JPH10229183A - Solid-state imaging device - Google Patents

Abstract

(57) [Problem] In a frame transfer type CCD solid-state imaging device, even if signal charges are full at the time of accumulation,
This prevents signal charges from flowing out of the transfer path to the drain region during transfer, and secures a dynamic range. SOLUTION: In a frame transfer type solid-state imaging device, drain voltages applied to an overflow drain are different from each other during charge accumulation and during charge transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to a frame transfer type CCD solid-state imaging device.

[0002]

2. Description of the Related Art A frame transfer type CCD solid-state imaging device in which a photoelectric conversion unit and a charge transfer unit are the same has a feature that a sensor aperture ratio can be increased as compared with an interline transfer type CCD solid-state imaging device. In a frame transfer type CCD solid-state imaging device, an excess charge generated when an excessive amount of light is incident generally causes a barrier adjacent to the sensor unit, that is, an overflow barrier (OF).
B) through the overflow drain (OFD) region.

The overflow drain structure has a horizontal overflow drain structure in which an overflow drain region is arranged in a horizontal direction of a sensor portion, and a vertical overflow drain structure in which an overflow drain region (also used as a substrate) is arranged in a vertical direction of a sensor portion. There is a drain structure.

[0004]

In a frame transfer type CCD solid-state imaging device employing an overflow drain structure, if the drain voltage applied to the overflow drain region is the same at the time of charge accumulation and at the time of charge transfer, the charge will be reduced. During the transfer, some signal charges flow out of the transfer path to the overflow drain region, and the dynamic range is reduced.

A frame transfer type CCD solid-state imaging device having a horizontal overflow drain structure formed of a p-type semiconductor substrate and having an overflow drain region arranged in the horizontal direction of the sensor section is also formed of an n-type semiconductor substrate. A similar phenomenon occurs in a frame transfer type CCD solid-state imaging device having a vertical overflow drain structure in which an overflow drain region is arranged in the vertical direction of the sensor section.

In view of the above, the present invention has been made in consideration of the above, even if the sensor section is full of signal charges during charge accumulation, the signal charges do not flow out of the transfer path to the overflow drain region during charge transfer, and the dynamic range is increased. An object of the present invention is to provide a frame transfer type solid-state imaging device which can be sufficiently secured.

[0007]

The solid-state imaging device according to the present invention has a configuration in which the drain voltage applied to the overflow drain is different from each other during charge accumulation and during charge transfer.

In this configuration, since the drain voltage is different between charge accumulation and charge transfer, the height of the overflow barrier during charge transfer is higher than the height of the overflow barrier during charge accumulation. Therefore, even when an excessive amount of light is incident upon charge accumulation and signal charges are full, signal charges do not flow out of the transfer path to the overflow drain during charge transfer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to the present invention is a frame transfer type solid-state imaging device in which drain voltages applied to an overflow drain are different from each other during charge accumulation and during charge transfer.

According to the present invention, the frame transfer type solid-state image sensor has a horizontal overflow drain structure.

According to the present invention, the frame transfer type solid-state image pickup device has a vertical overflow drain structure.

Hereinafter, an embodiment of a solid-state imaging device according to the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show examples of a frame transfer type CCD solid-state image pickup device applied to the present invention, respectively. In general, a frame transfer type CCD solid-state imaging device in which a photoelectric conversion unit and a charge transfer unit are the same includes a so-called frame transfer (FT) type CCD solid-state imaging device which is divided into portions called an imaging region and a storage region. F
There is a so-called full frame transfer (FFT) type CCD solid-state imaging device in which a storage area is omitted from a T-type CCD solid-state imaging device.

FIG. 1 shows a schematic configuration of the former FT type CCD solid-state imaging device 1. The FT-type CCD solid-state imaging device 1 has an imaging area including a CCD vertical transfer register in which common transfer electrodes are arranged in the vertical direction so as to be separated for each sensor section row (so-called pixel row) 2. 3
And a storage area 4 for temporarily storing signal charges from the imaging area 3 and a CCD.
Horizontal transfer register 5 and its CCD horizontal transfer register 5
And an output MOS circuit 6 connected to the output side.

The CCD vertical transfer register of the imaging area 3 is
It also functions as a so-called sensor unit having a photoelectric conversion function and a so-called charge transfer unit having a charge transfer function. 7
Indicates a sensor unit corresponding to each pixel.

In the FT-type CCD solid-state imaging device 1, signal charges generated by photoelectric conversion in the sensor section 7 in the imaging region 3 are accumulated. This signal charge is transferred within the imaging region 3 during the vertical blanking period and is temporarily stored in the storage region 4. Next, the signal charges for each horizontal line are transferred from the accumulation region 4 to the CCD horizontal transfer register 5 for each horizontal blanking period, and then transferred in the CCD horizontal transfer register 5 and output from the output MOS circuit 6.

FIG. 2 shows a schematic configuration of the latter FFT-type CCD solid-state imaging device 11. The FFT-type CCD solid-state imaging device 11 has a configuration in which the accumulation region 4 is removed from the FT-type CCD solid-state imaging device 1. Other configurations are shown in FIG.
Therefore, the same reference numerals are given and duplicate explanations are omitted.

In the FFT type CCD solid-state image pickup device 11, signal charges by photoelectric conversion are accumulated in the sensor section 7 of the image pickup area 3, and thereafter, the signal charges for each horizontal line are sequentially transferred from the image pickup area 3 to the CCD horizontally. The data is transferred to the register 5 and output from the output MOS circuit 6.

These CCD solid-state imaging devices 1 and 11 include:
FIGS. 3 and 4 show examples of a unit cell structure having an overflow drain. In this example, in each case, the unit cell structure in the imaging region 3 is, for simplicity of explanation,
The transfer electrodes are three-phase transfer electrodes driven by three-phase clock pulses φ ₁ , φ ₂ and φ ₃ .

FIGS. 3A and 3B show a vertical overflow drain type CCD solid-state imaging device in which a drain region is arranged in a vertical direction, that is, an excess charge in the sensor section 7 is swept away to the substrate side. In this vertical overflow drain method, the n-type silicon semiconductor substrate 21 has p
A p-type semiconductor well region 22 is formed, an n-type impurity diffusion region 23 is formed on the surface of the p-type semiconductor well region 22, and a photodiode is formed by a pn junction between the p-type semiconductor well region 22 and the n-type impurity diffusion region 23. Thus, the sensor unit 7 is formed. Further, a p-type channel stop region 24 for separating the sensor units 7 in each horizontal direction is formed. The substrate 21 has a function as an overflow drain region as described later.

A plurality of band-shaped transfer electrodes 26 made of, for example, polycrystalline silicon are provided on the n-type impurity diffusion region 23 via the gate insulating film 25 so as to be common to the horizontal sensor portions 7. The transfer electrodes 26 are arranged in the vertical direction, and three-phase drive clock pulses φ ₁ , φ ₂ , φ ₃ are applied to the transfer electrodes 26.

This vertical overflow drain type frame transfer type CCD solid-state image pickup device (1 or 1
In 1), at the time of light reception, a predetermined substrate voltage, that is, a drain voltage V _OFD1 is applied to the n-type silicon semiconductor substrate 21. As a result, an overflow barrier is formed in the p-type semiconductor well region 22, and excess charge generated by the incidence of an excessive amount of light in the sensor portion is transferred to the substrate 21 which exceeds the overflow barrier and becomes an overflow drain region.
Swept away to the side.

On the other hand, FIGS. 4A and 4B show a horizontal overflow drain type CCD solid-state imaging device in which overflow drain regions are arranged in the horizontal direction. In this horizontal overflow drain method, a p-type silicon semiconductor substrate 3 is used.
1 for separating the horizontal sensor unit 7 on the surface of
A channel stop region 32 is formed, and an overflow drain region 33 is formed in the channel stop region 32 by an n-type impurity diffusion region. Then, on the surface of the silicon semiconductor substrate 31, the gate insulating film 34 is interposed so as to be common to the sensor units 7 in the horizontal direction.
A plurality of band-shaped transfer electrodes 35 made of, for example, polycrystalline silicon are arranged in the vertical direction, and three-phase drive clock pulses φ ₁ , φ ₂ , φ ₃ are applied to the transfer electrodes 35. You.

In the horizontal overflow drain method, a predetermined drain voltage V _OFD2 is applied to the overflow drain region 33 during light reception. As a result, the channel stop region 32 becomes an overflow barrier, and excess charge generated by the incidence of an excessive amount of light in the sensor portion passes through the overflow barrier in the channel stop region 32 and overflows into the overflow drain region 33.
Swept away.

In this embodiment, the vertical overflow drain type or the horizontal overflow drain type FT type CCD solid-state image pickup device 1 or FFT is particularly preferred.
In the solid-state CCD solid-state imaging device 11, the drain voltage applied to the overflow drain region is changed between charge accumulation and charge transfer.

That is, for example, in the case of the vertical overflow drain method, the substrate voltage (ie, drain voltage) at the time of charge accumulation (so-called light receiving) is set to V _OFDH1 . At this time, the potential of the overflow barrier becomes φ _{OFBH1 as} shown in FIG. 5A. In this state, the signal charges e are accumulated in the sensor unit 7. Next, at the time of charge transfer for transferring the stored signal charges, the substrate voltage is set to V _OFDL1 (V _OFDL1 <V _OFDH1 ) lower than that at the time of charge storage. As a result, the potential of the overflow barrier becomes φ _OFBL1 as shown in FIG. 5B, and becomes shallower than the potential φ _OFBH1 of the overflow barrier during charge accumulation. In other words, in other words, the overflow barrier at the time of charge transfer is higher than that at the time of accumulation when viewed from the potential level in the sensor unit.

When an excessive amount of light is incident on the sensor unit 7 during charge accumulation and the signal charge becomes full, that is, when the charge sweeping function is activated, the overflow barrier between the charge accumulation and the charge transfer as in the related art is performed. If the potentials are the same (that is, the substrate voltage is the same), a phenomenon occurs in which charge flows out of the transfer portion to the substrate 21 which is an overflow drain region during transfer.

However, in the above-described embodiment, the substrate voltage which becomes the drain voltage at the time of charge storage and at the time of charge transfer is V
_OFDH1 varied and the V _OFDL1, since the shallower than the potential phi _OFBH1 the overflow barrier at the time of storing the overflow barrier of the potential phi _OFBL1 during transfer, without charge outflow is generated during the charge transfer, during the charge accumulation All the signal charges e can be transferred. Therefore, the dynamic range of the vertical overflow drain type CCD solid-state imaging device 1 or 11 can be sufficiently ensured by transferring all the signal charges e at the time of accumulation.

On the other hand, the same applies to the case of the horizontal overflow drain method. That is, the drain voltage at the time of charge accumulation (so-called light reception) is set to V _OFDH2 . The potential of the overflow barrier at this time is φ _OFBH2 as shown in FIG. 6A. In this state, the signal charges e are accumulated in the sensor unit 7. Next, at the time of charge transfer, as shown in FIG.
_OFDL2 ( _VOFDL2 < _VOFDH2 ). by this,
Potential of the overflow barrier becomes phi _OFBL2, shallower than the potential phi _OFBH2 the overflow barrier at the time of charge accumulation. Therefore, even when the signal charge e is full during accumulation, the signal charge e is transferred to all the signal charge e during transfer, and the dynamic range of the horizontal overflow drain type CCD solid-state imaging device 1 or 11 is sufficiently ensured. Can be.

[0030]

The frame transfer type (FT type, FFT) employing the overflow drain structure according to the present invention.
According to the solid-state imaging device (including both types), the drain voltage applied to the overflow drain region is varied between the time of charge accumulation and the time of charge transfer. Even in this case, the signal charge does not flow from the transfer unit to the overflow drain during the charge transfer, and the dynamic range can be secured.

In the present invention, the same effect can be obtained in the horizontal overflow drain system in which the overflow drain is arranged in the horizontal direction of the sensor unit and in the vertical overflow drain system in which the overflow drain is arranged in the vertical direction of the sensor unit. It is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a frame transfer (FT) type CCD solid-state imaging device applied to a solid-state imaging device according to the present invention.

FIG. 2 is a configuration diagram of a frame transfer (FFT) type CCD solid-state imaging device applied to the solid-state imaging device according to the present invention.

FIG. 3 is a plan view showing a main part of an imaging area of a vertical overflow drain structure. B is a cross-sectional view showing a main part of an imaging region of a vertical overflow drain structure.

FIG. 4 is a plan view of a main part of an imaging region having an A horizontal overflow drain structure. B is a cross-sectional view of a main part of an imaging region having a horizontal overflow drain structure.

FIG. 5 is a potential distribution diagram in the depth direction when charges are accumulated in the vertical overflow drain A. B is a potential distribution diagram in the depth direction at the time of charge transfer of the vertical overflow drain.

FIG. 6 is a horizontal potential diagram at the time of charge accumulation in the horizontal overflow drain A. B is a horizontal potential diagram at the time of charge transfer of the horizontal overflow drain.

[Explanation of symbols]

1 FT-type CCD solid-state imaging device, 2 sensor rows, 3
Imaging area, 4 storage area, 5 horizontal transfer register, 6
Output MOS circuit, 7 sensor unit, 11 FFT type CC
D solid-state imaging device, 21 n-type semiconductor substrate, 22 p-type semiconductor well region, 23 n-type impurity diffusion region, 24 channel stop region, 26 transfer electrode, 31 p-type semiconductor substrate, 32 channel stop region, 33 overflow drain region, V _OFD1 , V _OFDH1, V _OFDL1 drain voltage (substrate voltage), V _OFD2 , V _OFDH2, V _OFDL2 drain voltage

Claims (3)

[Claims] 1. A solid-state imaging device of a frame transfer type, wherein drain voltages applied to an overflow drain are different from each other during charge accumulation and during charge transfer. 2. The solid-state imaging device according to claim 1, wherein the frame transfer type solid-state imaging device has a horizontal overflow drain structure. 3. The solid-state imaging device according to claim 1, wherein the frame transfer type solid-state imaging device has a vertical overflow drain structure.