Film forming method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a film forming method for forming a Ti (titanium) film or a W (tungsten) film on the surface of an object to be processed such as a semiconductor wafer.

【0002】

[Conventional technology]

In general, semiconductor devices tend to have a multi-layer wiring structure in response to recent demands for higher density and higher integration. In this case, at the connection between the lower layer device and the upper layer aluminum wiring. Embedded technologies such as a certain contact hole and a via hole that is a connection between the lower layer aluminum wiring and the upper layer aluminum wiring are important for establishing an electrical connection between the two.

【0003】

Sputtered aluminum and CVD tungsten are generally used for embedding contact holes and via holes, but recently, CVD tungsten has tended to be mainly used because of its higher embedding performance. In this case, if the tungsten film is formed directly on the silicon layer or aluminum wiring of the lower layer, the diffusion layer formed in the silicon is destroyed by the attack by fluorine at the boundary portion between them, or the adhesion with the upper layer is deteriorated. Therefore, it is not preferable in the current semiconductor devices that require power saving and high-speed operation. When tungsten is used for embedding, WF is one of the processing gases used in this process.₆ Gas tends to enter the Si substrate side and deteriorate the electrical characteristics and the like, which is also not preferable in this case.

【0004】

Therefore, in order to prevent the above phenomenon, before embedding contact holes, through holes, etc. with tungsten, a barrier metal layer is thinly formed over the entire surface of the wafer including the surface inside the holes, and the holes are embedded from above with tungsten. Is being done. As the material of this barrier layer, Ti / TiN (titanium nitride) is generally used. As such prior art, Japanese Patent Application Laid-Open No. 6-89873 and Japanese Patent Application Laid-Open No. 10-106974 are disclosed, and the applicant also filed a related application in Japanese Patent Application No. 2000-351716.

【0005】

Here, the conventional method of embedding in the embedding hole will be described with reference to FIG. 8. In the figure, reference numeral 2 is a semiconductor wafer as an object to be processed, and 3 is an insulating film for forming a contact hole. A contact hole 4 as an embedded hole is formed on the surface of the wafer 2. Then, in order to achieve electrical conduction with, for example, a diffusion layer at the bottom of the hole, first, in order to achieve ohmic contact as shown in FIG. 8 (A), for example, TiCl.₄ Gas and H₂ The titanium film 6 is thinly formed by P-CVD (Physical Chemical Vapor Deposition) or the like using gas. Next, this wafer W is transferred to another thermal CVD apparatus, and TiCl is shown as shown in FIG. 8 (B).₄ Gas and NH₃ The TiN (titanium nitride) film 8 is thinly formed by thermal CVD using gas. Next, this wafer W is transferred to another thermal CVD apparatus, and WF as shown in Fig. 8 (C).₆ Gas and SiH₄ Gas or H₂ A W (tungsten) film 10 is formed using gas or both gases, and the inside of the contact hole 4 is embedded.

【0006】

[Problems to be Solved by the Invention]

By the way, as shown in FIG. 8C, the WF used when forming the tungsten film 10₆ Since the gas contains F (fluorine), this unreacted fluorine is very active and may form TiFx, which is WF in the temperature range of 400 to 450 ° C, which is the process temperature.₆ In order to prevent the titanium film 6 and the silicon layer below it from being damaged by the fluorine of the gas, it was necessary to form the TiN film 8 sufficiently thick, for example, at least about 200 Å. Therefore, since it is necessary to efficiently form a TiN film having a sufficient film thickness in this way, it is necessary to transfer the wafer from the plasma CVD apparatus on which the Ti film 6 is formed to the thermal CVD apparatus. As a result, a step of forming a TiN film 8 having a sufficient film thickness and a dedicated thermal CVD device for that step are required, which causes a problem that not only the number of steps increases but also the equipment cost increases. The present invention has been devised in order to effectively solve the above problems by paying attention to the above problems. An object of the present invention is to use a tungsten film forming step at a low process temperature, so that it is possible to omit the conventional TiN film forming step by thermal CVD in order to obtain a sufficient film thickness as a barrier layer. The purpose is to provide a suitable film forming method.

【0007】

[Means for solving problems]

By using a tungsten film forming step that can form a film at a relatively low process temperature when forming a tungsten film, the present inventors can make the barrier layer such as a TiN film relatively thin, and the barrier layer can be made relatively thin. The present invention was made based on the finding that the thin barrier layer can be easily formed by continuously performing plasma nitriding treatment after the Ti film forming step in the processing container on which the Ti film is formed. The invention defined in claim 1 is a method of forming a predetermined film on the surface of an object to be treated in a vacuum-pullable processing container, which comprises a titanium film forming step of forming a titanium film on the surface of the object to be processed. The nitriding step of nitriding the surface of the titanium film to form a nitride film, and alternately and intermittently supplying the reducing gas and the tungsten-containing gas to the surface of the object to be treated once or a plurality of times. It is a film forming method characterized by having a tungsten film forming step of forming a tungsten film at a relatively low temperature.

【0008】

As described above, by using the tungsten film forming step at a low process temperature, it is possible to omit the conventional TiN film forming step by thermal CVD in order to obtain a sufficient film thickness as the barrier layer. .. Therefore, it is possible to reduce the number of steps for embedding an embedded hole such as a through hole or a contact hole to improve the efficiency.

【0009】

In this case, for example, as defined in claim 2, after the tungsten film forming step, the reducing gas and the tungsten-containing gas are simultaneously supplied to form the second tungsten film at a process temperature higher than that of the tungsten film forming step. The second tungsten film forming step to be formed is performed. According to this, the film formation speed becomes faster due to the higher process temperature, and the process for forming the tungsten film can be efficiently performed.

【0010】

Further, for example, as defined in claim 3, in the titanium film forming step, TiCl is used as the raw material gas.₄ Gas is used and H is used as the reducing gas.₂ Gas is used. Further, for example, as defined in claim 4, in the nitriding step, NH is used as the reducing gas.₃ Gas or N₂ Gas is used and the treatment is performed in the presence of plasma. Further, for example, as defined in claim 5, SiH is used as a reducing gas in the tungsten film forming step at a relatively low temperature.₄ A gas is used, and in the second tungsten film forming step, H is used as the reducing gas.₂ Gas is used.

【0011】

Further, for example, as defined in claim 6, the lower limit of the thickness of the nitride film formed by the nitriding treatment is about 50 Å. Further, for example, as defined in claim 7, the process temperature of the relatively low temperature tungsten film forming step is in the range of about 250 to 350 ° C, and the process temperature of the second tungsten film forming step is 400. It is within the range of ~ 450 ° C. Further, for example, as defined in claim 8, plasma is used in the titanium forming step and the nitriding step, and thermal CVD is used in the tungsten film forming step.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the film forming method according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing a cluster tool apparatus for carrying out the method of the present invention, FIG. 2 is a process diagram showing a film forming process, FIG. 3 is a flowchart showing a film forming process, and FIG. 4 is a tungsten film forming process. It is a figure which shows the supply state of the gas in. As shown in FIG. 1, the cluster tool device 14 is a film forming plasma device 16 that continuously performs a titanium film forming process and a nitriding process on the surface of a semiconductor wafer 2 as an object to be processed, followed by a tungsten film forming process. It has a film forming device 18 that performs processing by thermal CVD, and both devices 16 and 18 enter a transfer chamber 22 provided with a transfer arm 20 that can be bent and stretched and swiveled inside via gate valves G1 and G2. It is connected in common.

【0013】

Similarly, the first and second cassette chambers 24 and 26 are connected to the transport chamber 22 via the gate valves G3 and G4. For example, the first cassette chamber 24 accommodates the cassette C1 accommodating the unprocessed substrate 2, and the second cassette chamber 26 accommodates the cassette C2 accommodating the processed wafer 2. The transfer of the wafer 2 between the devices and in the space is performed by bending and stretching and turning the transfer arm 20. Here, the film-forming plasma apparatus 16 has, for example, a 13.56 MHz plasma generator 28 because the titanium film is formed and the surface of the titanium film is nitrided in the presence of plasma. Then, in the processing container of the film-forming plasma apparatus 16, TiCl is used as a gas required for processing, for example, as a raw material gas.₄ Gas, H as reducing gas₂ Gas and NH₃ Ar gas can be selectively supplied as a gas, a carrier gas, or a gas for plasma conversion as needed, and the flow rate can be controlled.

【0014】

Further, the film forming apparatus 18 forms a tungsten film by thermal CVD as described above, but in order to accelerate the heating rate of the wafer W, a heating lamp group 30 is used here as a heating means, and this heating lamp is used. The group 30 rapidly heats and raises the temperature of the wafer W from, for example, the back surface side. Here, as the heating means, a resistance heating heater may be used instead of the heating lamp group 30. The cluster tool device 14 is merely an example of a device for carrying out the method of the present invention, and is not limited to this device for carrying out the method of the present invention.

【0015】

Next, the method of the present invention performed using the device example configured as described above will be described with reference to FIGS. 2 to 4. First, in the wafer 2, for example, a contact hole 4 or the like is formed as an embedding hole in, for example, the insulating layer 3 on the wafer 2 in the previous step, and such an untreated wafer 2 is in a vacuum state. A large number of wafers are housed in the cassette C1 in the first cassette chamber 24. Such an unprocessed wafer 2 is taken into the transfer chamber 22 which has been evacuated in advance by the transfer arm 20 in the transfer chamber 22, and after closing the gate valve G3, the gate valve G1 is then opened. The wafer 2 is carried into the film-forming plasma apparatus 16 which has been evacuated in advance, and the wafer 2 is placed on a mounting table (not shown) to complete the transfer.

【0016】

Next, the process proceeds to the titanium film forming step. That is, TiCl as a raw material gas₄ Supply gas and H as reducing gas₂ Supply gas. At this time, Ar gas that also serves as plasma gas is also supplied as a carrier gas. At the same time, the plasma generator 28 is driven to generate plasma, and as a result, as shown in FIG. 2 (A), a titanium film 32 is formed on the surface of the wafer 2 including the inner surface of the contact hole 4 with a predetermined thickness. Form (S1). In addition, H as a reducing gas₂ NH with or instead of gas₃ Gas may be used. The process temperature in the titanium film forming step is, for example, about 600 to 650 ° C, plasma is used, and the process pressure is about 500 to 1000 Pa. For each gas flow rate, TiCl₄ Gas is about 5 ~ 10sccm, H₂ The gas is about 1000 to 5000 sccm, and the Ar gas is about 500 to 3000 sccm. The thickness of the titanium film 32 at this time is, for example, about 100 Å.

【0017】

When the titanium film forming step is completed in this way, the process proceeds to the nitriding step of nitriding the surface of the titanium film 32. That is, here, the nitriding process is performed in the film-forming plasma apparatus 16 without transferring the wafer W to another processing apparatus. Specifically, TiCl, which is a raw material gas₄ Gas supply and reduction gas H₂ Stop gas supply together and instead NH₃ Supply gas. In addition, Ar gas is also continuously supplied as a gas for plasma, and as shown in FIG. 2 (B), the surface of the titanium film 32 is plasma nitrided in the presence of plasma to form a titanium nitride (TiN) film. Form 34 (S2). In addition, NH₃ N instead of gas₂ Gas may be supplied.

【0018】

The process temperature in the nitriding step is the same as in the case of the immediately preceding titanium film forming step, for example, about 600 to 650 ° C, and the process pressure is about 500 to 1000 Pa. In addition, about each gas flow rate, NH₃ The gas is about 500 to 3000 sccm, and the Ar gas is about 500 to 3000 sccm. The thickness of the titanium nitride film 34 at this time is a thickness that functions as a barrier layer, for example, about 50 Å. The lower limit of the thickness of the titanium nitride film 34 is the minimum thickness that can function as a barrier layer when the tungsten film is formed by the thermal CVD treatment described later, and is, for example, about 20 Å in the past. Since the thickness of 50 Å is much thinner than, for example, 200 Å, which is required by the conventional method, it can be easily and quickly formed by the nitriding treatment of the surface of the titanium film 32 as described above.

【0019】

After the nitriding step of the titanium film surface is completed in this way, the wafer W in the film forming plasma apparatus 16 is then transferred to the film forming apparatus 18 which is the other thermal CVD apparatus, and the tungsten film is transferred. Move to the forming process (S3). What is important here is that the film formation treatment of the tungsten film is performed at a relatively low temperature in view of the thinness of the TiN film 34, which is the barrier layer. In this way, in order to form the tungsten film at a relatively low temperature, the reducing gas and the tungsten-containing gas are alternately and intermittently supplied once or a plurality of times to form the tungsten film 36 ( S4). Specifically, as shown in FIG. 4, SiH, which is a reducing gas,₄ WF, a gas containing gas and tungsten₆ Gas and gas are alternately and intermittently supplied for a short period of time. At this time, SiH₄ One gas supply period T1 is, for example, about 0.5 to 5.0 seconds, WF₆ The gas supply period T2 is, for example, about 0.5 to 5.0 seconds, and the intermittent period T3 is, for example, about 0.5 to 3.0 seconds. SiH₄ Gas and WF₆ When supplying gas, for example, Ar, N as carrier gas₂ Etc. are also supplied, and a carrier gas or another gas is flowed as a purge gas during the intermittent period. It should be noted that each of the above periods T1 to T3 is merely an example and is not limited thereto.

【0020】

Thus, SiH₄ Gas and WF₆ By alternately and intermittently supplying the gas, a very thin tungsten film can be formed little by little with each repeated supply even at a relatively low process temperature, and the embedding is completed. Specifically, this process temperature is about 250 to 350 ° C, which is much lower than the process temperature of about 400 to 450 ° C, which is the process temperature at the time of conventional general thermal CVD film formation, and the film is formed even at this temperature. A tungsten film 36 having sufficiently inferior rate but sufficiently good characteristics is formed. The process pressure is about 100 to 1000 Pa. And for each gas flow rate, SiH₄ Gas is about 50 ~ 100sccm, WF₆ The gas is about 10 to 30 sccm. The above SiH₄ Instead of gas, H₂ Gas, Si₂ H₆Gas, SiH₂ Cl₂ Gas and the like can also be used.

【0021】

Also, in Fig. 4, SiH₄ From a certain point when the gas supply started, then SiH₄ Assuming that the period until the start of gas supply is one cycle, the thickness of the tungsten film 36 formed during this one cycle is relatively small, at most 3 to, although it depends on each gas flow rate at that time. It is about 20 Å, so this cycle will be repeated until the required film thickness is reached. In this way, the tungsten film 36 can be formed and embedded at a low process temperature of about 250 to 350 ° C. Therefore, even if the TiN film 34, which is the barrier layer, is as thin as about 50 Å as described above, It functions well as a barrier layer and does not damage this lower layer. In addition, this embedded hole 4 will eventually be embedded and plugged by the tungsten film 36, but W metal, which has a much lower electrical resistance than TiN metal, will occupy most of the plug metal. Therefore, the electrical resistance of the plug metal can be kept low even if the embedded hole diameter becomes smaller due to the miniaturization.

【0022】

In the above embodiment, as described above, the film thickness deposited in one cycle of gas supply is very small, and therefore, a considerably long process for forming a tungsten film having a thickness of, for example, about 2000 to 3000 Å. It takes time and the throughput is reduced. Therefore, in order to prevent this decrease in throughput, in the step of forming the tungsten film, after repeating the cycle of the gas supply form as described above a plurality of times, the gas type is changed and the process temperature is also raised to form a film. It is also possible to shift to the second tungsten film forming step having a high rate. FIG. 5 is a process diagram showing the process of film formation of such a modified example of the present invention, FIG. 6 is a flowchart for explaining the film forming process shown in FIG. 5, and FIG. 7 is the formation of a tungsten film in the modified example of the present invention. It is a figure which shows the gas supply form of a process.

【0023】

Here, FIGS. 5 (A) and 5 (B) are the same as those of FIGS. 2 (A) and 2 (B), and S1 to S4 in FIG. 6 are the same as S1 to S4 in FIG. Therefore, the explanation is omitted. In this tungsten film forming step, as shown in FIG. 7, the SiH is initially used.₄ Gas and WF₆ The point that the tungsten film 36 is formed by alternately and intermittently supplying the gas is the same as the case described above. And in this modification, the above SiH₄ Gas and WF₆ The gas supply cycle in which the gas is alternately and intermittently supplied is performed a plurality of times, for example, 3 cycles in the case shown in FIG. At the beginning and end of multiple cycles, SiH is shown in Fig. 7 for the purpose of suppressing F (fluorine) attack and residue as much as possible.₄ It is preferable to supply gas. Then, when the treatment is completed a plurality of times, SiH, which is a reducing gas, is completed.₄ Gas H₂ Switch to gas, this H₂ Gas and WF₆ Supply gas simultaneously and continuously. At this time, the process temperature is also raised to, for example, about 400 to 450 ° C. to shift to the second tungsten film forming step (S5), whereby the second tungsten film 38 is formed at a high film formation rate. To do. The process pressure at this time is, for example, about 2000 to 20000 Pa, WF.₆ The flow rate of gas is about 30 to 300 sccm, H₂ The flow rate of gas is about 300 to 3000 sccm. The film formation rate at this time is about 1000 to 5000 Å / min. Of course, the carrier gas is supplied here as well.

【0024】

As shown in FIG. 5C, the formation mode of the tungsten film in this case is SiH.₄Gas and WF₆ By repeating the cycle of alternately supplying gas three times, a very thin tungsten film 36 is deposited, and then, as shown in FIG. 5 (D), a second tungsten film is deposited in the second tungsten film forming step. The tungsten film 38 of the above will completely embed the embedding hole. Needless to say, the gas supply cycle is not limited to three times. According to this, since the film formation rate of the tungsten film can be increased, the throughput can be improved accordingly. In this case, even if the process temperature is raised to about 400 to 450 ° C in the second tungsten film forming step, the tungsten film 36 that is already thin but deposited at low temperature on the TiN film 34, which is the barrier layer. Since (see Fig. 5 (C)) is formed and protected, there is no risk of damaging the underlying Ti film 32 or the underlying layer.

【0025】

In each of the above examples, when forming the tungsten film, WF is always used as the tungsten-containing gas.₆ The case where a gas is used has been described as an example, but the description is not limited to this, and an organometallic gas containing no fluorine (F) as another tungsten-containing gas, for example, W (CO)₆ (Hexacarbonyl Tungsten), (C₅ H₅ )₂ WH₂ (Biscyclopentadienyl Tungsten), W₂[N (CH₃ )₂ ] ₆(Hexakisdimethylamide ditungsten) or the like can be used. When such a tungsten-containing gas containing no fluorine is used, it is not necessary to consider the damage of the underlying layer due to the attack of the fluorine gas. Therefore, when the underlying TiN film which is the barrier layer is described in each of the above examples. Since it can be made as thin as or even thinner than this, the lower limit of the thickness of the TiN film can be reduced to, for example, about 25 Å, and the conventional step of forming the TiN film by thermal CVD can be omitted. It becomes.

【0026】

As an organometallic gas, for example, W (CO)₆ If gas is used, thermal decomposition occurs at a process temperature of, for example, about 350 to 450 ° C., whereby the tungsten film 36 can be formed. In this case, in FIGS. 2 (C) and 5 (C), WF₆ / SiH₄ W (CO) instead of alternating intermittent supply₆ Flow gas continuously. In this case, the process condition is, for example, W (CO).₆ The gas flow rate is about 3 to 30 sccm, and the process pressure is, for example, about 1 to 100 pa. Carrier gas is Ar, He, H₂ Etc. can be used. If the film formation process is carried out by thermal CVD under such process conditions, a tungsten film 36 for seeds having a film thickness of, for example, about 25 to 150 Å can be deposited in about 1 to 3 minutes.

【0027】

In this case, if an attempt is made to increase the film formation rate of tungsten, as shown in step S5 in FIG. 6 described above, WF₆ Gas and H₂ It is also possible to deposit the second tungsten film 38 at a high film formation rate using gas. Further, in the above examples, the semiconductor wafer as the object to be processed has been described as an example, but the present invention is not limited to this, and the present invention can be applied to a glass substrate, an LCD substrate, and the like.

【0028】

[Effect of the invention]

As described above, according to the film forming method of the present invention, excellent effects can be exhibited as follows. According to the inventions according to claims 1, 3 to 8, the TiN film by thermal CVD, which has been conventionally performed in order to obtain a sufficient film thickness as a barrier layer, by using the step of forming the tungsten film at a low process temperature. The forming step can be omitted. Therefore, the number of steps for embedding an embedded hole such as a through hole or a contact hole can be reduced, and this efficiency can be improved. In addition, since the number of film forming steps is reduced, the number of processing devices can be reduced, and the equipment cost can be reduced. According to the invention of claim 2, the step for forming the tungsten film can be efficiently performed.

[Simple explanation of drawings]

[Figure 1]

It is a schematic block diagram which shows the cluster tool apparatus for carrying out the method of this invention.

[Figure 2]

It is a process diagram which shows the process of film formation.

[Fig. 3]

It is a flowchart which shows the film forming process.

[Fig. 4]

It is a figure which shows the supply state of the gas in the process of forming a tungsten film.

[Fig. 5]

It is a process diagram which shows the process of film formation of the modification of this invention.

[Fig. 6]

It is a flowchart explaining the film formation process shown in FIG.

[Fig. 7]

It is a figure which shows the gas supply form of the process of forming a tungsten film in the modification of this invention.

[Fig. 8]

It is a figure for demonstrating the conventional embedding method for an embedding hole.

[Explanation of symbols]

2 Semiconductor wafer (object to be processed) 14 Cluster tool device 16 Film deposition plasma equipment 18 Deposition equipment 28 Plasma generator 30 heating lamp group 32 Titanium film 34 Titanium nitride film 36 Tungsten film 38 Second tungsten film