JPH0647725B2 - Method for reducing internal stress in amorphous tungsten compound film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for reducing internal stress of an amorphous tungsten compound film deposited on a substrate.

Reducing the internal stress of a film deposited on a substrate and precisely controlling the internal stress to a predetermined value in the process of reducing the stress are especially essential techniques for manufacturing semiconductor integrated circuits and masks for X-ray lithography. The present invention realizes a method of reducing internal stress suitable for such a purpose of use.

[Prior Art] A film deposited on the surface of a substrate generally has a large internal stress. Conventionally, the reduction of the internal stress of a film has been performed by changing the deposition conditions at the time of deposition. For example, in high frequency (hereinafter referred to as rf) sputtering, the film stress has been reduced by changing the apparatus parameters such as sputtering gas pressure and rf power. In the plasma CVD method, rf power, reaction gas composition,
The film stress has been reduced by changing the apparatus parameters such as reaction gas pressure and substrate temperature during deposition.

However, the conventional method of reducing the internal stress of the film by changing the deposition conditions has the following drawbacks. First, it is difficult to obtain a film having a predetermined internal stress with good controllability and reproducibility. This is because it is difficult to optimize each of the parameters and to keep the deposition conditions constantly constant because there are multiple parameters that determine the deposition conditions. For example, in the thermal CVD method, the internal stress of the film is determined by the reaction gas composition and the deposition temperature, but it is very difficult to obtain a film having a predetermined stress while keeping these reaction conditions constant. In the plasma CVD method and the sputtering method, it is required to set the plasma state to be constantly constant. Setting the plasma state to be constantly constant includes gas composition, gas pressure,
It is nothing but keeping constant the deposition conditions such as the rf power and the deposition temperature. However, it is very difficult to keep these deposition conditions constant, and therefore it is extremely difficult to keep the plasma state constant. The fact that the plasma state is different also means that the reactive species in the plasma are different, which causes not only good internal reproducibility of the film but also good reproducibility of the film composition.

Secondly, when trying to obtain a film having a predetermined stress, a film having a predetermined film quality may not be obtained in the range of deposition conditions. That is, in order to obtain a film having a predetermined stress, it may be necessary to change the composition of the film or the film structure itself. An example of changing the film structure itself is a metal film deposited by a sputtering method. The sputtering method is widely used for depositing a metal film, and is almost the only method especially for a refractory metal film and its compound film. However, the metal film deposited by the sputtering method generally has a compressive stress, and in particular, the refractory metal film and its compound film often retain a large compressive stress. When the deposition conditions are changed to reduce the stress, the film structure often changes. For example, a tungsten nitride film in an amorphous state can be deposited by appropriately selecting the sputtering conditions, but the amorphous state film is 1 × 10 ¹⁰ dyn / cm ²
Has a large compressive stress. However, if the sputtering conditions are changed to reduce the stress, the film is crystallized and an amorphous film cannot be obtained.

The film stress can also be reduced by performing annealing after depositing the film. However, this method has poor controllability and requires a long time. Further, the film quality may be changed by annealing, which is not practical.

The film stress can also be reduced by ion irradiation at room temperature after the film is deposited. However,
This method has a drawback that the damage due to irradiation remains and the film stress is changed by applying heat after ion irradiation.

[Problems to be Solved by the Invention] As described above, since the conventional method controls the internal stress of the film depending on the film deposition conditions, the film stress cannot be reduced with good controllability. It also has a certain film quality,
Moreover, a film having a predetermined film stress is not always obtained.

An object of the present invention is to solve these drawbacks of the conventional method, to provide a method of reducing the film stress to a desired value with good controllability and reproducibility, and obtaining a film in which the stress is thermally stable.

[Means for Solving Problems] The present invention has been made in order to achieve the above-mentioned object, and heats accelerated ions to an amorphous Tungsten compound film deposited on a substrate. A method for reducing internal stress in an amorphous tungsten compound film, which comprises the step of irradiating below and using the same ion species as the constituent elements of the film as the ions.

Ion irradiation is performed by irradiating the deposited film with an ion beam. As the ion species of the beam, the same ion species as the constituent elements of the film are used in the sense that impurities are not mixed into the film. For example, in the case of a tungsten nitride film, it is desirable to select nitrogen ion (N ⁺ ).

In the present invention, ion irradiation is carried out under heating, and the temperature of the film during ion irradiation is preferably maintained at 200 to 550 ° C. by heating.

A specific example of the amorphous tungsten compound film to which the method of the present invention is applied is a tungsten nitride film deposited by a sputtering method, but other amorphous tungsten compound films can be similarly applied.

[Operation] The present invention is based on the fact that when a film having a large internal stress is subjected to ion irradiation while the temperature is raised by heating, the internal stress of the film is efficiently reduced.

FIG. 1 is a conceptual diagram of the present invention, and shows a situation in which a deposited film 2 formed on a substrate 1 is irradiated with an ion beam 3.
The ions irradiated into the film collide with the atoms forming the film, and in the process of losing energy, change the microscopic state in the direction of reducing the internal stress of the film. This action reduces the residual stress inside the film. At this time, since the film is heated at the same time, the microscopic state is changed rapidly. Therefore, the film stress can be efficiently reduced with a smaller irradiation amount, and the film stress can be provided with thermal stability. Such an effect cannot be obtained at all even if ion irradiation and heating are performed separately. Only when both of them are used together, a remarkable effect can be obtained. Since this action is physical, it can be widely applied to a film in which a large internal stress remains. Particularly effective is the case where the ion energy is selected so that the ion distribution becomes uniform in the film thickness direction. By selecting the energy of the ions in this way, the stress distribution in the film thickness direction can be made uniform.

The degree of stress reduction by the method of the present invention depends on the ion irradiation dose and does not depend on the ion current, as shown in Examples below. Therefore, the number of parameters required for reducing the film stress is one, and the ion irradiation amount is a precisely controllable amount, so that the stress can be accurately reduced.

By performing this method, the film stress can be reduced to a predetermined stress with almost no change in the film quality. This allows the deposition conditions to be selected to obtain optimum film quality. The stress may be reduced by irradiating ions with heating after obtaining a predetermined film quality. That is, it is possible to obtain a film satisfying both a predetermined film quality and a predetermined stress, which is difficult to obtain by the conventional method. Further, variations in film stress due to poor reproducibility of deposition conditions can be averaged by irradiating while heating. Further, it is possible to reduce the film stress while measuring the film stress.

Example An amorphous tungsten nitride film was formed on a Si substrate by rf sputtering. Sputtering gas is argon 39.0ss
cm (standard condition cc / min) and nitrogen 7.6 sccm were mixed and used. The sputtering conditions are rf power of 300 W and sputtering gas pressure of 5 mTorr. The deposition temperature is room temperature. The film thickness was 0.50 μm. Next, after cleaning the surface, an acceleration voltage of 400 keV and an ion current density of 1.0 μA / c
Irradiated with m ² of N ⁺ ions. The temperature at the time of film irradiation is 25
It was 0 degreeC, 300 degreeC, and 400 degreeC. As shown in FIG. 2, 1.07 × 10 ¹⁰ dyn / cm ² before ion irradiation.
As a result of ion irradiation of the film having the compressive stress of, the stress decreased sharply with the irradiation dose, and at 250 ° C., 7.0
× 10 ¹⁴ ions / cm ² , 4.0 × 10 ^{14 at} 300 ° C
ions / cm ² and 2.0 × 10 ¹⁴ ions at 400 ° C.
The film stress could be made zero at the irradiation dose of / cm ² . The film is not crystallized by ion irradiation. The current density of 400 keV N ⁺ ions was changed in the range of 0.1 to 2.5 μA / cm ² , but the stress after irradiation was not different from that at 1.0 μA / cm ² . .
Therefore, the above effect does not depend on the ion current density. The above effects could be similarly obtained when Ne ⁺ was irradiated. On the other hand, when N ⁺ ion irradiation with an accelerating voltage of 400 keV and an ion current density of 2.3 μA / cm ² is performed at room temperature, a larger irradiation dose is required to reduce the stress as shown in FIG. , 2.5 to remove membrane stress
An irradiation amount of × 10 ¹⁶ ions / cm ² or more was required. Further, a temperature of about 500 ° C. was required to reduce the stress as shown in FIG. 5 simply by heating without ion irradiation. At this time, if the heating temperature is changed, the internal stress of the amorphous tungsten film sensitively changes from compressive stress to tensile stress as shown in FIG. 5, so it is difficult to sufficiently remove the stress only by heating. It was Further, even if the heating was carried out for a long time of 5 hours or more, the film stress could not be reduced to 6.5 × 10 ⁹ dyn / cm ² or less simply by heating to 300 ° C. When ion irradiation and heating are used together as in this example, a remarkable effect that the internal stress can be reduced with good controllability with a small irradiation amount can be obtained.

Next, at 300 ° C., a dose of 4.0 × 10 ¹⁴ ions / cm ² of N
After irradiating ⁺ ions, the amorphous tungsten nitride film cooled to room temperature was further annealed at 300 ° C. Third
As shown in the figure, the film stress did not change even after annealing for 6 hours, and extremely excellent stress stability could be obtained by the method of the present invention. On the other hand, when the amorphous tungsten nitride film from which stress has been removed by irradiating 2.5 × 10 ¹⁶ ions / cm ^{2 of} N ⁺ ions accelerated to 400 keV at room temperature for 30 minutes, the stress as shown in FIG. Showed the change. Thus, even with heat treatment at 100 ° C. or less, 1 × 10 ⁹ dyn / c
A tensile stress of about m ² occurred. Especially, when the film is annealed at 300 ° C. for 30 minutes, the film stress is 4.0 × 10 ⁹
Since the tensile stress was increased to dyn / cm ² , it was not possible to obtain the stability of internal stress required for practical use.

The above results could be similarly obtained for other amorphous tungsten compound films deposited by sputtering.

[Effects of the Invention] As described in detail above, according to the method of the present invention, the film stress of an amorphous tungsten compound is hardly changed, and the film stress is controlled in the process of the reduction. be able to. Further, the thermal stability of film stress can be obtained. Since the film stress can be controlled by the ion irradiation dose that can be precisely set, the method of the present invention is excellent in reproducibility and in principle has high controllability.

For the above reasons, the method of the present invention has a remarkable effect when applied to a semiconductor integrated circuit and a mask for X-ray lithography, which require precise reduction of film stress and thermal stability of film stress. .

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing stress reduction of tungsten nitride, FIG. 3 is a diagram showing thermal stability of film stress of tungsten nitride, and FIG. 4 is tungsten nitride at room temperature. Fig. 5 shows the stress reduction when irradiated with 400 keV nitrogen or neon ions. Fig. 5 shows 400 kV at room temperature.
The change in stress when heat treatment was performed for 30 minutes at different temperatures for tungsten nitride irradiated with 2.5 × 10 ¹⁶ / cm ^{2 of} eV nitrogen ions and tungsten nitride not irradiated with ions was compared with the heat treatment temperature. FIG. In the figure, 1 ... Substrate 2 ... Deposited film 3 ... Ion beam.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Tatsuo MAMAKI “Basics of thin film production (2nd edition)” (Sho 59-7-30) Nikkan Kogyo Shimbun P. 94-96

Claims (2)

[Claims] 1. A step of irradiating an amorphous tungsten compound film deposited on a substrate with accelerated ions under heating, wherein the same ion species as the constituent elements of the film are used as the ions. Method for reducing internal stress in amorphous tungsten compound film. 2. The method according to claim 1, wherein the film is an amorphous tungsten nitride film and the ions are nitrogen ions.