JPH06302798A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To hold complete light-shielding characteristics in an OB picture element section, and to conform an output from the OB picture element section and a dark output from a light-receiving section accurately in a solid-state image sensing device using an amplification type image pick-up device with a photoelectric conversion section composed of a P-N junction photodiode. CONSTITUTION:In a solid-state image sensing device using an AM1 with a photoelectric conversion section consisting of a P-N junction photodiode, a transparent conductive film 103 is formed uniformly extending over a light- receiving section A and an OB picture element section B between a transparent insulator layer 101 shaped onto the light-receiving section A and the OB picture element section B and a metallic light-shielding layer 102 formed only on the OB picture element section B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to solid-state imaging using an amplification type imaging device such as an amplification type MOS imaging device (Amplified MOS Imager: abbreviated as AMI hereinafter) having a photoelectric conversion part composed of a P-N junction photodiode. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made for a solid-state image pickup device using an AMI, but a visible-light AMI image sensor is disclosed in, for example, “Amplification-type solid-state image pickup device AMI” announced by the present applicant. A detailed explanation is given in Technical Report of the Television Society Vol. 14, No. 16, pp33-38 (1990).

A solid-state image pickup device using this AMI basically has a plurality of AMI pixels arranged in a matrix.
The optical information signal output from the photoelectric conversion unit (photodiode) of each pixel is individually amplified in the pixel, and is sequentially read out through the vertical and horizontal scanning switch circuits, and is configured in an XY address type.

FIG. 2 shows the structure of one pixel of a conventional visible AMI solid-state image pickup device, and FIG. 3 shows its equivalent circuit. In FIG. 2, 1 is a p well, 2 is an n ⁺ type diffusion layer,
3 is a gate insulating film, 4 is an interlayer insulating film, 5 is a metal wiring, P
D is an n ⁺ -p type photodiode, T _rs is a reset MO
S transistors, T _y are vertical selection MOS transistors, T _a are amplification transistors, and Y _n and Y _{n + 1 are} row selection lines.

As shown in the equivalent circuit of FIG. 3, one pixel composed of this AMI has an n ⁺ -p type photodiode PD as a photoelectric conversion unit, a reset (T _rs ), an amplification (T _a ), and a vertical selection ( It is composed of three n-channel MOS transistors for T _y ). Also, the horizontal scanning switch T
_x is provided for each vertical signal line. In FIG. 3, V _S is a signal potential, I _S is a source current, R _L is an additional resistance, V _rs is a reset potential, V _rd is a read reference potential, V _P is a metal wiring potential, C _PD is a photodiode diffusion capacitance, XI indicates a column selection line.

Next, the operation of the visible light type AMI will be described with reference to FIG. The operation of the visible light type AMI is divided into a reset period, a storage period, and a read period.

First, in the reset period, the photodiode PD is set to the reset potential V _rs (positive potential) via the reset MOS transistor T _rs . Next, in the accumulation period, the electrons excited by the visible light illumination are accumulated in the diffusion capacitance C _PD of the photodiode PD.
Therefore, the potential of the photodiode PD decreases corresponding to the time of incidence of visible light. This potential is applied to the gate of the amplifying transistor T _a , and the photodiode P
The current amplified according to the potential of D is supplied to the vertical selection MOS.
Reading is performed via the transistor T _y and the horizontal scanning switch T _x (reading period). In this AMI, since the photoelectric conversion unit and the amplification unit are extremely close to each other, there is no mixing of noise and no signal attenuation, and ideal amplification can be performed, so that an output with good S / N can be obtained.

Next, FIG. 4 shows a basic arrangement configuration when the AMI is used as an area sensor, and FIG. 5 shows a drive signal waveform thereof. This area sensor has a plurality of AMI pixels 11 arranged in a matrix, and has horizontal and vertical scanning circuits.
12, 13 and horizontal scan switches T _x-1 , T _x , T _{x + 1} ,
Are respectively provided so that specific pixels can be selected.

In the AMI solid-state image pickup device configured as described above, when information is stored in each pixel, the vertical scanning circuit 13 selects the n-th row at the time of reading, and the time required for one horizontal scanning ( For one horizontal scanning period), the vertical selection MOS transistor T _y is turned on. In the meantime, the horizontal scanning circuit 12 sequentially turns on the horizontal scanning switch T _x to sequentially read signals for one horizontal line.

At the same time when the reading of the n-th row is completed and the operation moves to the next (n + 1) -th row, the reset MOS transistor T _{rs (} not shown) provided in the n-th row corresponds to one horizontal line of the next (n + 1) -th row. While all the signals are read out, that is, in one horizontal scanning period, the photodiode PD is turned on and the potential of the photodiode PD is reset to the reset potential V _rs .

The reset MOS transistor T
_{Since rs} is turned on during one horizontal scanning period, the photodiode PD is reliably reset to the reset potential V _rs , which solves the cause of an afterimage. When interlacing is further performed, 1
Since the data is read out for each pixel, the vertical resolution does not deteriorate.

[0012]

By the way, in the solid-state image pickup device, in the same solid-state image pickup device, in addition to the light receiving part, an optical black pixel part (Optical Black pixel part: OB pixel portion) is formed. The process of subtracting the output signal of the OB pixel unit from the output signal of the light receiving unit to correct the dark output is performed inside or outside the image pickup device chip.

FIG. 6 shows a sectional structure of a light receiving portion A and an OB pixel portion B of a conventional AMI solid-state image pickup device. In FIG.
Reference numeral 101 denotes an insulating layer such as a passivation layer or a surface flattening layer which is transparent to visible light and is made of a material such as SiO ₂ or SiN. Reference numeral 102 denotes a metal light shielding layer formed on the OB pixel portion B and made of a metal such as Al and having a light shielding effect on visible light.

In the AMI solid-state image pickup device configured as described above, the incident light (Photon) can be incident on the photodiode PD in the light receiving portion A, but the incident light is reflected and absorbed by the metal light shielding layer 102 in the OB pixel portion B. Therefore, it does not reach the photodiode PD. That is, in the OB pixel section B,
The dark state is always output regardless of the presence or absence of incident light.

The AMI solid-state image pickup device having such a conventional structure has the following drawbacks. That is, in the light receiving portion, the capacitance of the photodiode _{PD is} only the photodiode diffusion capacitance C _PD, but the capacitance of the photodiode PD in the OB pixel portion B is in addition to the photodiode diffusion capacitance C _PD , the metal light shielding layer 102 and the OB pixel. The additional capacitance C _A formed between the metal wirings 5b of the portion B is added.

Therefore, when light does not enter the AMI solid-state image pickup device, the potential of the metal wiring 5a of the light receiving portion and the potential of the metal wiring 5b of the OB pixel portion B are different. That is, the metal light-shielding layer 102 has a potential fluctuation (fl
This is because a predetermined fixed potential is applied in order to avoid the uctuation), and this applied potential modulates the potential of the metal wiring 5b of the OB pixel portion B via the additional capacitance C _A. That is, the output of the OB pixel portion B is not exactly the dark output of the light receiving portion A, which is a drawback of the conventional example.

Instead of the metal light shielding layer 102 of the OB pixel portion B, a black filter made of an insulating material such as an organic material is formed in the same manner as the metal light shielding layer is formed, so that the metal wiring 5b of the OB pixel portion B is formed. However, at present, the black filter has a light transmittance of about 1%, and a black filter alone does not form a complete light-shielding film. Normally, a black filter is formed on the metal light-shielding layer 102. At present, it is formed and used for the purpose of suppressing the light reflection on the surface of the metal light shielding layer 102.

The present invention has been made in order to solve the above problems in a solid-state image pickup device using an amplification type image pickup device having a photoelectric conversion portion composed of a P-N junction photodiode, and maintains a perfect light shielding characteristic. In addition, it is an object of the present invention to provide a solid-state imaging device in which the output of the OB pixel section exactly matches the dark output of the light receiving section.

[0019]

In order to solve the above problems, the present invention provides a solid-state image pickup device using an amplification type image pickup device having a photoelectric conversion portion formed of a PN junction photodiode, and a light receiving portion. An optical black pixel portion formed with a metal light shielding layer, and a transparent conductive film on the semiconductor surface side of the metal light shielding layer or on the light incident direction side directly above the metal light shielding layer, It is configured to be uniformly formed over the optical black pixel portion.

In the solid-state image pickup device having such a structure, since the transparent conductive film is uniformly formed in the light receiving portion and the OB pixel portion, the capacitance added to the photodiodes in the light receiving portion and the OB pixel portion is perfect. Therefore, an OB pixel section output that is exactly equal to the dark output of the light receiving section can be obtained.

[0021]

EXAMPLES Next, examples will be described. FIG. 1 is a sectional view showing an embodiment of the solid-state imaging device according to the present invention.
This embodiment is different from the conventional example shown in FIG. 6 in that a transparent conductive film 103 is provided between the transparent insulator layer 101 and the metal light shielding layer 102.
Is only provided uniformly over the light receiving portion A and the OB pixel portion B, and the other configurations are the same as those of the conventional example, and therefore the description of those same components will be omitted.

As a constituent material suitable for the transparent conductive film 103, an Indium Tin Oxide (ITO) film, a SnO ₂ film, or Au or Al that is thinned to about 200 Å or less and can be regarded as approximately transparent. And the like.
A predetermined fixed potential is applied to the transparent conductive film 103 formed of such a material in order to suppress the potential fluctuation.

In the embodiment shown in FIG. 1, the light receiving portion A
And the photodiode diffusion capacitance C _PD of the OB pixel portion B and the additional capacitance C _A formed between the transparent conductive film 103 and the metal wiring 5a or 5b are equal in the light receiving portion A and the OB pixel portion B. The output from the pixel section B coincides with the light receiving section output in a completely dark state. In addition, the transparent conductive film 103
When it is made of ITO, SnO ₂ or the like, it has a good light transmittance of 90% or more in the visible light region, so that the presence of this transparent conductive film 103 lowers the sensitivity of the light receiving part as compared with the conventional example. There is no fear.

In this embodiment, a metal light shielding layer 102 made of Al or the like is formed right above the transparent conductive film 103. Therefore, the same potential as the potential of the transparent conductive film 103 to which a constant potential is applied is applied to the metal light shielding layer 102.

The material of the metal light-shielding layer 102 is not limited to Al, and any conductive material having a light-shielding property may be used. In addition to Al, a metal film such as Au or Cu, or W, Mo or Ti.
A high melting point metal film such as Further, the metal light-shielding layer 102 does not necessarily have to be formed of a single-layer metal film.
A TiN film of about Å may be formed of a multilayer film made of two or more different materials such that a Ti film is sequentially laminated. In this case, if the metal light shielding layer is formed of the above-mentioned Ti / TiN multilayer film, the visible light reflectance in the lower portion of the metal light shielding layer can be significantly reduced. That is, it is possible to reduce stray light generated by being reflected multiple times between the lower portion of the metal light-shielding layer and the semiconductor surface, and it is very effective in reducing the floating of the OB signal that occurs when strong incident light is incident.

Further, in this embodiment, the transparent insulator layer 101
Although the transparent conductive film 103 and the metal light-shielding layer 102 are sequentially formed above, the metal light-shielding layer 102 is first formed on the transparent insulator layer 101, and immediately after that, the transparent conductive film is formed. Ten
Even if 3 is formed over the light receiving portion A and the OB pixel portion B, the same effect as in the above embodiment can be obtained.

Further, in this embodiment, a metal light shielding layer
Although 102 is formed right above the transparent conductive film 103, a film made of an insulator may be present between the metal light shielding layer 102 and the transparent conductive film 103. In this case, the transparent conductive film
Since a predetermined fixed potential is applied to 103 and electrically protects the semiconductor portion formed thereunder,
It is not necessary to apply a fixed fixed potential to the metal light shielding layer 102, and the metal light shielding layer 102 may be in a floating state in terms of potential.

Further, in the above embodiment, the transparent conductive film
Although 103 is formed on the transparent insulator layer 101, it is not necessarily limited to this arrangement state, and a conductive layer such as a metal wiring layer or a polysilicon wiring layer formed on the upper surface of the semiconductor can be used. The transparent conductive film 103 may be embedded in the transparent insulator layer 101 as long as a good electrically insulating state can be maintained.

Needless to say, like the conventional example,
A black filter can be formed on the metal light shielding layer 102, and a color filter or an on-chip microlens can be formed on the surface of the light receiving portion.

Further, in the present embodiment, the solid-state image pickup device using the AMI type amplification type image pickup device having the photoelectric conversion part formed of the P-N junction photodiode is shown, but the present invention is the AMI type amplification type image pickup device. The invention is not limited to one using an AMP, but an amplification type image pickup device (BASIS, SI) having a photoelectric conversion part formed of another PN junction photodiode.
T, FGA, CMD, BCMD, etc.) and O
Of course, it can also be applied to a solid-state imaging device having a B pixel portion.

[0031]

As described above on the basis of the embodiments, according to the present invention, an OB which has a perfect light-shielding characteristic and which outputs an OB output which completely matches the dark output of the light receiving portion.
It is possible to realize a solid-state imaging device including a pixel section.
Therefore, as compared with the conventional solid-state image pickup device using the amplification type image pickup device, more accurate dark output correction can be performed by using the OB output, and the amplification type image pickup device having a higher S / N than the conventional one is used. A solid-state imaging device can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a diagram showing a structure of one pixel of a conventional visible AMI solid-state imaging device.

FIG. 3 is a diagram showing an equivalent circuit of the AMI pixel shown in FIG.

FIG. 4 is a diagram showing a basic layout configuration of an area sensor configured using AMI pixels.

5 is a diagram showing drive signal waveforms for explaining the operation of the area sensor shown in FIG.

FIG. 6 is a cross-sectional view showing an AMI solid-state imaging device including a conventional light receiving unit and an OB pixel unit.

[Explanation of symbols]

1 p-well 2 n ⁺ type diffusion layer 3 gate insulating film 4 interlayer insulating film 5a light receiving part metal wiring 5b OB pixel part metal wiring 101 transparent insulator layer 102 metal light shielding layer 103 transparent conductive film

Claims (5)

[Claims] 1. A solid-state imaging device using an amplification type imaging device having a photoelectric conversion part made of a P-N junction photodiode, which has a light-receiving part and an optical black pixel part having a metal light-shielding layer. A solid-state imaging device characterized in that a transparent conductive film is uniformly formed on the semiconductor surface side of the light-shielding layer or on the light-incident direction side directly above the metal light-shielding layer over the light receiving portion and the optical black pixel portion. apparatus. 2. The solid-state image pickup device according to claim 1, wherein the amplification type image pickup device is an amplification type MOS image pickup device. 3. The transparent conductive film is made of ITO or SnO.
The solid-state imaging device according to claim 1, wherein the solid-state imaging device is formed of ₂ . 4. The solid-state imaging device according to claim 1, wherein the metal light shielding layer is formed of an Al thin film. 5. The solid-state imaging device according to claim 1, wherein a predetermined fixed potential is applied to the transparent conductive film.