Patent Application
20160336388
The present application claims priority from Japanese Patent application serial no. 2015-099814, filed on May 15, 2015, the content of which is hereby incorporated by reference into this application.
1. Field of the Invention
The present invention relates to a method for producing a semiconductor device, in particular, a method for forming a Ti/TiN stacked film.
2. Description of Related Art
In a semiconductor device in which aluminum (expressed as Al hereinafter) interconnections are used, its Al film may be deteriorated in morphology (surface smoothness), so that at the time of dry-etching the Al film, there may be generated residues of a titanium (expressed as Ti hereinafter)/titanium nitride (expressed as TiN hereinafter) stacked film, which is an underlying film (barrier metal film). The generation may cause, for example, a short circuit between the interconnections.
For an Al interconnection, a stacked structure is generally used which has, from the lowermost position of the structure, a barrier metal film (Ti/TiN stacked film), an Al film, and a cap metal film (Ti/TiN stacked film) in turn. It is known that the crystal orientation of the barrier metal layer affects the morphology of the Al film, which is formed on the barrier metal layer.
As a background technique in the present technical field, a technique as described in Patent Literature 1 listed below is known. Patent Literature 1 discloses a technique of orienting the crystal orientation of a Ti film and that of a TiN film, these films being configured as a barrier metal film used as an underlying film below an Al interconnection, to (002) and (111), respectively, thereby intensifying the (111) orientation of the Al film to improve the morphology of the Al film.
Patent Literature 2 also discloses that in order to make individual crystal orientations of a barrier metal consistent with each other, it is effective to perform the so-called shutter deposition before Ti is formed, or deposited into a film.
Furthermore, Patent Literature 3 discloses that in order to control the crystal orientation of a barrier metal, it is effective to form a homogeneous TiO2 film between a Ti film and an interlayer film.
In the case of forming a stacked film of a Ti film and a TiN film which are configured as a barrier metal film by a sputtering method, the Ti film and the TiN film are formed in the same processing chamber; thus, after the formation of the TiN film, the front surface of the Ti target has been nitrided. Accordingly, when the next wafer is processed, the front surface of the nitrided target is sputtered at an initial stage of the formation of the Ti film. Consequently, nitrogen is contained in the film of barrier metal Ti that is formed on the wafer.
As described in Patent Literature 1, when, about the barrier metal film, the crystal orientation of Ti is directed to (002) and that of TiN is directed to (111), the crystal orientation of the Al film formed thereon becomes (111), so that this film is made good in morphology. It is also known that when the crystal orientation of the Al film becomes (111), the interconnection is also improved in reliability.
However, when nitrogen is contained in the Ti film, which is the lowest film, individual crystal orientations of the Ti film are not uniformly made consistent with each other into the (002) direction. Thus, the Al interconnection is deteriorated in morphology, and the interconnection is lowered in reliability.
In order to cause nitrogen not to be contained in a film of Ti, which is a barrier metal, for example, it is advisable to form a TiN film, and subsequently remove a nitrided film on the outermost layer of the target, as disclosed in Patent Literature 2. Specifically, a wafer-simulated plate, which is called a shutter disk, is carried onto a stage to cover the stage therewith, and further sputtering with argon (expressed as Ar hereinafter) gas is applied to the workpiece. According to this method, however, it is necessary to carry the shutter onto the stage whenever a single water is processed. Thus, the productivity of semiconductor devices to be produced is remarkably deteriorated.
An object of the present invention is to improve a semiconductor device in reliability. Another object thereof is to improve a semiconductor device in productivity. Other objects and novel features will be made evident from the description of the present specification and attached drawings.
According to an aspect of the present invention, in the formation of a Ti/TiN stacked film, about a mixed gas of Ar gas and nitrogen (hereinafter expressed as N2) gas that is used at the time of forming a TiN film by a sputtering method, the supply of the N2 gas is turned off (i.e., is stopped) before that of the Ar gas.
According to the aspect of the present invention, a semiconductor device is improved in reliability, and further the semiconductor device is improved in productivity.
Hereinafter, with reference to the drawings, examples of the present invention will be described. The same reference sings are attached to the same structures or members, respectively, in the individual drawings. About the same structures or members, any overlapped detailed description thereon is omitted.
An Al interconnection of a semiconductor device is generally formed through steps as described below.
A sputtering machine is initially used to form a stacked film having, from the lowermost position thereof, a Ti film, a TiN film, an Al film, a Ti film, and a TiN film in turn. Films (underlying films) below the Al film, that is, the Ti film and the TiN film of lower layers are called a barrier metal film. Films above the Al film, that is, the Ti film and the TiN film of upper layers are called a cap metal film. The Al film may be a pure Al film. However, the Al film is usually an Al film to which a different metal material, such as copper (expressed as Cu hereinafter) or silicon (expressed as Si hereinafter), is added in a trace amount to prevent electro-migration. An Al—Cu film, in which Cu is added to Al, is most frequently used.
These metal films are each formed by a sputtering method. In order that the films of the above-mentioned stacked film structure are stacked onto each other without being exposed to the atmosphere, a multi-chamber type film-depositing machine is usually used in which a wafer can be carried in a vacuum.
As illustrated in
The three chambers are composed of a barrier-metal-film-forming sputtering chamber (sputtering-chamber-A 24) for forming the Ti/TiN stacked film which is a barrier metal film, an Al-film-forming sputtering chamber (sputtering-chamber-B 25) for forming an Al film, and a cap-metal-film-forming sputtering chamber (sputtering-chamber-C 26) for forming a Ti/TiN film which is a cap metal film.
In each of the barrier-metal-film-forming chamber and the cap-metal-film-forming chamber, a Ti target is used as a raw material (target material).
In each Ti-film-forming step, Ar gas is supplied into the sputtering chamber, and a high frequency (RF) bias or a direct current (DC) bias is applied to the Ti target to make the Ar gas into plasma. By the Ar plasma, the Ti target is sputtered to form a Ti film over a wafer.
In each TiN-film-forming step, a mixed gas of Ar gas and N2 gas is supplied into the sputtering chamber, and a high frequency (RF) bias or a direct current (DC) bias is applied to the Ti target to make the Ar/N2 mixed gas into plasma. By the Ar/N2 plasma, the Ti target is sputtered to form a TiN film over the wafer.
Next, a bottom-anti-reflective-layer (BARL) is formed on the useful-for-Al-interconnection metal film (stacked film), which is formed as described above.
Subsequently, a photoresist is applied onto the bottom-anti-reflective-layer, and the resultant is exposed to light into a predetermined pattern by lithography.
Lastly, the workpiece is dry-etched to remove unnecessary portions of the useful-for-Al-interconnection metal film (stacked film) to form Al interconnections.
As a first comparatively investigating example,
As described above, at the time of TiN-film-formation, N2 gas is supplied, together with Ar gas, into the chamber; thus, a TiN layer 4 is formed on the outermost surface of the Ti target, which is a target 3. Since the TiN layer 4 has been formed on the outermost surface of the Ti target 3, the nitrided target surface is sputtered at an initial stage of Ti-film-formation when the next wafer is processed. Consequently, a Ti film 6 containing nitrogen is formed on this wafer, which is a wafer 5. As a result, individual crystal orientations of a Ti film 7 are not uniformly made consistent with each other to (002) orientation so that a TiN film 8 and an Al film (not illustrated) to be subsequently formed are not uniform in crystal orientation, either.
As a second comparatively investigating example,
For this reason, when the next wafer is processed, pure Ti is sputtered from an initial stage of Ti-film-formation. Thus, a Ti film containing nitrogen is not formed onto the wafer, which is a wafer 5. As a result, a Ti film 7 in which individual crystal orientations are uniformly made consistent with each other to (002) orientation can be formed on the wafer 5. Thus, individual crystal orientations of a TiN film 8 formed on this Ti film 7 can also be uniformly made consistent with each other to (111) orientation. Furthermore, individual crystal orientations of an Al film (not illustrated) formed on this TiN film 8 can also be uniformly made consistent with each other to (111) orientation. However, as described above, this method requires the step of performing the shutter deposition, so that the sputtering machine is deteriorated in producing performance.
Referring to
As illustrated in
A barrier metal film 14 is formed over the barrier metal film 10 and the electroconductive film 11. This barrier metal film 14 is constituted by a stacked film of a titanium film (Ti film) 12 and a titanium nitride film (TiN film) 13. About the respective film thicknesses of these films, the film thickness of the Ti film 12 is from about 10 to 30 nm, and that of the TiN film 13 is from about 15 to 50 nm.
The aluminum film (Al film) 15 is formed on the barrier metal film 14, and has a film thickness of about 150 to 390 nm. The Al film 15 is a film that becomes the main body of the useful-for-Al-interconnection metal film, and may be a film containing an additive such as Cu. In other words, the Al film 15 may be an Al—Cu film containing Al as a main component.
A cap metal film 18 is formed on the Al film 15. This cap metal film 18 is a stacked film of a titanium film (Ti film) 16 and a titanium nitride (TiN film) 17. About the respective film thicknesses of these films, the film thickness of the Ti film 16 is from about 5 to 15 nm, and that of the TiN film 17 is from about 20 to 100 nm.
A bottom-anti-reflective-layer 19 which is, for example, a silicon oxynitride film is formed on the cap metal film 18, and has a film thickness of, for example, about 20 to 50 nm. A between-interconnection insulating film 20 is formed on the bottom-anti-reflective-layer 19 to insulate the Al interconnections electrically from each other. In the present example, a case where the semiconductor device has the bottom-anti-reflective-layer 19 is demonstrated. However, this film is not necessarily required.
No nitrogen-containing layer is formed on the Ti film 12, which partially constitutes the barrier metal film 14, and thus individual crystal orientations of the Ti film 12 are uniformly made consistent with each other to (002) orientation. Moreover, individual crystal orientations of the TiN film 13 on the Ti film 12 are uniformly made consistent with each other to (111) orientation, and further individual crystal orientations of the Al film 15 formed thereon are also uniformly made consistent with each other to (111) orientation.
In the present example, the useful-for-Al-interconnection metal film (stacked film) is formed, using a sputtering machine as illustrated in
Initially, through a loader 22 of the sputtering machine, which is a machine 21, a wafer is carried into a vacuum carrying chamber 27. Next, through a wafer carrying mechanism (not illustrated) inside the vacuum carrying chamber 27, the wafer is carried into the sputtering-chamber-A 24, and the wafer (represented by reference number 5 in
Subsequently, the sputtering-chamber-A 24 is vacuum-evacuated, and then a sputtering processing shown in Table 1 is started.
In the sputtering processing shown in Table 1, Ar gas is first introduced into the sputtering-chamber-A 24 (step 1 in Table 1).
Next, the application of a direct current (DC) bias to a Ti target is started. In order to prevent a local arc discharge and a breakdown that are caused by an abrupt application of a high electric power, a relatively low electric power (of about 1000 W in this case) is applied for about 3.0 seconds (step 2 in Table 1).
Subsequently, the processing is shifted to a Ti-film-forming step (step 3 in Table 1) to form a Ti film.
Thereafter, the application of the direct current (DC) bias is once stopped, and then while the Ar gas is supplied, the supply of N2 gas is started. The flow rate of the supplied Ar/N2 mixed gas into the sputtering-chamber-A 24 is then made stable (step 4 in Table 1).
Subsequently, in the same way as in step 2, in order to avoid an abrupt application of a high electric power, a relatively low electric power (of about 1000 W in this case) is applied for about 3.0 seconds (step 5 in Table 1).
Subsequently, the processing is shifted to a TiN-film-forming step to form a TiN film (step 6 in Table 1).
Furthermore, the processing is shifted to step 7 in Table 1 to stop the supply the N2 gas while the supply of the Ar gas and the application of the direct current (DC) bias are continued (step 7 in Table 1).
Lastly, the supply of the Ar gas and the application of the direct current (DC) bias are stopped, and the sputtering-chamber-A 24 is vacuum-evacuated to end the processing (step 8 in Table 1).
The supply of the Ar gas and that of the N2 gas are attained, using gas supply lines as illustrated in
Furthermore, a gas exhaust line of the lines is equipped with a gate valve 29, a rough line valve 30, a cryopump 31, and a dry pump 32.
Referring to
As shown in
Thereafter, the supply of the N2 gas is started, and a direct current (DC) bias is applied to start the formation of a TiN film. After a period necessary for the formation of the TiN film into a desired film thickness elapses, the application of the direct current (DC) bias is stopped at the same time when the supply of the Ar gas and that of the N2 are stopped. Thus, the formation of the TiN film is ended.
In the meantime, in the process flow of the present example, its Ti-film-forming step is the same as in the conventional process. However, in its TiN-film-forming step, the supply of N2 gas is stopped before the supply of Ar gas is stopped and the application of a direct current (DC) bias is stopped. A difference in time (N2-off period) between the supply stop of the N2 gas and the respective supply stops of the Ar gas and the application of the direct current (DC) bias is set into the range of, for example, about 0.5 to 3.0 second, as shown in step 7 in Table 1.
However, conditions for removing a TiN layer formed on the outermost layer of the Ti target are determined in accordance with a balance between the direct current (DC) bias (DC power) and the N2-off period. Thus, the N2-off period is not limited into the range of 0.5 to 3.0 seconds, and may be set to an appropriate period while the state of the Ti film (the degree of the nitrogen content in the film) formed on the front surface of the wafer is monitored by a method of measuring the resistance value of the Ti film, or some other method.
By a method as described above, the barrier metal film 14 is formed, and subsequently the wafer is carried into the sputtering-chamber-B 25 in
Subsequently, the wafer is carried into the sputtering-chamber-C 26 in
Thereafter, the bottom-anti-reflective-layer 19 is formed onto the cap metal film 18 by, for example, a CVD method. As described above, the bottom-anti-reflective-layer 19 may be a silicon oxynitride film. In the present example, a case where the bottom-anti-reflective-layer 19 is used is demonstrated. However, this bottom-anti-reflective-layer 19 is not necessarily required. Thus, when an appropriate light exposure is conducted, the bottom-anti-reflective-layer 19 may be omitted.
Subsequently, a resist film is applied onto the bottom-anti-reflective-layer 19, and then the resultant workpiece is exposed to light into a predetermined pattern. Thereafter, the workpiece is subjected to dry-etching treatment to work each of the TiN film 17, the Ti film 16, the Al film 15, the TiN film 13 and the Ti film 12. In this way, interconnections are formed.
As described above, in the step of forming the TiN film, the supply of the N2 gas is turned off (the stop of the supply) before that of the Ar gas is turned off, thereby lowering the N2 partial pressure in the sputtering chamber. In this way, N2 ions and N2 radicals in the sputtering chamber are each lowered in quantity, so that the nitriding of the surface of the target is restrained. Moreover, the nitride layer of the outermost layer of the target is removed by the Ar sputtering.
Accordingly, when a Ti film is formed onto a surface (main surface) of a wafer to be next carried, the target surface is realizing a clean state so that no nitrogen is incorporated into the Ti film.
As described above, according to the method of the present example for forming the Ti/TiN stacked film, individual crystal orientations of the Ti film, which partially constitutes the useful-for-Al-interconnection barrier metal film, can be uniformly made consistent with each other to (002). As a result, individual crystal orientations of the TiN film formed thereon can be uniformly made consistent with each other to (111). Individual crystal orientations of the Al film further formed thereon can also be uniformly made consistent with each other to (111). In this way, the Al film is improved in morphology (surface smoothness). In other words, the semiconductor device according to the present invention example can be improved in reliability.
Differently from the second comparatively investigating example described with reference to
The use of the present example makes it possible to prevent a short circuit between such interconnections. Specifically, the example is particularly useful for a case where a space between interconnections of a semiconductor device is made narrow to have a space width of less than 0.16 μm by making the semiconductor device fine. Thus, a short circuit between the interconnections can be prevented.
Accordingly, the use of the method of the present example for forming a Ti/TiN stacked film makes it possible to improve an Al film of the example in morphology to improve Al interconnections thereof in reliability and improve the production yield of such stacked films.
Referring to
The semiconductor device illustrated in
For the semiconductor device of the present example, as shown in Table 1 and
Also in the formation of the TiN film 17, which partially constitutes the cap metal 18, the TiN film 17 may be formed by the method shown in Table 1 and
The above has described the invention made by the inventors specifically on the basis of the examples thereof. However, the invention is not limited to the examples. Thus, of course, the examples may each be variously changed as far as the changed example does not depart from the subject matter of the invention. When at least one of the plural interconnection layers is, for example, an Al interconnection layer, the method of Example 1 is usable for the Al interconnection. When the plural interconnection layers are Cu interconnections formed through the damascene process, the method of Example 1 is usable for an Al interconnection functioning as a pad electrode of the topmost layer. A semiconductor device including such plural interconnection layers is not limited to an SOC, a microcomputer, a flash memory, or any other device similar thereto. Thus, the semiconductor device may be an optical element such as a CMOS image sensor or a photodiode.
1: sputtering chamber, 2: backing plate, 3: Ti target, 4: TiN layer, 5: semiconductor substrate (wafer), 6: Ti film containing nitrogen, 7, 12 and 16: Ti films, 8, 13 and 17: TiN films, 9: insulating film, 10: barrier metal, 11: electroconductive film, 14: barrier metal film, 15: Al film, 18: cap metal film, 19: bottom-anti-reflective-layer, 20: between-interconnection insulating film, 21: sputtering machine, 22: loader, 23: unloader, 24: sputtering-chamber-A, 25: sputtering-chamber-B, 26: sputtering-chamber-C, 27: vacuum carrying chamber, 28: stage, 29: gate valve, 30: rough line valve, 31: cryopump, 32: dry pump, 33, 34, 35 and 36: gas supply valves, 37 and 38: MFCs, 39: high dielectric film, and 40: metal film.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-099814 | May 2015 | JP | national |
