JPH11154676A - Metal wiring and forming method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form the minute metal wiring having the high allowable current density. SOLUTION: First, a wiring groove 2 is formed in a thermally oxidized film 1. Then, metal fine grains 4, made of Al fine grains 5 and a W thin film 6 covering this Al fine grains 5, is deposited on the entire surface of the thermally oxidized film 1 so as to fill the metal fine grains 4 in the wiring groove 2. Then, by sintering the metal fine grains 5, an Al film 4a as the metal wiring, wherein the respective Al crystal particles 5a are separated from each other by a W layer 6a as a diffusion barrier layer is formed. Finally, the Al film 4a outside of the wiring groove 2 is removed by CMP(chemical-mechanical polishing).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal wiring used for a semiconductor device.

[0002]

2. Description of the Related Art To increase the integration and speed of LSI, it is necessary to continuously increase the allowable current density of metal wiring for electrically connecting fine elements. For this purpose, it is necessary to improve resistance to disconnection of wiring caused by one-diffusion of metal atoms under high current density called electromigration.

Conventionally, metal wiring has been formed, for example, as follows. That is, a metal thin film is grown on an insulating film having a wiring groove formed on its surface by a film forming method such as a sputtering method, an evaporation method, or a chemical vapor deposition (CVD) method, and the grown metal thin film is reflowed. It is formed by embedding in a wiring groove and removing an excess metal thin film outside the wiring groove by a chemical mechanical polishing (CMP) method (damascene method).

[0004] In the case of a film forming method such as a sputtering method, an evaporation method or a CVD method, it is not possible to control the size, distribution and orientation of crystal grains of a metal thin film as a metal wiring.

On the other hand, it is known that the allowable current density of a metal wiring depends on the size of crystal grains, the distribution of crystal diameters, and the degree of uniformity of crystal orientation. For example, when a metal wiring is formed from a metal thin film having a certain crystal grain size, the allowable current density differs depending on the width (wiring width) of the formed metal wiring.

That is, when the wiring width is smaller than the average crystal grain size, a structure having a bamboo-shaped crystal grain boundary crossing the metal wiring (bamboo structure) is obtained, and the allowable current density becomes extremely high. .

On the other hand, when the wiring width is larger than the average crystal grain size, the structure has a grain boundary triple point, and hillocks or hillocks are formed at the crystal grain boundary triple point, which is a fast diffusion path of the element forming the metal wiring. Since the probability that the void grows and breaks particularly due to the growth of the void increases, the allowable current density decreases.

[0008] Metal wirings of various wiring widths exist in LSIs. Therefore, in the above-described conventional method in which the size of the crystal grain cannot be controlled, all of the metal wirings having various wiring widths in the LSI cannot have a bamboo structure, and the allowable current density of the entire wiring cannot be increased. .

It is known that one-way diffusion of atoms due to electromigration can be suppressed by reducing the length of metal wiring (wiring length) to a certain length (critical length) or less. The mechanism is as follows.

When a DC current flows through the metal wiring, a one-way diffusion of atoms due to electromigration progresses, and a stress gradient accompanying movement of the atoms is generated in the metal wiring.
This stress gradient causes the flow of atoms in a direction opposite to the electromigration.

For this reason, when the wiring length becomes below the critical length, the electromigration and the flow of the atoms due to the above-described stress gradient cancel each other, and the growth of voids and hillocks due to the electromigration is substantially suppressed.

By applying this effect, the allowable current density of the metal wiring can be significantly improved by dividing the metal wiring in the LSI into a plurality of unit wirings having a critical length or less.

As a technique for dividing a metal wiring into a plurality of unit wirings having a critical length or less, for example, in the case of an Al wiring, a C wiring is used.
A method has been proposed in which an Al wiring is divided into a plurality of unit Al wirings having a critical length or less by forming a compound of Al and Cu that suppresses Al diffusion at a crystal grain boundary by alloying by adding u. Was.

However, in this method, since the effect of suppressing Al diffusion is insufficient, Al is diffused over a long distance in the longitudinal direction of the Al wiring, and as a result, excess or excessive Al is formed at the hillock or void growth point. There is a problem that the shortage or hillocks or voids grow and appear as macroscopic defects such as substantial wiring short circuit or breakage.

Further, there is a problem that it is very difficult at present to design a metal wiring in an actual LSI by giving a restriction that the metal wiring is made a plurality of unit wirings having a critical length or less.

[0016]

As described above, in order to increase the allowable current density of the metal wiring, a metal wiring having a bamboo structure is formed, or the metal wiring divided into a plurality of unit wirings having a critical length or less is formed. Although it has been proposed to form such a metal wiring, there is a problem that it is technically difficult to form such a metal wiring.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a metal wiring having a high allowable current density, which can be easily formed, and a method of forming the same.

[0018]

[Means for Solving the Problems] To achieve the above object, a metal wiring according to the present invention (claim 1) is formed in a wiring groove, and each of the crystal grains of the metal has a diffusion barrier layer. Are separated from each other.

In the wiring groove, the wiring width may vary along the longitudinal direction, the depth direction, or both directions. The diffusion barrier layer is formed of, for example, a refractory metal, a nitride, a fluoride, a carbide or an oxide thereof, or a compound of Al and a refractory metal or a compound of Cu and a refractory metal. 3).

Further, in the method for forming a metal wiring according to the present invention (claim 4), a step of forming a wiring groove in an insulating film, the fine metal particles made of a first metal, and the first metal covering the fine metal particles are provided. Depositing wiring particles including a metal thin film made of a second metal acting as a diffusion barrier with respect to the metal over the entire surface of the insulating film so as to fill the wiring grooves; and heating and heating the wiring particles. Forming a metal film as metal wiring in which each of the crystal grains of the first metal is separated from each other by a diffusion barrier layer made of the second metal by pressing, and forming the metal film outside the wiring groove. And a step of removing

[0021] In the insulating film, a wiring groove having a wiring width changed along a longitudinal direction, a depth direction, or both directions may be formed. Is performed, for example, by polishing the entire surface of the metal film by chemical mechanical polishing (claim 6).

In order to secure the adhesion between the wiring groove and the metal wiring, it is preferable to deposit wiring particles after forming an adhesion layer on the surface of the wiring groove, for example. Alternatively, a diffusion barrier layer covered with a first metal may be used as the wiring particles (claim 8).

In order to form a metal wiring having a low specific resistance, it is preferable to use, for example, a plurality of wiring particles having different particle sizes as wiring particles. [Operation] According to the present invention (claims 1 and 2), since each of the metal crystal grains is separated from each other by the diffusion barrier layer, diffusion of the metal between all the crystal grains constituting the metal wiring is prevented. Is done. Therefore, according to the present invention, it is possible to realize a metal wiring having a high allowable current density even if miniaturization is advanced.

According to the present invention (claims 3 to 7),
By using metal particles whose surface is covered with the diffusion barrier layer as the wiring material, it becomes possible to easily form a metal wiring in which each of the crystal grains of the metal is separated from each other by the diffusion barrier layer.

[0025]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a process sectional view showing a method of forming a metal wiring (damascene wiring) according to a first embodiment of the present invention.

First, as shown in FIG.
A wiring groove 2 having a depth of 0.4 μm and a width of 5 μm is formed on the surface of the m thermal oxide film 1. The thermal oxide film 1 is formed on a silicon substrate (not shown).

Next, as shown in FIG. 1B, after a Ti thin film 3 having a thickness of 10 nm as an adhesion film is formed on the entire surface, metal fine particles 4 (wiring particles) overflowing from the wiring groove 2 are removed by Ti.
It is deposited on the entire surface of the thin film 3. FIG. 2A is a sectional perspective view of this step.

Here, the metal fine particles 4 are composed of Al fine particles 5 having a diameter of 50 nm and a W thin film 6 having a thickness of 5 nm which covers the surface of the Al fine particles 5. Such metal fine particles 4 can be formed by, for example, electroless plating in which W is precipitated on the surface of Al powder in an aqueous solution of W by a chemical reaction.

The step of forming the Ti thin film 3 and the step of depositing the metal fine particles 4 are continuously performed in a vacuum. These steps are performed in separate vacuum chambers or in the same vacuum chamber.
However, the latter is preferred.

Next, as shown in FIG. 1 (c), the metal fine particles 4 are subjected to a heat treatment (temporary sintering) at 400 ° C. for 10 minutes, and then, at a temperature of 250 ° C. and a pressure of 200 MPa, in a vacuum. Is heated and pressed (main sintering). As a result,
An Al film 4a is formed in which each of the Al crystal grains 5a is separated from each other by the W diffusion barrier layer 6a.

Next, as shown in FIG. 1D, the excess Al film 4a and the Ti thin film 3 outside the wiring groove 2 are removed by using the CMP method. As a result, a metal wiring (damascene wiring) made of the Al film 4a is completed. FIG. 2B is a sectional perspective view of this step. Thereafter, the sample is taken out of the vacuum chamber.

Thereafter, an SiO ₂ film having a thickness of 400 nm was formed as a passivation film using a plasma CVD method.
A silicon nitride film having a thickness of 700 nm is sequentially formed, and a pad hole reaching the Al film 4a is formed in the laminated film as the passivation film.

In the present embodiment, the metal wiring is made of Al crystal grains 5.
Since a is separated from each other by the W diffusion barrier layer 6a as a diffusion barrier layer, diffusion of Al between all the crystal grains constituting the metal wiring is prevented.

As a result, even if miniaturization is advanced, electromigration, growth of voids and hillocks can be prevented. Therefore, according to the present embodiment, a fine metal wiring having a high allowable current density can be realized. Also,
By using such a metal wiring, it is possible to increase the speed of the device and increase the operating temperature.

Further, the Al wiring having such a structure is easily formed by sintering the Al fine particles 5 whose surface is covered with the W thin film 6 as a wiring material as in the present embodiment. it can. (First Comparative Example) The steps up to the formation of the Ti thin film 3 are the same. Then, maintain a vacuum and maintain a thickness of 300 at room temperature.
nm Al-0.5w% Cu film is formed, followed by 450 nm.
At 300C, an Al-0.5w% Cu film having a thickness of 300 nm is formed. Thereafter, the excess Al outside the wiring groove is formed by using the CMP method.
After removing the -0.5 w% Cu film, the Al-0.5 w% Cu
A metal wiring made of a film is formed.

An electromigration test was performed on the metal wiring of this comparative example and the metal wiring of this embodiment. This electromigration test was performed at a temperature of 20.
Under the environment of 0 ° C, the length of the bonding package is 30
A current having a current density of 2 MA / cm ² flows through a 0 mm metal wiring.

As a result, the resistance value of the metal wiring of the present embodiment did not change even after 500 hours from the passage of the current. When the wiring pattern after 500 hours was observed using a scanning electron microscope (SEM), no voids and hillocks were generated. On the contrary,
In the metal wiring of the comparative example, a disconnection failure occurred about 100 hours after the current was passed. Second Embodiment FIG. 3 is a process sectional view showing a method of forming a metal wiring (damascene wiring) according to a second embodiment of the present invention.

First, as shown in FIG.
A wiring groove 12 having a depth of 0.4 μm and a width of 5 μm is formed on the surface of the thermal oxide film 11 of m. The thermal oxide film 11 is formed on a silicon substrate (not shown). Up to this point, the operation is the same as in the first embodiment.

Next, as shown in FIG.
The fine metal particles 13 overflowing from the wiring grooves 12 are removed from the thermal oxide film 1.
1 is deposited on the entire surface. Here, the metal fine particles 13 are Al fine particles 14 having a diameter of 50 nm, a 1-nm thick TiN thin film 15 covering the surface of the Al fine particles 14,
1 nm thick Al thin film 16 covering the surface of N thin film 15
It is composed of

Next, as shown in FIG. 3C, as in the first embodiment, by sintering and sintering the fine metal particles 13, each of the Al crystal grains 14a becomes a TiN diffusion barrier. An Al film 13a separated from each other by the layer 15a is formed. Thereafter, the sample is taken out of the vacuum chamber.

Next, as shown in FIG. 3D, the excess Al film 13a outside the wiring groove 12 is removed by using the CMP method.
As a result, a metal wiring (damascene wiring) made of the Al film 13a is completed.

Thereafter, a 400 nm thick SiO ₂ film was formed as a passivation film by using a plasma CVD method.
A silicon nitride film having a thickness of 700 nm is sequentially formed, and a pad hole reaching the Al film 13a is formed in the laminated film as the passivation film.

In this embodiment, the same effects as in the first embodiment can be obtained. Further, in the case of the present embodiment, the Al thin film 16
As a result, the adhesion between the base (thermal oxide film 11) and the metal fine particles 13 and the adhesion between the metal fine particles 13 are increased, and an alloying reaction between Al and W, an alloying reaction between Ti and W during sintering, Alternatively, since there is no alloying reaction of both, as shown in Table 1, the specific resistance of the metal wiring was smaller than that of the first embodiment. (Second Comparative Example) The difference from this embodiment is that metal fine particles (Al fine particles 14,
That is, a TiN thin film 15) is used. In the case of the comparative example, the metal fine particles were missing during the CMP, and as shown in Table 1, the specific resistance of the metal wiring was higher than that of the first embodiment.

[0044]

[Table 1]

In the present embodiment, the outermost surface of the Al fine particles 14 is covered with the Al thin film 16, but may be covered with a Ni thin film or a Cu thin film instead. In short, any film that improves the adhesion may be used. Third Embodiment Next, a method of forming a metal wiring (damascene wiring) according to a third embodiment of the present invention will be described.

The main difference between this embodiment and the first embodiment is that two kinds of fine metal particles having different diameters are used as the wiring material. Specifically, Cu fine particles having a diameter of 50 nm covered with a W thin film having a thickness of 5 nm,
Cu fine particles with a diameter of 10 nm covered with a W thin film of 10 nm were used. In addition, a 3 nm-thick Ti thin film was used as the adhesion film. The main sintering was performed at 250 ° C. in a vacuum of 300 MPa.

In this embodiment, effects similar to those of the first embodiment can be obtained. Furthermore, according to the present embodiment, the sintering density is increased by using the Cu fine particles having different diameters. As a result, as shown in Table 2, only the Cu fine particles having a diameter of 50 nm covered with the W thin film are used. The specific resistance of the metal wiring was smaller than that in the case (third comparative example).

[0048]

[Table 2]

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the case of the damascene wiring is described. However, the present invention can be applied to a dual damascene wiring in which the wiring width is changed in the depth direction. Further, the present invention can also be applied to a metal wiring in which the wiring width changes along the longitudinal direction.

In any case, the effects of the present invention can be obtained. That is, since the size of crystal grains and the like cannot be controlled by the conventional method, for example, the allowable current density is limited by the metal wiring having the widest wiring width. However, in the present invention, each of the metal crystal grains has a diffusion barrier layer. , There is no such restriction.

Also, the material of the diffusion barrier layer is not limited to those described in the above embodiment, and for example, various materials described in [Configuration] can be used. In addition, various modifications can be made without departing from the scope of the present invention.

[0052]

As described in detail above, according to the present invention, by using metal particles whose surface is covered with a diffusion barrier layer as a wiring material, each of the metal crystal grains is separated from each other by the diffusion barrier layer. As a result, a metal wiring having a high allowable current density can be easily realized.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing a method for forming a metal wiring (damascene wiring) according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional perspective view of the metal wiring in the steps of FIG. 1 (b) and FIG. 1 (d).

FIG. 3 is a process sectional view showing a method for forming a metal wiring (damascene wiring) according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Thermal oxide film 2 ... Wiring groove 3 ... Ti thin film 4 ... Metal fine particles (wiring particles) 4a ... Al film 5 ... Al fine particles (metal fine particles) 5a ... Al crystal grains 6 ... W thin film 6a ... W diffusion barrier layer 11 ... thermal oxide film 12 ... wiring groove 13 ... metal fine particles (wiring particles) 13a ... Al film 14 ... Al fine particles 14a ... Al crystal grains 15 ... TiN thin film 15a ... TiN diffusion barrier layer

Claims (9)

[Claims] 1. A metal wiring formed in a wiring groove, wherein each of metal crystal grains is separated from each other by a diffusion barrier layer. 2. The metal wiring according to claim 1, wherein the wiring width of the wiring groove changes along the longitudinal direction, the depth direction, or both of these directions. 3. The diffusion barrier layer is formed of a refractory metal, a nitride, a fluoride, a carbide or an oxide thereof, a compound of Al and a refractory metal or a compound of Cu and a refractory metal. The metal wiring according to claim 1, wherein: 4. A step of forming a wiring groove in an insulating film, comprising: metal fine particles made of a first metal; and a second metal covering the metal fine particles and acting as a diffusion barrier for the first metal. Depositing wiring particles including a metal thin film on the entire surface of the insulating film so as to fill the wiring grooves; and heating and pressing the wiring particles, whereby each of the crystal grains of the first metal becomes Forming a metal film as a metal wiring separated from each other by a diffusion barrier layer made of the second metal; and removing the metal film outside the wiring groove. Forming method. 5. The method according to claim 4, wherein a wiring groove whose wiring width is changed in the longitudinal direction, the depth direction, or both directions is formed in the insulating film. 6. The metal wiring according to claim 4, wherein the metal film outside the wiring groove is removed by polishing the entire surface of the metal film as the metal wiring by chemical mechanical polishing. Formation method. 7. After forming an adhesion layer on the surface of the wiring groove,
The method according to claim 4, wherein the wiring particles are deposited. 8. The method according to claim 4, wherein said diffusion barrier layer is covered with said first metal. 9. The method according to claim 4, wherein the wiring particles are composed of a plurality of wiring particles having different particle diameters.