JPH03240944A - Method and device for focusing target sputtering for forming thin aluminum film - Google Patents

Abstract

PURPOSE:To stably form an Al film in superthin sheet like state having extremely high purity and free from damage of film on the surface of a substrate by uniformizing the density of a columnar plasma between both targets at the time of forming a thin Al film on a substrate by a focusing target sputtering method. CONSTITUTION:At the time of forming a thin Al film on a substrate disposed in a position apart from a plasma by disposing two Al targets 1 in a manner to be opposed to each other, impressing vertical magnetic fields by means of permanent magnets 3 arranged on the peripheries of respective rear surfaces, and producing the plasma between both Al targets 1, permanent magnets 5 having a polarity reverse to that of the above permanent magnets 5 are disposed in the respective central parts of the rear surfaces of the Al targets 1 and respective spaces between these magnets 5 and the Al targets 1 are regulated, and, as a result, the distribution of magnetic fields is controlled and the magnetic field in the central part A is practically regulated to zero and plasma density is uniformized, by which self-sputtering is allowed to occur under low gase pressure and sputtering by means of Ar ions is minimized. By this method, the Al film free from Ar grains etc., having high purity, and extremely reduced in film thickness can be formed in a damage-free state on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a facing target sputtering technique, and more specifically, a facing target sputtering technique that can form a high-quality aluminum thin film with extremely few impurities and no film damage. Related to sputtering method and apparatus.

(Prior Art) In recent years, aluminum thin films have played an important role in various fields of electronic engineering, such as wiring for integrated circuits, thin film capacitors, display devices, surface acoustic wave filters, and thermal printers. Examples include wiring for heads, etc., and surface coatings for magneto-optical recording media, etc.
It is also required for research and development of ultra-thin light-transparent aluminum films.

For an aluminum thin film that can be used for such purposes, it is essential that it has excellent migration resistance against electromigration, stress migration, etc., and excellent contact characteristics. In addition, the film thickness ranges from micron order to half micron (0.5 μ■) order and even quarter micron (0.2 to 0.4 μ■).
m) Custom-made items are required.

In order to achieve this, the aluminum thin film must contain extremely few impurities, especially do not contain particles such as Ar, have good crystallinity, and be flat, hard, and dense without damage to the film surface. It is also necessary to have high productivity.

By the way, conventional methods for forming aluminum thin films include:
Magnetron sputtering was widely used. but,
In this method, electric discharge occurs between the substrate and the target, so the thin film deposited on the substrate is easily exposed to plasma and damaged by collisions with high-energy particles such as secondary electrons emitted from the target. . In particular, aluminum is a highly reactive metal and is easily affected by particle collisions, resulting in crystal defects and difficulty in achieving film surface flatness.

(Problems to be Solved by the Invention) In response to this problem, formation of an aluminum thin film by a facing target sputtering method has recently been attracting attention. According to this method, since the substrate is plasma-free and is not exposed to plasma, the film being deposited is not damaged, and the substrate is not bombarded by gamma electrons or negative ions, so it is possible to control the structure and properties of the film. The effect is remarkable when a substrate bias voltage for this purpose is applied. Since sputtering can be performed even at relatively low gas pressure, step coverage is also good.

The present inventors previously proposed a method for forming an aluminum thin film using the facing target sputtering method in Japanese Patent Application Laid-Open No.
No. 15365 was proposed.

However, the technology for forming extremely thin aluminum films of high quality as mentioned above is not always satisfactory, especially when high power is used for high-speed film formation. As a result, arcs are generated and the target surface is locally melted, which becomes splats and adheres to the substrate, resulting in a reduction in film quality.

In order to meet the above-mentioned demands, the present invention aims to provide a facing target sputtering technique that can form a high-quality aluminum thin film, especially an ultra-thin film, with extremely few impurities and no film damage.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have developed a method in which plasma is maintained between two targets in the facing target sputtering method to keep the substrate in a plasma-free state. Considering that controlling the plasma density distribution is extremely important since sputtering is performed using a magnetic field, we conducted extensive research on the state of the magnetic field distribution.

As a result, the conventional magnet arrangement produces a uniform magnetic field distribution, but the plasma density distribution does not.

The distribution is almost normal, and the generated plasma diffuses from the outer periphery, so the plasma density is low in the region with a large plasma radius, and the non-uniform plasma density makes it difficult to use particularly high power. When it is injected, an arc is generated locally on the target surface and splats fly to the substrate.

It was found that this had an adverse effect on the structure and properties of the substrate. Furthermore, since the atmospheric gas pressure cannot be lowered too much, impurities in the aluminum thin film deposited on the substrate cannot be effectively reduced, and a good quality thin film cannot be obtained.

Therefore, as a result of further research into ways to make the distribution of plasma density uniform, the present invention has been made.

That is, the present invention holds two targets (cathode) made of high-purity aluminum with a holder and makes them face each other.
In this method, a perpendicular magnetic field is applied by a permanent magnet placed on the back of the target to generate plasma between the targets, and a thin aluminum film is formed on a substrate placed in a plasma-free position. Aluminum thin film formation characterized by making the magnetic field at the center substantially zero and forming a magnetic field distribution that becomes stronger toward the outer periphery to make the plasma density uniform and self-sputtering under low gas pressure. This paper focuses on the facing target sputtering method.

In addition, in another aspect of the present invention, two targets (cathode) made of high-purity aluminum are held by a holder and made to face each other,
In facing target sputtering equipment, plasma is generated between the targets by applying a perpendicular magnetic field using a permanent magnet placed on the back of the target, and a thin aluminum film is formed on a substrate placed in a plasma-free position. A facing target type sputtering device for forming an aluminum thin film, characterized in that permanent magnets are arranged so that the magnetic field at the center of a cylindrical plasma is substantially zero, and the magnetic field distribution becomes stronger toward the outer periphery. This is a summary.

The present invention will be explained in more detail below.

(Example) FIG. 1 is a diagram showing the magnet arrangement and plasma generation state in a conventional facing target type sputtering apparatus.

Inside the vacuum chamber, first, a pair of targets 1 (cathode) made of high-purity aluminum are supported by a target holder. A permanent magnet 3 is placed on the back surface of the target 1 near its outer periphery.

These permanent magnets 3 have a symmetrical electrode structure so that they sandwich the target 1 and have opposite magnetic poles.

A shield ring is provided around the target.

With this configuration, plasma P is generated when the same voltage is applied to both electrodes to cause a glow discharge and the atmospheric gas (usually Ar) is ionized.

On the other hand, a perpendicular magnetic field is applied by the permanent magnet 3, but the magnetic field is formed in a shape (cylindrical; ECR mode) that becomes a mirror magnetic field (mirrortron), so a stable discharge is obtained and the γ electrons are generated in the plasma. Trapped inside.

Since the substrate 4 is placed outside the plasma, it is placed in a plasma-free state. Therefore, only sputtered particles (aluminum atoms) fly toward the substrate.

In the case of the facing target sputtering method, the electrons undergo a Larmor motion in front of the target surface, wrapping around the magnetic field, so that the electrons can be ionized quickly. Therefore, when the gas pressure is lowered, self-sputtering occurs. Self-sputtering is related to the input power and gas pressure, and occurs when the gas pressure on the target surface is approximately 10-3 to 10''Pa. However, when sputtering is performed under low gas pressure, sputtering due to argon is small, but Since the neutral particles that have been ejected are turned into positive ions by the electrons and hit the target, efficient sputtering is possible without increasing the gas pressure. Incidentally, under low gas pressure, there are more target material ions than Ar ions on the target surface, making it difficult for Ar ions to cause sputtering, which prevents Ar particles from recoil and flying toward the substrate. , the mixing of argon particles into the aluminum thin film is suppressed, and the crystallinity can be improved.

However, in the case of the above conventional magnet arrangement configuration.

Although self-sputtering can be expected because the gas pressure can be lowered to a certain extent, it is impossible to avoid localized arcing on the target surface, especially when a large amount of power is applied. Splash occurs and the aluminum thin film deposited on the substrate is not homogeneous. This problem is particularly noticeable in ultra-thin films. This also means that the target is not consumed uniformly.

After extensive research into the cause of these problems, it was discovered that they were caused by non-uniformity in plasma density. That is, in the conventional magnet arrangement, a uniform magnetic field can be obtained because the difference between the magnetic field at the center of the plasma and the magnetic field at the outer periphery is relatively small.

However, the distribution of plasma density is approximately normal, and although plasma is initially generated along this magnetic field distribution, it begins to diffuse from the outer periphery.

As a result, the plasma density inevitably becomes lower in the area where the plasma radius is large (the outer periphery), so the plasma density cannot be made uniform, and as a result, arcs are more likely to occur locally on the target surface. found.

In contrast, the present invention makes it possible to form a magnetic field distribution that does not cause such non-uniformity of plasma density.

Specifically, a magnetic field distribution is created in which the magnetic field at the center of the plasma is substantially zero and the difference between the magnetic field and the outer circumference is large. Such a magnetic field distribution can be easily obtained by adjusting the shape, dimensions, and arrangement of the permanent magnet, yoke (iron piece), and shield ring. It is also possible to adjust the thickness of the target.

The case of magnet arrangement is shown below.

FIG. 2 shows an example of the magnet arrangement. Note that since the electrode structure is symmetrical, only the lower half is shown.

First, as in the conventional case, a permanent magnet 3 is placed on the back surface near the outer periphery of the target. However, this alone does not provide a uniform plasma density as described above. Therefore, another permanent magnet 5 is further arranged near the back surface of the central portion of the target 1 so as to have a magnetic pole opposite to that of the magnet 3. When this permanent magnet 5 is placed close to the back surface of the target, the magnetic field lines from the magnet 3 placed on the outer periphery are absorbed greatly, so it is possible to make the magnetic field of the target material, that is, the central part A of the plasma, close to zero. be. By changing the distance between the magnet 5 and the target 1, the attraction becomes weaker as the magnet 5 is moved away from the target.

It is possible to control the rate of attraction of magnetic lines of force, that is, the magnetic field distribution. However, if you move it further away so that most of the magnetic field lines are directed toward the opposing target.

The magnetic field in the central part A of the plasma does not become very weak, and the magnetic field distribution becomes the same as in the conventional case, so it should be avoided.

FIG. 3 shows another magnet arrangement, in which another permanent magnet 6 is arranged outside the target. This causes lines of magnetic force directed from the outer circumference of the target toward the opposing target (i.e.

Since the magnetic field at the outer circumference can be strengthened, the magnetic field at the plasma center A can be made substantially zero. The thickness of the permanent magnet 3 near the back surface of the target may be reduced to about 173 mm, or the shield ring 2 may be provided as shown in the figure.If the target 1 is rectangular (postcard-shaped), the opening of the shield ring may be It is also a good idea to round off the corners.

Of course, it is possible to obtain a desired magnetic field distribution by appropriately combining the magnet arrangement configurations shown in FIGS. 2 and 3.

Note that it is desirable that at least the shield ring 2 be made of aluminum; of course, the entire device can also be made of aluminum. This completely prevents impurities from entering the aluminum thin film.

An example of specifications when forming an aluminum thin film by the facing target sputtering method with the above configuration is shown below.

Target material Nialuminum (purity 99.999%) Dimensions: 100#X7t (a
(Peng) Substrate Ultimate gas pressure of vacuum chamber such as glass, Si wafer, etc.: <4. OX 10-'Pa atmospheric gas pressure PAr: 1.3XlO-2~9, OX 10'''1
Power source: DC power source, high frequency power source (substrate bias) Deposition rate: 150 to 1800 8/10 Next, the facing target sputtering method will be explained.

As long as the above-mentioned magnetic field distribution can be obtained, the following embodiments are possible.

■ First, since sputtering can be performed under low gas pressure, self-sputtering is possible.

As shown in Fig. 4, the lower the gas pressure, the higher the specular reflectance of the aluminum thin film, and as shown in Figs. However, an aluminum thin film with high specular reflectance can be obtained. In other words, as shown in FIG. 7, a high quality aluminum thin film with high specular reflectance and an extremely thin film thickness can be formed by lowering the gas pressure.

(2) It is also possible to apply a low substrate bias.

In other words, in the conventional two-pole sputtering method and magnetron sputtering method, the self-bias applied to the substrate from the beginning is greater than minus several volts, and it is impossible to apply a minute substrate bias. It was impossible to form a film. In addition, even in conventional facing target type sputtering equipment, a bias effect can be obtained by applying a substrate bias of about -100V to -200V by taking advantage of its unique plasma-free substrate arrangement. For example, it is possible to apply a smaller bias than this, and even a very small bias (for example, -3V to -5V) to a large-area substrate. Therefore, the crystallinity of aluminum is improved, hardness is obtained, step coverage is improved and flattened, and particle size can be controlled very easily. It is possible to apply a bias such as DC bias and use an insulating substrate, so it is possible to increase the diameter of the substrate.
Alternatively, since it can be heated (cooled), it is easy to control the temperature. FIG. 8 shows that an aluminum thin film with high specular reflectance can be formed by reducing the substrate bias voltage.

Of course, good results can be obtained without applying a substrate bias, but the above-mentioned effects can be obtained by applying a substrate bias.

■ Also, microwave assist is possible.

In the case of facing target sputtering, the plasma is held between two targets, so by injecting microwaves into the plasma mass and heating mainly the electrons, ionization is dramatically promoted. Capable of generating large-capacity, high-density plasma. Therefore, high-speed film formation is possible. When microwaves are irradiated, there are more negative-like portions of magnetic lines of force than in the magnetron sputtering method, which is advantageous in that the resonance region can be widened. It can also be expected to have a cleaning effect inside the vacuum chamber.

Furthermore, since this is the conventional facing target sputtering method with uniform plasma density, the following effects can be expected.

If the gas pressure is kept low and the substrate bias voltage is made very small, the crystallinity can be significantly improved as shown in FIG.
) A crystal with orientation can be obtained.

Forming a thin film under low gas pressure increases specular reflectance and improves surface properties (see Figure 10).

Even with the same film thickness, the resistivity can be lowered by lowering the gas pressure (see Figure 11).

Moreover, the thin film deposited on the substrate has uniform crystallinity (Fig. 12) and uniform hardness (Fig. 13) at any position.
, a uniform resistivity (FIG. 14) is obtained.

In particular, the desired crystal orientation (111) can be obtained, which is advantageous in terms of strength, uniform etching properties, and migration resistance. Furthermore, since it contains extremely few impurities and is free of Ar particles, it has excellent migration resistance. Therefore, a high-quality aluminum thin film can be formed on a large-sized substrate.

In addition, since the target surface wears out uniformly in both the central and peripheral areas, large and thick targets can be used, and the effort of adjustment such as target replacement can be saved, resulting in good workability and high productivity.

(Effects of the Invention) As detailed above, according to the present invention, self-sputtering can be performed at low gas pressure under uniform plasma density in facing target sputtering.
A high quality aluminum thin film with very few impurities and no film damage can be formed.

In particular, ultra-thin films of half micron or quarter micron can be obtained. It also has high productivity, and therefore has a significant effect in various applications.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are diagrams showing the magnet arrangement and plasma generation state of a conventional facing target type sputtering apparatus. FIG. 2 and FIG. 3 are diagrams showing an example of the magnet arrangement configuration in the one-facing target type sputtering apparatus according to the present invention.
Figures (a), (b), and Figure 3 are examples of the present invention, Figure 2 (C) is a comparative example, and Figures 4 to 6 are the specular reflectance of the aluminum thin film, the gas pressure, and the film. A diagram showing the relationship between thickness, FIGS. 7 and 8 are diagrams showing the relationship between the reduction rate of specular reflectance and film thickness or substrate bias voltage, and FIG. 9 is a diagram showing the relationship between crystallinity and substrate bias voltage. Figure 10 is a diagram showing the dependence of film surface properties and specular reflectance on film thickness, Figure 11 is a diagram showing the relationship between film resistivity and gas pressure, and Figure 12 is a diagram showing the relationship between film resistivity and gas pressure.
The figures show the substrate position dependence of (111) plane spacing, crystal size, and (111) plane orientation dispersion, Figures 13 and 1.
FIG. 4 is a diagram showing the relationship between Knoop hardness or resistivity and substrate position. 1...Target, 2...Shield ring, 3.5
．． 6...Permanent magnet, 4...Substrate.

Claims (9)

[Claims] (1) Two targets made of high-purity aluminum (
In this method, a thin aluminum film is formed on a substrate placed in a plasma-free position by holding two cathodes (cathode) in a holder and facing each other, applying a perpendicular magnetic field using a permanent magnet placed on the back of the target to generate plasma between the targets, and forming a thin aluminum film on a substrate placed in a plasma-free position. , the magnetic field at the center of the cylindrical plasma confined between the targets is made virtually zero, and a magnetic field distribution that becomes stronger toward the outer periphery is created, thereby making the plasma density uniform, and under low gas pressure. A facing target sputtering method for forming aluminum thin films characterized by self-sputtering. (2) The method according to claim 1, wherein a low substrate bias is applied. (3) The method according to claim 1 or 2, wherein microwaves are introduced into the plasma. (4) Two targets made of high-purity aluminum (
A facing target in which a permanent magnet placed on the back of the target applies a perpendicular magnetic field to generate plasma between the targets, forming a thin aluminum film on a substrate placed in a plasma-free position. In a type sputtering apparatus, permanent magnets are arranged so that the magnetic field at the center of the cylindrical plasma confined between targets is substantially zero, and a magnetic field distribution that becomes stronger toward the outer periphery is formed. Opposed target sputtering equipment for forming aluminum thin films. (5) The apparatus according to claim 4, wherein the permanent magnet is arranged on the back surface near the outer periphery of the target, and the opposite magnetic pole is arranged on the back surface near the center of the target. (6) The apparatus according to claim 5, wherein the magnetic field distribution can be controlled by changing the distance between the magnetic pole placed near the center of the target and the target. (7) The apparatus according to claim 5, further comprising a permanent magnet arranged outside the target. (8) The device according to claim 5, wherein at least the shield ring is made of aluminum. (9) The apparatus according to claim 5, further comprising means for injecting microwaves into the plasma.