Method of manufacturing semiconductor device having through hole with adhesion layer thereon

An adhesion layer for causing a plug for electrically connecting a lower wiring and an upper wiring opposite to each other with an interlayer insulating film interposed therebetween to adhere to the interlayer insulating film is formed within a through hole for forming the plug, based on a predetermined aspect ratio represented by a ratio of a depth dimension of the through hole to a diameter dimension of the through hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method of manufacturing the same, and more specifically to a semiconductor device in which wiring is carried out in multilayered form, and a manufacturing method thereof.

2. Description of the Related Art

A highly integrated semiconductor device has been formed with wirings provided in multilayered form. The semiconductor device includes wirings provided in multilayered form with an interlayer insulating film low in dielectric constant interposed therebetween. The wirings of the respective layers are electrically connected to each other via a through hole defined in the interlayer insulating film. Such a conventional semiconductor device200will be explained usingFIG. 10.

The semiconductor device200includes a semiconductor substrate211formed with an unillustrated semiconductor element, an insulating film212formed on the substrate211, a high melting-point metal layer213formed on the insulating film212, a lower wiring216made up of an aluminum alloy layer214made of aluminum and copper, which is formed on the high melting-point metal layer213, and a cap metal layer215formed on the alloy layer214, an interlayer insulating film217formed on the insulating film212so as to cover the lower wiring216, a through hole218defined in the interlayer insulating film located on the lower wiring216, an adhesion layer219provided within the through hole218, a plug220formed within the through hole218in which the adhesion layer219is formed, and an upper wiring221electrically connected to the lower wiring216.

A method of manufacturing the above-described conventional semiconductor device200will next be described.

An insulating film212is deposited on a semiconductor substrate211formed with an unillustrated semiconductor element. Thereafter, a layer of a high melting-point metal, which is obtained by laminating titanium nitride (TiN) and titanium (Ti), is formed on the insulating film212. Afterwards, a layer of an aluminum alloy made of aluminum (Al) and copper (Cu) is formed on the high melting-point metal layer. Further, a laminated layer of titanium nitride and titanium, or a layer made of titanium alone is formed on the aluminum alloy layer as a layer of a cap metal. These high melting-point layer, aluminum alloy layer and a cap metal layer are patterned to predetermined shapes to form a lower wiring216comprising a high melting-point layer213, an aluminum alloy layer214and a cap metal layer215. After the formation of the lower wiring216, an interlayer insulating film217is formed on the insulating film212so as to cover the lower wiring216. Thereafter, a concave hole, which reaches from the surface on the interlayer insulating film217to the lower wiring216, is formed as a through hole218.

Afterwards, a cleaning process is effected on a bottom surface222of the through hole to remove a residual material developed upon formation of the through hole218. Thereafter, an adhesion layer219using titanium nitride is formed on an inner wall of the through hole218. A plug220using tungsten is formed within the through hole218in which the adhesion layer219is formed. After the formation of the plug220, an upper wiring221is formed on the plug220by a process similar to that at the formation of the lower wiring216.

In addition to the conventional semiconductor device200, there is known a conventional semiconductor device wherein respective wirings of individual layers are electrically connected to each other without using different types of metals to thereby reduce resistance in a through hole (see Patent Document 1: Japanese Unexamined Patent Publication No. Hei 05-047940 (FIG. 1)).

Although an alloy made of aluminum, silicon and copper is formed as a plug within the through hole of the semiconductor device disclosed in the patent document 1, it is difficult to scale down or miniaturize the semiconductor device by use of the alloy in today when the diameter of the through hole, which is less than or equal to 0.5 μm, be in the mainstream. Accordingly, a plug using tungsten is formed in place of the above alloy nowadays.

SUMMARY OF THE INVENTION

Meanwhile, semiconductor devices faulty in operation were subject to fabrication where semiconductor devices200having various specs were manufactured by use of the above manufacturing method.

It turned out that as a result of investigations of the cause of a failure of each of such semiconductor devices faulty in operation, the value (hereinafter called through hole resistance) of resistance in a through hole of the semiconductor device was large.

Accordingly, an object of the present invention is to provide a semiconductor device low in through hole resistance, and a method of manufacturing the semiconductor device.

The present invention adopts the following constitutions to solve the above-described points.

An adhesion layer for causing a plug for electrically connecting a lower wiring and an upper wiring opposite to each other with an interlayer insulating film interposed therebetween to adhere to the interlayer insulating film can be formed by sputtering within a through hole for forming the plug, based on a predetermined aspect ratio indicated by a ratio of a depth dimension of the through hole to a diameter dimension of the through hole.

The adhesion layer lying within the through hole can be formed only on a sidewall of the through hole.

A thickness dimension of the adhesion layer on the lower wiring can be formed to a thickness dimension which causes gas having corrosion behavior to be penetrable.

Each of the lower wiring and the upper wiring can be formed to a laminated structure wherein a cap metal layer is provided on an aluminum alloy layer.

A high melting-point metal layer can be formed to a position to form the aluminum alloy layer prior to the formation of the aluminum alloy layer.

The aluminum alloy layer can be formed using an alloy made of aluminum and copper.

The cap metal layer can be formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

The high melting-point metal layer can be formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

A linear dimension of the lower wiring can be formed long.

The lower wiring can be formed as a first wiring on a semiconductor substrate having a semiconductor element.

The lower wiring can be formed in a floating state of being not directly connected to the semiconductor substrate having the semiconductor element.

The plug can be formed using tungsten.

The adhesion layer can be formed using titanium nitride.

The sputtering can be performed in such a manner that the relationship between a thickness dimension of a material deposited on the interlayer insulating film by the sputtering and the aspect ratio results in the fact that when the aspect ratio is over 2.5 and less than 3, the thickness dimension of the deposited material ranges from over 7.5 nm to under 10 nm, when the aspect ratio is over 3 and less than 3.5, the thickness dimension of the deposited material ranges from over 7.5 nm to under 20 nm, and when the aspect ratio is over 3.5 and less than 4, the thickness dimension of the deposited material ranges from over 7.5 nm to under 30 nm.

The sputtering can be performed from every direction at an incident angle of 5° or more with respect to a target to be sputtered.

The sputtering can be performed in such a manner that the relationship between the aspect ratio and the incident angle results in the fact that the incident angle at the time that the aspect ratio is over 1 and less than 1.5, is 45° or more, the incident angle at the time that the aspect ratio is over 1.5 and less than 2, is 26° or more, and the incident angle at the time that the aspect ratio is over 2.5 and less than 3, is 18° or more.

There is provided a semiconductor device comprising lower wiring and an upper wiring opposite to each other via a through hole defined in an interlayer insulating film, a plug for electrically connecting the lower wiring and the upper wiring to each other within the through hole, and an adhesion layer for causing the plug to adhere to the interlayer insulating film within the through hole, wherein the adhesion layer is formed based on a predetermined aspect ratio represented by a ratio of a depth dimension of the through hole to a diameter dimension thereof.

The adhesion-layer lying within the through hole can be formed only on a sidewall of the through hole.

A thickness dimension of the adhesion layer on the lower wiring can be formed to a thickness dimension which causes gas having corrosion behavior to be penetrable.

Each of the lower wiring and the upper wiring can be formed to a laminated structure wherein a cap metal layer is provided on an aluminum alloy layer.

Each of the lower wiring and the upper wiring can be formed to a structure having a high melting-point metal layer provided below the aluminum alloy layer.

The aluminum alloy layer can be formed of an alloy made of aluminum and copper.

The cap metal layer can be formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

The high melting-point metal layer can be formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

A linear dimension of the lower wiring can be formed long.

The lower wiring can be formed as a first wiring on a semiconductor substrate having a semiconductor element.

The lower wiring can be formed as a wiring held in a floating state of being not directly connected to the semiconductor substrate having the semiconductor element.

The plug can be formed by a tungsten plug.

The adhesion layer can be formed using titanium nitride.

The adhesion layer can be formed such that the relationship between a thickness dimension of a material deposited on the interlayer insulating film by the sputtering and the aspect ratio results in the fact that when the aspect ratio is over 2.5 and less than 3, the thickness dimension of the deposited material ranges from over 7.5 nm to under 10 nm, when the aspect ratio is over 3 and less than 3.5, the thickness dimension of the deposited material ranges from over 7.5 nm to under 20 nm, and when the aspect ratio is over 3.5 and less than 4, the thickness dimension of the deposited material ranges from over 7.5 nm to under 30 nm.

The adhesion layer is formed by sputtering having directivity. Sputtering can be effected on an object to be sputtered from every direction at an incident angle of 5° or more.

The adhesion layer can be formed such that the relationship between the aspect ratio and the incident angle results in the fact that the incident angle at the time that the aspect ratio is over 1 and less than 1.5, is 45° or more, the incident angle at the time that the aspect ratio is over 1.5 and less than 2, is 26° or more, and the incident angle at the time that the aspect ratio is over 2.5 and less than 3, is 18° or more.

A prehistory of the present invention will be explained below prior to the description of embodiments of the present invention.

The present inventors have repeated experiments to determine whether in a multilayered wiring type semiconductor device, the resistant value of a through hole resistance of the semiconductor device is large in any specs and to specify specs thereof. As a result, the present inventors found out that the value of the through hole resistance increased in particular in the case of a certain specific wiring pattern. That is, the wiring pattern corresponds to a wiring corresponding to a first layer on a semiconductor substrate, which is very long, and is a wiring pattern which is floated from the semiconductor substrate, i.e., which is not directly connected to the semiconductor substrate.

Next, the present inventors have considered that at the wiring pattern, the whole wiring is charged when a wiring is formed, so that some substances (hereinafter called foreign substances) are adhered to the boundary (hereinafter called bottom surface of a through hole) between the wiring and the through hole formed on the wiring, or formed at the boundary, whereby the foreign substances could result in an increase in through hole resistance value. However, the present inventors could not clarify the cause of their production and their composition.

The present inventors have repeatedly conducted experiments even subsequently. The present inventors have found out a remarkable result from an experiment shown next.

Such an experiment is as follows: A semiconductor device wherein a thickness dimension of an adhesion layer (titanium nitride layer) deposited on a bottom surface of a through hole was set to 0.75 nm, and a semiconductor device wherein it was set to 3 nm, were respectively produced using a testing wiring pattern shown inFIG. 11. The values of through hole resistances employed in the respective semiconductor devices were measured. Results thereof were summarized in a graph shown inFIG. 12.

That is, the testing wiring pattern structure shown inFIG. 11includes a first wiring M1in which a wiring lying within a range surrounded by a broken line is configured as a lower wiring, a second wiring M2configured as an upper wiring, a through hole Via in which a plug for electrically connecting the first wiring M1and the second wiring M2to each other is formed, and measuring terminals Pad for electrically connecting the wirings and a measuring device. A linear dimension of the lower wiring M1is 100 mm and a width dimension thereof is 0.52 μm. Further, a diameter dimension of the through hole is 0.26 μm.

Using the testing wiring pattern referred to above, a semiconductor device wherein titanium nitride for an adhesion layer was deposited on a bottom surface of a through hole Via in a thickness dimension of 0.75 nm was produced. A semiconductor device wherein it was deposited thereon in a thickness dimension of 3 nm was produced. Then the values of through hole resistances employed in the former and latter semiconductor devices were respectively measured. Their measured results were summarized in the graph ofFIG. 12. The graph ofFIG. 12is a cumulative normal distribution diagram in which a distribution of through hole resistance values at the time that the thickness dimension of the deposited titanium nitride is 0.75, is represented by “+”, and a distribution of through hole resistance values at the time that the thickness dimension thereof is 3 nm, is represented by “◯”. It turned out that as the thickness dimension of the titanium nitride at the bottom surface of the through hole became thin as shown in the figure, the through hole resistance value became low.

It was found out by carrying out further repeated experiments that a semiconductor device formed with no adhesion layer at a bottom surface of a through hole was capable of reducing a through hole resistance value.

Further, this invention includes the following the aspects.

1. A method of manufacturing a semiconductor device, comprising the following step:

forming, by sputtering, an adhesion layer for causing a plug for electrically connecting a lower wiring and an upper wiring opposite to each other with an interlayer insulating film interposed therebetween to adhere to the interlayer insulating film, within a through hole for forming the plug, based on a predetermined aspect ratio indicated by a ratio of a depth dimension of the through hole to a diameter dimension of the through hole.

2. The method according to claim1, wherein the adhesion layer lying within the through hole is formed only on a sidewall of the through hole.

3. The method according to claim2, wherein a thickness dimension of the adhesion layer on the lower wiring is formed to a thickness dimension which causes gas having corrosion behavior to be penetrable.

4. The method according to claim1, wherein each of the lower wiring and the upper wiring is formed to a laminated structure wherein a cap metal layer is provided on an aluminum alloy layer.

5. The method according to claim4, wherein a high melting-point metal layer is formed to a position to form the aluminum alloy layer prior to the formation of the aluminum alloy layer.

6. The method according to claim4, wherein the aluminum alloy layer is formed using an alloy made of aluminum and copper.

7. The method according to claim4, wherein the cap metal layer is formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

8. The method according to claim5, wherein the high melting-point metal layer is formed of a laminated layer of titanium nitride and titanium, or a layer made of titanium nitride alone.

9. The method according to claim1, wherein a linear dimension of the lower wiring is formed long.

10. The method according to claim1, wherein the lower wiring is formed as a first wiring on a semiconductor substrate having a semiconductor element.

11. The method according to claim1, wherein the lower wiring is formed in a floating state of being not directly connected to the semiconductor substrate having the semiconductor element.

12. The method according to claim1, wherein the plug is formed using tungsten.

13. The method according to claim1, wherein the adhesion layer is formed using titanium nitride.

14. The method according to claim1, wherein said sputtering is performed in such a manner that the relationship between a thickness dimension of a material deposited on the interlayer insulating film by said sputtering and the aspect ratio results in the fact that when the aspect ratio is over 2.5 and less than 3, the thickness dimension of the deposited material ranges from over 7.5 nm to under 10 nm, when the aspect ratio is over 3 and less than 3.5, the thickness dimension of the deposited material ranges from over 7.5 nm to under 20 nm, and when the aspect ratio is over 3.5 and less than 4, the thickness dimension of the deposited material ranges from over 7.5 nm to under 30 nm.

15. The method according to claim1, wherein said sputtering is performed from every direction at an incident angle of 5° or more with respect to a target to be sputtered.

16. The method according to claim15, wherein said sputtering is performed in such a manner that the relationship between the aspect ratio and the incident angle results in the fact that the incident angle at the time that the aspect ratio is over 1 and less than 1.5, is 45° or more, the incident angle at the time that the aspect ratio is over 1.5 and less than 2, is 26° or more, and the incident angle at the time that the aspect ratio is over 2.5 and less than 3, is 18° or more.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter be explained using the accompanying drawings on the basis of the above-described findings.

FIG. 1is a cross-sectional view showing a semiconductor device10according to a specific embodiment 1.

The semiconductor device10includes a semiconductor substrate11formed with an unillustrated semiconductor element, an insulating film12formed on the substrate11, a high melting-point metal layer13produced at a predetermined position on the insulating film12, a lower wiring16made up of an aluminum alloy layer14produced on the high melting-point metal layer13and a cap metal layer15produced on the alloy layer14, an interlayer insulating film17formed for wiring lamination, a through hole18defined in the interlayer insulating film17located on the lower wiring16, an adhesion layer19formed within the through hole18, a plug20formed within the through hole in which the adhesion layer19is provided, and an upper wiring21formed on the plug20.

The lower wiring16is a first wiring on the semiconductor substrate11. The wiring is not directly electrically connected to the semiconductor substrate. The linear dimension of the wiring is long and has a linear dimension of a few tens of mm. Further, the lower wiring16has a multilayer structure comprising the high melting-point metal layer13, aluminum alloy layer14and cap metal layer15for the purpose of an improvement in performance and prevention of reflection in a photolithography process.

A method of manufacturing the semiconductor device10will next be explained usingFIGS. 1 through 4.

As shown inFIG. 2, an insulating film12is first formed on a semiconductor substrate11having an unillustrated semiconductor element.

Next, a layer for a high melting-point metal layer13, which is formed with a 20-nm film made of titanium and a 20-nm film made of titanium nitride, is formed on the insulating film12to form a lower wiring16sequentially laminated using a sputtering method. After the layer for the high melting-point metal layer13has been formed, a layer for an aluminum alloy layer14, which is made of aluminum and copper, is formed 400 nm thick on the layer13. Further, a layer for a cap metal layer15, which is formed with a 5-nm film made of titanium and a 50-nm film made of titanium nitride, is formed on the layer for the aluminum alloy layer14. Next, an unillustrated resist film is disposed on the layer for the cap metal layer15in a predetermined pattern. Afterwards, the layer for the cap metal layer15, the layer for the aluminum alloy layer14, and the layer for the high melting-point metal layer13are etched to form the lower wiring16having a predetermined wiring pattern, which is made up of the high melting-point metal layer13, the aluminum alloy layer14and the cap metal layer15.

After the formation of the lower wiring16, a silicon oxide film is formed on the insulating film12as an interlayer insulating film17by a high-density plasma method, for example. The interlayer insulating film17is formed in a predetermined thickness dimension so as to cover the lower wiring16. Next, an unillustrated resist film is disposed on the interlayer insulating film17in a predetermined pattern and thereafter the interlayer insulating film uncovered by the resist film is etched to define a through hole18.

As shown inFIG. 2, an aspect ratio represented by a ratio of a depth dimension b (b=3.5) of the through hole18to a diameter dimension a (a=1) of the through hole18is given as 3.5. The through hole18having such an aspect ratio is formed by suitably adjusting the thickness dimension of the interlayer insulating film17, the diameter dimension of the through hole18and the height dimension of the lower wiring16.

After the formation of the through hole18, a bottom surface22of the through hole18is etched by a sputter etching method. Consequently, the surface of the cap metal layer15of the lower wiring16, which is exposed at the bottom surface22of the through hole18, is cut or chipped away 5 nm thick.

Afterward, as shown inFIG. 3, a layer23of titanium nitride for an adhesion layer19is formed on the interlayer insulating film17and within the through hole by a sputter method.

While the titanium nitride layer23is deposited even on the lower wiring16exposed at the bottom surface22of the through hole, its linear dimension is set thinner than the thickness dimension of the layer deposited on the interlayer insulating film17. Assuming that a titanium nitride layer23having a thickness dimension of 10 nm is formed on the interlayer insulating film by the sputter method under the above aspect ratio 3.5, for example, a titanium nitride layer having a thickness dimension of about 0.6 nm is formed at the bottom surface22of the through hole. This relationship is shown inFIG. 9.FIG. 9shows the relationship between aspect ratios and bottom coverage at the bottom surface22of the through hole, which are obtained by three types of sputter methods different from one another. In the case of these sputter methods, particles applied from a target to an objective one or object are high in rectilinearity in order of a normal sputter, a long-range sputter B and a long-range sputter A.

On the other hand, it turned out that though the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17was set thin in order to make thin the thickness dimension of the titanium nitride layer23deposited at the bottom surface22of the through hole, peeling occurred in the inner wall of the adhesion layer19with respect to the plug20or the inner wall of the through hole18with respect to the adhesion layer19or both inner walls after the formation of the adhesion layer19and the plug20to be described later in the case where the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17was 7.5 nm or less, whereby sufficient adhesion was not ensured.

After the formation of the titanium nitride layer23, as shown inFIG. 4, a tungsten (W) portion for the plug20and a tungsten layer24(having a thickness dimension ranging from 300 nm to 500 nm) are next formed within the through hole18and on the titanium nitride layer23by a CVD (Chemical Vapor Deposition) method using tungsten hexafluoride gas (WF6). After the formation of the tungsten layer24, the extra titanium nitride layer23and tungsten layer24other than within the through hole are removed by CMP (Chemical Mechanical Polishing) or an etchback method as shown inFIG. 1. Afterwards, an upper wiring21having a structure identical to that of the lower wiring16is formed in the same manner as the lower wiring16.

Owing to the formation of the adhesion layer19based on the predetermined aspect ratio as mentioned above, the thickness dimension of the adhesion layer at the bottom surface22of the through hole18can be made thin. It is therefore possible to manufacture a semiconductor device low in through hole resistance value. Accordingly, a failure in operation developed due to an increase in through hole resistance value can be prevented and hence a satisfactory semiconductor device can be obtained.

Further, since the semiconductor device of the present invention can be fabricated without using a special manufacturing apparatus, a capital investment can be suppressed and hence the semiconductor device of the present invention can be economically fabricated.

Incidentally, as the cause of a reduction in through hole resistance value, it is conceivable that when the thickness dimension of the adhesion layer formed at the bottom surface of the through hole is made thin, the tungsten hexafluoride gas having corrosion behavior is penetrated from the adhesion layer and foreign substances are eroded by the penetrated tungsten hexafluoride gas, followed by being removed.

While the adhesion layer19employed in the specific embodiment 1 has been substantially uniformly formed in the predetermined thickness dimension from the upper portion of the inner wall of the through hole18to the lower portion thereof, the specific embodiment 2 will explain a method of forming an adhesion layer31whose thickness dimension gradually decreases as it extends from an upper portion of a through hole to a lower portion thereof.

FIG. 5is a cross-sectional view showing a semiconductor device30according to the specific embodiment 2.

The semiconductor device30includes a semiconductor substrate11formed with an unillustrated semiconductor element, an insulating film12formed on the substrate11, a high melting-point metal layer13produced at a predetermined position on the insulating film12, a lower wiring16made up of an aluminum alloy layer14formed on the high melting-point metal layer13and a cap metal layer15produced on the alloy layer14, an interlayer insulating film17formed to laminate a wiring over the lower wiring16, a through hole18defined in the interlayer insulating film17located on the lower wiring16, an adhesion layer31whose thickness dimension gradually decreases as it extends from an upper portion of an inner wall of the through hole18to a lower portion thereof, a plug20formed within the through hole in which the adhesion layer31is provided, and an upper wiring21formed on the plug20.

A method of manufacturing the semiconductor device30will next be described usingFIGS. 6 through 8.

In a manner similar to the specific embodiment 1, an insulating film12is first formed to a predetermined position on a semiconductor substrate11. Afterwards, a lower wiring16is formed which consists of a high melting-point metal layer13, an aluminum alloy layer14and a cap metal layer15.

Next, an interlayer insulating film17made up of a silicon oxide film is formed on the insulating film12so as to cover the lower wiring16. Afterwards, photolitho etching is effected thereon to define a through hole18which exposes the surface of the lower wiring16at its bottom surface. After the formation of the through hole18, the lower wiring exposed at the bottom surface22of the through hole18is etched by a sputter etching method so that the surface of the cap metal layer15of the lower wiring16is cut or chipped away 5 nm thick.

A titanium nitride layer used for the adhesion layer31, which shows the feature of the specific embodiment 2, is next formed by using a sputter system50shown inFIG. 6. The sputter system50is provided with a target51which applies particles of titanium nitride vertically from the surface of the ceiling thereof to its floor, and a susceptor53on which a wafer52comprising a plurality of semiconductor substrates11subjected to the processing up to the above-described manufacturing process is placed. The susceptor53has a predetermined angle with respect to the target51. When the titanium nitride is sputtered from the target51to the wafer52, the susceptor53is rotated counterclockwise while maintaining a predetermined speed.

The predetermined angle has been found out by repeating experiments and is determined depending on an aspect ratio of the through hole. When the aspect ratio is more than or equal to 1 and less than 1.5, the angle of incidence of the titanium nitride from the target51may preferably be 45° or more. When the aspect ratio is greater than or equal to 1.5 and less than 2, the angle of incidence of the titanium nitride from the target51may preferably be 26° or more. When the aspect ratio is greater than or equal to 2.5 and less than 3, the angle of incidence angle of the titanium nitride from the target51may preferably be 18° or more.

With the use of the sputter system50, the titanium nitride particles applied from the target51are applied to the interlayer insulating film17and the through holes18at a predetermined incident angle as shown inFIG. 7. With the rotation of the susceptor53counterclockwise while the predetermined speed is being maintained, a titanium nitride layer32is uniformly formed on its corresponding interlayer insulating film17as shown inFIG. 8. Thus, the titanium nitride layer32for an adhesion layer, whose thickness dimension gradually decreases from an upper portion of an inner wall of each through hole18defined in the interlayer insulating film17to a lower portion thereof, is formed on the inner wall of each through hole18.

The titanium nitride layer32for the adhesion layer is not substantially formed at the bottom surface of each through hole18.

After the formation of the titanium nitride layer32, a tungsten layer for plugs20is formed in the through holes18in a manner similar to the specific embodiment 1. The tungsten layer is formed by a W-CVD method using tungsten hexafluoride gas WF6.

After the formation of the tungsten layer, the extra titanium nitride layer32and tungsten layer other than within the through holes are removed. Thereafter, an upper layer wiring21having a structure identical to that mentioned above is formed in a manner similar to the specific embodiment 1.

As described above, the through holes18each having a predetermined aspect ratio are defined in the interlayer insulating film17and sputtered at a predetermined angle from all directions, whereby adhesion layers31each having a predetermined thickness dimension are formed on the inner walls of the through holes18without being deposited on the bottom surfaces22of the through holes. Therefore, adhesion is provided between the plug20and the interlayer insulating film17, and a semiconductor device30low in through hole resistance value can be fabricated. It is thus possible to obtain a satisfactory semiconductor device30free of the occurrence of a failure in operation.

Further, the adhesion layer31can be formed even when the aspect ratio of the through hole18is less than 2.5. The adhesion layer31can be adapted for use in the manufacture of a miniaturized semiconductor device low in aspect ratio.

Since the adhesion layer19employed in the specific embodiment 1 and the adhesion layer31employed in the specific embodiment 2 can respectively be formed without effecting etching processing on the titanium nitride layers (23and32) for the adhesion layers, the manufacturing process can be shortened and made efficient.

Although the specific embodiment 1 has shown an example in which the through hole18whose aspect ratio is 3.5, is formed and the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17is formed 10 nm, the present invention is not limited to it. It has been found out by experiments that a semiconductor device low in through hole resistance value can be manufactured even in terms of the relationship between each aspect ratio shown below and the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17by sputtering.

That is, the relationship between the aspect ratio and the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17is as follows. When the aspect ratio is over 2.5 and less than 3, the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17may preferably be formed so as to range from over 7.5 nm to under 10 nm. When the aspect ratio is over 3 and less than 3.5, the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17may preferably be formed so as to range from over 7.5 nm to under 20 nm. When the aspect ratio is over 3.5 and less than 4, the thickness dimension of the titanium nitride layer23deposited on the interlayer insulating film17may preferably be formed so as to range from over 7.5 nm to under 30 nm.

In the specific embodiment 2 described above, the titanium nitride layer32may be formed by a collimator sputter method, a long-range sputter method, an ion sputter method or the like. Any of the sputter methods is a sputter method having directivity.

According to the present invention, as described above, since the adhesion layer is formed based on the aspect ratio, the adhesion layer is not formed at the bottom surface of the through hole or the thickness dimension of the adhesion layer at the bottom surface of the through hole can be formed thin, thus making it possible to fabricate a semiconductor device low in through hole resistance value. Accordingly, a satisfactory semiconductor device can be obtained which does not incur a failure in operation developed due to a high through hole resistance value.

While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.