JP2994094B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal wiring and a method for forming the same, and more particularly to an alloy wiring using copper as a main wiring material.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated, reductions in wiring width and wiring film thickness and multilayer wiring have been promoted. As a wiring material, an aluminum alloy having a specific resistance as low as 2.75 μΩcm and containing aluminum as a main component, which has been corroded by a passive film, has been used.

However, since the signal current is not reduced with the reduction in the wiring cross-sectional area, the current density increases,
Disconnection failure due to electromigration has become a problem.

[0004] Further, with the increase in the number of multilayer wirings, the wirings receive a complicated thermal history, so that the thermal stress applied to the wirings increases.
Disconnection failure due to stress migration has also become a problem.

The main cause of these problems is that since aluminum has a low melting point of 660 ° C., diffusion of aluminum atoms, particularly diffusion along the crystal grain size, tends to occur even at a relatively low temperature. When added to the interconnect, this atomic diffusion is accelerated. Therefore, wiring using copper having a specific resistance as low as or higher than aluminum and a melting point higher than aluminum by 400 ° C. or more is being studied.

However, the electromigration disconnection failure life of a metal wiring using pure copper is improved only several times to several tens times that of an aluminum-silicon-copper (Al-Si-Cu) alloy wiring. It has been reported. This lifetime almost coincides with the lifetime expected from the activation energy of the grain boundary diffusion of copper atoms.

[0007] Further, since copper has a high oxidation rate, when a copper thin film is exposed to an oxidizing gas atmosphere, copper oxidation proceeds to the inside of the film. Moreover, the copper oxide film formed on the surface is not a dense film. As a result, in the ashing step for stripping the resist, acicular copper oxide is formed on the copper surface, which causes a problem that the wiring shape is deteriorated and the specific resistance is increased. Further, even if a passivation film or an interlayer insulating film is deposited on the copper wiring, there is a problem that peeling occurs due to poor adhesion.

In order to solve the problems of increase in specific resistance and peeling, a method of forming an antioxidant film on a copper surface has been proposed. For example, a method in which a Cu—Ti thin film obtained by sputtering an alloy target composed of copper (Cu) and titanium (Ti) is heat-treated in a nitriding gas atmosphere to form a titanium nitride film on the copper surface. It has been known.

In this method, the specific resistance can be reduced to 2.5 μΩcm by heat treatment at 800 ° C. In addition, a metal or an intermetallic compound serving as a diffusion barrier is dispersed and deposited at the crystal grain boundaries, and the electromigration resistance is improved.

In this case, when the heat treatment is performed at a temperature lower than 800 ° C., the specific resistance of the Al—Si—Cu alloy film (3 μΩc
m), and no titanium nitride film is formed on the copper surface. That is, the effect cannot be obtained unless heat treatment at 800 ° C. or higher is performed. For this reason, transistors such as FETs have the following problems. That is,
In order to prevent the depth of the diffusion layer from increasing, heat treatment at 800 ° C. or higher had to be avoided, and the above method could not be applied.

[0011]

As described above, the conventional Al
In the case of the metal wiring using, there was a disconnection failure due to electromigration or stress migration. Therefore, metal wiring using copper has been studied. However, there has been a problem that the quality of the wiring surface is deteriorated due to oxidation and the wiring resistance is increased. In order to prevent oxidation, a method of forming a titanium nitride film on a copper surface has been proposed. However, this method requires a heat treatment of 800 ° C. or more, and in a FET or the like, the depth of a diffusion layer is increased. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to prevent electromigration resistance and stress migration, which can prevent the deterioration of the wiring surface and the increase in wiring resistance due to oxidation. An object of the present invention is to provide a metal wiring having excellent resistance and a method for forming the same.

[0013]

The gist of the present invention is to form a metal or a compound thereof that does not form an intermetallic compound with a main wiring material on the surface of the main metal wiring and to apply the above-mentioned metal to the crystal grain boundary of the main metal wiring. It consists in precipitating a metal or its compound.

That is, in order to achieve the above object, the metal wiring of the present invention is formed on a main metal wiring made of a main wiring material formed on a substrate, and on a surface and a crystal grain boundary of the main metal wiring. And a metal or a compound thereof that does not form an intermetallic compound with the main wiring material.

Further, the method for forming a metal wiring according to the present invention is directed to a laminated film of a first metal film made of a main wiring material and a second metal film made of a wiring material which does not form an intermetallic compound with the main wiring material. And a step of heat-treating and patterning the laminated film.

[0016]

In the metal wiring according to the present invention, the surface of the main metal wiring is covered with a metal or a compound thereof which does not form a compound with the main metal wiring, so that the surface of the main metal wiring is protected and the oxidation resistance of the wiring is improved. Is improved. Further, since the above-mentioned metal or its compound is formed at the crystal grain boundary of the main metal wiring, the resistance to electromigration can be improved without increasing the resistance.
The stress migration resistance is improved.

In the method for forming a metal wiring according to the present invention,
Since the heat treatment is performed on the laminated film of the first metal film and the second metal film, the metal of the second metal film passes through the first metal film via the crystal grain boundary of the first metal film. And also precipitates at the crystal grain boundaries. At this time, by controlling the atmosphere, the metal of the second metal film can be a metal compound. Therefore, the metal of the second metal film or a compound thereof can be easily formed on the surface and the crystal grain boundaries of the first metal film. As a result, without increasing the resistance due to the formation of the intermetallic compound,
Protection of the metal film and improvement of electromigration resistance and the like.

[0018]

Embodiments will be described below with reference to the drawings. FIG. 1 is a sectional view showing a process of forming a metal wiring according to a first embodiment of the present invention.

First, as shown in FIG. 1A, an interlayer insulating film 3 is formed on a semiconductor substrate 1 on which a desired element has been formed. Next, after setting the semiconductor substrate 1 in a chamber of a well-known magnetron sputtering apparatus, the pressure in the chamber is reduced to 2.0 × 10 ⁻⁵ Pa or less.
And 40cm ^{3 in the} chamber / Min of argon gas is introduced. At this time, the pressure in the chamber is maintained at 3.7 × 10 ⁻¹ Pa.

Next, as shown in FIG. 1B, a target of niobium (Nb) is sputtered by argon plasma to form a metal layer on the interlayer insulating film 3 where copper (Cu) and an intermetallic compound are not formed. As a niobium layer 5 having a thickness of about 50 nm.
Is deposited.

Next, as shown in FIG. 1C, a copper target is sputtered to form a copper layer 7 on the niobium layer 5 by, for example, 40 nm.
Deposit to a thickness of 0 nm. When the wiring resistance of the laminated film of the copper layer 7 and the niobium layer 5 at this time was examined, it was 1.95 μΩ.
cm. Note that the thickness of the copper layer 7 is 100 nm to 8 nm.
Desirably, it is about 00 nm. Next, after setting the semiconductor substrate 1 on which the copper / niobium laminated film is formed in an infrared image furnace, the inside of the furnace is evacuated to 1.3 × 10 ⁻⁴ Pa. Thereafter, 1 atm gas mixture comprising the above furnace hydrogen 10 vol%, argon 90 vol%, 300 cm ³ /
min.

Next, the temperature in the furnace is increased to, for example, 750 ° C. at a heating rate of 60 ° C./min. After maintaining the inside of the furnace at a temperature of 750 ° C. for 30 minutes, 60 ° C./min.
Cool at a heating rate of

By the heat treatment, a copper-niobium multilayer alloy film 9 was formed as shown in FIG. RBS (Ru
otherford Back Scattering)
When this copper niobium laminated alloy film 9 was examined using the method,
An RBS spectrum as shown in FIG. 2 was obtained. In addition,
As a comparative example, the case where the temperature of the heat treatment is 850 ° C. and the case where there is no heat treatment are also shown.

From this figure, it can be seen that a niobium layer 5 having a thickness of about 5 nm is formed on the surface of the copper-niobium multilayer alloy film 9. When the temperature is 850 ° C., a thick niobium layer is formed on the surface, and when the heat treatment is not performed, the niobium layer is hardly formed on the surface.

The grain boundary 1 of the copper-niobium multilayer alloy film 9
In No. 1, a precipitate 13 of niobium was deposited. Further, when the wiring resistance of the copper-niobium laminated alloy film 9 was examined,
The value was 1.75 μΩcm, which was confirmed to be smaller than that of the copper / niobium laminated film (1.95 μΩcm).
Finally, as shown in FIG. 1E, the copper-niobium multilayer alloy film 9 is patterned to complete the copper-niobium multilayer alloy wiring 15.

As described above, the copper-niobium multilayer alloy wiring 15 obtained by the above-described method has not only a lower specific resistance than the copper / niobium multilayer film but also a copper surface coated with niobium. The formation of copper is prevented, and the adhesion to the interlayer insulating film and the passivation film is also improved. Further, since a precipitate made of niobium is formed at the crystal grain boundary of copper in the copper-niobium multilayer alloy film 9, electromigration is performed.
This improves the durability of the device and prevents a decrease in reliability due to a disconnection failure or the like.

FIG. 3 is a characteristic diagram showing the relationship between the temperature of the heat treatment and the specific resistance of the copper-niobium multilayer alloy film 9. From this figure, the specific resistance of the copper-niobium multilayer alloy film 9 obtained by the method of the present embodiment is lower than that of the Al-Si
-Lower than the specific resistance of the Cu alloy (= 3 μΩcm). Therefore, if the method of this embodiment is applied to the manufacture of a TFT, metal wiring can be formed while suppressing an increase in the depth of the diffusion layer.

Table 1 shows the resistivity before and after the heat treatment at 400 ° C. for 30 minutes in a 100% oxygen atmosphere with respect to the copper-niobium multilayer alloy film 9 and the pure copper thin film obtained by the method of this embodiment. I have.

[0029]

[Table 1] From this table, it can be seen that the oxidation resistance is improved as compared with pure copper. This is because the oxidation inside the copper is suppressed by niobium formed on the copper surface.

Therefore, even if the heat treatment is performed in an oxidizing gas atmosphere, deterioration of the film surface and film quality hardly occurs.
Further, the adhesion to the passivation film or the interlayer insulating film is improved.

Further, according to the present embodiment, as described above, a wiring resistance lower than that of an Al-based alloy and close to that of pure copper can be obtained. Fine wiring can be realized.

Thus, according to this embodiment, it is possible to obtain a metal wiring having a low resistance and excellent in oxidation resistance, electromigration resistance and stress migration resistance, and formed at a low temperature of 800 ° C. or less. can do.

FIG. 4 is a sectional view showing a process of forming a metal wiring according to a second embodiment of the present invention. 1 are given the same reference numerals as in FIG. 1, and detailed description is omitted. The point that the forming method of this embodiment is different from that of the first embodiment is that heat treatment is performed after the patterning of the copper-niobium multilayer alloy film 9. First, FIG.
As shown in (1), an interlayer insulating film 3, a niobium layer 5, and a copper layer 7 are sequentially formed on a semiconductor substrate 1 in the same manner as in the first embodiment.

Next, as shown in FIG. 4B, the laminated film of the niobium layer 5 and the copper layer 7 is patterned by photolithography and reactive ion etching with a wiring pattern having a wiring width of 0.5.
Process into a shape. Note that an ion sputtering method may be used instead of the reactive ion etching method.

Finally, as shown in FIG. 4C, the semiconductor substrate 1 is subjected to a heat treatment to cover the surface of the copper layer 7 with a 5 nm-thick niobium layer 5 and to deposit a niobium precipitate at the crystal grain boundaries. To form Even in such a method, the same effect as in the previous embodiment can be obtained because niobium which does not form an intermetallic compound with copper is used.

FIG. 5 is a sectional view showing a step of forming a metal wiring according to a third embodiment of the present invention. 1 are given the same reference numerals as in FIG. 1, and detailed description is omitted. The point that the forming method of the present embodiment is different from that of the first embodiment is that a laminated film having a three-layer structure of the first copper layer 7a, the niobium layer 5, and the second copper layer 7b is formed.

That is, after forming an interlayer insulating film 3 on a semiconductor substrate 1 on which a desired element is formed as shown in FIG. 5A, the interlayer insulating film 3 is formed as shown in FIG. First on
A copper layer 7a, a niobium layer 5, and a second copper layer 7b are sequentially formed. Next, as shown in FIG. 5C, the semiconductor substrate 1 is subjected to a heat treatment to form a copper-niobium multilayer alloy film 9. Finally, as shown in FIG. 5D, the copper-niobium multilayer alloy film 9 is patterned into a wiring shape to complete the copper-niobium multilayer alloy wiring 15.

With the copper-niobium multilayer alloy wiring 15 obtained by the above-described method, the same effect as that of the above-described embodiment can be obtained. Copper niobium laminated alloy wiring 15 can be easily formed.

That is, when the thick copper layer 7 is formed on the niobium layer 5 as in the first embodiment, the distance to the surface of the copper layer 7 becomes long, so that a niobium film is formed on the surface of the copper layer 7. However, if the structure is such that the niobium layer 5 is sandwiched between the two copper layers 7a and 7b as in this embodiment, the thickness of the copper layers 7a and 7b can be reduced by the method of the first embodiment. About half of
Niobium can easily reach the surfaces of the copper layers 7a and 7b.

In this embodiment, both copper layers 7a, 7a
Although niobium is formed on b, niobium may be formed only on one copper layer, for example, only on copper layer 7b. In this case, since the copper layer 7a is formed below the copper layer 7b, there is almost no problem that the copper layer 7a is oxidized. Further, similarly to the second embodiment, after performing the heat treatment, the copper-niobium laminated alloy film 9 may be patterned.

The present invention is not limited to the embodiment described above. For example, in the above embodiment, a copper niobium laminated film is used as a wiring material.
A layer made of one or more elements of a metal group V such as niobium (Nb) or tantalum (Ta) or a metal group VI such as chromium (Cr), molybdenum (Mo) or tungsten (W); May be used. Furthermore,
Similar effects can be expected in the case of a main wiring layer made of a material other than copper (Cu). Furthermore, the lamination type and the lamination order can be appropriately changed. In the above embodiment, the heat treatment
Although the reaction is performed in a controlled reducing atmosphere in which oxygen and the like are mixed and oxidation is prevented, it may be performed in a controlled nitriding atmosphere, for example, a nitrogen gas or ammonia gas atmosphere. In this case, a nitride of a metal that does not form an intermetallic compound with copper can be formed on the crystal grain boundary or the surface of the copper, so that the oxidation resistance can be further improved. Further, it may be in a nitriding atmosphere containing hydrogen gas. Alternatively, the heat treatment may be performed in a controlled boride atmosphere such as a hydrogen fluoride atmosphere, a carbonization atmosphere such as a hydrocarbon atmosphere, a fluorine atmosphere such as a hydrogen fluoride atmosphere, a fluorine atmosphere, a vacuum atmosphere, or an inert gas atmosphere. Further, heat treatment may be performed in such a plasma atmosphere. If heat treatment is performed in such an atmosphere, a metal that does not form an intermetallic compound with copper or a nitride, boride, carbide,
Fluoride and oxide can be formed. In addition, various modifications can be made without departing from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, since the surface of the main metal wiring is covered with a metal which does not form an intermetallic compound with the main metal wiring or the compound thereof, the oxidation resistance of the main metal wiring is reduced. improves. Further, since the metal or its compound is formed at the crystal grain boundary of the main metal wiring, the electromigration resistance and the stress migration resistance can be improved without increasing the wiring resistance or lowering the wiring quality. Therefore, even if the semiconductor device is highly integrated and miniaturized, a metal wiring with sufficient reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a process of forming a metal wiring according to a first embodiment of the present invention.

FIG. 2 is an RBS spectrum of the copper-niobium multilayer alloy film of FIG. 1;

FIG. 3 is a characteristic diagram showing a relationship between the specific resistance of the copper-niobium multilayer alloy film of FIG. 1;

FIG. 4 is a sectional view showing a step of forming a metal wiring according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a step of forming a metal wiring according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 3 ... Interlayer insulating film, 5 ... Niobium layer, 7,
7a, 7b: copper layer, 9: copper niobium multilayer alloy film, 11: crystal grain boundary, 13: precipitate, 15: copper niobium multilayer alloy wiring.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Manabu Nanbashi 1 Toshiba Research Institute Co., Ltd., Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa (56) References Kaihei 4-106930 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 23/12 H05K 1/09 H05K 3/24

Claims (2)

(57) [Claims] 1. A main metal wiring formed of a main wiring material formed on a substrate, and a metal or a compound thereof which does not form an intermetallic compound with the main wiring material formed on a surface and a crystal grain boundary of the main metal wiring. And a semiconductor device comprising: 2. A step of forming a laminated film of a first metal film made of a main wiring material on a substrate and a second metal film made of a wiring material that does not form an intermetallic compound with the main wiring material; the laminated film was heat-treated, and pattern - N'ningu method of manufacturing a semiconductor device characterized by a step of.