JPH0582825A - Photodiode - Google Patents

Abstract

PURPOSE:To improve the dark current property, the photosensitivity, and the after-image property of a PIN or NIP-type photodiode wherein the amorphous semiconductor layer is I layer. CONSTITUTION:In a PIN or NIP-type photodiode wherein the I layer 13 consists of an amorphous semiconductor layer, the p-type semiconductor layer and/or the n-type semiconductor layer p composed of the two layers of first semiconductor layers 12a and 14a, which have polycrystalline structure, at least, with the same materials as the I layer, and second semiconductor layers 12b and 14b, which have polycrystalline or amorphous structure consisting of the constituent elements of the I layer and forbidden band width enlarged elements, and the first semiconductor layers 12a and 14a are arranged close by the I layer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode, and more particularly to a PIN type or N type in which the I layer is an amorphous semiconductor layer.
The present invention relates to an IP type photodiode.

[0002]

2. Description of the Related Art A semiconductor light receiving element for converting an optical signal into an electric signal is one of the most important and basic constituent elements in a video information system using light as a medium of an information signal, optical communication, other industries and consumer fields. This is one, and many have already been put to practical use. In general, the photoelectric conversion characteristics of the light receiving element are required to have a high signal-to-noise ratio (high S / N ratio), to realize highly sensitive reading, and to have a high response speed.

Among these, as an input element of an image processing apparatus such as a high speed facsimile, an image scanner, a copying machine, etc.,
With the miniaturization and personalization of devices, a contact type is desired, and it is required to form a large-area element array.

Area sensors such as CCDs used in industrial surveillance and consumer video cameras include:
Since the output signal becomes smaller as the density of pixels becomes higher, it is desirable to keep the pixel area as large as possible. On the other hand, in recent years, technological development has been advanced in the direction of effectively using the area by forming the signal processing circuit section and the light receiving element in a laminated structure.

A PIN photodiode made of amorphous silicon is promising as a means for realizing the above-described high-speed, high-sensitivity light-receiving element with a large area or a laminated structure.

In the PIN photodiode, the simplest form is to form each layer with amorphous silicon, but dark current is generated by blocking minority carriers, which is important as a function of the impurity layer of P layer or N layer. In order to reduce the incident current and transmit the incident light as much as possible to suppress the decrease in the photocurrent, the activation rate of impurities is not high and the absorption coefficient of visible light, especially short wavelength light is large. Therefore, sufficient characteristics could not be obtained.

For this reason, attempts have been made to reduce the dark current and suppress the decrease in photocurrent by changing the film structure or composition of the impurity layer. Regarding the film structure, switching from amorphous silicon to polycrystalline silicon reduces the electrical bandgap somewhat, but the activation rate of impurities is greatly improved, and the blocking property of minority carriers is greatly improved. To do. At the same time, the light absorption coefficient in the visible light region is reduced, and the light transmission is improved (note that amorphous here means that the near-range order of the nearest neighbor atom is preserved, but There is no long-range order,
A polycrystal is a set of single crystal grains that do not have a specific crystal orientation and are isolated by grain boundaries.

Furthermore, by changing the composition of the film and widening the electrical band gap, such as Si _1-x N _x and Si _1-x C _x , the activation rate of impurities may be slightly different. In addition, a sufficient blocking property of minority carriers can be obtained, and the dark current can be suppressed to be small. Further, by widening the band gap, absorption of visible light is considerably suppressed, and the loss of light transmission due to the impurity layer is considerably reduced.

FIG. 12 shows a dark current of a PIN photodiode made of amorphous silicon, and a PIN photodiode having an impurity layer of amorphous silicon carbide (Eg = 2.1 eV), which is a conventional improvement example. It is a characteristic view showing the difference of.

FIG. 13 is a characteristic diagram showing the difference in spectral sensitivity characteristic.

The effect of reducing the dark current and suppressing the decrease of the photocurrent is
It is becoming more apparent as amorphous silicon changes to polycrystalline silicon and amorphous silicon carbide. When the composition is changed and the band gap is increased, a sensor with good characteristics can be obtained by static operation. I understand that.

[0012]

However, in the above-mentioned conventional example, in the case of polycrystalline silicon in which only the structure is changed, an impurity layer which can satisfy both the reduction of the dark current and the suppression of the reduction in sensitivity is formed. There is a problem that the degree of freedom in designing the film thickness, the impurity concentration, and the like is not so large, and the characteristics of the impurity layer do not always have sufficient margin.

In an example such as amorphous silicon carbide in which the composition is changed to widen the band gap,
As mentioned above, static behavior is sufficient, but dynamic behavior has not been considered. That is, in the actual reading operation, since pulse driving is performed, the photoresponse characteristic called afterimage is an important point as a sensor characteristic, but the composition is different from that of the I layer such as amorphous silicon carbide. When the material is bonded to the I layer,
Many defect levels are formed at the interface with the layer, which adversely affects the afterimage. In general, in amorphous and polycrystalline materials, a material having a different composition does not sufficiently reduce the defect level density of the film as compared with silicon, and afterimages are also produced when a junction is formed with the I layer. There was a problem of making it worse.

FIG. 14 is a characteristic diagram showing the difference in afterimage characteristics when a wide gap material is used for the impurity layer and when amorphous or polycrystalline silicon is used as the impurity layer.

The present invention has been made to solve the above problems, and is a PIN type or NIP which simultaneously realizes reduction of dark current, suppression of deterioration of photosensitivity, and high-speed response.
Type photodiode is provided.

[0016]

That is, according to the present invention, in a PIN type or NIP type photodiode in which the I layer is an amorphous semiconductor layer, the P type semiconductor layer and / or the N type semiconductor layer is at least the I layer. And a second semiconductor layer having a polycrystalline or amorphous structure composed of a constituent element of the I layer and a band gap widening element. And the first semiconductor layer is
Characterized by being arranged adjacent to the layer.

According to the present invention, it is possible to obtain a high-sensitivity photosensor in which the dark current is reduced and the photosensitivity is improved without deteriorating the afterimage characteristic.

FIG. 1 is a sectional view showing the structure of an embodiment of the photodiode of the present invention.

The embodiment example shown here is a case where the P-type semiconductor layer and the N-type semiconductor layer have a two-layer structure of a first semiconductor layer and a second semiconductor layer.

As shown in FIG. 1, the photoelectric conversion device according to the present embodiment has a first electrode 11 formed on an insulating substrate or a semiconductor substrate 10 coated with an insulating thin film, and the first electrode. 11, a semiconductor layer 16 for forming a non-single-crystal PIN or NIP junction, and a transparent electrode 15 formed on the semiconductor layer 16, and the N-type semiconductor layer 12 and the P-type having the PIN or NIP junction. Both of the semiconductor layers 14 are first semiconductor layers 12a and 14a each made of the same material as the I layer 13 and having a polycrystalline structure, and a polycrystalline or amorphous structure composed of a constituent element of the I layer and a band gap widening element. The first semiconductor layers 12a and 14a are arranged adjacent to the I layer.

In the present invention, each of the two impurity layers separately plays the role of reducing the dark current and the role of reducing the afterimage, so that the prior art cannot satisfy both characteristics at the same time. Can be achieved by the present invention. Further, the means for reducing the dark current coincides with the direction of improving the light transmittance in the impurity layer, and in the polycrystalline layer for reducing the afterimage, the activation of impurities is increased, so that the film thickness can be reduced. It leads to improvement of light transmittance. Therefore, it is possible to improve the photosensitivity at the same time.

The material used in the present invention is an a-SiGe: H, a-Si, which is made of an amorphous silicon-based alloy for forming a large-area thin film in the I layer which is the light absorption layer.
C: H, a-SiN: H, a-SiSn: H, a-Si
O: H and a-GeC: H.

Carbon (C), nitrogen (N) and oxygen (O) are used as the band gap widening element used to form one of the two-layered impurity layers. Is I
When added to the layer and another impurity layer,
The content ratio of the elements such as C, N and O in the film is increased. For example, when the I layer is formed of a-Si _0.8 C _0.2 : H, the impurity layer that expands the band gap has a
-Si _0.5 C _0.5 : H is used.

The impurity added to the impurity layer is P
Group III atoms of the Periodic Table are used for type control, and Group V atoms are used for N-type control.

Specifically, the group III atom is B
(Boron), Al (aluminum), Ga (gallium), In (indium), Tl (thallium) and the like can be mentioned, but B and Ga are particularly preferable. Further, as the group V atom, P (phosphorus), As (arsenic), Sb (antimony), Bi (bismuth) and the like can be mentioned, but P and Sb are particularly preferable.

The material used as the transparent electrode is IT
O, SnO ₂ , ZnO ₂ or the like is used.

As the lower electrode, any commonly used metal electrode such as Cr, Al, or Ti can be used, and it is also possible to use an N-type or P-type polysilicon film doped with a high concentration of impurities. When the semiconductor substrate is used as the substrate, the high-concentration impurity layer formed in the semiconductor substrate can be used as the lower electrode through the contact hole formed in the deposited insulating layer.

The film thickness d _c of the impurity layer of the polycrystalline semiconductor formed adjacent to the I layer and made of the same material as the I layer is I
If the depletion layer that has penetrated into the impurity layer due to the electric field applied to the layer is given with a minimum film thickness that does not reach the impurity layer containing the forbidden band widening element, deterioration of afterimage and deterioration of photosensitivity will not occur. You can That is,

[0029]

[Equation 2] Is the minimum required film thickness, in other words, the optimum film thickness,
It may be determined in consideration of the maximum value of the drive voltage of the sensor.

Here, d _I : I layer film thickness N: Impurity concentration ε: Dielectric constant of impurity layer V _R : Applied voltage φ _BI : Built-in potential of PIN junction q: Unit charge

Further, in order to suppress the deterioration of photosensitivity as much as possible, it is desirable that the impurity concentration is as high as possible. For example, the activated impurity concentration in polycrystalline silicon is 10 ²⁰
If the applied voltage is 10 V, the minimum required film thickness is d _c ≈10 ⁻⁸ (cm) = 1 Å. In reality, it is necessary to consider the size of the grain size of the polycrystal, so it can be seen that several hundred Å is sufficient.

As mentioned above, a polycrystal is a collection of single crystal grains having no specific crystal orientation, separated by grain boundaries, and having a grain size of about 30 to 300Å. What is used.

[0033]

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

FIG. 2 shows a first photodiode of the present invention.
It is a schematic plan view which shows an Example.

FIG. 3 is a sectional view taken along the line AA 'of FIG.

FIG. 4 is a sectional view taken along the line BB 'of FIG.

The manufacturing process of the photodiode of this embodiment will be described below with reference to FIGS.

First, a 2000 Å thick Cr film was deposited on a # 7059 glass substrate 400 manufactured by Corning Co. by a sputtering method. Then, by a normal photolithography process,
The lower electrode 401 of the photodiode was formed by etching into a desired shape.

After that, the substrate temperature was set to 300 ° C. by a capacitive coupling type CVD apparatus, and SiH ₄ 40SCCM, H ₂
Introduce diluted 10% PH ₃ 20SCCM, NH ₃ 20SCCM, and high frequency 0.2W under the condition of gas pressure 0.2 Torr.
/ Cm ² discharge for 1 minute and 40 seconds to deposit an N-type amorphous silicon nitride layer 402b (thickness 300 Å) which is a blocking layer for the second hole, and then the substrate temperature is also measured by the capacitive coupling type CVD device. To 300 ° C,
SiH ₄ 6SCCM, H ₂ diluted 10% PH ₃ 24SCC
Introduced M, H ₂ 450 SCCM, gas pressure 2.0 Tor
Under the condition of r, a high frequency of 0.5 W / cm ² is discharged for 16 minutes and 40 seconds to deposit an N-type polycrystalline silicon layer 402a (thickness 300 Å) which is a blocking layer of the first hole to complete the blocking layer of the hole. did.

Next, the substrate temperature was set to 300 ° C. by the same capacitive coupling type CVD apparatus, and SiH ₄ 30SCCM, H was added.
The ₂ 30 SCCM is introduced, at a gas pressure of 0.3Torr at high frequencies 0.2 W / cm ² performs 75 minutes discharge, it was deposited a light-absorbing layer 403 (thickness 8000 Å).

Further, similarly, the substrate temperature was set to 300 ° C. by the capacitive coupling type CVD apparatus, and SiH ₄ 6SCCM, B was used.
Introducing ₂ H ₆ 12 SCCM and H ₂ 450 SCCM, discharging under a gas pressure of 2.0 Torr at a high frequency of 0.5 W / cm ² for 16 minutes and 40 seconds, and a P-type polycrystalline silicon layer as a first electron blocking layer. 404a (film thickness 300Å)
Was deposited, and then the substrate temperature was set to 300 ° C. by the same capacitive coupling type CVD apparatus, and SiH ₄ 24SCCM, H
₂ dilution 10% B ₂ H ₆ 20SCCM, CH ₄ 36SCC
M was introduced, and discharge was performed at a high frequency of 0.2 W / cm ² for 1 minute 40 seconds under a gas pressure of 0.3 Torr, and a P-type amorphous silicon carbide layer 404b (film) serving as a second electron blocking layer. A thickness of 300Å) was deposited to complete the electron blocking layer.

After that, 70% of ITO was sputtered.
Then, the upper transparent electrode 405 was formed by depositing 0Å and then etching it into a desired shape by a normal photolithography process.

Then, the semiconductor layers 404a, 404b, 403, 402a,
402b was etched into a desired shape to isolate the semiconductor layer.

Next, with a capacitively coupled CVD apparatus, the substrate temperature was set to 300 ° C. and hydrogen diluted 10% SiH ₄ gas was added to 10 times.
0 SCCM, NH ₃ gas at a flow rate of 100 SCCM, gas pressure is adjusted to 0.4 Torr, and high frequency power is 0.01 W
/ Cm ² was discharged for 1 hour to form a protective layer 406 of 3000 Å SiN _x film. Subsequently, the SiN _x layer 406 was etched into a desired shape by a normal photolithography process to form contact holes for taking out the upper electrode and the lower electrode.

After that, 1.0 μ of Al was formed by the sputtering method.
m deposition, followed by a conventional photolithography process,
An element was created by etching into a desired shape and forming a wiring electrode 407 for drawing out the upper electrode.

When the photodiode manufactured as described above was evaluated, the following results were obtained. (1) As shown in the IV characteristic of FIG. 6, the dark current was suppressed to about 3 × 10 ⁻¹¹ A / cm ² when the reverse bias of 5 V was applied. (2) As shown in the spectral sensitivity characteristic of FIG.
The sensitivity of the light of m as quantum efficiency is maintained up to 91%. (3) As shown in the afterimage characteristic of FIG. 8, the afterimage in the first field was suppressed to about 0.5%.

FIG. 9 shows a second photodiode of the present invention.
It is a schematic plan view which shows an Example.

FIG. 10 is a sectional view taken along the line AA 'of FIG.

FIG. 11 is a sectional view taken along the line BB 'of FIG.

The manufacturing process of the photodiode of this embodiment will be described below with reference to FIGS.

First, a 2000 Å thick Cr film was deposited on a # 7059 glass substrate 800 manufactured by Corning Incorporated by a sputtering method. Then, by a normal photolithography process,
The lower electrode 801 of the photodiode was formed by etching into a desired shape.

Then, the substrate temperature was set to 300 ° C. with an ECR-CVD apparatus, and H ₂ diluted 10% SiH ₄ 10S was used.
CCM, H ₂ diluted 10% CH ₄ 10 SCCM, H ₂ 50
SCCM, introducing diluted with H ₂ 500ppmPH ₃ 40SCCM, in the magnetic flux density of 875 gauss at a gas pressure of 1.0 mTorr, 2.45 GHz, performed 5 minutes the decomposition of the gas by the microwave 300 W, N-type polycrystalline silicon carbide Layer 802b (thickness 300Å) was deposited.

Subsequently, the substrate temperature was set to 300 ° C. by a capacitive coupling type CVD apparatus, SiH ₄ 6SCCM, H ₂ diluted 10% PH ₃ 24SCCM, H ₂ 450SCCM were introduced, and high frequency was applied under the condition of gas pressure of 2.0 Torr. 0.5W / c
A discharge was performed at m ² for 16 minutes and 40 seconds to deposit an N-type polycrystalline silicon layer 802a (thickness 300Å) as a blocking layer for the first hole to complete the hole blocking layer.

Next, the substrate temperature was set to 300 ° C. by the same capacitive coupling type CVD apparatus, and SiH ₄ 30SCCM, H
The ₂ 30 SCCM is introduced, at a gas pressure of 0.3Torr at high frequencies 0.2 W / cm ² performs 75 minutes discharge, it was deposited a light-absorbing layer 803 (thickness 8000 Å).

Similarly, the substrate temperature was set to 300 ° C. by the capacitive coupling type CVD apparatus, and SiH ₄ 6SCCM, B was used.
Introducing ₂ H ₆ 12 SCCM and H ₂ 450 SCCM, and discharging under a gas pressure of 2.0 Torr at a high frequency of 0.5 W / cm ² for 16 minutes and 40 seconds, and a P-type polycrystalline silicon layer as a first electron blocking layer. 804a (film thickness 300Å)
Was deposited.

Then, the substrate temperature was set to 300 ° C. by an ECR-CVD apparatus, and H ₂ diluted 10% SiH ₄ 10S was set.
CCM, H ₂ diluted 10% CH ₄ 10 SCCM, H ₂ 50
SCCM, H ₂ diluted 500ppm B ₂ H ₆ 40SCCM
Is introduced, and the gas is decomposed by a microwave of 2.45 GHz and 300 W in a magnetic flux density of 875 Gauss at a gas pressure of 1.0 mTorr to deposit a P-type polycrystalline silicon carbide layer 804b (thickness 300 Å). , Formed an electron blocking layer.

After that, 70% of ITO was formed by the sputtering method.
Then, the upper transparent electrode 805 was formed by depositing 0Å and then etching it into a desired shape by a normal photolithography process.

Then, the semiconductor layers 804a, 804b, 803, 802a,
802b was etched into a desired shape to isolate the semiconductor layer.

Next, the substrate temperature was set to 300 ° C. with a capacitively coupled CVD apparatus, and 10% SiH ₄ gas diluted with hydrogen was used.
0 SCCM, NH ₃ gas at a flow rate of 100 SCCM, gas pressure is adjusted to 0.4 Torr, and high frequency power is 0.01 W
/ Cm ² and discharged for 1 hour to form a protective layer 806 of 3000 Å SiN _x film. Subsequently, the SiN _x layer 806 was etched into a desired shape by a normal photolithography process to form contact holes for taking out the upper electrode and the lower electrode.

After that, Al is 1.0 μm by the sputtering method.
m deposition, followed by a conventional photolithography process,
An element was prepared by etching into a desired shape and forming a wiring electrode 807 for drawing out the upper electrode.

When the photodiode manufactured as described above was evaluated, the following results were obtained. (1) Dark current is 3 × 10 ⁻¹² when reverse bias of 5 V is applied.
It was suppressed to about A / cm ² . (2) The quantum efficiency of light with a wavelength of 560 nm is maintained at 93%. (3) The afterimage in the first field was suppressed to about 0.5%.

In the embodiment described above, P
A first semiconductor layer having the same material as that of the I layer and having a polycrystalline structure for both the n-type semiconductor layer and the n-type semiconductor layer, and a polycrystalline or amorphous material including a constituent element of the I layer and a band gap widening element Although the second semiconductor layer having a structure and two layers are used, the present invention uses P
The effect of the present invention can be obtained even if either one of the type semiconductor layer and the N-type semiconductor layer has a two-layer structure composed of the first semiconductor layer and the second semiconductor layer.

FIG. 5 is a constitutional view in the case where only the P-type semiconductor layer of the first embodiment of the photodiode of the present invention has a two-layer constitution. The same components as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

As compared with FIG. 4 which is a sectional view taken along line BB ′ of FIG. 2 showing the first embodiment, as shown in FIG.
The two-layer structure of the N-type polycrystalline silicon layer 402a and the N-type polycrystalline silicon layer 402a has a single-layer structure, and only the P-type semiconductor layer has the two-layer structure. The type semiconductor layer has a single layer structure.

Further, according to the present invention, three layers are provided as long as the structure is provided with the first semiconductor layer and the second semiconductor layer, which can simultaneously improve the dark current characteristic, the photosensitivity and the afterimage characteristic. The above layer structure may be used. For example, a graded bandgap layer may be sandwiched between the first semiconductor layer (narrow gap layer) and the second semiconductor layer (wide gap layer) so that carriers can enter and exit smoothly.

[0066]

As described above, according to the photodiode of the present invention, the PI having the amorphous semiconductor layer as the I layer is used.
The dark current characteristic, photosensitivity, and afterimage characteristic of the N or NIP type photodiode can be remarkably improved at the same time.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of a photodiode of the present invention.

FIG. 2 is a schematic plan view showing a first embodiment of the photodiode of the present invention.

FIG. 3 is a sectional view taken along the line A-A ′ in FIG.

4 is a sectional view taken along line B-B ′ of FIG.

FIG. 5 is a configuration diagram when only the P-type semiconductor layer has a two-layer configuration in the first embodiment.

FIG. 6 is an IV characteristic diagram of the photodiode of the first embodiment.

FIG. 7 is a spectral sensitivity characteristic diagram of the photodiode of the first embodiment.

FIG. 8 is an afterimage characteristic diagram of the photodiode of the first embodiment.

FIG. 9 is a schematic plan view showing a second embodiment of the photodiode of the present invention.

10 is a cross-sectional view taken along the line A-A ′ of FIG.

11 is a sectional view taken along line B-B ′ of FIG.

FIG. 12 is a characteristic diagram showing a difference in dark current in an improved example of a conventional PIN photodiode.

FIG. 13 is a characteristic diagram showing a difference in spectral sensitivity characteristic.

FIG. 14 is a characteristic diagram showing a difference in afterimage characteristics of conventional photodiodes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Base | substrate 11 1st electrode 12 N-type semiconductor layer 14 P-type semiconductor layer 12a, 14a 1st semiconductor layer 12b, 14b 2nd semiconductor layer 13 I layer 15 Transparent electrode 16 Semiconductor layer 400,800 Glass substrate 401,801 Lower electrode 402a, 802a N-type polycrystalline silicon layer 402b N-type silicon nitride layer 802b N-type polycrystalline silicon carbide layer 403, 803 Light absorption layer 404a, 804a P-type polycrystalline silicon layer 404b P-type amorphous silicon carbide layer Bit layer 804b P-type polycrystalline silicon carbide layer 405,805 Upper transparent electrode 406,806 Protective layer 407,807 Lead wiring electrode

Claims (4)

[Claims] 1. A PIN-type or NIP-type photodiode in which the I layer is an amorphous semiconductor layer, wherein the P-type semiconductor layer and / or the N-type semiconductor layer is at least I.
A first semiconductor layer made of the same material as the layer and having a polycrystalline structure;
It is composed of two layers of a second semiconductor layer having a polycrystalline or amorphous structure composed of a layer constituent element and a bandgap widening element, and the first semiconductor layer is arranged adjacent to the I layer. Photodiode characterized by being processed. 2. The photodiode according to claim 1, wherein the I layer is hydrogenated amorphous silicon. 3. The photodiode according to claim 1, wherein at least one of carbon atom, nitrogen, and oxygen atom is used as the band gap widening element. 4. The photodiode according to claim 1, wherein the film thickness d of the first semiconductor layer is determined by the following equation. [Equation 1] (Where di is the film thickness of the amorphous semiconductor I layer, ε is the dielectric constant of the first semiconductor layer, N is the impurity concentration of the first semiconductor layer, and V is V
_R is the maximum voltage applied to the photodiode, φ _B is PI
Built-in potential of N-junction, q represents unit charge amount. )