JPH04283965A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To completely prevent a dark current from being produced. CONSTITUTION:A P-type diffusion layer 8 for prevention of dark current production is formed so as to cover the entire region of an N-type diffusion layer 3 in a photodiode formation region, and so as to be connected with an N-type diffusion layer 6 in a charge transfer path formation region under a read gate 30B. Further, voltage applied to the read gate 30B is enough to produce a punch-through phenomenon between the N-type diffusion layer 3 in the photodiode formation region and an N-type diffusion layer 5 in the charge transfer path formation region. The N-type diffusion layer 3 constituting the photodiode is completely buried by the P type diffusion layer 8 and hence is prevented from being exposed to a semiconductor surface forming an interface with an insulating film 10.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a solid-state imaging device.
In particular, the device includes a photodiode formation region, a charge transfer path formation region provided adjacent to the photodiode formation region, and a readout gate that transfers charges generated in the photodiode formation region to the charge transfer path formation region. Related to solid-state image sensors.

0002

2. Description of the Related Art As shown in FIG.
3, an N-type diffusion layer 56 is formed to form a photodiode formation region, and a charge transfer path formation region is located adjacent to this photodiode formation region. For example, a CCD element is used as this charge transfer path, and the P
An N-type diffusion layer 54 is formed on the type well layer 53, and transfer electrodes (not shown) are formed on the N-type diffusion layer 54, which are arranged in parallel in the charge transfer direction with an insulating film 60 interposed therebetween. It becomes.

A readout gate 58 is provided for transferring the charges generated in the photodiode formation region to the charge transfer path formation region. This readout gate 58 is formed through an insulating film 60, and by applying a voltage to this readout gate 58, each N in the photodiode formation region and the charge transfer path formation region is
An N-type channel layer serving as an inversion layer is formed between the type diffusion layers 56 and 54.

Furthermore, in the solid-state imaging device configured as described above, generation of so-called dark current on the surface of the N-type diffusion layer 56 (interface with the insulating film 60) in the photodiode formation region can be prevented. By forming the P-type diffusion layers 57 in a substantially overlapping state, the dark current is prevented from reaching the N-type diffusion layer below the P-type diffusion layer.

[0005]The CCD solid-state imaging device is, for example,
"Video Information", "Recent Trends in Solid-State Image Sensors and Solid-State Cameras", pp. 25-31, May 1986, published by Japan Industrial Development Corporation.

[0006]

[Problems to be Solved by the Invention] However, in a solid-state imaging device having such a configuration, the readout gate 58
Below, the N-type diffusion layer 5 in the photodiode formation region
6 and the N-type diffusion layer 54 in the charge transfer path forming region must be formed so as to face each other (that is, an N-type channel layer must be formed to connect the N-type diffusion layers 56 and 54 to each other). Therefore, the P-type diffusion layer 57 for preventing dark current generation could not be formed to completely cover the entire region where the N-type diffusion layer 56 was formed.

Therefore, the N-type diffusion layer 56 is exposed at the surface around the formation region of the P-type diffusion layer 57 for preventing generation of dark current, and the exposed N-type diffusion layer 56 is connected to the insulating film 60. It was supposed to constitute an interface.

[0008] Therefore, measures to prevent the generation of dark current are not perfect, and it has been recognized that so-called white spots due to the dark current occur on the video device side.

[0009] Therefore, the present invention has been made based on these circumstances, and its object is to provide a solid-state imaging device that can completely prevent the generation of dark current. .

0010

[Means for Solving the Problems] In order to achieve the above object, the present invention basically comprises a diffusion layer of a second conductivity type formed on the surface of a semiconductor substrate of a first conductivity type. a photodiode formation region; a charge transfer path formation region including a second conductivity type diffusion layer formed on the first conductivity type semiconductor substrate surface adjacent to the photodiode formation region; A first conductivity type diffusion layer for preventing dark current generation is provided with a readout gate for transferring charges generated in the photodiode formation region to a charge transfer path formation region, and a second conductivity type diffusion layer in the photodiode formation region. In the solid-state imaging device formed on the surface of the photodiode, a first conductivity type diffusion layer for preventing dark current generation is formed to cover the entire area of the second conductivity type diffusion layer in the photodiode formation region. and is formed so as to be connected to the second conductivity type diffusion layer of the charge transfer path formation region under the readout gate, and the voltage applied to the readout gate is connected to the second conductivity type diffusion layer of the photodiode formation region. The present invention is characterized in that the voltage is sufficient to cause a punch-through phenomenon between the diffusion layer of the mold and the second conductivity type diffusion layer of the charge transfer path forming region.

[0011]

[Function] In the solid-state imaging device configured as described above, the first conductivity type diffusion layer for preventing the generation of dark current is formed so as to cover the entire area of the second conductivity type diffusion layer in the photodiode formation region. ing. Therefore, the second conductivity type diffusion layer constituting the photodiode is completely buried by the first conductivity type diffusion layer, and is no longer exposed to the semiconductor surface constituting the interface with the insulating film.

[0012] Therefore, the probability that electrons generated on the surface with high charge ejection efficiency are accumulated in the photodiode, resulting in dark current, can be extremely reduced.

[0013] With this configuration, even if an inversion layer is formed directly under the readout gate to which a voltage is applied, as in the conventional case, the second conductivity type diffusion layer and the charge transfer path constituting the photodiode are Since the diffusion layer of the second conductivity type constituting the region is not electrically conductive, the diffusion layer of the first conductivity type is read out to prevent the generation of dark current, and the second conductivity of the charge transfer path forming region is read out under the gate. connected to the diffusion layer of the mold,
The readout gate is provided with a second portion of the photodiode formation region.
A voltage sufficient to cause a punch-through phenomenon between the conductivity type diffusion layer and the second conductivity type diffusion layer in the charge transfer path forming region is applied to the second conductivity type diffusion layer constituting the photodiode.
The conductivity type diffusion layer and the second conductivity type diffusion layer constituting the charge transfer path region can be brought into a conductive state.

From the above, it is possible to perform charge transfer from the photodiode to the charge transfer path without any problem, and also to completely bury the diffusion layer (of the second conductivity type) constituting the photodiode from the semiconductor surface. This makes it possible to completely prevent the generation of dark current.

[0015]

Embodiment FIG. 2 is a schematic diagram showing an embodiment of a solid-state imaging device according to the present invention.

In the figure, each element is formed on the main surface of a single chip semiconductor substrate in the arrangement shown in the figure. In the figure, a plurality of photodiodes 21 are arranged in a matrix in a light image projection area on the main surface of the semiconductor substrate.

Further, there is a vertical register 23 formed along the column direction for each group of photodiodes 21 arranged in the column direction, and each of these vertical registers 23 is composed of a CCD element.

These vertical registers 23 read out the charges generated in the respective photodiodes 21 arranged in the column direction, and transfer them to the outside of the light image projection area along the column direction.

Note that charge readout from each photodiode 21 to the vertical register 23 is performed by a charge readout gate (not shown).

Furthermore, the charges transferred from each vertical register 23 are output to a horizontal shift register 24, and are transferred in the horizontal direction by this horizontal shift register 24. This horizontal shift register 24 is a CCD similar to each of the vertical shift registers 23.
It is composed of elements.

The output from the horizontal shift register 24 is input to an output circuit 25, where it is converted into, for example, a voltage and taken out to the outside.

[0022] In the main surface of the semiconductor substrate on which each element is formed in this way, an opening is formed in the region where each photodiode 21 is formed.
A light shielding film (not shown) is formed to expose only each photodiode 21.

FIG. 3 is a plan configuration diagram showing more specifically each photodiode 21 and vertical shift register 23 in FIG. 2 described above.

In the figure, among the photodiodes 21 arranged in a matrix (areas marked with dots in the figure), there are photodiodes extending in the column direction between each photodiode group arranged in the column direction. A vertical shift register 23 is disposed. This vertical shift register 23
It consists of a charge transfer path formed on the surface of a semiconductor substrate and a transfer electrode formed through an insulating film, and is a so-called two-layer structure.
It is a phase frame transfer type.

The transfer electrode is common to the photodiode side arranged in each column direction, and the transfer electrode 3 of the first layer
It consists of a transfer electrode 0A and a second layer transfer electrode 30B, which are arranged in a partially overlapping state.

Note that the second layer transfer electrode 30B has a shape in which a part of it extends slightly toward the photodiode 21 side compared to the first layer electrode 30A, so that the second layer transfer electrode 30B has a shape that is slightly extended toward the photodiode 21 side. It also serves as a charge readout gate for reading out the generated charges to the vertical shift register 23 side.

FIG. 1 is a configuration diagram showing a cross section taken along the line II in FIG. 3.

In the figure, there is an N-type semiconductor substrate 1,
On the surface of this N-type semiconductor substrate 1, a P-type well layer 2 made of a low concentration P-type semiconductor layer is formed. and,
An N-type diffusion layer 3 is formed on the surface of this P-type well layer 2, and a photodiode 21 is formed together with the P-type well layer 2.
It consists of

In addition, N constituting the photodiode 21
In the vicinity of the type diffusion layer 3, an N type diffusion layer 5, which is a charge transfer path of the vertical shift register 23, is formed on the surface of the P type well layer 2. Note that this N-type diffusion layer 5 is formed on the surface of a high-concentration P-type well layer 46 formed in the P-type well layer 2 in order to prevent so-called smearing.

Here, a highly concentrated P-type diffusion layer 8 is formed on the surface of the N-type diffusion layer 3 constituting the photodiode 21, covering the entire surface of the N-type diffusion layer 3. This P-type diffusion layer 8 serves as a diffusion layer for preventing thermoelectrons generated at the interface with an insulating film 10, which will be described later, from reaching the N-type diffusion layer 3 side, thereby preventing the generation of dark current. There is. Therefore, the entire surface of the N-type diffusion layer 3 no longer forms an interface with the insulating film 10 due to the P-type diffusion layer 8.

The P-type diffusion layer 8 is formed so as to be connected to the N-type diffusion layer 5, which is a charge transfer path of the vertical shift register 23, directly under a formation region of a readout gate 30B, which will be described later.

A second layer transfer electrode 30B is formed on the main surface on which the various diffusion layers are formed, with an insulating film 10 made of, for example, a silicon oxide film interposed therebetween. A part of the second layer transfer electrode 30B constitutes a charge readout gate, extends toward the N-type diffusion layer 3 that constitutes the photodiode 21, and slightly overlaps the N-type diffusion layer 3. It looks like this.

Furthermore, an insulating film 10 made of an oxide film is formed to cover the areas of the transfer electrode 30B and the photodiode 21, and the upper surface of this insulating film 10 has no openings except for the area where the photodiode 21 is formed. A light shielding film 15 made of, for example, aluminum is formed.

As described above, according to the solid-state image sensing device shown in the above embodiment, the P-type diffusion layer 8 for preventing the generation of dark current is
It is formed so as to cover the entire area of the N-type diffusion layer 3 in the photodiode formation region. Therefore, the N-type diffusion layer 3 constituting the photodiode is different from the P-type diffusion layer 8.
Therefore, the semiconductor layer is completely buried and is no longer exposed to the semiconductor surface forming the interface with the insulating film 10.

Therefore, no dark current is generated in the photodiode.

With this configuration, even if an inversion layer is formed directly under the readout gate to which a voltage is applied, as in the conventional case, the N-type diffusion layer 3 and the charge transfer path region constituting the photodiode can be separated. Since the constituting N-type diffusion layer 5 is not in a conductive state, the P-type diffusion layer 8 for preventing dark current generation is connected to the N-type diffusion layer 5 in the charge transfer path formation region under the readout gate. A voltage sufficient to cause a punch-through phenomenon between the N-type diffusion layer 3 in the photodiode formation region and the N-type diffusion layer 5 in the charge transfer path formation region is applied to the readout gate to read the photodiode. The N-type diffusion layer 3 forming the structure and the N-type diffusion layer 5 forming the charge transfer path region can be brought into a conductive state.

[0037] From the above, the charge transfer from the photodiode to the charge transfer path can be performed without any trouble, and the N-type diffusion layer 3 constituting the photodiode can be completely buried from the semiconductor surface. It becomes possible to completely prevent the generation of dark current.

Next, an embodiment of the method for manufacturing a solid-state image sensing device according to the present invention will be described with reference to FIG.

Step 1 As shown in (a), a P-type well layer 2 made of a low concentration P-type semiconductor layer is formed on the upper surface of an N-type semiconductor substrate 1. Then, a P-type impurity with a high concentration is selectively diffused into one region of the main surface of this P-type well layer 2 to form a P-type well layer 6. This P-type well layer 6 is formed in the CCD element formation region, and serves as a so-called diffusion layer for preventing smear.

Step 2 As shown in (b), an N-type diffusion layer 5 is selectively formed in a region of the surface of the P-type well layer 6. This N-type diffusion layer 5 serves as a charge transfer path in the CCD element. Then, at the same time as this N-type diffusion layer 5, an N-type diffusion layer 11 is formed. This N-type diffusion layer 11 is formed so as to overlap the P-type well layer 6 on the side where the photodiode 21 is formed.

Step 3 As shown in (c), each of the above-mentioned N-type diffusion layers 5 and 1
A P-type diffusion layer 12 is selectively formed between the N-type diffusion layers 5 and 11, and the P-type diffusion layer 12 is formed so as to overlap each of the N-type diffusion layers 5 and 11 at both ends thereof.

Note that this P-type diffusion layer 12 is formed directly below the readout gate of the second layer transfer electrode 30B.

Step 4 As shown in (d), an insulating film 10 made of an oxide film is formed on the main surface of the P-type well layer in which various diffusion layers are formed,
A second layer transfer electrode 30B is formed on the surface of this insulating film 10.

Step 5 As shown in (e), an N-type diffusion layer 3 constituting a photodiode is formed. N selectively from the top surface of the insulating film 10
After ion-implanting type impurities, heat treatment is performed to form the N-type diffusion layer 3. In this case, the N-type diffusion layer 3 is formed so as to be connected to the N-type diffusion layer 11 formed in step 3 above.

Step 6 As shown in (f), a P-type diffusion layer 8 for preventing dark current is formed.
form. After ion-implanting P-type impurities from the upper surface of the insulating film 10, heat treatment is performed to form the P-type diffusion layer 8. In this case, the mask for selective implantation employs a so-called self-alignment method using the second layer transfer electrode 30B and the first layer transfer electrode 30A (not shown).

After that, as shown in FIG. 1, an insulating film 10 is further formed and a light shielding film 15 is formed.

FIG. 4 shows an embodiment of the method for manufacturing a solid-state image sensor according to the present invention, and the method is not necessarily limited thereto. For example, as shown in FIG. 6, an N-type diffusion layer 3 constituting a photodiode and an N-type diffusion layer 5 constituting a charge transfer path region are formed in a connected state, and then a P-type diffusion layer is formed. Of course, the N-type diffusion layers 3 and 5 may be separated by the N-type diffusion layers 16.

According to the above-described embodiment, the charge transfer path is formed using a CCD element, but it is not limited to this, and the same effect can be achieved by forming it using a MOS transistor array, for example. Needless to say, this effect can be obtained.

[0049]

[Effect of the invention] As is clear from the above explanation,
According to the solid-state imaging device according to the present invention, generation of dark current can be completely prevented.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of a solid-state image sensing device according to the present invention, and is a sectional view taken along the line II in FIG. 3.

FIG. 2 is a schematic overall plan view showing an embodiment of a solid-state image sensor according to the present invention.

FIG. 3 is a partial plan view showing an embodiment of a solid-state image sensor according to the present invention.

FIGS. 4(a) to 4(f) are partial process diagrams showing an embodiment of a method for manufacturing a solid-state image sensor according to the present invention.

FIG. 5 is a configuration diagram showing an example of a conventional solid-state image sensor.

FIG. 6 is an explanatory diagram showing another embodiment of the method for manufacturing a solid-state image sensor according to the present invention.

[Explanation of symbols]

1 N-type semiconductor substrates 2, 6 P-type well layer 3 N-type diffusion layer 5 forming a photodiode N-type diffusion layer 8 forming a charge transfer path P-type diffusion layer 10 for preventing dark current Insulating film 21 Photodiode Formation region 23 Charge transfer path formation region

Claims (1)

[Claims] 1. A photodiode formation region including a second conductivity type diffusion layer formed on a surface of a first conductivity type semiconductor substrate, and a first conductivity type semiconductor adjacent to the photodiode formation region. A charge transfer path formation region formed by forming a second conductivity type diffusion layer on the substrate surface, and a readout gate for transferring the charge generated in the photodiode formation region to the charge transfer path formation region. In a solid-state imaging device, a first conductivity type diffusion layer for preventing current generation is formed on a surface of a second conductivity type diffusion layer in the photodiode formation region, the first conductivity type diffusion layer for preventing dark current generation. A diffusion layer is formed to cover the entire area of the second conductivity type diffusion layer in the photodiode formation region, and a diffusion layer of the second conductivity type in the charge transfer path formation region is formed under the readout gate. The voltage applied to the readout gate is
A solid-state imaging device characterized in that the voltage is sufficient to cause a punch-through phenomenon between a second conductivity type diffusion layer in a photodiode formation region and a second conductivity type diffusion layer in a charge transfer path formation region.