JP4595989B2 - Deposition method - Google Patents

Description

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

  In general, semiconductor devices tend to have a multilayer wiring structure in response to recent demands for higher density and higher integration. In this case, the connection between the lower layer device and the upper layer aluminum wiring An embedding technique such as a contact hole or a via hole which is a connecting portion between a lower layer aluminum wiring and an upper layer aluminum wiring is important in order to establish an electrical connection between them.

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

  Therefore, in order to prevent the above phenomenon, a barrier metal layer is thinly formed over the entire surface of the wafer including the surface in the hole before filling the contact hole, the through hole, etc. with tungsten, and the hole is buried with tungsten from above. Has been done. As a material for this barrier layer, Ti / TiN (titanium nitride) is generally used. JP-A-6-89873 and JP-A-10-106974 are disclosed as such prior arts, and the present applicant also filed a related application in Japanese Patent Application No. 2000-351716.

Here, a conventional filling method for filling holes will be described with reference to FIG. 8. In the figure, reference numeral 2 denotes a semiconductor wafer as an object to be processed, and 3 denotes an insulating film for forming contact holes. A contact hole 4 as a buried hole is formed on the surface of the wafer 2. Then, for example, TiCl ₄ gas and H ₂ gas are used in the contact hole 4 in order to establish electrical continuity with, for example, the diffusion layer at the bottom of the hole, as shown in FIG. The titanium film 6 is thinly formed by P-CVD (Plasma Chemical Vapor Deposition) or the like. Next, this wafer W is transferred to another thermal CVD apparatus, and a TiN (titanium nitride) film 8 is thinned by thermal CVD using TiCl ₄ gas and NH ₃ gas as shown in FIG. 8B. Form.
Next, this wafer W is transferred to another thermal CVD apparatus, and W (tungsten) is formed using WF ₆ gas and SiH ₄ gas or H ₂ gas or both gases as shown in FIG. A film 10 is formed to fill the contact hole 4.

By the way, as shown in FIG. 8C, since the WF ₆ gas used when forming the tungsten film 10 contains F (fluorine), there is a possibility that this unreacted fluorine is very active and forms TiFx. In order to prevent the titanium film 6 and the underlying silicon layer from being damaged by fluorine of the WF ₆ gas in the temperature range of about 400 to 450 ° C. which is the process temperature, the TiN film 8 is made sufficiently thick. For example, it has been necessary to form at least about 200 mm. For this reason, since it is necessary to efficiently form a TiN film having a sufficient thickness as described above, it is necessary to transfer the wafer from the plasma CVD apparatus in which the Ti film 6 is formed to the thermal CVD apparatus.
As a result, a process for forming a TiN film 8 having a sufficient thickness and a dedicated thermal CVD apparatus for the process are required, which increases the number of processes and increases the equipment cost.
The present invention has been devised to pay attention to the above problems and to effectively solve them. The object of the present invention is to use a process for forming a tungsten film at a low process temperature, so that it is possible to omit the process for forming a TiN film by thermal CVD, which is conventionally performed to obtain a sufficient film thickness as a barrier layer. Is to provide a simple film forming method.

When forming the tungsten film, the present inventors can make the barrier layer such as the TiN film relatively thin by using a tungsten film forming process that can be formed at a relatively low process temperature. The present inventors have reached the present invention by obtaining the knowledge that a thin barrier layer can be easily formed by continuously performing a plasma nitriding treatment after a Ti film forming step in a processing container in which a Ti film is formed.
The invention defined in claim 1 is a method of forming a laminated film composed of a barrier film and a tungsten film on a semiconductor substrate, a titanium film forming step of forming a titanium film on the surface of the semiconductor substrate, and a surface of the titanium film. Nitriding to form a titanium nitride film having a predetermined thickness as the barrier film ; supplying a reducing gas and a tungsten-containing gas to the semiconductor substrate; and at least reducing the reducing gas and the tungsten-containing gas. gas intermittently and repeatedly supplying a plurality of times, the first data tungsten film forming step of forming a first tungsten film at a process temperature of the titanium film is not damaged, reducing gas and WF ₆ gas to the semiconductor substrate And a second tungsten film forming step of forming a second tungsten film. This is a film forming method.

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

In this case, after the data tungsten film forming step In example embodiment, the second tungsten film forming the second tungsten film at a higher process temperature than the tungsten film forming step by supplying a reducing gas and a tungsten-containing gas at the same time If the formation process is performed, the film formation speed is increased by the high process temperature, and the process for forming the tungsten film can be performed efficiently.

For example, as defined in claim 2, in the nitriding step, NH ₃ gas or N ₂ gas is supplied to the semiconductor substrate, and the surface of the titanium film is plasma-nitrided in the presence of plasma.
For example, as defined in claim 3, the tungsten-containing gas is WF ₆ gas, and the reducing gas and the WF ₆ gas are alternately and intermittently applied to the semiconductor substrate in the first tungsten film forming step. Repeatedly supply several times .
For example, as defined in claim 4, the process temperature is set corresponding to the predetermined film thickness.
For example, as defined in claim 5, the process temperature is about 250 to 350 ° C.

For example, as defined in claim 6, the lower limit of the predetermined film thickness is about 50 mm.
For example, as defined in claim 7, in the first tungsten film forming step, a reducing gas is supplied to the semiconductor substrate at the beginning and at the end.
For example, as defined in claim 8, the tungsten-containing gas is an organometallic gas not containing fluorine.
For example, as defined in claim 9, the organometallic gas is W (CO) ₆ gas.
For example, as defined in claim 10, the process temperature is about 350 to 450 ° C.
For example, as defined in claim 11, the lower limit of the predetermined film thickness is about 25 mm.

According to the film forming method of the present invention, the following excellent effects can be exhibited.
By the present invention lever, by using the process of forming the tungsten film by low temperature process temperature, it is possible to omit the step of forming the TiN film by the conventional performed thermal CVD in order to obtain a sufficient thickness as a barrier layer It becomes possible. Therefore, this efficiency can be improved by reducing the number of steps of the embedding operation of the embedding holes such as through holes and contact holes. Further, since the number of film forming steps is reduced, the number of processing apparatuses can be reduced, and the equipment cost can be reduced.

Hereinafter, an embodiment of a film forming method according to the present invention will be described in detail with reference to the accompanying drawings.
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, this cluster tool apparatus 14 includes a film forming plasma apparatus 16 for continuously performing a titanium film forming process and a nitriding process on the surface of a semiconductor wafer 2 as an object to be processed, and then a tungsten film forming process. A film forming apparatus 18 for performing the process by thermal CVD is provided. Both apparatuses 16 and 18 are connected to a transfer chamber 22 having a transfer arm 20 that can be bent and stretched inside through gate valves G1 and G2. Commonly connected.

Similarly, first and second cassette chambers 24 and 26 are connected to the transfer chamber 22 via gate valves G3 and G4. For example, in the first cassette chamber 24, a cassette C1 that stores an unprocessed substrate 2 is stored, and in the second cassette chamber 26, a cassette C2 that stores a processed wafer 2 is stored. The transfer of the wafer 2 between the apparatuses and in the space is performed by bending and extending and turning the transfer arm 20.
Here, the film-forming plasma apparatus 16 has a plasma generator 28 of 13.56 MHz, for example, in order to form a titanium film and perform nitriding treatment on the surface in the presence of plasma. And into the processing container of this film-forming plasma apparatus 16, as a gas required for processing, for example, TiCl ₄ gas as a source gas, H ₂ gas or NH ₃ gas as a reducing gas, carrier gas or gas for plasma generation Ar gas can be supplied selectively and controllable as required.

The film forming apparatus 18 forms a tungsten film by thermal CVD as described above. In order to increase the temperature rising rate of the wafer W, the heating lamp group 30 is used here as a heating unit. The group 30 causes the wafer W to be heated and heated rapidly from the back side, for example. Here, instead of the heating lamp group 30, a resistance heater may be used as the heating means.
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.

Next, the method of the present invention performed using the apparatus example configured as described above will be described with reference to FIGS.
First, in the wafer 2, for example, a contact hole 4 or the like is formed as a buried hole in the insulating layer 3 on the wafer 2 in the previous process, and the unprocessed wafer 2 is in a vacuum state. A large number of sheets are accommodated in the cassette C 1 in the first cassette chamber 24. Such an unprocessed wafer 2 is taken into the transfer chamber 22 which has been in a vacuum state by the transfer arm 20 in the transfer chamber 22, and after closing the gate valve G3, the gate valve G1 is then opened. Then, the wafer 2 is carried into the film-forming plasma apparatus 16 which has been previously in a vacuum state, and this is placed on a mounting table (not shown) to complete the transfer.

Next, the process proceeds to a titanium film forming step. That is, the TiCl ₄ gas is supplied as a source gas for supplying _{H 2} gas as the reducing gas. At this time, Ar gas that also serves as a plasma gas is also supplied as a carrier gas. At the same time, the plasma generator 28 is driven to generate plasma, whereby 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 as shown in FIG. Form (S1). It should be noted that NH ₃ gas may be used as the reducing gas together with H ₂ gas or instead.
The process temperature in the titanium film forming step is, for example, about 600 to 650 ° C., using plasma, and the process pressure is about 500 to 1000 Pa. The gas flow rates are about ₅ to 10 sccm for TiCl ₄ gas, about 1000 to 5000 sccm for H ₂ gas, and about 500 to 3000 sccm for Ar gas. At this time, the thickness of the titanium film 32 is, for example, about 100 mm.

When the titanium film forming process is completed in this way, the process proceeds to a nitriding process in which the surface of the titanium film 32 is nitrided. 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, the supply of the TiCl ₄ gas that is the raw material gas and the supply of the H ₂ gas that is the reducing gas are both stopped, and NH ₃ gas is supplied instead. Further, Ar gas is also continuously supplied as a plasma gas, and the surface of the titanium film 32 is plasma-nitrided in the presence of plasma as shown in FIG. 2B to form a titanium nitride (TiN) film. 34 is formed (S2). Note that N ₂ gas may be supplied instead of NH ₃ gas.

The process temperature in the nitriding step is the same as that in the immediately preceding titanium film forming step, for example, about 600 to 650 ° C., and the process pressure is about 500 to 1000 Pa. Further, for each gas flow rate, NH ₃ gas is about 500～3000Sccm, Ar gas is about 500～3000Sccm. At this time, the thickness of the titanium nitride film 34 functions as a barrier layer, for example, about 50 mm. The lower limit value of the thickness of the titanium nitride film 34 is the minimum thickness that can function as a barrier layer when a tungsten film is formed by thermal CVD processing described later, and is conventionally about 200 mm , for example. Since the thickness of 50 mm is much thinner than, for example, 200 mm required in the conventional method, it can be easily formed in a short time by nitriding the surface of the titanium film 32 as described above.

When the nitriding process 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 The process proceeds to the forming process (S3). The important point here is, film formation process of the tungsten film is relatively performed at a low temperature when viewed Kan the film thickness of the TiN film 3 4 is the barrier layer, is that.
In this way, in order to form the tungsten film at a relatively low temperature, the tungsten film 36 is formed by supplying the reducing gas and the tungsten-containing gas alternately and repeatedly one or more times. S4).
Specifically, as shown in FIG. 4, SiH ₄ gas that is a reducing gas and WF ₆ gas that is a tungsten-containing gas are supplied alternately and repeatedly for a short time. At this time, SiH ₄ supply period T1 of one gas, for example, about 0.5 to 5.0 seconds, once the supply period of the WF ₆ gas T2 is for example, about 0.5 to 5.0 seconds, the intermittent period T3 Is, for example, about 0.5 to 3.0 seconds. When supplying SiH ₄ gas or WF ₆ gas, for example, Ar, N ₂ or the like is also supplied as the carrier gas, and the carrier gas or another gas is allowed to flow as the purge gas during the intermittent period. In addition, each said period T1-T3 is only an example, and is not limited to these.

Thus, by supplying repeatedly intermittently alternating with SiH ₄ gas and WF ₆ gas, a very thin tungsten film at a relatively low process temperature, it can be formed little by little in each repeated feed , The embedding is completed. Specifically, this process temperature is about 250 to 350 ° C., which is much lower than about 400 to 450 ° C., which is a conventional process temperature for thermal CVD film formation. A slightly inferior tungsten film 36 with sufficiently good characteristics is formed.
The process pressure is about 100 to 1000 Pa. Then, for each gas flow rate, SiH ₄ gas is about 50~100sccm, WF ₆ gas is about 10～30Sccm. In place of the SiH ₄ gas, H ₂ gas, Si ₂ H ₆ gas, SiH ₂ Cl ₂ gas, or the like can be used.

Further, in FIG. 4, if a period from a certain time point at which the supply of SiH ₄ gas is started to a time point at which the next supply of SiH ₄ gas is started is one cycle, the tungsten film 36 formed during this one cycle. Depending on the gas flow rate at that time, the thickness is relatively small and is about 3 to 20 mm at most. Therefore, this cycle is repeated until the required film thickness is obtained.
As described above, since the tungsten film 36 can be formed at a low process temperature of about 250 to 350 ° C. and the embedding operation can be performed, as described above, even if the TiN film 34 as a barrier layer is as thin as 50 mm, the barrier It functions sufficiently as a layer and does not damage this lower layer.
The buried hole 4 is finally buried and plugged with the tungsten film 36, but W metal, which has a much lower electrical resistance than TiN metal, occupies most of the plug metal. Therefore, even if the hole diameter becomes smaller due to miniaturization, the electrical resistance of the plug metal can be kept low.

In the above embodiment, as described above, the film thickness deposited in one cycle of gas supply is very small. Therefore, for example, to form a tungsten film having a thickness of about 2000 to 3000 mm, a considerably long process is required. Time is required and throughput is reduced.
Therefore, in order to prevent this decrease in throughput, in the step of forming the tungsten film, after repeating the gas supply mode cycle as described above a plurality of times, the film type is changed and the process temperature is also increased. You may make it transfer to the 2nd tungsten film formation process with a high rate.
FIG. 5 is a process diagram showing the film forming process of the 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 a tungsten film forming process of the modified example of the present invention. It is a figure which shows the gas supply form of a process.

Here, FIGS. 5A and 5B are the same as FIGS. 2A and 2B, respectively, 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, initially, the tungsten film 36 is formed by alternately and intermittently supplying SiH ₄ gas and WF ₆ gas as in the case described above. It is.
In this modification, the gas supply cycle for alternately and intermittently supplying the SiH ₄ gas and the WF ₆ gas is performed a plurality of times, for example, 3 cycles in the case shown in FIG. Further, it is preferable to supply SiH ₄ gas as shown in FIG. 7 for the purpose of suppressing F (fluorine) attack and residual as much as possible at the beginning and end of the plurality of cycles. When the processing of a plurality of times has been completed, it switches the SiH ₄ gas as a reducing gas to H ₂ gas, simultaneously and continuously supplied and the H ₂ gas and WF ₆ gas. At this time, by raising the process temperature to, for example, about 400 to 450 ° C., the process proceeds to the second tungsten film formation step (S5), thereby forming the second tungsten film 38 at a high film formation rate. . The process pressure at this time is, for example, about 2000 to 20000 Pa, the flow rate of WF ₆ gas is about 30 to 300 sccm, and the flow rate of H ₂ gas is about 300 to 3000 sccm. Further, the film formation rate at this time is about 1000 to 5000 kg / min. Of course, the carrier gas is also supplied here.

As shown in FIG. 5C, the tungsten film is formed in such a manner that a very thin tungsten film 36 is deposited by repeating the cycle of alternately supplying SiH ₄ gas and WF ₆ gas three times. Next, as shown in FIG. 5D, the buried hole is completely filled with the second tungsten film 38 deposited in the second tungsten film forming step. Of course, the gas supply cycle is not limited to three.
According to this, since the deposition 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 formation step, the tungsten film 36 (which is already deposited at a low temperature on the TiN film 34 which is a barrier layer) ( 5 (see FIG. 5C) is formed and protected, there is no possibility of damaging the underlying Ti film 32 or its underlying layer.

In each of the above embodiments, when the tungsten film is formed, the case where WF ₆ gas is always used as the tungsten-containing gas has been described as an example. However, the present invention is not limited thereto, and fluorine (F ) -Free organometallic gases such as W (CO) ₆ (hexacarbonyltungsten), (C ₅ H ₅ ) ₂ WH ₂ (biscyclopentadienyl tungsten), W ₂ [N (CH ₃ ) ₂ ] ₆ ( Hexakisdimethylamide ditungsten) or the like.
When such a tungsten-containing gas containing no fluorine is used, it is not necessary to consider damage to the underlying layer due to the fluorine gas attack, so the TiN film as the barrier layer is equivalent to the case described in each of the above embodiments. Alternatively, since the thickness can be further reduced, the lower limit of the thickness of the TiN film can be reduced to, for example, about 25 mm, and the TiN film forming process by thermal CVD, which has been conventionally performed, can be omitted. .

If, for example, W (CO) ₆ gas is used as the organometallic gas, 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 FIG. 2C and FIG. 5C, W (CO) ₆ gas is continuously flowed instead of the intermittent intermittent supply of WF ₆ / SiH ₄ . In this case, the process conditions, e.g., W _{(CO) 6} gas flow rate of about 3～30Sccm, process pressure is, for example, about 1 to 100 Pa. Ar, He, H ₂ or the like can be used as the carrier gas. If a film formation process is performed by thermal CVD under such process conditions, a seed tungsten film 36 having a film thickness of, for example, about 25 to 150 mm can be deposited in about 1 to 3 minutes.

In this case, if an attempt is made to increase the tungsten film formation rate, the second tungsten is formed at a high film formation rate using WF ₆ gas and H ₂ gas as shown in step S5 in FIG. 6 described above. It is also possible to deposit a film 38.
In the above embodiments, the semiconductor wafer is described as an example of the object to be processed. However, 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.

It is a schematic block diagram which shows the cluster tool apparatus for implementing this invention method. It is process drawing which shows the process of film-forming. It is a flowchart which shows a film-forming process. It is a figure which shows the supply state of the gas in the formation process of a tungsten film. It is process drawing which shows the process of the film-forming of the modification of this invention. It is a flowchart explaining the film-forming process shown in FIG. It is a figure which shows the gas supply form of the formation process of the tungsten film in the modification of this invention. It is a figure for demonstrating the conventional embedding method with respect to an embedding hole.

Explanation of symbols

2 Semiconductor wafer (object to be processed)
DESCRIPTION OF SYMBOLS 14 Cluster tool apparatus 16 Film-forming plasma apparatus 18 Film-forming apparatus 28 Plasma generator 30 Heating lamp group 32 Titanium film 34 Titanium nitride film 36 Tungsten film 38 2nd tungsten film

Claims (11)

In a method of forming a laminated film composed of a barrier film and a tungsten film on a semiconductor substrate ,
A titanium film forming step of forming a titanium film on the surface of the semiconductor substrate;
A nitriding step of forming a predetermined film thickness of the titanium nitride film as the barrier film by nitriding the surface of the titanium film,
Supplying a reducing gas and a tungsten-containing gas to the semiconductor substrate and supplying at least the reducing gas among the reducing gas and the tungsten-containing gas intermittently and repeatedly a plurality of times, at a process temperature at which the titanium film is not damaged. a first capacitor tungsten film forming step of forming a first tungsten film,
A film forming method comprising: a second tungsten film forming step of simultaneously supplying a reducing gas and a WF ₆ gas to the semiconductor substrate to form a second tungsten film . The film forming method according to claim 1 , wherein in the nitriding step, NH ₃ gas or N ₂ gas is supplied to the semiconductor substrate, and the surface of the titanium film is plasma-nitrided in the presence of plasma. The tungsten-containing gas is WF ₆ gas, and in the first tungsten film forming step, the reducing gas and the WF ₆ gas are alternately and repeatedly supplied to the semiconductor substrate a plurality of times. Item 3. The film forming method according to Item 1 or 2. 4. The film forming method according to claim 3, wherein the process temperature is set in accordance with the predetermined film thickness . The film forming method according to claim 4, wherein the process temperature is about 250 to 350 ° C. 6. The film forming method according to claim 1, wherein a lower limit value of the predetermined film thickness is about 50 mm. 7. The film forming method according to claim 3, wherein in the first tungsten film forming step, a reducing gas is supplied to the semiconductor substrate at the beginning and at the end . 3. The film forming method according to claim 1, wherein the tungsten-containing gas is an organometallic gas containing no fluorine . 9. The film forming method according to claim 8, wherein the organometallic gas is W (CO) ₆ gas . The film forming method according to claim 9, wherein the process temperature is about 350 to 450 ° C. 11. The film forming method according to claim 9, wherein the lower limit of the predetermined film thickness is about 25 mm .

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