JP3247100B2 - Method for forming electrode structure and method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing an electrode structure having a lower film made of polysilicon or amorphous silicon and an upper film made of a refractory metal, and a gate electrode made of the electrode structure. The present invention relates to a method for manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In a conventional MOS transistor,
The gate electrode was formed by a polysilicon film,
With the progress of miniaturization and high-speed LSI, the demand for lowering the resistance of the gate electrode of a MOS transistor has increased.

In order to reduce the resistance of the gate electrode, there has been proposed a technique using a polymetal gate electrode composed of a laminated film of a lower polysilicon film and an upper refractory metal film as the gate electrode. As an upper refractory metal film, a tungsten film has been proposed. When a tungsten film is used as the upper refractory metal film, the resistance value of the gate electrode can be reduced.

By the way, between the polysilicon film and the tungsten film, in order to prevent impurities (for example, B, P, As) introduced into the polysilicon film from diffusing into the tungsten film, a tungsten nitride film is used. A barrier film composed of WN _x ) or titanium nitride (TiN) is required (for example, Japanese Patent Application Laid-Open No.
No. 35542).

FIG. 12A shows a sectional structure of an electrode structure according to a first conventional example. As shown in FIG. 12A, a gate electrode is formed on a semiconductor substrate 1 with a gate insulating film 2 interposed therebetween, and the gate electrode is formed of a polysilicon film 3 and a nitride film sequentially formed from the lower side. Barrier film 4A and tungsten film 5 made of tungsten (WN _x )
It consists of.

FIG. 12B shows a sectional structure of an electrode structure according to a second conventional example. As shown in FIG. 12A, a gate electrode is formed on a semiconductor substrate 1 with a gate insulating film 2 interposed therebetween, and the gate electrode is formed of a polysilicon film 3 and a nitride film sequentially formed from the lower side. Titanium (Ti
N) and a tungsten film 5.

In the first conventional example, when a heat treatment is performed in a later step, as shown in FIG. 12C, nitrogen of the barrier film 4A made of tungsten nitride evaporates, and the barrier film 4A becomes thin. While changing to the tungsten film 5, the nitrogen of the barrier film 4A reacts with the silicon of the polysilicon film 3 to form the polysilicon film 3 and the tungsten film 5
Silicon nitride (SiN) with an extremely large resistance value between
This causes a problem that the resistance value of the gate electrode is increased.

In Japanese Patent Application Laid-Open No. Hei 7-235542, when the area density of nitrogen in the reaction layer 6 made of silicon nitride is set to a predetermined value or less, the sheet resistance of the reaction layer 6 becomes low and the resistance value of the gate electrode becomes low. Can be reduced.

[0009]

By the way, the present inventor cannot reduce the resistance value of the gate electrode in the first conventional example even if the area density of nitrogen in the reaction layer 6 is lower than a predetermined value. Faced the fact that.

Then, as a result of various studies on the reason why the resistance value of the gate electrode cannot be reduced in the first conventional example, the following was found. That is, if the thickness of the barrier film 4A is reduced to about 0.1 to 1.0 nm in order to reduce the areal density of nitrogen in the reaction layer 6, the barrier film 4A cannot exhibit a barrier function and the tungsten silicide ( since the WSi _x) will be formed, it is not possible to lower the resistance of the gate electrode. On the other hand, when the thickness of the barrier film 4A is increased to a level exceeding 1.0 nm, a barrier function is exhibited, but a reaction composed of silicon nitride having an extremely large resistance value is formed between the polysilicon film 3 and the tungsten film 5. Since the layer 6 is formed, the interface resistance between the polysilicon film 3 and the tungsten film 5 increases.

In addition, since the tungsten nitride film is inferior in heat resistance, if the heat treatment is performed at 750 ° C. or more, there is a problem that a large amount of nitrogen in the tungsten nitride film diffuses and becomes a tungsten film.

When a barrier film made of titanium nitride is used as in the second conventional example, a silicon nitride film having an extremely large resistance value is placed between the polysilicon film and the tungsten film for the following reason. Is formed, the interface resistance between the polysilicon film 3 and the tungsten film 5 increases.

First, as shown in FIG. 13A, a polysilicon film 3 is formed on a semiconductor substrate 1 with a gate insulating film 2 interposed therebetween. A p-type impurity such as boron is doped when forming a gate electrode, and an n-type impurity such as phosphorus is doped when forming an n-type gate electrode. Next, in order to deposit a titanium nitride film 4B on the polysilicon film 3, the semiconductor substrate 1 is carried into a chamber in which a titanium target 7 containing titanium as a main component is disposed, and then argon gas is introduced into the chamber. A gas mixture of nitrogen and nitrogen gas is introduced, and discharge is caused in the chamber. As a result, plasma composed of argon gas and nitrogen gas is generated, and nitrogen ions in the plasma react with silicon in the polysilicon film 3 to form a reaction layer made of a silicon nitride film on the surface of the polysilicon film 3. 6 are formed. Then, as shown in FIG. 13B, the titanium target 7 is nitrided to form the titanium nitride film 8, and at the same time, the titanium nitride is flipped off from the titanium nitride film 8, and the titanium nitride is formed on the reaction layer 6. Is formed.

Next, the semiconductor substrate 1 is transferred into a chamber in which a tungsten target 9 containing tungsten as a main component is disposed, and then argon gas is introduced into the chamber and discharge is caused in the chamber. In this way, plasma composed of argon gas is generated, and tungsten is sputtered from the tungsten target 9 by sputtering of argon ions in the plasma, and the sputtered tungsten is deposited on the surface of the titanium nitride film 4B. As shown in FIG. 13C, a tungsten film 5 is formed on the titanium nitride film 4B via the reaction layer 6.

Next, after an impurity layer serving as a source or a drain of a MOS transistor is formed on the semiconductor substrate 1,
When a heat treatment of, for example, 750 ° C. or more is performed to activate the impurity layer, as shown in FIG.
Since the excess nitrogen in B diffuses into the upper portion of the polysilicon film 3, the thickness of the reaction layer 6 made of titanium nitride increases as shown in FIG.

The present inventor has also examined the relationship between the heat treatment temperature and the interface resistance of the barrier film after the heat treatment. FIG. 15 shows the relationship between the heat treatment temperature (° C.) and the interface resistance (R _c ) between the polysilicon film and the refractory metal film after the heat treatment. In FIG. Tungsten nitride (W) is deposited on a silicon film (denoted as NPS).
_Nx ) indicates the case where a barrier film was formed,
Shows a case in which a barrier film made of tungsten nitride is formed on a polysilicon film (indicated as PPS) of a mold type.
Shows a case where a barrier film made of titanium nitride (TiN) is formed on a p-type polysilicon film, and ◇ shows a case where a barrier film made of titanium nitride is formed on a p-type polysilicon film. Further, FIG. 15 shows a resistance value when a current of 1 mA / μm ² is applied as the interface resistance because it is non-ohmic.

FIG. 15 shows that when the barrier film 4B made of titanium nitride is used, the interface resistance is high even when the heat treatment temperature is low. Further, in the experiments of the present inventors, when the barrier film 4B made of titanium nitride is used, the interface resistance is high without performing the heat treatment. This is because a reaction layer 6 made of titanium nitride is formed between the polysilicon film 3 and the barrier film 4B, as shown in FIGS.

When the barrier film 4A made of tungsten nitride is used, the barrier film 4A made of titanium nitride is used.
It can be seen that the interface resistance is lower than that in the case of using B, but the interface resistance sharply increases when a heat treatment at a temperature of 750 ° C. or more is performed. The reason is that when a barrier film 4A made of tungsten nitride is used and a heat treatment at a temperature of 750 ° C. or more is performed, nitrogen in the tungsten nitride is diffused, and silicon nitride is formed between the polysilicon film 3 and the tungsten film 5. This is because the reaction layer 6 made of is formed.

As the interface resistance (R _c ) between the polysilicon film 3 and the tungsten film 5 increases, the operation speed of the MOS transistor decreases. That is, if the gate electrode is AC
In the case of the (AC) operation, the charge and discharge are repeatedly performed on the distributed capacitance generated in the gate insulating film, so that a current flows through the distributed interface resistance, so that the influence of the distributed interface resistance appears. The operating speed slows down. When the operation speed of the MOS transistor becomes slow, there is a problem that the operation speed of the LSI becomes slow and the signal delay time increases. At present, when the operation speed of the LSI is regarded as important, even if the operation speed of the MOS transistor deteriorates by only about several percent, it becomes a serious problem.

In view of the above, it is an object of the present invention to reduce the interface resistance between a polysilicon film and a refractory metal film.

[0021]

In order to achieve the above object, a method for forming an electrode structure according to the present invention comprises the steps of: forming a barrier film on a silicon-containing film containing silicon as a main component; Depositing a refractory metal film on the barrier film,
A method for forming an electrode structure, comprising: forming a stacked film including the silicon-containing film, the barrier film, and the refractory metal film; and performing a heat treatment on the stacked film at a temperature of 750 ° C. or higher. The step of forming the barrier film includes: forming a first metal film made of a metal nitride on the silicon-containing film; and forming the first metal film on the first metal film from the metal. Or a second metal film made of a nitride of the metal and having a lower nitrogen content than the first metal film.
Forming a metal film, and on the second metal film,
Forming a third metal film made of the metal nitride and having a higher nitrogen content than the second metal film.

According to the method for forming an electrode structure according to the present invention, when heat treatment is performed, a part of each of nitrogen contained in the first metal film and nitrogen contained in the third metal film becomes the second metal film. Since the amount of nitrogen consumed in the nitridation of the metal film and contributing to the nitridation of the silicon-containing film among the nitrogen contained in the first metal film is reduced, a silicon nitride film is formed at the interface between the silicon-containing film and the barrier film. Since a reaction layer having a very high resistance value is not formed or its thickness is small even if it is formed, the interface resistance between the silicon-containing film and the refractory metal film is low.

In the method for forming an electrode structure according to the present invention, the metal is preferably titanium.

In the method for forming an electrode structure according to the present invention, the step of forming the barrier film may include the step of forming a nitrogen gas on the metal nitride film formed on the surface of the target containing the metal as a main component. By performing sputtering using an inert gas substantially free from the above, the metal nitride is deposited on the silicon-containing film to form the first nitride.
Forming a second metal film by depositing the metal on the first metal film after the formation of the metal film, and mixing a nitrogen gas and an inert gas with respect to the target. By performing sputtering using a gas, a nitride of the metal formed by a reaction between the metal and nitrogen contained in the mixed gas is deposited on the second metal film to form the third metal film. And a step of forming.

As described above, in the step of forming the first metal film, since the sputtering using the inert gas substantially containing no nitrogen gas is performed, no silicon nitride film is formed on the surface of the silicon-containing film. The interface resistance between the silicon-containing film and the refractory metal film is further reduced. Also,
The first metal film, the second metal film, and the third metal film can be continuously formed only by switching the sputtering gas using the same target, so that the throughput is improved.

In this case, after the step of forming the barrier film, nitrogen gas is substantially applied to the metal nitride film formed on the surface of the target in the step of forming the third metal film. It is preferable that the method further includes a step of performing sputtering using an inert gas not included in the above.

As described above, the method includes the step of sputtering the metal nitride film formed on the surface of the target in the step of forming the third metal film with an inert gas substantially containing no nitrogen gas. And the concentration of nitrogen contained in the metal nitride film is reduced, so that the nitrogen concentration of the first metal film formed using the metal nitride film is reduced. Is further reduced. For this reason, at the interface between the silicon-containing film and the barrier film, a reaction layer made of a silicon nitride film is more difficult to be formed, and even if it is formed, its thickness is further reduced. And the interface resistance between them is even lower.

In the method of forming an electrode structure according to the present invention, in the step of forming the barrier film, a target mainly composed of the metal having a nitride film of the metal formed on a surface is disposed. An inert gas substantially free of nitrogen gas is introduced into the chamber, and a discharge is caused in the chamber to remove the metal nitride that has been blown off from the metal nitride film by the silicon-containing film. Forming the first metal film by depositing on the first metal film, and then forming the second metal film by depositing the metal on the first metal film; While introducing a mixed gas of a nitrogen gas and an inert gas into the chamber, a discharge is caused in the chamber, and the metal and nitrogen contained in the mixed gas react. Wherein a nitride of the metal of the second
Forming the third metal film by depositing the third metal film on the metal film.

In this case, in the step of forming the first metal film, since an inert gas substantially containing no nitrogen gas is introduced into the chamber, a silicon nitride film is formed on the surface of the silicon-containing film. Therefore, the interfacial resistance between the silicon-containing film and the refractory metal film is further reduced. Also,
The first metal film, the second metal film, and the third metal film can be continuously formed only by switching the sputtering gas using the same target placed in the same chamber. Therefore, the throughput is improved.

In this case, after the step of forming the barrier film, there is further provided a step of introducing an inert gas substantially containing no nitrogen gas into the chamber and causing a discharge in the chamber. Is preferred.

As described above, after the step of forming the barrier film, the step of introducing an inert gas substantially containing no nitrogen gas into the chamber and causing a discharge in the chamber is provided. The metal nitride film formed on the surface of the target in the step of forming the metal film of No. 3;
Since sputtering can be performed with an inert gas substantially free of nitrogen gas, the concentration of nitrogen contained in the metal nitride film is reduced, and the first metal film formed using the metal nitride film is formed. Nitrogen concentration is reduced. Therefore, since the amount of nitrogen contributing to the nitridation of the silicon-containing film is further reduced, a reaction layer made of a silicon nitride film is more difficult to be formed at the interface between the silicon-containing film and the barrier film, and even if it is formed, Since the thickness is smaller, the interface resistance between the silicon-containing film and the refractory metal film is lower.

In the method of manufacturing a semiconductor device according to the present invention, a step of forming a polysilicon film on a semiconductor region; a step of forming a barrier film on the polysilicon film; Depositing a metal film and forming a gate electrode comprising the silicon-containing film, the barrier film and the refractory metal film, and ion-implanting impurities into the semiconductor region using the gate electrode as a mask to form a source or a drain. Forming a barrier film based on a method of manufacturing a semiconductor device including a step of forming an impurity layer to be formed and a step of performing a heat treatment at a temperature of 750 ° C. or more to activate the impurity layer. Forming a first metal film made of a metal nitride on the silicon-containing film;
Forming a second metal film made of the metal or a nitride of the metal and having a lower nitrogen content than the first metal film on the first metal film; 2
Forming a third metal film made of a nitride of the metal and having a higher nitrogen content than the second metal film on the metal film.

According to the method for manufacturing a semiconductor device according to the present invention, a semiconductor device is manufactured using the method for forming an electrode structure according to the present invention, and 750 ° C. is used for activating an impurity layer serving as a source or a drain. Even with the above heat treatment, the interface resistance between the polysilicon film and the high melting point metal film in the gate electrode can be reduced.

In the method for manufacturing a semiconductor device according to the present invention, the metal is preferably titanium.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a method for forming an electrode structure according to a first embodiment of the present invention will be described.
FIGS. 1A to 1C show a method of forming a gate electrode.
This will be described with reference to FIGS. 2 (a) to 2 (c) and FIG.

First, as shown in FIG. 1A, a gate insulating film 1 made of a silicon oxide film is formed on a silicon substrate 10.
1 is formed, a reduced pressure CV is formed on the gate insulating film 11.
An amorphous silicon film is deposited by the D method.

Next, n in the amorphous silicon film
(P) ions at 10 KeV in the gate electrode formation region
Implantation energy and a dose of 8 × 10 ¹⁵ cm ⁻² , and boron (B) ions are doped with 5 Ke into the p-type gate electrode formation region in the amorphous silicon film.
Doping is performed at an implantation energy of V and a dose of 5 × 10 ¹⁵ cm ⁻² . Next, the amorphous silicon film doped with phosphorus ions or boron ions
By performing a heat treatment at a temperature of 0 ° C. for 30 seconds, the amorphous silicon film is crystallized to form an n-type or p-type polysilicon film 12, and then a silicon oxide film formed on the surface of the polysilicon film 12 is formed. The film is removed using a hydrofluoric acid-based cleaning solution.

Next, as a preparation step, as shown in FIG. 3, a mixed gas of argon gas and nitrogen gas is introduced into a chamber in which a titanium target containing titanium as a main component is disposed, and discharge is performed in the chamber. To form a titanium nitride film on the surface of the titanium target.

Next, as a wafer replacement step, after the semiconductor substrate (wafer) used in the preparation step is carried out,
As shown in (b), the semiconductor substrate 10 is carried into a chamber A in which a titanium target 13 having a surface on which a titanium nitride film 13a is formed is disposed.

Next, as shown in FIG.
An argon gas is introduced into the chamber A and a discharge is caused in the chamber A. In this manner, a plasma composed of argon gas is generated, and argon ions in the plasma are converted into titanium nitride film 1 on the surface of titanium target 13.
Since 3a is sputtered, a first titanium nitride film 14 as a first metal film is deposited on the surface of the polysilicon film 12, as shown in FIG. In this step, the titanium nitride film 13a formed on the surface of the titanium target 13 disappears.

Next, when the introduction of the argon gas into the chamber A and the discharge in the chamber are continued, the argon ions in the plasma sputter the titanium target 13, and as shown in FIG. The titanium film 1 as a second metal film is formed on the titanium nitride film 14 of FIG.
5 is deposited.

Next, as shown in FIG. 3, after the discharge is once stopped, a mixed gas of argon gas and nitrogen gas is introduced into the chamber A, and the discharge is caused again.
As shown in FIG. 2A, the third surface of the titanium film 15
A second titanium nitride film 16 as a metal film is formed, and a titanium nitride film 13 a is also formed on the surface of the titanium target 13.

According to the first embodiment, an argon gas is introduced into a chamber A in which a titanium target 13 having a titanium nitride film 13a formed on its surface is disposed, so that titanium nitride as a first metal film is formed. Membrane 14 and second
A titanium film 15 as a metal film can be continuously deposited, and then, by introducing a mixed gas of an argon gas and a nitrogen gas into the chamber A, the third film is formed on the titanium film 15. Titanium nitride film 1 as metal film
6 can be formed. That is, without changing the titanium target 13, only by switching the gas introduced into the chamber A, the first titanium nitride film 14,
Since the titanium film 15 and the second titanium nitride film 16 can be formed continuously, the throughput is improved.

The titanium nitride film 13a formed on the surface of the titanium target 13 in the step of forming the second titanium nitride film 16 is
Can be used in the step of depositing the titanium nitride film 14. That is, the step of forming the third metal film and the above-described preparation step can be performed in the same step. This further improves the throughput.

Next, as shown in FIG. 2B, the semiconductor substrate 10 is transferred into a chamber B in which a tungsten target 17 containing tungsten as a main component is disposed, and then argon gas is supplied into the chamber B. At the same time, a discharge is caused in the chamber B. In this way, a plasma composed of argon gas is generated, and argon ions in the plasma sputter the tungsten target 17, so that a tungsten film 18 as a high melting point metal film is deposited on the second titanium nitride film 16. You. The gate electrode as an electrode structure is constituted by the polysilicon film 12, the first titanium nitride film 14, the titanium film 15, the second titanium nitride film 16 and the tungsten film 18 as described above. The titanium film 14, the titanium film 15, and the second titanium nitride film 16 form a barrier film. Note that the thickness of the barrier film is 5 nm to 5 nm in order to prevent the thickness of the gate electrode from becoming too large.
It is preferably about 20 nm.

Next, although not shown, the semiconductor substrate 10 is doped with impurities using the gate electrode as a mask to form an impurity layer serving as a source or a drain.
For example, a heat treatment at 750 ° C. or higher is performed to activate the impurities.

By the way, since the first titanium nitride film 14 is interposed between the polysilicon film 12 and the titanium film 15, even if a heat treatment at 750.degree. , Titanium silicide (T
iSi ₂ ) is not formed.

In a heat treatment step at 750 ° C. or higher, nitrogen present in the first titanium nitride film 14 diffuses into the titanium film 15 and the polysilicon film 12. At this time, since excessive nitrogen in the first titanium nitride film 14 and the second titanium nitride film 16 diffuses into the titanium film 15, the titanium film 15 changes into a titanium nitride film. )
As shown in FIG. 7, a new titanium nitride film 19 is formed.
The nitrogen in the first titanium nitride film 14 diffuses into the polysilicon film 12, so that a reaction layer 20 containing silicon and nitrogen as main components is formed at the interface between the polysilicon film 12 and the titanium nitride film 19. Is done.

As described above, since the resistance value of the reaction layer 20 containing silicon and nitrogen as its main components is extremely large, when the thickness of the reaction layer 20 is large, the resistance between the polysilicon film 12 and the tungsten film 18 is increased. Has an increased interface resistance.

However, in the first embodiment, since the titanium film 15 is formed on the first titanium nitride film 14, nitrogen in the first titanium nitride film 15 is used for nitriding the titanium film 15. Since the amount of nitrogen consumed and contributing to the nitridation of the polysilicon film 12 is reduced, the thickness of the reaction layer 20 is significantly smaller than that of the related art.

In the heat treatment step, nitrogen in the second titanium nitride film 16 also diffuses. However, since the titanium film 15 exists under the second titanium nitride film 16, Since the nitrogen in the film 16 is consumed for nitriding the titanium film 15, the nitrogen does not reach the polysilicon film 12, so that a reaction layer due to the nitrogen in the second titanium nitride film 16 is not formed.

Therefore, according to the first embodiment, the interface resistance between the polysilicon film 12 and the tungsten film 18 is greatly reduced.

The thickness of the first titanium nitride film 14 is preferably 3 nm or less, and most preferably about 2 nm. The reason is that the thickness of the first titanium nitride film 14 is 3n.
If the thickness exceeds m, the thickness of the reaction layer 20 formed in the heat treatment step at 750 ° C. or more increases, and the interface resistance between the polysilicon film 12 and the tungsten film 18 may increase.

FIGS. 4A and 4B show the distribution of the nitrogen content in the first titanium nitride film 14, the titanium film 15, and the second titanium nitride film 16, which constitute the barrier film. The horizontal axis indicates the distance from the interface between the barrier film and the polysilicon film to the substrate side.

In the nitrogen content distribution shown in FIG. 4A, the interface between the first metal film (the first titanium nitride film 14) and the polysilicon film is TiN, but the nitrogen content increases toward the substrate side. The content gradually decreases, and the nitrogen content becomes 0 at the interface between the first metal film and the second metal film (titanium film 15). Further, the nitrogen content at the interface between the second metal film and the third metal film (the second titanium nitride film 16) is 0, but the nitrogen content gradually increases toward the substrate side, and eventually. It is TiN.

In the nitrogen content distribution shown in FIG. 4B, the interface between the first metal film (the first titanium nitride film 14) and the polysilicon film is TiN, but the nitrogen content increases toward the substrate side. The content gradually decreases, and the nitrogen content at the interface between the first metal film and the second metal film (titanium film 15) is about half that of TiN, and the depth direction of the second metal film is In the central part, the nitrogen content is greatly reduced. At the interface between the second metal film and the third metal film (second titanium nitride film 16), the nitrogen content is about half that of TiN, but the nitrogen content gradually increases toward the substrate side. Eventually, it has become TiN.

In order to realize the nitrogen content distribution as shown in FIG. 4B, it is necessary to shorten the time for introducing an argon gas for forming the titanium film 15 or to lower the power of the discharge. Good.

In the first embodiment, the first titanium nitride film 14, the titanium film 15, and the second titanium nitride film 16 are formed by using a titanium target 13 having a titanium nitride film 13a formed on the surface. Because of the continuous formation, the nitrogen content is gradually decreasing and gradually increasing.However, when the target mainly composed of titanium nitride and the target mainly composed of titanium are properly used, the nitrogen content is reduced. The first and second titanium nitride films 14 without continuously changing,
16 and the titanium film 15 change the nitrogen content at a stretch.

Second Embodiment Hereinafter, as a method of forming an electrode structure according to a second embodiment of the present invention, a method of forming a gate electrode will be described with reference to FIGS.
This will be described with reference to (a) to (c) and FIG.

As in the first embodiment, as shown in FIG. 1A, after a gate insulating film 11 is formed on a silicon substrate 10, a polysilicon film 1 is formed on the gate insulating film 11.
2 is deposited.

Next, as a preparatory step, as shown in FIG. 6, a mixed gas of argon gas and nitrogen gas is introduced into a chamber in which a titanium target containing titanium as a main component is disposed, and discharge is performed in the chamber. To form a titanium nitride film on the surface of the titanium target.

Next, the semiconductor substrate 10 is carried into a chamber A in which a titanium target 13 having a surface on which a titanium nitride film 13a is formed is placed, and as in the first embodiment, as shown in FIG. As shown in FIG. 1, after forming a titanium nitride film 14 as a first metal film on the surface of the polysilicon film 12, a titanium film 15 is formed on the first nitride film 14 as shown in FIG. To form

Next, as shown in FIG. 6, after the discharge is stopped, a mixed gas of argon gas and nitrogen gas is introduced into the chamber A, and the discharge is caused again.
As shown in FIG. 5A, the third surface of the titanium film 15
Forming a second titanium nitride film 16 as a metal film, and also forming a titanium nitride film 1 on the surface of the titanium target 13.
3a is formed.

Next, as shown in FIG. 6, a target cleaning step of introducing only argon gas into the chamber A and continuing discharge in the chamber A is performed. By doing so, the titanium nitride film 13a on the surface of the titanium target 13 is sputtered with argon ions, so that the nitrogen content of the titanium nitride film 13a is reduced and, as shown in FIG. A third titanium nitride film 21 is deposited on the titanium nitride film 16.

Next, as shown in FIG. 5C, the semiconductor substrate 10 is transferred into a chamber B in which a tungsten target 17 containing tungsten as a main component is disposed, and then argon gas is supplied into the chamber B. At the same time, a discharge is caused in the chamber B, and a tungsten film 1 as a refractory metal film is formed on the third titanium nitride film 21.
8 is deposited. The gate electrode as an electrode structure is constituted by the polysilicon film 12, the first titanium nitride film 14, the titanium film 15, the second titanium nitride film 16, the third titanium nitride film 21, and the tungsten film 18 described above. And
The first titanium nitride film 14, the titanium film 15, the second titanium nitride film 16, and the third titanium nitride film 21 form a barrier film.

FIGS. 7A and 7B show the distribution of the nitrogen content in the first titanium nitride film 14, the titanium film 15, and the second titanium nitride film 16, which constitute the barrier film. The horizontal axis indicates the distance from the interface between the barrier film and the polysilicon film to the substrate side. Note that the nitrogen content in the third titanium nitride film 21 is omitted.

In the nitrogen content distribution shown in FIG. 7A, at the interface between the first metal film (first titanium nitride film 14) and the polysilicon film, the nitrogen content is smaller than that of TiN, and The nitrogen content gradually decreases toward the side, and the nitrogen content becomes zero at the interface between the first metal film and the second metal film (titanium film 15). Further, the nitrogen content at the interface between the second metal film and the third metal film (the second titanium nitride film 16) is 0, but the nitrogen content gradually increases toward the substrate side, and eventually. It is TiN.

In the nitrogen content distribution shown in FIG. 7B, at the interface between the first metal film (first titanium nitride film 14) and the polysilicon film, the nitrogen content is smaller than that of TiN, and The nitrogen content gradually decreases toward the side, and at the interface between the first metal film and the second metal film (titanium film 15), the nitrogen content is less than half of TiN. At the interface between the second metal film and the third metal film (second titanium nitride film 16), the nitrogen content is about half that of TiN, but the nitrogen content gradually increases toward the substrate side. Eventually, it has become TiN.

According to the second embodiment, after the second titanium nitride film 16 is formed on the surface of the titanium film 15, a target cleaning step of introducing only argon gas into the chamber A is performed. The nitrogen content of the titanium nitride film 13a used for depositing the titanium film 14 is reduced. Therefore, as can be seen from the comparison between FIG. 7A and FIG. 4A and the comparison between FIG. 7B and FIG. 4B, the polysilicon film 12 in the first titanium nitride film 14 Is lower in the vicinity of the interface than in the first embodiment. Therefore, when the electrode structure is subjected to a heat treatment at 750 ° C. or more, the amount of nitrogen diffused from first titanium nitride film 14 to polysilicon film 12 is reduced. Reaction layer 20 formed on
The thickness of the polysilicon film 1 (see FIG. 2C) becomes thinner or the reaction layer 20 is substantially not formed.
2 and the tungsten film 18 have a lower interface resistance.

FIG. 8 shows the first titanium nitride film 14 and the titanium film 15 when the time of the target cleaning step is changed to 0 second, 1 second, 2 seconds, 3 seconds, 5 seconds and 7 seconds. The relation between the thickness of the stacked film and the interface resistance between the polysilicon film 12 and the tungsten film 18 is shown. In this case, the polysilicon film 12 forms a p-type gate electrode. FIG. 8 shows that the first titanium nitride film 14 and the titanium film 15 are formed with a DC power of 300 W,
A second titanium nitride film 16 having a constant thickness of 10 nm is formed by discharging for 20 seconds with a DC power of W,
It is experimental data when a target cleaning process is performed with a DC power of 00 W. Also, the second nitride film 1
A tungsten film 18 having a thickness of 60 nm was formed on 6 with a DC power of 1000 W. The heat treatment after the formation of the laminated film is performed at a temperature of 760 ° C.
A furnace treatment for 40 minutes and a lamp annealing treatment at a temperature of 975 ° C. for 30 seconds were performed.

As can be seen from FIG. 8, when the time of the target cleaning step becomes longer, the first titanium nitride film 1
4, the content of nitrogen is reduced, so that the reaction film 20 is hardly formed, thereby lowering the interface resistance. This tendency becomes more pronounced when the total thickness of the first titanium nitride film 14 and the titanium film 15 is small.
The point where the film thickness is 0 in FIG. 8 corresponds to the conventional example (a single-layer film of titanium nitride).

FIG. 9 shows the target cleaning time,
The relationship between the amount of nitrogen contained in the stacked film of the first titanium nitride film 14 and the titanium film 15 is shown. In FIG.
● corresponds to the first embodiment in which the target cleaning is not performed, and ○ corresponds to the second embodiment in which the target cleaning is performed.
Corresponds to the embodiment. As can be seen from FIG. 9, an increase in the target cleaning time and a decrease in the amount of nitrogen in the stacked film have a linear relationship.

(Third Embodiment) Hereinafter, a method of manufacturing a semiconductor device according to a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. 11 (a) and 11 (b) and FIGS. 11 (a) and 11 (b).

First, as shown in FIG. 10A, a silicon oxide film 3 serving as a gate insulating film is formed on a semiconductor substrate 30.
After forming 1, a polysilicon film 32 is deposited on the silicon oxide film 31.

Next, a first titanium nitride film 34, a titanium film 35, and a second titanium nitride film 36 serving as barrier films are formed on the polysilicon film 32 in the same manner as in the first embodiment.
Are sequentially formed, a tungsten film 38 is deposited on the second titanium nitride film 36, and the polysilicon film 32 and the first
Of a titanium nitride film 34, a titanium film 35, a second titanium nitride film 36, and a tungsten film 38, and then a silicon nitride film is formed on the laminate to form a gate electrode. A hard mask 39 is formed.

Next, as shown in FIG. 10B, the stacked body is etched using the hard mask 39 to form a gate electrode made of the stacked body, and then the gate electrode is washed.

Next, after the semiconductor substrate 30 is doped with an impurity using the gate electrode as a mask to form a low-concentration impurity layer 40, a silicon nitride film is deposited over the entire surface of the semiconductor substrate 30. By performing anisotropic etching on the silicon nitride film, sidewalls 41 are formed on the wall surfaces of the gate electrode as shown in FIG. Next, the semiconductor substrate 30 is doped with an impurity using the gate electrode and the side wall 41 as a mask to form a high-concentration impurity layer 43.

Next, a heat treatment at a temperature of 750 ° C. or higher is performed on the semiconductor substrate 30 to activate the low-concentration impurity layers 40 and the high-concentration impurity layers 43. In this case, since nitrogen present in the first titanium nitride film 34 and the second titanium nitride film 36 diffuses into the titanium film 35, FIG.
As shown in (b), a new titanium nitride film 45 is formed between the polysilicon film 32 and the tungsten film 38, and silicon and nitrogen are added to the interface between the polysilicon film 32 and the titanium nitride film 45. A reaction layer 56 as a main component is formed.

According to the third embodiment, even after the heat treatment at 750 ° C. or higher, the titanium silicide layer is not formed and the interface resistance can be reduced, so that the operating speed of the MOS transistor can be prevented from lowering. Also,
A situation in which the tungsten film 38 is peeled off due to the formation of the titanium silicide layer can also be prevented.

[0080] In the first to third embodiments, as the high melting point metal film, but with a tungsten film, instead of this, molybdenum (Mo) film, a tungsten silicide (WSi _x) layer, or a molybdenum silicide (MoSi
₂ ) A membrane may be used.

The metal constituting the barrier film is as follows.
Although titanium was used, tantalum (Ta), tungsten (W), or the like may be used instead.

Further, in the first to third embodiments, a silicon substrate is used, but an SOI substrate may be used instead.

[0083]

According to the method for forming an electrode structure according to the present invention, even when a heat treatment at 750 ° C. or more is performed, metal silicide having a large resistance value is hardly formed on the surface of the silicon-containing film, and the silicon-containing film is hardly formed. If a reaction layer having an extremely high resistance value is not formed at the interface between the silicon-containing film and the barrier film, the thickness of the reaction layer is reduced, so that the interface resistance between the silicon-containing film and the refractory metal film is reduced.

According to the method of manufacturing a semiconductor device of the present invention, even if a heat treatment at 750 ° C. or more is performed to activate an impurity layer serving as a source or a drain, the polysilicon film in the gate electrode and the high melting point metal Interfacial resistance with the film can be reduced. Therefore, the operation time of the MOS transistor can be improved by reducing the delay time of the MOS transistor.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views illustrating respective steps of a method for forming an electrode structure according to a first embodiment.

FIGS. 2A to 2C are cross-sectional views illustrating respective steps of a method for forming an electrode structure according to the first embodiment.

FIG. 3 is a sequence diagram showing a relationship between a type of gas introduced into a chamber and discharge in the first embodiment.

FIGS. 4A and 4B are diagrams showing the relationship between the distance from the interface and the nitrogen content in the barrier film obtained according to the first embodiment.

FIGS. 5A to 5C are cross-sectional views illustrating respective steps of a method for forming an electrode structure according to a second embodiment.

FIG. 6 is a sequence diagram showing the relationship between the type of gas introduced into a chamber and discharge in the second embodiment.

FIGS. 7A and 7B are diagrams illustrating a relationship between a distance from an interface and a nitrogen content in a barrier film obtained according to a second embodiment.

FIG. 8 is a diagram showing the relationship between the thickness of a laminated film composed of a first titanium nitride film and a titanium film obtained according to a second embodiment and the interface resistance between a polysilicon film and a tungsten film. .

FIG. 9 is a diagram showing a relationship between a target cleaning time performed in the second embodiment and an amount of nitrogen contained in a stacked film including a first titanium nitride film and a titanium film.

FIGS. 10A and 10B are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor device according to a third embodiment.

FIGS. 11A and 11B are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor device according to a third embodiment. FIGS.

12A is a cross-sectional view of an electrode structure according to a first conventional example, FIG. 12B is a cross-sectional view of an electrode structure according to a second conventional example, and FIG. FIG. 10 is a cross-sectional view when a heat treatment of 750 ° C. or more is performed on the electrode structure according to the conventional example.

FIGS. 13A to 13C are cross-sectional views illustrating respective steps of a method for forming an electrode structure according to a second conventional example.

FIGS. 14A and 14B are cross-sectional views illustrating problems in a method of forming an electrode structure according to a second conventional example.

FIG. 15 is a diagram showing the relationship between the temperature of the heat treatment for the gate electrode obtained by the method for forming the electrode structure according to the first conventional example and the second conventional example, and the interface resistance after the heat treatment.

[Explanation of symbols]

 A chamber B chamber 10 semiconductor substrate 11 gate insulating film 12 polysilicon film 13 titanium target 13a titanium nitride film 14 first titanium nitride film (first metal film) 15 titanium film (second metal film) 16 second Titanium nitride film (third metal film) 17 Tungsten target 18 Tungsten film 19 Titanium nitride film 20 Reaction layer 21 Third titanium nitride film 30 Semiconductor substrate 31 Gate insulating film 32 Polysilicon film 34 First titanium nitride film 35 Titanium Film 36 second titanium nitride film 38 tungsten film 39 hard mask 40 low concentration impurity layer 41 side wall 43 high concentration impurity layer 45 titanium nitride film 46 reaction layer

Continuation of front page (56) References JP-A-2-35774 (JP, A) JP-A-8-321503 (JP, A) JP-A-2000-22852 (JP, A) IEEE TRANSACTIONS ON ELECTRON DEVIC ES, USA, Vol. 43, No. 11, November 1996, p. 1864-1869 1999. International Symposium VLSI Technology, Systems, and Applications, USA, p. 247-250 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 29/78 H01L 21/336 H01L 21/28 301 H01L 29/43 INSPEC (DIALOG) JICST file (JOIS)

Claims (8)

(57) [Claims] A step of forming a barrier film on a silicon-containing film containing silicon as a main component; and depositing a refractory metal film on the barrier film to form the silicon-containing film, the barrier film and the barrier film. In the method for forming an electrode structure, the method includes a step of forming a laminated film made of a high melting point metal film and a step of performing a heat treatment on the laminated film at a temperature of 750 ° C. or more. Forming a first metal film made of a metal nitride on the silicon-containing film; and forming the first metal film made of the metal or the metal nitride on the first metal film. Forming a second metal film having a lower nitrogen content than the first metal film; and forming a second metal film on the second metal film, the second metal film being made of a nitride of the metal and having a lower nitrogen content than the second metal film. Forming a third metal film having a high content; The method of forming the electrode structure, which comprises. 2. The method for forming an electrode structure according to claim 1, wherein the metal is titanium. 3. The step of forming the barrier film includes the step of: forming an inert gas substantially free of a nitrogen gas with respect to a nitride film of the metal formed on a surface of the target containing the metal as a main component. By performing sputtering using, the metal nitride is deposited on the silicon-containing film to form the first metal film, and then the metal is deposited on the first metal film. Forming the second metal film; and performing sputtering using a mixed gas of a nitrogen gas and an inert gas on the target, whereby the metal and nitrogen contained in the mixed gas react with each other. And depositing a nitride of said metal on said second metal film to form said third metal film. 3. The method of forming an electrode structure according to claim 1, wherein . 4. After the step of forming the barrier film, nitrogen gas is substantially supplied to the metal nitride film formed on the surface of the target in the step of forming the third metal film. The method for forming an electrode structure according to claim 3, further comprising a step of performing sputtering using an inert gas not included. 5. The step of forming the barrier film, wherein a nitrogen gas is substantially contained in a chamber in which a target having the metal as a main component and having a metal nitride film formed on a surface is disposed. The first gas is discharged by introducing an inert gas which is not generated and causing a discharge in the chamber, and depositing the metal nitride which has been repelled from the metal nitride film on the silicon-containing film. Forming the second metal film by depositing the metal on the first metal film after the formation of the metal film, and nitrogen gas in the chamber in which the target is disposed. Introducing a mixed gas with an inert gas and causing a discharge in the chamber to cause the metal and the nitride of the mixed gas to react with the nitride of the metal to form the second metal film The method of forming the electrode structure according to claim 1, characterized in that a step of forming the third metal film by depositing thereon. 6. The method according to claim 1, further comprising the step of: introducing an inert gas substantially free of nitrogen gas into the chamber and causing a discharge in the chamber after the step of forming the barrier film. 6. The method according to claim 5, wherein
3. The method for forming an electrode structure according to 1. 7. A step of forming a polysilicon film on a semiconductor region, a step of forming a barrier film on the polysilicon film, and depositing a refractory metal film on the barrier film to form the silicon film. A step of forming a gate electrode comprising the containing film, the barrier film and the refractory metal film, and a step of forming an impurity layer serving as a source or a drain by ion-implanting impurities into the semiconductor region using the gate electrode as a mask. Performing a heat treatment at a temperature of 750 ° C. or more to activate the impurity layer. The step of forming the barrier film, comprising: forming a metal nitride on the silicon-containing film; Forming a first metal film made of: a metal containing the metal or a nitride of the metal on the first metal film, containing nitrogen more than the first metal film. Forming a second metal film having a smaller amount; a third metal film made of nitride of the metal and having a higher nitrogen content than the second metal film on the second metal film Forming a semiconductor device. 8. The method according to claim 7, wherein the metal is titanium.