JPH06138317A - Interference filter and photodetector with interference filter - Google Patents

Abstract

PURPOSE:To improve the transmittance of the interference filter having dielectric layers of low refractive indices and dielectric layers of high refractive indices by decreasing the ripples in the transmission band on a short wavelength side than in the non-transmission band. CONSTITUTION:This IR cut filter 4 consists of 25 layers provided with the low-refractive index dielectric layers 2 in the layers of the odd numbers counted from a glass substrate 1 on this glass substrate 1 and the high-refractive index dielectric layers 3 likewise in the layers of even numbers and ending with the low-refractive index dielectric layer 2 in the final layer counted from the glass substrate 1. The above-mentioned filter is so formed that the optical film thickness of the second layer counted from the glass substrate 1 is larger than lambda/4, the optical film thickness of the third layer larger, than lambda/4 and likewise the optical film thickness of the fourth layer larger than lambda/4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference filter and a light receiving element with an interference filter used in, for example, an automatic exposure system of a camera.

[0002]

2. Description of the Related Art Conventionally, when a light receiving element such as a photodiode is used in a camera automatic exposure system or the like, it is necessary to measure the light amount in the visible light range of a human, so an infrared cut filter is provided on the silicon light receiving element. It is necessary to provide a photodiode in which the wavelength sensitivity characteristic of silicon is corrected to the luminosity by providing the above. Generally, a glass optical absorption filter is used for such a conventional photodiode, but since the cost is high, an interference filter using a multilayer film is suitable from the viewpoint of a high degree of freedom in design. .

FIG. 9 shows a block diagram of a conventional interference filter. In order to provide the infrared cut filter 4 on a substrate such as the glass substrate 1, when the central wavelength is λ, the low refractive index dielectric layer (SiO ₂ ) 2 and the high refractive index dielectric are provided on the glass substrate 1. Layer (TiO ₂ ) 3, low-refractive index dielectric layer 2, high-refractive index dielectric layer 3, ... Up to 25 low-refractive index dielectric layers 2 are formed, and the optical film thicknesses thereof are the first layer and Λ / 8 for the 25th layer
And the other layers were λ / 4. FIG. 10 shows a spectral characteristic curve diagram of the infrared cut filter 4 having this configuration.

FIG. 11 shows a block diagram of another conventional interference filter. In order to provide the infrared cut filter 4 on the silicon light receiving element 10, when the central wavelength is λ, a low refractive index dielectric (S) is formed on the light receiving surface of the silicon light receiving element 10.
io ₂ ) 2, high refractive index dielectric layer (TiO ₂ ) 3, low refractive index dielectric layer 2, high refractive index dielectric layer 3, ... The optical thicknesses of the first and 25th layers were λ / 8, and the other layers were λ / 4. FIG. 12 shows a spectral characteristic curve diagram of the infrared cut filter 4 having this configuration.

[0005]

In the structure in which the infrared cut filter is provided on the conventional glass substrate, as is apparent from FIG. 10, ripples in the transmission band near the wavelength shorter than the non-transmission band, that is, near 700 nm. It turns out that is large.

Further, also in the configuration in which the infrared cut filter is provided on the other conventional silicon light receiving element, as is apparent from FIG. 12, the wavelength is shorter than the non-transmission band, that is, 7
The ripple in the transmission band near 00 nm was large, and the transmittance was low as a whole.

When ripples remain in the transmission band on the shorter wavelength side than the non-transmission band, the ripples in the transmission band lower the transmittance, which is a problem.

The present invention aims to solve the above problems.

[0009]

According to the present invention, on a light receiving surface of a substrate or a light receiving element, a dielectric layer having a low refractive index is formed in an odd layer in the odd layer counted from the substrate or the light receiving surface and in an even layer. Is a high-refractive-index dielectric layer, and the final layer counting from the substrate or the light-receiving surface is an interference filter or a light-receiving element with an interference filter consisting of N layers ending with a low-refractive-index dielectric layer. The optical film thickness of the second layer is greater than λ / 4, and the optical film thickness of the third layer is λ
It is characterized in that the optical film thickness is made thicker than / 4 and the optical film thickness of the fourth layer is made thicker than λ / 4.

[0010]

The optical film thickness of the second layer is greater than λ / 4, and the optical film thickness of the third layer is also λ, counting from the substrate or the light receiving surface.
/ 4 and also the fourth layer has an optical film thickness greater than λ / 4, so that the shorter wavelength side than the non-transmission band,
That is, it is possible to reduce the ripple in the transmission band near 700 nm and improve the transmittance.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of an infrared cut filter according to the present invention. 25 layers of low-refractive-index dielectric layer 2, high-refractive-index dielectric layer 3, low-refractive-index dielectric layer 2, high-refractive-index dielectric layer 3, ... Low-refractive-index dielectric layer 2 on glass substrate 1. The infrared cut filter 4 is composed of SiO ₂ having a refractive index of 1.46 for the low refractive index dielectric layer 2 and TiO ₂ having a refractive index of 2.25 for the high refractive index dielectric layer 3. Has been. Further, as a method for laminating these dielectric films, an electron beam vapor deposition method or the like is used. Further, when the length of the central wavelength of the light to be reflected is λ, the optical film thickness as the first layer is 0.59 × λ / 4, and the optical film thickness as the second layer is 1. 18 × λ / 4, the optical thickness of the third layer is 1.1 × λ / 4, the optical thickness of the fourth layer is 1.1 × λ / 4, and the 25th layer is The film thickness is 0.5 × λ / 4, and the optical film thickness of other layers is λ / 4.
It is composed of.

FIG. 2 shows a spectral characteristic curve diagram of the infrared cut filter 4 on the glass substrate 1 thus constructed.
As is clear from FIG. 2, the ripple in the transmission band near the wavelength shorter than the non-transmission band, that is, near 700 nm is shown in FIG.
It can be greatly reduced compared to the conventional spectral characteristic curve diagram of 0.

FIG. 3 shows a configuration diagram in which the infrared cut filter 4 according to the above embodiment is installed on the light input surface of the package for sealing the light receiving element. In this structure, the light receiving element chip 7 is mounted in the concave portion 6 of the ceramic substrate (stem) 5, the resin 8 is coated thereon, and the infrared cut filter 4 is further installed. In the figure, 9 is a metal lead pin.

FIG. 4 shows a block diagram of another embodiment. On the light receiving surface of the light receiving element 10, the low refractive index dielectric layer 2, the high refractive index dielectric layer 3, the low refractive index dielectric layer 2, the high refractive index dielectric layer 3 ,.
..The infrared cut filter 4 composed of 25 layers of the low refractive index dielectric layer 2 is configured, and the light receiving element 10 generally uses a semiconductor, and has a pin structure,
Many use pn junction structures, photoconductors, and the like. In the present embodiment, a silicon light receiving element and a pn junction structure will be described, but the photodetectors made of other semiconductors have the same structure of the dielectric thin film, and there is no particular difference. Further, the low-refractive-index dielectric layer 2 is made of SiO having a refractive index of 1.46.
₂ , the high refractive index dielectric layer 3 has a refractive index of 2.25 TiO ₂
The case of using will be described.

As a method for laminating these dielectric films, a low refractive index dielectric layer 2 and a high refractive index dielectric layer 3 are alternately formed on the entire surface of a semiconductor wafer having a pn junction formed by using an electron beam evaporation method or the like. After laminating in multiple layers, it is possible to fabricate the silicon light receiving element 10 having the infrared cut filter 4 in which the electrode terminal portion is formed by using the etching method and divided into each chip and the luminosity correction is performed.

In the present invention, when the length of the central wavelength of the light to be reflected is λ, the optical film thickness as the first layer on the silicon light receiving element 10 is 0.59 × λ / 4, and the second thickness is The optical thickness of the layer is 1.18 × λ / 4, the optical thickness of the third and fourth layers is 1.1 × λ / 4, and the 25th
The optical film thickness of the layer is 0.5 × λ / 4, and the optical film thickness of the other layers is λ / 4.

FIG. 5 shows a spectral characteristic curve diagram of the infrared cut filter thus constructed. As is clear from FIG. 5, the wavelength is shorter than the non-transmission band, that is, 700 nm.
The transmittance of the nearby transmission band is higher than the conventional transmittance shown in FIG. 12, but the overall transmittance is low and ripples remain.

Therefore, as shown in FIG. 6, in the above embodiment, the silicon light receiving element 10 and the infrared cut filter 4 are used.
In order to match the refractive index difference between the matching layer 11 and the light receiving surface of the silicon light receiving element 10 and the first interlayer of the infrared cut filter 4, the matching layer 11 has a refractive index of 2.25. the TiO ₂ used in the optical film thickness 0.8 × lambda /
4 is set.

FIG. 7 shows a spectral characteristic curve diagram when the matching layer 11 is provided in this manner. As is apparent from FIG. 7, the ripple in the transmission band near the short wavelength side of the non-transmission band, that is, near 700 nm can be greatly reduced, and the overall transmittance can be further improved.

FIG. 8 shows a sensitivity characteristic curve diagram of a silicon light receiving element having an infrared cut filter obtained by multiplying the spectral characteristic of FIG. 7 by the sensitivity characteristic of silicon. From FIG. 8, it can be confirmed that it is possible to fabricate a silicon light receiving element having an infrared cut filter with ripple-free luminosity correction. Further, since the dielectric thin film can be processed by using the photolithography technique, it is possible to improve the miniaturization and high accuracy of the light receiving element.

The present invention is not limited to the above-described embodiment, and for example, the low refractive index dielectric 2 may be Al ₂ O ₂ having a refractive index of 1.63, and the high refractive index dielectric 3 may be a refractive index 2. Of course, a similar effect can be obtained by using a dielectric material such as ZrO _{2 of} 0.05.

[0022]

As described above, according to the present invention, in the interference filter on the substrate, the optical thickness of the second high-refractive-index dielectric layer, which is counted from the substrate, is larger than λ / 4, By forming the optical film thickness of the three low refractive index dielectric layers to be thicker than λ / 4 and the optical film thickness of the fourth high refractive index dielectric layer to be thicker than λ / 4, It is possible to reduce ripples on the shorter wavelength side, that is, in the 700 nm transmission band.

In the interference filter on the light receiving element, the optical film thickness of the second high refractive index dielectric layer, which is counted from the light receiving surface, is larger than λ / 4, and the third low refractive index dielectric layer is formed. By making the optical film thickness of the fourth layer of high refractive index dielectric layer thicker than λ / 4,
It is possible to improve the transmittance in the shorter wavelength side than the non-transmission band, that is, in the transmission band near 700 nm. Furthermore, by interposing a matching layer between the light receiving surface and the first layer, ripples in the transmission band on the shorter wavelength side than the non-transmission band, that is, near 700 nm can be reduced, and the overall transmittance can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a spectral characteristic curve diagram of the embodiment shown in FIG.

FIG. 3 is a configuration diagram in which the embodiment shown in FIG. 1 is formed on a light receiving element.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

5 is a spectral characteristic curve diagram of the embodiment shown in FIG.

FIG. 6 is a configuration diagram showing still another embodiment of the present invention.

7 is a spectral characteristic curve diagram of the embodiment shown in FIG.

8 is a sensitivity characteristic curve diagram of the embodiment shown in FIG.

FIG. 9 is a configuration diagram showing a conventional example.

10 is a spectral characteristic curve diagram of the conventional example shown in FIG.

FIG. 11 is a configuration diagram showing another conventional example.

12 is a spectral sensitivity characteristic curve diagram of the conventional example shown in FIG.

[Explanation of symbols]

 1 Glass Substrate 2 Low Refractive Index Dielectric Layer 3 High Refractive Index Dielectric Layer 4 Infrared Cut Filter 5 Ceramic Substrate 6 Recess 7 Photoreceptor Chip 8 Resin 9 Metal Lead Pin 10 Photoreceptor 11 Matching Layer

Claims (4)

[Claims] 1. A low-refractive-index dielectric layer is provided on an odd-numbered layer of the substrate, and a high-refractive-index dielectric layer is provided on the even-numbered layer of the substrate. The final layer is an interference filter consisting of an N layer terminated with a low-refractive-index dielectric layer. In the interference filter, the optical thickness of the second layer, which is counted from the substrate, is larger than λ / 4, and the optical layer of the third layer is the same. Thickness is λ / 4
An interference filter characterized in that it is made thicker and the optical thickness of the fourth layer is also made thicker than λ / 4. 2. A light receiving element with an interference filter, wherein the interference filter according to claim 1 is installed on a light input surface of a package enclosing the light receiving element. 3. A light-receiving surface of a light-receiving element is provided with a low-refractive-index dielectric layer in odd layers and a high-refractive-index dielectric layer in even layers counting from the light-receiving surface. In a light-receiving element with an interference filter, wherein the last layer counted from the light-receiving surface is an interference filter made of an N layer that ends with a low-refractive-index dielectric layer, the second optical film counted from the light-receiving surface. The thickness is greater than λ / 4, the optical thickness of the third layer is also greater than λ / 4, and the optical thickness of the fourth layer is λ /.
4. A light receiving element with an interference filter, which is formed thicker than 4. 4. The light receiving element with an interference filter according to claim 3, wherein a matching layer is interposed between the light receiving surface and the first layer.