JP3422345B2 - Method of forming tungsten film - Google Patents

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, which stably forms an α-tungsten (hereinafter referred to as α-W) film having a low resistance phase in chemical vapor deposition of tungsten. .

[0002]

2. Description of the Related Art In recent years, in a film forming process by a chemical vapor deposition method in an LSI manufacturing process, a vacuum device such as a chemical vapor deposition device used in the process has been made higher in vacuum, and a gas supply pipe is It has less degassing such as the inner polishing tube. Further, the raw material gas itself has been highly purified, and the impurity concentration in the gas is becoming lower. For example, in the case of tungsten hexafluoride, which is one of the raw material gases for growing tungsten (W), the one with a purity of 99.99% (so-called 4N) has been commercially available until now, but now it is the same price. Purity 99.999% (5
N) has come to be easily available. As mentioned above, high vacuum, high cleanliness, and high purity (hereinafter collectively referred to as clean) show a seemingly desirable tendency, and in fact, in many cases, contribute to improving the quality of the grown film. is doing.

[0003]

On the other hand, however, it has become apparent that such a tendency may adversely affect the film quality of the film formed by the chemical vapor deposition method.
In other words, a film with a desired property, which was obtained by the existence of a small amount of leak (mixing of gas and liquid from the outside into the vacuum device) that had been neglected up to now, was removed by cleaning. There is a problem that it cannot be obtained because it is greatly reduced.

For example, in the process of growing W by the reaction of tungsten hexafluoride and silane, an internal polishing gas pipe is used, and an apparatus having a leak rate about one digit smaller than that of a conventional chemical vapor deposition apparatus is used. When W is grown to grow .beta.-W, the range of conditions under which .alpha.-W can be formed is significantly reduced by cleaning. W has two crystal phases, an α phase and a β phase, and a large difference lies in its resistivity. When the film is formed by the chemical vapor deposition method, the former is 13 μΩcm, and the latter is 100 μΩcm.
It becomes μΩcm or more.

When W is used as the electrode material of the LSI,
As a matter of course, α-W having a low resistivity is desirable. Craneing itself is an effective means for reducing dust, reducing heavy metal contamination, and reducing mobile ions, so returning it to a conventional chemical vapor deposition system or stopping the internal polishing gas piping is a good idea. is not.
Therefore, there is a problem that the film forming conditions for suppressing the appearance of the β phase as described above must be achieved by some means.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and the purpose thereof is to carry out β-deposition in the case of performing chemical vapor deposition of W under a cleaning facility.
It is an object of the present invention to provide a method for forming a tungsten film which can prevent the formation of W and stably form a low resistance α-W.

[0007]

[Means for Solving the Problems] In order to achieve such an object, the present invention is under the condition that β-W should be obtained when chemical vapor deposition of W is carried out under a cleaning facility. Even has tungsten hexafluoride, silane and hydrogen
A low resistance α-W is obtained by controlling a small amount of oxygen in the mixed gas and introducing it into the reaction chamber.

[0008]

In the present invention, tungsten hexafluoride, silica
By introducing a trace amount of oxygen into the mixed gas containing orchi and hydrogen, the growth of β-W is suppressed.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. Table 1 below shows the results of comparing the temperature dependence of the crystal phase of W grown in the case where W is grown while a small amount of oxygen is introduced into the reaction chamber and when oxygen is not introduced. .

[0010]

[Table 1]

A Si (100) wafer is used as the substrate,
Before W growth, it is treated with a mixed solution of hydrogen peroxide water and sulfuric acid for 5 minutes, then boiled in water for 10 minutes and washed with water for 10 minutes.
After treatment with buffered hydrofluoric acid for 30 seconds and washing with water for 10 minutes,
The one stored in the pre-reaction chamber kept at 1 × 10 ⁻⁷ Torr or less was used.

All the wafers are transferred from the pre-reaction chamber to the reaction chamber for growing W in a vacuum of 5 × 10 ⁻⁷ Torr or less, and the wafers once wet-cleaned are exposed to the atmosphere. Instead, it was transferred to the reaction chamber, and W was allowed to grow under predetermined conditions. Therefore, the effect of introducing oxygen, which will be described later, is not due to the oxidation during the transportation of the wafer, but is due to the effect of the oxygen introduced into the reaction chamber.

The growth of W in this embodiment is performed as follows. First, transfer the above-mentioned wafer into the reaction chamber,
After heating to the temperature shown in Table 1 above, 10 sccm of tungsten hexafluoride was introduced into this for 1 second at 3 mTorr as the first step, and exhaustion was repeated 3 times for 2 seconds. Is grown, and then, 5 sccm of silane, 10 sccm of tungsten hexafluoride and 50 sccm of hydrogen.
W was grown by introducing 0 sccm at a pressure of 0.1 Torr for 60 seconds.

This W film forming method has already been proposed by the present inventors in Japanese Patent Application No. 6-107438, and it has already been confirmed that a low contact resistance can be obtained. The confirmation of the α-W and β-W crystal phases was confirmed by X-ray diffraction and the film resistivity. Also, the oxygen used for introduction into the reaction chamber has a purity of 99.999.
High purity oxygen of 9% was used. Oxygen was continuously introduced during film formation. In addition, the amount of oxygen introduced was adjusted by a minute flow rate leak valve (variable leak valve). Also,
The amount of oxygen introduced was estimated using an ion gauge.

As shown in Table 1 above, when oxygen is not introduced, α-W can be grown in the temperature range of 300 ° C to
It is 330 ℃, β-W of high resistance phase at other temperature
Grows up. On the other hand, when a small amount of oxygen is introduced and the oxygen introduction amount is 1.5 × 10 ⁻³ Torr · l / s or more, the temperature range in which α-W can be formed over a wide range from 220 ° C. to 390 ° C. Further, when the introduced amount of 1.0 × 10 ⁻⁴ Torr · l / s becomes β-W at 220 ° C., at other temperatures, α-W can be grown up to 390 ° C.

The dependency of oxygen introduction amount clearly indicates that the introduction of oxygen is effective for the stable formation of α-W. Further, the appearance of the α phase and β phase is determined in the early stage of the film formation process, and once the growth of the α phase begins, the crystal phase of the film that continues to grow even if the introduction of oxygen is interrupted changes. It becomes α phase without doing. Therefore, in order to obtain α-W, it suffices to introduce oxygen at the initial stage of chemical vapor deposition.

By the way, it was confirmed from the film thickness measurement by fluorescent X-ray that the film thickness of W required for this initial growth is about 3 nm. Therefore, if oxygen is introduced only during the film formation of at least about 3 nm of W, α-W can be obtained, and thus the chemical vapor deposition method of W is not limited to the above-mentioned method.

In the above-described embodiment, the substrate is S
Although the i (100) wafer was used, the effect of oxygen introduction is not limited to this substrate, and the same effect can be obtained with any p ⁺ type or n ⁺ type Si substrate doped with impurities at a high concentration. The effect is obtained.

FIG. 1 shows that Si (10
0) The secondary ion mass spectrometry result of α-W formed on the wafer is shown in FIG. 2 as α-W formed without introducing oxygen (O).
The results of secondary ion mass spectrometry of Si (10
0) It is a figure explaining relative comparison of the amount of oxygen (O) in the tungsten (W) film grown on the wafer. As is apparent from FIG. 1, tungsten (W) formed by introducing oxygen (O) contains more oxygen (O) in the film. However, the resistivities of both are about 13 μΩcm, and there is no difference in their properties electrically.

Further, to manufacture a diode, contact resistivity in the case of forming the W electrode in the process of introduction of oxygen on a substrate doped with impurities at a high concentration, about the n ⁺ -type 1.
2 × 10 ⁻⁷ Ωcm ² and about 2.5 × 10 for p ⁺ type
It becomes ^-7 Ωcm ² and a good value can be obtained,
The contact characteristics were not deteriorated by introducing oxygen.

In the above-mentioned embodiment, the introduction of oxygen was carried out within the range shown in Table 1, but the amount of oxygen required for stable growth of α-W is to grow W. Since it depends on the degree of cleaning of the system, the introduction amount is not limited to the range shown by the inventors of the present application in Table 1 as can be easily guessed by those skilled in the art. Further, it goes without saying that the introduction method is not limited to the variable leak valve and may be controlled by using a mass flow controller.

The same effect can be obtained even when the introduced gas is an inert gas containing oxygen. In the study by the present inventors, for example, the mixing ratio of nitrogen and oxygen was set to 3: 1 and the introduction amount of this mixed gas was 9.0 × 10.
^{Even at −3} Torr · l / s, it was possible to grow α−W in a wide temperature range. Further, even a mixed gas of oxygen and argon or a mixed gas of oxygen and helium mixed in the same ratio was effective for the growth of α-W.

Further, the inert gas introduced together with oxygen is not limited to one kind as described above, and may be a mixed gas thereof, which is easily understood by those skilled in the art of the present invention. Can be inferred. As described above, when performing chemical vapor deposition of W under a system that has been cleaned, it is necessary to introduce a small amount of oxygen into the film formation reaction system in order to form α-W having a low resistance phase. It is extremely effective when used for.

[0024]

As described above, according to the present invention,
By introducing a small amount of oxygen during the chemical vapor deposition step of W, it is possible to suppress the growth of β-W and obtain a low resistance α-W in a wide range of growth conditions. Have.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a method for forming a tungsten film according to the present invention, in which oxygen content in a tungsten film formed by chemical vapor deposition when oxygen is introduced is measured by secondary ion mass spectrometry. FIG.

FIG. 2 is a diagram showing the amount of oxygen in a tungsten film formed by chemical vapor deposition when oxygen is not introduced in the method of forming a tungsten film, by secondary ion mass spectrometry.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-2-314 (JP, A) JP-A-3-31476 (JP, A) JP-A-4-125923 (JP, A) JP-A-59- 202629 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C23C 16/00-16/56 H01L 21/285 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A method of forming a tungsten film for an electrode of a semiconductor device, comprising: a mixture containing tungsten hexafluoride, silane and hydrogen.
The gas, adding oxygen or gas containing at least oxygen
Then, the tungsten film is formed by chemical vapor deposition . 2. The method for forming a tungsten film according to claim 1, wherein the gas is nitrogen, argon, helium or a mixed gas thereof.