JPH0996701A - Antireflection film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an antireflection film which is an antireflection film having two- layered constitution, exhibits desired reflectivity and is wider in the band width exhibiting this reflectivity than heretofore by constituting the first layer of a layer of a material having the refractive index lower than the refractive index of a transparent substrate. SOLUTION: This antireflection film of the two-layered constitution is constituted by successively providing the surface of the transparent substrate 11 with the first layer 13 and the second layer 15 which has the refractive index lower than the refractive index of the first layer 13 and is composed of a fluororesin. The first layer 13 is composed of the layer of the material having the refractive index lower than the refractive index of the transparent substrate 11. The material constituting the transparent substrate 11 includes optical glass, quartz, plastics, etc. The constituting material of the first layer 3 may be composed of various kinds meeting the design on premise that the condition of the refractive index is satisfied. The constituting material of the second layer 15 may be composed of arbitrary and suitable fluororesins. Since the fluororesins are generally low in the refractive index, the fluororesins are adequately usable as the constituting material of the second layer 15 in the antireflection film of the two-layered constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-layer antireflection film and a method for manufacturing the same.

[0002]

2. Description of the Related Art In optical elements such as lenses, prisms and filters, an antireflection film is often formed on the surface of the element in order to obtain desired optical characteristics. Among such antireflection films, a conventional example of a two-layered antireflection film is disclosed in, for example, JP-A-6-18705. This antireflection film is formed of a first layer of a high refractive index substance having a refractive index of 1.58 or more and an amorphous transparent fluororesin having a refractive index of 1.35 or less on the transparent substrate toward the air side. The antireflection film was formed by laminating the second layer (for example, in the claims). That is, the antireflection film was composed of a first layer sequentially provided on a transparent substrate and a second layer having a lower refractive index than the first layer and made of a fluororesin. Further, as described in column 4, lines 6 to 8 of this publication, it is preferable that the first layer of the antireflection film has a higher refractive index than that of the substrate. The film was also an antireflection film in which the refractive index of the first layer was made higher than that of the transparent substrate. Also,
This antireflection film was formed by a coating solution such as a dipping coating method or a spin coating method (for example, column 2, lines 33 to 34). According to the antireflection film disclosed in this publication, an optical element having an excellent antireflection property can be obtained (for example, column 2, lines 30 to 32).

[0003]

However, in the case of the two-layered antireflection film disclosed in Japanese Patent Laid-Open No. 6-18705, the bandwidth showing the desired reflectance is not necessarily wide. For example, the bandwidth in which the reflectance is 1% or less is about 200 nm at most (see, for example, FIGS. 3, 5, and 6 of the above publication). There is also a technology that uses a multilayer structure of three layers or more as a technology that shows the target reflectance and widens the bandwidth, but in that case, the number of layers increases, so it is difficult to manage the manufacturing process or when a defect occurs. There is a problem that processing of is very difficult. There is a demand for an antireflection film having a two-layer structure, which exhibits a desired reflectance and has a wider bandwidth showing the reflectance than ever before. Further, there is a demand for a method capable of easily producing such an antireflection film which exhibits a desired spectral reflectance characteristic.

[0004]

According to the first invention of this application, therefore, the first layer is provided on the transparent substrate in order, and the first layer has a refractive index lower than that of the first layer and is made of a fluororesin. In the two-layer antireflection film including the second layer, the first layer is formed of a layer of a substance having a lower refractive index than the transparent substrate.

Further, according to the second invention of this application, in manufacturing a two-layered antireflection film composed of a first layer and a second layer which are sequentially provided on a transparent substrate, first, the transparent substrate is used. A first layer formed of a layer of a substance having a refractive index lower than that of the transparent substrate is formed thereon, and then a refractive index lower than that of the first layer and made of a fluororesin is formed on the first layer. The second layer thus formed is formed by a vacuum vapor deposition method, and at least one of the vapor deposition rate and the substrate heating temperature during the vapor deposition is controlled to control the characteristics of the antireflection film.

In the first and second inventions, typical materials for forming the transparent substrate include optical glass, quartz, and plastics. But,
The material forming the transparent substrate is not limited to these examples. Further, the shape of the transparent substrate mentioned here can be arbitrary according to the purpose. A plate-shaped material, a material having a shape corresponding to the shape of an optical element such as a lens or a prism, and a film-shaped material are naturally included in the transparent substrate.

Further, in these first and second inventions, the constituent material of the first layer can be various according to the design on condition that the above-mentioned condition of the refractive index is satisfied. For example, (a) an oxide that satisfies the above refractive index conditions, (b) a metal fluoride that satisfies the above refractive index conditions, and (c) a polymer compound A material satisfying the above condition of the refractive index can be used as a constituent material of the first layer. Examples of oxides include SiO ₂ , and examples of metal fluorides include MgF ₂ and Al ₂ F ₃ .

Further, in the first and second inventions, the constituent material of the second layer can be any suitable fluororesin. This is because the fluororesin generally has a low refractive index and is suitable for use as a constituent material of the second layer in the antireflection film having a two-layer structure. Particularly in the case of the first invention, it may be a fluororesin formed by a dip coating method. In the case of the second invention, any suitable fluororesin can be used as long as it can be made into a thin film by a vacuum deposition method. For example, tetrafluoroethylene
And 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (2,2-bistrifluoromethyl-4,
A fluororesin (specifically, AF2400 (trade name) manufactured by DuPont) made of a copolymer with 5-difluoro-1,3-dioxole) can be formed into a thin film by a vacuum vapor deposition method and is low. It is known that a thin film having a refractive index can be obtained, and the refractive index of the thin film can be changed by changing at least one of the vapor deposition rate and the substrate heating temperature during vapor deposition (see, for example, Document I “SPIE”). Vol.2253 (1
994), pp. 512-519, for example, FIG. 1,
Fig. 3), which is suitable as the fluororesin used in the second invention.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the invention of this application will be described below together with comparative examples with reference to the drawings. Here, FIG. 1 is a cross-sectional view showing a stacking relationship of the transparent substrate 11, the first layer 13, and the second layer 15, and FIGS. 2 to 6 are reflections of some embodiments of the invention. It is a figure showing the spectral reflectance characteristic of each antireflection film or the antireflection film of a comparative example. However, all of the drawings are merely schematic representations so that the present invention can be understood. Further, the refractive index of each of the transparent substrate, the first layer, and the second layer described below is the refractive index for light having a wavelength of 500 nm. The spectral reflectance characteristics shown in FIGS. 2 to 6 are results obtained by simulation using general-purpose calculation software called TF-CALC. However, the refractive index at the time of this calculation is unified with the refractive index for light with a wavelength of 500 nm. This is because the wavelength dependence of the refractive index can be ignored in order to know the effect of the present invention.

[0010] 1. First Embodiment The transparent substrate 11 is made of quartz (refractive index 1.48), and
Layer 13 of magnesium fluoride (refractive index 1.38) and the second layer 15 of AF2400 manufactured by DuPont.
The antireflection film of the first embodiment can be formed by using a layer made of a fluororesin having a refractive index of 1.25. However, the film thicknesses of the first layer 13 and the second layer 15 are such that their optical film thickness is 500 nm.
The film thickness is set to correspond to λ / 4 of the light (the same applies to other embodiments and comparative examples below). In addition,
The layer of magnesium fluoride forming the first layer 13 can be formed by, for example, a vacuum vapor deposition method. In addition, the layer of the AF2400 having the refractive index of 1.25, which constitutes the second layer 15, is
As described in Reference I “SPIE Vol.2253 (1994), page 515, FIG. 3, for example, the vapor deposition rate is set to approximately 4.5 to 22 Å / sec, and the substrate heating temperature is set to approximately no heating. It can be formed under any of the vapor deposition conditions of up to 85 ° C.

The spectral reflectance characteristic obtained by the antireflection film in the first embodiment is shown in FIG. Note that FIG.
In the graph, the horizontal axis represents wavelength (nm) and the vertical axis represents reflectance (%) (the same applies in FIGS. 3 to 6 below). As can be seen from FIG. 2, the antireflection film of the first embodiment is an antireflection film having a reflectance of 1% or less over the wavelength range of about 330 nm to about 1000 nm. That is, it can be seen that the antireflection film has a bandwidth of about 670 nm with a reflectance of 1% or less. In the case of the prior art in which the refractive index of the first layer was higher than that of the substrate, the superiority of the present invention can be understood considering that the bandwidth showing the reflectance of 1% or less was about 200 nm at the most.

2. Second Embodiment In contrast to the configuration of the first embodiment, the second layer 15 is made of a fluororesin AF2400 manufactured by DuPont that has a refractive index of 1.20. Except for this, the antireflection film of the second embodiment can be formed by making it similar to that of the first embodiment. The layer of AF2400 having a refractive index of 1.20 is the same as F on page 515 of Document I above.
ig. As described in No. 3, it can be formed under the vapor deposition condition that the vapor deposition rate is approximately 10 to 22Å / sec and the substrate heating temperature is any of the ranges from no heating to approximately 50 ° C.

FIG. 3 shows the spectral reflectance characteristics obtained with the antireflection film according to the second embodiment. As can be seen from FIG. 3, the antireflection film of the second embodiment is an antireflection film exhibiting a reflection characteristic that the reflectance is 1% or less over the wavelength range of 340 nm to 980 nm. Furthermore, it can be seen that the antireflection film exhibits a reflection characteristic of 0.5% or less in the wavelength range of about 360 nm to about 820 nm or more. That is, the bandwidth for which the reflectance is 1% or less becomes 640 nm or more, and the bandwidth for which the reflectance is 0.5% or less is about 460 nm.
It can be seen that it becomes an antireflection film that also becomes. In the case of the prior art in which the refractive index of the first layer was higher than that of the substrate, the superiority of the present invention can be understood considering that the bandwidth showing the reflectance of 1% or less was about 200 nm at the most.
In addition, as can be seen by comparing the spectral reflectance characteristics of the first embodiment and the second embodiment, the second
It can be seen that the refractive index of the second layer can be changed by changing the vapor deposition conditions when forming the layer, and as a result, the spectral reflectance characteristic of the antireflection film can be controlled.

3. Third Embodiment The transparent substrate 11 is composed of a glass substrate having a refractive index of 1.60 (for example, optical glass called F15 made by Schott),
The antireflection film of the third embodiment can be formed by using the same method as that of the first embodiment except that the first layer 13 is made of a layer of SiO ₂ (refractive index 1.47). .

FIG. 4 shows the spectral reflectance characteristics obtained with the antireflection film according to the third embodiment. As can be seen from FIG. 4, the antireflection film of the third embodiment is an antireflection film having a reflectance of 1% or less over a wavelength range of about 330 nm to about 1000 nm or more. Furthermore, the wavelength of about 360 nm to about 82
It can be seen that the antireflection film exhibits a reflection characteristic that the reflectance is 0.5% or less over a range of 0 nm or more and the low reflectance band is wider than that of the second embodiment. That is,
The bandwidth for which the reflectance is 1% or less becomes a little over 670 nm, and the bandwidth for which the reflectance is 0.5% or less is about 46.
It can be seen that it becomes an antireflection film having a thickness of 0 nm. In the case of the prior art in which the refractive index of the first layer was higher than that of the substrate, the superiority of the present invention can be understood considering that the bandwidth showing the reflectance of 1% or less was about 200 nm at the most.

4. Comparative Example 4-1. Comparative Example 1 The refractive index of the transparent substrate 11 was fixed to 1.48, and the second
When the refractive index of the layer 15 of is fixed at 1.25,
The refractive index of the first layer 13 is variously changed to be larger than that including the case where it is equal to the refractive index of the transparent substrate 11. The first layer 1 of the various levels of Comparative Example 1 thus carried out
FIG. 5 shows the spectral reflectance characteristics obtained with the antireflection coating at three levels of 1.58, 1.53, and 1.48 (when the refractive index of the substrate is equal to that of substrate 3). However, in order to clarify the relationship between Comparative Example 1 and the present invention in FIG. 5, some examples within the scope of the present invention, that is, the refractive index of the first layer 13 is smaller than that of the substrate 1 .4
Spectral reflectance characteristics of the antireflection films of Examples 3, 1, and 38 are also shown.

As can be seen from FIG. 5, the first layer 13
If the refractive index of the transparent substrate 11 is made larger than that of the transparent substrate 11, the maximum bandwidth of the reflectance is 1% or less.
It can only be about 00 nm. From this, the first
It is considered preferable that the layer 13 is formed of a material layer having a lower refractive index than the transparent substrate 11.

4-2. Comparative Example 2 As Comparative Example 2, a transparent substrate made of quartz (refractive index 1.4
8), and the first layer 13 is AF240 manufactured by DuPont.
A layer having a refractive index of 1.25 and a second
Consider an antireflection film in which the layer (1) is composed of a layer of magnesium fluoride (refractive index 1.38). That is, the first aspect of the present invention
Consider a configuration in which the constituent materials of the first and second layers are exchanged with respect to the above embodiment. The spectral reflectance characteristics obtained with the antireflection film of Comparative Example 2 are shown in FIG. As can be seen from FIG. 6, in the case of the structure of Comparative Example 2, a band having a reflectance of 1% or less cannot be obtained, and a preferable antireflection film cannot be formed. From this, the second layer 15 is
It is considered preferable to use a material having a refractive index lower than that of the layer 13. Since the fluororesin can form a layer having a low refractive index, the fluororesin is used as the constituent material of the second layer 15 in the present invention.

From the spectral reflectance characteristics shown in FIGS. 5 and 6, the following can be considered. First
When the refractive index of the first layer is made smaller than that of the transparent substrate, the low reflectance band in the antireflection film becomes wider with a decrease in the refractive index of the first layer (n in FIG. 5). ₁ =
Examples of 1.58 to 1.43). Then, when the refractive index of the first layer becomes a certain value or less, the characteristic diagram portion which has been convex downward until then is inverted convex upward (n ₁ = 1.
38 and FIG. 6). From this, if it is desired to make the bandwidth as wide as possible when the reflectance is less than a certain value, it may be better to set the refractive index of the first layer within a certain range before and after the convex portion is inverted. Conceivable. In the case of the above-described embodiment, the convex portion is inverted with respect to the refractive index of 1.48 of the substrate when the refractive index of the first layer is 1.4.
Since it is considered to be somewhere within the range from 1.38 after it becomes smaller than 3, the refractive index of the first layer is 1.43.
It is considered that when the value is set to any of the ranges of ˜1.38, the characteristic that the reflectance is lowered in a wider band is obtained.

In the above description of the embodiments, some examples of the refractive indexes of the transparent substrate, the first layer and the second layer have been shown, but these examples are only examples within the scope of the present invention. Only. Therefore, it should be understood that the present invention is not limited to the combination example of the refractive indexes in the above-mentioned embodiment.

[0021]

As is apparent from the above description, according to the first invention of this application, the first layer sequentially provided on the transparent substrate, the refractive index lower than that of the first layer, and the fluororesin. In the two-layer antireflection film including the second layer formed by, the first layer is formed of a layer of a substance having a refractive index lower than that of the transparent substrate. Therefore, it is possible to provide an antireflection film exhibiting a desired reflectance and having a wider bandwidth showing the reflectance than ever before.

Further, according to the second invention of this application, a first layer composed of a layer of a substance having a refractive index lower than that of the transparent substrate is formed on the transparent substrate, and the first layer is formed on the transparent substrate. The second layer having a lower rate than that of the first layer and formed of a fluororesin is formed by a vacuum vapor deposition method, and at least one of the vapor deposition rate and the substrate heating temperature during the vapor deposition is controlled to control the antireflection film. The characteristics are controlled to produce a two-layered antireflection film. Therefore, it is possible to easily manufacture an antireflection film which exhibits a desired reflectance and has a wider bandwidth showing the reflectance than the conventional one, and which exhibits an arbitrary desired spectral reflectance characteristic. Further, since it is based on the vacuum vapor deposition method, it is possible to obtain an effect that the film thickness can be easily controlled and a film having excellent film strength can be formed as compared with the dip coating method.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the invention and a comparative example, and is a cross-sectional view showing a laminated relationship of a transparent substrate, a first layer and a second layer.

FIG. 2 is an explanatory diagram of characteristics obtained in the first embodiment of the invention.

FIG. 3 is an explanatory diagram of characteristics obtained in the second embodiment of the invention.

FIG. 4 is an explanatory diagram of characteristics obtained in the third embodiment of the invention.

FIG. 5 is a diagram for explaining Comparative Example 1;

FIG. 6 is a diagram for explaining a comparative example 2;

[Explanation of symbols]

 11: transparent substrate 13: first layer 15: second layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C23C 14/06 C23C 14/06 R

Claims (3)

[Claims] 1. An antireflection film having a two-layer structure comprising a first layer and a second layer having a lower refractive index than the first layer and formed of a fluororesin, which are sequentially provided on a transparent substrate. The antireflection film, wherein the first layer is composed of a layer of a substance having a refractive index lower than that of the transparent substrate. 2. A method for producing an antireflection film having a two-layer structure comprising a first layer and a second layer, which are sequentially provided on a transparent substrate, wherein a material having a refractive index lower than that of the transparent substrate is formed on the transparent substrate. A first layer composed of a layer is formed, and a second layer having a refractive index lower than that of the first layer and composed of a fluororesin is formed on the formed first layer by a vacuum deposition method. At the same time, at least one of the deposition rate and the substrate heating temperature during the deposition is controlled to control the characteristics of the antireflection film. 3. The method for producing an antireflection film according to claim 2, wherein the fluororesin is tetrafluoroethylene,
A method for producing an antireflection film, which comprises using a copolymer with 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole.