JPH02177379A - Infrared photodetector - Google Patents

Abstract

PURPOSE:To facilitate a diffusion process by a method wherein a diffused layer, which is used for forming a P-N junction and consists of an N-type or P-type dopant, is formed on the rear of a substrate and a filter layer, in which a dopant identical with that in the substrate is diffused in a high concentration, is formed on the photodetecting surface of the substrate. CONSTITUTION:A diffused layer 3, which is used for forming a P-N junction and consists of an N-type or P-type dopant, is formed on the rear of a P-type or N-type silicon substrate 1 and a diffused layer 2, which acts as a filter layer to decide the lowest limit of the wave-length of a spectral sensitivity of silicon by a film thickness and in which a dopant identical with that in the substrate 1 is diffused in a high concentration, is formed on the side of the photodetecting surface of the substrate 1. By this constitution, as the sensitivity of the wavelength is controlled by the thickness of the layer 2 on the side of the photodetecting surface, a bulk resistivity and a bulk thickness and moreover, carriers produced by the P-N junction, which is formed by the layer 3 formed by diffusion on the surface of the rear, are captured and collected, an infrared photodetecting element can be manufactured by an easy diffusion process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared light receiving element that can be easily recognized by conventional diffusion techniques without using a visible light cut filter.

[Conventional technology and its problems]

The general structure of an infrared receiving element using a conventional crystalline silicon substrate is to form a visible light cut filter on the light-receiving surface side of a P-N junction silicon substrate (same structure as a solar cell). The output corresponding to infrared irradiation was obtained by cutting wavelengths in the visible light region of the spectral sensitivity of the spectral sensitivity.However, adding a visible light cut filter on the light receiving surface like this would be expensive. Furthermore, in order to protect this visible light cut filter from mechanical damage, the entire light receiving element must be enclosed in a casing, resulting in an increase in size.

JP-A-55-52277 and JP-A-55-46556 are examples of devices that can receive infrared light without a visible light cut filter. These have two P-N junctions formed on a silicon substrate, and the photodiode on the light-receiving surface side converts wavelength light in the visible light region, and the photodiode on the bottom side converts wavelength light in the near-infrared region. This is what each of them is doing. In the photodiode on the lower layer side, what acts as the above-mentioned visible light cut filter is the thickness of the substrate and the photodiode on the light receiving surface side, so the visible light cut filter can be made unnecessary. Ta.

Based on this idea, the structure of a conventional light-receiving element is shown in a sectional view in FIG.

A P-N junction 65 is provided on the light-receiving surface side of the P-type silicon substrate 61.
In addition, so that each P-P" junction is formed at a predetermined depth,
The structure includes an N layer 62, a second layer 63, and a P'' layer 64 from the light receiving surface side.

However, the above-mentioned infrared light receiving element is normally used with a reverse bias voltage applied thereto, and the current in the dark state must be made sufficiently low.

To achieve this, it was necessary to make the diffusion depth of the N layer 62 sufficiently thick from the light-receiving surface side, and to make the concentration of phosphorus atoms, which are dobints in the N layer 62, uniform. This poses a problem in that diffusion control in the diffusion process becomes difficult.

In addition, regarding the extraction of the signal from the light receiving element, Japanese Patent Laid-Open No. 58
In the case of a mesa-type light-receiving element (Fig. 8) as in No. 50783, the diffusion layer 72 that forms a P-N junction on the substrate 71 is diffused, and the output terminals 74, 75 are connected to the diffusion layer 72, which is the light-receiving surface.
was used to derive the output signal.

However, in the above-mentioned light receiving element, the output terminal 74.7
5 is formed on the light-receiving surface side, and in addition to the effective light-receiving area, an area for forming the output terminal is required.Furthermore, when mounted on a measuring device, etc., the lead wire from the output terminal is connected to the inside of the mounting device. The control circuit, that is, the light receiving element had to be routed to the back side of the light receiving element, and the light receiving element had extremely many restrictions.

[Object of the present invention]

The present invention was devised in view of the above problems, and
The purpose is to provide an infrared receiving element that can be achieved through a simple diffusion process without using a visible light cut filter.

Another object is to provide an infrared light receiving element that can be made into a chip.

[Specific Means for Solving Problem C] According to the present invention, in order to achieve the above-mentioned object, an N-type silicon substrate for forming a P-N junction is formed on the back surface of a P-type or N-type silicon substrate. An infrared light receiving element is provided in which a diffusion layer is formed using a type or P type dopant, and a filter layer in which the same dopant as that of the substrate is diffused at a high concentration is formed on the light receiving surface of the substrate.

In addition, a plurality of N-type or P-type silicon substrates are separated from each other so that a P-N junction is formed on the back surface of the P-type or N-type silicon substrate, and two electrodes to which a bias voltage is applied are formed.
An infrared light-receiving element is provided in which a diffusion layer is formed using a type dopant, and a filter layer in which the same dopant as that of the substrate is diffused at a high concentration is formed on the light-receiving surface of the substrate.

〔Example〕

Hereinafter, the infrared light receiving element of the present invention will be explained in detail based on the drawings.

FIG. 1 is a sectional view showing the structure of an infrared receiving element according to the present invention.

The infrared light-receiving element of the present invention includes a P-type or N-type silicon substrate 1, and a light-receiving surface of the silicon substrate 1, which acts as a visible cut filter in which a dopant of the same conductivity type as the substrate 1 is diffused at a high concentration. a first diffusion layer 2; a second diffusion layer 3 in which an N-type or P-type dopant is diffused to form a P-N junction with the P-type or N-type substrate 1 on the back side of the substrate 1; , and electrodes 4.5 formed on both sides.

The silicon substrate 1 is a P-type or N-type, for example, a substrate in which a P-type dopant is mixed in advance (hereinafter also referred to as P bulk).
It is.

The P bulk 1 is a silicon ingot with a thickness of 200 to 50 mm formed by a known method such as a pulling method or a casting method from a molten silicon liquid containing boron atoms at a predetermined concentration.
The slices were sliced at 0μ, and both sides of the slices were treated with a fluoronitric acid solution.

The first diffusion layer 2 is a high concentration P layer of the same conductivity type (hereinafter referred to as P'' layer 2) formed on the light-receiving surface side of the P bulk 1, and due to the thickness of this P'' layer 2, It acts as a filter layer that determines the lower wavelength limit of silicon's spectral sensitivity. The thickness of this P'' layer 2 is approximately 10 to 20 microns.

Specifically, in a diffusion furnace, for example, boron tribromide (B
Diffusion by gas phase reaction in a diffusion gas atmosphere such as Bri), diborane (BZ H & ) to form.

The second diffusion layer 3 is a high concentration N layer of a different conductivity type (hereinafter referred to as N layer 3) formed on the back surface of the P bulk 1. -N junction is formed, and an electric field is applied to carriers generated in the P bulk 1 by long wavelength light incident from the light receiving surface side.

Specifically, a resist is formed on the light-receiving surface side of the above-mentioned P bulk 1, and the back surface side and end surface are etched again.
2) and is formed by diffusing in a gas phase reaction in an atmosphere of a diffusion gas such as a carrier gas such as Ox or Nz.

The electrode 4.5 is for collecting carriers generated by the P-N junction, and is connected to the P″ layer 2 on the light-receiving surface and the N+ layer on the back surface.
Each layer 3 is made of a fully flexural material that can be ohmically bonded to the layer 3 . The electrode 4 on the light-receiving surface side is formed on a part of the light-receiving surface or in a comb shape so that infrared light is sufficiently irradiated from the front surface side, and the electrode 5 on the back surface side is formed on the resistance component with the back surface. is formed on the entire surface in order to minimize the

In the infrared receiving element with the above structure, P which is the light receiving surface
When light is incident from the + layer side, electrons are generated in the P bulk 1.
Hole pairs are generated, electrons are collected in the N+ layer 3 by the electric field of the PN junction formed between the N4 layer 3 and the P bulk 1, and holes are collected in P''B2.

On the other hand, a crystalline silicon substrate has a unique absorption coefficient relationship (FIG. 2) with respect to the incident wavelength, and light with a shorter wavelength than that in FIG. 2 is absorbed in a shallow part of the silicon substrate. That is,
In the infrared receiving element of the present invention, highly doped P″N2 is formed in the shallow part on the receiving surface side, so that light having a relatively short wavelength absorbed by this P″F2 The generated electron-hole pairs disappear immediately, and the photocurrent for wavelength light in the P layer 2 absorption region is attenuated more than the total photocurrent. That is, by controlling the thickness of this P layer 2, sensitivity to wavelengths in the visible light region can be effectively cut.

FIG. 3 is a characteristic diagram showing the attenuation (absorption) state of light with a wavelength of 700 nm with respect to the depth of the substrate. The attenuation rate of incident light is expressed as d=e-''.

(α: absorption coefficient, X: distance from the surface) From the diagram, wavelength 7
At a depth of IOμ from the surface, light of 00 nm is attenuated to 1/10 of that of irradiation, and most of it is absorbed.

Therefore, the thickness of the P'' layer 2 in the present invention may be at least 10 μm, which is sufficient to attenuate light with a large red component in the visible light region of wavelength 700 nm. In view of the processing time and uniformity of diffusion in the diffusion process, less than 50 μl is sufficient at most.

FIG. 4 shows the spectral sensitivity of the infrared receiving element of the present invention.

Note that for line A, the thickness of the P+ layer 2 was set to 10 μl, and for line B, the thickness of the 27 layer 2 was set to 3 μm. Line C is a reference example when the back surface (N' layer side) of the infrared receiving element of the present invention is set as the light receiving side.

From the figure, both line A and line B' have sensitivity peaks at a wavelength of 11,000 nm, and are sufficiently sensitive to infrared light. Furthermore, there is a difference in the lower limit of the sensitivity wavelength between line A and line B, but this is due to the difference in attenuation due to the thickness of the P+ layer 2, as described above.

Further, this difference in spectral sensitivity is also caused by the bulk resistivity and the thickness of the substrate. For example, if the bulk resistivity is 10ΩCO+, the minority carrier diffusion length is 232μ
1, and the carriers generated near the P''FF2/P bulk 1 interface are P-N when the substrate thickness is around 200 μm.
It reaches the junction and contributes to the photocurrent.

On the other hand, when the bulk resistivity is 0.1ΩC@, the diffusion length of minority carriers is 52 μm, and the carriers generated near the 20 layer 2/P bulk 1 interface do not reach the P-N junction, so they contribute to the photocurrent. do not.

Therefore, the spectral sensitivity is determined by the specific resistance and thickness of the bulk and the thickness of the P'' layer 2. Considering the carrier diffusion length due to the bulk specific resistance, the bulk thickness and the thickness of the 21 layer 2 are determined. It may be set to a predetermined value.

In this example (infrared receiving element exhibiting the characteristics shown in FIGS. 3 and 4), the bulk resistivity is 5ΩCIII.

A P-type silicon single crystal substrate with a bulk thickness of 450 μm was used.

As a result, in the present invention, it is possible to achieve a highly accurate infrared receiving element, which has a sufficient sensitivity peak for infrared light, and can also cut out the visible light region that can cause noise.

According to the present invention, the wavelength sensitivity is controlled by the thickness of the P layer 2 on the light-receiving surface side, the specific resistance of the bulk, and the bulk thickness, and the P- layer 3 formed by the N0 layer 3 diffused on the back surface is controlled.
Since the carriers generated at the N junction are collected, it can be manufactured easily and stably by using known diffusion or ion implantation techniques on the light-receiving surface side and the front side, respectively.

In addition, the present invention has a sufficient depth from the light-receiving surface to the PF part that contributes to the generation of effective carriers and a sufficient depth to the P-N junction part for collecting carriers, so that the light-receiving surface has a sufficient impact resistance. Even without a protective resin or the like, an infrared light-receiving element with stable characteristics can be achieved without any bonding failure due to impact or external trauma.

Furthermore, when mounting on a measuring device, a surface cover is not required, making mounting on the device extremely simple.

FIG. 5 is a sectional view showing a mesa-type structure of an infrared receiving element according to the present invention. Note that the same parts as those of the infrared light receiving element in FIG. 1 are given the same reference numerals.

The infrared light receiving element of this embodiment includes a P-type or N-type silicon substrate 1, and a first diffusion layer 2 having the same conductivity type as the substrate 1 and having a dopant diffused at a high concentration on the light-receiving surface of the silicon substrate 1. and a P-type or N-type substrate 1 and a P- type substrate on the front side of the substrate 1.
formed in at least island-like separated second diffusion layers (N″) 3a, 3b in which N-type or P-type dopants are diffused to form an N-junction, and the second diffusion layers F3a, 3b; Electrodes 4a, 4 to which a bias voltage is applied from an external power source
It is composed of b. That is, in this embodiment, the electrode 4a
, 4b is an infrared light receiving element arranged on the back side.

The N''Bs 3a and 3b are formed on the back side of the P bulk 1 and are separated from each other so that no leakage current occurs between them.

Specifically, as mentioned above, the N+ layer is formed by diffusion in a diffusion furnace in a gas phase reaction in an atmosphere of a diffusion gas such as phosphorous oxychloride (POCh) and a carrier gas such as N2. The back side of the P bulk 1 is etched with a hydrofluoric acid solution or the like so that 3a and 3b have a predetermined shape.

The electrodes 4a and 4b are formed on the N''B 3a and 3b, respectively. Specifically, the metal electrodes 4a and 4b are formed by attaching a mask to the N+ layers 3a and 3b, and using a metal such as nickel or aluminum. After depositing a metal film such as nickel or aluminum on N''Fj3a, 3b, resist etching is performed to form a predetermined pattern, or by using a thick film method, nickel or aluminum , a conductive paste containing metal powder such as silver is applied to the N'' layer 3a.
, 3b by coating, drying, and baking.

Then, a constant voltage is applied between the electrodes 4a and 4b from an external circuit (not shown).

6 is a back protection resin that blocks light from entering from the back side and accurately detects incident light from the front side, and its material is a resin material such as acrylic or epoxy with light blocking properties. A mixture of pigments is used.

As described above, the element of this embodiment has a structure in which diode a and diode b, which are connected to each other in a PN junction, are held together.

Next, the operation of the infrared light receiving element of the present invention will be explained.

Now, if we apply a + bias voltage to electrode 4a of diode a and - to electrode 4b of diode b, diode a
A reverse bias is applied to the side, and a forward bias is applied to the diode b.

In the dark state, the resistance between the electrodes 4a and 4b is the sum of the reverse resistance Ra of diode a and the forward resistance Rb of diode b, and the current flowing between the electrodes 4a and 4b is equal to the resistance (
(Ra+Rb) and the bias voltage.

In the bright state in which light is irradiated from the P'' layer 2 side of the infrared receiving element described above (a state in which long wavelength light that can pass through the P'' layer 2 is irradiated), carriers are generated in each of diode a and diode b, A photovoltaic force is generated, but since they have opposite potentials, they cancel each other out, and no photovoltaic current actually flows. but,
Since a bias voltage is applied between the electrodes 4a and 4b, a reverse photocurrent is generated in the diode a. Note that diode b is a resistor consisting of forward resistance.

The current between the two electrodes 4a and 4b is caused by the diode a.
Flows to electrode 4a-N'' layer 3a-P-N junction-P bulk 1-P-N junction of diode b-N1 layer 3b electrode 4b.

FIG. 6 is a sectional view showing the structure of a planar infrared receiving element according to another embodiment of the present invention.

The differences from the structure of the mesa-type infrared receiving element in Fig. 5 are as follows.
This step is a step of diffusing a P-type dopant and a subsequent step to form a P-N junction on the back side of the substrate 1.

The 21 layers 23a and 23b are high concentration diffusion layers of different conductivity types formed separately from each other on the back surface of the N bulk 21. These two P'' layers 23a and 23b are formed sufficiently apart from each other so that no leakage current occurs between them.

The P+ layers 23a and 23b are formed by the following steps. First, a silicon oxide film 28 is formed over the entire N bulk 21 on which the N″ layer 22 has been formed.

Next, the silicon oxide film 28 of the P+ layers 23a and 23b is
is removed with hydrofluoric acid, etc. Furthermore, in a diffusion furnace, N is exposed from the silicon oxide film 28 by a gas phase reaction in an atmosphere of a diffusion gas such as boron tribromide (BBr:+).
It diffuses from the surface of the bulk 21, and diffuses P''Ff23a, 23b to a predetermined depth.

As described above, since the electrodes 4a and 4b are formed on the back side of the infrared receiving element, mounting becomes easy, and by forming a solder layer on the surface of the electrodes, a simple chip component becomes possible.

In the second embodiment (mesa type), a P bulk is used for the silicon substrate, and the structure is P'' layer-PFj-N layer from the light receiving side. ,
It is also possible to have a structure of N layer-N layer-P layer from the light receiving side.

Furthermore, in the third embodiment (planar type), it is desirable to use N bulk because of the influence of the inversion layer between silicon oxide and the silicon substrate. Furthermore, both single crystal and polycrystalline silicon substrates are used because their spectral sensitivities extend to longer wavelengths in the visible light region.

〔Effect of the invention〕

As described above, the present invention forms a diffusion layer made of an N-type or P-type dopant for forming a P-N junction on the back surface of a P-type or N-type silicon substrate, and forms a diffusion layer on the light-receiving surface of the substrate. By controlling the thickness of the filter layer in which the same dopant as that of the substrate is diffused in a high concentration, light in the visible light region that becomes a noise component with respect to infrared light is eliminated. Since it can be completely cut, it is possible to detect infrared light with high precision.

Moreover, it is an infrared light receiving element that can be achieved by an extremely simple structure in which the light is diffused from a diffusion layer on the light receiving surface side and from the back surface side.

Furthermore, since the electrodes 4a and 4b are formed on the back side of the infrared light receiving element, mounting becomes easy, and a simple chip component can be formed by forming a solder layer on the electrode surface.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an infrared receiving element according to the present invention. FIG. 2 is a characteristic diagram showing the relationship between the specific absorption coefficient and the incident wavelength of crystalline silicon. FIG. 3 is a characteristic diagram showing the attenuation situation with respect to the depth of the substrate at a wavelength of 700 nm in the infrared receiving element of the present invention. FIG. 4 is a characteristic diagram showing the spectral sensitivity of the infrared receiving element of the present invention. FIG. 5 is a sectional view of an infrared receiving element according to a second embodiment of the present invention. FIG. 6 is a sectional view of an infrared receiving element according to a third embodiment of the present invention. 7 and 8 are cross-sectional views showing the structure of a conventional light receiving element.

Claims (2)

[Claims] (1) A diffusion layer made of an N-type or P-type dopant to form a P-N junction is formed on the back surface of a P-type or N-type silicon substrate, and the same dopant as the substrate is highly concentrated on the light-receiving surface of the substrate. An infrared receiving element characterized by forming a filter layer that is diffused in concentration. (2) A plurality of N-type or P-type silicon substrates are separated from each other so that a P-N junction is formed on the back surface of a P-type or N-type silicon substrate, and two electrodes to which a bias voltage is applied are formed.
1. An infrared light-receiving element comprising: a diffusion layer made of a type dopant; and a filter layer in which the same dopant as that of the substrate is diffused at a high concentration on the light-receiving surface of the substrate.