JP3580159B2 - Method of forming tungsten film - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a tungsten film capable of improving specific resistance.
[0002]
[Prior art]
Generally, in a manufacturing process of a semiconductor integrated circuit, W () is used to form a wiring pattern on a surface of a semiconductor wafer to be processed, to bury holes between wirings, or to perform both of them simultaneously. A thin film is formed by depositing a metal or a metal compound such as tungsten (Tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), and TiSi (titanium silicide).
[0003]
The method for forming the metal thin film of this kind, three methods, for example, _{H 2} (hydrogen) reduction method, SiH ₄ (silane) reduction method, _SiH 2 Cl ₂ (dichlorosilane) and reduction methods are known, SiH ₂ The Cl ₂ reduction method is a method of forming a W or WSi (tungsten silicide) film at a high temperature of about 600 ° C. using dichlorosilane as a reducing gas in order to form a wiring pattern, and the SiH ₄ reduction method is the same. In order to form a wiring pattern, this is a method of forming a W or WSi film using silane as a reducing gas at a lower temperature of about 350 ° C. than before.
[0004]
The H ₂ reduction method is a method of depositing a W film at a temperature of about 400 to 460 ° C. using, for example, hydrogen as a reducing gas in order to fill a hole on a wafer surface such as a hole between wirings. .
In each of the above cases, for example, WF ₆ (tungsten hexafluoride) is used. Here, a conventional method of forming a tungsten film will be described. First, before forming a tungsten film, a thin Ti / TiN film, for example, is formed as a barrier metal on the surface of a semiconductor wafer. Next, WF ₆ , SiH ₄ , H ₂ , Ar, N _2, or the like is introduced as a film forming gas into the film forming chamber, and a tungsten nucleus crystal is adhered to the surface of the barrier metal to be formed.
[0005]
Next, after the inside of the film forming chamber is once evacuated to a base pressure to remove the residual gas, Ar, H ₂ , and N ₂ gases are supplied into the chamber, and the pressure is increased to the process pressure in a short time. WF ₆ gas is supplied at a predetermined flow rate, and the WF ₆ gas is hydrogen-reduced with H ₂ gas without using SiH ₄ gas to form a tungsten film. For example, the burying of holes and the formation of a wiring layer are simultaneously performed. Do.
[0006]
[Problems to be solved by the invention]
By the way, with the demand for multi-layered semiconductor integrated circuits, higher fineness and higher integration, it is required to further reduce the line width and the hole diameter accordingly. In this case, when the wiring pattern and the like are miniaturized, the resistance value increases accordingly. However, although the specific resistance value was sufficient in the conventional design, it is necessary to further reduce the specific resistance value by miniaturization. Has occurred.
However, it is difficult to obtain a tungsten film that has a sufficiently small specific resistance and conforms to a new design by the conventional method of forming a tungsten film as described above.
[0007]
Therefore, as a method of solving the above problem, a boron-containing gas, for example, diborane (B ₂ H ₆ ) is added to the chamber together with Ar and N ₂ gas at the time of forming a tungsten film after the formation of the tungsten core crystal. Attempts have been made to increase the crystal grain size of tungsten and thereby lower the specific resistance value. However, there is also a problem that the nitrogen-diluted diborane gas is polymerized, for example, and solidifies in the piping system in the course of the supply to cause clogging of the piping.
The present invention has been devised in view of the above problems and effectively solving the problems. An object of the present invention is to provide a method for forming a tungsten film capable of reducing a specific resistance value.
[0008]
[Means for Solving the Problems]
The present inventor has conducted intensive studies on a method of forming a tungsten film. As a result, after the formation of the tungsten core crystal and immediately before the tungsten film is actually formed, the semiconductor wafer is boronized with a boron-containing gas such as diborane. The present inventors have found that the surface treatment can increase the crystal grain size at the time of the subsequent film formation, thereby leading to the present invention.
The invention defined in claim 1 is a method for forming a tungsten film on a surface of a target object in a vacuum processing apparatus, wherein a tungsten nucleus is formed on the surface of the target object in the presence of a deposition gas containing a tungsten element. nuclear crystal growth step of growing the crystal, after this step, the a bleached to boron exposing step to an atmosphere of boron containing gas to be processed, after this step, the data tungsten film in the absence of a boron-containing gas And a tungsten film forming step to be formed.
[0009]
As described above, after the tungsten core crystal is grown and immediately before the tungsten film is actually formed, the target object is exposed to the atmosphere of the boron-containing gas, so that the tungsten core crystal is subjected to the boron surface treatment. By doing so, the crystal grains (grain) of the tungsten film are increased during the subsequent film growth, and the specific resistance value can be reduced.
In this case, when 5% hydrogen-diluted diborane gas is used as the boron-containing gas, the flow rate is set to be approximately 0.85% or more with respect to the total gas flow rate. Thereby, the specific resistance value can be considerably reduced.
[0010]
As defined in claim 3, for example, the tungsten film forming step is a step of simultaneously burying holes formed in the surface of the object to be processed and wiring.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for forming a tungsten film according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing a vacuum processing apparatus for performing the tungsten film forming method of the present invention.
First, a vacuum processing apparatus for performing the method of the present invention will be described.
The vacuum processing apparatus 2 has a processing container 4 formed in a cylindrical shape from, for example, aluminum or the like. In the processing container 4, a cylindrical reflector 6 standing upright from the bottom of the processing container is provided. A mounting table 10 for mounting, for example, a semiconductor wafer W as an object to be processed is provided on the reflector 6 via an L-shaped holding member 8. The mounting table 10 is made of, for example, a carbon material having a thickness of about several mm, or an aluminum compound such as AlN.
[0012]
A transmission window 12 made of quartz or the like is provided airtightly at the bottom of the processing container directly below the mounting table 10, and a box-shaped heating chamber 14 is provided below the transmission window 12 so as to surround the transmission window 12. In the heating chamber 14, a plurality of heating lamps 16 are mounted on a turntable 18 also serving as a reflecting mirror, and the turntable 18 is rotated by a rotation motor 20. Accordingly, the heat rays emitted from the heating lamp 16 pass through the transmission window 12 and irradiate the lower surface of the mounting table 10 to indirectly heat the wafer W thereon.
An exhaust port 22 is provided around the bottom of the processing container, and an exhaust passage 24 connected to a vacuum pump (not shown) is connected to the exhaust port 22 so that the inside of the processing container 16 can be evacuated. It has become. A gate valve 26 that is opened and closed when a wafer is loaded and unloaded is provided on a side wall of the processing container 4.
[0013]
On the other hand, a shower head portion 28 for introducing a processing gas or the like into the processing container 4 is provided on a ceiling portion of the processing container facing the mounting table 10, and a plurality of emission surfaces 28A of the shower head portion 28 are provided. Are provided. A gas supply system for supplying a gas necessary for a film forming process or the like is connected to the gas inlet 32 of the shower head unit 28.
Specifically, in this case, in order to form a tungsten core crystal, form a tungsten film, and perform exposure treatment with a boron-containing gas, which is a feature of the present invention, WF ₆ gas, Ar gas, SiH ₄ gas, H ₂ gas Gas sources of gas, N ₂ gas, and B ₂ H ₆ gas are connected. The piping of each gas source is provided with a mass flow controller 34 as a flow controller and two on-off valves 36 and 38 with the mass flow controller 34 interposed therebetween, and can control the flow of each gas and select whether or not to supply each gas. It has become.
[0014]
Diborane (B ₂ H ₆ ) is used as the borane-containing gas. However, here, 100% concentration of diborane is not used, but hydrogen (H ₂ ) gas is used up to 5% in order to prevent polymerization solidification. 5% hydrogen diluted siborane gas is used.
The capacity of the processing container 4 used here is about 1200 cm ³ , and the diameter of the mounting table 10 is set to about 200 mm so that an 8-inch wafer can be processed.
[0015]
Next, the method of the present invention performed using the apparatus configured as described above will be described with reference to FIG.
First, the gate valve 26 provided on the side wall of the processing container 4 is opened, and the wafer W is loaded into the processing container 4 by the transfer arm (not shown), and the wafer W is mounted on the mounting table 10. As shown in FIG. 2A, a thin barrier metal 40 of, for example, Ti / TiN is formed on the surface of the wafer W in the previous step. The barrier metal 40 is also formed on the inner surface of a hole 42 such as a contact hole or a via hole. The diameter of the hole 42 is, for example, about 0.5 to 1.0 μm, and the aspect ratio of the hole 42 is about 1 to 2. In the figure, 44 is a doped polysilicon film, and 46 is an insulating film.
[0016]
Next, WF ₆ , Ar, SiH ₄ , H ₂ , and N ₂ as processing gases are supplied from the respective processing gas sources to the shower head unit 28 by a predetermined amount and mixed. It is supplied almost evenly into the inside of the forty. Here, B ₂ H ₆ gas is not supplied. At the same time, the inside of the processing container 4 is set to a predetermined degree of vacuum, for example, a value of about 4 Torr by sucking and exhausting the internal atmosphere from the exhaust port 22, and the heating lamp 16 in the heating chamber 14 is driven while rotating. And radiates heat energy.
[0017]
The emitted heat rays pass through the transmission window 12 and then irradiate the back surface of the mounting table 10 to heat it. Since the mounting table 10 is very thin, about several mm as described above, it is quickly heated, and therefore, the wafer W mounted thereon can be quickly heated to a predetermined temperature. The process temperature at this time is, for example, about 460 ° C. The supplied mixed gas causes a predetermined chemical reaction. In this case, as shown in FIG. 2B, WF ₆ is reduced, and a tungsten nucleus crystal 48 is formed on the surface of the barrier metal 40. , A nuclear crystal growth step is performed. This nuclear crystal growth step is performed, for example, for about 30 seconds to form a nuclear crystal layer having a thickness of about 30 nm.
[0018]
After the nucleus crystal growth step is completed in this way, the process proceeds to the boron exposure step.
First, the supply of the reactive gas is stopped, the chamber is once evacuated to a base pressure, for example, about 10 ⁻³ Torr, and a predetermined gas such as B ₂ H ₆ gas is supplied to increase the pressure to about 80 Torr. A boron exposure step is performed as shown in FIG. The supply gas species here are Ar gas, H ₂ gas, and B ₂ H ₆ gas, and the respective gas amounts are 4000 sccm, 1800 sccm, and 100 sccm (5% concentration). Here, WF ₆ gas, SiH ₄ gas and N ₂ gas are not supplied. As a result, the tungsten core crystal 48 is exposed to boron, and a boron surface is formed by the B ₂ H ₆ gas. This makes it possible to increase the grain size of the core crystal as described later. This boron exposure step is performed, for example, for about 28 seconds. Note that the process temperature at this time is about 460 ° C., which is the same as the previous step.
[0019]
When the boron exposing step is completed in this way, the process proceeds to an actual tungsten film forming step.
First, WF ₆ gas, Ar gas, H ₂ gas, and N ₂ gas are supplied at 80 sccm, 900 sccm, 750 sccm, and 100 sccm, respectively, to actually form a tungsten film. Here, the supply of the SiH ₄ gas and the B ₂ H ₆ gas is stopped. The process pressure and the process temperature are the same as those in the previous step, that is, 80 Torr and 460 ° C. Thus, as shown in FIG. 2D, the hole 42 (see FIG. 2A) is buried, and at the same time, a tungsten film 50 for wiring is formed on the surface. The processing time at this time is, for example, about 98 seconds, and the tungsten film 50 having a total thickness of 800 nm is formed.
[0020]
As described above, by incorporating a boron exposure step between the nuclear crystal growth step and the tungsten film formation step of actually forming a tungsten film, the tungsten core crystal is exposed to, for example, diborane to form a boron surface. In addition, the grain size of the tungsten nucleus crystal (grain) grown in a later step can be increased. Therefore, the crystal structure of the formed tungsten film 50 is close to that of a bulk crystal, and the specific resistance can be reduced.
[0021]
As a result of comparing the conventional film forming method using no B ₂ H ₆ gas with the method of the present invention, the specific resistance value (converted to 1500 °) of the tungsten film according to the conventional method was about 12.2 μΩcm. The specific resistance (converted to 1500 °) of the film was about 8.5 μΩcm, and it was found that the specific resistance was significantly improved.
[0022]
FIG. 3 is an electron micrograph of a cross section of a hole buried portion formed by a tungsten film formed by the above-described method. Compared with the conventional method shown in FIG. 3A, the method of the present invention shown in FIG. It is clear that the grain size of the tungsten nucleus crystal is clearly large and is in a state close to a bulk crystal.
Further, in the case of the method of the present invention, there was no problem regarding the filling of the holes 42, and the filling state was as good as in the conventional method.
[0023]
Furthermore, in the method of the present invention, in the above-described boron exposure step, 100 sccm of B ₂ H ₆ gas diluted with hydrogen is added at a concentration of 5%, but the gas flow rate is about 50 sccm or more, that is, about the total gas amount. It is preferably at least 0.85% (≒ 50 × 100 / (4000 + 1800 + 50)), and if it is smaller than this, the specific resistance value does not become so small. This will be described with reference to FIG. FIG. 4 is a graph showing the relationship between the flow rate of B ₂ H ₆ gas (5% concentration) and the specific resistance in order to show the above results (1800 ° conversion). Note that, as described above, the Ar gas flow rate and the H ₂ gas flow rate are fixed to 4000 sccm and 1800 sccm, respectively.
[0024]
As is clear from this graph, when the flow rate of the B ₂ H ₆ gas (5% hydrogen dilution) is less than 50 sccm, the specific resistance value of the tungsten film is preferably larger than 11.3 μΩcm, but when the flow rate becomes 50 sccm or more, the specific resistance value becomes larger. The resistance value is smaller than 11 μΩcm, and therefore, the flow rate of the B ₂ H ₆ gas (hydrogen diluted 5% concentration) gas should be set to 50 sccm or more (about 0.85% or more with respect to the total gas total flow rate). Turns out to be good.
[0025]
Further, in the method of the present invention, because of the use of dilution gas to dilute the gas as B ₂ H ₆ gas concentration of 5% by hydrogen gas, B ₂ H ₆ gas as in the conventional method with nitrogen gas or argon gas Unlike the case where the diluted gas is used, the B ₂ H ₆ gas does not polymerize in the gas source container or the B ₂ H ₆ gas supply piping system, and the piping system may be clogged with the polymerized solid matter. Can be prevented. This will be described with reference to FIG. FIG. 5 is a graph showing a change in diborane (B ₂ H ₆ ) concentration when N ₂ gas (conventional method) is used as the diluent gas and when H ₂ gas (the method of the present invention) is used. As is apparent from this graph, in the case of N ₂ gas dilution, the concentration of diborane decreases as the number of elapsed days increases, and thus it is found that diborane causes polymerization. On the other hand, in the case of the H ₂ gas dilution used in the method of the present invention, the concentration of siborane is substantially constant irrespective of the number of elapsed days, and it is clear that polymerization is not occurring and the condition is good. . This is considered to be because the use of N ₂ gas as the dilution base gas makes B ₂ H ₆ molecularly unstable.
[0026]
It should be noted that the gas flow rate, the process temperature, and the process pressure in the above embodiment are merely examples, and are not limited thereto. Further, in this embodiment, B ₂ H ₆ gas of 5% concentration by hydrogen dilution is used, but if the concentration of this dilution changes, the above-mentioned limit value of each supply amount naturally changes in proportion thereto. It is. Further, the boron-containing gas to be used is not limited to diborane, and other borane such as tetraborane and pentaborane, BCl _{3 and the} like can be used, and a wafer having another size can be used. Further, as the object to be processed, not only a semiconductor wafer but also a glass substrate, an LCD substrate, or the like can be used.
[0027]
【The invention's effect】
As described above, according to the method for forming a tungsten film of the present invention, the following excellent operational effects can be exhibited.
When a tungsten film is formed on a surface of an object, a boron exposing step of exposing the object to a boron-containing gas is performed between a nuclear crystal growth step and a tungsten film forming step of actually forming a film. Therefore, the specific resistance can be reduced by increasing the grain size of the tungsten crystal grains (grains).
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a vacuum processing apparatus for performing a tungsten film forming method of the present invention.
FIG. 2 is a process chart for explaining a film forming method of the present invention.
FIG. 3 is an electron micrograph of a cross section of a hole buried portion with a tungsten film.
FIG. 4 is a graph showing a relationship between a flow rate of B ₂ H ₆ gas (5% concentration) and a specific resistance value.
FIG. 5 is a graph showing a change in diborane (B ₂ H ₆ ) concentration when N ₂ gas (conventional method) is used as a diluent gas and when H ₂ gas (method of the present invention) is used.
[Explanation of symbols]
2 Vacuum processing device 4 Processing container 10 Mounting table 12 Transmission window 16 Heating lamp 28 Shower head unit 40 Barrier metal 42 Hole 44 Doped polysilicon film 46 Insulating film 48 Tungsten crystal 50 Tungsten film W Semiconductor wafer (workpiece)

Claims (3)

A step of forming a tungsten film on the surface of the object in the vacuum processing apparatus, a step of growing a nuclear crystal of tungsten in the presence of a deposition gas containing a tungsten element on the surface of the object; after this step, includes the a bleached to boron exposing step to an atmosphere of an object to be processed boron-containing gas, after this step, a tungsten film forming step of forming a data tungsten film in the absence of a boron-containing gas A method for forming a tungsten film. 2. The tungsten film forming method according to claim 1, wherein a hydrogen-diluted diborane gas is used as the boron-containing gas in the boron exposing step, and a flow rate thereof is about 0.85% or more with respect to a total flow rate of all the gases. . 3. The tungsten film forming method according to claim 1, wherein the tungsten film forming step is a step of simultaneously burying a hole formed in the surface of the object to be processed and wiring.

Images