JPH06326102A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To realize a practical low-resistance metallic wiring instead of an Al wiring by laminating a first metal film and a second metal film composed mainly of silver on a semiconductor substrate and forming a protective film containing the same metal as the first metal film to cover the surface of the second metal film. CONSTITUTION:An SiO2 film 2 is formed on a semiconductor substrate 1, and a groove for a buried wiring is formed in the SiO2 film 2. Then, a TiN film 3, a Ti film 4 and an Ag film 5 are formed sequentially on the whole face of the SiO2 film 2. Then, the TiN film 3, the Ti film 4 and the Ag film 5 in parts other than the groove part are removed, and a buried Ag wiring layer is formed. After that, an annealing operation is performed in an Ar gas atmosphere at 600 deg.C for 30 minutes, and a TiO2 film 6 is formed on the surface of the Ag film 5. Lastly, an interlayer insulating film 7 is deposited on the whole face, and the buried wiring is finished. Thereby, it is possible to restrain Ag from agglomerating in the Ag film 5, and wiring which utilizes the low resistivity of Ag can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using Ag as a wiring material and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the high integration of semiconductor devices, reduction of wiring width and wiring film thickness and multilayer wiring have been promoted. Al has conventionally been used as a wiring material. However, even if the wiring cross-sectional area is reduced due to the miniaturization of the element, the signal current has not been reduced, so that the current density increases and disconnection due to electromigration poses a problem. Further, with the multi-layered wiring, the wiring undergoes a complicated thermal history, so that disconnection due to stress migration due to thermal stress applied to the wiring is also a problem.

Therefore, the resistance is lower than that of Al, and
Electro migration and stress migration
Cu and Ag as next-generation wiring materials with excellent resistance to ionization
The examination of is started. However, Cu is oxidized even at the low temperature of about 200 ° C. Such oxidation causes an increase in resistance and must be prevented.

In order to realize this, a method of coating Cu with a protective film has been proposed (Japanese Patent Laid-Open No. 63-15).
6341). In this technique, as shown in FIG. 9A, first, a SiO ₂ film 82 is formed on a silicon substrate 81, and a Ti film 83, a TiN film 84, and a Cu film are formed on the SiO ₂ film 82.
A laminated film including the film 85 and the TiN film 86 is formed.

Next, as shown in FIG. 9B, the entire surface of the laminated film is covered with the TiN film 87 so that the side surface of the laminated film is covered with Ti.
The N film 87 is deposited.

Finally, by selectively removing the TiN film 87 other than the side surface of the laminated film, the Cu film 85 becomes Ti.
A Cu wiring having a structure covered with the films 86 and 87 is obtained.

However, this method has a problem that it has many steps and is complicated, and it is difficult to put it into practical use.

[0008] Further, other Cu coating the Cu film with a protective film
A method using heat treatment has been proposed as a method for forming wiring (Japanese Patent Laid-Open No. 64-59938). This is
As shown in (a), first, a diffusion barrier metal film 92 and a Cu · Ti alloy film 93 are sequentially deposited on the insulating film 91.

Next, as shown in FIG. 10B, the diffusion barrier metal film 92 and the Cu / Ti alloy film 93 are patterned into a wiring shape.

Finally, as shown in FIG. 10C, heat treatment in a gas atmosphere containing N diffuses Ti in the Cu.Ti alloy film 93 to the upper surface and side surfaces of the Cu.Ti alloy film 93. , Cu.Ti alloy film 93 as a protective film T
The iN film 94 and the Cu wiring 95 which is the wiring are changed.

However, using this method, the T
When the iN film 93 is formed, the heat treatment temperature must be raised in order to obtain the Cu wiring 95 having a low resistance, and there is a problem that impurities in the diffusion layer of the element are rediffused and the element is deteriorated. It was Further, when the heat treatment temperature is low, there is a problem that Ti remains in the Cu wiring 95 and the wiring resistance increases.

[0012] On the other hand, Ag easily aggregates when heated to about 70 ° C or higher in the atmosphere, and thus its study has hardly been conducted until now.

[0013]

As described above, studies on Cu and Ag have begun as a next-generation wiring material. However, Cu is oxidized even at the low temperature of about 200 ° C. Therefore, a technique of coating Cu with a protective film has been proposed.

However, there are problems that the number of steps is large and it is not practical, and that high-temperature heat treatment is required to reduce the wiring resistance, and that the high-temperature heat treatment re-diffuses impurities in the diffusion layer and deteriorates the element. It was

On the other hand, Ag easily aggregates when heated to about 70 ° C. or higher in the atmosphere, and thus its study has hardly been conducted until now.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a semiconductor device having a practical low resistance metal wiring in place of an Al wiring and a method for manufacturing the same. is there.

[0017]

In order to achieve the above object, a semiconductor device of the present invention comprises a first metal film formed on a semiconductor substrate and a first metal film formed on the first metal film. A second metal film containing silver as a main component, and a protective film that covers at least the upper surface of the second metal film and contains the metal element of the first metal film are provided.

The semiconductor device manufacturing method of the present invention is
A step of forming a first metal film on a semiconductor substrate, a step of forming a second metal film containing silver as a main component on the first metal film, and a heat treatment in a gas atmosphere containing a predetermined element. To diffuse a part of the metal in the first metal film to the surface of the second metal film to prevent silver agglomeration consisting of the predetermined element and a part of the metal in the first metal film. Forming a protective film on the surface of the second metal film.

The first metal film is preferably a titanium film. Further, it is preferable that the temperature of the heat treatment is 450 ° C. or higher and 750 ° C. or lower, and the predetermined element is oxygen.

[0020]

According to the semiconductor device of the present invention, the second metal film containing silver as a main component suppresses the aggregation of silver by the amount covered by the protective film, thereby improving the reliability.

Further, since at least the upper surface of the second metal film is covered with the protective film, it is advantageous for forming a laminated wiring. That is, by forming a wiring layer of the present structure composed of a first metal film and a second metal film with an interlayer insulating film interposed, for example, contact holes with different depths for connecting wirings that contact each wiring layer. Since the protective film can be used as an etching stopper film when forming
Contact holes with different depths can be formed at once.

Further, according to the research conducted by the present inventors, in the laminated film of the first metal film and the second metal film containing silver as a main component, the first metal film with respect to the second metal film is It was found that the diffusion rate of the metal was sufficiently higher than the diffusion rate of the metal of the first metal film to the compound or alloy composed of the metal of the first metal film and the metal of the second metal film. This is probably because the metal of the first metal film diffuses mainly via the grain boundaries of the second metal film.

Therefore, according to the method of manufacturing a semiconductor device of the present invention, in the heat treatment step, it is sufficient to form a protective film on the surface of the second metal film containing silver as the main component, which is the main wiring. Since the amount of the metal in the first metal film is supplied by diffusion, a protective film can be formed on the surface of the second metal film.

Therefore, according to the method for manufacturing a semiconductor device of the present invention, even if silver, which has a low resistance value but is prone to agglomeration, is used as the wiring material, the protection formed on the second metal film which becomes the main wiring. Since the film can suppress the aggregation of silver in the second metal film, it is possible to obtain a practical metal wiring that takes advantage of the characteristic of silver, which is low resistance. Further, since the metal diffusion rate of the first metal film is high, the first metal is prevented from remaining in the second metal film containing silver as a main component, and the wiring resistance can be suppressed low.

Further, if the first metal film and the second metal film are formed in the groove, a sufficient amount of the first metal film in the upper surface portion of the second metal film above the groove can be selectively formed. Since the metal can be supplied, the protective film can be selectively formed on the upper surface portion of the second metal film.

Therefore, as compared with the conventional technique shown in FIG. 9 in which a wiring layer is covered with a protective film, a simpler process is required.

[0027]

Embodiments will be described below with reference to the drawings.

FIG. 1 shows an embedding A according to an embodiment of the present invention.
FIG. 6 is a process cross-sectional view showing the method for forming the g-wiring. Also, FIG.
1 to 13 show S showing a sectional structure of an actually formed shape.
11 to 13 are EM photographs, and FIG. 11 to FIG.
It corresponds to (c).

First, as shown in FIG. 1A, a SiO ₂ film 2 is formed on a silicon substrate 1, and a groove for a buried wiring is formed in the SiO ₂ film 2. Although the SiO ₂ film 2 is used as the insulating film here, another insulating film, for example, a polyimide film may be used.

Next, a TiN film 3 having a thickness of 70 nm is formed as a diffusion barrier film. The TiN film 3 is formed by, for example, a sputtering method under the following conditions: sputter pressure 10 ⁻¹ Pa, Ar / N ₂ ratio 50/50%,
The residual O ₂ concentration is about 10 ppm or less, and the current is 5A. After that, the TiN film 3 is densified by a heat treatment at a temperature of 600 ° C.

Next, a Ti film having a thickness of 50 nm is formed on the TiN film 3.
The film 4 (first metal film) and the Ag film 5 (second metal film) having a thickness of 400 nm are sequentially formed. The Ti film 4 and the Ag film 5 are formed by, for example, a sputtering method under the following conditions.
For example, the sputtering pressure is 10 ⁻¹ Pa, Ar 100%, residual O ₂ concentration is about 10 ppm or less (common to Ti film 4 and Ag film 5), 1.5 A (Ti film 4), 1 kW (Ag film 5). It is preferable that each of the sputtering steps be continuously performed without breaking the vacuum. Next, as shown in FIG.
The film 5 is flattened. When the Ag film 5 is formed by a sputtering method, this flattening is performed by, for example, annealing at 400 ° C. during or after the Ag film 5 is formed by sputtering to reflow the Ag film 5 for flattening. To do.

Next, as shown in FIG. 1C, the TiN film 3, the Ti film 4, and the Ag film 5 other than the groove are removed and the embedded Ag is removed.
A wiring layer is formed. These TiN film 3, Ti film 4, Ag
The film 5 is removed by wet etching, RIE, ion milling, polishing or the like. Specifically, a dilute nitric acid solution is used for wet etching, and alumina or silica is used as an abrasive for polishing.

Here, the Ag film 5 is removed so that the surface becomes flat, but the Ag film 5 may be located below the groove surface. Further, TiN film 3 other than the groove portion, Ti
If there is no problem even if the film 4 and the Ag film 5 are removed, the TiN film 3, the Ti film 4, and the Ag film 5 other than the groove may be left in this step.

After that, the silicon substrate 1 is loaded into the annealing treatment chamber, and the annealing treatment chamber is set to 10 ^-6 Torr.
Reduce the pressure to the following vacuum.

Next, as shown in FIG. 1C, a rare gas containing O ₂ (predetermined element), for example, Ar gas is introduced, and annealing is performed in this Ar gas atmosphere at a temperature of 600 ° C. for 30 minutes. A TiO ₂ film 6 is formed on the upper surface of the Ag film 5.
In this annealing step, the partial pressure of O ₂ is 10 ^−10.
At or above Torr, Ar is at normal pressure. At this time, FIG.
As shown in (c), it can be seen that Ti has diffused to the surface of the Ag film 5. In addition, XP on the upper surface of the Ag film 5
When the S spectrum was obtained, the results shown in FIG. 2 were obtained, and it was confirmed that the TiO ₂ film 6 was formed on the upper surface of the Ag film 5.

In the annealing process, the TiO ₂ film 6 is formed on the upper surface of the Ag film 5 because the Ti in the Ti film 4 is A
It is considered that this is because it diffuses in the g film 5 and reaches the surface of the Ag film 5, and Ti reaching the surface reacts with O ₂ in the atmosphere.

Moreover, since the diffusion rate of Ti into the Ag film 5 is sufficiently higher than the diffusion rate of Ti into the compound or alloy of Ag and Ti, re-diffusion of impurities in the diffusion layer is prevented as in this embodiment. Even if it is possible to anneal at a low temperature of 600 ° C., the amount of Ti necessary for forming the protective film can be reduced to the Ag film
Can be supplied to the surface.

FIG. 4 is a diagram showing that the diffusion rate of Ti into the film composed of Ag and Ti is slow. Specifically, it shows the change in the sheet resistance of the compound or alloy of Ag and Ti before and after annealing. It is a figure. Here, the film thickness is 4
00 nm.

Before annealing (curve a) and after annealing (curve b), the sheet resistance does not change much, and the sheet resistance remains high even after annealing. This is because the diffusion rate of Ti is slow and, as in the case of the laminated film of the Ag film 5 and the Ti film 4, Ti does not collect on the surface and much Ti remains in the compound or alloy of Ag and Ti. is there.

In the case of a compound or alloy of Ag and Ti, the diffusion type of Ti is body diffusion with a slow diffusion rate, whereas in the case of a laminated film of Ag film 5 and Ti film 4, T
This is because the diffusion type of i is grain boundary diffusion with a high diffusion rate.

Here, when annealing is performed at a temperature higher than 750 ° C., Ag reacts with Ti as shown in FIG. It is necessary to perform the above annealing at 750 ° C. or lower.
In addition, when annealing is performed at a temperature lower than 450 ° C., FIG.
As shown in (b), Ti is not diffused to the surface of the Ag film 5, it can not form a TiO ₂ film 6, a TiO ₂ film 6
In order to surely form the above, it is necessary to perform the annealing at 450 ° C. or higher. Note that FIG. 14A shows the Ag film 5 immediately after the sputter deposition.

Therefore, in order to form the TiO ₂ film 6, it is necessary to anneal at a temperature of 450 ° C. or higher and 750 ° C. or lower. In particular, if annealing is performed at a low temperature of about 600 ° C. as in this embodiment, re-diffusion of impurities in the diffusion layer can be suppressed more effectively, and deterioration of the element can be prevented.

FIG. 15A shows the surface of the Ag film when annealed in the air, and FIG. 15B shows the surface of the Ag film annealed in the air of this embodiment. . It can be seen from FIG. 15 that the presence of the TiO ₂ film 6, which is a protective film, suppresses Ag aggregation and forms a good Ag wiring layer. Further, since the TiO ₂ film 6 functions as a diffusion barrier film against Ag, the Ag in the Ag film 5 is
Can be prevented from diffusing into the film formed on the SiO ₂ film 12 in a later step.

Further, when the RBS spectrum of the sample (a laminated film of SiO ₂ film, Ti film, Ag film, and TiO ₂ film) prepared according to the method of this embodiment was obtained, as shown in FIG. Was found to be below the detection limit (1 atom%).

FIG. 5 is a diagram showing the electromigration resistance of the Ag wiring (curve d) produced according to the method of this embodiment.

This is 1.6 × 10 ⁷ A / cm for Ag wiring.
² shows the change in the resistance value before and after the current is applied and the current is applied (the resistance value after the current is applied / the resistance value before the current is applied). Further, in FIG. 5, a curve c shows a comparative example, and shows a change in resistance value when the Ag wiring is not covered with the TiO ₂ film.

[0047] The present embodiment from FIG. 5 in the case of the Ag wiring, whereas the disconnection increases sharply resistance change ratio at a later since flowing a current 10 ³ seconds or more occurs, the comparative examples In some cases, it can be seen that the resistance change rate suddenly increased after a few seconds and a wire break occurred. From this result, it can be seen that the Ag wiring of this example has a very excellent electromigration resistance.

Finally, as shown in FIG. 1D, an interlayer insulating film 7 such as PSG is deposited on the entire surface, and the buried wiring process is completed.

As described above, according to the Ag wiring forming method of the present embodiment, Ag is prevented from aggregating on the surface of the Ag film 5 by annealing at a temperature that does not cause re-diffusion of impurities in the diffusion layer. Therefore, the TiO ₂ film 6 can be formed. Therefore, the embedded Ag is prevented from deteriorating the element and reducing the reliability.
Wiring is obtained. Moreover, even if the above annealing is performed, Ag
Since almost no Ti remains in the film 5, the low resistance of Ag is not impaired. Further, since the TiO ₂ film 6 can be selectively formed on the upper surface of the Ag film 5, a simple process is required as compared with the process of covering the wiring layer with the protective film as in the conventional technique shown in FIG. .

In the present embodiment, the annealing was performed in a gas atmosphere containing Ar and O ₂ , but instead, the surface of the Ag film 5 was nitrided by annealing in a nitrogen gas atmosphere, and the TiO ₂ film 6 was formed. If a TiN film is formed instead of
Similar to the TiO ₂ film 6, good cohesion resistance and diffusion resistance were obtained.

By the way, for comparison, the above method is applied to Cu.
It was also applied to a (400 nm) / Ti (50 nm) laminated film. FIG. 7 is a characteristic diagram showing the relationship between the annealing temperature and the sheet resistance of the Cu film for this Cu / Ti laminated film. The annealing time is 30 minutes and the atmosphere is an Ar gas atmosphere containing O ₂ .

In the case of Cu, the sheet resistance value of about 600 ° C. or more becomes about 100 or more as shown in FIG. 7, but Ag (4
In the case of a (00 nm) / Ti (50 nm) laminated film, the sheet resistance value is about 53 or less at a temperature of 450 ° C. or more from FIG. It is considered that the reason why the sheet resistance is high in the case of Cu is that Ti is more likely to remain in the Cu film than in the case of the Ag film, and the resistance increases due to impurities due to the remaining Ti. In particular, since the diffusion and the like proceed from a temperature of about 600 ° C. and a protective film starts to be formed, this effect becomes large.

FIG. 8 is a view showing a buried Ag wiring structure according to another embodiment of the present invention. This is an example in which the present invention is applied to laminated wiring.

This will be described according to the forming process. First,
After forming the SiO ₂ film 2 on the silicon substrate 1, the TiN film 3, the Ti film 4, the Ag film 5 and the TiO ₂ film 6, and the interlayer insulating film 7 are formed as in the previous embodiment.

Next, after a groove for a buried wiring is formed on the surface of the interlayer insulating film 7, the TiN film 3 is formed by the same method as that of the TiN film 3, the Ti film 4, the Ag film 5 and the TiO ₂ film 6.
a, a Ti film 4a, an Ag film 5a and a TiO ₂ film 6a are formed.

Next, after depositing an interlayer insulating film 8 on the entire surface, T
Using the TiO ₂ film 6 and the TiO ₂ film 6a as etching stopper films, the interlayer insulating films 7 and 8 are etched until the TiO ₂ film 6 and the TiO ₂ film 6a are exposed. As described above, even if the distances from the surface of the interlayer insulating film 8 to the TiO ₂ film 6 and the TiO ₂ film 6a are different, since the TiO ₂ film 6 and the TiO ₂ film 6a function as an etching stopper film, the depth is Two different grooves can be formed at the same time.

Finally, after removing the TiO ₂ film 6 and the TiO ₂ film 6a in the groove, connection wirings 7 and 7a are formed.

Thus, according to the present embodiment, since contact holes having different depths can be formed at the same time, it is possible to form a highly reliable multi-layered buried Ag wiring in a simple process.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case of the buried wiring has been described, but the present invention can be applied to the wiring of other structures.

Although Ti is used as the material for the protective film in the above embodiment, other materials such as Si, In,
Nb, Pb, Sb, Sn, Mg, Al, Cr, Be, Z
You may use r. That is, in the above embodiment, the combination of Ag and Ti has been described, but the point is that other substances may be combined as long as the substance to be the protective film does not remain in the wiring layer.

In addition, various modifications can be made without departing from the scope of the present invention.

[0062]

As described above in detail, according to the present invention, Ag
Since aggregation of Ag in the film can be suppressed, it has a low resistance but easily aggregates. Therefore, Ag, which has not been considered as a wiring material until now, can be used.
A wiring that takes advantage of the low resistance of g can be obtained.

[Brief description of drawings]

FIG. 1 is a process cross-sectional view showing a method of forming a buried Ag wiring according to an embodiment of the present invention.

FIG. 2 is an XPS spectrum showing that a TiO ₂ film is formed on the upper surface of the Ag film.

FIG. 3 is an RB showing that no Ti remains in the Ag film.
S spectrum.

FIG. 4 is a diagram showing changes in sheet resistance before and after heat treatment, which shows that the heat treatment (annealing) of the present invention is not effective for a compound of Ag and Ti.

FIG. 5 is a diagram showing a relationship between a rate of change in resistance and time showing improvement in electromigration resistance according to the present invention.

FIG. 6 is a characteristic diagram showing the relationship between annealing temperature and sheet resistance for Ag.

FIG. 7 is a characteristic diagram showing the relationship between the annealing temperature and sheet resistance of Cu.

FIG. 8 is a diagram showing a buried Ag wiring structure according to another embodiment of the present invention.

FIG. 9 is a process cross-sectional view showing a conventional Cu wiring forming method.

FIG. 10 is a process cross-sectional view showing another conventional Cu wiring forming method.

FIG. 11 is a photograph showing a fine pattern formed on a substrate.

FIG. 12 is a photograph showing a fine pattern formed on a substrate.

FIG. 13 is a photograph showing a fine pattern formed on a substrate.

FIG. 14 is a photograph showing a fine pattern formed on a substrate.

FIG. 15 is a photograph showing a fine pattern formed on a substrate.

[Explanation of symbols]

1 ... Silicon substrate 2 ... SiO ₂ film 3, 3a ... TiN film 4, 4a ... Ti film (first metal film) 5, 5a ... Ag film (second metal film) 6, 6a ... TiO ₂ film 7, 8 ... Interlayer insulating film 81 ... Silicon substrate 82 ... SiO ₂ film 83, 86, 87 ... Ti film 84 ... TiN film 84 85 ... Cu film 91 ... Insulating film 92 ... Diffusion barrier metal film 93 ... Cu.Ti alloy film 94 ... TiN film 95 ... Cu wiring

Claims (4)

[Claims] 1. A first metal film formed on a semiconductor substrate, and a second metal film containing silver as a main component formed on the first metal film.
And a metal film of at least the upper surface of the second metal film,
And a protective film containing a metal element of the metal film of. 2. A step of forming a first metal film on a semiconductor substrate, a step of forming a second metal film containing silver as a main component on the first metal film, and including a predetermined element. By heat treatment in a gas atmosphere, a part of the metal in the first metal film is diffused to the surface of the second metal film, and the predetermined element and the part of the metal in the first metal film are separated from each other. Forming a protective film formed on the surface of the second metal film, the manufacturing method of the semiconductor device. 3. The method of manufacturing a semiconductor device according to claim 2, wherein the first metal film is made of titanium. 4. The temperature of the heat treatment is 450 ° C. or higher and 750 ° C.
The method for manufacturing a semiconductor device according to claim 3, wherein: