JPH0517309B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method of forming a laser mirror film using ICB (ionized cluster beam) vapor deposition.

[Conventional technology]

FIG. 1 is a sectional view showing an ICB vapor deposition apparatus disclosed in, for example, Japanese Patent Publication No. 54-9592. In the figure, 1 is a closed crucible having at least one injection nozzle, and 2 is a crucible injection nozzle, 3
4 is the material that forms the deposited film contained in the crucible 1; 4 is the steam generated when the material 3 is heated;
5 is a vacuum area where the steam 4 is injected; 6 is a vacuum area where the steam 4 is injected;
is a cluster formed in the vacuum region 5; 7 is a cluster ion in which the cluster 6 is ionized; 8 is an ionizing filament that emits electrons for ionization to ionize the cluster 6 to form the cluster ion 7; 9; 10 is an electron emitted by the ionization filament 8; 10 is a substrate; 11 is an acceleration power source that supplies an acceleration voltage for accelerating the cluster ions 7; 12 is a deposited film; and 13 is an ionization current for ionizing the clusters. This is an ionization power source consisting of a variable power source for generating ionization.

Next, the operation will be explained.

The crucible 1 containing the material 3 is heated by resistance heating or electronic bombardment heating (electronic bombardment heating method shown in FIG. 1) to evaporate the material 3. The vapor pressure of the vapor 4 from which the material 3 has evaporated is
When the temperature exceeds 10 ^-2 Torr, it passes through the injection nozzle 2.
Steam 4 is ejected into a vacuum region 5 below 10 ^-5 Torr.
At this time, the steam that has passed through the injection nozzle 2 undergoes adiabatic expansion due to the pressure difference between the crucible 1 and the vacuum region 5, resulting in a supercooled state, resulting in clusters of about 100 to 1000 atoms (or molecules) bonded together. (Clumped atomic group) 6 is formed. When this cluster 6 reaches the region sandwiched by the ionized filaments 8, it collides with the electrons 9 extracted from the ionized filaments 8, and the electrons in the atoms that make up the cluster 6 (electrons in the atoms in the molecules) collide with the electrons 9 extracted from the ionized filaments 8. is blown away and becomes cluster ion 7. After this, the cluster ions 7 are accelerated by the acceleration power source 11,
The cluster ions 7 collide with the substrate 10 due to the kinetic energy and acceleration force when they are ejected from the crucible. Due to this collision, most of the kinetic energy of the cluster ions 7 is converted into thermal energy and applied to the substrate 10, heating the surface of the substrate 10, and the cluster ions 7 are decomposed into individual atoms (molecules). It moves on the substrate surface and adheres to the substrate surface due to the so-called migration effect, forming a deposited film. In addition, in the process of forming a deposited film on the substrate surface in this way, the substrate surface is cleaned by the spatter cleaning effect caused by the bombardment of heated cluster ions onto the substrate surface, and this cleaning cleans the substrate surface. A strong bonding force can be obtained between the evaporated film and the deposited film.

In addition, in this device, the ionization power source is a variable power source because even if the same amount of electron irradiation is performed, each substance (atom, molecule) is ionized differently, so the ionization power source is variable for each substance. This is to change the voltage value of the ionized filament and the amount of electrons generated from the ionized filament.

[Problem that the invention seeks to solve]

By the way, when forming a film that specularly reflects laser light on a substrate, that is, a laser mirror film, using the above-mentioned ICB vapor deposition apparatus, the following problems occur.

In other words, in the method of forming a vapor deposited film using a conventional ICB vapor deposition apparatus, as mentioned above, the voltage value of the ionization power source is changed for each substance to be vaporized (adhered) to the substrate. While forming a film by colliding with the cluster ions, the voltage value of the ionization power source is kept constant, and the amount of ionization of the cluster ions is kept constant. The amount of ionization is usually determined by increasing the amount of electrons generated from the ionization filament so that the spatter cleaning effect mentioned above becomes noticeable and the adhesion of the film to the substrate becomes stronger. The ionization amount is set to be at least twice as large as the lowest level ionization amount that allows the reflectance to maintain its highest value.

However, using such an ICB deposition device,
When forming a laser mirror film that specularly reflects laser light, as described above, the amount of ionization of cluster ions should be lower than the minimum level of ionization that can maintain the highest reflectance of the laser mirror film. If the ionization amount is more than twice as large, during the ionization of this cluster, the gas remaining in the vacuum region will also be ionized by the electron irradiation from the ionization filament, and the atoms (molecules) in the film during the film formation process will be ionized. This ionized gas causes sputtering, forming a stain-like non-uniform surface on the film surface, resulting in a problem in that the reflectance of the film decreases.

Although it is possible to solve the above problems by reducing the amount of ionization of cluster ions, the above-mentioned spall cleaning effect is only effective if the amount of ionization of cluster ions is reduced to the minimum level mentioned above. It will not work significantly unless the ionization amount is at least twice as large as the ionization amount, and especially when using a substrate with a surface oxide film such as a copper plate, the substrate surface must be thoroughly cleaned. Such a large amount of ionization was necessary because the deposited film could not be tightly adhered to the substrate surface.

This invention was made to solve the above-mentioned problems, and it has a strong bonding force (adhesion force) with the substrate, and also has a stain-like non-uniform surface on the surface. The purpose of the present invention is to provide a method for forming a laser mirror film that can obtain a laser mirror film with a high reflectance.

[Means for solving problems]

In the method for forming a laser mirror film according to the present invention, the accelerating voltage is kept constant, and the amount of ionization of cluster ions is initially lower than the minimum level of ionization that allows the reflectance of the laser mirror film to maintain its highest value. The ionization amount is increased by more than twice the size, and about 10 to 40 atomic (molecule) layers of atoms or molecules of the vapor-deposited substance are attached to the surface of the substrate, and then the amount of ionization is reduced to the minimum level.

[Effect]

In this invention, in the early stage of film formation, the amount of ionization of cluster ions is increased to adhere about 10 to 40 atoms (molecules) of the atoms or molecules of the vapor deposition material, so that during this time, the ionization amount of cluster ions is increased to attach about 10 to 40 atoms (molecules) of layers to the substrate surface. It is possible to form a thin film with few irregularities that adheres to the surface and completely fills the surface, and then by reducing the ionization flow, the evaporated film is created by ionizing the gas that remained in the vacuum area without being evacuated. The thickness of the thin film can be increased to such a level that the laser beam does not reach the substrate surface, without producing a smudge-like non-uniform surface by suppressing the spatter effect.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

The ICB deposition equipment used in the laser mirror film forming process according to this example is shown in Figure 1 above.
The ionization power supply 13, which has basically the same configuration as the ICB evaporation apparatus and is a variable power supply, is configured so that the voltage value is switched at a predetermined timing such that the voltage value is high for a certain period of time at the beginning and becomes low afterward during the film formation process. It's summery. That is, for the first certain period of time,
The ionization current of the cluster ions emitted within the constant electric field formed by the accelerating power source 11 is 2.
A high voltage is applied to the ionization filament 8 so that the ionization current is more than twice as large, and after about 10 to 40 atoms (molecules) of atoms or molecules of the vapor deposition material have adhered, the ionization current of cluster ions is set to the above-mentioned minimum. The structure is such that a low voltage is applied to the ionization filament 8 so that the ionization current is reduced to about the same level. The above ionization current is the amount of charge carried by cluster ions when they arrive at the substrate per unit time, and corresponds to the ionization amount (degree of ionization) of cluster ions, and the above timing varies depending on experiments. From the relationship between the ionization current and the film formation rate under a constant acceleration voltage, it was found that the atoms or molecules of the vapor deposited substance
The time for adhesion of about 40 atomic (molecule) layers is preset.

Figure 2 is a diagram showing the relationship between the ionization current of cluster ions and the thickness of the deposited film when film formation was performed using Au as the deposition material and a copper plate as the substrate, with the accelerating voltage set at 5KV. , the vertical axis shows the accelerating voltage and ionization current, the vertical axis shows the deposited film thickness, and the right end of the horizontal axis shows the film thickness at the end of the vapor deposition. still,
In the figure, the solid line indicates the accelerating voltage, and the dashed line indicates the ionization current.

Next, the operation will be explained.

As shown in FIG. 2, the heating power source 11 and the ionization power source 13 cause the accelerating voltage to rise for a certain period of time.
Conditions were set such that the voltage was 5 KV and the ionization current was 1.0 μA/cm ² or more, and Au atoms were deposited on the substrate.
During this period, the cluster ions have an ionization current of
1.0 μA/cm ² or more, that is, the lowest level of ionization current (0.4 μA/cm ² ) at which the reflectance of the laser mirror film can maintain the highest value (99.3%).
Therefore, a large kinetic energy is applied under an accelerating voltage of 5KV, sputtering impurities (oxides, etc.) adhering to the surface of the substrate 10, cleaning the surface of the substrate 10, and making Au atoms.
Approximately 20 layers are attached, forming a thin film of approximately 200 Å that is firmly bonded to the substrate surface and has no irregularities on the surface.

Next, while keeping the acceleration voltage the same, the ionization current of the cluster ions was adjusted to be about 0.4 μA/cm ² , that is, the lowest level of ionization that can maintain the reflectance of the laser mirror film at its highest value. The voltage of the ionization power source 13 decreases, and the amount of electrons emitted from the ionization filament decreases.
The cluster ions reach the surface of the thin film while the ionization of residual gases such as oxygen, nitrogen, carbon dioxide, and hydrogen existing in the vapor deposition apparatus with a partial pressure of about 10 ^-6 Torr is suppressed. The residual gas does not sputter the atoms in the film, and the Au layer further smooths the film surface and increases the film thickness.
Atoms stick together. And this film formation state is
The film is maintained until the film thickness reaches a level (about 3000 Å in this case) that does not allow laser light to pass through the substrate.
Film formation is completed. Note that during this attachment, the ionization current of the cluster ions becomes smaller, so the kinetic energy of the cluster ions in the electric field also becomes smaller, and the proportion of Au atoms being spattered by the cluster ions during the film formation decreases. The net deposition rate is also increased.

In the method for forming a laser mirror film of this example, until the substrate surface is completely filled with Au atoms, the clusters are ionized to such an extent that the spatter cleaning effect on the substrate surface is noticeable. After this, the clusters are ionized to form a film under ionization conditions that do not ionize the gas in the vacuum region, so the adhesion to the substrate is strong, the film surface is free of irregularities, and the laser beam is mirror-like. A deposited film of Au atoms that can be reflected can be formed.

In addition, in the above example, the acceleration voltage was set to 5KV, but it is not limited to this.
Although it can be changed as appropriate within the range of 10 KV or less, it goes without saying that the ionization current of cluster ions that can make the cluster ions reach the substrate changes depending on the magnitude of the accelerating voltage.

〔Effect of the invention〕

As described above, according to the present invention, in forming a laser mirror film by vapor deposition, the accelerating voltage during vapor deposition is kept constant, and the cluster ions have a remarkable sputter cleaning effect on the substrate surface in the initial stage of film formation. After that, under the above acceleration voltage, the substrate was ionized to the lowest level of ionization that could maintain the highest reflectance of the laser mirror film. This has the effect of making it possible to create a laser mirror film that has a strong bonding force between the substrate and the substrate, and has high reflectance characteristics without stain-like inhomogeneity.

[Brief explanation of the drawing]

FIG. 1 shows ICBs according to a conventional method and an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the vapor deposition apparatus, and is a diagram showing the relationship between acceleration voltage and ionization current in the process of forming a laser mirror film according to an embodiment of the present invention. 11... Acceleration power source, 12... Vapor deposited film, 13...
Ionization power supply.

Claims (1)

[Claims] 1. Injecting the vapor of the vapor deposited substance contained in the crucible from inside the crucible into a vacuum region at least 1/100 of the vapor pressure inside the crucible and about 1.0 ^-2 Torr or less. 100 atoms or molecules of the vapor-deposited substance
A cluster of approximately 1,000 atoms is formed, and then electrons emitted from an ionizing filament connected to a variable power source collide with the cluster to generate cluster ions, and then the cluster ions are placed in a constant electric field. In the method of forming a laser mirror film in which the laser mirror film is accelerated by colliding with the surface of the substrate on which the laser mirror film is to be formed and is deposited, the amount of ionization of the cluster ions is maintained at the highest value for the reflectance of the laser mirror film. at least 2 times the lowest level of ionization that can be achieved.
After depositing about 10 to 40 atoms (molecules) of atoms or molecules of the vapor deposition substance on the substrate by setting the ionization amount to be more than twice as large, the ionization amount of the cluster ions is set to be more than twice as large as the reflectance of the laser mirror film. A method for forming a laser mirror film characterized by reducing the amount of ionization to the lowest level that can maintain the highest value.