JP3191344B2 - Copper film etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a copper film, and more particularly to a method for forming a copper wiring used in a semiconductor device by dry etching.

[0002]

2. Description of the Related Art In recent years,
The electrode wiring tends to be miniaturized with high integration of LSI. Al or an Al alloy is frequently used as an electrode wiring material. However, as the line width decreases, electromigration becomes severe, and it becomes difficult to guarantee reliability. Therefore, high-melting-point metals such as Mo and W have been tried as wiring materials in place of Al, but the resistance is twice as high as that of Al in the bulk, and even higher in the thin film. Therefore, a material which is resistant to electromigration and has low resistance is required. Therefore, it has been considered to use Cu as a wiring material instead of Al. This Cu has a low resistance and is resistant to electromigration,
Enables fine devices.

However, one of the reasons that Cu wiring has not been applied to devices so far is that dry etching is difficult. As a conventional etching technique for a Cu film, there are a method of etching with a hydrochloric acid solution containing nitric acid, ammonium persulfate, and iron chloride, and an etching using an Ar ion beam (the 47th Autumn Applied Physics Society Preprints, 30p-N). -12, p. 513, 198
6). The former has an undercut and is not suitable for fine processing, and the latter has problems such as a low etching rate, damage to a base, and a low selectivity with respect to a resist.

[0004] Also, JP-A-2-83930 discloses that
It discloses anisotropic etching of Cu, and uses Ar + CCl ₄ as an etching gas. Ar
Therefore, there is a problem that the substrate is damaged because the Cu film is hit by physical sputtering, and a sufficient selectivity cannot be obtained. Further, although it is described that copper chloride is formed as a side wall protective film, since this chlorine proceeds inside and reacts, processing accuracy in a submicron region is low.

The present invention has been made in view of such conventional problems, and has no damage to the base.
An object of the present invention is to provide a method for etching a copper film which has a sufficient selectivity and has a sidewall protection effect.

[0006]

SUMMARY OF THE INVENTION In view of the above, the invention according to claim 1 is to dilute a gas composed of iodine (I) and carbon (C) in a molecule with an inert gas, and to use the diluted gas. With etching gas at a pressure of about 0.02 Torr
Copper iodide produced by the reaction with the copper film is heated to a substrate temperature of 150 ° C. or more.
In order to solve this problem, the copper film is etched by being separated at a low temperature , and a side wall protective film made of carbon is formed.

According to a second aspect of the present invention, a gas containing iodine (I) and a CH ₄ gas are used as an etching gas in a range of about 0.1 to 1.0.
Copper iodide produced by reacting with a copper film at a pressure of 02 Torr
The solution is to remove the copper film at a substrate temperature of 150 ° C. or more to etch the copper film and to form a sidewall protective film of carbon.

[0008]

According to the present invention, in order to achieve high-precision dry etching of a copper film, RIE using an alkyl iodide containing iodine (I) and carbon (C) in a molecule as a reaction gas is used.
Performed by technology. Alkyl iodide is a compound of an alkyl group and iodine.

Examples of the alkyl iodide include methyl iodide (CH ₃ I) and methyl iodide (C ₂ H
₅ I), propyl iodide _{(C 3 H} 7 I), iodide heptyl _{(C 4} H 9 I), iodide amyl _(C 5 _H 11 I), there is hexyl iodide _{(C 5 H 13} I) and the like .

In such dry etching, during the etching, copper reacts with iodine ions or iodine radicals to form copper iodide. In addition, the substrate is kept at 150 ° C.
By heating as described above, detachment of the reaction product from the substrate is promoted. Then, during the etching, carbon contained in the alkyl iodide adheres to the wiring side wall. This carbon adhesion protects the side walls and performs anisotropic etching.

FIG. 3 shows a vapor pressure curve of copper iodide. For example, at a pressure of 10 ^-2 Torr, copper iodide evaporates at 290 ° C. During the reactive ion etching, there is a temperature rise due to ion irradiation in addition to the temperature caused by heating on the substrate surface. Therefore, the temperature for actually heating the substrate is not required to be 290 ° C., but may be 150 ° C. or more.

The same effect can be obtained by using an etching gas containing iodine and carbon other than the alkyl iodide.

Further, according to the present invention, by mixing and using a gas containing iodine and a gas containing carbon, copper reacts with iodine ions or iodine radicals to form copper iodide, Carbon adheres to the side walls from the gas containing, and acts as a protective film, enabling anisotropic processing.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the method for etching a copper film according to the present invention will be described below based on embodiments shown in the drawings.

Embodiment 1 Embodiment 1 of the present invention will be described below. FIG. 2 is a schematic diagram of an RIE apparatus used in the present invention. In the figure, 11 is a vacuum chamber, 12 is a sample stage, 13 is an internal heater, 14 is a counter electrode, 15 is a gas introduction pipe, 16 is an exhaust pipe, and 17 is an RF power supply. This is a normal RIE apparatus, but uses methyl iodide as a gas system. An internal heater 13 is incorporated in the electrode on the substrate side so that the substrate can be heated. Evacuation uses a turbo molecular pump. An example of the etching conditions is shown below.

Gas: Methyl iodide 100 _SCCM Pressure: 0.02 Torr RF power: 250 W Substrate temperature: 170 ° C. When etching Cu under the above etching conditions, an etching rate of about 0.3 μm / min is obtained. . To increase the etching rate, the RF power may be increased.

Hereinafter, the etching process of Cu will be described with reference to FIG. In FIG. 1 (A), after a SiO ₂ film 22 is formed on a semiconductor substrate 21 on which a predetermined element has been formed, a contact hole is opened, a natural oxide film of the contact hole is removed, and Cu is removed by DC magnetron sputtering.
A three-layer film of a film 25, a TiN film 24, and a Ti film 23 is continuously formed as shown in the figure. Here, the TiN film 24 functions as a copper diffusion barrier metal, and the Ti film 23 is used for making ohmic contact with a contact hole. Each film thickness is
The Cu film 25 is 5000Å, the TiN film 24 is 1000Å,
The Ti film 23 has a thickness of 250 °. Cu film 25, TiN film 2
4, The thickness of the three-layered film of the Ti film 23 is a recommended value, and does not need to be the same. Next, a resist pattern 26 is formed on the Cu copper film 25 using a normal photolithography technique. FIG. 1B shows a state during the etching. As mentioned above, during etching Cu
Reacts with iodine ions or iodine radicals to form copper iodide. When the substrate is heated to 150 ° C. or more, copper iodide is separated from the substrate and etching is performed. Since alkyl iodide (CH ₃ I in the embodiment) is a gas containing carbon, the carbon adheres to the side wall of the wiring during etching to form the side wall protective film 27. FIG.
(C) shows the state after the etching. Carbon adheres not only to the side walls of the copper wiring but also to the side walls of the resist.
Thus, a Cu wiring having a rectangular cross section is obtained. Next, the resist is removed by a resist ashing technique. Since copper is a substance that is easily oxidized, ashing is performed using a microwave downflow ashing apparatus that can be processed at a low temperature. The resist is removed with 300 _SCCM oxygen, a pressure of 2 Torr, a substrate temperature of 150 ° C., and a microwave power of 400 W. When the resist is removed, carbon attached to the wiring side wall can be removed (see FIG. 1D).

In this embodiment, a resist is used as an etching mask. However, if it is necessary to further raise the substrate temperature in order to increase the etching rate, a heat resistant material such as a silicon oxide film or a silicon nitride film is used. A mask may be used.

Embodiment 2 An example in which a gas containing carbon is added to alkyl iodide as an etching gas for copper will be described. The etching conditions are shown below.

Gas: CH ₃ I (70 _SCCM ) + CH ₄ (30 _SCCM ) Pressure: 0.02 Torr RF power: 250 W Substrate temperature: 170 ° C. Under the above conditions, an etching rate of about 0.2 μm / min can be obtained. The formation mechanism of the side wall protective film at this time is described in Example 1.
It is similar to Example the addition of CH ₄ 1 (CH ₃ I
Since the carbon concentration in the gas is higher than that of the single layer, the sidewall protective film is firmly formed. This is useful for etching with a wiring width of 0.3 μm or less. The gas containing carbon to be added is preferably CHF ₃ , CF ₄ , C ₂ F ₅ or the like in addition to CH ₄ .

(Embodiment 3) An example in which alkyl iodide is diluted with an inert gas as a copper etching gas will be described. The following shows the etching conditions.

Gas: CH ₃ I (30 _SCCM ) + N ₂ (70 _SCCM ) Pressure: 0.02 Torr RF power: 400 W Substrate temperature: 150 ° C. Under the above conditions, an etching rate of about 0.3 μm / min can be obtained. . Nitrogen dilution reduces the reactivity of the alkyl iodide with copper, but increases the physical sputter etch factor, causing iodine ions to be perpendicular to the substrate. The dilution lowers the carbon concentration in the reaction gas,
Although the side wall protective film is thinner than that of the first embodiment, as described above, copper is vertically etched because of a large amount of ions which are incident vertically. In this embodiment, the RF power was increased to 400 W to increase the ion energy. further,
Since etching is mainly performed by physical sputter etching, the substrate heating temperature can be reduced. Considering the heat resistance of the resist, the lower the temperature, the more precise the etching can be performed. This is useful for etching with a wiring width of 0.3 μm or less. Gas for diluting the Ai other than _{N 2, He, Ne, Kr} , Xe, Rn , etc. are good.

Although the embodiments have been described above, the present invention is not limited to these, and various design changes accompanying the gist of the configuration are possible.

In addition to the above embodiment, reactive ion etching may be performed using, for example, hydrogen iodide (HI) and carbon tetrafluoride (CF ₄ ). In this case, for example,
Substrate temperature 170 ° C., HI flow rate 100 _SCCM , CF ₄ flow rate 100 _SCCM , pressure 0.02 Torr, RF power 250
Under the condition of W, an etching rate of about 0.2 to 0.4 μm / min can be obtained. Also, this etching mechanism
This is the same as the above embodiment.

Further, by forming a high melting point metal under the copper film formed according to the present invention, the electromigration resistance can be further enhanced.

[0026]

As is apparent from the above description, according to the present invention, the following effects can be obtained.

The reaction between copper and alkyl iodide produces copper iodide (Cu ₂ I ₂ ), which has the effect of enabling dry etching of copper.

When the substrate is heated, the reaction and desorption are promoted, and there is an effect that a high etch rate can be obtained.

Since the chemical reactivity is high, a high etching selectivity between copper and the underlying oxide film can be obtained unlike the physical sputter etching.

The side wall protection effect is produced by the carbon of alkyl iodide, and a copper wiring having a vertical shape can be obtained.

The selectivity with respect to the resist is high, the etching can be performed with high precision, and the copper wiring can be applied according to the 0.35 micron rule.

The practical use of copper wiring becomes possible, and the high potential of Cu makes it possible to realize a highly reliable and high-density device.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views showing steps of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an RIE apparatus used in the embodiment.

FIG. 3 is a graph showing a vapor pressure curve of copper iodide.

[Explanation of symbols]

21: semiconductor substrate, 22: SiO ₂ film, 23: Ti film,
24 ... TiN film, 25 ... Cu film, 27 ... Sidewall protective film.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00

Claims (2)

(57) [Claims] 1. A gas comprising iodine (I) and carbon (C) in a molecule is diluted with an inert gas, and the diluted gas is used as an etching gas for about 0.02 T
The copper iodide produced by reacting with the copper film at
A method for etching a copper film, comprising etching a copper film by separating at a substrate temperature of not less than ° C. and forming a sidewall protective film by carbon. Wherein iodine gas and CH ₄ gas containing (I), copper at a pressure of about 0.02Torr as an etching gas
Substrate temperature of 150 ° C or higher with copper iodide generated by reacting with film
Etching the copper film by detaching with
A method for etching a copper film, comprising forming a sidewall protective film with carbon.