JPH09139486A - Solid state image pick up element and drive of solid state image pick up element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the generation of blooming and smear. SOLUTION: An image sensor used here is structured by a light receiving means 1 for photo-electrically converting an incident light from an object into signal charge depending on the amount of light during the exposure period, a transfer channel region 14 for transferring signal charge to the output side during the charge transfer period, a read gate 17 for transferring signal charge stored in the light receiving means 1 to the transfer channel region 14 during the read period and an overflow barrier region 12 for deciding amount of saturation of signal charge stored in the light receiving means 1, which are formed on a silicon substrate 11. Moreover, a substrate voltage applying circuit 36 is also provided to continuously change the level of substrate voltage applied to the silicon substrate 11 in order to continuously change the height of potential barrier formed by the overflow barrier region 12 up to the specified height from the lower position during the exposure period.

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 pickup device and a driving method thereof, and more particularly to improving the substrate voltage applied to the substrate of the solid-state image pickup device for the purpose of reducing the occurrence of blooming and smear. .

[0002]

2. Description of the Related Art Fixed pattern noise including flaw defects, blooming and smear are the most serious problems in the characteristics of solid-state image pickup devices. Of these, blooming and smear are false signals unique to the solid-state imaging device and are generally used in distinction.

In blooming, when strong light is incident, pixels are saturated, signal charges overflow, enter adjacent pixels, signal lines, vertical transfer registers, etc., and white parts spread around just like flowers bloom. It is a phenomenon.

The smear is generated when light is mixed into a signal line, a vertical transfer register, or the like, or electric charges generated inside the semiconductor substrate are spread by diffusion and mixed into an adjacent pixel or a transfer register. Smear occurs at a constant rate regardless of the intensity of light. Therefore, when the amount of light is small, it does not matter, but when strong light is incident, the white spots appear in a vertically striped pattern.

Conventionally, various means have been proposed and tried in order to reduce the occurrence of blooming and smear.

At present, the following two methods have been put into practical use. That is, one method is to form a P-type well region on an N-type silicon substrate in a MOS-type image pickup device, and form an N-type high-concentration impurity in a pixel portion on the surface of the P-type well region. Forming a diffusion region to form an npn structure in the vertical direction. by this,
Unwanted charges are discharged to the N-type silicon substrate, and as a result,
Blooming does not occur even with 100 times or more of the saturated light amount, and smear can be suppressed to about 52 dB or less of the signal.

Another method is applied to a CCD solid-state image pickup device in which a charge transfer portion is composed of a CCD. A P-type well region is formed on an N-type silicon substrate, and the P-type well region is formed.
A vertical transfer register and a light receiving portion (photodiode) are formed on the surface of a well region of a rectangular shape to form a so-called VOD (vertical overflow drain) structure.

Specifically, the configuration of the solid-state image pickup device having the VOD structure will be described with reference to FIG. 9. This solid-state image pickup device is a P-type which forms an overflow barrier region formed on an N-type silicon substrate 101. Well region 102
An N-type impurity is introduced into a pixel portion of the inside to form an N-type impurity diffusion region 103, and p of the N-type impurity diffusion region 103 and the P-type well region 102 is formed.
It has a light receiving portion 104 formed of an n-junction photodiode.

The solid-state image pickup device further includes a vertical transfer register 106 composed of an N-type transfer channel region 105 formed by an N-type impurity introduced in a region different from the n-type impurity diffusion region 103. A P-type channel stopper region 107 is formed by introducing P-type impurities.

Then, a vertical transfer electrode 108 made of a polycrystalline silicon layer is selectively formed on the transfer channel region 105 via a gate insulating film (not shown). A silicon oxide film (not shown) is formed by the oxidation process. A PSG film 109 is formed on the entire surface including the vertical transfer electrode 108,
Further, on the PSG film 109, a light-shielding Al film 110 (hereinafter referred to as an Al light-shielding film) is formed so as to cover the lower transfer electrode 108.
Are formed. The P-type region between the light receiving unit 104 and the transfer channel region 105 constitutes the read gate 111.

Further, the Al light-shielding film 110 is provided in the light receiving portion 1
04, the light is selectively etched away, and the light is exposed through the opening 110 formed by this etching away.
The light is incident on the light receiving unit 104 through a.

Then, by controlling the substrate voltage applied between the silicon substrate 101 and the P-type well region 102, the excess charges generated in the light receiving portion 104 do not flow into the transfer channel region 105, and the excess charge of the silicon substrate 101 is prevented. It will flow in the thickness direction. In addition, the silicon substrate 1
The electric charges generated in the deep portion of 01 also flow toward the substrate and disappear. This reduces blooming and smear.

[0013]

By the way, the conventional VO
In the D-structure solid-state imaging device, the substrate voltage applied to the silicon substrate 101 is fixed when the signal charges are not swept away toward the substrate as in the charge accumulation period (exposure period).

The potential barrier of the overflow barrier region 102, which determines the amount of saturated charge accumulated in the light receiving portion 104, changes depending on the amount of incident light, so-called kne.
Since it has the e characteristic, the potential barrier of the overflow barrier region 102 becomes shallower than the potential barrier of the read gate portion 111 when an excessive amount of light is incident, and the signal charges accumulated in the light receiving portion 104 flow into the transfer channel region 105. Therefore, there is a fear that the blooming phenomenon will eventually occur.

Further, there is a problem that a part of the signal charges photoelectrically converted in the vicinity of the overflow barrier region 102 also flows into the transfer channel region 105 and appears as smear on the reproduction screen.

Since the blooming and smear deteriorate the quality of reproduced images, there has been a long-felt demand for reducing blooming and smear.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid-state image sensor capable of reducing the occurrence of blooming and smear, and a driving direction thereof.

[0018]

A solid-state image sensor and a method of driving the same according to the present invention include a light-receiving portion for photoelectrically converting incident light from a subject into a signal charge of an amount corresponding to the amount of light in a storage period, and charge transfer. A charge transfer unit that transfers the signal charge to the output side during the period, a read gate unit that transfers the signal charge accumulated in the light receiving unit to the charge transfer unit during the reading period, and a read gate unit that accumulates the light receiving unit. For the solid-state imaging device in which the overflow barrier region that determines the saturation amount of the signal charge is formed on the same substrate, the height of the potential barrier formed by the overflow barrier region is defined from a position low during the accumulation period. It is characterized in that the level of the substrate voltage applied to the substrate is changed in order to change the height of the substrate.

In general, blooming occurs when the potential barrier in the overflow barrier region is shallower than the potential barrier in the read gate section. Therefore, the blooming can be suppressed by setting the level of the substrate voltage applied to the substrate to, for example, a high value so that the potential barrier of the overflow barrier region is lower than the potential barrier of the read gate portion.

However, since the potential barrier of the overflow barrier region controls the amount of saturated charge accumulated in the light receiving portion, if the substrate voltage is fixed at a high value as described above and the potential barrier of the overflow barrier region is lowered. The saturated charge amount is reduced, and the dynamic range of sensitivity of the solid-state image sensor is reduced.

Here, considering the photoelectric conversion in the light receiving portion, the signal charge generated by the incident light increases with time. Therefore, at the start of the accumulation period, the height of the potential barrier in the overflow barrier region is saturated. It can be seen that the height of the charge amount is not necessary.

Therefore, at the start of the accumulation period,
The substrate voltage is set so that the potential barrier in the overflow barrier region is at a low position, and with the passage of time thereafter, the potential barrier is continuously increased so that the necessary signal charges can be accumulated in the light receiving portion during the accumulation period. The substrate voltage is continuously changed in the following direction.

According to the present invention, the level of the substrate voltage applied to the substrate is set so that the height of the potential barrier formed by the overflow barrier region continuously changes from a low position to a prescribed height during the accumulation period. Since it is continuously changed, the potential barrier of the overflow barrier region gradually increases from the start time to the end time of the accumulation period as the signal charge accumulated in the light receiving portion gradually increases. Then, at the end of the accumulation period, the potential barrier has a prescribed height, that is, a height at which a predetermined saturated charge amount can be accumulated in the light receiving portion.

Therefore, in the solid-state imaging device and the method of driving the same according to the present invention, the potential barrier of the overflow barrier region does not become higher than the potential barrier of the read gate portion during the accumulation period, so that the blooming phenomenon occurs. Can be suppressed. Further, unlike the case where the potential barrier of the overflow barrier region is fixed at a position lower than the regulation from the beginning, finally, it becomes possible to accumulate the determined saturated charge amount in the light receiving part, so that the dynamic range of the dynamic range is reduced. Does not cause deterioration.

Regarding smear, in the conventional case,
Some signal charges photoelectrically converted in the vicinity of the overflow barrier region flowed into the charge transfer unit and caused smear, which caused deterioration of image quality. However, in the present invention, the potential of the overflow barrier region toward the substrate becomes deep. Therefore, that is, in the accumulation period, since the height of the potential barrier in the overflow barrier region is lower than the prescribed height, a part of the signal charge that has conventionally flowed in the charge transfer portion flows to the substrate side. As a result, it is possible to suppress the occurrence of smear.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments in which the solid-state image pickup device according to the present invention is applied to, for example, an interline transfer (IT) type CCD image sensor (hereinafter simply referred to as an image sensor according to the embodiment) will be described. Will be described with reference to FIGS.

The image sensor according to this embodiment is
As shown in FIG. 1, a large number of light receiving portions 1 for photoelectrically converting into an amount of electric charge according to the amount of incident light are arranged in a matrix, and among the large number of light receiving portions 1, the light receiving portions 1 arranged in the column direction are arranged.
A large number of vertical transfer registers 2 are provided in common, and an image unit (imaging unit) 3 arranged in the row direction is provided.

Further, one horizontal transfer register 4 adjacent to the image section 3 and common to a large number of vertical transfer registers 2 is provided in parallel.

Between the image part 3 and the horizontal transfer register 4, two vertical-horizontal transfers for transferring the signal charges transferred to the final stage of the vertical transfer register 2 in the image part 3 to the horizontal transfer register 4. The registers VH1 and VH2 are formed in common for the many vertical transfer registers 2 and in parallel with each other. These two vertical-
Vertical-horizontal transfer pulses φVH1 and φVH2 are supplied to the horizontal transfer registers VH1 and VH2, respectively, and these transfer pulses φVH1 and φVH are supplied.
By supplying 2, the signal charges from the vertical transfer register 2 are transferred to the horizontal transfer register 4.

An output unit 5 is connected to the final stage of the horizontal transfer register 4. The output unit 5 converts the signal charges transferred from the final stage of the horizontal transfer register 4 into an electric signal (for example, a voltage signal), for example, a charge-electric signal conversion unit including a floating diffusion or a floating gate. 6, a reset gate 7 that sweeps away the signal charge after the electric signal is converted in the charge-electrical signal converter 6 to the drain region D according to the input of the reset pulse φRG, and the charge-
It has an amplifier 8 for amplifying the electric signal from the electric signal converter 6. The power supply voltage Vdd is applied to the drain region D.

By supplying the vertical transfer pulses .phi.V1 to .phi.V4 to the image section 3, the potential distribution under each vertical transfer electrode in the image section 3 is sequentially changed, whereby the signal charges are respectively transferred to the vertical transfer registers in the image section 3. 2 is transferred in the vertical direction (on the side of the horizontal transfer register 4).

In the image section 3, the light receiving section 1
In the vertical blanking period, the signal charges stored in the first column are first read out to the vertical transfer register 2 and then transferred to the horizontal transfer register 4 side by row in the horizontal blanking period. As a result, the signal charges in the final stage of the vertical transfer register 2 are transferred to the horizontal transfer register 4 via the two vertical-horizontal transfer registers VH1 and VH2.

In the next horizontal scanning period, for example, by applying horizontal transfer pulses φH1 and φH2 of two phases different from each other to the horizontal transfer electrodes formed by, for example, two layers of polycrystalline silicon layers formed on the horizontal transfer register 4, The signal charges are sequentially transferred to the charge-electrical signal conversion unit 6 on the output unit 5 side,
The electric signal is converted into an electric signal in the electric-electrical signal converting unit 6, and is taken out from the corresponding output terminal 9 via the amplifier 8 as the image pickup signal S.

Here, looking at the cross section around the light receiving portion 1 of this image sensor, as shown in FIG. 2, for example, a P-type impurity (for example, boron (B)) is introduced into an n-type silicon substrate 11 by introducing a P-type impurity. The well region 12, the N-type impurity diffusion region 13 for forming the light receiving portion 1, the N-type transfer channel regions 14 and P forming the vertical transfer register 2.
Shaped channel stopper region 15 is formed.
A P-type positive charge storage region 16 is formed on the surface of the P-type impurity diffusion region 13. The N-type impurity diffusion region 1
The p-type region between 3 and the transfer channel region 14 constitutes the read gate section 17.

Further, in this image sensor, a photodiode is formed by a pn junction between the N-type impurity diffusion region 13 and the P-type well region 12, and a pn junction is formed between the N-type impurity diffusion region 13 and the read gate portion 17. Photodiode, photodiode by pn junction of N type impurity diffusion region 13 and channel stopper region 15, and N type impurity diffusion region 13 and P type hole accumulation region 1
A light-receiving portion 1 (photoelectric conversion portion) is configured by a photodiode formed by a pn junction with 6, and a plurality of light-receiving portions 1 are arranged in a matrix to form an image portion 3. In the case of the color imaging method, one pixel is formed in four light receiving units 1 adjacent to each other, for example, depending on the color arrangement of color filters (three primary color filters or complementary color filters) formed corresponding to the light receiving unit 1. It is designed to be configured.

On the transfer channel region 14, channel stopper region 15 and read gate portion 17, for example, S
A Si ₃ N ₄ film and a SiO ₂ film are sequentially laminated through an iO ₂ film, and these SiO ₂ film, Si ₃ N ₄ film and SiO ₂ film are laminated.
On the gate insulating film (not shown) having a three-layer structure made of a film, four transfer electrodes (typically the first layer in FIG. 2 are formed by the first polycrystalline silicon layer and the second polycrystalline silicon layer). A transfer electrode 18 made of a polycrystalline silicon layer is formed), and the transfer channel region 14, the gate insulating film, and the transfer electrode 18 form a vertical transfer register 2.

Further, in the image sensor according to this embodiment, as shown in FIG. 2, on the surface of the transfer electrode 18,
A thermal oxide film (not shown) is formed by thermal oxidation, and the PSG film 19 (Ph) which is an interlayer insulating film is formed on the entire surface including the thermal oxide film.
osphorate-Silica-Glass ； phosphorus-doped SiO
₂ film) is formed, a light shielding film 20 made of a metal such as Al or a metal compound is formed on the PSG film 19 so as to cover the lower transfer electrode 18, and a SiN film (not shown) formed by a plasma CVD method is further formed on the entire surface. ) Has been formed.

The light-shielding film 20 is selectively removed by etching on the light-receiving portion 1, and the light-receiving portion opening 20 of the light-shielding film 20 formed by this etching removal is used.
The light is incident on the inside of the light receiving portion 1 through a.

In the sectional view of FIG. 2, the protective film, the flattening film, the color filter, the micro condenser lens and the like on the light shielding film 20 are omitted for simplicity.

Here, the potential distribution of the light receiving portion 1 and its peripheral portion of the image sensor according to the present embodiment, particularly the potential distribution when a substrate voltage of a specified level conventionally used as the substrate voltage is applied will be described. Then, in the depth direction of the light receiving portion 1 (A-A 'in FIG. 2).
(Direction indicated by a line), as shown in FIG. 3, the substrate surface, that is, the surface of the P-type hole accumulation region 16 is set as the lower limit,
The maximum value φ2 is set in the approximate center of the N-type high-concentration impurity diffusion region 13 formed under the hole accumulation region 16 in the effective depth direction, and the above-described value is calculated from the approximate center of the P-type well region 12 in the effective depth direction. The position close to the impurity diffusion region 13 is set to the minimum value φ3, and the potential has a distribution that rises substantially linearly in the depth direction of the N-type silicon substrate 11.

Further, from the width direction of the transfer channel region 14-reading gate portion 17-N type impurity diffusion region 13 to the depth direction of the light receiving portion 1 (direction shown by line BB 'in FIG. 2).
Looking at the potential distribution over the above conditions (when a substrate voltage of a specified level conventionally used as the substrate voltage is applied), as shown in FIG. 4, the potential barrier (level φr) of the read gate portion 17 is It can be seen that the P-type well region 12 is located at a position shallower than the potential barrier (level φ3).

From this, the minimum value φ3 of the potential in the P-type well region 12, that is, the portion corresponding to the potential barrier constitutes the overflow barrier for the accumulated charges. Therefore, in the following description, the P-type well region 12 is referred to as the overflow barrier region 1
Write 2.

In the image sensor, as shown in FIG. 2, the overflow barrier region 12 is formed on the surface of the N-type silicon substrate 11, and the light receiving portion 1 is formed at a position shallower than the overflow barrier region 12. By forming the N-type impurity diffusion region 13 having the above-mentioned structure, it has a so-called electronic shutter function.

That is, by setting the substrate voltage supplied to the silicon substrate 11 to a high level in synchronization with the shutter pulse, the potential barrier (overflow barrier) in the overflow barrier region 12 is lowered and the charge accumulated in the light receiving portion 1 is lowered. (In this case, electrons) are swept away in the vertical direction, that is, toward the silicon substrate 11 side, beyond the overflow barrier. As a result, the period from the final application time of the shutter pulse to the electric charge read time becomes a substantial exposure period, and it is possible to prevent inconveniences such as an afterimage.

On the other hand, the peripheral circuit of the image sensor according to the above-described embodiment, as shown in FIG. 5, generates a reference clock Pc which is determined by the specifications and which is a reference clock generator 31.
And the reference clock P from this reference clock generator 31.
The horizontal synchronizing signal HD and the vertical synchronizing signal V based on the input of c
A synchronizing signal generation circuit 32 for generating D, and a vertical transfer of at least four phases based on the input of the reference clock Pc from the reference clock generator 31 and the horizontal synchronizing signal HD and the vertical synchronizing signal VD from the synchronizing signal generating circuit 32. Pulse φV1
.About..phi.V4 vertical drive circuit 33, and two-phase horizontal transfer pulses .phi.H1 and .phi.H2 are generated based on the input of the reference clock Pc from the reference clock generator 31 and the horizontal synchronizing signal HD from the synchronizing signal generating circuit 32. It has a horizontal drive circuit 34 that operates.

In addition to the above-mentioned circuit group, the peripheral circuit outputs the output section 5, especially the reset gate, based on the input of the reference clock Pc from the reference clock generator 31 and the horizontal synchronizing signal HD from the synchronizing signal generating circuit 32. 7, an output drive circuit 35 that generates a reset pulse φRG for supplying the voltage to the image sensor 7, a substrate voltage application circuit 36 that supplies the substrate voltage Vs to the silicon substrate 11 of the image sensor, and data Ds regarding the shutter speed input from the outside. A system controller 37 that controls the substrate voltage application circuit 36 and the like based on the above is configured.

The substrate voltage applying circuit 36, as shown in FIG. 2, has a first start signal Sd1 from the system controller.
Of the reference clock Pc and the synchronizing signal generation circuit 32 from the reference clock generator 31.
A shutter pulse generation circuit 41 for generating a shutter pulse Ps based on the input of the horizontal synchronizing signal HD from the above, and a change value of the substrate voltage for each predetermined time (reference clock Pc) in the exposure period in a storage area where data is stored in advance. That is, the ROM 42 in which the substrate voltage data Dv for each reference clock Pc is sequentially stored in an address, and the system controller 37.
And a data read circuit 43 which is activated by the input of the second activation signal Sd2 from the ROM, and which reads the substrate voltage data Dv from the ROM 42 in the address order in accordance with the input timing of the reference clock Pc from the reference clock generator 31, The D / A converter 44 for converting the substrate voltage data Dv read by the reading circuit 43 into an analog substrate voltage signal Vs, and a switching circuit 45.

The switching circuit 45 has a first fixed contact 45a connected to the output side of the shutter pulse generation circuit 41 and a second fixed contact 45a connected to the output side of the D / A converter 44.
Fixed contact 45b and the silicon substrate 1 of the image sensor
1 has a movable contact 45c connected through an extraction electrode (not shown) to the movable contact 45c.
Is switched to the first fixed contact 45a or the second fixed contact 45b according to the level of the switching control signal Ss from the system controller 37.

The level of the switching control signal Ss is obtained by the system controller 37 by calculating the charge accumulation period (exposure period) from the data Ds regarding the shutter speed (hereinafter simply referred to as shutter speed data) input from the outside. In this embodiment, the level is set to a low level in the charge discharging period from the charge reading time to the start of the exposure period, and is set to a high level in the exposure period. The first activation signal Sd1 is output from the system controller 37 at the start of the charge reading period, and the second activation signal Sd2 is output from the system controller 37 at the start time of the exposure period.

The substrate voltage data Dv stored in the storage area of the ROM 42 is set as follows.

That is, regarding the amount of change in the substrate voltage Vs with time, when the amount of light is constant, the amount of signal charge accumulated in the light receiving portion 1 is Q, and the potential barrier formed by the overflow barrier region 12 is. Assuming that the saturated charge amount of the light receiving portion 1 is Qsat and the exposure period is ts when Q is at a prescribed height, as shown by a straight line a in FIG. 6, Q = (Qsat / ts) × t (0 ≤t≤ts) The substrate voltage data Dv is set so as to satisfy the relational expression (1).

Actually, since the incident light quantity may change with time, as shown by the curve b in FIG. 6, the exposure period t
It is preferable to set the substrate voltage data so that the accumulated charge amount at the beginning of s becomes larger than the equation (1). Further, when t = 0 (exposure start time), it is not necessary to set Q = 0, and as shown by the curve c in FIG. 6, the substrate voltage data is set so as to have a certain amount of accumulated charge in the initial state. You may do it.

Next, the operation of the image sensor according to the present embodiment will be described with reference to FIG. 7 as well. At the time of reading charges in the vertical blanking period, the signal charges accumulated in the light receiving portion 1 are vertical. The first activation signal Sd1 is output from the system controller 37 to the shutter pulse generation circuit 41 at the same time as being read out to the transfer register 2, and the system controller 37 also outputs a low level switching control signal Ss to the switching circuit 45.

As a result, the shutter pulse generation circuit 41
The shutter pulse Ps synchronized with the horizontal synchronizing signal HD, for example, is applied to the silicon substrate 11 of the image sensor through the switching circuit 45, and the signal charge accumulated in the light receiving unit 1 is synchronized with the horizontal synchronizing signal HD. It will be swept away to the substrate 11 side (electronic shutter operation).

Then, the exposure period ts is started at the end of the electronic shutter operation. At the start of the exposure period ts, the system controller 37 outputs the second activation signal Sd2 to the data reading circuit 43, and at the same time, the system is activated. From the controller 37 to the switching circuit 4
The high-level control signal Ss is output to 5.

As a result, the substrate voltage data Dv stored in the storage area of the ROM 42 is sequentially read out through the data read circuit 43, and the read substrate voltage data Dv is read in the subsequent D / A converter 44. Is converted into an analog substrate voltage signal Vs at the switching circuit 4
The voltage is applied to the silicon substrate 11 of the image sensor via 5.

At this time, first, at the start of the exposure period ts (when t = 0), a voltage Vs sufficiently higher than a prescribed value is applied to the silicon substrate 11, as shown by the curve a in FIG. As a result, the potential level of the overflow barrier region 12 becomes higher, and the height of the potential barrier of the region 12 becomes lower than the potential height of the light receiving unit 1, or the light receiving unit 1 is exposed at the start of exposure. The height is such that the accumulated signal charges can be accumulated.

After that, the level of the substrate voltage Vs applied to the silicon substrate 11 gradually decreases with the lapse of time, so that the potential barrier of the overflow barrier region 12 gradually increases. The rate of change of the barrier in the height direction corresponds to the increase amount of the signal charge accumulated in the light receiving unit 1 with the passage of time.

Then, at the end of the exposure period ts (t = t
In s), as shown by the curve b in FIG. 7, the substrate voltage Vs of the specified level is applied to the silicon substrate 11, and as a result, the light receiving unit 1 is caused to reach the saturation charge determined in advance by the specifications. It is possible to store the signal charge of the amount Qsat. Here, the specified level is a substrate voltage level for determining the saturated charge amount Qsat that has been conventionally used.

In general, blooming occurs when the potential barrier in the overflow barrier region 12 is shallower than the potential barrier in the read gate section 17. Therefore, by setting the level of the substrate voltage Vs applied to the silicon substrate 11 to a high value, for example, and making the potential barrier of the overflow barrier region 12 lower than the potential barrier of the read gate section 17,
The blooming can be suppressed.

However, the potential barrier of the overflow barrier region 12 is the saturated charge amount Q accumulated in the light receiving portion 1.
Since sat is adjusted, when the substrate voltage Vs is fixed to a high value as described above and the potential barrier of the overflow barrier region 12 is lowered, the saturation charge amount Qsat is increased.
Will be reduced, which will cause deterioration of the sensitivity of the image sensor.

Here, in consideration of photoelectric conversion in the light receiving portion 1, since the signal charges generated by the incident light increase with time, at the start of the exposure period ts, the potential barrier of the overflow barrier region 12 is high. As a result, it is understood that the height of the saturated charge amount Qsat is not necessary.

Therefore, at the start of the exposure period ts, the substrate voltage Vs is set so that the potential barrier of the overflow barrier region 12 is at a low position, and with the passage of time thereafter, the light receiving portion 1 is set during the exposure period ts. The substrate voltage Vs is continuously changed in the direction of continuously increasing the potential barrier so that the necessary signal charge can be stored.

In the image sensor according to this embodiment,
The level of the substrate voltage Vs applied to the silicon substrate 11 is continuously changed in order to continuously change the height of the potential barrier formed by the overflow barrier region 12 from the lower position to the specified height during the exposure period ts. Therefore, the overflow barrier region 1 is increased in accordance with the increase of the signal charges accumulated in the light receiving unit 1 from the start time point to the end time point of the exposure period ts.
The potential barrier of 2 will gradually increase. Then, at the end of the exposure period ts, the potential barrier has a prescribed height, that is, a height at which a predetermined saturated charge amount Qsat can be accumulated in the light receiving unit 1.

Therefore, in the image sensor according to the present embodiment, the potential barrier of the overflow barrier region 12 is the read gate portion 1 during the exposure period ts.
Since it does not become higher than the potential barrier of No. 7, it is possible to suppress the reduction of the blooming phenomenon. Further, unlike the case where the potential barrier of the overflow barrier region 12 is fixed at a position lower than the regulation from the beginning, finally, the saturation charge amount Qsa determined is determined.
Since t can be stored in the light receiving unit 1, the sensitivity is not deteriorated.

In the image sensor according to this embodiment, the blooming margin itself cannot be improved, but the blooming state on the output image on the monitor screen is greatly improved. As an example, when an excessive amount of light is incident, in the conventional method, vertical stripes 63 due to blooming appear above and below a subject image 62 having an excessive amount of light in a reproduced image 61, as shown in FIG. 8A. On the other hand, in the image sensor according to the present embodiment, blooming does not occur up to a certain substrate voltage level. Therefore, as shown in FIG. 8B, the vertical stripe 63 of blooming generated around the subject image 62 having an excessive light amount is short. It becomes a thing and becomes inconspicuous.

Regarding smear, in the conventional case,
In the light receiving portion, a part of the signal charges photoelectrically converted in the vicinity of the overflow barrier region 12 flowed into the transfer channel region 14 to cause smear, which caused deterioration of image quality. However, in the image sensor according to the present embodiment, The potential of the overflow barrier region 12 toward the silicon substrate 11 side becomes deep, that is, since the height of the potential barrier of the overflow barrier region 12 is lower than the prescribed height in the exposure period ts, the conventional transfer channel is long. A part of the signal charges flowing in the region 14 will flow to the silicon substrate 11 side, and as a result, it becomes possible to suppress the occurrence of smear.

In the above embodiment, an example in which the invention is applied to the IT type image sensor is shown.
The present invention can also be applied to a (frame interline transfer) type image sensor.

[0069]

As described above, according to the solid-state image pickup device and the method of driving the solid-state image pickup device according to the present invention, the incident light from the subject is photoelectrically converted into the signal charge of the amount corresponding to the light amount during the accumulation period. A light receiving section, a charge transfer section that transfers the signal charge to an output side during a charge transfer period, a read gate section that transfers the signal charge accumulated in the light receiving section to the charge transfer section during a read period, and For a solid-state imaging device in which the overflow barrier region that determines the saturation amount of the signal charge accumulated in the light receiving unit is formed on the same substrate, the height of the potential barrier formed by the overflow barrier region is equal to the accumulation period. Since the level of the substrate voltage applied to the above-mentioned substrate is changed in order to change from a low position to a specified height in the inside, blooming and smear are prevented from occurring. It can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an embodiment (hereinafter simply referred to as an image sensor according to an embodiment) in which a solid-state image sensor according to the present invention is applied to, for example, an interline transfer (IT) type CCD image sensor. is there.

FIG. 2 is a configuration diagram showing a configuration of a light receiving portion and its peripheral portion and a configuration of a substrate voltage applying circuit of the image sensor according to the present embodiment.

FIG. 3 is a characteristic diagram showing a potential distribution in a direction indicated by a line AA ′ in FIG.

FIG. 4 is a characteristic diagram showing a potential distribution in a direction indicated by a line BB ′ in FIG.

FIG. 5 is a block diagram showing a configuration of a peripheral circuit of the image sensor according to the present embodiment.

FIG. 6 is a characteristic diagram showing a change over time in the amount of accumulated charge in the light receiving unit with a change in substrate voltage by the substrate voltage application circuit according to the present embodiment.

FIG. 7 is a characteristic diagram showing a temporal change of the potential in the depth direction of the light receiving unit during the exposure period of the image sensor according to the present embodiment.

FIG. 8 is an explanatory diagram showing a comparison of blooming appearance degrees on a reproduced image, and FIG. 8A shows a case of a conventional method;
FIG. 9B shows the case of the image sensor according to the present embodiment.

FIG. 9 is a cross-sectional view showing a general configuration of a light receiving portion of a solid-state image sensor and its peripheral portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light receiving part 2 Vertical transfer register 3 Image part 11 Silicon substrate 12 Overflow barrier region 13 N type impurity diffusion region 14 Transfer channel region 17 Read gate part 31 Reference clock generator 32 Synchronous signal generation circuit 33 Vertical drive circuit 34 Horizontal drive circuit 35 output drive circuit 36 substrate voltage application circuit 37 system controller 41 shutter pulse generation circuit 42 ROM 43 data read circuit 44 D / A converter 45 switching circuit

Claims (9)

[Claims] 1. A light receiving section for photoelectrically converting incident light from a subject into a signal charge in an amount corresponding to the amount of light during a storage period, a charge transfer section for transferring the signal charge to an output side during a charge transfer period, and reading. A read gate unit that transfers the signal charge accumulated in the light receiving unit to the charge transfer unit during a period and an overflow barrier region that determines the saturation amount of the signal charge accumulated in the light receiving unit are formed on the same substrate. In the above solid-state imaging device, the level of the substrate voltage applied to the substrate so that the height of the potential barrier formed by the overflow barrier region continuously changes from a low position to a specified height during the accumulation period. A solid-state image pickup device having a substrate voltage changing means for continuously changing the voltage. 2. The amount of signal charge accumulated in the light receiving portion during the accumulation period is Q, and the saturated charge amount of the light receiving portion when the potential barrier formed by the overflow barrier region is at the specified height. Is Qsat, and the accumulation period is ts, the substrate voltage varying means sets the substrate voltage so that Q = (Qsat / ts) × t (0 ≦ t ≦ ts) (1) The solid-state imaging device according to claim 1, wherein the level is changed. 3. The substrate voltage varying means makes the accumulated charge amount larger than the accumulated amount determined by the equation (1) at the beginning of the accumulation period and then gradually decreases the increment of the accumulated charge amount. 3. The solid-state imaging device according to claim 2, wherein the level of the substrate voltage is changed so that the accumulated charge amount becomes the saturated charge amount Qsat at the end of the accumulation period. 4. The initial value of the accumulated charge amount is from 0 to Qs.
The solid-state image pickup device according to claim 2, wherein the solid-state image pickup device has an arbitrary value between at. 5. The light receiving portion is configured to have at least a pn junction between the impurity diffusion region of the second conductivity type and the impurity diffusion region of the first conductivity type formed on the surface side from the impurity diffusion region. The read gate portion is formed by another impurity diffusion region of the second conductivity type that is continuously formed on the surface side from the impurity diffusion region of the second conductivity type, and the charge transfer portion is the second conductivity type. The impurity diffusion region of the first conductivity type formed on the surface side of the impurity diffusion region of the second conductivity type continuously formed on the surface from the impurity diffusion region of the second conductivity type. The solid-state image sensor according to any one of claims 1 to 4, characterized in that: 6. A light receiving section for photoelectrically converting incident light from a subject into a signal charge of an amount corresponding to the amount of light during a storage period, a charge transfer section for transferring the signal charge to an output side during a charge transfer period, and reading. A read gate unit that transfers the signal charge accumulated in the light receiving unit to the charge transfer unit during a period and an overflow barrier region that determines the saturation amount of the signal charge accumulated in the light receiving unit are formed on the same substrate. In the method for driving a solid-state imaging device, the level of the substrate voltage applied to the substrate so that the height of the potential barrier formed by the overflow barrier region changes from a low position to a specified height during the accumulation period. A method for driving a solid-state image sensor, comprising: 7. The amount of signal charge accumulated in the light receiving portion during the accumulation period is Q, and the saturated charge amount of the light receiving portion when the potential barrier formed by the overflow barrier region is at the specified height. Is Qsat and the accumulation period is ts, Q = (Qsat / ts) × t (0 ≦ t ≦ ts) ... (1) The substrate voltage level is changed so that The method for driving a solid-state image sensor according to claim 6. 8. At the beginning of the accumulation period, the accumulated charge amount is made larger than the accumulated amount determined by the equation (1), and thereafter the increment of the accumulated charge amount is gradually decreased, and at the end of the accumulation period. The accumulated charge amount is the saturated charge amount Qsa
8. The method for driving a solid-state image pickup device according to claim 7, wherein the level of the substrate voltage is changed so as to be t. 9. The initial value of the accumulated charge amount is from 0 to Qs.
9. The method for driving a solid-state image sensor according to claim 7, wherein the value is an arbitrary value between at.