JPH01134401A - Beam splitter and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the stable beam splitter and to reduce absorption by using a thin metallic film which is formed by incorporating Cu in a principal component Ag or metallic thin film consisting of two layers of Ag and Cu as a translucent film for the beam splitter. CONSTITUTION:The translucent film of TiO2-(Ag,Cu)-TiO2 constitution is formed by vapor-depositing Ag and Cu at the same time. The beam splitter used to reproduce a color image is so constituted that image information light 5 from a camera lens is incident on the incidence surface 4 of a 1st prism 1 and split by the translucent film 3 into brightness signal light 6 and color signal light 7. This brightness signal light 6 is reflected by the translucent film 3, and then reflected totally by the incidence surface 4 to become a brightness signal through a solid-state image pickup element 8. The color signal 7 which is transmitted through the translucent film 3, on the other hand, enters a solid-state image pickup element 9. Consequently, the beam splitter is realized which reduces the absorption and has flat characteristics over the entire visible range.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a beam splitter used in a viewfinder of a video camera, an imaging optical system, and the like.

BACKGROUND OF THE INVENTION Beam splitters for transmitting and processing color images do not have polarization characteristics and are required to have flat characteristics for all wavelengths in the visible range. Up until now, many semitransparent films with a dielectric-metal-dielectric structure have been used, but among them, a translucent film with a dielectric-Ag-dielectric structure is based on the example shown in Figure 8. As can be seen, the characteristics are flat throughout the visible range, and the absorption is relatively low.
In addition, there is little deviation in characteristics due to differences in polarization components.
It has unique features.

Problems to be Solved by the Invention However, the thickness of the Ag film in the beam slurry as described above must be extremely thin (10 nm to 20 nm), and although it is possible in terms of design, in reality it is not possible to use such a thin Ag film. It is very difficult to stably form Ag.
However, in such a thin state, it becomes a granular or island-like structure, which results in a continuous and homogeneous film structure.

As a result, the characteristics unique to Ag cannot be obtained, and Cr (chromium) and AI (aluminum), which are generally considered to have high absorption properties, cannot be obtained.
On the contrary, there were cases where the amount of absorption increased.

Continuous and homogeneous AgR in pursuit of ideal Ag characteristics
Many process approaches have been taken to form m. For example, the vacuum evaporation method uses a process at room temperature and at a high evaporation rate, but this method has several problems.

First, the adhesion strength of the dielectric thin film decreases in the room temperature process. To avoid this, methods include cooling the substrate after depositing a dielectric thin film at a high temperature and performing Ag deposition at room temperature, or further heating the substrate and depositing a dielectric thin film at a high temperature. However, the cooling process from high temperature to room temperature is extremely long (incurring large process losses. At the same time, the homogeneous Ag thin film formed at room temperature may be damaged in the high temperature atmosphere during the next dielectric thin film deposition. As a result, the properties may deteriorate, making it difficult to maintain stable film quality.

Additionally, a high evaporation rate is generally an advantage in the process, but since extremely thin Ag films like this require thickness control of less than 1 nm, a high evaporation rate has the opposite effect. This becomes a factor that makes process control difficult.

Now, although the Ag thin film that can be realized by such a room temperature process and a high vapor deposition rate does not have an island structure, it has many cavity defects and does not have the ideal characteristics of Ag, resulting in slightly increased absorption. At the same time, since defects can become the core of corrosion, it is considered unfavorable from the viewpoint of ensuring environmental resistance. In fact, although many design examples have been shown in patents and literature, no beam splitter that has good characteristics over the entire visible range and has excellent environmental resistance has yet been obtained.

Means for Solving the Problems In order to solve these problems, the present invention uses the main component A.
Metal thin film containing Cu in g, or 2 of Ag and Cu
A thin metal film consisting of layers was applied to a semitransparent film for a beam splitter.

Function: This kind of metal thin film can be obtained in a continuous, defect-free state through a high-temperature, low-rate film formation process, so by using it, it is possible to create a stable, low-absorption semitransparent film for beam splitters. This will be realized as a typical film.

EXAMPLE FIG. 1 shows a sample obtained in a film forming experiment observed with a scanning electron microscope. FIGS. 1(a) and 1(b) show metal thin films according to the present invention, and FIGS. 1(c) and 1(d).

(e) is an Ag thin film obtained in a conventional experiment.

The photographic magnification in each case was 50,000 times, and the experimental conditions for each are as shown in Table 1. Although the comparison is made here at a substrate temperature of 120° C., the results are similar at lower temperatures.

In both cases, the total film thickness was 20 rv in terms of mass film thickness, the substrate was white glass, and the vacuum was 1X10-' (mb). Note that the mass film thickness referred to here is the indicated value of a film thickness monitor using, for example, a quartz crystal resonator, which converts the film thickness from the mass of the substance deposited on the substrate, and is an indication of film continuity or discontinuity. It is a film thickness that is related to gender (defined as film thickness).

FIG. 1(a) shows simultaneous vapor deposition using a mixed target of Ag and Cu, and it can be seen that a continuous and defect-free film is formed. This film has extremely good absorption characteristics and, as will be described later, provides excellent effects as a beam splitter.

In FIG. 1(b), Cu was deposited as an underlayer to a mass film thickness of 1 nm, and then Ag was deposited to a thickness of 19 nm. It can be seen that a continuous and defect-free film was also formed.

FIG. 1(C) shows an Ag thin film obtained when the film formation rate is slow and the substrate temperature is high.The film has a discontinuous structure in which large particles are lined up, so absorption is extremely large.

In FIG. 1(d), a continuous Ag film was formed by increasing the film forming speed, but the particles were coarse and void defects were observed here and there. This causes increased absorption and membrane deterioration.

Figure 1(e) shows an Ag film deposited in the same atmosphere as in Figures (a) and (b), but the film quality according to the present invention is thicker, discontinuous, and extremely absorbent. In other words, according to the present invention, a continuous metal thin film layer with little absorption (and without defects) was obtained under conditions where a continuous film could not be obtained with Ag alone.

Here, the membrane quality and its manufacturing method will be briefly described.

As shown in FIG. 1(a), the structure of the film obtained by simultaneous vapor deposition of Ag and Cu is characterized by the segregation of Cu on the surface of the continuous Ag layer. If the content of Cu increases and the amount of segregation becomes large (in this case, the characteristics specific to Cu will become noticeable and the absorption will increase. Therefore, A
It is desirable to choose the weight ratio of Cu to g between 2%, which is necessary for continuous film formation, and 10%, which allows good absorption to be maintained. Suitable manufacturing methods include two-source vapor deposition of Ag and Cu, or sputtering, or vapor deposition or sputtering of a target prepared by mixing Ag and Cu.

Next, as shown in FIG. 1(b), even when Cu is provided as an underlayer and an Ag layer is formed thereon, diffusion of Cu and segregation to the Ag surface are observed.

However, in this case, the characteristics of the two-layer structure of the Cu base layer and the Ag layer clearly appear, so it is desirable to keep the absorption low by setting the thickness of the Cu base layer to 2 nm or less in terms of mass film thickness. is good in both vapor deposition and sputtering.

The results from the two methods suggest that the presence of Cu at the initial stage of film formation is a necessary condition for continuous film formation. In addition, dielectric thin films such as TiO2, ZrTi0a, and Y2O3 were formed on glass substrates, and attempts were made to form metal thin films thereon using the method described above, but similar results were not obtained regardless of the type of dielectric thin film. Got the results.

Embodiments of the beam splitter obtained by the present invention will be described in detail below with reference to the drawings.

In addition, the metal thin film obtained by the above-mentioned process (Ag, Cu
).

FIG. 2 shows an example of an imaging optical unit for separating image information into a color signal and a luminance signal, which is used in a video camera using two solid-state imaging devices. This consists of a first prism 1 and a second prism 2, and a semi-transparent film 3 having characteristics as shown in FIG. 3(a) is provided at the junction thereof, which functions as the beam splitter of the present invention. do.

First, the function of the imaging optical unit will be explained. Image information light 5 from the camera lens enters the entrance surface 4 of the first prism 1 and is split by the semi-transparent film 3 into luminance signal light 6 and color signal light 7. This luminance signal light 6 is transmitted through the semi-transparent film 3
After being reflected by the incident surface 4, the light is further totally reflected by the solid-state image sensor 8 and converted into a luminance signal. On the other hand, the color signal 7 transmitted through the semi-transparent film 3 enters the solid-state image sensor 9.

Color filter 10 placed in front of this solid-state image sensor 9
The color signal light 7 is decomposed into RGB components and becomes a color signal. Now, in this configuration, the angle at which the image information light 5 is incident on the semitransparent film 3 is approximately 25 degrees. This is the angle necessary to satisfy the total reflection condition at the entrance surface 4 of the first prism 1. In this case, when light is not incident perpendicularly, the semitransparent film 3 generally has polarization properties.

For example, a semitransparent film composed of a dielectric multilayer film is
Although it has the advantage of no absorption, as shown in FIG. 9, the transmittance (reflectance) of the P-polarized light component and the S-polarized light component are significantly different. This is because the P-polarized light component and the S-polarized light component are unevenly distributed to the luminance signal light 6 and the color signal light 7, which causes unevenness in contrast and saturation, making it difficult to reproduce images faithfully. In particular, if the difference in transmittance (reflectance) between the P-polarized light component and the S-polarized light component exceeds 10%, the image quality will be significantly degraded.

For this reason, as a beam splitter used for color image reproduction, the transmittance (reflectance) is approximately constant (flat) between wavelengths of 400 nm and 700 nm.
, and transmittance (reflectance) for any polarized light component.
The property that the two are equal is required. Therefore, a metal thin film having good properties except for absorption loss is used.

Now, in the embodiment shown here, as shown in FIG. 3(b), T
It is a semi-transparent film composed of iO2-(Ag, Cu)TiO2. The metal thin film layer used is one obtained by simultaneous vapor deposition of AgaCu as shown in FIG. 1(a). From this characteristic diagram, it can be seen that the characteristics are flat over the entire visible range, there is little absorption, and there is little deviation in characteristics due to differences in polarization components. Therefore, it is extremely suitable as a beam splitter for the optical unit for a video camera described here.

In order to make a comparison with FIG. 8 shown as a conventional example, Table 2 shows the amount of absorption for each of P waves and S waves. The conventional Ag layer is shown in FIG. 1(d).

(Margin below) Table 2 Comparison of Absorption Amount From this, it can be seen that in the beam splitter using a metal thin film (Ag, Cu), the absorption amount is halved over the entire wavelength range. In particular, its flat absorption characteristics from 450 nm to 700 nm are unprecedented.

That is, according to the present invention, it was possible to realize an unprecedented beam splitter that has less absorption over the entire visible range and flat characteristics than a beam splitter using Ag alone.

This characteristic is the same in a prism made by joining two parallel flat plates as shown in FIG. 4(a), or in a cube-shaped prism with an incident angle of 45 degrees as shown in FIG. 4(b).

FIG. 5(a) shows the (
Characteristics of beam splitter using Ag, Cu), Figure 5 (
b) is a conventional Ag film, in which TiO2 is placed on both sides of a metal thin film layer. As can be seen from this, those made of (Ag, Cu) have low absorption over the entire visible range and have flat characteristics.

Moreover, since a continuous, defect-free metal thin film layer can be obtained regardless of the film thickness, transmittance and reflectance can be arbitrarily set by selecting the film thickness.

FIG. 6(a) shows an example with a reflectance of 70% and a transmittance of 30%, and FIG. 6(b) shows an example with a reflectance of 30% and a transmittance of 70%. This is also similar to FIG. 5, with Ti on both sides of the metal thin film layer.
It is equipped with O2. The thickness of each metal thin film layer at this time was 28n+++.

The number of layers is 14.5 m, which has been difficult to achieve until now, especially in the case of thin films such as the latter.

FIG. 7 shows an example of a beam splitter constructed by laminating one (Ag, Cu) layer and one TiO2 layer. As mentioned above, although the difference in characteristics due to polarization is slightly increased compared to the configuration in which Ag and Cu layers are sandwiched between T f O2 layers, it can be said that it is a good beam splitter with little absorption and flatness.

Effects of the Invention As described above, according to the present invention, absorption is small;
A beam splitter having flat characteristics over the entire visible range can be realized. This is very useful from the point of view of improving the imaging characteristics of video cameras, etc.
It has extremely high industrial value.

[Brief explanation of the drawing]

Fig. 1 is a scanning electron micrograph of a metal thin film obtained by the beam splitter manufacturing method of the present invention and a conventional Ag thin film, and Fig. 2 is a photograph of a beam splitter in an embodiment of the present invention on an imaging optical unit. Application configuration diagram, 3rd
Figure (a) is a characteristic diagram of a beam splitter in an embodiment of the present invention, Figure 3 (b) is its configuration diagram, and Figure 4 (a) is a parallel plate junction of a beam splitter in another embodiment of the present invention. Fig. 4(b) is a block diagram of an application to a cube prism; Fig. 5(a) is a diagram showing the characteristics of the beam splitter of the present invention in a cube prism with a ray incident angle of 45 degrees; Figure (b) shows a similar configuration.
Characteristic diagram when using g, Figure 6 (a) has a reflectance of 70%
, when the transmittance is 30%, FIG. Characteristic diagram of the beam splitter of the present invention constructed layer by layer, No. 8
The figure shows the characteristics of a conventional beam splitter using Ag.
FIG. 9 is a characteristic diagram of a beam splitter composed of a dielectric thin film. 1...first prism, 2...second prism, 3...
- Semi-transparent film (beam splitter), 5... Image information light, 6... Brightness signal light, 7... Color signal light 1.8.
9... Solid-state image sensor, 10... Color filter. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1(e) A1μNet-12 (it I--1st Brism 2=;t'2 Prism S-Picture congratulatory light b-s crossing signal light 7- Color signal light Fig. 2 Fig. 10-m-Color filter Fig. 3 (α) Sleeve length (n layer) (b Fig. 4 (b) Fig. 5 Fig. 6 Fig. 7 Fig. 7 1%) Fig. 8 1 length (nM) Section manager tn'w+) Figure 9 (%n

Claims (11)

[Claims] (1) A beam splitter having a semi-transparent film on the joint surface of two substrates, characterized in that the semi-transparent film is composed of a metal thin film whose main component is Ag containing Cu and a dielectric thin film. beam splitter. (2) The beam splitter according to claim 1, wherein the weight ratio of Cu to Ag is 2% to 10%. (3) The beam splitter according to claim 1, characterized in that the dielectric thin film is composed of a single layer. (4) The beam splitter according to claim 1, characterized in that a metal thin film is formed between two dielectric thin films. (5) A beam splitter having a semi-transparent film on the joint surface of two substrates, characterized in that the semi-transparent film is composed of a metal thin film consisting of two layers of Ag and Cu and a dielectric thin film. splitter. (6) The beam splitter according to claim 5, wherein the Cu film thickness is 2 nm or less in terms of mass film thickness. (7) The beam splitter according to claim 5, characterized in that the dielectric thin film is composed of a single layer. (8) The beam splitter according to claim 5, characterized in that a metal thin film is formed between two dielectric thin films. (9) A beam splitter in which a translucent film made of a metal thin film and a dielectric thin film is provided on the joint surface of two substrates, and the metal thin film is obtained from a target whose main component is Ag containing Cu. A method for manufacturing a beam splitter. (10) A beam splitter with a semi-transparent film made of a metal thin film and a dielectric thin film on the bonding surface of two substrates.
A method for manufacturing a beam splitter, characterized in that the metal thin film is obtained from a two-layer target of u. (11) Using a beam splitter in which a translucent film made of a metal thin film and a dielectric thin film is provided on the bonding surface of two substrates, Ag is deposited on Cu provided as a base layer to obtain the metal thin film. Features: A method for manufacturing a beam splitter.