Method of forming multilayered wiring structure in semiconductor device

What is claimed is:

1. A method of manufacturing a semiconductor device having a multilayered structure including a lower wiring layer that contacts an upper surface of a substrate and an insulating interlayer formed on the lower wiring layer, the method comprising:

forming a via hole in said insulating interlayer;

applying a thin film on at least part of a sidewall of the via hole formed in the insulating interlayer and on an entire upper surface of the insulating interlayer in which the via hole is formed, the thin film including a high melting point metal or a high melting point metal compound selected from the group consisting of a nitride, an oxynitride, a boride, and a boronitride;

entirely removing the thin film from the upper surface of the insulating interlayer; and

performing selective chemical vapor deposition to fill the remaining portion of the via hole with a conductive material including one of Al and an Al alloy, thereby forming a via plug.

2. A method according to claim 1, further comprising forming the lower wiring layer including one of Al and an Al alloy film on said upper surface of said substrate.

3. A method according to claim 1, further comprising removing said thin film deposited on a bottom portion of said via hole; and providing said lower wiring layer with

a conductive film including one of Al and an Al alloy, and

an upper film in contact with an upper side of said conductive film and comprising a high melting point metal or a high melting point metal compound selected from the group consisting of a nitride, an oxynitride, a boride and a boronitride.

4. A method according to claim 3, wherein the forming comprises removing part of said upper film, positioned on said bottom portion of said via hole, and exposing part of said conductive film positioned at said via hole.

5. A method according to claim 3, wherein said forming comprises exposing part of said upper film positioned on said bottom portion of said via hole.

6. A method according to claim 4, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate the selective chemical vapor deposition.

7. A method according to claim 6, wherein the cleansing comprises performing plasma etching using a chlorine-based gas.

8. A method according to claim 7, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

9. A method according to claim 4, further comprising forming an upper wiring layer including one of Al and an Al alloy film on said upper surface of said insulating interlayer, wherein said via plug connects said upper wiring layer with said lower wiring layer with no heterogeneous metal interface.

10. A method according to claim 5, wherein the removing further comprises 1) simultaneously removing said thin film deposited on said upper surface of said insulating interlayer and on said bottom portion of said via hole, and, thereafter, 2) removing said exposed portion of said upper film, positioned on said bottom portion of said via hole.

11. A method according to claim 10, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate the selective chemical vapor deposition.

12. A method according to claim 6, wherein the cleansing comprises performing plasma etching using a chlorine-based gas.

13. A method according to claim 12, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

14. A method according to claim 10, further comprising forming an upper wiring layer including one of Al and an Al alloy film on said upper surface of said insulating interlayer, wherein said via plug connects said upper wiring layer with said lower wiring layer with no heterogeneous metal interface.

15. A method according to claim 2, further comprising removing said thin film deposited on a bottom portion of said via hole to expose part of said lower wiring layer, positioned on said bottom portion of said via hole.

16. A method according to claim 15, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate the selective chemical vapor deposition.

17. A method according to claim 14, wherein the cleansing comprises performing plasma etching using a chlorine-based gas.

18. A method according to claim 17, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

19. A method according to claim 15, further comprising forming an upper wiring layer comprising a conductive material including one of Al and an Al alloy on said upper surface of said insulating interlayer, said upper wiring layer being directly connected with said via plug; with no heterogeneous metal interface.

20. A method according to claim 1, further comprising forming, as said lower wiring layer, a diffusion layer in which an impurity is diffused on said upper surface of said substrate.

21. A method according to claim 20, further comprising maintaining said thin film at least on part of said side wall of said via hole and on an entire bottom portion of said via hole.

22. A method according to claim 21, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate the selective chemical vapor deposition.

23. A method according to claim 22, wherein the cleansing comprises performing plasma etching using a chlorine-based gas.

24. A method according to claim 23, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

25. A method according to claim 20, further comprising forming a metal silicide on said diffusion layer formed as said lower wiring layer.

26. A method according to claim 25, further comprising maintaining said thin film on at least part of said side wall of said via hole and on an entire bottom portion of said via hole.

27. A method according to claim 26, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate the selective chemical vapor deposition.

28. A method according to claim 27, wherein the cleansing comprises performing plasma etching using a chlorine-based gas.

29. A method according to claim 28, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

30. A method according to claim 1, further comprising removing said thin film deposited on a bottom portion of said via hole.

31. A method according to claim 1, further comprising maintaining said thin film on at least part of said side wall of said via hole and on an entire bottom portion of said via hole.

32. A method according to claim 1, further comprising cleansing by applying a cleansing agent to a surface of the thin film after removing the thin film from the insulating interlayer to facilitate said selective chemical vapor deposition.

33. A method according to claim 32, wherein said cleansing comprises performing plasma etching using a chlorine-based gas.

34. A method according to claim 33, wherein said chlorine-based gas used for plasma etching includes BCl.sub.3.

35. A method according to claim 1, further comprising forming an upper wiring layer including one of Al and an Al alloy film on said upper surface of said insulating interlayer, said upper wiring layer being directly connected with said via plug with no heterogeneous metal interface.

36. A method according to claim 1, wherein the thin film is a multilayered film, and wherein the applying includes applying the multilayered film to the insulating interlayer.

37. A method according to claim 36, wherein the applying includes applying a metal selected from the group consisting of Ti, Zr and Hf to form a bottom portion of said multilayered film, and applying a high melting point metal compound selected from the group consisting of a nitride, an oxynitride, a boride, and a boronitride to form a top portion of the multilayered film.

38. A method according to claim 37, wherein the applying includes applying titanium as the metal and applying titanium nitride as the high melting point metal compound.

39. A method according to claim 1, further comprising providing an inner wall of said via hole at an angle within the range of 80.degree.-87.degree. with respect to the surface of said substrate.

40. A method according to claim 1, wherein the filling includes directly contacting the conductive material to the metal compound.

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayered wiring structure in a semiconductor device and, more particularly, to a method of forming a multilayered wiring structure including a via hole. The present invention also relates to a semiconductor device having a characteristic multilayered wiring structure formed by this method.

2. Related Background Art

In recent years, a multilayered wiring technology has received a great deal of attention as a highly integrated high-density semiconductor element. In the multilayered wiring structure, different metal wiring layers are connected by using a via structure. The via structure in the multilayered wiring structure used in a conventional LSI having a design rule of 1 .mu.m or more is formed in the following process. A lower wiring layer is formed on the upper surface of a substrate, and a via hole is formed in an insulating interlayer formed on the lower wiring layer. Thereafter, a metal film is deposited in the via hole and on the insulating interlayer at the same time, and patterned to form an upper wiring layer.

In a micropatterned LSI, however, the yield and reliability of connection are greatly degraded in the via structure formed by this method. This is because the metal film to be formed into the upper wiring layer is normally deposited by using the sputtering method which is poor in step coverage, so that the metal film on the wall surface of the via hole becomes thinner to cause disconnection at this portion.

To solve this problem, for example, a method of forming a via hole into a tapered shape, or a method of improving step coverage by controlling the temperature of the substrate surface during deposition of an aluminum (hereinafter referred to as Al) alloy film to be formed into an upper wiring layer is proposed by S. R. Wilson et al., Proceeding of the Seventh International IEEE Multilevel Interconnection Conference, p. 42, 1990.

As a method of forming a via plug inside a via hole, a method of depositing a metal film serving as a barrier metal such as TiW inside the via hole and on an insulating interlayer, depositing a W (tungsten) film on the entire surface, and then, removing the W film from the insulating film is proposed by C. A. Bollinger et al., Proceeding of the Seventh International IEEE Multilevel Interconnection Conference, p. 21, 1990.

An interface between heterogeneous metals in the above-described via structure causes a deterioration in electrical characteristics in the via structure. For example, it is reported by S. R. Wilson et al., Proceeding of the Seventh International IEEE Multilevel Interconnection Conference, p. 42, 1990 that the via contact resistance in a via structure having a heterogeneous metal interface becomes higher than that in a via structure formed by contact of Al alloys.

In addition, it is reported by T. Kwok et al., Proceeding of the Seventh International IEEE Multilevel Interconnection Conference, p. 106, 1990 that, since the heterogeneous metal interface in the via structure causes discontinuity of the carrier movement in the wiring layer when a current flows, reliability against electromigration is greatly degraded as compared to a wiring layer on a flat substrate.

In Japanese Patent Laid-Open No. 63-260051, a method of forming a via plug consisting of Al which is selectively formable on the inner surface (side wall) of a via hole formed in an insulating interlayer on an Si substrate to form a via plug not only on the bottom portion but also on the side wall and bury the via hole.

A method of forming this via structure is shown in FIGS. 1 to 5.

As shown in FIG. 1, a lower wiring layer 300 and an insulating interlayer 40 are formed on an underlying insulating layer 20 formed on the surface of a substrate 10, and a via hole 50 is formed in the insulating interlayer 40.

As shown in FIG. 2, W silicide is then deposited to form a W silicide film 53a having a thickness of 50 nm on the entire surface of the insulating interlayer 40 by the CVD method.

As shown in FIG. 3, the W silicide film 53a on the upper surface of the insulating interlayer 40 and the bottom portion of the via hole 50 is etched by the reactive ion etching method (to be referred to as RIE hereinafter) to form the W silicide film 53a left only on the side wall of the via hole 50, thereby obtaining a via film 53b.

As shown in FIG. 4, Al is deposited and buried only in the via hole 50 by the selective CVD method to form a via plug 52. At this time, Al is deposited not only on the surface of the lower wiring layer 300 consisting of an Al alloy on the bottom surface of the via hole 50 but also on the surface of the via film 53a formed on the side wall of the via hole 50.

Finally, as shown in FIG. 5, the Al alloy is deposited by the sputtering method to form an Al alloy film having a thickness of 400 to 1,000 nm. The Al alloy film is formed into a predetermined pattern to form an upper wiring layer 60, thereby completing a semiconductor device having the via structure.

However, W silicide easily reacts with Al by annealing performed after formation of the via structure, so that a reacted layer is formed on the side wall of the via hole 50. Since the resistivity of the reacted layer is much higher than that of Al, the resistance of the via plug 52 is increased. In addition, the reaction between W silicide and Al may cause a change in volume to add a mechanical stress or form a cavity inside the via hole 50. These phenomena degrade the electrical characteristics of the via structure.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and has as its object to provide a method of forming a multilayered wiring structure including a via hole in a semiconductor device, and a semiconductor device having a characteristic multilayered wiring structure formed by this method.

As a typical constitution, a method of forming a multilayered wiring structure in a semiconductor according to the present invention is characterized by comprising

a first step of forming a lower wiring layer on an upper surface of a substrate,

a second step of forming an insulating interlayer on the lower wiring layer,

a third step of forming a via hole in the insulating interlayer,

a fourth step of forming a thin film (via film) on at least part of a side wall of the via hole formed in the insulating interlayer, the thin film including one of a high melting point metal and a high melting point metal compound selected from the group of including a nitride, a oxynitride, a boride, and a boronitride of the high melting point metal,

a fifth step of burying a conductive material including one of Al and an Al alloy in the via hole having the thin film formed on at least part of the side wall to form a via plug, and

a sixth step of forming an upper wiring layer on an upper surface of the insulating interlayer.

One of the characteristic steps of the present invention is the fourth step. In the fourth step, since the thin film formed on at least part of the side wall of the via hole contains a high melting point metal or a high melting point metal compound, no reacted layer is formed between the via plug and the thin film by annealing after formation of the via plug.

In addition, when a high melting point metal or a high melting point metal compound is used as a material for the thin film, the thin film can be formed at a relative low temperature, and etching can be performed at an etching rate equal to or higher than that of Al or an Al alloy. Formation of a very rigid oxide film such as an alumina film can be prevented.

Furthermore, the fifth step is characterized by supplying a gas containing an organoaluminum compound, and selectively depositing a conductive material including Al or an Al alloy, by a chemical reaction, inside the via hole in which the thin film is formed, thereby forming the via plug.

In particular, in the fifth step, plasma etching using a chlorine-based gas such as BCl.sub.3 is performed. The present inventors confirmed that burying performance of the via plug was improved when plasma etching was performed as a pretreatment.

Other than the above-described constitution of the method of forming a multilayered wiring structure in a semiconductor device, various modifications can be made. As a result, by this method, many semiconductor devices having characteristic multilayered wiring structures can be obtained.

As a typical structure, there is provided a semiconductor device having a multilayered wiring structure, characterized by comprising

a lower wiring layer formed on an upper surface of a substrate,

an insulating interlayer formed on the lower wiring layer,

a via hole formed in the insulating interlayer, in which a via plug is to be buried,

a thin film (via film) formed on at least part of a side wall of the via hole, the thin film including one of a high melting point metal and a high melting point metal compound selected from the group consisting of a nitride, a oxynitride, a boride, and a boronitride of the high melting point metal,

an upper wiring layer formed on an upper surface of the insulating interlayer, and

a via plug, making of a conductive material including one of Al and an Al alloy, for connecting the upper wiring layer with the lower wiring layer.

In addition, there is provided an example in which the lower wiring layer in the semiconductor device has a stacked wiring structure comprises a layer making of a high melting point metal or a high melting point metal compound.

Furthermore, there is provided an example in which a diffusion layer is formed as the lower wiring layer on the surface of the substrate, and a thin film making of a high melting point metal or a high melting point metal compound is formed on the side wall and the bottom portion of the via hole. Here the high melting point metal means a metal such as Ti, Zr, Hf, W, Ta, Mo, V, Nb, et al.; melting points of these metals are respectively as high as about 1500.degree. C. or more (for example, the melting point of Si is 1412.degree. C.).

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art form this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 5 are views for explaining steps in forming a multilayered wiring structure in a conventional semiconductor device;

FIG. 6 is a flow chart for explaining the first embodiment of the present invention;

FIGS. 7 to 14 are views for explaining steps in the first embodiment of the present invention;

FIG. 15 is a sectional view of a semiconductor device obtained by the first embodiment of the present invention;

FIG. 16 is a view for explaining the effect of the present invention, in which the illustrated semiconductor device is obtained by the first embodiment of the present invention;

FIG. 17 is a table showing evaluation results of materials used as thin film materials formed on the side walls of via holes;

FIG. 18 is a flow chart for explaining the second embodiment of the present invention;

FIGS. 19 to 24 are views for explaining steps in the second embodiment of the present invention;

FIG. 25 is a sectional view of a semiconductor device obtained by the second embodiment of the present invention;

FIGS. 26 to 31 are views for explaining steps in the third embodiment of the present invention;

FIG. 32 is a sectional view of a semiconductor device obtained by the third embodiment of the present invention;

FIG. 33 is a view showing an application of the semiconductor device (FIG. 32) obtained by the third embodiment of the present invention; and

FIG. 34 is a view showing an application of the semiconductor device obtained by the above-described first and third embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below with reference to FIGS. 6 to 34. The same reference numerals denote the same parts throughout the drawings, and a detailed description thereof will be omitted.

The first embodiment of the present invention will be described with reference to a flow chart in FIG. 6 and views of manufacturing steps in FIGS. 7 to 14. The embodiment to be explained here is the best mode.

As shown in FIG. 7, an underlying insulating film 20 is formed on the surface of an Si substrate 10. An Al alloy is deposited on the underlying insulating film 20 by the sputtering method to form an Al alloy film 31 having a thickness of 300 to 800 nm (step 201).

When step 201 is finished, a structure needed for a semiconductor device, e.g., a diffusion layer and a gate electrode, is formed on the surface of the substrate 10.

The Al alloy film 31 is formed into a predetermined wiring pattern to form a lower wiring layer 30 (step 202).

The wiring pattern is formed by the RIE using a chlorine-based gas after a resist pattern is formed by using an exposure apparatus.

As shown in FIG. 8, an insulating interlayer 40 is formed on the underlying insulting layer 20 on which the lower wiring layer 30 is formed (step 203).

SiO.sub.2 is deposited by the plasma CVD method to form an SiO.sub.2 film having a thickness of 300 nm, SOG is coated to form an SOG film having a thickness of 300 nm on the flat portion, and annealing is performed at 400.degree. C. Thereafter, SiO.sub.2 is deposited by the plasma CVD method again to form an SiO.sub.2 film having a thickness of 200 nm, thereby completing the insulating interlayer 40. To form the insulating interlayer 40 in an LSI having a wiring size as small as 0.6 .mu.m or less, the following method is used. SiO.sub.2 is deposited by the plasma CVD method using tetraethoxysilane (to be referred to as TEOS hereinafter) and oxygen to form an SiO.sub.2 film having a thickness of 100 nm. Further, SiO.sub.2 is deposited on the SiO.sub.2 film by the atmospheric pressure CVD method using TEOS and ozone to form an SiO.sub.2 film having a thickness of 1.0 .mu.m. After SOG is coated to form an SOG film having thickness of 1.0 .mu.m on the SiO.sub.2 film and annealing is performed at 400.degree. C., etchback is performed to obtain a 400 nm-thick SiO.sub.2 film on the flat portion. SiO.sub.2 is deposited again to a thickness of 400 nm by the plasma CVD method.

A photomask is set on the insulating interlayer 40, and a resist pattern is formed by using the exposure apparatus. Thereafter, a via hole 50 is formed in the insulating interlayer 40 by the RIE using a fluorine-based gas, as shown in FIG. 9 (step 204).

To increase the wiring density, it is preferable that the side wall of the via hole 50 is substantially perpendicular to the surface of the Si substrate 10. On the other hand, to minimize the possibility of generation of a cavity during formation of a via plug 52, it is preferable that the side wall of the via hole 50 has a tapered shape. Taking the two conditions into consideration, the spread angle of the inner wall preferably falls within the range of 80.degree. to 87.degree. with respect to the surface of the Si substrate 10.

Reactive sputtering is performed in an atmosphere containing nitrogen by using a Ti target to form a TiN film 51a having a thickness of 10 to 50 nm on the upper surface of the insulating interlayer 40, as shown in FIG. 10 (step 205). At this time, the deposition temperature during formation of the TiN film 51a is preferably about 300.degree. C. This is because, when the deposition temperature (surface temperature of the substrate) is about 300.degree. C., the lower wiring layer 30 is not adversely affected, and high film quality can be obtained.

At this time, as the thickness of the TiN film 51a (via film) on the side wall of the via hole 50 is increased, the diameter of the portion where the via plug 52 is buried is decreased to cause an increase in contact resistance. For this reason, the thickness of the TiN film 51a is preferably as thin as possible, for example, 50 nm or less in a fine via hole 50 (having a diameter of 0.6 .mu.m or less). When a collimator plate is inserted between the Ti target and the upper surface of the insulating interlayer 40 to limit the angle of particles landing on the upper surface of the insulating interlayer 40, coverage on the side wall of the fine via hole 50 is prevented from being degraded, so that the deposit can be further thinner.

Although, in this embodiment, TiN is used as the via film (51b) formed on the side wall of the via hole 50, TiON may also be used. It is confirmed by the present inventors that a group IVa metal, especially Ti can be effectively used, though Ti easily reacts with Al. More specifically, when Ti is formed thinner as compared to the diameter of the via hole 50 (for example, when a film having a thickness of 50 nm or less is formed while the diameter of the via hole 50 is 0.5 .mu.m), an uniform alloy layer (Al.sub.3 Ti) is formed, while an increase in contact resistance caused due to formation of a nonuniform reacted layer on the side wall of the via hole 50 can be prevented. The via plug 52 shown in FIG. 13 can be equally or more effectively formed (by the Al-CVD method) as compared to use of TiN. Other high melting point metals (for example, W, Ta, Mo et al.) can be used without reacting with the via plug 52, in condition that the annealing temperature after formation of the via plug 52 is limited at less than 400.degree. C. The via film 51b may be a stacked wiring structure constituted by forming a high melting point metal compound on a high melting point metal film. For example, TiN or TiON is formed on a Ti film.

When TiN is left also on the bottom portion of the via hole 50, it is necessary to use this stacked structure to reduce the contact resistance between the via film and the lower wiring layer 30. It is also necessary to remove an alumina film formed on the surface of the lower wiring layer 30, i.e., the Al alloy film on the bottom portion of the via hole 50 by Ar sputter etching before step 205.

The TiN film 51a (via film) can also be formed by the CVD method. More specifically, it is known to use TiCl.sub.4 and methylhydrazine, or the ECR-CVD method.

The TiN film 51a on the surface of the insulating interlayer 40 and on the bottom portion of the via hole 50 is removed by plasma etching using a gas atmosphere containing fluorine and chlorine. As shown in FIG. 11, the TiN film 51a is left only on the side wall of the via hole 50 (it may be part thereof) to form the via film 51b (step 206).

In more detail, an ECR etching apparatus using a radio-frequency bias is used to remove the TiN film 51a under the conditions that the BCl.sub.3 flow rate was 50 sccm, the SF.sub.6 flow rate was 30 sccm, the total pressure was 8 mtorr, the microwave current was 300 mA, and the radio-frequency power was 50 W. Under these conditions, removal of 30-nm TiN film 51a takes 20 seconds. Under these removal conditions, the selectivity ratio between TiN and Al is more than 20:1. Etching can be performed under the same conditions when Ti is used as a material of the via film 51b.

At this time, the etching rate of the lower wiring layer 30, i.e., the Al alloy layer is very low as compared to that of the via film 51b consisting of TiN, so that a high selectivity ratio can be obtained to prevent the Al alloy film on the bottom portion of the via hole 50 from being overetched.

The lower wiring layer 30 (Al alloy film) exposed to the bottom portion of the via hole 50, as shown in FIG. 12, is cleaned by plasma etching using a chlorine-based gas (BCl.sub.3 +Ar).

Etching was performed under the conditions that the BCl.sub.3 flow rate was 80 sccm, the Ar flow rate was 18 sccm, and the total pressure was 0.1 torr, by using a parallel plate type etching apparatus for ten minutes.

A deposit or alumina film is adhered to the surface of the lower wiring layer 30 exposed to the bottom portion of the via hole 50 when plasma etching is performed on the TiN film 51a or the surface of the lower wiring layer is exposed to air after plasma etching. The deposit and the alumina film must be removed because they interfere with Al deposition by the CVD method. On the other hand, the surface of the via film 51b, i.e., the TiN film on the side wall of the via hole 50, contains a large amount of oxygen absorbed during the air exposure. However, its influence is much smaller than that of the deposit or the alumina film on the surface of the lower wiring layer 30. In addition, cleaning of the surface of the lower wiring layer 30 facilitates deposition. For this reason, no special treatment must be performed on the surface of the via film 51b.

Al is selectively deposited only inside the via hole 50 by the CVD method using, e.g., DMAH and hydrogen as materials to form the via plug 52, as shown in FIG. 13 (step 208).

The Al-CVD method was performed under the conditions that the partial pressure of DMAH (dimethylaluminuhydride) was 30 mtorr, the total pressure was 2 torr, and the surface temperature of the substrate 10 was 210.degree. C. Under these conditions, the deposition time was 90 seconds when the diameter of the via hole 50 was 0.5 .mu.m.

Other than DMAH, an intermolecular compound between DMAH and trimethylaluminum, and another organoaluminum compound such as tri-isobutylaluminum, trimethylamine allan, dimethylethylamine allan, trimethylaluminum, or triethylaluminum can also be used as a material for the CVD method. At this time, the Al deposition is performed not only on the surface of the lower wiring layer 30 (Al alloy film) exposed to the bottom portion of the via hole 50 but also on the surface of the via film 51b. Therefore, ideally, it is possible to bury Al within a period of time to obtain a thickness half of the diameter of the via hole 50.

Assume that Al (via plug 52) is most ideally deposited. When the via hole 50 having a diameter of 0.6 .mu.m is buried at a deposition rate of 200 nm/min, the deposition time is 90 seconds. When the via hole 50 having a diameter of 0.4 .mu.m is buried at the same deposition rate, the deposition time is 60 seconds. Practically, the diameter of the via hole 50 or the deposition rate varies. Taking this into consideration, the deposition time increases by about 20%. However, it is apparent that the deposition time can be greatly shortened as compared to Al deposition only on the bottom surface of the via hole 50. By shortening the deposition time, productivity needed for mass-production can be obtained. Further, the selectivity of the Al alloy can be maintained, and generation of Al grains caused due to the non-selective deposition can be easily prevented.

When the aspect ratio of the via hole 50 (ratio of the depth to the diameter of the via hole 50) is 1/2 or more, the deposition time needed for burying is determined in accordance with the diameter of the via hole 50, and does not depend on the depth. For this reason, ideally, when all via holes 50 have a predetermined diameter, all via holes 50 can be completely buried even if the depths of the via holes 50 are different from each other.

FIG. 16 shows a sectional view of a semiconductor device showing this state.

Practically, it is difficult to form the via holes 50 all having the exactly same diameter because of a variety of reasons. Therefore, when the diameter of the via hole 50 is designed, two types of via holes, i.e., one having a minimum diameter and the other having a larger diameter, are prepared. The deposition time is set in accordance with the via hole having a larger diameter. In the via hole having a small diameter, Al is excessively deposited to form projections. However, the present inventors confirmed by an experiment that, when the diameter was as large as 0.4 .mu.m for the former, and 0.6 .mu.m for the latter, the projection was as high as 0.1 .mu.m, i.e., half of the difference between the two diameters, and it did not adversely affect on the characteristics. Other than the two types of via holes, a via hole having a much larger diameter (e.g., 1.5 .mu.m or more), which can reliably obtain good electrical characteristics without forming a via plug, may be present. In addition, when the surface temperature of the substrate 10 is increased (300.degree. C. or more, preferably 400.degree. to 470.degree. C.) during deposition of the Al alloy film serving as an upper wiring layer to improve the flow property of Al, the Al alloy film can be flattened. In this case, after the via plug 52 is formed, the Al alloy film is deposited before the surface of the via plug 52 is exposed to air, or the Ti film (having a thickness of 10 to 50 nm) is deposited before the Al alloy film is deposited, thereby obtaining the Al alloy film having satisfactory flatness. If the temperature used in the Al-sputtering method is more than 350.degree. C., an unified Al.sub.3 Ti film is formed by reacting Ti with Al. In this case, the via contact resistance is not increased.

Al is deposited by the sputtering method to form the Al alloy film having a thickness of 400 to 1,000 nm. By using the same method as in formation of the lower wiring layer 30, as shown in FIG. 14, an upper wiring layer 60 is formed, thereby completing a semiconductor device having a multilayered wiring structure (step 209) .

When the upper wiring layer 60 is to be formed, if an Al alloy film is deposited by using an apparatus other than that used for formation of the via plug 52 when the upper wiring layer 60 is formed, the alumina film formed on the upper surface of the via plug 52 must be removed by sputter etching using Ar ions or the like just before deposition to obtain good electrical contact.

After the via plug 52 is formed, if the Al alloy film is deposited to form the upper wiring layer 60 without unloading the resultant structure to the outer atmosphere, better electrical contact can be obtained because no alumina film is formed on the upper surface of the via plug 52 at all.

Until the semiconductor device using the via structure of the present invention is completed, a surface protective film is formed after formation of the via plug 52, and annealing is performed to remove process damage. Annealing is performed at a temperature of about 400.degree. to 450.degree. C. Since the reaction between the TiN film 51b and the via plug 52 does not notably progress until about 500.degree. C., no reacted layer is formed at the interface between the TiN film 51b and the via plug 52. Therefore, the electrical characteristics in this via structure are not degraded.

The semiconductor device obtained by the above-described first embodiment is shown in FIG. 15.

In this semiconductor device, the underlying insulating film 20 is formed on the Si substrate 10, and the lower wiring layer 30 constituted by the Al alloy film 31 is formed on the underlying insulating film 20. The insulating interlayer 40 is formed on the underlying insulating film 20 on which the lower wiring layer 30 is formed. The via hole 50 is formed in the insulating interlayer 40, and the via film 51b consisting of TiN is formed on the side wall of the via hole 50. The via plug 52 including of Al is formed inside the via film 51b. The upper wiring layer 60 and the lower wiring layer 30 are electrically connected by the via plug 52. The upper wiring layer 60 is constituted by the Al alloy film, like the lower wiring layer 30. The Al alloy used for the upper wiring layer 60 may have the same components as those used for the lower wiring layer 30, or it may have different components.

Therefore, there is no heterogeneous metal interface in the via structure of this semiconductor device, and the electrical characteristics of the via structure are not degraded.

A structure needed for a semiconductor device, such as a diffusion layer and a gate electrode, is formed inside the Si substrate and on the surface thereof. A contact hole is formed at the required position of the underlying insulating layer 20, and a contact structure is formed to connect the lower wiring layer 30 with the diffusion layer, the gate electrode, or any other structure.

One or more insulating interlayers 40 and metal wirings may respectively be stacked on the upper wiring layer 60.

The material used for the via film 51b needs to have the following characteristics.

(a) The material can form a via film at a low temperature (400.degree. C. or less) so as not to degrade the lower wiring layer 30.

(b) The material can be etched at a rate equal to or higher than that of the Al alloy film, and the material causes no overetching in the lower wiring layer 30 when the film on the bottom portion of the via hole 50 is removed.

(c) The material produces no rigid oxide film for inhibiting selective deposition of Al by the CVD method, or even if the oxide film is formed, the oxide film can be easily removed by plasma etching or the like.

(d) The material does not react with the via plug by annealing (at a temperature of about 400.degree. C.) after formation of the via plug 52, or form an unified reaction film in the case of t