JPH01100255A - How to form an anti-reflection film - Google Patents

Abstract

PURPOSE:To form the title novel antireflection film with increased strength by respectively specifying the gaseous Ar pressure in a vacuum vessel, the refractive index, etc., of a vaporized substance, a grid impressed voltage, and a film forming rate in the formation of the antireflection film. CONSTITUTION:A vaporization source 4, counter electrode 10 for holding a substrate 11, grid 8 having gaps for passing the vaporized substance, power source 14 for impressing a positive potential on the grid 8, and a filament 6 for generating a thermoelectron are provided in the vacuum vessel into which gaseous Ar is to be introduced, and an antireflection film is formed on the substrate 11. At this time, the pressure of gaseous Ar to be introduced into the vacuum vessel is controlled to 2X10<1>-10<-2>Pa, and a transparent substance solid at ordinary temp. and having a lower refractive index than the substrate 11 is used as the substance 4 to be vaporized. The voltage to be impressed on the grid 8 is controlled to 50-300V, and the film is formed at the rate of 1-50Angstrom /sec. By this method, an antireflection film is formed on a substrate with low heat resistance such as plastics as well as on a glass substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for forming an antireflection film capable of reducing reflected light from lenses, prisms, filters, etc.

BACKGROUND ART Conventionally, various methods for forming an antireflection film on a substrate on which a thin film is to be formed (hereinafter simply referred to as a substrate) have been proposed, and a wide variety of film forming methods have been used.

For example, so-called ion beam deposition is performed in which a high-frequency electromagnetic field is generated between an evaporation source and an object to be evaporated in a vacuum chamber to ionize a substance evaporated in an active gas or an inert gas to perform vacuum evaporation. There is a rating law (Tokuko Sho 52-
(See Publication No. 29971). There is also an activated reactive vapor deposition method (Thinsolid films, 83.1981).
reference).

However, in such a conventional method for forming an antireflection film, in order to improve the strength of the antireflection film, a so-called hard coating is performed in which the film is formed while maintaining the temperature of the substrate at a high temperature. Therefore, it is difficult to apply a hard coat to plastic lenses, etc., which have poor heat resistance.

Purpose The present invention has been made in view of the above points, and makes it possible to form an anti-reflection film on a substrate that is not heat resistant. , even if the substrate temperature is low, e.g. room temperature,
It is an object of the present invention to provide a novel method for forming an antireflection film that can improve film strength, which is the main film property.

Structure In order to achieve the above object, the present invention comprises: a vacuum chamber into which the pressure is reduced to a vacuum and argon gas is introduced; an evaporation source for evaporating an evaporable substance in the vacuum chamber; and an evaporation source disposed within the vacuum chamber. a counter electrode that holds the substrate so as to face the evaporation source; a grid that is disposed between the evaporation source and the counter electrode and has a gap through which the evaporated substance passes; and the grid is set to the potential of the counter electrode. On the other hand, in a method for forming an anti-reflection film using a thin film forming apparatus comprising a power source having a positive potential and a filament for generating thermoelectrons disposed closer to the evaporation source than the grid in the vacuum chamber, The pressure of argon gas introduced into the vacuum chamber is set to 2×101 to 10−
2 Pa, the evaporated substance is a transparent substance that has a refractive index lower than the optical refractive index of the substrate and is solid at room temperature, the grid applied voltage is in the range of 50 to 300 μ, and the film formation rate is 1 to 50 people/day. The film is formed in seconds.

That is, we provide a vapor deposition method that can form a hard coat film for an antireflection film by using a thin film forming apparatus already proposed by the applicant in Japanese Patent Application Laid-Open No. 59-89763, and by using its plasma to perform low-temperature film formation. It is something to do.

Here, the structure and principle of the thin film forming apparatus proposed by the present applicant are as follows. First, it has a vacuum chamber, a counter electrode, a grid, a filament for generating thermoelectrons, and an evaporation source. An active gas, an inert gas, or a mixture of both is introduced into the vacuum chamber. A counter electrode is disposed within the vacuum chamber to hold the substrate and to oppose the substrate to the evaporation source. Further, the evaporation source and the counter electrode are placed at the same potential, or the counter electrode is placed at a negative potential. The grid is capable of passing the evaporated substance and is disposed between the evaporation source and the counter electrode and is at a positive potential with respect to the potentials of the counter electrode and the filament. Therefore, in the vacuum chamber, an electric field from the grid toward the substrate and an electric field from the grid toward the evaporation source are formed in opposite directions.

On the other hand, a filament for generating thermoelectrons is disposed closer to the evaporation source than the grid in the vacuum chamber, and the thermoelectrons generated by this filament are used to ionize a part of the evaporated substance. Therefore, part of the evaporated material from the evaporation source is ionized into positive ions by the electrons from the filament. The partially ionized vaporized substance passes through the grid, is further ionized into positive ions by the ionized gas, and is accelerated toward the substrate by the action of the electric field described above.

Note that the electrons from the filament are emitted from the filament with kinetic energy that corresponds to the filament temperature, so they are not immediately attracted to the positive potential grid.
It passes through this once, is pulled back by the Coulomb force by the grid, and then passes through the grid, and so on.
The vibration motion is repeated around the grid, and it is finally absorbed by the grid, so it does not reach the substrate. Therefore, since the substrate is not subjected to electron bombardment, there is no heating caused by this, and a rise in temperature of the substrate can be prevented. Therefore, even materials without heat resistance, such as plastics, can be used as the substrate.

An embodiment of the present invention using such a thin film forming apparatus will be described with reference to the drawings. First, the base plate 1 and the Pelger 2 are integrated via a backing 15 to form a vacuum chamber. An electrode 3°5.7.9 that also serves as a support body passes through the base plate l.
The penetrating portions of these support electrodes 3 and the like are of course airtight, and furthermore, these support electrodes 3, 5, 7.9 and the space plate 1 are electrically insulated. or,
A hole 1a bored in the center of the base plate 1 is connected to a vacuum exhaust system (not shown).

A pair of support electrodes 3 support a resistance heating type evaporation source 4 made of metal such as tungsten or molybdenum formed into a boat shape (or a coil shape or the like). Note that instead of such an evaporation source, an evaporation source used in a conventional vacuum evaporation method, such as a beam evaporation source, may be used as appropriate. In addition, a pair of electrodes 5 that also serve as supports
A filament 6 made of tungsten or the like for generating thermionic electrons is supported between them. The shape of the filament 6 is determined by arranging a plurality of filaments in parallel or in a mesh shape so that the particles of the evaporated substance evaporated from the evaporation source cover the spread. A grid 8 is supported on the support electrode 7 . The shape of this grid 8 is determined so that it has gaps through which the evaporated substance passes. For example, in this embodiment, it has a mesh shape. Further, a counter electrode 10 is provided on the support 9.
is supported, and a substrate 11 is held on the lower surface thereof by an appropriate method. If this state is viewed from the side of the evaporation source 4, the counter electrode 10 is disposed behind the substrate 11.

Here, these support electrodes 3, 5, and 7°9 are all conductors and also serve as electrodes, and the ends that protrude outside the vacuum chamber are connected as shown in the figure. Connected to various power sources. First, a pair of support electrodes 3
are connected via an evaporation power source 12. Further, the support electrode 5 is connected to a power source 13. Further, in the illustrated example, the support electrode 7 is connected to the positive terminal of the DC electric power source 14, and the support electrode 9 is grounded.

Actually, these electrical connections include various switches, and the operation of these switches realizes the film forming process, but these switches are not shown in the figure.

Formation of an antireflection film using such a thin film forming apparatus will be described.

First, the substrate 11 is set as shown in the figure, and the evaporation source 4 holds a substance such as magnesium fluoride, cryolite, or calcium fluoride as an evaporation substance. Here, for example, it is assumed that the evaporation substance is magnesium fluoride and the evaporation source 4 is a tungsten boat.

On the other hand, the inside of the vacuum chamber is brought to a pressure of 10-1 to 10-'Pa in advance, and argon gas is introduced thereto at a pressure of 10-10-2Pa.

In this state, when the power supply device is activated and a positive potential is applied to the grid 8, the counter electrode 10 is grounded and power flows through the filament 6.

Here, for example, it is assumed that the grid 8 has a mesh shape and a power of 100 cm is applied, and that the filament 6 is a tungsten wire and a power of 400 W is applied to the filament 6. The filament 6 is heated by resistance heating and emits thermoelectrons. Argon molecules in the vacuum chamber are ionized by collision with thermionic electrons emitted from the filament 6. The evaporated magnesium fluoride particles (molecules) spread out and fly toward the substrate, but some of them and the introduced gas are ionized by collision with thermionic electrons emitted from the filament 6.

In this way, the partially ionized particles (molecules) of magnesium fluoride pass through the grid 8, but at this time, as mentioned above, thermionic electrons vibrating up and down in the vicinity of the grid 8 and the ionized particles as mentioned above are generated. Ionization is further promoted by the collision of the introduced gas.

On the other hand, the portion of the evaporated material that has passed through the grid 8 that has not yet been ionized is further ionized into positive ions λ by collision with the ionized introduced gas between the grid 8 and the substrate 11, and the ionization rate is is enhanced.

In this way, the magnesium fluoride particles (molecules) ionized into positive ions are accelerated toward the substrate 11 by the action of the electric field from the grid 8 toward the counter electrode 12.
It collides with the substrate 11 with high energy, forming a magnesium fluoride thin film on the substrate. In this magnesium fluoride thin film, particles (molecules) of magnesium fluoride collide with the substrate 11 with very high energy. Therefore, it is possible to obtain an antireflection film having an excellent film strength equivalent to or higher than that of a magnesium fluoride thin film formed by the conventional method of forming a film by heating the substrate temperature to 300° C. to 500° C.

Then, most of the thermionic electrons end up in grid 8.
Some of the thermionic electrons pass through the grid 8, but
Since it is decelerated by the action of the electric field described above between the grid 8 and the substrate 11, even if it reaches the substrate 11, it will not heat the substrate 11.

According to this embodiment, it is possible to form an antireflection film with high film strength in this manner.

Incidentally, Table 1 shows examples of film strength test results for antireflection films formed according to the present invention. That is, it is a low-temperature anti-reflection film formed by plasma deposition, and the substrate temperature is 35.
9MgF achieves the same performance as 0℃ hard coat at room temperature.
, plasma deposited film test results. In this example, the film thickness is magenta.

Table 1 However, Adhesion: After bringing Scotch tape (15M width) into close contact with the anti-reflection film, it is strongly pulled upward perpendicular to the adhesive surface.

Solvent resistance: Apply ethyl ether to lens cleaning paper and rub vigorously back and forth 10 times.

Pencil test: Press the lead of a 0.4mmφ, H pencil and rub it strongly 5 times.

Eraser test: Press a drafting eraser (pen type) and rub hard 20 times.

Alkali resistance test: After being immersed in a 1% NaOH aqueous solution for 15 minutes, visual observation shall be made. All test results show strong <O
This is what became K.

In addition, when considering the film forming conditions in general, the pressure of argon gas is not limited to the conditions described above, but is 2 x 10' to 10'.
Within the range of ''Pa, the grid applied voltage is 50~300
Good results were obtained within the range of V and the film forming rate within the range of 1 to 50 persons/sec.

Effects Since the present invention uses the film forming method as described above, the rise in substrate temperature is small, the adhesion between the substrate and the film is strong, and
Since we want to use equipment that can form anti-reflective films with excellent film strength, we can form anti-reflective films not only on glass substrates but also on substrates that lack heat resistance such as plastics, and in the future, we will be able to use equipment that can form anti-reflective films on plastic optical parts. It is expected that this technology will make a significant contribution to the field of optical technology, where the use of optical technology is increasing.

[Brief explanation of the drawing]

The drawing is a sectional view of a thin film forming apparatus showing an embodiment of the present invention. 4... Evaporation source, 6... Filament, 8... Grid, 10... Counter electrode, 11... Substrate, 14...
DC power supply (power supply means)

Claims (1)

[Claims] a vacuum chamber into which the pressure is reduced to a vacuum and argon gas is introduced; an evaporation source for evaporating the evaporation substance in the vacuum chamber; and a substrate placed in the vacuum chamber and holding the substrate so as to face the evaporation source. a counter electrode, a grid disposed between the evaporation source and the counter electrode and having a gap through which the evaporated substance passes; power supply means for bringing the grid to a positive potential with respect to the potential of the counter electrode; and the vacuum chamber. In a method for forming an antireflection film using a thin film forming apparatus equipped with a filament for generating thermionic electrons disposed closer to the evaporation source than the grid in the vacuum chamber, the pressure of the argon gas introduced into the vacuum chamber is set to 2.
×10^1 to 10^-^2 Pa, the evaporated material is a transparent material that has a refractive index lower than the optical refractive index of the substrate and is solid at room temperature, and the grid applied voltage is 50 to 300 V.
A method for forming an antireflection film, characterized in that the film is formed at a film forming rate of 1 to 50 Å/sec.