JPH06208999A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve electromigration resistance while suppressing occurrence of corrosion in Al alloy interconnection by providing the step of heat treating to precipitate Cu after the step of forming an Al alloy thin film containing a predetermined quantity of Cu and Si equivalent or less to the predetermined quantity of the Cu. CONSTITUTION:A silicon oxide film 2 is formed on a silicon substrate 1. Then, a metal thin film made of Al alloy containing 0.5wt.% of Cu and 0.5wt.% of Si is deposited on the film 2. Thereafter, the thin film is formed to metal interconnection 3. Then, a passivation film 4 is deposited on the interconnection 3 so as to cover the interconnection 3. An obtained silicon substrate 1 is die bonded to be packaged. In order to improve reliability of electromigration, a heat treatment for precipitating Cu in Al grain boundaries of the film 3 is conducted. As such a heat treatment, a constant-temperature storage is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an LSI or other semiconductor device, and more particularly to a method for manufacturing a wiring metal in such a semiconductor device.

[0002]

2. Description of the Related Art Generally, A containing Cu added as a wiring metal of a semiconductor integrated circuit.
In the case of using the 1-alloy, metal thin film deposition by the sputtering method is used for forming the wiring. When forming this wiring,
It is known that the wiring metal is subjected to a rapid heating and cooling history. Further, an alloying process at about 400 ° C. is included in the final process of manufacturing the semiconductor integrated circuit. Also in this alloying process, the heat history of rapid heating and cooling is added to the wiring metal. Due to such rapid heating and cooling thermal processes, the Al-Cu alloy is not sufficiently precipitated in the wiring formation, and the Al-Cu alloy is preferentially precipitated at grain boundaries to improve the electromigration resistance. There was a problem that the improving effect was reduced.

On the other hand, it has been reported that the wiring life can be improved by performing an aging treatment at 226 ° C. for 24 hours after wiring the Al-2% Cu-1% Si alloy thin film (Reference). `` J. Appl. Phys. 72 (5), 1 Sept. 19
92, p.1837]. ) However, Al as described above
Since the wiring of the alloy thin film contains a relatively large amount of Cu, the problem of corrosion generation becomes more serious as the wiring becomes finer. That is, when the concentration of Cu was 1.5% or more in wiring of the Al alloy thin film, there was a problem that corrosion was prominently caused by the resist treatment in wiring (Reference "J. Vac. Sci. . Tec
hnol. A, Vol.8, No.3, May / Jun 1990, p.2025 ”).

Therefore, it is an object of the present invention to provide a method of manufacturing a semiconductor device capable of improving the electromigration resistance while suppressing the occurrence of corrosion in Al alloy wiring.

[0005]

In order to solve the above-mentioned problems, a method of manufacturing a semiconductor device according to the present invention comprises a predetermined amount of Cu of less than 1.5% and a Si of equal or less than the predetermined amount.
After the step of forming the Al alloy thin film containing and, a heat treatment step of precipitating Cu is provided.

[0006]

According to the method of manufacturing a semiconductor device described above, since the Al alloy thin film containing a predetermined amount of Cu less than 1.5% is used, the occurrence of corrosion can be suppressed. Further, since the heat treatment for precipitating Cu is performed after the step of forming the Al alloy thin film, the Al—Cu based alloy or metallic Cu can be precipitated in the grain boundaries of the Al alloy thin film, etc., and the reliability of the Al alloy thin film against electromigration is high. Is improved. Further, since the content of Si in the Al alloy thin film is equal to or less than the content of Cu, it is possible to prevent a large amount of Si from precipitating at the grain boundaries and sufficiently improve the electromigration resistance. it can.

In the manufacturing of the above semiconductor device, if there is a rapid heating step or a rapid cooling step of about 400 ° C. or more during packaging, the packaged semiconductor device is subjected to the heat treatment as described above. Is desirable. This is because it is considered that the Al-Cu alloy once precipitated at the grain boundaries is taken into the crystal grains due to rapid heating or rapid cooling during packaging.

[0008]

EXAMPLES Before describing specific examples, a method of manufacturing a semiconductor device according to the present invention will be described in detail.

In general, when an Al--Cu based alloy is used as a material for forming fine wiring or the like constituting a semiconductor device for the purpose of improving electromigration resistance, the problem of corrosion that occurs with the use of a resist is solved. It is an indispensable prerequisite.

In order to effectively prevent the occurrence of such corrosion, an Al alloy thin film containing Cu in an amount of less than 1.5%, preferably less than 1.0% is usually used. ing.

On the other hand, when an Al--Cu alloy thin film is used to improve the electromigration resistance of fine wiring, there arises a problem that sufficient electromigration resistance cannot be obtained due to the thermal history of the alloy wiring. Was there. As described above, this phenomenon is caused by Al
It is considered that this is due to a rapid heat history of heating / cooling being applied to the wiring during the deposition of the alloy thin film or alloying in die bonding.

Therefore, in order to obtain a highly reliable wiring having resistance to electromigration, as a general rule, in a packaged semiconductor device, Cu in the wiring is finally deposited at grain boundaries. It is considered that a heat treatment step is required.

On the other hand, A is used as a material for forming fine wiring.
When using an l-based metal, an Al alloy thin film added with Si is used to prevent an Al spike from being formed at a position where the Al thin film contacts the silicon substrate.

However, according to the study by the present inventors,
It has been found that when the final heat treatment for precipitating Cu on the Al grain boundaries is applied to the Al-Si-Cu alloy thin film, the electromigration characteristics may not be effectively improved.

This phenomenon will be specifically described. Figure 1
The measured values of the diffusion coefficients of Si and Cu in Al are shown in FIG. The solid line shows the diffusion coefficient of Cu in Al, and the dotted line shows S in Al.
The diffusion coefficient of i is shown. As is clear from the figure, the diffusion coefficient of Cu is much smaller than that of Si.
Therefore, for an Al alloy thin film containing a large amount of Si,
Si grains are pre-deposited at the Al grain boundaries.

FIG. 2 shows the electromigration life of fine wiring made of an Al alloy thin film containing a relatively large amount of Si. As shown, Al-1% Si-0.5% C
In the case of u alloy wiring, the electromigration life is shortened only by the final heat treatment for precipitating Cu. That is, with respect to an Al alloy thin film containing a large amount of Si, Si particles are preliminarily precipitated at the Al grain boundaries, so that the electromigration characteristics cannot be effectively improved even by the precipitation of Cu. More specifically, the presence of Si particles precipitated in the wiring effectively reduces the cross-sectional area of the wiring and locally increases the current density, resulting in a reduction in electromigration life. . For example, Si is sufficiently diffused in the Al grain boundary by storage at 250 ° C. for 0.45 hours in a constant temperature. on the other hand,
It takes 45 hours for Cu to diffuse to the Al grain boundaries. Therefore, in the case of constant temperature storage for about 5 hours, the electromigration life due to the Si particles was rather shortened. In addition, in constant temperature storage for 10 hours or more, C
The electromigration life once reduced due to the precipitation effect of the u-Al alloy is recovered to some extent.

In view of the above circumstances, an Al alloy thin film to which less than 1.5% Cu is added and Si which is equal to or less than the Cu addition amount is used,
After the formation of such an Al alloy thin film (in principle, after packaging), a final heat treatment for precipitating a Cu element on the Al grain boundaries can be performed to obtain fine wiring having high reliability against electromigration. Conceivable. This is because it is considered that the effect of enhancing electromigration resistance due to Cu precipitation exceeds the effect of decreasing electromigration resistance due to Si particles.

Specific embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a cross section of a sample of a semiconductor integrated circuit. First, a silicon substrate 1 is prepared, and a thin silicon oxide film 2 is formed on the silicon substrate 1. afterwards,
On this silicon oxide film 2, 0.5 wt% Cu and 0.
A metal thin film made of an Al alloy containing 5% by weight of Si is deposited by the sputtering method. Next, this metal thin film is processed into the metal wiring 3 by using the photolithography technique and the anisotropic etching technique, and the wiring process is completed. Next, the passivation film 4 is deposited on the metal wiring 3 by using the CVD method so as to cover the metal wiring 3. Finally, the obtained silicon substrate 1 is die-bonded and packaged to complete a sample. In order to improve the reliability of such a sample against electromigration, a heat treatment for depositing Cu on the Al grain boundaries of the metal thin film 3 is performed. As such a heat treatment, constant temperature storage (hereinafter referred to as aging) in which the sample is held at a predetermined storage temperature for a predetermined time is performed.

The aging applied to the sample of FIG. 3 and its effect on electromigration will be described below. The storage temperature of the sample of FIG. 3 was changed and the change of wiring resistance was investigated. FIG. 4 is a graph showing the change of the wiring resistance with respect to the storage temperature. The horizontal axis shows the storage temperature, and the vertical axis shows the reduction rate of the wiring resistance per hour with respect to the logarithmic value. As shown, the storage temperature is 100
The wiring resistance is effectively reduced between ~ 300 ° C. This is because the Al grain boundary of the metal thin film 3 is Al in such a temperature range.
This means that a Cu-based alloy is effectively precipitated, and it is considered that the resistance to electromigration can be effectively increased by setting the storage temperature to 100 to 300 ° C. Next, improvement in electromigration resistance was investigated while changing the storage temperature. Table 1 shows the time until a 10% disconnection of the sample aged for 100 hours.

[0021]

[Table 1]

As is clear from the table, the sample not subjected to aging (room temperature) has a temperature of 200 ° C. or 25
The sample aged at 0 ° C. had significantly improved electromigration life. This result also proves that the resistance to electromigration can be increased by setting the aging temperature to 100 to 300 ° C.

Further, the sample subjected to the aging treatment at 300 ° C. had lower electromigration resistance than the sample not subjected to the aging treatment. This is 30
It is considered that aging at 0 ° C. or higher causes excessive temperature, and subsequent quenching causes adverse effects such as re-incorporation of Al—Cu alloy into crystal grains.

From the above results, it was revealed that the electromigration resistance was improved by aging at 100 to 300 ° C.

The present invention is not limited to the above embodiment. For example, various Al alloys containing less than 1.5% Cu can be used as the wiring metal. However, in this case, the Si concentration is equal to or lower than the Cu concentration. Further, it is considered that the storage time is preferably 10 hours or more, but it is considered that aging for less than 10 hours may be sufficient in some cases. Further, this aging may be divided constant temperature storage instead of continuous constant temperature storage. However, it is not desirable to perform heat treatment at about 300 ° C. or higher for a long time after aging.

[0026]

As described above, according to the method of manufacturing a semiconductor device of the present invention, since the Al alloy thin film containing a predetermined amount of Cu less than 1.5% is used, the occurrence of corrosion does not occur. Can be suppressed. Further, since the heat treatment for precipitating Cu is performed after the step of forming the Al alloy thin film, the Al—Cu based alloy or metallic Cu can be precipitated in the grain boundaries of the Al alloy thin film, etc., and the reliability of the Al alloy thin film against electromigration is high. Is improved. Furthermore, since the content of Si in the Al alloy thin film is equal to or less than the content of Cu, it is possible to prevent a large amount of Si from precipitating at grain boundaries and to sufficiently improve the electromigration resistance. You can Further, as a result, the wiring resistance is reduced, so that the performance of a semiconductor device such as an LSI can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing measured values of diffusion coefficients of Si and Cu in Al.

FIG. 2 is a graph showing the electromigration life of Al-Si-0.5Cu alloy wiring.

FIG. 3 is a sectional view of a sample for an electromigration test.

FIG. 4 is a graph showing resistance changes when the sample of FIG. 1 is stored in a constant temperature environment.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Silicon oxide film, 3 ... Metal wiring, 4 ... Passivation film.

Claims (1)

[Claims] 1. A semiconductor device comprising a heat treatment step of precipitating Cu after a step of forming an Al alloy thin film containing a predetermined amount of Cu of less than 1.5% and Si equal to or less than the predetermined amount. Production method.