JP4084129B2 - Method for forming tungsten film and CVD apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the formation of a tungsten film.
[0002]
[Prior art]
In recent years, a tungsten film formation technique by a CVD method has been widely adopted in the manufacture of semiconductor devices. This is because the CVD method can form a tungsten film having excellent step coverage and migration resistance. In this film forming technique, tungsten hexafluoride (WF ₆ ) and monosilane (SiH ₄ ) are supplied as source gases into the chamber of the CVD apparatus. A tungsten film is formed on the substrate by the chemical reaction of these gases. This film formation technique is used, for example, when interlayer connection of multilayer wiring is performed by filling tungsten in a contact hole.
[0003]
[Problems to be solved by the invention]
In general, in an opening such as a contact hole, the growth of a tungsten film is less likely to proceed at the bottom than at the top. This tendency becomes more prominent as the aspect ratio of the opening is higher. In this case, even if the introduction time of the source gas is increased, the film formation at the bottom of the opening is not improved much. For this reason, it is difficult to form a tungsten film with good coverage.
[0004]
Therefore, an object of the present invention is to form a tungsten film with good coverage on the surface of an opening having a high aspect ratio.
[0005]
[Means for Solving the Problems]
In the method according to the present invention, a tungsten film is formed by a chemical vapor deposition method on the surface of the opening having an aspect ratio of 5 or more which the layer structure on the substrate has. This opening is, for example, a contact hole or a through hole. In this method, a first step of introducing tungsten hexafluoride gas and monosilane gas as a source gas into a vacuum chamber in which a substrate is accommodated, and the introduction of tungsten hexafluoride gas and monosilane gas are stopped to react the source gas. A second step of extracting the by-product from the opening having an aspect ratio of 5 or more and a third step of reintroducing tungsten hexafluoride gas and monosilane gas into the vacuum chamber are included.
[0006]
When the tungsten hexafluoride gas and the monosilane gas are intermittently introduced into the vacuum chamber, reaction by-products can easily escape from the bottom of the opening. Accordingly, the film forming speed around the bottom of the opening is improved. For this reason, even if the opening has a high aspect ratio, a tungsten film is formed on the surface with excellent coverage.
[0007]
The CVD apparatus according to the present invention includes a vacuum chamber, a first gas supply source, a first valve, a second gas supply source, and a second valve. Each of the first gas supply source and the second gas supply source communicates with the vacuum chamber. The first gas supply source can supply tungsten hexafluoride gas to the vacuum chamber. The second gas supply source can supply monosilane gas to the vacuum chamber. A first valve is disposed on the gas flow path between the first gas supply source and the vacuum chamber. The first valve adjusts the flow rate of tungsten hexafluoride gas from the first gas supply source to the vacuum chamber. A second valve is disposed on the gas flow path between the second gas supply source and the vacuum chamber. The second valve adjusts the flow rate of monosilane gas from the second gas supply source to the vacuum chamber. This CVD apparatus sequentially executes the first to third steps. In the first step, the first and second valves are opened to introduce tungsten hexafluoride gas and monosilane gas into the vacuum chamber. In the second step, the first and second valves are closed, and the introduction of tungsten hexafluoride gas and monosilane gas is stopped. In the third step, the first and second valves are opened again, and tungsten hexafluoride gas and monosilane gas are reintroduced into the vacuum chamber.
[0008]
When a substrate provided with a layer structure having an opening is accommodated in a vacuum chamber, this CVD apparatus can form a tungsten film on the surface of the opening. This CVD apparatus intermittently introduces tungsten hexafluoride gas and monosilane gas into a vacuum chamber to form a tungsten film. As a result, reaction by-products can easily escape from the bottom of the opening, so that the film forming rate around the bottom of the opening is improved. For this reason, even if the opening has a high aspect ratio, a tungsten film is formed on the surface with excellent coverage.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. For the convenience of illustration, the dimensional ratios in the drawings do not necessarily match those described.
[0010]
FIG. 1 is a schematic diagram showing a configuration of a CVD apparatus 10 according to the present embodiment. The CVD apparatus 10 performs thermal CVD. The CVD apparatus 10 includes a vacuum chamber 12, a gas mixing chamber 28, gas supply sources 31 to 34, gas flow rate adjustment valves 41 to 44, an exhaust pump 45, and a control device 50. The CVD apparatus 10 can form a tungsten film on the substrate accommodated in the vacuum chamber 12 according to the method of the present invention.
[0011]
A pedestal 16 and a gas distribution plate 18 are installed in the vacuum chamber 12. An exhaust port 22 is also provided in the bottom wall of the chamber 12. The exhaust port 22 communicates with the exhaust pump 45.
[0012]
The pedestal 16 is a substrate support. The pedestal 16 is made of a metal such as aluminum. When forming the tungsten film, the silicon wafer 14 is placed on the upper surface of the pedestal 16 as a substrate.
[0013]
The gas distribution plate 18 is disposed above the pedestal 16. The gas distribution plate 18 is also made of a metal such as aluminum. The gas distribution plate 18 is hollow. The lower surface 18 a of the gas distribution plate 18 faces the upper surface of the pedestal 16 in parallel. A large number of gas outlets 20 are formed on the lower surface 18a. The gas distribution plate 18 is a device for uniformly mixing the process gas, which is connected to the gas mixing chamber 28 via a pipe 26 penetrating the upper wall of the chamber 12. The gas mixing chamber 28 is installed outside the vacuum chamber 12. The gas mixing chamber 28 communicates with the vacuum chamber 12 via the pipe 26. The gas mixing chamber 28 supplies process gas into the gas distribution plate 18 through the pipe 26. A WF ₆ gas supply source 31, a SiH ₄ gas supply source 32, an H ₂ gas supply source 33, and an Ar gas supply source 34 are connected to the gas mixing chamber 28 via gas flow rate adjustment valves 41 to 44, respectively. .
[0014]
The WF ₆ gas supply source 31 and the SiH ₄ gas supply source 32 supply tungsten hexafluoride (WF ₆ ) gas and monosilane (SiH ₄ ) gas, which are raw material gases, respectively. The H ₂ gas supply source 33 supplies hydrogen (H ₂ ) gas that is a carrier gas. The Ar gas supply source 34 supplies argon (Ar) gas which is an inert gas. These gas supply sources 31 to 34 communicate with the vacuum chamber 12 via the gas flow rate adjustment valves 41 to 44 and the gas mixing chamber 28.
[0015]
A control device 50 is connected to the gas flow rate adjusting valves 41 to 44. The control device 50 controls opening and closing of the valves 41 to 44. Thereby, the flow rate of each process gas can be adjusted, and the mixing ratio of the process gas can be set to a desired value. The control device 50 is also connected to the exhaust pump 45. The control device 50 controls the exhaust speed of the pump 45 so that the pressure in the chamber 12 becomes a desired value. The control device 50 is a computer having a CPU and a storage device. In this storage device, programs for controlling the opening amounts of the valves 41 to 44 and the pumping speed of the pump are recorded.
[0016]
Next, a method for forming a tungsten film on the silicon wafer 14 using the CVD apparatus 10 will be described. The tungsten film formed in this embodiment is a so-called tungsten plug that fills the opening in the layer structure provided on the wafer 14.
[0017]
FIG. 2 is a partial cross-sectional view showing the layer structure on the wafer 14 before the tungsten film is formed. Before the wafer 14 is carried into the chamber 12, a lower layer 52, an interlayer insulating film 54, and a barrier metal layer 56 are provided on the wafer 14. The lower layer 52 is deposited on the upper surface of the wafer 14. The lower layer 52 is made of a semiconductor (for example, silicon (Si)) or a metal. The interlayer insulating film 54 is deposited on the upper surface of the lower layer 52. The interlayer insulating film 54 is made of, for example, silicon oxide (SiO ₂ ). A contact hole 57 is provided in the interlayer insulating film 54. The contact hole 57 extends from the upper surface of the interlayer insulating film 54 to the vicinity of the upper surface of the lower layer 52. A barrier metal layer 56 is deposited on the upper surface of the interlayer insulating film 54 and the surface of the contact hole 57. The barrier metal layer 56 is made of, for example, titanium nitride (TiN).
[0018]
The lower layer 52, the interlayer insulating film 54, and the barrier metal layer 56 are formed using a known technique in a processing chamber apparatus separate from the CVD apparatus 10 described above. Thereafter, the wafer 14 is loaded into the vacuum chamber 12 through a vacuum transfer chamber (not shown) by an appropriate transfer robot and placed on the pedestal 16.
[0019]
Next, the control device 50 drives the exhaust pump 45 to evacuate the vacuum chamber 12 and depressurize the vacuum chamber 12 to a predetermined pressure. In this embodiment, the pressure in the chamber 12 is about 30 Torr. This pressure is maintained in subsequent steps.
[0020]
Thereafter, the CVD apparatus 10 forms a tungsten film 58 on the surface of the barrier metal layer 56 and fills the contact hole 57 with tungsten. FIG. 3 is a partial cross-sectional view showing the layer structure on the wafer 14 after the tungsten film 58 is formed. Hereinafter, a method for forming the tungsten film 58 will be described in detail.
[0021]
In the method of this embodiment, a WF ₆ gas and a SiH ₄ gas, which are source gases, are intermittently introduced into the chamber 12 to form the tungsten film 58. During film formation, the temperature of the wafer 14 is maintained in the range of 400 to 475 ° C. The pressure in the chamber 12 is maintained at about 30 Torr. The control device 50 continuously operates the pump 45 while adjusting the exhaust speed of the pump 45 so as to maintain the pressure in the chamber 12 at this value.
[0022]
First, the control device 50 opens the valves 41 and 42 and introduces the WF ₆ gas and the SiH ₄ gas into the chamber 12 over a predetermined source gas introduction time (for example, 3 seconds). At the same time, the control device 50 opens the valves 43 and 44 to introduce H ₂ gas and Ar gas into the chamber 12. The flow ratio of WF ₆ / SiH ₄ is adjusted to 1 or more (for example, 30/25). By introducing these source gases, the film formation of tungsten is started on the surface of the contact hole 57.
[0023]
When the source gas introduction time has elapsed, the control device 50 closes the valves 41 and 42 and shuts off the WF ₆ gas and the SiH ₄ gas for a predetermined pause time (for example, 4 seconds). At this time, valves 43 and 44 are left open. For this reason, H ₂ gas and Ar gas are continuously introduced into the chamber 12.
[0024]
The control device 50 adjusts the exhaust speed of the pump 45 when shutting off the WF ₆ gas and the SiH ₄ gas. The controller 50 reduces the pumping speed of the pump 45 so that the pressure in the chamber 12 is maintained at about 30 Torr. This is to prevent the pressure in the chamber 12 from excessively decreasing due to the stop of the introduction of the source gas.
[0025]
When the pause time elapses, the control device 50 opens the valves 41 and 42 again, and introduces the WF ₆ gas and the SiH ₄ gas into the chamber 12 for the same time (for example, 3 seconds) as the previous introduction. The flow rate ratio of WF ₆ / SiH ₄ is the same as in the previous introduction. By reintroducing the source gas, the tungsten film is formed again on the surface of the contact hole 57.
[0026]
The control device 50 adjusts the exhaust speed of the pump 45 when re-introducing the source gas. The controller 50 increases the pumping speed of the pump 45 so that the pressure in the chamber 12 is maintained at about 30 Torr. This is to prevent the pressure in the chamber 12 from excessively rising due to the restart of the introduction of the source gas.
[0027]
When the source gas introduction time elapses, the control device 50 closes the valves 41 and 42 and shuts off the WF ₆ gas and the SiH ₄ gas for the same period of time (for example, 4 seconds) as the previous pause. During the current stop, the valves 43 and 44 are kept open, and H ₂ gas and Ar gas are continuously introduced into the chamber 12. As in the previous pause, the control device 50 reduces the exhaust speed of the pump 45 and keeps the pressure in the chamber 12 at about 30 Torr.
[0028]
As described above, in the present embodiment, the tungsten film is grown on the surface of the contact hole 57 by alternately introducing and blocking the source gas. The feed gas introduction time and the downtime for one time are preferably 2 to 5 seconds. Such intermittent introduction of the source gas is repeated an arbitrary number of times until a tungsten film having a desired thickness is formed. Meanwhile, Ar gas and H ₂ gas are continuously introduced into the chamber 12.
[0029]
According to the knowledge of the present inventor, the film forming rate at the bottom of the opening is improved by introducing the source gas intermittently. At the bottom of the opening, reaction by-products resulting from the chemical reaction of the source gas tend to stay. This is more conspicuous as the aspect ratio of the opening is higher. This reaction by-product seems to be preventing the film formation at the bottom of the opening. In this embodiment, since the source gas is intermittently introduced, the reaction by-product can escape from the opening while the introduction of the source gas is stopped. This improves the film formation speed around the bottom of the opening. Therefore, according to the method of the present embodiment, a tungsten film can be formed with excellent coverage on the surface of the opening having a high aspect ratio. The improvement in coverage is particularly noticeable in tungsten film formation at openings having an aspect ratio of 5 or more.
[0030]
The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.
[0031]
In the said embodiment, the tungsten film formation method of this invention is implemented using a thermal CVD apparatus. However, instead of this, another CVD apparatus such as a plasma CVD apparatus may be used.
[0032]
【The invention's effect】
In this invention, by introducing the source gas intermittently into the vacuum chamber, reaction by-products are easily removed from the bottom of the opening, and the film formation rate around the bottom of the opening is improved. Therefore, according to the present invention, even if the opening has a high aspect ratio, the tungsten film can be formed on the surface with excellent coverage.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a configuration of a CVD apparatus according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view showing a layer structure on a wafer before a tungsten film is formed.
FIG. 3 is a partial cross-sectional view showing a layer structure on a wafer after a tungsten film is formed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... CVD apparatus, 12 ... Vacuum chamber, 14 ... Silicon wafer, 16 ... Pedestal, 18 ... Gas distribution plate, 28 ... Gas mixing chamber, 31-34 ... Gas supply source, 41-44 ... Gas flow control valve, 50 ... Control device 52... Lower layer 54. Interlayer insulating film 56. Barrier layer 57. Contact hole 58. Tungsten film

Claims (6)

A method of forming a tungsten film by a chemical vapor deposition method on a surface of an opening having an aspect ratio of 5 or more included in a layer structure on a substrate,
A first step of introducing tungsten hexafluoride gas and monosilane gas as source gases into a vacuum chamber containing the substrate;
A second step of stopping the introduction of the tungsten hexafluoride gas and the monosilane gas and extracting the reaction by-product of the source gas from the opening having an aspect ratio of 5 or more ;
A third step of reintroducing the tungsten hexafluoride gas and the monosilane gas into the vacuum chamber, and forming a continuous tungsten film on the surface of the opening and on the upper surface of the layer structure.   The method of claim 1, wherein the second step comprises introducing an inert gas into the vacuum chamber.   The method of claim 2, wherein the inert gas is argon gas. The method of claim 1, wherein the vacuum chamber is evacuated so that the pressure in the vacuum chamber is maintained substantially constant during the first, second, and third steps.
The second step includes reducing the pumping speed of the vacuum chamber;
The method of claim 1, wherein the third step includes increasing the evacuation rate of the vacuum chamber. The method of claim 1, wherein the substrate is a silicon wafer . The layer structure has a lower layer made of a semiconductor or a conductor provided on the substrate, and an insulating film provided on the lower layer,
The method according to claim 1, wherein the opening extends from an upper surface of the insulating film to an upper surface of the lower layer or the vicinity thereof.

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