaces) and uniformity of nitride, and the low resistance of copper.

High electromigration resistance and stress migration properties may deteriorate.

Furthermore, the copper alloy does not completely diffuse to the surface due to heat treatment, but is partially dissolved in the copper wiring. Therefore, even if stable nitride is formed on the copper surface (upper surface and side surfaces), the characteristics, resistance, and migration properties of the internal copper alloy become problems.

In order to address the above technical problems, it is conceivable to form a good sidewall protective film at the same time as etching. An object of the present invention is to propose a copper wiring method that does not add high-temperature thermal history and does not require additional steps.

[Means to solve the problem]

To achieve reactive ion etching of copper, it is necessary to generate and sublimate copper chloride. A chlorine gas containing a high melting point metal is used as the etching gas.

Helium at the same time.

A gas such as nitrogen may be introduced. As a copper sidewall protective film, M o + W r T a g T iH
By using these chlorine-based gases, copper can be etched with chlorine and at the same time Mo,
A high melting point metal such as W can be attached to the sidewall. Although these chlorine-based gases are normally liquid, they can be introduced as a gas by reducing the pressure inside the etching chamber. The tri-etching device is preferably one that can accomplish reactive ion etching. Due to anisotropic etching, Mo, W, etc. attached to areas other than the side walls are etched away by chlorine ions and do not remain as etching residues.

[Effect]

A chlorine-based gas of a high melting point metal, such as MoCQs, introduced into the dry etching apparatus is turned into plasma by applying a high frequency voltage. Of the molybdenum and chlorine turned into plasma, chlorine reacts with copper to form copper chloride and sublimate. Molybdenum adheres to the copper surface, but reacts with chlorine and sublimates. At this time, the molybdenum attached to the steel side wall is
Since chlorine ions hit the substrate vertically, compounds with chlorine are not generated. When the final copper pattern is formed, the molybdenum will cover the entire copper sidewall. The copper and molybdenum will now cover the entire copper sidewall.

Copper and molybdenum do not form a solid solution and are thermally stable, so they do not degrade copper's resistance fluctuations, high electromigration, or stress migration resistance.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

A case where Mo Ca2 is used as the etching gas will be explained. A silicon oxide film 3 is grown on a silicon substrate 4, and copper 2 is deposited thereon to a thickness of, for example, 500 nm. The method of depositing the copper 2 is, for example, a DC magnetron sputtering method at a pressure of 10 m Torr (7) A r i X and a DC 4 KW. Thereafter, the resist 1 is patterned using a normal exposure method (FIG. 1(a)).

The copper target for sputtering with a DC magnetron may be pure copper or a copper alloy. The copper alloy at this time is preferably an element that improves electromigration resistance, stress migration resistance, corrosion resistance, and oxidation resistance of copper. - Examples include silver, aluminum, and nickel.

Examples include iron, zinc, and zirconium.

Next, as shown in (b), a high melting point metal chlorine gas such as MoCQ56 is introduced to reactively ion-etch the copper 2. At this time, RF of 100 W, for example, is applied onto the substrate. The flow rate of MoCf156 is, for example, 2 Q sccm. The pressure at this time is, for example, 5 pa. In consideration of problems such as plasma stability, thermal conductivity, and etching residue, it is desirable to simultaneously introduce helium, nitrogen, etc. into the etching gas. Plasma Mo, CQ is RF
It moves straight onto the substrate due to the bias. Copper 2 becomes anisotropic due to the influence of chlorine ions traveling straight. Molybdenum 5 adheres to the entire surface, but any portion other than the side walls is etched away by chlorine ions. The molybdenum 5 on the side wall is also etched by several nm by isotropic chlorine radicals, but most of it remains.

(c) shows that after the etching of copper 2 has been completed, molybdenum 5 is attached to the side wall.
This is the shape in which resist 1 has been removed. By using this method, the oxidation resistance and corrosion resistance of copper, which have been problems until now, are improved because they are protected by molybdenum 5. The side wall thickness of molybdenum 5 is determined by the etching time, MoCQr+flow rate, etc., but it is preferably several nm+ when considering the protective effect of copper, line width, etc.

Next, as shown in Figure 2, the entire surface of copper 2 (top, bottom and side surfaces)
A case will be described in which the molybdenum is covered with molybdenum 5.5a and 5.5b. In order to improve the adhesion with the copper 2 and to prevent the reaction between the copper 2 and the silicon substrate 4, molybdenum 5b is deposited on the silicon oxide film 3 using, for example, a DC magnetron sputtering method.
n deposited.

The sputtering conditions at this time are, for example, 1.0 mTo.
DCIKW is set at an Ar pressure of rr. Next, Figure 1(a)
Copper 2 is deposited to a thickness of, for example, 500 nm in a similar manner. Next, 1100 nm of molybdenum 5a is deposited in the same manner as above. The molybdenum 5a on the upper surface of the copper 2 is used to prevent the reaction between the resist 1 and the copper 2, to prevent the copper 2 from being oxidized by oxygen plasma when the resist 1 is removed after patterning, or as an antireflection film during exposure. After that, resist 1 is patterned. This three-layer structure of molybdenum 5a/copper 2/molybdenum 5b is etched.
), molybdenum 5a, copper 2. Etch with molybdenum 5b.

(c) shows the shape after etching has been completed and the resist 1 has been removed using oxygen plasma. At this time, since the upper surface of the copper 2 is covered with molybdenum 5a, there is no problem of oxidation. In this way, the entire surface (upper and lower surfaces and side surfaces) of copper 2 is covered with molybdenum 5a, 5
, 5b, the structure is strong against external corrosion and oxidation, and is also strong against electromigration and stress migration of the copper 2.

Thereafter, even if a glabellar insulating film, for example a silicon oxide film 6, is deposited by the usual CVD method as shown in FIG. 2(d), there is no problem of oxidation of the copper 2 because the entire surface is covered with highly heat-resistant molybdenum.

Figure 3 shows the case where there is no protective film on the side wall of copper 2 and when the entire surface is covered with molybdenum 5, the width is 2 μm and the length is 2 mm.

A pattern is shown in which a wiring with a thickness of 500 nm is formed and the resistance at both ends is measured. (a) shows the case when etched with CQ 2, and (b) shows the case when etched with Mo CQ s. (c) is the wiring pattern of (a) and (b) seen from above.

FIG. 4 shows the results of evaluating the heat resistance of the wiring pattern formed by the method shown in FIG. The substrate was heated to 200° C. and the resistance at both ends was measured. The resistance of wiring without a protective film increases with heating time. On the other hand, wiring with a protective film has almost no resistance change. For example, when the heating time is 2 minutes, the resistance increases by 0.3% with the protective film and by 4.5% without the protective film.

This indicates that the molybdenum on the side walls has increased heat resistance.

FIG. 5 shows an investigation of resistance changes after exposure to oxygen plasma using a pattern similar to that of FIG. 4. Oxygen plasma conditions were 1 OOW and 0.5 Torr.

2Q/win. Figure 4 similarly shows that the resistance of wiring without a protective film gradually increases, while that of wiring with a protective film gradually increases.
remains almost unchanged.

As can be seen from FIGS. 4 and 5, by providing the sidewall protective film, the heat resistance and oxygen plasma resistance of copper are improved, and a highly reliable copper wiring can be formed.

〔Effect of the invention〕

According to the present invention, the sidewall protective film can be formed at the same time as copper tri-etching, leading to a reduction in process steps. Furthermore, since the formation method is a sputtering method, there is little thermal influence on other semiconductor elements.

In addition, the process protects pure copper, resulting in low resistance.

High migration resistance does not deteriorate.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a copper single-layer film tri-etched with Mo CQ 5, and Figure 2 is a cross-sectional view of a copper single-layer film tri-etched with Mo CQ 5. Figures 3(a) and 3(b) are cross-sectional views with and without using a chlorine-based gas of a high-melting point metal as the dry etching gas, and (c) is a diagram showing the resistance measurement pattern and measurement method. , FIG. 4 is a diagram showing the heat resistance of the pattern of the structure shown in FIGS. 3(a) and 3(b), and FIG. 5 is a diagram showing the oxygen plasma resistance. 1...Resist, 2...Copper, 3...Silicon oxide film,
4... Silicon substrate, 5, 5a, 5b... Molybdenum, 6 Silicon oxide film.

Claims (1)

[Claims] 1. A method for forming wiring containing at least copper,
The method includes a step of depositing copper on a silicon oxide film, a step of patterning a resist after this step, and a step of dry etching the copper with a chlorine-based gas containing a high melting point metal after this step. Characteristic copper wiring formation method. 2. In a method of forming a wiring containing at least copper,
A process of depositing copper on a copper diffusion barrier metal, a process of depositing a copper diffusion barrier metal again after passing through this process, a process of patterning a resist after passing through this process, and a process of patterning a resist after passing through this process. A method for forming a copper wiring, comprising the step of dry etching the three-layer film with a chlorine-based gas containing a high melting point metal. 3. The chlorine-based gas containing a high melting point metal according to claim 2 is M
oCl_5, WCl_5, TaCl_4, TiCl_4
, ZrCl_4 and another chlorine-based gas. 4. A method for forming a copper wiring, characterized in that the etching gas is at least one of the chlorine-based gas containing the refractory metal according to claim 3, helium, and nitrogen. 5. Other chlorine-based gases according to claim 3 include Cl_2, C
A method for forming a copper interconnection characterized by using at least one of Cl_4, SiCl_4, and BCl_3.