JPH0318390B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device having a CCD (Charge Coupled Device) configuration, and particularly to a solid-state imaging device using an interline transfer method.

By normal interline transfer method
As shown in FIG. 1, a CCD type solid-state imaging device has a common semiconductor substrate, for example, a silicon substrate, and a light-receiving section, that is, a sensor section, which serves as a picture element, is arranged in one direction (hereinafter referred to as the horizontal direction) and perpendicularly to this, as shown in FIG. A plurality of sensor units 1 are arranged in each direction (hereinafter referred to as the vertical direction), and a CCD-configured vertical shift register 2 is disposed on one side of the sensor unit 1 arranged on the same line in each vertical direction. similarly to
A horizontal shift register 3 having a CCD configuration is provided.
For example, in the case of television images, during the vertical blanking period, the signal charge generated according to the amount of light received by the sensor unit 1 is transferred to the corresponding vertical shift register 2, and during each horizontal blanking period, the signal charges are sequentially shifted to each vertical shift register 2. The signal charges of each horizontal line of the register 2 are transferred to the horizontal shift register 3, and are sequentially read out from the output terminal t in each horizontal video period. In this case, charge is transferred from each sensor unit 1 to the vertical shift register 2, for example, every other horizontal line, and each sensor on every other horizontal line is transferred in an odd-numbered field section. A so-called interlaced scanning method is adopted in which the signal of sensor unit 1 is read out, and the signals of each sensor unit 1 on every other horizontal line are read out in even-numbered field sections.

Even in such a solid-state imaging device, it is desirable to control the amount of accumulated charge and perform, for example, gamma correction. As a method for this gamma correction, for example, it is possible to use an external electric signal to move charges to the overflow drain region to prevent blooming.
If this control is performed at an arbitrary timing in the vertical period, the electric signal for control may leak into the imaging signal and deteriorate the quality of the imaging signal.

The present invention provides a solid-state imaging device using an interline transfer method that can reliably control the amount of charge by controlling the overflow of charges to the overflow drain region without causing such drawbacks. This is what we intend to provide.

The present invention will be described in detail below. In the present invention, as well, a large number of sensor sections 1, that is, light receiving sections are arranged and formed on a common semiconductor substrate, and a vertical shift register is provided. 2 and a horizontal shift register 3.

An example of the present invention will be described with reference to FIGS. 1 to 4. FIG. 2 is a top view of a part of the sensor section 1 and the main parts related to it, and FIG. 4 is a sectional view along the - line. FIG. 4 is a sectional view along the - line. In the figure, reference numeral 4 denotes a semiconductor substrate, for example a silicon substrate having a P-type conductivity, on the surface of which an insulating layer 5, for example a SiO ₂ layer, is deposited.
In the illustrated example, the shift register 2 has a buried channel type structure, and therefore, the N-type region 6, which has a conductivity type different from that of the base 4, is perpendicular to the portion constituting the shift register 2. It is formed in a band-like shape along one main surface 4a of the base 4. Reference numeral 7 denotes a channel stopper region having the same conductivity type as the substrate 4 and having a high impurity concentration, which is located between each sensor section 1 and between these sensor sections 1 and the shift register 2, as indicated by diagonal lines in FIG. are provided facing the main surface 4a so as to separate them from each other. An overflow drain region 9 made of an N-type high impurity concentration region of a conductivity type different from that of the substrate 4 is provided adjacent to each sensor section 1 and facing the main surface 4a via the overflow control section 8.

Furthermore, a gate section 10 is provided between each sensor section 1 and the corresponding shift register 2.

The shift register 2 is composed of an array of transfer sections 11 provided corresponding to each sensor section 1 on a corresponding vertical line. In the illustrated example, the shift register 2 is configured as a two-phase clock type, and in this case, each transfer section 11 is composed of, for example, a portion having a relatively thin insulating layer 5A and a portion having a thick insulating layer 5B. , on which electrodes 12A and 12B are formed, forming a so-called transfer gate section 13A and a storage gate section 13B. Electrodes 12A and 12B in each transfer section 11 are electrically connected to each other. In the example shown in FIG. 4, the electrode 12A,
Although the thicknesses of the insulating layers 5A and 5B under the insulating layer 12B are made different, the depth of the potential can also be made different using the difference in the impurity concentration of the semiconductor instead of using the difference in the oxide film thickness. In this case storage electrode 12
The thickness of the insulating layer under B and the transfer electrode 12A is the same, but the thickness of the insulating layer under the transfer electrode 12A is the same.
A shallow region of P-type conductivity is formed below. This P-type region can be formed, for example, by selectively implanting ions.

In the gate section 10 between each sensor section 1 and the corresponding shift register 2, a region 14 having the same conductivity type as the base body 4 but having a higher impurity concentration than the base body 4 is formed on the main surface 4a. An insulating layer 5, for example an insulating layer 5B, is extended and formed on the insulating layer 5, and a gate electrode 15 is deposited thereon. The gate electrode 15 of the gate section 10 corresponding to each sensor section 1 and the electrodes 13A and 13B of each transfer section 11 of the shift register 2 are connected to each other by a common electrode, as shown by the chain line a in FIG. In this case, even if the same voltage is applied to each electrode of the gate section 10 and transfer section 11, the minimum potential of each section is The impurity concentration or the thickness of the insulating layer of each portion 10, 11 shall be selected so that the depth is always shallow at the gate portion. Then, every other transfer section 11 is connected in common, and terminals t _r1 and t _r2 are led out.

Further, the overflow control section 8 is formed such that, for example, a region 16 having the same conductivity type as the substrate 4 but having a higher impurity concentration than the main surface 4a is formed facing the main surface 4a, and a region 16 is formed on the main surface 4a with an insulating layer 5 interposed therebetween. A control electrode 17 is attached thereto.

The sensor section 1 is constructed by depositing a sensor electrode 18 on a light-transmissive insulating layer 5 via an insulating layer 5. This sensor electrode 18 and the corresponding control electrode 17 of the overflow control section 8 may be formed by a continuous common transparent electrode, or may be electrically connected to a terminal _ts that applies a common voltage. derived.

Note that each region 6, 7, 9, 14, and 16 can be formed by a well-known technique, such as a selective diffusion method or an ion deposition method. Further, the electrodes 15, 12A and 12B can be formed by sequentially depositing polycrystalline silicon layers doped with impurities to have low resistance by chemical vapor deposition, and oxidizing their surfaces. By doing so, an insulating layer is formed, and a transparent electrode constituting the sensor electrode 18 and the overflow control electrode 17 can be entirely coated on the entire surface including on these electrodes 12A and 12B.

Then, a light shielding layer 19 is deposited on the portion other than the sensor section 1. This light-shielding layer 19 may be composed of, for example, an aluminum layer, and when the light-shielding layer 19 is composed of a conductor in this way, an insulating layer 5 is formed covering each electrode, and then A light shielding layer 19 is applied.

As described above, in the device of this example, the sensor electrode 18 of each sensor section 1 and the control electrode 17 of the corresponding overflow control section 8 are electrically common; When a common voltage is applied, the minimum potential of the sensor section 1 and the overflow control section 8 (in the illustrated example, the minimum potential is generated on the surface, and in this case, the minimum potential corresponds to the surface potential. The difference in potential is made such that a difference occurs between the two potentials, and the difference in potential changes depending on the applied voltage. In the above example, the surface concentration of the sensor section 1 is selected to be the concentration of the substrate 4, and the surface concentration of the overflow control section 8 is made higher than that of the sensor section 1. In this case, the sensor section 1 and the overflow control section The sensor electrode 1 when the thickness of each insulating layer 5 of 8 is 3000 Å, the surface concentration of the sensor part 1 is 5 x 10 ¹⁴ cm ^-3 , and that of the control part 8 is 5 x 10 ¹⁵ cm ^-3 .
The surface potentials ψs and ψc of the sensor section 1 and the control section 8, respectively, with respect to the common applied voltage to the terminal _ts and the control electrode 17, that is, the voltage φs applied to the terminal ts.
As shown in curves 20 and 21 in FIG. 5, respectively,
The difference between the two becomes larger as the applied voltage φs becomes larger. In the above example, the surface concentrations of the sensor section 1 and the control section 8 are selected so that the surface potentials of the sensor section 1 and the control section 8 differ. are kept constant or are made different, and the thickness of the insulating layer under the electrodes 18 and 17 of each part 1 and 8 is made different from each other, so that the thickness of the insulating layer in the sensor part 1 is made greater than that in the control part 8. It is also possible to select a smaller value. With this configuration, as will be detailed later, the control section 8 and the sensor section 1 are controlled depending on the magnitude of the voltage φs applied to the terminal _ts .
In other words, the control unit 8 changes the height of the barrier between the sensor unit 1 and the overflow drain region 9 so that the difference in surface potential (ψs−ψc) of control the amount of overflow.

For convenience of later explanation, the sensor units 1 on each horizontal line are sequentially arranged as S ₁ , S ₂ , S ₃ . . . as shown in FIG.
...and the corresponding transfer section 1 of the shift register 2
1 as T ₁ , T ₂ , T ₃ ..., and every other transfer section
It is assumed that the electrodes of T ₁ , T ₃ , T ₅ . . . are connected to the terminal t ₁ and the electrodes of every other transfer section T ₂ , T ₄ , T ₆ . . . are connected to the terminal t ₂ .

Next, to explain the operation of this example device, in this case as well, during the vertical blanking period, signal charges corresponding to the amount of light received by the sensor section 1 are transferred to the corresponding transfer section 11 of the vertical shift register 2 (hereinafter referred to as readout). ) and the terminal t _r1 of shift register 2
As shown in FIGS. 6A and _6B , two-phase clocks φ _v1 and φ _v2 are applied to t r2 and t r2, and during the horizontal blanking period, this signal charge is sequentially transferred to the adjacent transfer section in one direction. The signal for each horizontal line is transferred to the horizontal shift register 3 shown in FIG. 1, and the signal for each horizontal line is read out from the terminal t during the horizontal video period. FIGS. 7 to 9 are minimum potential diagrams of each part in the cross section shown in FIG. It is expressed as ψd, ψc, ψs, ψg, and ψb, and the potential at each applied voltage state is shown with a suffix. FIG. 7 shows the light reception/storage mode. In this light reception/storage mode, a voltage that forms a deep potential well in the sensor section 1, that is, a large positive voltage φs is applied to the terminal _ts . Then, at the time point t _p of the vertical blanking period corresponding to the beginning of the odd-numbered field period,
As shown in FIG. 6A and B, the shift register 2
With the required positive voltages applied to the terminals t _r1 and t _r2 as voltages φ _v1 and φ _v1 and φ _v2 , the voltage φs applied to the terminal t _s is lowered as shown in FIG. As shown in the minimum potential diagram in Fig. 8, a potential ψ s is set to make the potential well of the sensor section 1 sufficiently shallow, and a potential ψ _s is set to make the potential well of the storage section of the transfer section 11 corresponding to this sensor section 1 sufficiently deep. Make it _b2 . In this way, each sensor section S ₁ , S ₂ ,
The signal charge (carrier) generated and accumulated in S ₃ ... according to the amount of light received is transferred to each transfer section T ₁ M, T ₂ , T ₃ ...
... is transferred, that is, read out, as shown by arrow b in FIG. 8, to the storage unit. Next, during this vertical blanking period, as shown in FIGS. 6A and 6B, for example, while the voltage φ _v2 of the terminal t ₂ is maintained at the above-mentioned positive required voltage, the voltage φ _v1 of the terminal t ₁ is For example, lower it to 0V. In this way, each electric charge of every other transfer section T ₁ , T ₃ , T ₅ . . . is transferred to every other transfer section T ₂ , T ₄ , T ₆ .
The charges of two transfer sections are added. That is, each signal charge of the sensor sections S ₁ , S ₃ , S ₅ . . . is superimposed on the adjacent sensor sections S ₂ , S ₄ , S ₆ . This charge is transferred to the horizontal shift register in the normal manner during vertical and horizontal blanking periods, but in this example a gamma correction operation is performed during an appropriate number of selected horizontal blanking periods. That is, when the voltages applied to the terminals t _r1 and t _r2 during the horizontal blanking period are both a low voltage of 0V, for example,
Each transfer section T ₁ , T ₂ , T ₃ ... and each sensor section S ₁ ,
When the potential barrier ψg of the gate portion between S ₂ , S ₃ ... is relatively high as shown as ψ _g1 in FIG. 9, at each time point t ₁ , t ₂ ,
At t ₃ ..., the voltages φ _s1 , φ _s2 , φ _s3 gradually increase at the terminal t _s as shown in FIG. 6C, that is, φ _s1 <φ _s2 <
As shown in FIG _{. 9} , sensor parts S ₁ , S ₂ , S ₃ ... potentials ψ _s1 , ψ _s2 , ψ _s3 ...
... is made shallow, and the potentials of the overflow control section 8 are set to ψ _c1 , ψ _c2 , and ψ _c3 . in this case,
As explained in FIG. 5, as the applied voltage is increased, the difference in potential between the sensor section and the overflow control section, that is, the potential barrier, is increased, so the amount of overflow is reduced. This operation will be explained in detail with reference to FIGS. 9 and 10 for the case where, for example, light having an intensity of I ₄ is incident. In other words, when light with an intensity of I ₄ is incident,
First, when φ _s4 is applied to the terminal t _s , the charge amount q ₄ or more determined by the difference between the potential φ _s4 of the sensor section and the potential ψc ₄ of the overflow control section is discarded to the overflow drain.
The amount of charge accumulated in the sensor section is saturated at q ₄ .
Next, at a point in time t ₁ during a certain horizontal blanking period, a relatively low potential φs ₁ is applied to the terminal t ₁ A.
As a result, charges exceeding the accumulated amount q ₁ determined by the potential φs ₁ of the sensor section and the potential φc ₁ of the overflow control section are removed to the overflow drain. Then, the potential applied to the terminal t _s is again set to φs ₄ , so the intensity of the incident light
Based on I ₄ , charge is again accumulated in the sensor section determined by the difference between the potential φs ₄ of the sensor section and the potential of the overflow control section, and the amount of charge q ₄
The excess charge is discarded to the overflow drain. Next _, at a point in time t ₂ during another predetermined horizontal blanking period, a potential φs 2 B higher than the previous φs ₁ is applied to the terminal t _s , thereby increasing the potential φs ₂ of the sensor section and the overflow control section. The storage amount determined by the potential φc ₂
Charges above q ₂ B are rejected to the overflow drain. Thereafter, the potential φs ₄ is applied to the terminal t _s again to accumulate charges, and at a certain point t ₃ during the third selected horizontal blanking period, a potential φs ₃ C higher than φs ₂ is applied. Charges with an accumulated amount q ₃ or more are eliminated. Thereafter, the potential φs ₄ is applied to the terminal t _s again, so that charges are accumulated in accordance with the incident light and then read out at a point in time t ₄ during the vertical blanking period. Therefore, now the intensity I of light is I ₀ <
When receiving light with the relationship I ₁ < I ₃ < I ₄ ,
Looking at the amount of charge q accumulated in the sensor unit 1 at time points _t0 to _t4 , as shown in FIG.
The charge of the sensor unit 1 determined by the value of ψs−ψc at t ₁ , t ₂ , t _{3 ,} and t 4 q ₁ to q ₄ D or more is overflowed and removed. The charge amount is subjected to a power function curve, that is, gamma correction, as shown in FIG. That is, the 10th
In the figure and Fig. 11, when light I ₀ of intensity I _pM or less is incident, the amount of charge accumulated in the sensor is expressed by a straight line l ₁
When light I ₁ with an intensity between I _0M and I _1M is incident,
The amount of charge accumulated in the sensor is shown by the straight line l ₂ and so on.

Then, gamma correction can be performed on the next even-numbered field by performing the same operation, but in this even-numbered field, as shown in Figure 6, it corresponds to the beginning of the field. The transfer section of the shift register 2 from each sensor section S ₁ , S ₂ , S ₃ ... during the vertical blanking period
After reading to T ₁ , T ₂ , T ₃ . . . Contrary to the case of the odd-numbered fields described above, while the voltage of terminal t ₁ is held at a positive predetermined voltage, the voltage of terminal t ₂ is
Assuming 0V, the charges of sensor parts S ₂ , S ₃ , S ₄ ...
They are added to other adjacent sensor sections S ₁ , S ₂ , S ₃ . . . which are different from the combination in the odd field. That is, in an even field, one pixel signal is formed by each combination of S ₁ and S ₂ , S ₃ and S ₄ , S ₅ and S ₆ , and in an odd field, another combination of S ₂ and S ₃ , S ₄ and S ₅ , S ₆ and S ₇
Each combination of... forms one picture element signal.

In this way, one screen (one frame) is formed by two fields, and an effect similar to interlaced scanning is obtained.

In the above configuration, in order to adjust the sensitivity, the width of the overflow control section 8 is kept sufficiently small, and the bias of the overflow drain region 9 is deepened as shown in FIG. This can be done by lowering this barrier and allowing the carriers of the sensor part 1 to escape into the region 9. That is, when a large bias is applied to the overflow drain, signal charges generated in the sensor region flow into the overflow drain and are not accumulated. Therefore, the light reception accumulation period can be shortened depending on the amount of light received.

As described above, according to this example, gamma correction can be performed without providing an electrically independent electrode in the overflow control section, which reduces the complexity of manufacturing and reliability due to the complicated electrode structure. It is possible to avoid problems such as deterioration and yield deterioration, and the benefits are great in practical use.

Furthermore, with the above configuration, the charge from all the sensor sections S ₁ , S ₂ , S ₃ . . . is read out at the beginning of each field, so the problem of afterimages can be solved. In other words, when reading out the charge of every other sensor section in each field as in the past, light is received in each sensor section even during the field section where every other sensor section is read out. Since two fields of light are received each, the problem of afterimages occurs.
According to the device of this example described above, this problem is solved.

In the above example, the signal charge of each sensor part is read out in each field using a common sensor electrode, but in some cases, the sensor part S on every other horizontal line is connected to a sensor electrode. ₁ , S ₃ , S ₅ . . . , S ₂ , S ₄ , S ₆ .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an interline transfer type solid-state imaging device, FIG. 2 is a top view of the main parts of the device of the present invention, and FIGS. 3 and 4 are cross-sectional views on the - line and - line, respectively. FIG. 5 is a curve diagram showing the relationship between the minimum potential and the applied voltage of the sensor section and the overflow control section, FIG. 6 is a voltage timing diagram for explaining the operation, and FIGS. Figure 10 is a potential diagram showing the mode, Figure 10 is a diagram showing the accumulated charge in the sensor section at each point in time when the light intensity is changed, Figure 11 is a gamma correction curve diagram, and Figure 12 is the minimum potential of automatic sensitivity adjustment mode. It is a diagram. 1, S ₁ , S ₂ , S ₃ ... are sensor sections, 2 is a vertical shift register, 3 is a horizontal shift register, 4 is a semiconductor substrate, 5 is an insulating layer, 7 is a channel stopper region, 8 is an overflow control section , 9 is an overflow drain region, 10 is a gate portion, 11,
T ₁ , T ₂ , T ₃ ... are transfer parts of shift register 2,
13A and 13B are transfer electrodes, 15 is a gate electrode, 17 is an overflow control electrode, and 18 is a sensor electrode.

Claims (1)

[Claims] 1. A plurality of sensors arranged in a matrix in the horizontal and vertical directions, and a plurality of vertical sensors that read out the charges accumulated in the sensors for each vertical period of a television signal and transfer the charges in the vertical direction. a shift register; a horizontal shift register that receives the charge transferred by the vertical shift register and transfers the charge in the horizontal direction; and an overflow drain section that absorbs a predetermined amount or more of the charge generated by the sensor. In an interline transfer type solid-state imaging device having an overflow drain section configured to control the above-mentioned predetermined amount by an electric signal, in one of two consecutive vertical periods, , among the vertically arranged sensors, charges of two vertically adjacent sensors are combined according to the first combination and transferred by the vertical shift register; In the other of the two vertical periods, the charges of two vertically adjacent sensors are combined according to a second combination different from the first combination among the sensors arranged in the vertical direction, and the charges of the two vertically adjacent sensors are combined. The data is transferred by a shift register, and in each vertical period,
A solid-state imaging device characterized in that an electric signal for controlling the predetermined amount is supplied during a predetermined horizontal blanking period to control the amount of charge accumulated in the sensor.