JPH0138871B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is a method for forming a desired layer on a substrate by a physical vapor deposition method (hereinafter abbreviated as PVD) using ionized particles such as an ion plating method or an ion beam method. This invention relates to a thin film production method for producing a thin film.

Conventional configurations and their problems In general, the PVD method has various advantages as a dry plating technology, such as non-pollution and workability, and is known as a thin film production technology that is applied in many industrial fields. Among these, the method of generating particles by ionizing them has attracted attention as a thin film generation method with many advantages and characteristics in terms of adhesion strength to a substrate, film quality, etc., and has been put into practical use. In the thin film produced by such a method, internal stress is generated due to various factors such as lattice defects, surface tension, and phase dislocation. Furthermore, it is known that the strength and direction of this internal stress vary depending on the material and thickness of the produced film, as well as the production conditions. When a thin film containing such stress is used, there is a problem in that the stress balance is lost due to external force or heat, resulting in phenomena such as deformation, cracking, and peeling of the thin film. Therefore, in order to prevent the occurrence of such problems, methods for reducing residual stress by examining thin film production conditions and by annealing after production have been considered. on the other hand,
It is being considered to actively utilize residual stress depending on the application of the thin film. For example, the sputtering method is used in applications where residual stress in the produced thin film is effective. This is because compressive stress ultimately remains in the thin film produced by the sputtering method. However, even after thin film formation conditions and post-formation annealing, the stress remaining in the thin film is determined by the material and production method, so it is difficult to obtain a thin film with arbitrary residual stress characteristics. This was extremely difficult.

Purpose of the Invention The present invention solves these conventional drawbacks, and provides a thin film production method that can control the residual stress generated in the thin film produced on a substrate and obtain a thin film with a desired residual stress. The purpose is to provide

Structure of the Invention The thin film production method of the present invention limits the ionic valence of ions incident on the substrate during the production of the thin film when producing a desired thin film on a substrate by a PVD method using ionized particles. The impact energy of the ions is made uniform. According to this method, the vector and strength of the residual stress accumulated in the thin film formed on the substrate can be controlled by the electric field strength applied to the substrate, so the direction and amount of the residual stress can be controlled arbitrarily. It has the advantage that a thin film having desired residual stress properties can be obtained. Here, the mechanism by which the residual stress of the produced film is controlled by changing the valence of the ions and the amount of kinetic energy of the ions is thought to be due to the following effects. One of these is the depth at which ions are embedded into the formed film due to the kinetic energy of the ions entering the formed film, and the damage inflicted on the formed film changes with the film thickness, and its distribution affects the directionality of the formed film as a whole. show.
In addition, most of the energy of ion bombardment is dissipated as heat, so if we consider the surface of the formed film from a microscopic perspective, the part that receives ion bombardment will receive thermal shock with a very high energy density, and the thin film This is equivalent to performing annealing simultaneously during the generation of . By limiting the ionic valence of the ion particles, the impact energy of the ions is determined by the electric field strength applied to the substrate, and the amount and direction of residual stress are determined by the annealing effect caused by constant energy being applied to the substrate. is assumed to be determined.

In addition, when controlling residual stress according to the present invention, the ion valence of the ions is a problem, but at the same time, the control effect changes depending on the mass of the ions, the energy at the time of incidence on the substrate, the amount of ions, etc., so the ionization method, The control range is limited by the generation conditions, generated substances, substrate material, shape, etc.

Next, control of the ion valence of evaporated particles, which is the gist of the present invention, will be explained along with the principle of the ion plating method used.

FIG. 1 shows a diagram of the principle of the plating device.
In FIG. 1, the gas pressure inside the apparatus is maintained at about 10 ^-5 Torr, but at the very surface of the evaporation source 4, the gas pressure rises to approximately the saturated vapor pressure of the evaporation material.
Further, during evaporation of the evaporation material, thermoelectrons, secondary electrons, etc. are emitted from the evaporation source 4 together with evaporation particles. When a positive DC electric field is applied to the thermionic accelerating electrode 3 in this state, electrons emitted from the evaporation source 4 are accelerated and enter the thermionic accelerating voltage. Since the electrons accelerated in this way move through a gas pressure of the order of 10 ^-1 to 10 ^-3 Torr, there is a high probability that they will collide with the evaporated particles and ionize the particles, but the ion valence of the evaporated particles will accelerate. Since it is determined by the kinetic energy of electrons, the ion valence of the ionized particles can be changed by controlling the DC electric field applied to the thermionic accelerating electrode 3. When the evaporator is boron, the first ionization potential is 8.3eV and the second ionization potential is 25.1eV. However, in reality, it is said that sufficient ionization is not achieved unless an energy of about 2 to 3 times the ionization potential is applied.

In addition, in Fig. 1, 1 is a bell gear, 2 is a substrate, and 3
4 is a thermionic accelerating electrode, 4 is a crucible, 5 is an electron beam gun, 6 is a thermionic accelerating power source, and 7 is an ion accelerating power source (substrate voltage source).

Description of examples Examples of the present invention will be described below.

Example 1 Using the DC ion plating apparatus shown in Fig. 1, the EB output was
Boron was evaporated with 7KW and sweep O (7KW-1 in Figure 3). At this time, the gas pressure is 1~3×
10 ^-5 Torr, +25V applied to thermionic accelerating electrode 3,
A voltage of -1.0 kV was applied to the substrate 2, and a 20 μm thick boron film was formed on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Example 2 Using the DC ion plating apparatus shown in Figure 1, an electron beam evaporation source was used to
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +25V is applied to the thermionic accelerating electrode 3, and the substrate 2
-1.2 kV was applied to form a 20 μm boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Example 3 Using the DC ion plating apparatus shown in Fig. 1 and using an electron beam evaporation source,
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +25V is applied to the thermionic accelerating electrode 3, and the substrate 2
A voltage of -1.5 kV was applied to form a 20 μm thick boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Comparative Example 1 Using the DC ion plating apparatus shown in Figure 1 and using an electron beam evaporation source,
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +70V is applied to the thermionic accelerating electrode 3, and the substrate 2
-0.1 kV was applied to form a 20 μm boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Comparative Example 2 Using the DC ion plating apparatus shown in Fig. 1, an electron beam evaporation source was used to
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +70V is applied to the thermionic accelerating electrode 3, and the substrate 2
-0.5 kV was applied to form a 20 μm boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Comparative Example 3 Using the DC ion plating apparatus shown in Figure 1, an electron beam evaporation source was used to
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +70V is applied to the thermionic accelerating electrode 3, and the substrate 2
A voltage of -1.0 kV was applied to form a 20 μm thick boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Comparative Example 4 Using the DC ion plating apparatus shown in Figure 1, an electron beam evaporation source was used to
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, +70V is applied to the thermionic accelerating electrode 3, and the substrate 2
A voltage of -1.5 kV was applied to form a 20 μm thick boron film on the titanium substrate 2 at a deposition rate of about 1 μm/min.

Comparative Example 5 Using the DC ion plating apparatus shown in Figure 1, an electron beam evaporation source was used to
Boron was evaporated in a gas pressure of 10 ^-5 Torr. At this time, no electric field was applied to the thermionic accelerating electrode 3 substrate 4, and a 20 μm boron film was formed on the titanium substrate 2 by vacuum evaporation at a deposition rate of about 1 μm/min.

The concentration of substrates treated according to Examples and Comparative Examples
A titanium substrate was etched off by immersing it in a 0.5wt% hydrofluoric acid solution, and the shape (amount of warpage) of the boron film formed on the substrate was evaluated. The results are shown in FIG. The amount of warpage is compressibility (concave on the board side) + tensile property (convex on the board side)
is displayed as -.

As shown in Fig. 2, in this example, there was a correlation between the voltage applied to the substrate and the amount and direction of stress (warp) remaining in the produced film, and the residual stress was determined by the voltage applied to the substrate. It can be seen that it is possible to control the
However, the changes in residual stress in Comparative Examples 1 to 3 exhibit random behavior in response to changes in the voltage applied to the substrate, and the strength of the residual stress is also higher than in Examples, simply due to the acceleration energy of ions. Even if the stress is changed, it is impossible to control the stress.

This is thought to be due to the annealing effect that occurs when ionized particles collide with the substrate or coating, and their kinetic energy is converted into heat.

Therefore, in order to obtain a uniform annealing effect, particles with a constant ionic valence are easier to control because they exhibit simpler phenomena and changes, and the lower the ion valence, the less thermal energy is converted during ion bombardment. ,
Effective for gentle annealing.

That is, when boron B is used as the evaporation material as described in Examples and Comparative Examples, it is said that the first ionization energy of boron is 8.3eV and the second valence ionization energy is about 25eV. In the ion plating apparatus shown in FIG. 1, when we examine the relationship between the voltage applied to the thermionic accelerating electrode 3 and the ion current flowing from the substrate 2 to the ion accelerating power source 7 to ground due to the incidence of ions, we find that As shown in Fig. 3, the voltage applied to the lowest thermionic accelerating electrode 3 through which the ion current flows (the evaporated particles are ionized) is approximately 35V. This means that the kinetic energy of thermionic electrons required for actual ionization is approximately three times the ionization energy described above, and the conditions shown in the example are those in which the evaporated particles are ionized to the first valence; The conditions shown are in a region where the evaporated particles include not only monovalent ionized particles but also divalent ionized particles. For this reason,
As described above, in this example, since low ion valence particles with an ion valence of 1 are used, the residual stress can be controlled by the voltage applied to the substrate.

In FIG. 3, V _i represents the voltage of the thermionic acceleration power source 6, and I _i represents the current flowing through the ion acceleration power source 7. Also, the last 1 to 3 of EB output 7KW-1 to 3
Number 3 is the output voltage of the electron beam power supply (7KW)
This figure shows three states with different related conditions such as the sweep state of the electron beam.

In other words, if the suffix number is 1, the state in which the irradiation direction of the electron beam remains unchanged is 2.
In the case of , the electron beam is swayed and uniformly applied to a wide surface, and when the suffix number is 3, compared to the case of 2, the electron beam is swayed further.

As described above, under the same EB output, the discharge start voltage (the voltage at which I _i starts flowing when V _i is increased) is not much different under any conditions. this voltage
It is considered that V _i becomes the voltage that ionizes the evaporated particles (the voltage that generates monovalent ions).

Incidentally, it is generally known that once a glow discharge starts in a vacuum, the discharge is stably maintained within a certain voltage range even if the discharge voltage is lower than the initial discharge pressure. The same applies to the ionization of evaporated particles described in the present invention, where the collision between thermionic electrons and the evaporated particles causes an ionization phenomenon, and when the thermionic current begins to flow, the electron density increases due to the electrons liberated from the evaporated particles. It is possible to maintain stable discharge even at a lower voltage (25V) than at the start of discharge.

Next, a method of shifting the discharge starting voltage and the like to the lower voltage side will be described.

In the ion plating method used in the present invention, the electrons that control the discharge are basically thermionic electrons emitted from the melted evaporator, and neutral particles that are ionized by collision with the thermionic electrons. , are free electrons dissociated from neutral particles. Generally, elements with a small atomic number emit a small amount of thermoelectrons, so the voltage required to start and maintain discharge is relatively high compared to the ionization potential determined by the material.

To improve this, add thermoelectrons from the outside,
All you have to do is increase the density of electrons. Specifically, as shown in FIG. 1, a tungsten W filament is provided near the evaporation source, and the filament is heated with electricity to emit thermoelectrons.

By adding thermoelectrons from the outside in this way, it is possible to move and expand the discharge start voltage, stop voltage, and discharge stability region to the lower voltage side, and even when the EB output is 5KW, it is possible to move and expand the discharge start voltage, stop voltage, and discharge stability region to 25V even when the EB output is 5KW. It is possible to maintain the discharge.

Next, we will show the results for _Si using materials other than boron.

Figure 4 is a characteristic diagram showing the relationship between thermionic acceleration voltage V _i and thermionic current I _i in the case of S _i , and the discharge starting voltage is
23V, discharge stop voltage is 13V. The ionization potential of S _i is 8.1 V for monovalent and 16.3 V for divalent, and it is thought that below about 20 V, most of the ionized particles become monovalent.

Figure 5 shows the gas pressure, 8 to 10×, similar to boron.
S _i was evaporated with an electron beam output of 6KW (beam sweep mode 3) in 10 ^-6 Torr, approximately 1.2μ/min,
This figure shows the relationship between the amount of warpage of a _Si film formed to a thickness of approximately 20 μm on an aluminum substrate at an evaporation rate of 20 μm and the voltage applied to the substrate during evaporation.

As shown in Figure 5, the amount of warpage caused by stress differs due to differences in detailed conditions such as the substrate material, but the tendency is the same as in the case of boron, and when only monovalent ions are used. The amount of warpage that occurs with respect to the substrate voltage shows a simple change from (+) to (-).

Effects of the Invention As detailed above, according to the present invention, by forming a thin film on a substrate using particles with a low ionic valence of 1, stress remaining in the formed film can be arbitrarily and easily reduced. It becomes possible to control
It becomes possible to provide a produced membrane that meets the intended use. Further, the heating process during thin film formation or secondary heat treatment, which has been conventionally used as a method for relaxing residual stress, is no longer necessary, which has the advantage of simplifying equipment and processes and reducing costs.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the DC ion plating apparatus, Figure 2 is a residual stress characteristic diagram of the film obtained by the method of the present invention, and Figure 3 is the thermionic acceleration voltage V _i and thermionic current of boron. Figure ₄ is a characteristic diagram showing the relationship between silicon thermionic acceleration voltage and thermionic current, and Figure 5 is a characteristic diagram showing the relationship between silicon film warpage and substrate applied voltage during evaporation. It is a characteristic diagram showing a relationship. 1... Belgear, 2... Substrate, 3... Thermionic accelerating electrode, 4... Boron crucible, 5... Electron beam gun, 6... Thermionic accelerating power source, 7... Ion accelerating power source (substrate voltage power source).

Claims (1)

[Claims] 1. A means for vaporizing a material forming a thin film in a vacuum container, a means for ionizing vaporized particles,
means for holding the substrate, and a thin film is generated on the substrate by a physical vapor deposition method while keeping the ion valence of the evaporated particles at monovalent and controlling the electric field intensity applied to the substrate. A thin film production method.