JPH09321333A - Infrared detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection sensitivity of an infrared detecting device having an optical cavity structure. SOLUTION: A metal silicide film 13 is formed on the upper part of a p-type Si substrate 7 to form Schottky junctions and a reflective film 5 for reflecting infrared lights 12 is formed on the upper part of the silicide film 13 through a dielectric film 6 of specified thickness to form an optical cavity structure of the infrared detecting device which is used as a pixel of the image pickup device. A wiring to be connected to the Si substrate 7 is made of Si-contained Al, while the reflective film 5 is made of Al not contg. Si so as to suppress the lowering of the reflective index due to deposition of Si at the interface between this film 5 and dielectric film 6.

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 and an image pickup element equipped with this infrared detecting element.

[0002]

2. Description of the Related Art Recently, as a sensor for detecting infrared rays,
An infrared detection element using a semiconductor is used. In addition, an infrared imaging device such as a two-dimensional CCD system in which the infrared detection elements are integrated as each pixel and a vertical CCD and a horizontal CCD for transferring a detection signal from each integrated pixel to an output circuit is provided. It has been put to practical use by incorporating VLSI manufacturing technology. Recently, a charge sweep method (CSD) has been used as a vertical charge transfer means.
Method) has also been developed.

As a highly sensitive infrared detecting element utilizing a semiconductor, an element utilizing a Schottky junction between a semiconductor and a metal film has been developed. A Schottky junction type infrared detection element using this Schottky junction in a photoelectric conversion part is a process for manufacturing a general silicon semiconductor integrated circuit (hereinafter, simply referred to as “silicon semiconductor process”).
It is also used to realize an infrared imaging device because it has good compatibility with.

In this Schottky junction type infrared detecting element, a metal silicide film is generally formed on one surface of a semiconductor substrate, and infrared energy incident on the Schottky junction between the metal silicide film and the semiconductor substrate is photoelectrically converted. It has a configuration in which it is converted and taken out to the output circuit via the wiring material. In this case, if the surface of the substrate opposite to the infrared incident surface is left as it is, part of the infrared light incident on the substrate is
Since the Schottky junction is not photoelectrically converted and is transmitted as it is, the utilization efficiency of infrared rays is reduced. Therefore, a reflection film that reflects infrared rays through the dielectric film is provided on the metal silicide film, and the infrared rays reflected by the reflection film are configured to increase sensitivity by passing through the Schottky junction again. Sensing elements have been developed. In this type of infrared detection element, the surface of the substrate opposite to the surface on which the Schottky junction is formed serves as an infrared incident surface. In this case, when the optical path length, which is the product of the refractive index and the film thickness of the dielectric film, is set to 1/4 of the center wavelength of infrared rays, the antinode portion of the standing wave generated by the incident light and the reflected light to the reflective film Coincides with the Schottky junction surface, and sensitivity can be greatly increased. This structure is called an optical cavity structure, and is used in a Schottky junction type infrared detection element to enhance the detection sensitivity.

Further, aluminum (Al) is usually used as a wiring material of an image pickup device using such an infrared detecting element as each pixel. Since aluminum has a function of reducing the natural oxide film on the silicon substrate, it easily forms a contact with the silicon substrate. In particular, when the silicon substrate has a high impurity concentration, it has an advantage that an ohmic contact can be obtained, so that it is generally used as a wiring material for semiconductors.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Infrared detector with optical cavity structure
If a silicon substrate is used as the semiconductor substrate,
Due to the compatibility with the conductor process, silicon is used as the dielectric film.
Oxide film (SiO_Two Film) and silicon nitride film (Si _Three N_Four 
Film) and the reflective film is formed at the same time when the wiring material is formed.
Had formed. That is, the reflective film is made of the same material as the wiring material.
It had been.

In the silicon semiconductor process, aluminum containing usually 1% to several% of silicon (Si) is used as a wiring material. This is to prevent the phenomenon that the silicon of the impurity diffusion layer formed in the silicon substrate diffuses into the wiring material leading to the impurity diffusion layer during the heat treatment and the impurity diffusion layer is destroyed. This phenomenon is a well-known phenomenon, and by mixing silicon in aluminum in advance, diffusion of silicon from the impurity diffusion layer to the wiring material is prevented.

As described above, when the infrared detecting element is manufactured based on the silicon semiconductor process, the infrared reflecting film is formed of the same material as the wiring material. Therefore, the reflection film is formed of an aluminum film mixed with about 1% to several% of silicon. When an aluminum film mixed with silicon is formed as the reflective film by, for example, the sputtering method, a phenomenon occurs in which excess silicon is deposited on the interface between the reflective film and the dielectric when the temperature returns to room temperature after heat treatment. Since silicon has a low reflectance with respect to infrared rays, the deposited silicon lowers the reflectance of infrared rays on the reflective film, which causes a problem that the detection sensitivity of the infrared detecting element is lowered.

In view of the above problems, it is an object of the present invention to provide an infrared detecting element having an optical cavity structure which further enhances the infrared detecting sensitivity, and an imaging element using the infrared detecting element as a pixel. .

[0010]

A first infrared detecting element according to the present invention comprises a metal film (1) on one surface of a semiconductor substrate (7).
3) and the semiconductor substrate (7) are formed with a Schottky junction, and a photoelectric conversion section is formed on the photoelectric conversion section with a dielectric film (6) interposed therebetween to form an optical cavity. In an infrared detection element having a tee structure, the sensitivity to infrared rays incident from the surface of the semiconductor substrate (7) opposite to the photoelectric conversion part is increased by the optical cavity structure, and the reflection film (5) is
This is a metal film containing no impurities.

In the present invention, a substance mixed for a predetermined purpose in a metal (including an alloy) which is a material of the reflective film is defined as an "impurity". Therefore, a very small amount of naturally existing substance may be mixed in the metal film.
According to the first infrared detecting element of the present invention, since the optical cavity structure for increasing the infrared detection sensitivity is provided, the reflecting film (5) is formed of a metal film containing no impurities. In addition, the detection sensitivity of infrared rays is improved without causing adverse effects such as a decrease in reflectance due to impurities.

In this case, examples of the semiconductor substrate (7) and its impurities are a silicon substrate and silicon, respectively. In this case, the reflection film (5) is an aluminum film containing no silicon. This suppresses the phenomenon that silicon is deposited on the reflecting surface of the reflecting film (5) to reduce the reflectance with respect to infrared rays. Further, the second infrared detection element according to the present invention comprises a photoelectric conversion part formed of a Schottky junction between the metal film (13) and the semiconductor substrate (7) on one surface of the semiconductor substrate (7), and this photoelectric conversion part. The optical cavity structure is provided by forming the wiring material (15) for transmitting the photoelectric conversion signal of (1) and forming the reflection film (5) on the photoelectric conversion part via the dielectric film (6), and the semiconductor substrate thereof. In an infrared detecting element having an optical cavity structure that enhances the sensitivity to infrared rays incident from the surface of (7) opposite to the photoelectric conversion part, the wiring material (15) is diffused into the substance constituting the semiconductor substrate. In order to prevent the above, as the metal film containing a predetermined impurity, the reflection film (5) is a metal film containing no impurities.

According to the second infrared detecting element of the present invention as described above, the optical cavity structure enhances the detection sensitivity of infrared rays and a metal film containing no impurities is used as the reflecting film (5). Similar to the first infrared detection element according to the invention, the infrared detection sensitivity is improved without causing any adverse effects such as a decrease in reflectance due to impurities. In this case, since the wiring material (15) contains a predetermined impurity, for example, the wiring material (1) is transferred from the semiconductor substrate (7).
The impurity is not diffused into 5) and the impurity diffusion layer of the semiconductor substrate (7) is not destroyed.

The image pickup device according to the present invention includes a plurality of pixels (D _{1,1 to} D _{m, n} ) formed by the first or second infrared detection device of the present invention and detection signals of the plurality of pixels. And a transfer unit (2 ₁ to 2 _m , 3) for transferring. According to such an image pickup device of the present invention, the pixel according to the first or second aspect of the present invention has high sensitivity to infrared rays.
Since the infrared detecting element is used, a highly sensitive infrared observation image can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of an infrared detecting element and an image pickup element according to the present invention will be described below with reference to the drawings. This example is a charge-coupled device (CCD: Charge).
The present invention is applied to an infrared ray imaging device composed of a coupled device. FIG. 2 is an enlarged plan view of the image sensor of this example. In FIG. 2, pixels D _{1,1 to} D in n rows in the vertical direction and m columns in the horizontal direction (n and m are integers of 2 or more) are shown.
_{m and n} are formed at equal intervals. Hereinafter, a series of pixels arranged in the vertical direction will be referred to as a “vertical pixel”. The image pickup device of this example is an IT (Interline Transfer) type image pickup device, and the main part of the image pickup device is a plurality of vertical pixels, and a plurality of vertical Cs that vertically transfer photoelectric conversion signals of the vertical pixels.
It is composed of a CD and one horizontal CCD for transferring photoelectrically converted signals from the vertical CCD in the horizontal direction.

That is, the pixel D in the first column_1,1 Photoelectric conversion signal
Is the transfer gate C_1,1 Vertical CCD2 via
₁ Sent to the vertical CCD2₁ Once stored in the capacitor
It is. Other pixel D in the first column_1,2 ~ D_{1, n} Photoelectric conversion from
The signal is also vertical CCD2₁To each capacitor of
Stored, vertical CCD2₁ Once stored in the capacitor
Obtained pixel D_1,1 ~ D_{1, n} Photoelectric conversion signal of the gate
Vertical CCD2 is transferred sequentially by pulse₁ From the end of
Transfer gate unit CA₁ To the horizontal CCD3 via
Transferred. Vertical pixels D in the second and subsequent columns_2,1 ~ D_{2, n} ,
…, D_{m, 1} ~ D _{m, n} Similarly, the photoelectric conversion signals from
Vertical CCD 2_Two ,…, 2_m Transfer to horizontal CCD3
Is done. Each pixel D transferred to the horizontal CCD 3_1,1 ~ D
_{m, n} The photoelectric conversion signal of the
D3 is sequentially transferred in the horizontal direction and imaged via the output circuit 4.
It is configured to output as an image signal to the outside of the device.
You.

Further, the structure of the image pickup device shown in FIG. 2 is the same as the image pickup device (C) for visible light used in a general video camera.
The structure is basically the same as that of the CD) and can be manufactured by adding a step of forming a metal silicide film or the like for the Schottky junction to the photoelectric conversion part of the infrared detection element forming each pixel. Next, the configuration of the infrared detection element that constitutes each pixel of the image sensor of FIG. 2 will be described with reference to FIG. Since the pixels D _{1,1 to} D _{m, n} in FIG. 2 are composed of the same detection element, the pixel D _{3,1 in} FIG. 2 will be described as an example.

FIG. 1 is a cross-sectional view of the detection element constituting the pixel D _{3,1 taken} along the line AA in FIG. 2. In FIG.
An antireflection film 8 for preventing reflection of infrared light is provided on the bottom surface (incident surface of infrared light) of the P-type silicon substrate 7. A metal silicide film 13 that forms a Schottky junction with the silicon substrate 7 is formed on the surface of the silicon substrate 7 opposite to the surface on which the antireflection film 8 is formed, and photoelectric conversion including this Schottky junction is formed. The light energy of infrared light is photoelectrically converted by the unit.

A silicon thermal oxide film 11 is formed on both ends of the metal silicide film 13, and the metal silicide film 1 is formed.
A guard ring 9 in which N-type impurities are diffused is provided in contact with the bottom surface of the end portion 3 and the bottom surface of the silicon thermal oxide film 11 to prevent an increase in dark current due to electric field concentration. Also,
This detection element is separated from the detection elements constituting other pixels by the channel stopper 10 in which P-type impurities are diffused. A reflective film 5 is formed on the metal silicide film 13 via a dielectric film 6 having a predetermined thickness.

The antireflection film 8 is used for the incident infrared light 1
Formed with a thickness of approximately 1/4 of the center wavelength of 2 (converted to optical path length)
The vacuum evaporation method of silicon monoxide (SiO) etc.
Formed by vapor deposition on the surface of the silicon substrate.
You. In addition, the metal series used to form the Schottky junction
The side film 13 is formed of platinum silicide (PtSi or Pt). _Two 
Si), palladium silicide (PdSi or Pd_Two S
i) or iridium silicide (IrSi or Ir_Two 
Si) etc. from several angstroms to several tens of angstroms
Is a film formed to a thickness of. The metal silicide film is silicon
Metal on the substrate by electron beam or
PVD (Physical Vapor Depositio) such as sputtering
n) method or CVD (Chemical Vapor Deposition) method
After forming, heat to form by silicidation reaction
You.

As the dielectric film 6, a silicon oxide film or a silicon nitride film formed by a chemical vapor deposition method or the like is generally used. In this case, if the refractive index of the dielectric film 6 is n and the film thickness is d, the optical path length L, which is the product (= n · d) of the refractive index n and the film thickness, of the infrared light 12 is When the central wavelength is λ ₁ , the following relationships are set.

L = n · d = (1/4) λ ₁ The infrared detecting element of this example has a wavelength band of infrared light 12 as
It is assumed that the window of the atmosphere is in the 3 to 5 μm band, and if the center wavelength λ ₁ of the infrared light 12 is set to the center wavelength of 4 μm in the 3 to 5 μm band, the dielectric film 6 has a refractive index n of 1 When the silicon oxide film of 0.46 is used, from the above formula,
The film thickness of the dielectric film 6 may be about 0.7 μm. As a result, an optical cavity structure is formed between the metal silicide film 13 and the reflective film 5 via the dielectric film 6, and the infrared light 12 incident on the silicon substrate 7 can be detected with high sensitivity. There is.

The reflection film 5 is formed on the dielectric film 6 by vapor deposition or sputtering of an aluminum film (Al film) containing no impurities such as silicon after the dielectric film 6 is formed. It is formed by growing with a film thickness of about 4 μm to 1 μm. The infrared light 12 enters the silicon substrate 7 through the antireflection film 8 formed on the surface of the silicon substrate 7 opposite to the surface on which the Schottky junction is formed. Since the silicon substrate 7 is transparent to infrared light, the infrared light 12 reaches the Schottky junction and a part thereof is photoelectrically converted. The infrared light 12 that has not been photoelectrically converted by the Schottky junction is reflected by the reflective film 5 formed on the dielectric film 6 and is incident on the Schottky junction again and photoelectrically converted. The photoelectric conversion signal from the Schottky junction is passed through the impurity diffusion layer (not shown) formed in a part of the silicon substrate 7 and the vertical CC of FIG.
D2 ₃ and through the transfer portion consisting of the horizontal CCD3 is transferred.

FIG. 3 is a sectional view of a part of the transfer portion. In FIG. 3, a wiring material 15 is formed on the silicon thermal oxide film 11 formed on the upper surface of the silicon substrate 7 by vapor deposition or the like. There is. The wiring material 15 is the silicon thermal oxide film 1.
C through the contact hole 18 formed in a part of
It is connected to the gate electrode 16 of the CD, and a transfer pulse is applied to the gate electrode 16 via the wiring material 15. The gate electrode 16 is a high-concentration N-type impurity diffusion layer, and the photoelectric conversion signal from each pixel is sequentially transferred in time series in synchronization with the transfer pulse. In this case, the wiring material 15 is formed by depositing aluminum (Al) containing 1 to 2% by weight of silicon (Si) on the silicon thermal oxide film 11 by using an electron beam or by a sputtering method. . That is,
In this example, the reflective film 5 above the Schottky junction of each pixel is aluminum with no impurities, whereas the wiring material 1
Silicon as an impurity is mixed in 5. When both are formed by vapor deposition, for example, aluminum and silicon may be used as vapor deposition substances when forming the wiring member 15, and aluminum may be simply used as vapor deposition substance when forming the reflective film 5, so that the manufacturing process is so complicated. Does not turn into

The characteristics of the infrared detecting element having the above structure will be described with reference to FIGS. 4 and 5. FIG.
The spectral sensitivity characteristic of the infrared detecting element of this example is shown in comparison with the spectral sensitivity characteristic of the conventional infrared detecting element. In FIG. 4, the horizontal axis indicates the wavelength of infrared light (μm) and the vertical axis indicates the spectral sensitivity (m
A / W). The curve 19 shown by the solid line in FIG. 4 shows the spectral sensitivity of the infrared detection element of this example using an aluminum film in which silicon is not mixed in the reflection film 5, and the curve 20 shown by the dotted line shows that the reflection film contains about 1% of silicon. 9 shows the spectral sensitivity of a conventional infrared detection element using an aluminum film mixed with 100%. As shown by the curves 19 and 20, in the wavelength range of 1 to 5 μm, the infrared detection element of this example has higher spectral sensitivity than the conventional infrared detection element.

FIG. 5 shows the effect of improving the spectral sensitivity of the infrared detecting element of this example with respect to the conventional infrared detecting element. In FIG. 5, the horizontal axis indicates the wavelength (μm) of infrared light and the vertical axis indicates the spectral sensitivity. Shows the improvement rate (%). Further, each point in FIG. 5 represents the improvement rate. As shown by points A1 and A2 in FIG. 5, the improvement rate varies between about 2% and 6%, but is scattered between 3% and 5% in the wavelength range of about 3 μm to 5 μm. The spectral sensitivity of the infrared detector of this example is about 3μ.
In the wavelength range of m to 5 μm, it is improved by about 4% on average as compared with the conventional one.

That is, according to the infrared detecting element of this embodiment, since the aluminum film in which silicon is not mixed is used for the reflection film 5, excess silicon is formed on the boundary surface between the reflection film 5 and the dielectric film 6. Is not deposited and the detection sensitivity to infrared rays is improved. Further, since the infrared imaging element using the infrared detection element of this example as each pixel uses the infrared detection element with high sensitivity as the pixel, a high-sensitivity observation image can be obtained.

Although the silicon substrate 7 is used as the semiconductor substrate in this example, a semiconductor substrate made of selenium (Se), germanium (Ge), gallium-arsenic (GaAs), or the like can also be used. Also, wiring material 1
Although aluminum mixed with silicon is used as the material 5, a material mixed with silicon in a noble metal such as gold (Au) or platinum (Pt) may be used. Although pure aluminum containing no silicon is used as the reflective film 5, other than aluminum, tungsten (W), titanium (Ti), gold, platinum, or an alloy thereof may be used. it can.

Further, the infrared detecting element of the present invention is not limited to the IT type image pickup element, but the photoelectric conversion signal of each pixel is stored in the storage section CC.
F which is transferred to D in parallel and then output via a horizontal CCD
F (Smear) is reduced by providing a storage unit in the T (Frame Transfer) type image sensor or the IT type image sensor.
The same can be applied to an IT (Frame Interline Transfer) type image sensor. The infrared detecting element of the present invention is C
It can also be applied to an SD type image pickup device. Further, it goes without saying that the infrared detecting element of the present invention can be used as a single light receiving element.

As described above, the present invention is not limited to the above-mentioned embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0031]

According to the first infrared detecting element of the present invention, the optical cavity structure enhances the detection sensitivity to infrared rays, and the metal film containing no impurities is used as the reflecting film. Without causing a harmful effect such as a decrease in the reflectance of the reflective film,
There is an advantage that the detection sensitivity of infrared rays is improved.

When the semiconductor substrate and the impurities are a silicon substrate and silicon, respectively, and the reflection film is an aluminum film containing no silicon, silicon is deposited on the reflection surface of the reflection film to reflect infrared rays. There is an advantage that the phenomenon that the rate drops is suppressed. Further, since aluminum has a high reflectance for infrared rays, there is an advantage that the detection sensitivity to infrared rays is particularly high.

Further, according to the second infrared detecting element of the present invention, the optical cavity structure enhances the infrared detecting sensitivity, and since the reflective film does not contain impurities, the first infrared detecting element of the present invention is provided. alike,
There is an advantage that the detection sensitivity of infrared rays is improved. Further, since the wiring material contains a predetermined impurity, the diffusion of the substance forming the semiconductor substrate is prevented, and the reflection film does not diffuse to the reflection film because the dielectric film is interposed therebetween.

Further, according to the image pickup device of the present invention, since the first or second infrared detection device of the present invention having a high detection sensitivity to infrared rays is used as a pixel, a highly sensitive infrared observation image can be obtained. There is an advantage.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing the configuration of an example of an embodiment of an infrared detection element according to the present invention.

FIG. 2 is an enlarged plan view showing the configuration of an example of an embodiment of an image sensor according to the present invention.

FIG. 3 is an enlarged cross-sectional view showing the configuration of part of the transfer unit in FIG.

FIG. 4 is a diagram for explaining the spectral sensitivity characteristic of the infrared detection element in comparison with the spectral sensitivity characteristic of the conventional infrared detection element in the embodiment of the present invention.

FIG. 5 is a diagram showing an improvement rate of the spectral sensitivity characteristic of the infrared detection element in the embodiment of the present invention.

[Description of symbols] D _1,1 ~D _{m, n} pixels 2 ₁ to 2 _m vertical CCD 3 horizontal CCD 4 output circuit 5 reflecting film 6 dielectric layer 7 silicon substrate 8 antireflection film 11 silicon thermal oxide film 12 infrared Light 13 Metal silicide film 15 Wiring material 16 Gate electrode

Claims (4)

[Claims] 1. An optical conversion device comprising: forming a photoelectric conversion part formed of a Schottky junction between a metal film and the semiconductor substrate on one surface of a semiconductor substrate, and forming a reflection film on the photoelectric conversion part via a dielectric film. With a cavity structure,
In an infrared detection element in which the sensitivity to infrared rays incident from the surface of the semiconductor substrate opposite to the photoelectric conversion unit is increased by the optical cavity structure, the reflection film is a metal film containing no impurities. Infrared detector element. 2. The infrared detection element according to claim 1, wherein the semiconductor substrate and the impurities are a silicon substrate and silicon, respectively, and the reflection film is an aluminum film in which silicon is not mixed. Infrared detector element. 3. A photoelectric conversion part formed of a Schottky junction between a metal film and the semiconductor substrate and a wiring material for transmitting a photoelectric conversion signal from the photoelectric conversion part are formed on one surface of the semiconductor substrate, and the photoelectric conversion part is formed on the photoelectric conversion part. An optical cavity structure is provided by forming a reflective film on the
In an infrared detection element having increased sensitivity to infrared rays incident from a surface of the semiconductor substrate opposite to the photoelectric conversion unit by the optical cavity structure, the wiring member prevents diffusion of a substance forming the semiconductor substrate. Therefore, the infrared detection element is a metal film containing predetermined impurities, and the reflection film is a metal film in which the impurities are not mixed. 4. An image pickup device comprising: a plurality of pixels each including the infrared detection device according to claim 1, 2, or 3, and a transfer unit that transfers a detection signal of the plurality of pixels.