JPH07211879A - Solid-state image pick up device - Google Patents

Abstract

PURPOSE:To uniformalize the dark-current characteristics of an individual photodiode, to make the occurrence of defective pixels and the like hard to occur by decreasing the noises of a fixed pattern, and to make the time delay of image display hard to occur by simplifying an external correcting circuit. CONSTITUTION:Surface protecting insulating films 5 and 6 are formed on semiconductor layers 2 and 3 so as to cover the outer surface of a p-n junction 4 of each photodiode 1. Electric charge, which neutralizes the surface potential of the insulating films 5 and 6 and an interface 10 of the semiconductor layer/ surface protecting insulating films around the p-n junction 4, is infected. A first electrode 9, which is formed around the p-n junction 4 and on the surface protecting insulating films 5 and 6, is provided. Furthermore, a second electrode 11, which holds the electric charge injected from the first electrode 9 and is held on the periphery of the p-n junction 4 and in the surface protecting insulating films 5 and 6, is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor,
More specifically, it can be applied to a solid-state imaging device having a photodiode for detecting a plurality of lights and a signal processing circuit for reading out an electric signal of each photodiode by electronic scanning. The present invention relates to a solid-state imaging device that can be made uniform and can reduce fixed pattern noise to make it difficult to generate defective pixels and the like, and further can simplify an external correction circuit to make it difficult to cause a time delay in image display.

In recent years, in a solid-state image pickup device having a plurality of photodiodes for detecting light and a signal processing circuit for reading out an electric signal of each photodiode by electronic scanning, high performance such as a large number of pixels and high sensitivity has been achieved. In accordance with the demand, individual photodiode characteristics such as dark current and sensitivity are likely to vary, and this variation in individual photodiode characteristics tends to cause fixed pattern noise on the image. ing. For this reason, improvements are being made in the manufacturing process,
It is necessary to calculate the signal from the solid-state image pickup device by an external circuit to make the characteristics uniform and to form an image. However, in particular, in a solid-state imaging device using a compound semiconductor for a photodiode, it is difficult to form a stable surface protective film because the uniformity of individual photodiode characteristics is high on the semiconductor surface and it is difficult to form a stable surface protection film. Therefore, the photodiode characteristics tend to vary easily, which complicates external signal processing.

[0003]

2. Description of the Related Art A conventional solid-state image pickup device is known which has a photodiode for detecting a plurality of lights and a signal processing circuit for reading out an electric signal of each photodiode by electronic scanning. The photodiode used in this solid-state image sensor usually has a small dark current, but has a very small energy gap, so
Due to the generation of fixed charges at the semiconductor interface, dark current is likely to occur, and when forming each photodiode element, the dark current tends to vary among individual photodiodes. In this conventional solid-state imaging device, because the number of photodiodes is large, only the same bias condition can be applied to each photodiode within the device, and the dark current variation of each photodiode is included. It is accumulating charges.

Further, the conventional solid-state image pickup device has a semiconductor memory in an external circuit, and the photodiode characteristics such as individual dark currents are stored in this semiconductor memory, and the individual characteristics read from the memory by an external arithmetic circuit. The signal is corrected for the dark current of the photodiode.

[0005]

As described above, in the conventional solid-state image pickup device, only the same bias condition can be applied to each photodiode in the device, and the dark current variation of each photodiode is included. However, when a photodiode that generates a large amount of dark current is included because the charge is accumulated, the storage capacitance of that portion becomes less than the storage capacitance (reference value) of other photodiodes, and C
There is a problem in that the output of the CD reaches the ceiling and the pixel becomes defective.

Therefore, the bias condition of the entire photodiode element constituting the solid-state image pickup device is lowered to relieve the photodiode which generates a large amount of these dark currents. However, the bias condition of the entire photodiode element is lowered. Therefore, there is a problem that the signal injection efficiency is lowered as a whole, and the sensitivity is lowered. Further, as described above, conventionally, in a solid-state image sensor having a semiconductor memory in an external circuit, after reading a signal, the semiconductor memory forming the circuit stores the photodiode characteristics such as individual dark currents, and the external arithmetic circuit As a result, the signal of the dark current of each photodiode read out from the memory was corrected, so that the external circuit of the solid-state image sensor became complicated and it took time to perform arithmetic processing. There was a problem that it would end up. In particular, when the target object deviates from the reference image state that has been offset-corrected or sensitivity-corrected, the corrected pixels may be noticeable as fixed pattern noise.

Therefore, according to the present invention, the dark current characteristics of the individual photodiodes can be made uniform, fixed pattern noise can be reduced to prevent defective pixels from occurring, and the external correction circuit can be simplified to achieve image display. It is an object of the present invention to provide a solid-state image sensor that can prevent a time delay from occurring.

[0008]

The invention according to claim 1 is
In a solid-state imaging device having a photodiode configured to detect a plurality of lights and composed of a p-type semiconductor layer and an n-type semiconductor layer, and a signal processing circuit for reading out an electric signal of each photodiode by electronic scanning, For neutralizing the surface protective insulating film formed on the semiconductor layer so as to cover the periphery of the pn junction of the photodiode 1 and the surface potential potential of the semiconductor layer / surface protective insulating film interface around the pn junction. In addition to injecting charges, the first electrode formed around the pn junction and on the surface protective insulating film and the charges injected from the first electrode or the semiconductor layer are retained, and the pn The second electrode is formed on the periphery of the junction and in the surface protection insulating film.

According to a second aspect of the present invention, there is provided a signal processing which detects a plurality of lights and which comprises a p-type semiconductor layer and an n-type semiconductor layer and an electric signal of each photodiode is read out by electronic scanning. In a solid-state imaging device having a circuit, a surface protective insulating film formed on the semiconductor layer so as to cover the periphery of the pn junction of each photodiode, and a semiconductor layer / surface protective film interface around the pn junction. A charge for injecting a surface potential potential is injected, and a first electrode formed on the periphery of the pn junction and on the surface protection insulating film, and on the periphery of the pn junction, and the surface protection. An insulating film made of a material different from that of the surface protective insulating film formed in the insulating film, and insulating the charge injected from the first electrode or the semiconductor layer from the surface protective insulating film. Among charge trapping and charge trapping in the insulating film between and it is characterized by comprising retaining at least one of the charge trapping.

The invention according to claim 3 is the same as claims 1 and 2 above.
In the invention described above, the charge injection into the surface protective insulating film of the first electrode is performed by electrical or optical charge injection.
The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the charge injected from the first electrode to the second electrode or the insulating film is the semiconductor layer / surface around the pn junction. According to the magnitude of the surface potential of the interface of the protective insulating film, the charges are of opposite polarities that cancel the fixed charges existing at the interface.

According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the first electrode has a function of randomly accessing, a function of injecting an arbitrary positive or negative charge, and a charge amount. It has a function of adjusting. According to a sixth aspect of the present invention, in the above-mentioned fifth aspect, the amount of charges injected from the first electrode is adjusted by at least one of an applied voltage and an applied time. To do.

According to a seventh aspect of the present invention, in the above first to sixth aspects, the n-type semiconductor layer (3) is formed on the p-type semiconductor layer (2). To do. The invention according to claim 8 is the same as the invention according to any one of claims 1 to 6, wherein the p-type semiconductor (2) is used.
Is formed on the n-type semiconductor layer (3).

[0013]

1 to 3 are explanatory views of the principle of the present invention. FIG. 1 shows a basic structure of a solid-state image pickup device of the present invention having a photodiode and an electrode which stores an electric charge for neutralizing a fixed electric charge arranged around a pn junction. In FIG. 1, 1 is a photodiode composed of a p-type semiconductor layer 2 and an n-type semiconductor layer 3, and 4 is a pn junction formed between the p-type semiconductor layer 2 and the n-type semiconductor layer 5. , 6 are surface protection insulating films sequentially formed on the semiconductor layers 2 and 3 so as to protect the periphery of the pn junction 4, and 7 is formed on the surface protection insulating film 6 and the surface protection insulating film 5, and the photodiode 1 Is an opening where the n-type semiconductor layer 3 is exposed, 8 is a diode electrode formed so as to contact the n-type semiconductor layer 3 of the photodiode 1 through the opening 7, and 9 is a pn
A charge for neutralizing the surface potential potential of the interface 10 of the p-type semiconductor layers 2 and 3 / surface protection insulating film 5 around the junction 4 is injected, and at the periphery of the pn junction 4 and on the surface protection insulating film 6. The charge injection electrode formed in
Holds the charges injected from the charge injection electrode 9, and is provided on the periphery of the pn junction 4 and on the surface protective insulating film 5,
6, which is a floating electrode for storage. The storage floating electrode 11 is formed so as to be deposited on the surface protection insulating film 5, patterned, and then covered with the surface protection insulating film 6.

Next, FIG. 2 shows a method of injecting charges from the charge injection electrode 9 to the storage floating electrode 11 having a storage function. The storage function to the storage floating electrode 11 is shown in FIG.
As can be seen from the above, electrons (or holes) under the charge injection electrode 9 are electrically injected into the storage floating electrode 11 embedded in the surface protection insulating films 5 and 6, or This is performed by irradiating and injecting light having energy exceeding the barrier.

Now, in the conventional solid-state image pickup device, as shown in FIG.
As shown in (a), in the photodiode 1 with a large dark current, fixed charges exist at the interface 10 of the surface protective insulating film 5 / semiconductor layers 2 and 3, and the surface potential of the semiconductor is bent to induce charges at the interface 10. As a result, the pn junction 4
The electric field of the depletion layer in the surroundings becomes strong. For this reason,
There is a problem that a tunnel leak current is generated and a dark current becomes non-uniform.

Therefore, according to the present invention, as shown in FIGS. 1 and 2, the surface protective insulating film 5 / semiconductor layers 2 and 3 interface 1 is used.
The charge for neutralizing the fixed charge existing at 0 is injected from the charge injection electrode 9 to the storage floating electrode 11 with a storage function via the surface protection insulating film 6 and then injected to the storage floating electrode 11. The charge neutralizes the fixed charge of the interface 10.
Therefore, the fixed charges on the interface 10 can be neutralized by the injected charges injected into the storage floating electrode 11.
Generation of tunnel current can be prevented, and dark current can be made uniform. Furthermore, since the storage floating electrode 11 with a storage function has a floating electrode structure, the injected charges can be left in the storage floating electrode 11 even when the power is turned off.
The correction function can be protected and operated as it is for a long period of time, and rewriting can be performed as necessary.

Next, in the present invention, the effects of the present invention can be achieved even if the following configuration is adopted. Hereinafter, a specific description will be given with reference to the drawings. FIG. 4 is a diagram illustrating the principle of the present invention. FIG. 4 shows a basic structure of a solid-state image pickup device of the present invention having an insulating film for arranging charges for neutralizing fixed charges arranged around a photodiode and a pn junction.
In FIG. 4, the same reference numerals as those in FIG. 1 denote the same or corresponding portions, and 21 holds the charges injected from the charge injection electrode 9 by the charge traps in the film, and protects the surface around the pn junction 4 and the surface. It is an insulating film made of a material different from the surface protection insulating films 5 and 6 formed in the insulating films 5 and 6.
At this time, the insulating film 21 is formed so as to be deposited on the surface protection insulating film 5, patterned, and then covered with the surface protection insulating film 6.

The method of injecting charges from the charge injecting electrode 9 into the insulating film 21 having a memory function here is also the same as in FIG. 1, and the floating floating insulating film 2 for memory embedded in the surface protective insulating films 5 and 6 is used.
Electrons (or holes) under the charge injection electrode 9 are electrically injected into the first electrode 1, or light having energy exceeding the barrier of the surface protective insulating film 6 is irradiated and injected.

In the present invention, as shown in FIG. 4, charges for neutralizing fixed charges existing at the surface protective insulating film 5 / semiconductor layer 2, 3 interface 10 are transferred from the charge injection electrode 9 to the surface protective insulating film 6. It is injected into the insulating film 21 having a memory function via the insulating film 21, and the fixed charges of the interface 10 are neutralized by the injected charges injected into the insulating film 21. Therefore, the fixed charges at the interface 10 can be neutralized by the injected charges injected into the insulating film 21, so that the tunnel current can be prevented from occurring and the dark current can be made uniform. Further, the insulating film with a memory function 21
Has a floating structure, the injected charges can be left in the insulating film 21 even when the power is turned off, and the correction function can be maintained as it is for a long period of time. Rewriting can also be performed. In addition, here
The case where the charge injected from the charge injection electrode 9 is held by the charge trap in the insulating film 21 is shown, but the charge trap between the insulating film 21 and the surface protection insulating film 5 may be performed. Alternatively, both of the charge trapping in the insulating film 21 and the charge trapping between the insulating film 21 and the surface protection insulating film 5 may be performed.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a diagram showing the configuration of a solid-state image sensor according to Embodiment 1 of the present invention. The illustrated example is a case where the photodiode and an electrode arranged around the pn junction have electrodes for storing charges for neutralizing fixed charges. In FIG. 5, 31 is a photodiode including a p-type semiconductor layer 32 and an n-type semiconductor layer 33, 34 is a pn junction formed between the p-type semiconductor layer 32 and the n-type semiconductor layer 33, and 35. , 36 are semiconductor layers 32, 33 so as to protect the periphery of the pn junction 34.
37 is a surface protection insulating film sequentially formed on the surface of the photodiode 3 and is formed on the surface protection insulating films 35 and 36.
This is the opening where the n-type semiconductor layer 33 of No. 1 is exposed. Then, 38 is the photodiode 3 through the opening 37.
1 is a diode electrode formed so as to be in contact with the n-type semiconductor layer 33 of No. 1, and 39 is p around the pn junction 34.
-Type semiconductor layers 32 and 33 / interface 40 of surface protective insulating film 35
Is a charge injection electrode formed on the surface of the pn junction 34 and on the surface protection insulating film 36, while 41 is injected from the charge injection electrode 39. Stored charge is retained, and the surface protection insulating film 3 is provided on the periphery of the pn junction 34.
5, which is a floating electrode for storage formed inside. The storage floating electrode 41 is formed so as to be deposited on the surface protection insulating film 35, patterned, and then covered with the surface protection insulating film 36. Further, 42 is a column selection shift register or decoder, 43 is a row selection shift register or decoder, 44 is a pulse applying power supply, and 45
Is a characteristic feedback function unit.

Next, in the method of injecting charges from the charge injection electrode 39 to the storage floating electrode 41 with a storage function, the storage floating electrode 41 embedded in the surface protective insulating films 35 and 36 is used.
Then, electrons (or holes) under the charge injection electrode 39 are electrically injected, or light having energy exceeding the barrier of the surface protective insulating film 36 is irradiated and injected.

In the present embodiment, the external circuit is composed of a column selection shift register or decoder 42, a row selection shift register or decoder 43, a pulse applying power supply 44, a characteristic feedback function section 45, etc., whereby the charge injection electrode 39 is formed. Are randomly accessed, a function of injecting an arbitrary positive or negative charge, and a function of adjusting the amount of charges. Then, when the electric charge is stored, only the dark current is taken out without making the light incident on the photodiode 31 or the constant light is made incident on each photodiode. Next, from the output characteristics at this time, positive charges are injected into the storage floating electrode 41 arranged around the photodiode 31 which greatly deviates from the average value.
The amount of injected charges is adjusted by adjusting the magnitude of the applied voltage or the time for applying the voltage. Further, the fixed charge amount determined from the output characteristics is used to determine the individual injected charge amount. Next, the output characteristic is measured again without light, and a negative charge is injected into the peripheral electrode of the diode whose characteristic becomes worse. By repeating this operation several times, a more optimal injection of the neutralizing charge amount can be performed.

As described above, in this embodiment, the charges for neutralizing the fixed charges existing at the surface protection insulating film 35 / semiconductor layer 32, 33 interface 40 are transferred from the charge injection electrode 39 through the surface protection insulating film 36. The fixed charges at the interface 40 can be neutralized by the injected charges injected into the storage floating electrode 41 having a storage function and injected into the storage floating electrode 41. Therefore, the fixed charges at the interface 40 can be neutralized by the injected charges injected into the storage floating electrode 41, so that the tunnel current can be prevented from occurring and the dark current can be made uniform. Furthermore, a floating electrode 4 for storage with a storage function
Since No. 1 has a floating electrode structure, the injected charges can be left in the memory floating electrode 41 even when the power is turned off, and the correction function can be retained and operated for a long period of time. Rewriting can also be performed if necessary.

(Second Embodiment) FIG. 6 shows a second embodiment according to the present invention.
It is a figure which shows the structure of the solid-state image sensor of FIG. The illustrated example is a case where the photodiode and an insulating film arranged around the pn junction for storing charges for neutralizing fixed charges are provided. In FIG. 6, the same reference numerals as those in FIG. 5 indicate the same or corresponding portions, and 51 holds the charges injected from the charge injection electrode 39 by the charge traps in the film, and at the periphery of the pn junction 34,
Further, it is an insulating film made of a material different from the surface protective insulating films 35 and 36 formed in the surface protective insulating films 35 and 36. The insulating film 51 is formed so as to be deposited on the surface protection insulating film 35, patterned, and then covered with the surface protection insulating film 36. The surface protective insulating film 35 and the surface protective insulating film 36 are made of SiO ₂ , and the insulating film 51 is made of Si ₃ N ₄ .

The method of injecting charges from the charge injecting electrode 39 to the insulating film 51 having a memory function here is also the same as in the first embodiment, that is, the floating floating insulating film 51 for memory embedded in the surface protective insulating films 35 and 36. Then, electrons (or holes) under the charge injection electrode 39 are electrically injected, or light having energy exceeding the barrier of the surface protective insulating film 36 is irradiated and injected. Also in this embodiment, as in the case of FIG. 5, the external circuit is composed of the column selection shift register or decoder 42, the row selection shift register or decoder 43, the pulse applying power supply 44, the characteristic feedback function unit 45, etc. It is configured to have a function of randomly accessing 39, a function of injecting arbitrary positive and negative charges, and a function of adjusting the amount of charges. Then, when the electric charge is stored, only the dark current is taken out without making the light incident on the photodiode 31 or the constant light is made incident on each photodiode. Next, from the output characteristics at this time, the photodiode 3 that greatly deviates from the average value
A positive charge is injected into the storage floating insulating film 51 arranged around 1. The amount of injected charges is adjusted by adjusting the magnitude of the applied voltage or the time for applying the voltage. Further, the fixed charge amount determined from the output characteristics is used to determine the individual injected charge amount. Next, the output characteristic is measured again without light, and a negative charge is injected into the peripheral electrode of the diode whose characteristic becomes worse. By repeating this operation several times, a more optimal injection of the neutralizing charge amount can be performed.

As described above, in this embodiment, the charges for neutralizing the fixed charges existing at the surface protection insulating film 35 / semiconductor layer 32, 33 interface 40 are transferred from the charge injection electrode 39 through the surface protection insulating film 36. To the insulating film 51 with memory function,
The fixed charges on the interface 40 can be neutralized by the injected charges injected into the insulating film 51. Therefore, the insulating film 5
Since the fixed charges at the interface 40 can be neutralized by the injected charges injected into the device 1, the tunnel current can be prevented from occurring and the dark current can be made uniform. Furthermore,
Since the insulating film 51 with a memory function has a floating structure,
Even if the power is turned off, the injected charges can be left in the insulating film 51, and the correction function can be maintained as it is for a long period of time, and rewriting can be performed as necessary.

In the second embodiment, the charge injection electrode 39 is used.
The case where the charges injected from the above are held by the charge traps in the insulating film 51 has been described, but it may be configured so as to be held by the charge traps between the insulating film 51 and the surface protection insulating film 35. It may be configured to perform both the charge trap in 51 and the charge trap between the insulating film 51 and the surface protection insulating film 35.

In the above embodiment, p on the p-type substrate is used.
Although the n-junction has been described, the same effect can be expected in a pn-junction on an n-type substrate with a similar configuration.

[0029]

According to the present invention, the dark current characteristics of individual photodiodes can be made uniform, fixed pattern noise can be reduced and defective pixels can be made less likely to occur, and the external correction circuit can be simplified to achieve image display. There is an effect that a time delay can be made less likely to occur.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is a diagram illustrating the principle of the present invention.

FIG. 4 is a diagram illustrating the principle of the present invention.

FIG. 5 is a diagram showing a configuration of a solid-state image sensor according to a first embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a solid-state image sensor according to a second embodiment of the present invention.

[Explanation of symbols]

 1,31 Photodiode 2,32 p-type semiconductor layer 3,33 n-type semiconductor layer 4,34 pn junction 5,6,35,36 Surface protective insulating film 7,37 Opening 8,38 Diode electrode 9,39 Charge injection Electrode 10,40 interface 11,41 storage floating electrode 21,51 insulating film 42 column selection shift register or decoder 43 row selection shift register or decoder 44 pulse application power supply 45 characteristic feedback function unit

Claims (8)

[Claims] 1. A photodiode (1) for detecting a plurality of lights and comprising a p-type semiconductor layer (2) and an n-type semiconductor layer (3), and an electric signal of each photodiode (1). In a solid-state imaging device having a signal processing circuit for reading by electronic scanning, p of each photodiode (1) is
The semiconductor layer (2, 3) so as to cover the periphery of the n-junction (4)
The surface protection insulating film (5, 6) formed above and the semiconductor layer / surface protection insulating film interface (1 around the pn junction (4)
0) to inject a charge for neutralizing the surface potential potential of the first electrode (9) formed around the pn junction (4) and on the surface protective insulating film (5, 6). ) And the first electrode (9) or the semiconductor layer (2,
3) Holds the charge injected from
On the periphery of the junction (4) and on the surface protection insulating film (5, 6)
A solid-state image sensor, comprising: a second electrode (11) formed therein. 2. A photodiode (1) which detects a plurality of lights and is composed of a p-type semiconductor layer (2) and an n-type semiconductor layer (3), and an electric signal of each photodiode (1). In a solid-state imaging device having a signal processing circuit for reading by electronic scanning, p of each photodiode (1) is
The semiconductor layer (2, 3) so as to cover the periphery of the n-junction (4)
While injecting charges for neutralizing the surface potential potential of the surface protective insulating film (5, 6) formed above and the semiconductor layer / surface protective film interface (10) around the pn junction (4), A first electrode (9) formed around the pn junction (4) and on the surface protection insulating film (5, 6),
The surface protective insulating film (5, 6) formed on the periphery of the pn junction (4) and in the surface protective insulating film (5, 6).
And an insulating film (21) made of a material different from that of the first electrode (9) or the p-type semiconductor (2) for insulating the surface protective insulating film (5) A solid-state imaging device characterized by being held by at least one of a charge trap between the films (21) and a charge trap in the insulating film (21). 3. The charge injection of the first electrode (9) into the surface protective insulating film (6) is performed by electrical or optical charge injection. 2. The solid-state image sensor according to 2. 4. The charges injected from the first electrode (9) to the second electrode (11) or the insulating film (21) are the semiconductor layer / surface protection insulation around the pn junction (4). 4. The solid-state imaging device according to claim 1, wherein the solid-state imaging device has opposite polarities that cancel fixed charges existing at the interface (10) according to the magnitude of the surface potential of the film interface (10). 5. The first electrode (9) has a function of randomly accessing and a function of injecting an arbitrary positive or negative charge.
The solid-state imaging device according to claim 1, which has a function of adjusting the amount of charges. 6. The solid-state image pickup device according to claim 5, wherein the adjustment of the amount of charge injected from the first electrode (9) is performed by at least one of the applied voltage and the applied time. . 7. The solid-state imaging device according to claim 1, wherein the n-type semiconductor layer (3) is formed on the p-type semiconductor layer (2). 8. The solid-state imaging device according to claim 1, wherein the p-type semiconductor (2) is formed on the n-type semiconductor layer (3).