JP2000178735A - Method of forming tungsten film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a tungsten film to reduce the specific resistance of the film. SOLUTION: When a tungsten film 50 is to be formed on the surface of the body W to be treated in a vacuum treating device, this method includes the following processes. The processes are, a seed crystal growing process to grow a tungsten seed crystal 48 on the surface of the body W in the presence of a film-forming gas containing a tungsten element, a boron exposing process to expose the treated body to an atmosphere of a gas containing boron in a short time after the first process, and a tungsten film forming process to grow the seed crystal to form a tungsten film in the presence of a film-forming gas containing a tungsten element. Thereby, the specific resistance of the tungsten film can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a tungsten film capable of improving specific resistance.

[0002]

2. Description of the Related Art In general, in a process of manufacturing a semiconductor integrated circuit, a wiring pattern is formed on a surface of a semiconductor wafer to be processed, or a hole between wirings is buried, or both of them are simultaneously formed. W to do
2. Description of the Related Art Thin films are formed by depositing metals or metal compounds such as (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), and TiSi (titanium silicide).

[0003] There are three methods of forming this kind of metal thin film, for example, H ₂ (hydrogen) reduction method, SiH ₄ (silane).
A reduction method, a SiH ₂ Cl ₂ (dichlorosilane) reduction method, and the like are known. The SiH ₂ Cl ₂ reduction method uses, for example, dichlorosilane as a reducing gas at a high temperature of about 600 ° C. to form a wiring pattern. And a method of forming a WSi (tungsten silicide) film using SiH ₄
The reduction method uses silane as a reducing gas, for example, to form a wiring pattern.
This is a method of forming a W or WSi film at a low temperature of about ° C.

In the H ₂ reduction method, a W film is deposited at a temperature of about 400 to 460 ° C. using hydrogen as a reducing gas, for example, to fill holes on the wafer surface such as holes between wirings. Is the way. 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, prior to the formation of a tungsten film,
For example, Ti /
A thin TiN film is formed in advance. Next, W is used as a film forming gas.
F ₆ , SiH ₄ , H ₂ , Ar, N _{2, and the} like are introduced into the film forming chamber, and a tungsten nucleus crystal is adhered to the surface of the barrier metal to be formed.

Next, after the inside of the film forming chamber is once evacuated to a base pressure to remove residual gas, Ar, H ₂ , N
₂ gas is supplied into the chamber to raise the pressure to the process pressure in a short time, and further, WF ₆ gas is supplied at a predetermined flow rate, and WF ₆ gas is reduced with H ₂ gas without using SiH ₄ gas. Then, for example, filling of holes and formation of a wiring layer are performed simultaneously.

[0006]

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 hole diameter. . 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 has been difficult to obtain a tungsten film having a sufficiently small specific resistance and conforming to a new design by the conventional method of forming a tungsten film as described above.

Therefore, as a method of solving the above problem, a boron-containing gas such as diborane (B ₂
Attempts have been made to add and introduce H ₆ ) into the chamber together with Ar or N ₂ gas, thereby increasing the tungsten crystal grain size and lowering the specific resistance. 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 them. 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 As a result of intensive studies on the method of forming a tungsten film, the present inventor has found that after forming a tungsten core crystal and immediately before forming a tungsten film, a semiconductor wafer is formed. By performing a borated surface treatment with a boron-containing gas, for example, diborane,
The crystal grain size can be increased during subsequent film formation,
Thus, the present invention has been accomplished by obtaining the above-mentioned knowledge. The invention defined in claim 1 is a method of forming a tungsten film on a surface of a target object in a vacuum processing apparatus in the presence of a deposition gas containing a tungsten element on the surface of the target object. A nuclear crystal growth step of growing a crystal, and after this step, a boron exposure step of exposing the object to be processed to a boron-containing gas atmosphere for a short time, and after this step, in the presence of a deposition gas containing a tungsten element. And forming a tungsten film by growing the nucleus crystal.

As described above, after the tungsten core crystal is grown and immediately before the tungsten film is actually formed, the object to be processed is exposed to the atmosphere of the boron-containing gas, whereby the tungsten core crystal is formed. By performing the boron surface treatment, the crystal grains (grains) of the tungsten film are increased during the subsequent film growth, and the specific resistance can be reduced. In this case, when 5% hydrogen-diluted diborane gas is used as the boron-containing gas as defined in claim 2, the flow rate is approximately 0.85 times the total gas flow rate.
% Or more. Thereby, the specific resistance value can be considerably reduced.

According to a third aspect of the present invention, 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for forming a tungsten film according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing a vacuum processing apparatus for performing the method of forming a tungsten film according to the present invention. First,
A vacuum processing apparatus for carrying out the method of the present invention will be described. The vacuum processing apparatus 2 has a processing container 4 formed into a cylindrical shape by, 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 on the upper surface of the reflector 6 via an L-shaped holding member 8.
Is provided. The mounting table 10 is made of, for example, a carbon material having a thickness of about several mm and an aluminum compound such as AlN.

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. Therefore, 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 to evacuate the processing container 16. 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.

On the other hand, a shower head portion 28 for introducing a processing gas or the like into the processing container 4 is provided at a ceiling portion of the processing container opposite to the mounting table 10, and an emission surface 28A of the shower head portion 28 is provided. Is provided with a large number of gas ejection holes 30. Gas inlet 3 of this shower head 28
2 is connected to a gas supply system for supplying a gas necessary for a film forming process or the like. Specifically, here, WF ₆ gas, Ar gas, SiH ₄ gas, and H ₂ gas are used 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. gas,
Each gas source of N ₂ gas and B ₂ H ₆ gas is connected.
A mass flow controller 34 as a flow controller and two open / close valves 36, 3
8 are provided so that the flow rate of each gas can be controlled and whether or not each gas is supplied can be selected.

As the borane-containing gas, diborane (B ₂
Although using H _6), where instead of using 100% concentration of diborane, the polymerized and hardened hydrogen in order to prevent the (H ₂₎ dilution of hydrogen concentration of 5% diluted concentration up to 5% gas 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.
Inch size wafers can be processed.

Next, the method of the present invention performed by using the above-configured apparatus will be described with reference to FIG. First, the gate valve 2 provided on the side wall of the processing container 4
6 is opened, the wafer W is carried 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 made of, for example, Ti / TiN is formed on the surface of the wafer W in the previous step. This barrier metal 40
It 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.

Next, W is used as a processing gas from each processing gas source.
F ₆ , Ar, SiH ₄ , H ₂ , N ₂ are supplied to the shower head 2
The mixture is supplied and mixed in a predetermined amount to the processing container 8, and the mixture is supplied substantially uniformly into the processing container 40 from the gas ejection hole 30 on the lower surface. Here, B ₂ H ₆ gas is not supplied. At the same time, the inside of the processing chamber 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 is driven while rotating the heating lamp 16 in the heating chamber 14. And radiates heat energy.

The emitted heat rays pass through the transmission window 12, and then irradiate the back surface of the mounting table 10 to heat it. The mounting table 10 is quickly heated because it is as thin as several mm as described above, 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. Then, 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.

After the nuclear crystal growth step has been completed in this way, the process proceeds to a boron exposure step. First, the supply of the reactive gas is stopped, and the base pressure is once set to, for example, 10 ⁻³ T.
A vacuum is drawn to about orr, and a boron exposing step is performed as shown in FIG. 2C while supplying a predetermined gas such as a B ₂ H ₆ gas and increasing the pressure to about 80 Torr. The supply gas species here are Ar gas, H ₂ gas and B gas.
₂ H ₆ gas, each gas amount is 4000 sccm, 1
800 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. The process temperature at this time is 4
The temperature is about 60 ° C., which is the same as the previous step.

After the boron exposing step has been 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 were respectively supplied at 80 sccm, 900 sccm and 750 s.
Ccm and 100 sccm are supplied, and an actual tungsten film is formed. Here, the supply of the SiH ₄ gas and the B ₂ H ₆ gas is stopped. The process pressure and the process temperature were the same as in the previous step, respectively, 80 Torr and 4
60 ° C. As a result, as shown in FIG.
At the same time as the hole 42 (see FIG. 2A) is buried, 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.

As described above, a boron exposure step is incorporated between the nuclear crystal growth step and the tungsten film formation step of actually forming a tungsten film, and the boron surface is formed by exposing the tungsten core crystal to, for example, diborane. By doing so, the grain size of the tungsten nucleus crystal (grain) grown in the subsequent step can be increased. For this reason, the crystal structure of the formed tungsten film 50 is close to that of a bulk crystal, and the specific resistance can be reduced.

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 by the conventional method is 12.2 μΩcm.
However, the resistivity (converted to 1500 °) of the tungsten film according to the method of the present invention was about 8.5 μΩcm, and it was found that the resistivity was significantly improved.

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, and is different from the conventional method shown in FIG. It is clear that the grain size of the tungsten nucleus crystal in the method of the invention 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 with the filling of the holes 42, and the filling state was as good as in the conventional method.

Further, in the method of the present invention, in the above-mentioned boron exposing step, B ₂ H ₆ gas having a hydrogen dilution
The gas flow rate is about 50 s
ccm or more, that is, approximately 0.85 with respect to the total amount of all gases.
% ($ 50x100 / (4000 + 1800 + 50))
The specific resistance is not so small. In this regard, FIG.
This will be described with reference to FIG. FIG. 4 shows B
5 is a graph showing the relationship between the flow rate of ₂ H ₆ gas (5% concentration) and the specific resistance (converted to 1800 °). Note that, as described above, the Ar gas flow rate and the H ₂ gas flow rate are each 4000 sc.
cm and 1800 sccm.

As is apparent 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 of the tungsten film is 11.3 μΩc.
m, the specific resistance becomes less than 11 μΩcm at 50 sccm or more. Therefore, the flow rate of the B ₂ H ₆ gas (hydrogen diluted 5% concentration) gas becomes
50 sccm or more (approximately 0.85% of the total gas flow rate)
It turns out that setting above is good.

Further, in the method of the present invention, since the gas as B ₂ H ₆ gas is used dilution gas diluted to 5% concentration with hydrogen gas, nitrogen gas B ₂ H ₆ gas as in the conventional method Ya Unlike the case of using a gas diluted with argon gas, B ₂ H ₆ gas does not polymerize in the gas source container or in the B ₂ H ₆ gas supply piping system, and the piping system is clogged with polymerized solids. Can also 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 a diluent gas and when H ₂ gas (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, so that 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 was substantially constant regardless of the number of days elapsed, and it was found that polymerization was not occurring and that the state was good. . this is,
It is considered that when N ₂ gas is used as the dilution base gas, it becomes molecularly unstable for B ₂ H ₆ .

It should be noted that the gas flow rate, process temperature, and process pressure in the above embodiment are merely examples,
Of course, it is not limited to them. Further, in this embodiment, B ₂ H ₆ gas of 5% concentration by hydrogen dilution is used. However, 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 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 a different size can be used. Further, the object to be processed is not only a semiconductor wafer, but also a glass substrate, LC
A D substrate or the like can also be used.

[0027]

As described above, according to the method for forming a tungsten film of the present invention, the following excellent operational effects can be obtained. 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 value 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 the relationship between the flow rate of B ₂ H ₆ gas (5% concentration) and the specific resistance.

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]

 Reference Signs List 2 vacuum processing apparatus 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 nucleus crystal 50 tungsten film W semiconductor wafer (workpiece)

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4K030 AA04 AA07 AA17 BA20 BA26 BB12 CA04 CA12 JA06 LA15 5F033 HH18 HH19 HH33 JJ01 JJ18 JJ19 JJ33 KK04 LL04 LL08 MM08 MM13 NN06 NN07 PP04 PP10 PP33 QQ00 QQ

Claims (3)

[Claims] When a tungsten film is formed on a surface of an object to be processed in a vacuum processing apparatus, a nucleus crystal of tungsten is grown on the surface of the object to be processed in the presence of a deposition gas containing a tungsten element. A nucleus crystal growth step, after this step, a boron exposure step of exposing the object to be processed to a boron-containing gas atmosphere for a short time, and after this step, the nucleus crystal is removed in the presence of a deposition gas containing a tungsten element. A tungsten film forming step of forming a tungsten film by growing the film. 2. The tungsten according to claim 1, wherein a hydrogen-diluted diborane gas is used as the boron-containing gas in the boron exposure step, and a flow rate of the diborane gas is about 0.85% or more with respect to a total gas flow rate. Film formation method. 3. The tungsten film according to claim 1, wherein the tungsten film forming step is a step of simultaneously burying holes formed in the surface of the object to be processed and wiring. Film formation method.