JPH049866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of reducing internal stress in a film by implanting accelerated ions after the film has been deposited. Reducing the internal stress of a film and precisely controlling the internal stress to a predetermined value during the reduction process are essential technologies, especially for the production of semiconductor integrated circuits, masks for X-ray lithography, etc. The present invention realizes a stress reduction method suitable for such purposes of use.

[Prior Art] A film deposited on a substrate surface generally has a large internal stress. As a method of depositing the film,
CVD and sputtering methods are often used. Films deposited by these methods generally retain large residual internal stresses. Among the CVD methods, low-pressure and normal-pressure CVD methods cause deposition through a thermal reaction, so films deposited by these methods retain residual thermal stress in addition to the internal stress inherent in the film. Therefore, as a means of depositing the film,
Plasma CVD and sputtering methods, which allow deposition at low temperatures, are preferred. Depositing films at low temperatures is also necessary to maintain device properties.
However, even with these low-temperature deposition methods, it is inevitable that large internal stress inherent to the film remains in the film.

Conventionally, the internal stress of a film has been reduced by changing the deposition conditions during deposition. For example, in high frequency sputtering (hereinafter referred to as RF sputtering), film stress has been reduced by changing equipment parameters such as sputtering gas pressure and high frequency power (hereinafter referred to as RF power, etc.). In plasma CVD method, RF power,
Film stress has been reduced by varying equipment parameters such as reactant gas composition, reactant gas pressure, and substrate temperature during deposition.

However, the conventional method of reducing the internal stress of a film by changing the deposition conditions has the following drawbacks. The first problem is that it is difficult to obtain a film having a predetermined internal stress with good controllability and good reproducibility. This is because there are multiple parameters that determine the deposition conditions, and it is difficult to optimize each parameter and keep the deposition conditions constant. For example, in the thermal CVD method, the internal stress of the film is determined by the reaction gas composition and deposition temperature, but it is difficult to maintain these reaction conditions constant, so it is difficult to obtain a film with a predetermined stress. extremely difficult. In plasma CVD and sputtering methods, it is required to maintain a constant plasma state, but to meet this requirement, deposition conditions such as gas composition, gas pressure, RF power, and deposition temperature must be adjusted. must always be kept constant.
However, it is very difficult to keep these deposition conditions constant, and therefore it is extremely difficult to keep the plasma state constant. Fluctuations in the plasma state cause poor reproducibility of the internal stress in the film.

The second drawback is that when attempting to obtain a film with a predetermined stress, a film with a predetermined film quality may not be obtained within the range of deposition conditions. That is,
In order to obtain a film with a predetermined stress, it may be necessary to change the composition of the film or change the film structure itself. As an example of changing the film composition, when depositing silicon nitride (Si _x N _{y Hz} ) using the plasma CVD method, in order to obtain a film with low tensile stress, the composition must contain a large amount of Si. However, in this case, it is not possible to obtain a film having a composition close to stoichiometry (Si ₃ N ₄ ) and low tensile stress. Furthermore, an example of changing the film structure itself is a metal film deposited by a sputtering method. Sputtering is widely used for depositing metal films. However, metal films deposited by sputtering generally have compressive stress, and particularly high melting point metal films and films of their compounds often have large residual compressive stress. Changing deposition conditions to reduce stress often results in changes in film structure. For example, by appropriately selecting sputtering conditions, it is possible to deposit a tungsten nitride film in an amorphous state.
It has a large compressive stress of 10 ¹⁰ dyn/ ^cm2 . However, if sputtering conditions are changed to reduce stress, crystallization occurs, making it impossible to obtain an amorphous film.

Film stress can also be reduced by performing annealing after depositing the film. However, this method has poor controllability and is impractical because the annealing causes new changes in film quality and thermal distortion.

[Problems to be Solved by the Invention] As mentioned above, the conventional method controls the internal stress of the film by controlling the film deposition conditions, so it is not possible to reduce the internal stress of the film with good controllability. Can not. Further, with the conventional method, it is not always possible to obtain a film having a predetermined film quality and a predetermined internal stress. It is an object of the present invention to provide a method capable of eliminating the drawbacks of these conventional methods and reducing the internal stress of a film to a desired value at low temperatures with good controllability and reproducibility.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and according to the method for reducing internal stress of a film of the present invention, accelerated stress is applied to a film deposited on a substrate. The method is characterized in that the internal stress of the film is reduced by implanting ions and making the ions exist in the film.

The method of the present invention is applicable to all deposited films, and specific examples of such deposited films include tungsten films, tantalum films, tungsten nitride films, and tantalum nitride films deposited by sputtering. Examples include silicon nitride films and boron nitride films deposited by plasma CVD.

Ion implantation is performed by irradiating the deposited film with accelerated ions, and as the accelerated ion generator, for example, a Kotscroft-Walton type accelerator is generally used. Although the ion species at this time can be selected arbitrarily, it is preferable to select the same ion species as the constituent elements of the film in order to avoid contamination of the film with impurities.

[Operation] The present invention is based on the fact that when ions are implanted into a film having a large internal stress, the internal stress of the film is reduced.

FIG. 1 is a conceptual diagram of the method of the present invention, showing a situation in which a deposited film 2 formed on a substrate 1 is irradiated with accelerated ions 3. The ions implanted into the film collide with the atoms that make up the film, and in the process of losing energy, the microscopic state of the film changes in a direction that reduces the internal stress of the film. The internal stress of the film can be most effectively reduced by selecting ion implantation conditions such that the implanted ions are present in the film. This is because this effect is based on a physical mechanism, and energy is most effectively released just before the ions stop in the membrane, and the effect of changing the microscopic state of the membrane is large.
This action reduces the residual stress inside the film.

According to the method for reducing the internal stress of a membrane of the present invention, the internal stress of the membrane can be reduced to a predetermined value in both cases where the internal stress of the membrane is compressive stress and when it is tensile stress. . Since this effect is physical, it can be applied to a wide range of films that have large residual internal stresses. Particularly effective is the case where the ion energy is selected so that the ion emission energy distribution is uniform in the thickness direction of the film. By selecting the ion energy in this way, the internal stress distribution in the thickness direction of the film can be made uniform.

The process of internal stress reduction by the method of the present invention depends on the ion implantation dose and does not depend on the ion current.
Therefore, the only parameter required to reduce stress in the film is the amount of ion implantation, and since the amount of ion implantation can be precisely controlled,
Internal stress can be easily reduced precisely. Furthermore, since internal stress is reduced at low temperatures, thermal distortion does not occur.

By carrying out this method as well, the internal stress of the film can be reduced to a predetermined stress without substantially changing the film quality. Therefore, when forming a film, it is possible to select the deposition conditions necessary to obtain the optimum film quality. Then, after obtaining a predetermined film quality, the internal stress may be reduced by ion implantation. That is, according to the method of the present invention, it is possible to obtain a film that satisfies both a predetermined film quality and a predetermined stress, which have been difficult to obtain using conventional methods. Furthermore, variations in internal stress in the film due to poor reproducibility of deposition conditions can be averaged out by ion implantation. Furthermore, it is also possible to reduce the internal stress of the film while measuring the internal stress of the film.

[Example] (1) An amorphous tungsten nitride film was formed on a Si substrate by RF sputtering. The sputtering gas used was a mixture of 39.0 sccm of argon (standard condition CC/min) and 7.6 sccm of nitrogen. The sputtering conditions are RF power 300W and sputtering gas pressure 5m.
It's Torr. The deposition temperature is room temperature. The film thickness is
After cleaning the membrane surface at a temperature of 0.70 μm, an ion current with an acceleration energy of 400 keV was applied at room temperature.
10 μA of N ⁺ ions were implanted. As shown in Figure 2, as a result of ion implantation into a film that had a compressive stress of 1.07×10 ¹⁰ dyn/cm ² before ion implantation,
The stress decreases rapidly with the injection amount to 7.5×
It was possible to reduce the film stress to zero at an implantation dose of 10 ¹⁶ ions/cm ² or more. Ion implantation does not crystallize the film. The above effect could be obtained similarly when Ne ⁺ was injected.

(2) A tungsten film was formed on the Si substrate by RF sputtering. Argon was used as spatuta gas. The flow rate is 45.0 sccm. Spats condition is rf
The power is 500W and the sputtering gas pressure is 5mTorr. The deposition temperature is room temperature. The film thickness was 0.55 μm. Next, after cleaning the membrane surface, an acceleration energy of 400 keV and an ion current of 10 μA were applied at room temperature.
N ⁺ ions were implanted. As shown in FIG. 3, ions were implanted into a film having a compressive stress of 2.11×10 ¹⁰ dyn/cm ² before ion implantation, and the compressive stress could be reduced. The above results were also obtained when Ne ⁺ was injected.

(3) A tantalum nitride film was formed on the Si substrate by RF sputtering. Spatuta gas is argon
A mixture of 44.0 sccm and 2.4 sccm of nitrogen was used. The sputtering conditions were an RF power of 500 W and a sputtering gas pressure of 5 mTorr. The deposition temperature is room temperature.
The film thickness was 0.62 μm. Next, after cleaning the membrane surface, the acceleration energy was 400keV at room temperature.
N ⁺ ions were implanted with an ion current of 10 μA. Fourth
1.72× before ion implantation as shown in the figure.
By performing ion implantation into a film with a compressive stress of 10 ¹⁰ dyn/cm ² , we were able to rapidly reduce the compressive stress. The above results were also obtained when Ne ⁺ was injected.

(4) A tantalum film was formed on the Si substrate by RF sputtering. Argon was used as the spatuta gas. The flow rate is 45.0sccm. The spatuta conditions are
The RF power was 300W and the sputter gas pressure was 5mTorr. The deposition temperature is room temperature. Film thickness is 0.65μm
It was hot. Next, after cleaning the membrane surface, the acceleration energy is 400keV and the ion current is 10μA at room temperature.
N ⁺ ions were implanted. As shown in FIG. 5, ions were implanted into a film having a compressive stress of 1.38×10 ¹⁰ dyn/cm ² before ion implantation, and the compressive stress could be reduced. The above results were also obtained when Ne ⁺ was injected.

(5) An amorphous SiN film was deposited on a Si substrate by plasma CVD. The deposition conditions are
SiH ₄ 6.0sccm, N ₂ 90.0sccm, RF power 100W,
The deposition temperature was 200°C and the reaction gas pressure was 1.0 mTorr. The film thickness was 1.4 μm. Next, after cleaning the membrane surface, the acceleration energy was 400keV at room temperature.
Ne ⁺ ions were implanted with an ion current of 6 μA. 6th
3.38× before ion implantation as shown in the figure.
As a result of ion implantation into a film with a tensile stress ^of 10 ⁹ dyn/cm ² , the tensile stress rapidly decreased as ^the implantation dose increased; Internal stress 1.00×
It was possible to reduce it to below 10 ⁹ dyn/cm ² . The above results were also obtained when N ⁺ was injected. Similar results were also obtained with amorphous BN obtained by using B ₂ H ₆ gas instead of SiH ₄ gas.

[Effect of the invention] As detailed above, according to the method of the present invention,
It is possible to reduce the internal stress of the film at low temperatures without substantially changing the film quality, and to control the internal stress of the film during the reduction process. The method of the present invention includes:
Since membrane stress can be controlled by precisely setting the amount of ion implantation, it has excellent reproducibility and is theoretically highly controllable.

For the above reasons, the method of the present invention can be applied to semiconductor integrated circuits, masks for X-ray lithography, etc., which require precise reduction of film stress at low temperatures, to produce remarkable effects.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of the method of the present invention, Figure 2 is a diagram showing stress reduction in tungsten nitride in Example 1, Figure 3 is a diagram showing stress reduction in tungsten in Example 2, and Figure 4 is an example Figure 5 shows the stress reduction of tantalum nitride in Example 4.
FIG. 6 is a diagram showing stress reduction in tantalum in Example 5. FIG. 6 is a diagram showing stress reduction in silicon nitride in Example 5. 1...Substrate, 2...Deposited film, 3...Ion beam.

Claims (1)

[Claims] 1. Reducing the internal stress of a film, characterized by reducing the internal stress of the film by implanting accelerated ions into a film deposited on a substrate and causing the ions to exist in the film. Method. 2. A method for reducing internal stress in a film, characterized in that the accelerated ions according to claim 1 are ions of one of the constituent elements of the film.