JPH0225427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of forming a thin film of metal, metal compound, etc. using sputtering.

[Technical background of the invention and its problems]

As a technology for forming thin films using the sputtering phenomenon, gas ions generated by glow discharge of a rare gas such as Ar, Kr, or Xe are accelerated in a strong electric field region formed near a target, and the gas ions are Techniques are known in which a target material is sputtered and deposited on a substrate opposite the target. This sputtering can form metals and metal compounds on large-area substrates with a simple equipment configuration.
It is used in a wide range of fields, including corrosion-resistant, decorative, and other functional thin film coatings.

However, the quality of thin films formed by sputtering depends not only on the target material but also on the parameters of the glow discharge.
The current situation is that even at a practical level, accidents (low quality, lack of reproducibility, etc.) are caused by inadequate discharge parameters.

[Purpose of the invention]

In view of the above-mentioned points, the present invention makes it possible to uniformly form a dense, high-quality thin film over a large area with less incorporation of impurities and damage by specifying glow discharge conditions. The purpose of the present invention is to provide a method for forming a thin film.

[Summary of the invention]

The present invention firstly reduces the supply gas pressure P [torr] in the sputtering container to 0.5×10 ^-3 or more, 20×10 ^-3
The following shall apply. The lower limit is necessary to obtain a thin film with little damage, and the upper limit is a necessary condition to obtain a uniform thin film over a large area. Second, when the supply gas flow rate is Q [SCCM], the value of P/Q is set to 2×10 ⁻³ or less. This is an important condition for sufficiently reducing the incorporation of impurities into the formed thin film. Third, the atomic mass of the target
When M _T is the atomic weight of the supplied gas, M _G is the atomic weight of the supplied gas, and d [cm] is the distance between the target and the substrate, the conditions are set such that Pd≦(M _G +M _T ) ² /20 M _G M _T. This is important in obtaining a dense thin film. However, if Pd is too small, the discharge will become unstable, so the lower limit is set to 0.001. Furthermore, when the supplied gas is a multi-component gas, M _G is the sum of the atomic weight of each element x the atomic component ratio, and the same applies to M _T when the target is multi-component.

〔Effect of the invention〕

According to the present invention, by optimally designing glow discharge conditions, it is possible to obtain a dense, high-quality, and uniform thin film over a large area with less incorporation of impurities and damage to the thin film obtained by sputtering. .

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to the drawings. FIG. 1 is a schematic diagram of a parallel plate type sputtering apparatus used in carrying out the present invention. In the figure,
1 is a thin film forming container, 2 is an 8 inch diameter target, 3 is a 120 m diameter substrate, 4 is an RF power source, 5 is a gas supply system, and 6 is an exhaust system. With the above configuration,
After evacuating the container 1, operate the gas supply system to introduce gas into the container 1 at a constant flow rate, keep the gas pressure inside the container 1 constant, and then turn on the power source 4 to supply power to the target 2. Apply. As a result, a gas glow discharge is excited between the target 2 and the substrate 3, and a high electric field region called a cathode dark region is formed near the target. Gas ions during the glow discharge are accelerated in the direction of the target 2 in this high electric field region, collide with the target 2, sputter and release the target material, and the released particles are deposited on the substrate 3 placed opposite the target 2. It will be deposited as a thin film.

Using the above device configuration, as target 2
Two types of Fe and Tb are used with Ar gas as the supply gas.
Using two types of Xe gas, the pressure of the supply gas P,
An experiment was conducted in which a thin film was formed by varying the flow rate Q and the distance d between the target 2 and the substrate 3. Hereinafter, the usefulness of the present invention will be clarified with reference to the experimental data.

FIG. 2 shows data obtained by measuring the thickness distribution of the formed thin film. This is a combination of Fe target and Ar
Using gas, the gas flow rate Q is 24 [SCCM], the RF power is 300 [W], and the target-substrate distance d is 75.
[mm] and the gas pressure is 2 [mtorr] and 50 [mtorr]
Sputtering was performed for 10 minutes for two types of cases, and samples were formed with a radius of 3 [cm] on the substrate.
This is the result of measuring film thickness in the range of ~6 [cm].
The vertical axis in FIG. 2 is the film deposition rate (the value obtained by dividing the film thickness by the sputtering time), and the horizontal axis is the distance from the center of the substrate. As is clear from the figure, the film deposition rate is higher when the gas pressure is 50 [mtorr] than when it is 2 [mtorr], but the film thickness is significantly non-uniform at 50 [mtorr]. FIG. 3 shows data showing the relationship between deposition rate gradient and Ar gas pressure. The vertical axis in FIG. 3 is indicated by the slope of the straight line connecting the plot points in FIG. 2, and the smaller the numerical value in FIG. 3, the better the uniformity of the film thickness.

Depending on the application of the thin film, the uniformity of the film thickness may not be so important, but for example, an average film thickness of 1000 [Å]
Even in the case of loose specifications such as allowing a film thickness distribution within ±250 [Å] on a substrate with a radius of 5 [cm],
It is clear from Figure 3 that the gas pressure must be kept below 20 [mtorr]. The reason why the film thickness becomes non-uniform when the gas pressure is high is that the distribution of gas ion density during glow discharge becomes biased toward the vicinity of the central axis of the discharge as the gas pressure increases.

On the other hand, if the gas pressure is too low, the film deposition rate will decrease as described above. For example, under the same conditions as in Figure 2 except for the gas pressure, the gas pressure is 0.5
In the case of mtorr, the deposition rate is 50 [Å/min],
It is reduced to about 1/2 compared to the case of 2 [mtorr].
Furthermore, at lower gas pressures, the energy of gas ions incident on the membrane surface increases excessively, resulting in greater damage to the membrane.

For the reasons stated above, the gas pressure is set at 20 [mtorr] in order to form a thin film with a uniform thickness on a large area substrate.
In addition, in order to quickly form a film, it should be set to 0/5 [mtorr] or more.

Next, the relationship between gas pressure P and gas flow rate Q will be explained. The amount of leakage from the container in the normal thin film formation method is
10 ^-3 [mtorr・1/sec], which is
When converted to SCCM units, it becomes 7.9×10 ^-5 [SCCM]. When a process gas (in the case of the present invention, Ar, Kr, Ke, etc.) is flowed Q [SCCM] into a container with this degree of vacuum leakage and the pressure inside the container is maintained at P [torr], the impurity gas partial pressure Pc[torr] is (Q≫
7/9×10 ^-5 ), Pc=7.9×10 ^-5 P/Q [torr], and impurity gas particle density n _C [cm ^-2 sec ^-1 that is incident per second per unit area of the substrate] ] is n _C ≒3.54×10 ²⁰ ×Pc=2.8×10 ¹⁵ P/Q. On the other hand, the density of target particles incident per second per unit area of the substrate, n _T [cm ^-2 sec ^-1 ], is given by D [Åsec ^-1 ] for the film deposition rate and a [Å] for the atomic diameter of the target particles. , n _T ≈D×10 ¹⁶ /a ³ . a≒3[Å] and D≒2[Å]
sec ^-1 ], then n _T ≒7.4×10 ¹⁴ . In order to obtain a film with few impurities, n _T ≫ n _C must be satisfied. Ar as gas, Tb as target
A TbFe film was formed using a Fe mixed target (30% Tb) and changing P/Q with RF power of 300 [W]. As a result, P/Q≦2×10 ^-3 [torr/SCCM]
(N _C ≧1.1×10 ^-2 n _T ), whereas a perpendicularly magnetized film was obtained in the range of P/Q≧3×10 ^-3 [torr/SCCM]
In the range of (n _C ≧1.1×10 ^-2 n _T ), the influence of impurities was large and the film became an in-plane magnetized film. The allowable amount of impurities contained in the membrane varies depending on the use of the membrane, but according to the results of the above examples, the ratio P/Q of the process gas pressure P and the gas flow rate Q is 2×10 ^-3 [torr/ SCCM] or below.

FIG. 4 is a diagram showing actually measured data of the atomic number density of the film (corresponding to the density of the film). Gas is Ar
Two types of Xe were used, two types of targets were Fe and Tb, RF power was 300 [W], gas flow rate [SCCM],
A sample was formed with a target-substrate distance of 75 [mm], the mass of the film was measured by emission spectroscopy using inductively coupled plasma, and the atomic number density was calculated by dividing the mass by the volume of the film. To avoid errors due to film thickness gradients, the shape of the sample was a ring concentric with the substrate holder. In the combination of Ar gas and Fe target, the atomic number density of the film is 8.5×10 ²² [cm
^-3 ], but the density of the film decreases above 10 [mtorr]. In the Ar gas-Tb-target combination, the film electron number density is maintained at a value close to 3.1×10 ²² which is the density of bulk hexagonal Tb in a gas pressure range of 30 [mtorr] or less. Xe
For gas-Tb target combinations, gas pressure 10
The density of the film decreases above [mtorr].

In addition to target particles, particles that enter the substrate surface include sputter gas particles and impurity gas particles.
Among these, sputter gas particles have the highest incidence frequency. In order for the film to be dense, it is necessary for the target particles to repel the layer of sputter gas particles physically absorbed on the substrate surface or film surface when the target particles are deposited on the substrate surface, and to become a film constituent factor. For this purpose, it is necessary that the target particle has a certain amount of energy. The average energy of target particles when sputtering from the target surface is 10
[eV] is sufficiently large, but the sputtered particles collide with gas particles in the gas phase and lose energy before adhering to the substrate surface. The energy lost from spatter emission to the time it hits the substrate is:
It is given by the product of the number of collisions and the energy lost in one collision. The coefficient of energy lost in one collision is given by 2M _G M _T /(M _G + M _T ) ² using the atomic mass M _T of the target particle and the atomic mass M _G of the gas particle, and the number of collisions is given by the gas pressure P and the target-substrate distance d, Pd. Therefore, in order to obtain a dense film, Pd×2M _G M _T /(M _G +M _T ) ² must be smaller than a certain value, and from the above data, Pd≦(M _G +M _T ) ² /20M It can be seen that _{with GMT} , the density of the film is maintained at about 90% or more of the bulk.

On the other hand, if Pd is too small, disadvantages such as increased discharge start time and unstable discharge will occur, so the lower limit of Pd is 0.001 [torr cm]
The degree is appropriate.

As described above, by sputtering according to the set conditions of the present invention, it is possible to uniformly form a dense thin film over a large area with little damage or impurity incorporation.

Note that the present invention is based on the parallel average plate type described in the Examples.
Thin film forming methods are not limited to those using RF sputtering equipment, but include DC sputtering, magnetron sputtering, coaxial sputtering, multipolar sputtering,
It can be applied to all thin film forming methods that utilize sputtering phenomena, such as reactive sputtering.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a sputtering apparatus for explaining an embodiment of the present invention, FIG. 2 is a diagram showing the film deposition rate distribution of the formed thin film, and FIG. 3 is a diagram showing the film deposition rate gradient and gas pressure. FIG. 4 is a diagram showing the relationship between the atomic number density and gas pressure of a similarly formed film. 1...Thin film forming container, 2...Target, 3...
...Substrate, 4...RF power supply, 5...Gas supply system, 6
...exhaust system.

Claims (1)

[Claims] 1. A target and a substrate facing the target are placed in a container having a gas supply system and an exhaust system, and the target is sputtered onto the substrate by gas ions generated by glow discharge of the supply gas. In the method of forming a _{predetermined} thin film in
M _T , when the distance between the target and the substrate is d [cm], 0.5×10 ^-3 ≦P≦20×10 ^-3 P/Q≦2×10 ^-3 0.001≦Pd, and Pd≦(M _G +M _T ) ² /20M _G M _T A thin film forming method characterized by satisfying the following conditions.