JP3082683B2 - Tungsten CVD film forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a tungsten CVD.
The present invention relates to a film forming method, and more particularly to a technology effective in a process of embedding a contact hole by a tungsten CVD method in a manufacturing technology of a semiconductor integrated circuit device.

[0002]

2. Description of the Related Art Conventionally, a refractory metal material such as tungsten has been used as a wiring material for a semiconductor integrated circuit device. Among them, there is a technique of forming a blanket tungsten film in a wiring of a semiconductor substrate or filling a contact hole connecting between wiring layers.

A blanket tungsten film is formed on the entire surface of a portion where a semiconductor integrated circuit is to be formed by a CVD method using WF ₆ and H ₂ as source gases, and then isotropically etched on the entire blanket tungsten film by a plasma etching method. I do. As a result, the contact hole can be buried with tungsten, and a low-resistance metal such as aluminum is deposited on the contact hole and patterned to form a semiconductor integrated circuit. Alternatively, there is a technique of directly patterning a blanket tungsten film. In this case, for example, in the case of a semiconductor integrated circuit having a contact hole having a diameter of 0.5 μm or more, the blanket tungsten film needs to have a thickness of at least the diameter in order to sufficiently bury the contact hole. If the film thickness is small, cavities (voids) are formed in the contact holes, and the connection resistance of the contact holes increases, which greatly affects the electrical characteristics of the semiconductor integrated circuit and the delay in processing time. Therefore, it is necessary to maintain a film thickness enough to completely bury the contact holes.

[0004] When a blanket tungsten film is formed to have a large thickness using such a conventional technique, the surface of the tungsten film becomes rough. This is because the blanket tungsten film forms tungsten nuclei in the initial stage, and tungsten crystals grow from the nuclei.
This is because the size of the crystal grains varies from one individual to another, and as the film thickness increases, the variation in crystal grain size increases. Due to such roughness of the surface of the tungsten film, a possibility that a residue of tungsten is generated when the tungsten film is removed by the etching method is increased. The residue due to this etching is not preferable because it leads to a short circuit between the wirings and to a reduction in the production yield of the semiconductor integrated circuit.

As a method for solving the above-described surface roughness of the tungsten film, as shown in FIG. 4A, during the formation of the tungsten film under the reaction rate-limiting condition of WF ₆ by the H ₂ reduction method, the SiH ₄ reduction is performed. law to form a tungsten or tungsten-silicon alloy (WSi _X) layer at a feed rate limiting conditions of WF ₆ by a method that prevents the grain growth of tungsten is disclosed in Japanese Patent Laid-Open No. 6-275624.

That is, in FIG. 4A, an insulating film 2 is formed on a main surface of a substrate 1, and an interlayer insulating film 3 provided with a contact hole 5 reaching a diffusion layer 10 is formed. A barrier metal 4 is formed from the upper surface of the interlayer insulating film to the inner surface of the contact hole, on which a W nucleation layer 6 and W by H ₂ reduction are formed.
Tungsten film 7 in the reaction rate-limiting conditions F _6, SiH ₄ reduction method by the supply rate-determining condition of tungsten or tungsten-silicon alloy of WF ₆ (WSi _X) layer 9 and tungsten in reaction rate-limiting conditions WF ₆ by H ₂ reduction method The films 7 are sequentially formed.

As another method, as shown in FIG. 4 (B), a tungsten film is formed by the H ₂ reduction method several times under the condition of WF ₆ reaction rate control, and several times by SiH ₄ or H _2.
Japanese Patent Application Laid-Open No. 6-29236 discloses a method in which a tungsten film is formed under a supply-limiting condition by a reduction method alternately every time, and a laminated film of a reaction-limiting film and a supply-limiting film is formed. I have.

That is, in FIG. 4B, an interlayer insulating film 3 provided with a contact hole 5 is formed on a substrate 1. Interlayer insulating barrier metal 4 from the upper surface of the film on the inner surface of the contact hole is formed, WF ₆ by H ₂ reduction method thereon
Plural Tungsten Films 7 and SiH
A plurality of tungsten films 9 and 8 are alternately and sequentially formed for each film under the supply-limiting condition by the ₄ or H ₂ reduction method.

Note that the supply rate-determining condition is a condition in which a film is formed by CVD in a relationship of (amount of material gas) <(energy required for the material gas to react: thermal energy in this case). This refers to a certain condition. In the case of tungsten, since the material gas is poor under this condition, abnormal growth of grains is suppressed, and a dense film having a uniform grain size is generated. On the contrary, the reaction rate-limiting condition means a condition in which (amount of material gas)> (energy required for the material gas to react), and in the case of tungsten, the material gas is Therefore, the grain growth varies (abnormal grain growth occurs), and the state of the film surface becomes very rough.

[0010]

However, FIG.
In the formation of a tungsten film by the SiH ₄ reduction method shown in FIG. 3A, since SiH ₄ is used as a reaction gas, an alloy of tungsten and silicon is formed, so that the specific resistance increases and the processing time of the semiconductor integrated circuit increases. There is a problem of delay.

On the other hand, the method shown in FIG. 4B is considered to be the most effective in suppressing the grain growth of tungsten. However, when changing from the reaction rate-limiting condition to the supply rate-limiting condition or vice versa, it is necessary to change the type of the reaction gas or the gas flow rate ratio. Requires at least several seconds to several tens of seconds. Therefore, in the method shown in FIG. 4B, the formation under the reaction rate-determining conditions and the formation under the supply rate-determining conditions are performed several times, respectively.

Accordingly, an object of the present invention is to provide a tungsten CVD film forming method capable of improving productivity without forming an alloy of tungsten and silicon which leads to an increase in specific resistance.

[0013]

A feature of the present invention is that a contact hole is provided in an interlayer insulating film on a substrate, and the contact hole is filled to form a tungsten film having a predetermined thickness on the interlayer insulating film. Forming a W nucleation layer by reducing WF ₆ with SiH _4, and forming a first W film on the W nucleation layer by H ₂ reduction under a WF ₆ reaction rate-determining condition. Completely filling and forming the contact hole; and forming WF ₆ on the first W film.
Forming a second W film by H ₂ reduction under a supply-limiting condition; and forming a third W film by H ₂ reduction under a WF ₆ reaction-limiting condition on the _second W film. And a tungsten CVD film forming method for forming a tungsten film having the predetermined thickness only from the W nucleation layer, the first W film, the second W film, and the third W film .

According to the present invention, H _{2 of} WF ₆ is used.
In the tungsten film formed under the supply-limiting condition by the reduction method, the progress of the tungsten grain growth is considered to be slow due to the shortage of WF ₆ gas, so that the brain size can be kept small. In addition, by changing the reaction rate-limiting condition to the supply rate-limiting condition only once, the time required for film formation can be shortened, and the inhibition of productivity can be suppressed.

[0015]

Next, an embodiment of the present invention will be described.

FIG. 2 is a view showing a tungsten CVD film forming apparatus. FIG. 2A shows a layout configuration.
(B) shows a deposition chamber (deposition chamber).

First, as shown in FIG. 2A, a wafer forming a semiconductor integrated circuit is transferred to a film forming chamber 13 to 15 through a load lock chamber 11 and an orientation flat (orientation flat) aligner 12.

As shown in FIG. 2B, the film forming chamber includes a wafer stage 16 for heating the wafer and a shower head 17 for supplying gas.

A reaction gas (WF ₆ , SiH ₄ ,
H ₂ ) are supplied from independent supply sources, mixed immediately before the shower head 17, and supplied to the wafer on the stage. 40 wafer stages to heat the wafer
The temperature is maintained at 0 to 500 ° C., and a tungsten film is formed on the wafer. Note that each of the film forming chambers has a similar function, and performs the same operation in each of the chambers. Further, each of the film forming chambers is provided with a vacuum exhaust port 18, which is evacuated, and the degree of vacuum in the film forming chamber is adjusted by the opening degree of a valve 19 provided in front thereof.

Next, a method of forming a tungsten film according to an embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1A, a silicon substrate 1
Alternatively, an insulating film and interlayer insulating films 2 and 3 are formed on the metal wiring 1. The insulating film 2 is formed only on the silicon substrate, and a thermal oxide film is formed by a thermal oxidation method. CV as interlayer insulating film 3
BPSG (Boro Phospho Si)
(Late glass) film is formed. Thereafter, a contact hole 5 is formed using a photoresist. At this time, since the silicon substrate or the metal wiring 1 under the opening is exposed, the barrier metal film 4 covering the opening of the insulating film 2 and the upper part of the interlayer insulating film 3 is formed by the sputtering method.

At this time, the barrier metal film 4 is preferably a titanium nitride film having a thickness of 150 to 160 nm in consideration of corrosion resistance and adhesion to a tungsten film formed thereon.

Next, a method for forming a tungsten film will be described. First, in order to form a nucleus of tungsten, a film formation pressure of 20 to 40 Torr and WF ₆ = 20 to 40 sccc
A W nucleation layer 6 for forming tungsten nuclei is formed under the conditions of m and SiH ₄ = 10 to 20 sccm. At this time, the nucleation of the tungsten film was performed at a film thickness of about 50 nm.

Thereafter, a tungsten film 7A, which is a first W film, is formed under the rate-limiting condition of WF ₆ for H ₂ reduction. In the embodiment of the present invention, the film forming pressure is 80 to 100 Torr, W
F ₆ = 90-100 sccm, H ₂ = 500-1000
The condition of sccm was used.

The film thickness of the WF ₆ reaction-limiting condition film by the H ₂ reduction method depends on the diameter of the contact hole to be buried. For example, when burying a contact hole having a diameter of 0.6 μm, a tungsten film thickness of 350 to 400 nm is required.

Next, as the second W film, a tungsten film 8 is formed by the H ₂ reduction method under the condition of controlling the supply of WF ₆ . The tungsten film 8 under the supply control condition is formed after the contact hole is buried with the tungsten film 7A under the reaction control condition.

In this embodiment, the film forming pressure is 80 to Torr.
_{r, WF 6 = 10~30sccm, H} 2 = 1500~2
Using a condition in the range of 000 sccm, a film thickness of about 50 nm
The tungsten film 8 is formed under the supply rate-determining conditions.

Thereafter, a first W film is further formed as a third W film.
About 50% of the tungsten film 7B under the same reaction control conditions as the film is used.
It is formed to a thickness of nm.

Next, the result of improving the smoothness of the tungsten film surface according to the present invention will be described with reference to the drawings. In the present invention, an oxide film is grown to 450 nm on a silicon wafer by a thermal oxidation method, and then a 150 nm titanium nitride film is deposited as a barrier metal film. Thereafter, a tungsten film was formed by the three methods of X, Y, and Z shown in Table 1 so as to have the same film thickness (500 nm).

X is the general prior art method, Y is the method of the present invention, and Z is the prior art method of FIG. 4B.

[0031]

[Table 1]

Next, the surface reflectivity (reflectivity) of the tungsten film formed by the above three methods was measured.

In general, the surface reflectance is used as an index indicating the roughness of the film surface. An Ar laser beam having a wavelength of 480 nm is perpendicularly incident on the wafer, and the surface reflectance is calculated from the intensity ratio of the incident wave and the reflected wave. , To measure the smoothness of the surface.

The comparison of the surface reflectivity of the tungsten film formed by the above three methods was performed using bare silicon (Bare S).
The relative surface reflectivity of each tungsten film with respect to bare silicon was calculated with the surface reflectivity of (i: silicon itself) being 1, and the value was used for comparison.

FIG. 3A shows the result. FIG. 3 (A)
From the surface reflectance of the tungsten film method was formed by Y in the present invention is slightly inferior to the surface reflectance of Tanguten film formed by the method Z of the prior art of FIG. 4 (B), the reaction of WF ₆ The reflectivity is much higher than the surface reflectivity of the tungsten film formed by the general method X formed only under the rate-determining condition, and it can be seen that the effect of smoothing the surface of the tungsten film is obtained.

After the tungsten film formed by the film forming method Y of the present invention was plasma-etched, the surface was observed by a scanning electron microscope. As a result, it was confirmed that no tungsten residue was generated.

Next, the required film formation time (Deposition Time) when a tungsten film having the same thickness is formed by the above three methods of forming a tungsten film is shown in FIG.
(B) shows.

FIG. 3B shows that the tungsten film forming method Z requires about 1.7 times as long a film forming time as the tungsten film forming method X in which the film is formed only under the reaction supply rate-limiting condition of WF _6. Is expected to decrease by about 45%. On the other hand, in the tungsten film forming method Y of the present invention, the decrease in throughput can be suppressed by about 15% as compared with the method X.

Referring to FIGS. 3A and 3B, when the smoothness and the throughput are comprehensively evaluated, the method Y of the present invention is the general method X of the prior art and the conventional method X of FIG. 4B. It turns out that it is more practical and superior to the technical method Z.

[0040]

The first effect of the present invention is that during the growth of the tungsten film by the H ₂ reduction method under the WF ₆ reaction rate-determining condition,
The surface of the tungsten film can be made smooth by interposing a tungsten film formed by the H ₂ reduction method under the condition of F ₆ supply control.

The reason is that the grain size of tungsten near the surface is reduced by hindering the grain growth of tungsten on the way.

The second effect of the present invention is that by using a tungsten film formed only by the H ₂ reduction method, an increase in the specific resistance of the tungsten film can be suppressed.

[0043] This is because it is possible to prevent alloying of tungsten and silicon when using SiH ₄ reduction method (WSi _X).

The third effect of the present invention is that the productivity is minimized by using only one tungsten film having a small grain size which is interposed during the growth of the tungsten film.

The reason is that the time required for changing the conditions can be minimized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a tungsten CVD film forming method according to an embodiment of the present invention in the order of steps.

FIGS. 2A and 2B are schematic diagrams of a manufacturing apparatus used in an embodiment of the present invention, wherein FIG. 2A shows a layout configuration, and FIG. 2B shows a film forming chamber.

3A and 3B are diagrams comparing the result of the method of the present invention with the result of the prior art method, wherein FIG. 3A shows the reflectance of the tungsten film surface due to the difference in the tungsten film forming method, and FIG. The film forming time depending on the method of forming the film is shown.

FIG. 4 is a sectional view showing a tungsten CVD film according to the related art.

[Explanation of symbols]

1 substrate 2 insulating film 3 interlayer insulating film 4 Pariametaru 5 contact hole 6 W nucleation layer 7, 7A, W film 9 by H ₂ reduction of the W film 8 WF ₆ supply-limited condition by H ₂ reduction of 7B WF ₆ reaction rate conditions W film by reduction of SiH _{4 under the} condition of WF ₆ supply control 10 Diffusion layer 11 Load lock chamber 12 Orifice aligner 13, 14, 15 Deposition chamber 16 Wafer stage 17 Shower head 18 Vacuum exhaust port 19 Throttle valve

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/28-21/288 H01L 21/44-21/445 H01L 29/40-29/51

Claims (1)

(57) [Claims] 1. A contact hole is formed in the interlayer insulating film on the substrate, the tungsten CVD film forming method for forming a tungsten film having a predetermined film thickness on the interlayer insulating film to fill the contact hole, WF SiH ₄ reduction of ₆
A step of forming a W nucleation layer, and the first W film by H ₂ reduction of WF ₆ reaction rate-limiting conditions on the W nucleation layer completely fills the contact hole formed by said first Forming a second W film on the first W film by H ₂ reduction under a WF ₆ supply-determining condition; and forming a WF ₆ on the second W film.
Forming a third W film by H ₂ reduction under a reaction-determining condition, wherein only the W nucleation layer, the first W film, the second W film, and the third W film are formed. Forming a tungsten film having a predetermined thickness.