Patent Application
20060086958
1. Field of the Invention
The present invention relates to a wire structure, a semiconductor device, an MRAM, and a manufacturing method of a semiconductor device. In particular, the present invention relates to a wire structure that includes carbon nanotubes, a semiconductor device, an MRAM, and a manufacturing method of a semiconductor device.
2. Description of the Background Art
Conventional semiconductor devices having a copper wire structure formed in accordance with a Damascene method have existed conventionally (see “Research Report of Trends in Technologies Filed as Patent Applications in Fiscal Year 2003, Multilayer Wire Technologies of LSI (Abridged Version), March 2004, p. 3, FIGS. 1 and 2,” by Japan Patent Office).
Here, in the case where a current of which the current density is about 107 A/cm2 flows through a copper wire, this copper wire is fused and cut. In addition, in the case where a current of which the current density is about 105 A/cm2 flows through a copper wire, a migration phenomenon occurs in this copper wire.
Together with recent downsizing of semiconductor devices, copper wire structures have also required to be downsized. Thus, the value of the current that is allowed to flow through these downsized copper wires cannot help being made smaller, taking into consideration the migration phenomenon and the like that occurs in copper wires.
An object of the present invention is to provide a wire structure where reduction in the amount of current that can be made to flow through the wire can be suppressed, even in the case where the wire is downsized, as well as a semiconductor device, an MRAM and a manufacturing method of a semiconductor device.
According to a first aspect of the present invention, there is provided a wire structure for a semiconductor device, where the semiconductor device includes an insulating film that is formed on a base. The wire structure includes a trench and carbon nanotubes. The trench is formed in the surface of the insulating film. The carbon nanotubes exist within the trench. In addition, the plurality of carbon nanotubes is great.
A current having a large current density can be made to flow through this wire. Accordingly, even in the case where the wire is downsized, it is not necessary to reduce the amount of current that flows through it.
According to a second aspect of the present invention, there is provided a semiconductor device comprising the wire structure according to claim 1.
It is possible to provide a semiconductor device having a wire where a current driving force has increased.
According to a third aspect of the present invention, there is provided an MRAM including a first wire, a second wire and an MTJ film. The first wire is provided above a semiconductor substrate. The second wire exists above the semiconductor substrate and below the first wire, and crosses the first wire in a plan view. The MTJ film exists between the first wire and the second wire. In addition, at least one of the first wire and the second wire comprises a wire structure according to claim 11. In addition, no catalyst film is formed on a surface that faces the MTJ film in this wire structure.
Shield effects are attained in the first wire or the second wire, and an increase in the current driving force of such a wire can be achieved.
According to a fourth aspect of the present invention, there is provided a manufacturing method of a semiconductor device, including the steps (a) to (d). In the step (a), an insulating film is formed on a base. In the step (b), a trench for a wire is formed in the surface of the insulating film. In the step (c), a catalyst film is formed inside the trench. In the step (d), carbon nanotubes are grown on the catalyst film.
The carbon nanotubes can be grown in a direction comprising a direction component direction in which the trench extends. Accordingly, the resistance of the entire wire can be reduced. Here, an electrical field comprising a direction component in which the trench extends, for example, is applied, so that the carbon nanotubes can be grown in a desired direction on the catalyst film.
According to a fifth aspect of the present invention, there is provided a manufacturing method of a semiconductor device, including the steps (A) to (D). In the step (A), an insulating film is formed on a base. In the step (B), a trench for a wire is formed inside the surface of the insulating film. In the step (C), a plurality of catalyst films in island form are formed on at least one inner surface of the trench in the direction in which the trench extends. In the step (D), carbon nanotubes are grown in a state where the catalyst films in island form are attached to tip ends of the carbon nanotubes which do not make contact with an inner surface of the trench.
It becomes unnecessary to attach a catalyst film to the sides or the like of the trench in a completed wire. Accordingly, the occurrence of a junction leak in the insulating film, which may be caused by a catalyst film being attached to the inside of the trench, can be prevented.
According to a sixth aspect of the present invention, there is provided a semiconductor device including the wire structure according to claim 22.
It is possible to provide a semiconductor device comprising a wire of which the current driving force is increased.
According to a seventh aspect of the present invention, there is provided a manufacturing method of a semiconductor device, including the steps (a) to (d). In the step (a), an insulating film is formed on a base. In the step (b), a trench for a wire is formed in the surface of the insulating film. In the step (c), a plurality of partitioning conductive films, which are formed of catalyst films and partition the trench along the direction in which the trench extends, are formed. In the step (d), carbon nanotubes are grown so as to connect the partitioning conductive films.
The carbon nanotubes can be grown in a direction comprising a direction component in which the trench extends. Accordingly, the resistance of the entire wire can be reduced. Furthermore, effects such as an increase in the current density of a current that flows through the wire, suppression of fusion cutting of the wire, and restriction of the occurrence of migration can be attained.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
FIGS. 4 to 7 are cross-sectional views showing steps for illustrating a manufacturing method of the wire structure according to the first embodiment;
FIGS. 9 to 12 are cross-sectional views showing steps for illustrating a manufacturing method of the wire structure according to the second embodiment;
FIGS. 15 to 17 are cross-sectional views showing steps for illustrating a manufacturing method of the wire structure according to the third embodiment;
FIGS. 26 to 28 are cross-sectional views showing steps for illustrating a manufacturing method of the wire structure according to the fifth embodiment;
FIGS. 33 to 37 are cross-sectional views showing steps for illustrating a manufacturing method of the wire structure according to the sixth embodiment;
FIGS. 40 to 43 are cross-sectional views showing steps for illustrating a manufacturing method of a wire structure according to a seventh embodiment;
FIGS. 55 to 59 are cross-sectional views showing steps for illustrating a manufacturing method of a wire structure according to a thirteenth embodiment; and
FIGS. 60 to 63 are cross-sectional views showing steps for illustrating a manufacturing method of a wire structure according to a fourteenth embodiment.
The present invention has a feature in that cylindrical structures formed of carbon elements are included in at least a part of a wire. These structures are typically carbon nanotubes. Here, a wire structure according to the present invention can be provided within an interlayer insulating film of a semiconductor device.
Carbon nanotubes form a new carbon-based material that has recently received attention because of its unique characteristics. Carbon nanotubes have a structure where a graphite sheet where carbon atoms are assembled into six-membered ring form with sp2 bonds, which are the strongest type of bond, is rolled into a cylindrical form. In addition, a tip end of a tube is closed with several six-membered rings, including five-membered rings.
The diameter of a tube can be miniaturized to the order of sub-nanometers, and the minimum is about 0.4 nm.
In addition, carbon nanotubes have a thermal conductivity which exceeds that of diamond, and a permissible current density of 109 A/cm2 or more. In addition, these carbon nanotubes are known to have a high Young's modulus.
Carbon nanotubes can be formed by means of arc discharge, laser ablation or the like. In recent years, it has become possible to form nanotubes by means of a plasma CVD method, a thermal CVD method or the like.
In the following, the present invention (wire structures that include carbon nanotubes, and the like) is concretely described with reference to the drawings which show embodiments thereof.
Here,
As shown in FIGS. 1 to 3, an interlayer insulating film 1 is formed on a semiconductor substrate 10. A trench 2 of which the cross section is approximately rectangular is formed in the surface of the interlayer insulating film 1. In addition, conductive catalyst films 3 are formed on the surface on both sides of the trench 2.
Here, the catalyst films 3 are formed on the entirety of the surfaces, in the direction in which this trench 2 extends. In addition, the catalyst films 3 for the carbon nanotubes 4 can be made of a transition metal or a compound having a transition metal. Zinc, cobalt, nickel, iron, rhodium, palladium and the like, for example, can be applied.
In addition, as shown in FIGS. 1 to 3, a great number of carbon nanotubes 4 are formed so as to reach from one catalyst film 3 to the other catalyst film 3. Here, the carbon nanotubes 4 are formed at angles which are not perpendicular to the direction in which the trench 2 extends (the carbon nanotubes 4 are formed at predetermined angles relative to the direction of the normal of the sides of the trench 2).
Next, a manufacturing method of the wire structure according to this embodiment is concretely described with reference to the cross-sectional views showing the steps thereof.
First, as shown in
Next, a photolithographic process is carried out, so that a trench 2 of which the cross section is in rectangular form is formed in the surface of the interlayer insulating film 1 as shown in
Next, as shown in
Next, anisotropic etching is carried out on the catalyst film 3. As a result of this, the catalyst film 3 remains only on the two sides of the trench 2 as shown in
After that, a process is carried out in accordance with a thermal CVD method or the like, so that the carbon nanotubes 4 grow on the catalyst film 3. Here, the carbon nanotubes 4 grow so as to reach from one side (one catalyst film 3) to the other side (the other catalyst film 3) of the trench 2.
Here, a process for growing the carbon nanotubes 4 is carried out simply in accordance with a thermal CVD method, without applying an electrical field. In this case, the carbon nanotubes 4 grow in random directions.
As a result of the aforementioned steps, the wire structure shown in FIGS. 1 to 3 is completed.
As described above, the wire structure according to this embodiment is formed by growing a great number of carbon nanotubes in the trench 2. Accordingly, the wire structure according to this embodiment has the following effects.
The carbon nanotubes 4 are not made of a metal; therefore, no migration phenomenon occurs. Accordingly, no defects, such as an increase in the resistance or disconnection, which are caused by a migration phenomenon and become problems in the case of copper wires, occur in the wires.
In addition, the carbon nanotubes 4 allow a current of which at least the current density is 109 A/cm2 or more to flow. Accordingly, at least in the case where a current of which the current density is about 109 A/cm2 flows through the carbon nanotubes 4, these carbon nanotubes 4 do not disconnect.
Accordingly, by adopting this wire structure that includes the carbon nanotubes 4, a current of which the amount is greater than that in the case of a copper wire can be allowed to flow through the wire structure. Therefore, the wire structure according to this embodiment can be adopted, and a sufficient amount of current for the operation of a semiconductor device can be allowed to flow through this wire structure, even in the case where the wire structure is miniaturized (downsized) with the progress of recent trends. That is, even in the case where a wire is downsized, it is not necessary to reduce the amount of current that flows through it.
Here, the more densely the carbon nanotubes 4 are grown in the trench 2, the more the average amount of current that flow through a wire can be increased.
In this embodiment, the catalyst film 3 is conductive. This is because the catalyst film 3 is also utilized as a means for conveying a current.
However, the carbon nanotubes 4 are usually formed so densely as to make contact with each other. Thus, a current can be made to flow between the carbon nanotubes 4 via these portions that make contact.
Accordingly, in the case of such a configuration (that is, a case other than the case where the carbon nanotubes 4 are intentionally formed sparsely), it is not always necessary for the catalyst film 3 to have conductivity, which is the same in the following embodiments.
Here, in the case where the catalyst film 3 is formed continuously along one inner surface of the trench 2, as in the wire structure according to this embodiment, the carbon nanotubes 4 are formed so densely as to make contact with each other.
The carbon nanotubes 4 grow on the catalyst film 3 by creating their own tissue, and it is very difficult to grow these carbon nanotubes 4 to a length of several μm or longer. That is, there is a limit to the length of the grown carbon nanotubes 4.
Accordingly, the catalyst films 3 are formed on the two sides of the trench 2, as in the wire structure according to this embodiment, so that the length to which the carbon nanotubes 4 grow is limited only by the width of the wire (width in the lateral direction in
As shown in
This barrier film 5 is formed on the inner surfaces of the sides and the bottom of the trench 2. Here, the barrier film 5 is formed between the interlayer insulating film 1 and the conductor 6 on the bottom and between catalyst films 3 and the interlayer insulating film 1 on the sides of the trench 2. This is because the carbon nanotubes 4 are not prevented from growing on the catalyst films 3.
The other configurations are the same as those of the wire structure according to the first embodiment.
Next, a manufacturing method of the wire structure according to this embodiment is concretely described with reference to the cross-sectional views showing the steps thereof.
First, a structure as shown in
Next, a barrier film 5, having a predetermined film thickness, is formed on the interlayer insulating film 1 and inside the trench 2 as shown in
Next, a catalyst film 3, having a predetermined film thickness, is formed on the barrier film 5, as shown in
Next, anisotropic etching is carried out on the catalyst film 3. As a result of this, as shown in
Next, carbon nanotubes 4 are grown on the catalyst films 3 as shown in
Next, a conductor (for example, copper) 6 is formed so as to fill in the trench 2 in which the carbon nanotubes 4 are formed as shown in
After that, the portions of the conductor 6 and the barrier film 5 which exist on the interlayer insulating film 1 are removed by carrying out a CMP (Chemical and Mechanical Polishing) process.
As a result of the aforementioned steps, a wire structure as shown in
In the wire structure according to this embodiment, the inside of the trench 2 where the carbon nanotubes 4 have grown is filled in with the conductor 6 as described above.
Accordingly, it becomes possible in the wire structure according to this embodiment to allow a greater amount of current to flow in the wire structure having the same size than in the wire structure according to the first embodiment. This is because the conductor 6 also conveys the current.
Here, the aforementioned effects become greater by adopting copper, having lower resistance than other materials, as the conductor 6.
In addition, even in the case where cracking occurs in the conductor 6 as a result of a migration phenomenon, there are no influences on the carbon nanotubes 4 from this migration phenomenon. In addition, even in the case where cracking occurs on the conductor 6, the carbon nanotubes 4 do not disconnect. Accordingly, even in the case where cracking occurs, for example, in the conductor 6, the wire functions normally.
Here, the catalyst films 3 serve, to a certain extent, to suppress the diffusion of the conductor 6 into the interlayer insulating film 1. Accordingly, it is also possible to omit the barrier film 5 in the case where the catalyst films 3 are formed inside the trench 2.
However, the barrier film 5 is additionally provided as in this embodiment, so that the diffusion of the conductor 6 into the interlayer insulating film 1 can surely be prevented.
As described above, the barrier film 5 is provided for the purpose of preventing the diffusion of the conductor 6 into the interlayer insulating film 1. This diffusion becomes a problem in the case where copper, for example, is adopted as the conductor 6. Accordingly, in the case where a conductor 6 (for example, aluminum or the like), in which the aforementioned diffusion does not become a problem, is adopted, the barrier film 5 can be omitted.
In the following embodiments, a myriad of variations of the wire configuration where the trench 2 is not filled in with a conductor 6 are described. It is of course possible to fill in the trench with a conductor 6 in these variations of the wire structure.
Here, in the case where this conductor 6 does not cause a problem of the aforementioned diffusion, it is not necessary to form a barrier film 5 as described above. In addition, in the case where the aforementioned diffusion of the conductor 6 becomes a problem, only the formation of catalyst films 3 can suppress to a certain extent the diffusion of the conductor 6 into the interlayer insulating film 1. However, the aforementioned diffusion can surely be prevented by providing the barrier film 5 as described above.
It is assumed that the diffusion of the conductor 6 into the interlayer insulating film 1 does not become a problem when the trench 2 is filled in with the conductor 6, for example, in the wire structure (FIGS. 1 to 3) according to the first embodiment. Then, it is sufficient to fill in the trench in the wire structures shown in FIGS. 1 to 3 with the conductor 6 (
Here, in this embodiment, the carbon nanotubes 4 and the conductor 6 become a carrier of electrons (that is, means for conveying a current); therefore, the catalyst films 3 may not have conductivity.
As shown in
The other configurations are the same as those in the wire structure according to the first embodiment.
Next, a manufacturing method of the wire structure according to this embodiment is concretely described with reference to the cross-sectional views showing the steps thereof.
First, a structure as shown in
Next, as shown in
Next, etch back is carried out on the resist 11. As a result of this, as shown in
Next, anisotropic etching is carried out using the remaining resist 11 as a mask. As a result of this, the portions of the catalyst film 3 on the upper surface of the interlayer insulating film 1 are removed. That is, as shown in
Next, carbon nanotubes 4 are grown on the catalyst film 3 in accordance with a thermal CVD method or the like. Here, the carbon nanotubes 4 are grown so as to reach from one surface (one catalyst film 3) to the other surface (the other catalyst film 3) of the trench 2.
Concretely speaking, as shown in
As a result of the aforementioned steps, a wire structure as shown in
As described above, the catalyst film 3 is provided on the entirety of the inner surfaces (the two sides and the bottom) of the trench 2 having a cross section of a rectangular shape in the wire according to this embodiment. Accordingly, the carbon nanotubes 4 can be grown within the trench 2 more densely in the wire structure according to this embodiment than in the wire structure according to the first embodiment.
In addition, as described above, the inside of the trench 2 may be filled in with a conductor 6 (
As shown in
Here,
Thus, a current that flows through one carbon nanotube 4 also flows through another carbon nanotube 4 that makes contact with this carbon nanotube 4 through the contact between these carbon nanotubes 4.
The other configurations are the same as those in the wire structure according to the second embodiment.
Next, a manufacturing method of the wire structure according to this embodiment is concretely described with reference to the cross-sectional views showing the steps thereof.
First, a structure as shown in
Next, as shown in
As described above, the carbon nanotubes 4 that have grown on one side of the trench 2 can be made to not reach the other side by making the time for growing the carbon nanotubes 4 shorter.
Next, as shown in
After that, a CMP process is carried out, so that the portions of the conductor 6 and the barrier film 5 which exist on the interlayer insulating film 1 are removed.
As a result of the aforementioned steps, a wire structure shown in
The wire structure according to this embodiment is configured as described above, and therefore, the same effects as in the wire structure according to the second embodiment can be attained. The wire structure according to this embodiment is effective in that it can still effectively function as the wire even in the case where cracking occurs in the conductor 6 as described in the second embodiment.
That is, it is assumed that a current flows through a wire structure where no cracking initially occurs in the wire as shown in the top view of
Then, in the case where a predetermined amount or more of a current flows through this wire, a migration phenomenon occurs in the conductor 6. Thus, as a result of the occurrence of the migration phenomenon, as shown in
However, the carbon nanotubes 4 are not affected even in the case where the crack 12 occurs in the conductor 6 as shown in
Here, the same description can be applied to the wire structure according to the second embodiment.
As described above, the barrier film 5 can be omitted in the case where the diffusion of the conductor 6 into the interlayer insulating film 1 does not become a problem.
In addition, the catalyst films 3 are formed only on the two sides of the trench 2 in this embodiment. However, the catalyst film 3 may be provided on the two sides and the bottom of the trench 2 as in the wire structure according to the third embodiment.
As shown in
In addition, carbon nanotubes 4 grow on this catalyst film 3 so as to form an inverted U shape. That is, the carbon nanotubes 4 grows on the catalyst film 3 that exists on the bottom of the trench 2 so as to reach a different place on the same catalyst film 3.
Next, a manufacturing method of the wire structure according to this embodiment is concretely described with reference to the cross-sectional views showing the steps thereof.
First, a structure shown in
Next, isotropic etching is carried out using the remaining resist 11 as a mask. As a result of this, the portions of the catalyst film 3 that have been formed on the upper surface of the interlayer insulating film 1 as well as the two sides of the trench 2 are removed. That is, as shown in
Next, carbon nanotubes 4 are grown on the catalyst film 3 in accordance with a thermal CVD method or the like. Here, an electrical field is applied in the direction as shown below during the process in accordance with the thermal CVD method.
That is, as shown in
Next, as shown in
As a result of this, as shown in
Finally, an electrical field is applied in the direction from the top to the bottom of the figure. As a result of this, the carbon nanotubes 4 that have grown in the horizontal direction of the figure start declining in the downward direction of the figure while growing. Then, the carbon nanotubes 4 keep growing in the downward direction of the figure, and these carbon nanotubes 4 reach the catalyst film 3 that exists on the bottom of the trench 2.
As a result of the aforementioned steps, a wire structure as shown in
It is needless to say that the wire structure according to this embodiment naturally has the same effects as in the wire structure according to the first embodiment.
Here, the trench 2 may be filled in with a conductor in a wire structure as shown in
In addition, the configuration where the catalyst film 3 is provided only on the bottom of the trench 2 is described according to this embodiment. However, it is not necessary to limit the wire structure to this, but the wire may be formed by providing the catalyst film 3 on either side of the trench 2.
In recent years, the development of an MRAM (Magnetoresistive Random Access Memory) that is formed inside a semiconductor device has been actively progressive.
As shown in
In addition, a transistor is formed of a drain region D1, a gate electrode G1, and a source region S1 on a semiconductor substrate. In addition, a via v1 for connecting the strap s1 to the drain region D1, and a via (not shown) for connecting the MTJ film f1 to the bit line b1, are provided. Here, the gate electrode G1 includes an insulating film (the black portion in the gate electrode G1).
In an MRAM shown in
In addition, a current in a predetermined direction is made to flow through the bit line b1. Then, an amount of current that is determined in accordance with the direction of the spin of the MTJ film f1 flows through the MTJ film f1. Thus, the current that has flown via the MTJ film f1 flows into the drain region D1 via the strap s1 and the via v1. Then, the connecting/blocking of a current into the source region S1 is controlled (read out) through the operation for turning on/off the gate electrode G1.
It is necessary to make a current of about mA order flow through a bit line b1 and a digit line d1 that form an MRAM for carrying out such an operation. However, further miniaturization of semiconductor devices has progressed in recent years. Accordingly, the wires have naturally been miniaturized (downsized).
It is necessary to increase the current density of a current that flows through such wires as those that have been downsized as described above in order to maintain the same amount of current (current of about mA order) as before. However, in the case where a conventional wire such as a copper wire is adopted, a migration phenomenon or fusion cutting occurs in the wire as described above.
However, any of the wire structures according to the present invention can be adopted for a bit line b1 or a digit line d1, so that a current having a higher current density (109 A/cm2 or more) can be made to flow through each wire (wires that include at least carbon nanotubes 4) according to the present invention. That is, even in the case where the miniaturization of the structure, for example, has progressed, the amount of the current that flows through the wires can be maintained and a problem of wire defects such as disconnection does not occur.
In addition, the wire structure according to the third embodiment (the structure where the catalyst film 3 is provided on the two sides and the bottom of the trench 2) is adopted in a bit line b1 and a digit line d1, and furthermore, a magnetic material is adopted for the catalyst film 3, so that the effects shown below can be attained.
That is, a wire (which is referred to as wire P) where the two sides and the bottom of the trench 2 are covered with a catalyst film 3 that is a magnetic material is formed. As a result of this, as shown in
Furthermore, the intensity of the magnetic field that occurs from the upper surface of the wire can be increased to about two times higher than that of the magnetic field that occurs from a wire (which is referred to as wire X) of which the surroundings are not covered with a catalyst film 3 that is a magnetic material. In other words, only half of the amount of current that flows through a wire X is required to flow through a wire P in order for the same intensity of magnetic fields to occur in the surroundings of the wires.
Here, the aforementioned shield effect and the effect of increasing the magnetic field which are attained by covering a copper wire with a ferromagnetic material are reported in, for example, “A 1-Mbit MRAM Based on 1T1MTJ Bit Cell Integrated with Copper Interconnects” (IEEE JOURNAL OF SOLID-STATE CIRCUIT, Vol. 38, No. 5, May 2003) and the like.
Accordingly, the structure of a wire P is adopted for a digit line d1 and an MTJ film f1 is provided so as to face the surface of this digit line d1 that is not covered with the catalyst film 3 as shown in the cross-sectional view of
As a result of this, other MTJ films (not shown) which are adjacent to the MTJ film f1 that is shown can be prevented from being subject to the influences of the magnetic field that occurs from the digit line d1 that is shown.
Furthermore, a stronger magnetic field is applied to the MTJ film f1 that is shown with the same amount of current than in a case where a wire X is adopted for the digit line d1. In other words, only half the amount of current that flows through the digit line d1 for which a wire X is adopted and can be made to flow through the digit line d1 for which a wire P is adopted in order to apply magnetic fields of the same intensity to MTJ film f1.
Here, a case where a wire P is adopted for a digit line d1 is described above. However, the same argument can naturally be made in a case where a wire P is adopted for a bit line b1. Here, the catalyst film is formed on the walls on the two sides and the top in the bit line b1.
In addition, the aforementioned effects are increased by adopting a ferromagnetic material such as cobalt, nickel, or iron as the catalyst film 3.
In addition, a case where a wire structure shown in
In addition, a wire that is fabricated in accordance with the following manufacturing method may be adopted for a digit line d1 or the like.
First, a structure shown in
Next, as shown in
Next, a resist 11 is applied to the barrier film 5 so as to fill in the trench 2. After that, etch back is carried out, so that the resist 11 remains only on the bottom of trench 2 as shown in
Next, the resist 11 is utilized as a mask and isotropic etching is carried out on the barrier film 5. As a result of this, the barrier film 5 is partially removed. Then, as shown in
Next, the barrier film 5 is utilized as a mask, and anisotropic etching is carried out on the catalyst film 3. As a result of this, the portions of the catalyst film 3 on the upper surface of the interlayer insulating film 1 are removed. Then, as shown in
After that, as shown in
Here, a barrier film (a growth suppressing film having the function of suppressing the growth of the carbon nanotubes 4 on the catalyst film 3) is formed on the catalyst film 3 that is formed on the bottom of the trench 2.
Accordingly, the growth of the carbon nanotubes 4 on the bottom of the trench 2 can be suppressed. As a result of this, the carbon nanotubes 4 can be easily grown between the two sides of the trench 2 since the growth on the bottom is suppressed.
A wire structure as shown in
In addition, a wire structure (
In the following, another method for manufacturing a wire that at least includes carbon nanotubes is described.
First, a structure shown in
Next, as shown in
Here, the time for sputtering is set so that the sputtering can be stopped at a stage where the catalyst films 3 starts growing. As a result of this, a number of catalyst films 3 in island form can be formed.
In addition, heat treatment may be carried out after the formation of a thin catalyst film 3 on the barrier film 5. As a result of this, the catalyst film 3 aggregates, so that a number of catalyst films 3 in island form are formed.
Next, some catalyst films 3 are removed in accordance with an etch back method or the like using a resist. As a result of this, as shown in
Next, as shown in
After that, as shown in
A wire structure according to the present invention can be fabricated also in accordance with the aforementioned method. Thus, a current having a large current density can flow also in the case of a wire structure shown in
Here, in some cases, it is more preferable for the catalyst film 3 (impurities) such as iron not to remain on the sides and the bottom of the trench 2 after the formation of the carbon nanotubes. This is because impurity particles such as remaining iron partially pass through the interlayer insulating film 1 so as to provide a junction to the wafer substrate, causing the occurrence of a junction leak.
Therefore, catalyst films 3 are formed in an island form and carbon nanotubes 4 are grown in a state where these catalyst films 3 are attached to the tip ends of the carbon nanotubes 4 (carbon nanotubes 4 are grown, for example, in accordance with a plasma CVD method) as in a manufacturing method according to this embodiment.
As a result of this, the catalyst films 3 can be prevented from being attached to a side or the like of the trench in the completed wire structure. Accordingly, there is no possibility of a junction leak as described above.
A manufacturing method according to this embodiment is a modification of the manufacturing method according to the seventh embodiment.
Here, in the seventh embodiment, a case is described where catalyst films 3 in island form are formed on the two inner sides and the bottom of the trench 2 (FIGS. 40 to 43).
In accordance with the manufacturing method according to this embodiment, however, catalyst films 3 in island form are formed only on one inner surface (for example, on the bottom) of the trench 2, and after that, carbon nanotubes 4 are grown.
First, a structure as shown in
Next, as shown in
Next, as shown in
Next, a conductor 6 such as copper is deposited on the barrier film 5 in such a manner as to fill in the trench 2.
Next, a CMP process is carried out on a structure as that shown in
Here, catalyst films 3 in island form may be provided on any inner surface of the trench 2. In the case where the catalyst films 3 are provided only on the bottom of the trench 2 as described above and a process is carried out in accordance with the aforementioned manufacturing method, however, the catalyst films 3 can be completely removed from the wire structure.
It is assumed that an electrical field is applied when the carbon nanotubes 4 are grown. Then, the carbon nanotubes 4 grow in the direction of this electrical field.
Accordingly, in the case where the carbon nanotubes 4 are grown in the direction from the bottom to the top of the trench 2 in accordance with this embodiment, the carbon nanotubes 4 may be grown while applying an electrical field in such a direction.
In addition, in the case where an electrical field is applied, it is preferable for the applied electrical field to have a component in the direction in which the wire is provided (the trench 2 is formed). In
This is because the carbon nanotubes 4 grow in the direction having the aforementioned component in which the trench 2 extends by applying an electrical field having a component in such direction. Thus, a wire having carbon nanotubes 4 that have grown in such direction is smaller in the average electrical resistance than a wire having carbon nanotubes 4 that have grown without having the aforementioned component in the direction in which the trench 2 extends.
A manufacturing method according to a ninth embodiment has a feature in that an electrical field is applied in a predetermined direction when carbon nanotubes 4 are grown.
As described above, in the case where an electrical field is applied when carbon nanotubes 4 are grown, the carbon nanotubes 4 grow in the direction of this electrical field. Then characteristics are utilized in the manufacturing method according to this embodiment.
In the case where carbon nanotubes 4 are grown without an application of an electrical field, the carbon nanotubes 4 are usually formed in different directions as shown in
However, there is a possibility that some carbon nanotubes 4z that grow in the direction perpendicular to the direction in which the wire is provided (in the direction in which the trench 2 extends) exist from among a great number of carbon nanotubes 4. That is, the carbon nanotubes 4z are formed in the direction of the normal of the sides of the trench 2.
Thus, in the case where the carbon nanotubes 4z that are formed in the aforementioned direction are included, the resistance of the entire wire becomes high in comparison with the resistance of the entire wire which has no carbon nanotubes 4z. This occurs because of the following reasons.
It is assumed that carbon nanotubes 4z grow in the direction perpendicular to the direction in which the trench 2 extends and these carbon nanotubes 4 link between the catalyst film 3 that exists on the two sides of the trench 2. Then, no difference in the potential occurs between one end and the other end of the carbon nanotubes 4z even when a voltage is applied in the direction of the wire (in the direction in which the trench 2 extends).
This means that there is no flow of current through the carbon nanotubes 4z. Accordingly, the more carbon nanotubes 4z are included, the higher the resistance of the entire wire having the same density of the carbon nanotubes becomes.
Therefore, as shown in
Then, as shown in
Accordingly, the resistance of the entire wire that is fabricated in accordance with the method according to this embodiment can further be reduced in comparison with a wire that includes carbon nanotubes 4z which are formed in the aforementioned direction.
Here, the greater the inclination of the carbon nanotubes 4 from the direction of the normal of the sides of the trench 2 becomes, the greater the difference in the potential between one end and the other end of these carbon nanotubes 4 becomes in the case where a voltage is applied in the direction in which the trench 2 extends.
Accordingly, a current more easily flows through the carbon nanotubes 4 in the aforementioned case. That is to say, the greater the inclination of the carbon nanotubes 4 from the direction of the normal of the sides of the trench 2 becomes, the further the resistance value of the entire wire can be reduced.
The aforementioned wire structures according to the present invention have a feature in that carbon nanotubes 4 are at least included in the wire. Accordingly, any wire structure that includes carbon nanotubes 4 other than those in the aforementioned embodiments may be possible.
A wire structure shown in
That is, as shown in
In addition, in the case where a wire structure according to the present invention is applied to a semiconductor device, a problem of an increase in the current density in the wires together with the miniaturization of the semiconductor device can be solved as described above.
As shown in
In addition, a plurality of partitioning conductive films 50 are formed inside the trench 2 in the wire structure according to this embodiment (
Here, as shown in
In addition, these partitioning conductive films 50 at least include a catalyst metal that becomes the core of the growth of the carbon nanotubes 4 as a component. The partitioning conductive films 50 themselves may naturally be made of such a catalyst (film). The partitioning conductive films 50 which are catalyst films may be, for example, made of cobalt (Co), iron (Fe), nickel (Ni), tungsten (W) or a compound that includes these.
Furthermore, as shown in
Here, the number of carbon nanotubes 4 that exist between these partitioning conductive films 50 is great. In addition, as shown in
Here, in the case where carbon nanotubes 4 are used as a wire according to the present invention, it is desirable for the carbon nanotubes 4 to be formed as multiple wall carbon nanotubes. This is because multiple wall carbon nanotubes are higher in conductivity than single layer carbon nanotubes.
In
As described above, the carbon nanotubes 4 form a current path in this embodiment (that is, in a wire structure having carbon nanotubes 4 that have grown in the direction in which the trench 2 extends between the partitioning conductive films 50 that are formed inside the trench 2).
Accordingly, the same effects as those described, for example, in the first embodiment can be attained in the wire structure according to this embodiment. That is, effects such as reduction in the resistance of the wire, an increase in the current density, restriction of fusion cutting of the wire and suppression of the occurrence of a migration can be attained as described above because of the characteristics of the carbon nanotubes 4.
In addition, it is assumed that the partitioning conductive films 50 are formed of catalyst films that become the core of the growth of carbon nanotubes 4. In this case, the carbon nanotubes 4 can be easily grown only by providing these partitioning conductive films 50.
In addition, the partitioning conductive films 50 are formed at equal intervals inside the trench 2. Accordingly, the time for the carbon nanotubes 4 to reach the adjacent partitioning conductive films 50 from the start of the growth is approximately the same in each space between the partitioning conductive films 50. That is, the control of the formation of these carbon nanotubes 4 between the partitioning conductive films 50 becomes easier.
Here, in the wire structure according to this embodiment, copper is not used; therefore, a barrier film having the function of preventing the diffusion of copper is not provided. Accordingly, a current having a greater current density can be made to flow and carbon nanotubes 4, which have a low resistance, can be formed densely within the entire volume of the trench 2. That is, approximately the entire volume in the trench 2 can be utilized as a current path by the carbon nanotubes 4. Namely, an increase in the limited amount of the current that flows through the wire and reduction in the resistance of the wire having such a structure can be achieved.
As shown in
In the wire structure according to this embodiment, as shown in
The other configurations are the same as those in the tenth embodiment; therefore, the descriptions thereof are herein omitted.
As described above, the first barrier film 51 is formed in the wire structure according to this embodiment. Accordingly, the diffusion of a catalyst (for example, cobalt, nickel, iron, or the like) from the partitioning conductive film 50 to the interlayer insulating film 1 can be suppressed (prevented).
As shown in
In addition, as shown in
The other configurations are the same as those in the tenth embodiment; therefore, the descriptions thereof are herein omitted.
As described above, the copper wires 52 are provided partially in the wire structure according to this embodiment. Accordingly, in the case where wires are provided above and beneath the interlayer insulating film 1 so as to sandwich the interlayer insulating film 1, a copper wire 52 can be made to function as a pad for a via. That is, a copper wire 52 is connected to another wire through a via. Here, it is very difficult, in the view of the manufacturing process, for a first section where carbon nanotubes 4 are formed to be made to function as a pad portion for a via.
Here, in the present invention, the term “copper wire” is used for the purpose of convenience in both cases where it functions only as a wire, and where it functions as a wire and a pad (that is, in a case where it functions as a means for conveying electricity).
Here, such a via may be formed of carbon nanotubes 4 as shown in
In addition, a second barrier film 53 is formed in the wire structure according to this embodiment. Accordingly, the diffusion of copper from a copper wire 52 to the interlayer insulating film 1 can be suppressed (prevented).
Here, in this embodiment, as shown in
In accordance with a thirteenth embodiment, a manufacturing method of the wire structure according to the eleventh embodiment is described. Here, the wire structure according to the tenth embodiment can be formed in accordance with the method of this embodiment in the case where the step of forming the first barrier film 51 is omitted.
As shown in
Here, silicon nitride, tantalum nitride, or the like can be adopted as this first barrier film 51. In addition, this first barrier film 51 can be formed in accordance with, for example, a CVD (Chemical Vapor Deposition) method or a sputtering method. In addition, the first barrier film 51 is a film used for suppressing (preventing) the diffusion of a catalyst into the interlayer insulating film 1 as described above.
Next, a plurality of partitioning conductive films 50 are formed of catalyst films so as to partition this trench 2 along the direction in which the trench 2 extends. A method for the formation of this is described below in detail.
First, as shown in
Here, only one base block 55 is formed in
In addition, concretely speaking, this base block 55 can be formed in the following process.
First, a film of polysilicon or the like is formed on the interlayer insulating film 1 so as to cover the trench 2. After that, the portions of the polysilicon other than those in the trench 2 are removed by means of CMP (Chemical and Mechanical Polishing). Next, a process using photolithographic technology and an etching process is carried out. As a result of this, the polysilicon inside the trench 2 is selectively removed. Thus, base blocks including the base block 55 remain at predetermined intervals, for example, inside this trench 2.
Here, after the completion of the formation of this base block 55, as shown in
In addition, cobalt, iron, nickel, tungsten, or a compound that includes these can be adopted as this catalyst film 56. In the case where cobalt or the like is adopted as the catalyst film 56, the following method for forming the catalyst film 56 can be adopted in this embodiment (that is, the base block 55 is made of polysilicon).
A sputtering process is carried out on the base block 55 made of polysilicon. As a result of this, cobalt, iron, nickel, or the like is formed on the base block 55. After that, heat treatment is carried out on this base block 55. At this time, the metal on the polysilicon reacts with the silicon so as to form a silicide. Accordingly, the metal (silicide) can be easily left on the polysilicon by means of a wet process. As a result of this, the catalyst film 56, which is a silicide film, can be formed on the base block 55.
In addition, a method for selectively depositing a metal on a silicon surface by means of plating, for example, is described in a document (Conference of Seven Chemistry Related Societies in Tohoku Region, “Electrolytic Deposition of Metal on Porous Silicon” by Norio Yasui et. al., October 2002). Here, silicon is once converted to porous silicon having microscopic pores. Then, a metal such as Cu, Co, Cr, Mn, Fe, Ni, Zn, Ag, Cd, Tl, Pb, or the like is attached to the silicon. Such polysilicon to which a metal is attached may be adopted as it is in this embodiment.
Next, the portion of the catalyst film 56 which is formed on the upper surface of this base block 55 is removed in order to expose the upper surface of the base block 55.
Here, as can be seen from
Next, the base block 55 is removed from the exposed portion (upper surface portion). As a result of this, as shown in
As well known, there is a great difference in the etching rate between polysilicon and a silicide, such as a cobalt silicide. Accordingly, an etching process is carried out on the aforementioned base block 55 under predetermined conditions. As a result of this, only partitioning conductive films 50, which are catalyst films 53, can be left within the trench 2.
Here, it can be seen from the above description that an arbitrary material can be selected for the base block 55 as long as it can be etched more easily than the catalyst films 56 under predetermined etching conditions.
Here, in the case where a material that does not include a catalyst as a component, is adopted as the conductive film 56 in the step shown in
As a result of this, the configuration shown in
In addition, additional catalysts may be formed on the partitioning conductive films 50 shown in
Finally, carbon nanotubes 4 are grown so as to connect the partitioning conductive films 50. At this time, the carbon nanotubes 4 grow on the base of the catalyst. Alternatively, the carbon nanotubes 4 grow in a state where the catalyst is attached to the tip ends of the carbon nanotubes. Here, if the carbon nanotubes 4 are grown in a state where an electrical field is applied, the direction in which these carbon nanotubes 4 grow can be controlled in a predetermined direction (direction of this electrical field) (for example, Japanese Patent Application Laid-Open No. 2002-329723).
The manufacturing method according to this embodiment is adopted as described above, so that the wire structure (
In addition, the following method is adopted at the time of the formation of the partitioning conductive films 50 in this embodiment. That is, the base block 55 is formed inside the trench 2 and the catalyst film 56 of the carbon nanotubes is formed on the surfaces of this base block 55. After that, the upper surface of the base block 55 is exposed and the base block 55 is selectively removed from this exposed portion. As a result of these sequential steps, the partitioning conductive films 50 are formed inside the trench 2.
Accordingly, the partitioning conductive films 50 which are spaced at predetermined intervals can be easily fabricated inside the trench 2.
In addition, the base block 55 is etched more easily than the catalyst films 56 under predetermined etching conditions. Accordingly, the base block 55 is etched under these predetermined conditions, so that the base block 55 can be removed from the aforementioned exposed portion. That is, only the catalyst films 56 that become partitioning conductive films 50 can be left in the trench 2.
In addition, in this embodiment, the step of forming a first barrier film 51 inside the trench 2 is additionally provided before the formation of the partitioning conductive films 50. Accordingly, the diffusion of the catalyst from the partitioning conductive films 50 into the interlayer insulating film 1 can be suppressed or prevented due to the function of this first barrier film 51.
Here, a material made of a catalyst of carbon nanotubes 4 may be adopted as the base block 55. Thus, a predetermined portion of the base block 55 is selectively removed, so that partitioning conductive films 50 are formed inside the trench 2.
By doing this, the formation of the catalyst film 56 on the base block 55, and the selective removal process of the catalyst film 56 from the upper surface of the base block 55, which are described above, can be omitted.
In a fourteenth embodiment, a manufacturing method of the wire structure according to the twelfth embodiment is described.
First, a structure as shown in
Next, in a trench 2, carbon nanotubes 4 are grown in first sections which is divided by partitioning conductive films 50 and a copper wire 52 is formed in second sections which is divided by partitioning conductive films 50 (
Before the formation of the copper wires 52, second barrier films 53 are formed inside the trenches 2 in the aforementioned second sections. Here, the second barrier films 53 are films used for suppressing (preventing) the diffusion of copper into the interlayer insulating film 1. TiN, Ta, TaN, or the like can be adopted as the second barrier films 53.
In order to form the second barrier films 53 in the aforementioned second sections, initially, a second barrier film 53 is formed on the interlayer insulating film 1 so as to cover the trenches 2 and the base block 55 of a structure as shown in
Next, this second barrier film 53 is selectively removed so that the second barrier films 53 remain only on the bottoms and the sides within the trenches 2 in the second sections.
Here, a CMP process that is carried out on the upper surface of a structure as shown in
Next, as shown in
Next, in
Next, as shown in
If a metal catalyst 61 is formed also on the upper surfaces of the partitioning conductive films 50, the portions of the metal catalyst 61 on these upper surfaces can be removed by means of a CMP process, anisotropic dry etching, or the like.
In addition, it is assumed that a film that includes a metal catalyst of carbon nanotubes 4 such as cobalt, iron, or nickel is adopted as the second barrier film 53 at the stage of the formation of the second barrier film 53. In such a case, the aforementioned step of selectively forming the metal catalyst 61 can be omitted.
Finally, carbon nanotubes 4 are grown so as to connect the partitioning conductive films 50 in the first sections. At this time, the carbon nanotubes 4 are grown on the base of the catalyst. Alternatively, the carbon nanotubes 4 grow in a state where the catalyst is attached to the tip ends of the carbon nanotubes. Here, if carbon nanotubes 4 are grown in a state where an electrical field is applied, the direction in which these carbon nanotubes 4 grow can be controlled in a predetermined direction (direction of this electrical field).
As described above, the manufacturing method according to this embodiment is adopted, so that the wire structure (
In this embodiment, the step of forming second barrier films 53 inside the trenches 2 in the second sections is further provided before the formation of copper wires 52. Accordingly, the diffusion of copper from a copper wire 52 to the interlayer insulating film 1 can be suppressed or prevented by the function of these second barrier films 53.
Each of the aforementioned wire structures can be applied to a general semiconductor product where the wire width is 50 nm or less, so that the desired effects thereof can be attained. In addition, in the case where a current of which the current density exceeds 105 A/cm2 flows through a wire for a long time, the desired effects thereof can be attained.
While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-308390 | Oct 2004 | JP | national |
| 2005-247860 | Aug 2005 | JP | national |
