JPH08181147A - Formation of wiring made mainly of copper - Google Patents

Abstract

PURPOSE: To provide formation of wiring made mainly of copper in which film separation is prevented even when etching is carried out at high temperatures. CONSTITUTION: A copper wiring preparation layer 23 including a lower barrier metal film 16, a copper film 18 and an upper barrier metal film 20 is formed on an underlying layer 13. Then, the structure composed of the copper wiring preparation layer 23 and the underlying layer 13 is annealed at a temperature higher than the recrystallization temperature of copper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a wiring mainly composed of copper.

[0002]

2. Description of the Related Art For a conventional method of forming a wiring mainly composed of copper (also referred to as a copper wiring), see a document (JAPANES).
E JOURNAL OF APPLIDE PHYS
ICS, Vol. 28, No. 6, June, 198
9, pp. L1070-L1072).

According to this document, first, a copper wiring preliminary layer including a SiO ₂ film, a lower titanium nitride film, a copper film and an upper titanium nitride film is formed on a silicon substrate.

Next, a resist pattern having the same shape as the wiring mainly composed of copper is formed on the upper titanium nitride.
Then, anisotropic etching is performed on the copper wiring preliminary layer in the depth direction of the substrate from the upper titanium nitride film by using a reactive ion etching (RIE) method to form SiO ₂
Etch until the surface of the film is exposed. Conventional RIE etching has been performed under the following conditions.

Etching gas: SiCl ₄ gas and N ₂
Mixed gas with gas Etching temperature: 250 ° C. When a wiring mainly composed of copper is formed by using the RIE method as described above, copper chloride (CuCl _x : where x is a composition ratio) is an etching product of copper. Is a numerical value that represents.)
Does not vaporize at room temperature due to its low vapor pressure. For this reason, it is necessary to carry out etching with the sample to be etched set at a temperature of at least 250 ° C.

[0006]

However, when the wiring mainly composed of copper is formed on the substrate by using the above-mentioned RIE method, there are the following problems.

Since copper (Cu) is generally weak in acid resistance and chemical resistance, a copper film is used by using a barrier material (barrier metal film) for preventing diffusion and reaction of copper on the front surface and the back surface of the copper film. Need to be sandwiched. However, when the front surface and the back surface of the copper film are sandwiched by the barrier metal film and then dry etching is performed at a high temperature (for example, 250 ° C.), the copper film and the barrier metal film have different thermal expansion coefficients, so that the copper film and the barrier film are different from each other. There is a problem that a difference in thermal expansion coefficient occurs between the metal film and the copper film, and film peeling mainly occurs between the copper film and the lower barrier metal film. Therefore, conventionally, R
A good wiring shape mainly composed of copper could not be obtained by using the IE method.

Therefore, there has been a demand for a method of forming a wiring mainly composed of copper that does not cause film peeling even if it is etched at a high temperature.

[0009]

Therefore, according to the present invention, a copper wiring preliminary layer including a lower barrier metal film / copper film / upper barrier metal film is formed on the underlayer, and then the upper barrier metal layer is applied to the underlayer surface. In the method of forming a wiring mainly composed of copper by etching until the copper is exposed, after the copper wiring preliminary layer is formed on the underlayer, the copper re-deposition is performed on the structure including the copper wiring preliminary layer and the underlayer. Annealing is performed at a temperature higher than the crystallization temperature. On the other hand, since the high temperature side limit temperature is determined by the barrier metal film used, it is preferable to set the temperature at which the barrier property is maintained without causing the diffusion or reaction of copper.

In carrying out the present invention, preferably, the carrier gas used for the annealing treatment is hydrogen (H ₂ ).
A mixed gas of nitrogen and nitrogen (N ₂ ) is preferable.

In implementing the present invention, it is preferable to form an etching resistant mask layer having heat resistance on the upper barrier metal film forming the copper wiring preliminary layer.

[0012]

According to the above-described method of forming a wiring mainly composed of copper in the present invention, after the copper wiring preliminary layer including the lower barrier metal film, the copper film and the upper barrier metal film is formed on the substrate, the copper wiring preliminary layer is formed. Annealing is performed on the structure including the underlayer and the underlayer at a temperature higher than the recrystallization temperature of copper. At this time, since the annealing treatment also reduces the stress between the lower and upper barrier metal films forming the copper wiring preliminary layer and the copper film,
There is no film peeling between the lower barrier metal film and the copper film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a copper-based wiring (hereinafter referred to as a copper wiring) according to an embodiment of the present invention will be described below with reference to the drawings. It should be noted that FIGS. 1 and 2 merely schematically show the shapes, sizes, and arrangement relationships of the respective constituents to the extent that the present invention can be understood. Therefore, it is not limited to this embodiment.

1A and 1B to 2A,
(B) And (C) is process drawing for demonstrating the formation method of the copper wiring of this invention.

First, as the base 13, Si on the substrate 10
A laminated structure having the O ₂ film 12 is used. The thickness of the SiO ₂ film 12 at this time is set to about 0.6 μm. Further, the substrate 10 used as the base 13 is a silicon (Si) substrate.

Next, a titanium (Ti) film 1 is formed on this underlayer.
4, the lower barrier metal film 16, the copper film 18, the upper barrier metal film 20, and the NSG film 22 are sequentially formed to obtain the structure shown in FIG. Hereinafter, a method of forming each film will be described.

A titanium (Ti) film 14 is formed on the SiO ₂ film 12 by using the sputtering method. Titanium film 1 at this time
The film thickness of No. 4 is 0.03 μm. The conditions of the stapper at this time are as follows.

Carrier gas: Argon (Ar) gas Gas flow rate: 24 sccm Pressure: 3 mTorr DC power: 500 W In this embodiment, the Ti film 14 is used in order to improve the adhesion at the interface with SiO ₂ / TiN. , SiO ₂ /
The Ti film 14 is not necessarily used if sufficient adhesion at the interface with TiN can be ensured.

Next, the lower barrier metal film 18 is formed on the titanium film 14 by using the sputtering method. In this example,
The lower barrier metal film 16 is made of titanium nitride (TiN) and has a film thickness of about 0.1 μm. Here, the lower barrier metal film 16 is also referred to as a lower TiN film. The sputtering conditions at this time are as follows.

Gas used: Mixed gas of Ar gas and N ₂ gas Gas flow rate ratio (sccm / sccm): Ar / N ₂ = 20
/ 20 (volume ratio) Pressure: 5 mTorr DC power: 2 kW Next, a copper film 18 is formed on the lower TiN film 16 by sputtering. The thickness of the copper film at this time is about 0.4μ
m. The sputtering conditions for forming the copper film are as follows.

Carrier gas: Ar gas Gas flow rate: 56 sccm Pressure: 3 mTorr DC power: 1 kW Subsequently, an upper barrier metal film 20 is formed on the copper film 18 by the sputtering method. In this embodiment, the upper barrier metal film 20 is a TiN film and the film thickness is about 0.1 μm. Here, the upper barrier metal film 20 is also referred to as an upper TiN film. The sputtering conditions at this time are the same as those for the upper TiN film 16 already described. Therefore, detailed description is omitted.

Next, the upper Ti is formed by using the plasma CVD method.
Etching resistant mask layer 22 having heat resistance on the N film 20
To form. At this time, the etching resistant mask layer 22 is formed of, for example, non-doped silicon glass (Non-doped).
The Silicate Glass (abbreviated as NSG) film 22 is used. At this time, the material of the NSG film 22 is a SiO ₂ film and the film thickness is 0.6 μm. The film forming conditions for this NSG film are as follows.

Gas used: mixed gas of silane (SiH ₄ ) gas and nitrous oxide (N ₂ O) gas Flow rate ratio (sccm / sccm): SiH ₄ : N ₂ O = 8
0: 1800 (volume ratio) Pressure: 300 mTorr Substrate temperature: About 115 ° C. RF power: 180 W In this embodiment, an NSG film was used as the etching resistant mask layer 22, but for example, SiN _x (x is a numerical value indicating a composition ratio). It is also possible to use a material such as

Next, in the present invention, the structure shown in FIG. 1A is carried into an annealing device (not shown) and an annealing process is performed. The annealing temperature at this time is higher than the recrystallization temperature of copper. In this embodiment, the annealing conditions are as follows.

Carrier gas and flow rate: mixed gas of hydrogen (H ₂ ) gas and nitrogen (N ₂ ) gas Gas flow rate ratio (sccm / sccm): H ₂ / N ₂ = 10
00/5000 (volume ratio) Annealing temperature and processing time: 400 ° C. (substrate temperature), 1
Time Note that the above-mentioned annealing treatment conditions indicate optimum temperature conditions. However, the annealing temperature may be higher than the recrystallization temperature of copper. In this embodiment, since the recrystallization temperature of copper starts from 150 ° C. from the experimental data, the structure including the copper wiring preliminary layer and the base is annealed at this temperature or higher. Since the recrystallization of copper is promoted by such an annealing treatment, the stress of each film forming the copper wiring preliminary layer forming the structure of FIG. 1A is reduced. Also, the upper limit temperature of annealing is determined by the material of the upper and lower barrier metal films, and in this embodiment, since the TiN film is used as the barrier material, it is about 700.
C becomes the upper limit temperature. Exceeding this upper limit temperature is not preferable because the effect of suppressing the diffusion or reaction of copper through the upper and lower TiN films is lost. Therefore, the preferred temperature range for annealing in this example is 150 ° C to 700 ° C.
The temperature range of ℃ is good.

Next, a resist layer 24 is formed on the NSG film 22, and a resist pattern 24 is formed by using the photolithography technique (FIG. 1B).

Next, the NSG film 22 is etched by using a magnetron RIE device (not shown) to obtain the structure shown in FIG. NSG film 2 formed at this time
2 is indicated by reference numeral 22a. The conditions of RIE at this time are as follows.

Etching gas: methane trifluoride (CHF
₃ ) Mixed gas of oxygen gas (O ₂ ) gas and gas flow ratio (sccm / sccm): CHF ₃ / O ₂ =
100/2 (volume ratio) Pressure: 45 mTorr RF power: 200 W Next, after removing the resist pattern 24 by any suitable method, dry etching is performed again by using a magnetron RIE apparatus, and then from the upper surface of the upper TiN film 22. Si
Each film is removed by etching until the surface of the O ₂ film 12 is exposed to obtain a structure as shown in FIG. The conditions of RIE at this time are as follows.

Etching gas: Silicon chloride (SiCl
₄ ) Gas / Chlorine (Cl ₂ ) gas / Nitrogen (N ₂ ) gas mixed gas Gas flow rate ratio (sccm / sccm): (SiCl ₄ / C
l ₂ / N ₂ = 20/10/120 (volume ratio)) Pressure: 30 mTorr RF power: 500 W Substrate temperature: about 300 ° C. Ti film 14 a and lower TiN film 16 remaining at this time
The copper wiring 25 is formed of the respective films of a, the copper film 18a, and the upper TiN film 20a ((C) of FIG. 2).

FIG. 3 is an X-ray diffraction curve diagram showing the result of the X-ray measurement of the copper crystal plane after the annealing treatment (450 ° C.). In the figure, the horizontal axis represents 2θ (the unit is an angle, where 2θ is the diffraction angle of the X-ray from the sample surface), and the vertical axis represents the count number (corresponding to the intensity). . The sample used for the measurement has a structure in which a Ti film, a lower TiN film and a copper film are sequentially formed on a silicon substrate.

As can be understood from the measurement results of FIG.
The (111) plane of Cu appears at a point where 2θ is about 45 degrees, and the (200) plane of Cu appears at a point where 2θ is about 50 degrees. Furthermore, 2θ of Cu (222) plane is about 9
It appears at the point of 5 degrees.

When no annealing treatment is performed, the Cu AS
Looking at the TM card, the peak intensity of the (111) plane of Cu is about 2.2 times that of the (200) plane. In addition, AST
As is well known, the M card is an American Society.
ty for Testing Materials
The strong line d of each substance is written on the card. In addition, the relative intensity (I / I ₁ ) and the crystal plane (hk
Since l) is also described, the strong line d and the relative intensity I / I ₁ for a specific crystal plane can be known by comparing the measured data with the card.

On the other hand, when the annealing treatment is performed, as can be understood from FIG. 3, the peak count number (intensity) of the (111) plane of Cu is 5612, and (20)
The peak intensity of the 0) plane is 251. Therefore, Cu
The intensity of the (111) plane is about 22 times that of the (200) plane. This is because, when annealing is performed at a recrystallization temperature of Cu or higher, copper atoms and fine voids in the copper film move in the copper film (this phenomenon is referred to as migration). It is considered that the orientation of is stronger. Further, since copper has a face-centered cubic structure as is well known, the (111) plane becomes the sloping surface. Therefore, since copper is plastically deformed in the (111) plane, the stress of the copper film is reduced. In this embodiment, upper and lower TiN films are formed on the front and back surfaces of the copper film. For this reason, stress is applied to the copper film even from the vertical direction of the copper, and the stress becomes larger in this embodiment than in the case of copper alone. Therefore, it is considered that the crystal structure of the copper film becomes stable and becomes dense by strongly orienting to the (111) plane of copper.

FIGS. 4A and 4B are views for explaining the sample used for measuring the warp and the measuring method thereof.
The measurement sample used here is SiO ₂ on a silicon substrate.
Film / Ti film / Lower TiN film / Cu film / Upper TiN film / N
A laminated structure of SG films is used. This sample is
It is the same as the structure of FIG. When measuring the warpage of this sample, the distance D from the both ends of the curved upper portion when viewed from the front of the cross-section sample to the upper surface of the convex portion with respect to the reference line is indicated by a plus sign, and with respect to the reference line. The distance D to the bottom of the recess is indicated by a minus sign.

The amount of warpage is measured as follows. The sample described above is loaded into a thin film internal stress measuring device (for example, Vacuum Riko Co., Ltd.). Then, a predetermined carrier gas is supplied into the apparatus to raise and lower the temperature at a predetermined temperature, and the amount of warpage is measured in real time.

FIGS. 5A and 5B are views showing the amount of warpage (D: μm) with respect to the annealing temperature (° C.). In the figure, (A) is a diagram showing warpage in the absence of annealing treatment, and (B) shows warpage in the presence of annealing treatment.

As can be understood from FIGS. 5A and 5B, without annealing, when the temperature is raised to 400 ° C. (curve I), a warp in the plus direction of about 30 μm at about 200 ° C. Occurs. Then, when the temperature is decreased from 400 ° C. (curve II), the temperature starts to warp in the opposite direction to the temperature increase, that is, in the negative direction until the temperature returns to room temperature. At this time, the warp at room temperature is about 20 μm. Therefore, the total warp when the temperature is raised and lowered is about 50 μm.

On the other hand, the annealing treatment (40
When the temperature is raised and lowered, the warp at a temperature rise of 400 ° C is about 35 μm in the positive direction, but when the temperature is lowered to room temperature, the warp is 0 μm.
Becomes Therefore, the total warp when the temperature is raised and lowered is about 35 μm. Thus, it can be seen that by performing the annealing treatment, the amount of warpage becomes about 70% of that when the annealing treatment is not performed, and the stress of the sample is reduced.

From the warp curve of FIG. 5A, it is considered that the following phenomenon occurs. First, when the temperature is raised from room temperature, the warp increases linearly up to about 150 ° C. After that, even if the temperature is raised to 400 ° C., the amount of warpage is gradually reduced. It is considered that this is because when the copper is treated at the recrystallization temperature or higher, the copper atoms and fine voids in the copper film migrate to change the structure of copper.

FIGS. 6A and 6B are schematic drawings of cross-sectional photographs of the cross-sections of the copper wiring with and without annealing, which are measured by SEM. In the figure, (A) shows the case where the annealing treatment is performed, and (B) shows the case where the annealing treatment is not performed.

As can be understood from FIG. 6, when the annealing treatment is performed ((A) of FIG. 6), the copper film is not peeled, whereas when the annealing treatment is not performed ((B) of FIG. 6). The copper film peeled between the copper film and the lower TiN film.

As is clear from the above results, a temperature (400 ° C.) higher than the recrystallization temperature (150 ° C.) of copper.
Since the structure including the copper wiring preliminary layer is annealed once, the stress of each film generated in the process of forming the copper wiring preliminary layer is reduced, so that the peeling of the copper film can be prevented.

In the above-mentioned embodiment, the TiN film is used as the barrier metal film for preventing the diffusion and reaction of copper.
The material is not limited to these materials, and examples thereof include tungsten (W), tantalum (Ta), tungsten titanium (TiW), chromium (Cr), cobalt (Co), vanadium (V) and niobium (Nb), and these. It is also possible to use one kind or a combination of two or more kinds of the above metal nitrides and ZrN.

Further, in this embodiment, a Ti film is formed between the SiO ₂ film and the lower TiN film to form the SiO ₂ film and the TiN film.
Although the adhesion between the films was improved, the Ti film is not limited to this Ti film. When the barrier material is changed, the barrier material has a thermal expansion coefficient close to that of the SiO ₂ film or the barrier metal film used. You may choose a material with good adhesion.

Further, among the annealing conditions of this embodiment, the gas flow rate ratio and the processing time are merely examples, and therefore are not limited to the above values.

[0046]

As is apparent from the above description, after the copper wiring preliminary layer including the lower barrier metal film, the copper film and the upper barrier metal film is formed on the underlayer, the temperature is higher than the recrystallization temperature of copper. Anneal at temperature. Therefore, when the temperature becomes higher than the recrystallization temperature of copper, the stress of the structure including the copper wiring preliminary layer and the base is relaxed. At this time, the stress generated in each film is also reduced, so that film peeling between the copper film and the lower barrier metal film or between the copper film and the upper barrier metal film can be prevented.

A mixed gas of hydrogen gas (H ₂ ) and nitrogen (N ₂ ) gas is used as a carrier gas for the annealing treatment. Therefore, during annealing, the structure including the copper wiring preliminary layer is not oxidized to generate an oxide, which increases the resistance of the wiring and is prevented from being contaminated and deposits. The main wiring can be formed.

In the invention, the heat-resistant etching mask layer is formed on the upper barrier metal film forming the copper wiring preliminary layer. Therefore, the etching mask layer is not deformed by heat even when the substrate temperature rises during etching by RIE, so that the wiring mainly composed of copper can be formed in a shape as designed.

[Brief description of drawings]

FIG. 1A to FIG. 1B are process drawings provided for explaining a process of forming a copper wiring of the present invention.

2A to 2C are process diagrams provided for explaining the method for forming a copper wiring according to the present invention, which is subsequent to FIG.

FIG. 3 is an X-ray diffraction curve diagram for explaining a crystal structure after annealing a copper wiring preliminary layer portion.

4 (A) to (B) are diagrams provided for explaining a sample used for warpage measurement and a measuring method thereof.

5A to 5B are explanatory diagrams provided for explaining the relationship between the presence or absence of annealing treatment and the amount of warpage.

FIGS. 6A to 6B are schematic views when observing a copper film peeling state with or without annealing treatment with an SEM.

[Explanation of symbols]

10: Substrate (Si substrate) 12: SiO ₂ film 13: Underlayer 14, 14a: Ti film 16, 16a: Lower TiN film 18, 18a: Cu film 20, 20a: Upper TiN film 22, 22a: NSG film 23: Copper wiring preliminary layer 24: Resist pattern 25: Copper wiring

Claims (3)

[Claims] 1. A copper wiring preliminary layer including a lower barrier metal film, a copper film and an upper barrier metal film is formed on a lower surface, and then the copper wiring preliminary layer is exposed from the upper barrier metal film to the underlying surface. In the method of forming a copper-based wiring by etching up to, a copper wiring preliminary layer is formed on the underlayer, and a copper re-deposition is performed on a structure including the copper wiring preliminary layer and the underlayer. A method for forming a wiring mainly composed of copper, which comprises performing an annealing treatment at a temperature higher than a crystallization temperature. 2. The method for forming a copper-based wiring according to claim 1, wherein the carrier gas used for the annealing treatment is hydrogen (H ₂ ).
A method of forming a wiring mainly composed of copper, characterized in that a mixed gas of nitrogen and nitrogen (N ₂ ) is used. 3. The copper-based wiring forming method according to claim 1, wherein an etching resistant mask layer having heat resistance is formed on the upper barrier metal film that constitutes the copper wiring preliminary layer. A method for forming a wiring mainly composed of copper.