JPH05203488A - Infrared light detector element - Google Patents

Abstract

PURPOSE:To obtain an infrared light detector element capable of detecting infrared light with high sensitivity by raising the absorption rate of infrared light without causing any problem in strength of an infrared absorption film and producability, etc. CONSTITUTION:An infrared light detector element is provided with an infrared light detector part 2 having an infrared absorption film 3 on one surface of a base plate 1. The infrared absorption film 3 is constituted of three infrared absorption film layers consisting of two low refractance infrared light absorber film layers 3a and 3c and in between them, a higher refractance film layer 3b than the two.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting element of a type which detects infrared rays by utilizing a change in electric resistance of a resistor due to a temperature change due to absorption of infrared rays.

[0002]

2. Description of the Related Art Recently, as an infrared detecting element of this kind,
Besides the hermetic shield type, a so-called one-chip type in which an infrared detecting section is provided on one surface of a substrate such as a semiconductor substrate has been developed. Here, the infrared detection unit provided on one surface of the substrate is an infrared absorption film that receives and absorbs infrared rays, a thin film resistor whose resistance value changes with temperature rise due to the absorption and absorption of infrared rays, and the thin film resistor It is composed of electrodes and the like for detecting changes in resistance value. In this type of infrared detection element, the higher the infrared absorption rate of the infrared absorption film is, the higher the infrared detection sensitivity can be. However, conventionally, the infrared absorption film is formed of silicon oxide, gold black, platinum black, or the like. In reality, it is composed of a single layer film made of a predetermined material.

[0003]

However, in the above-mentioned conventional technique, for example, when the infrared absorbing film is composed of a single layer film of silicon oxide, the infrared absorbing rate in the wavelength region around 10 μm is relatively good, but it is still unsatisfactory. There is room for improving the infrared absorption rate, and the infrared absorption rate is considerably reduced in the wavelength region other than 10 μm. Therefore, when the silicon oxide film is used, the sensitivity of the temperature rise of the thin film resistor due to the reception of infrared rays is not so good, and the infrared ray detection sensitivity is still unsatisfactory. On the other hand, when the infrared absorption film is composed of gold black or platinum black, although it has an advantage that the infrared absorption rate can be higher than that of the silicon oxide film, these gold black and the like are structurally different in their film composition. For this reason, there are many problems such as poor strength, poor adhesion to the surface of the infrared detecting portion, easy peeling, difficulty in manufacturing in a semiconductor process, and poor mass productivity.

The present invention has been proposed in view of the above points, and it is possible to increase the infrared absorptivity without causing any difficulty in the strength and productivity of the infrared absorptive film and to perform infrared detection with high sensitivity. To provide an infrared detection element capable of
That is the purpose.

[0005]

The infrared detecting element according to the present invention, which has been proposed to achieve the above object, is an infrared detecting element in which an infrared detecting portion having an infrared absorbing film is provided on one surface of a substrate. Therefore, the infrared absorbing film is configured to include three infrared absorbing film layers in which a high refractive index film layer having a higher refractive index than these is provided between two low refractive index film layers. ..

[0006]

In the infrared detecting element characterized by the above structure, when the infrared ray is incident on the infrared absorbing film, first, a part of the infrared ray is reflected by the outermost low refractive index film layer, and
A part of the infrared ray that is not reflected is transmitted through the low refractive index film layer, and a part thereof is reflected by the surface of the high refractive index film layer, and is absorbed by the outermost low refractive index film layer. The other part of the infrared light transmitted through the outermost low-refractive index film layer is incident on the high-refractive index film layer and part of it is absorbed, while the remaining part of the infrared ray has a low refractive index Also reflected on the surface of the rate film layer,
It is absorbed by the high refractive index film layer. Furthermore, a part of the infrared rays that are incident on the low refractive index film layer without being reflected on the surface of the lowermost low refractive index film layer are reflected on the infrared detection section surface and absorbed by the high refractive index film layer. Becomes

As described above, according to the present invention, the infrared absorption and reflection absorption are repeated between the three infrared absorption film layers having different refractive indexes, and the infrared light transmitted through each infrared absorption film layer is the original. It is possible to absorb the light by reflecting it toward the infrared absorbing film layer side, and the infrared absorption rate can be increased. Further, since the infrared absorbing film is composed of three layers of infrared absorbing film, the infrared absorbing wavelength region can be specified by making these infrared absorbing film layers have characteristics of absorbing infrared rays in different wavelength regions. It is also possible to solve the problem of being limited to a narrow constant wavelength region.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an infrared detecting element A according to the present invention, and FIG. 2 is a sectional view thereof. The infrared detection element A
Is a semiconductor substrate 1 made of silicon or the like, on the surface of which an infrared detecting section 2 provided with an infrared absorbing film 3 is provided.

Here, the semiconductor substrate 1 has an insulating film 4 formed of a silicon oxide film or a multilayer film of silicon oxide and silicon nitride or the like over the entire surface thereof. A heat separation space 5 is provided below the infrared detector 2 and below the insulating film 4. The heat separation space portion 5 is for suppressing the undesired flow of heat from the infrared detection portion 2 to the semiconductor substrate 1 side, and the KOH from the back surface side of the semiconductor substrate 1 located below the infrared detection portion 2 is adjusted to KOH.
The insulating film 4 is formed by performing anisotropic etching treatment with a liquid.
By removing a part of the lower layer, a desired cutout is formed.

The infrared detecting section 2 comprises a thin film resistor 2b, a pair of upper and lower electrodes 2a and 2a ', and an infrared absorbing film 3 provided on the surface of the upper electrode 2a. Of these, the infrared absorption film 3 is composed of two low refractive index film layers 3a and 3c.
Between them, a high refractive index film layer 3b having a higher refractive index than the low refractive index film layers 3a and 3c is provided.
The outermost low-refractive index film layer 3a is formed of, for example, a silicon oxide film, and its optical film thickness is formed to be ¼ of the infrared wavelength to be detected. The optical film thickness is the product of the refractive index of the film and the film thickness.
In the case where the infrared ray detection of 0 μm is mainly used and the silicon oxide film (refractive index 1.46) is applied, the film thickness thereof is set to about 1.7 μm. The lowermost low-refractive index film layer 3c may be formed with the same material and thickness as the outermost low-refractive index film layer 3a, but otherwise, silicon or various silicon compounds may be used. This is applicable, and in this embodiment, for example, a silicon nitride film having a thickness of about 1.2 μm is applied.

The high-refractive-index film layer 3b may be formed as a thin film having an appropriate thickness by using a metal having a small extinction coefficient. The extinction coefficient is the imaginary part k of the complex refractive index n + ik. As the high refractive index film layer 3b, for example, a nickel chromium alloy film having a thickness of 0.05 μm or less is applied. A nickel-chromium alloy having a film thickness of 0.01 μm has a high absorption efficiency of 93% in infrared absorption.

On the other hand, the thin film resistor 2b of the infrared detector 2
Is made of amorphous silicon or polycrystalline silicon having a film thickness of 0.1 to 5.0 μm, for example, and its resistance value changes with temperature change. The thin film resistor 2b includes both a resistor whose resistance value increases and a resistor whose resistance value decreases as the temperature rises, and any type may be used in the present invention.
The electrodes 2a and 2a ′ are provided on the upper and lower sides of the thin film resistor 2b so that the change in the resistance value of the thin film resistor 2b can be accurately detected, and are configured to contact the thin film resistor 2b in a wide area. Has been done. However, the electrodes 2a and 2a 'are not of a type that sandwiches the upper and lower sides of the thin film resistor 2b, but are electrodes of a type in which the planar shape is formed in a comb shape so as to widely contact only one side of the thin film resistor 2b. I don't care. The electrodes 2a, 2a 'are also preferably formed of a thin film material suitable for a semiconductor process, and examples of the material include Al and C
A metal thin film such as r is suitable.

Although each end of the electrodes 2a and 2a 'is connected to the signal processing circuit 6, the signal processing circuit 6 is appropriately provided in another portion of the semiconductor substrate 1 below the insulating film 4. It is possible to provide an amplifying circuit and other circuits similar to those of a normal infrared detecting device. Further, the infrared detecting element A may be integrally provided with an infrared transmitting filter that blocks only electromagnetic waves while blocking electromagnetic waves other than infrared by forming a thin film.

In the infrared detecting element A having the above structure, not only the electrodes 2a, 2a 'of the infrared detecting section 2 and the thin film resistor 2b but also the respective layers 3a to 3c of the infrared absorbing film 3 are formed in accordance with the semiconductor process. It is possible. In addition, the infrared detector 2
The outermost silicon oxide low-refractive-index film layer 3a is excellent in mechanical strength and can also function as a protective film for the infrared detecting section 2.

Next, the operation of detecting infrared rays using the infrared detecting element A will be described. First, when infrared rays are irradiated from above the front side of the semiconductor substrate 1, the infrared rays are absorbed by the infrared absorption film 3. , The temperature of the thin film resistor 2b rises. Then, as the temperature rises, the thin film resistor 2
Although the resistance value of b changes, this change in resistance value is
Infrared ray detection is performed by the detection through a, 2a ′ and the signal processing circuit 6.

When infrared rays enter the infrared absorption film 3, a part of the infrared rays is first reflected by the outermost low refractive index film layer 3a, but enters the low refractive index film layer 3a. Infrared rays pass through the low-refractive-index film layer 3a, and the next high-refractive-index film layer 3
When it reaches the surface of b, it is reflected upward due to the difference in refractive index. Therefore, the light reflected by the low-refractive index film layer 3a and the light reflected by the surface of the high-refractive index film layer 3b cancel each other out of phase, and as a result, are absorbed by the low-refractive index film layer 3a. Will be done. Further, most of the infrared rays that are not reflected by the surface of the high refractive index film layer 3b and enter the high refractive index film layer 3b are absorbed by the high refractive index film layer 3b as they are. Further, the infrared rays which are not directly absorbed by the high refractive index film layer 3b are incident on the lowermost low refractive index film layer 3c and are also reflected by the surface of the upper electrode 2a made of a material such as Al. The reflected light is also efficiently absorbed by the high refractive index film layer 3b.

As described above, each layer 3a of the infrared absorbing film 3 is
Since 3b and 3c efficiently absorb not only direct absorption of infrared rays but also reflected infrared rays, the infrared absorption rate of the infrared absorption film 3 as a whole is very high. In particular, if the optical film thickness of the low refractive index film layers 3a and 3c is set to ¼ of the infrared wavelength, the method disclosed in Japanese Patent Laid-Open No.
As can be understood from the known theory described in No. 1969929, it is possible to maximize the infrared absorption efficiency in the low refractive index film layers 3a and 3c. Further, when the outermost low-refractive index film layer 3a is a silicon oxide film, it becomes possible to further increase the infrared absorption rate in the wavelength band of 10 μm, which is convenient for detecting the human body emitting infrared rays in the wavelength band. Becomes Further, the low-refractive index film layers 3a and 3c and the high-refractive index film layer 3b are made of different materials. However, since each of these layers has a property of absorbing infrared rays in different wavelength regions, it absorbs infrared rays. It is also possible to eliminate that the wavelength region is limited to a specific narrow constant wavelength region. Therefore, the temperature rise width of the thin film resistor 2b due to infrared absorption can be further widened, and the temperature rise speed can be made faster.

FIG. 3 is an experimental data value showing the infrared absorption rate of the infrared absorption film having a predetermined three-layer structure according to the present invention in relation to the wavelength of the infrared light to be received. When the infrared absorptivity of the infrared absorptive film according to the present invention is compared with the infrared absorptivity of the silicon oxide single layer film also shown in the same figure, the infrared absorptivity of the present invention is excellent in any wavelength region. Be understood.

In the above embodiment, the heat separation space 5 is formed below the infrared detecting section 2 to prevent undesired heat outflow from the infrared detecting section 2 to the semiconductor substrate 1 and to further detect infrared rays. Although the advantage of improving the sensitivity can be obtained, the present invention is not limited to the presence or absence of the heat separation space portion 5 and the other specific configurations of the respective portions are not limited to those in the above embodiment. In addition, the low refractive index of the low refractive index film layer and the high refractive index of the high refractive index film layer according to the present invention mean that the refractive index in the relationship between the three infrared absorbing film layers is This is a comparative comparison, and the point is that the refractive index of the layer located in the middle between the outermost layer and the lowermost layer of the three infrared-absorbing film layers should be higher. Needless to say, each layer must have a function and characteristic of absorbing infrared rays. Further, the infrared absorbing film according to the present invention,
It is only necessary that the infrared ray absorbing film layer is configured to include the three infrared ray absorbing film layers, and for example, a configuration in which another infrared ray absorbing film layer is additionally provided below the lowermost low refractive index film layer is also included in the present invention. It does not deviate from the technical idea.

[0020]

As described above, according to the infrared detecting element of the present invention, infrared absorption is achieved without using a material such as gold black or platinum black which has many difficulties in strength and mass productivity. Since the infrared absorption rate of the film can be significantly increased,
The mechanical strength and mass productivity can be improved, and at the same time, the special effect that the sensitivity and responsiveness of infrared detection can be made extremely excellent can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an infrared detection element according to the present invention.

FIG. 2 is a sectional view of the infrared detection element shown in FIG.

FIG. 3 is an explanatory diagram comparing infrared absorption rates of an infrared absorption film according to the present invention and a conventional absorption film.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Infrared Detector 2a, 2a 'Electrode 2b Thin Film Resistor 3 Infrared Absorbing Film 3a Low Refractive Index Film Layer 3b High Refractive Index Film Layer 3c Low Refractive Index Film Layer 4 Insulating Film 5 Thermal Separation Space 6 Signal Processing Circuit A infrared detector

Claims (4)

[Claims] 1. An infrared detecting element comprising an infrared detecting section having an infrared absorbing film on one surface of a substrate, wherein the infrared absorbing film is provided between two low refractive index film layers. An infrared detecting element having a structure including three infrared absorbing film layers provided with a high refractive index film layer having a high refractive index. 2. The infrared detecting element according to claim 1, wherein the low refractive index film layer is configured so that its optical film thickness is ¼ of an infrared wavelength to be detected. 3. The infrared detection element according to claim 1, wherein the high refractive index film layer is a nickel chromium alloy. 4. The infrared detection element according to claim 1, wherein the outermost low-refractive index film layer of the two low-refractive index film layers is silicon oxide.