JPS6216599B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging device using a charge transfer device.

Imaging devices using charge transfer devices have been developed using methods called the frame transfer method and the interline transfer method, which are rapidly developing based on the characteristics of solid-state devices: small size, light weight, low power consumption, and high reliability. ing. However, when considering the advantages and disadvantages of charge transfer imaging devices as imaging devices, in addition to the advantages of solid-state devices mentioned above, they are superior to currently used image pickup tubes in terms of noise, afterimages, burn-in, etc., but blooming,
A major problem remains with the smear phenomenon (crosstalk).

As shown in FIG. 1, a conventional charge transfer imaging device using an interline transfer method has multiple columns of vertical shift registers 10 driven by the same charge transfer electrode group.
, a photoelectric conversion section 11 adjacent to one side of each vertical shift register and electrically isolated from each other, a transfer gate electrode 12 for controlling signal charge transfer between the vertical shift register and the photoelectric conversion section, A charge transfer horizontal shift register 13 electrically coupled to one end of the shift register and a device 14 for detecting signal charges are provided at one end of the horizontal shift register. FIG. 2a schematically shows a cross section of the imaging device shown in FIG. 1 taken along the - line. A charge transfer electrode 17 of a vertical shift register is provided on the main surface of the semiconductor substrate 15 via an insulating layer 16,
A photoelectric conversion section is formed of a transfer gate electrode 18 that controls signal charge transfer from the photoelectric conversion section to the vertical shift register, and a layer 19 of a conductivity type different from the substrate semiconductor (P-n junction). The sections are separated from adjacent vertical shift registers by a channel stop region 20 having, for example, an impurity layer higher than the substrate impurity concentration. Also,
The parts other than the photoelectric conversion section are shielded from light by, for example, a metal layer 21.

An imaging device using such an interline transfer method transfers signal charges accumulated in the photoelectric conversion unit 11 according to the amount of incident light to the transfer gate 12, for example.
through the corresponding vertical shift register 1
Transfer to 0. After transferring the signal charge to the vertical shift register, the transfer gate is closed, and the photoelectric conversion unit 11 accumulates the signal charge for the next cycle.
On the other hand, the signal charges transferred to the vertical shift register 10 are transferred in parallel in the vertical direction, and transferred to the horizontal shift register 13 for each horizontal line of each vertical shift register. The charge sent to the horizontal shift register is transferred in the horizontal direction while a signal is transferred from the next vertical shift register, and is taken out as a signal from the charge detection section 14 to the outside.

In such a conventional charge transfer imaging device, as shown in the potential distribution diagram of FIG.
As shown in FIG. b, a portion flows into the adjacent vertical shift register.

A portion of the signal charges generated outside the potential well 23 of the photoelectric conversion section is transferred to the adjacent vertical shift register 2.
4 or the vertical shift register 25 corresponding to the photoelectric conversion section. In addition, the light incident at an angle to the main surface of the photoelectric conversion section is reflected on the surface of the semiconductor substrate and is reflected multiple times through the insulating layer and the electrode layer formed of polycrystalline silicon, etc., as shown in Figure 2a. The charges propagate in the lateral direction of the cross section and are absorbed in the adjacent vertical shift registers and the vertical shift registers corresponding to each photoelectric conversion unit, generating a group of charges.

If such a phenomenon occurs during the period when signal charges are being transferred in the vertical shift register, the amount of charge leaking to each vertical shift register will differ depending on the amount of light irradiated to each vertical line. The difference in the average light intensity of the vertical lines appears as a difference in the dark output level, and a phenomenon generally called smear is observed. Another problem is that, as shown in the potential distribution diagram shown in Figure 2c, if strong light is incident on the photoelectric conversion unit and a charge greater than the maximum amount of charge that can be stored in the photoelectric conversion unit is generated, that charge will be transferred to the photoelectric conversion unit. It overflows from the potential well 23 and flows into the potential well 24 of the adjacent vertical shift register or the potential well 25 of the vertical shift register corresponding to the photoelectric conversion section. This phenomenon is generally called a blooming phenomenon, and appears as a white linear pattern in the captured image.

The present invention provides a solid-state imaging device with a new structure that eliminates the above-mentioned drawbacks and a method for driving the same.

According to the present invention, the junction region is formed on the main surface of a semiconductor substrate and has a conductivity type opposite to that of the substrate, the first region having the shallow junction depth and the second region having the deep junction depth. , a group of photoelectric conversion elements is formed on the main surface of the first region, and a device for reading signals from the group of photoelectric conversion elements is formed on the main surface of the second region. a solid-state imaging device;
The solid-state imaging device described above is characterized in that a reverse bias voltage necessary for at least the first region to be completely depleted is applied between the first region, the second region, and the semiconductor substrate. A method for driving a solid-state imaging device is obtained.

Next, embodiments of the present invention will be described using the drawings. Hereinafter, in the embodiments of the present invention, an N-channel semiconductor device will be described to simplify the explanation.

FIG. 3 shows an embodiment of the present invention, and similarly to FIG. 2a described in the conventional example, it schematically shows a cross section of the charge transfer imaging device shown in FIG. 1 on the - line. be. In FIG. 3, areas having the same functions as those in FIG. 2 are indicated by the same symbols. This third
The difference between the embodiment shown in the figure and the conventional example shown in FIG. It is in the fact that An example of a method for forming P-type regions 27 and 28 having different junction depths on an N-type semiconductor 26 will be described with reference to FIG. 4. First, a region 2 is formed on the substrate semiconductor 26 using ordinary photolithography technology.
P-type impurities are diffused into the portion corresponding to No. 8 by ion implantation or thermal diffusion. Thereafter, as shown in FIG. 4a, impurities are redistributed and diffused in an inert gas or a thin oxygen atmosphere. Next, in the same way as forming the P-type regions 28, P-type impurities are selectively diffused into the region 27 by photolithography, and then redistribution diffusion is performed to achieve the required junction depth and Impurity concentration can be obtained.

An example of another method for forming the regions 27 and 28 will be explained using FIG. 5. First, as shown in FIG. 5A, a high concentration region 29 of the same type of impurity as the substrate impurity is formed in a portion corresponding to region 27 on the N type substrate semiconductor 26 by photolithography. Thereafter, as shown in FIG. 5b, a P-type semiconductor layer 30 having a conductivity type opposite to that of the substrate semiconductor 26 is formed by, for example, vapor phase growth.
When high-temperature treatment is performed in such a state, impurities are diffused from the heavily doped buried layer 29 to the vapor-grown P-type layer 30, resulting in P-type layer regions with different junction depths as shown in FIG. 5c. 27 and 28 can be obtained.

Next, the operation of the embodiment of the present invention will be explained.
Since the basic operation as an imaging device is the same as that of the conventional imaging device shown in FIG. 1, the P-type region 27, which is an important element of the present invention shown in FIG.
The operation of 28 will be explained.

FIG. 6 shows the potential distribution on the - line of the photoelectric conversion section shown in FIG. 3, that is, in the depth direction of the photoelectric conversion section. In FIG. 6, the horizontal axis represents distance in the depth direction, and the vertical axis represents potential. Let us now assume that the potential of the channel stop region 20 shown in FIG. 3 is a reference potential (in this case, 0 volts). The N-type photoelectric conversion section 19 is set at a potential of V TG -V _T where the potential of the transfer gate 18 is V _TG and the threshold voltage of the transfer gate _{is V T .} Further, when the reverse bias voltage applied to the P-type region 27 and the substrate 26 is changed from a low voltage shown by curve 31 to a higher reverse bias voltage, curve 3
As shown in FIG. 2, the P type region 27 is completely depleted. When the photoelectric conversion region 19 is irradiated with light and signal charges are accumulated, the potential of the photoelectric conversion region 19 decreases as shown by a curve 32 to a curve 33, and finally, as shown in a curve 34, the potential of the photoelectric conversion region 19 and the P type The junction of the region 27 is in the forward direction, and any more charges generated in the photoelectric conversion section 19 are transferred to the substrate semiconductor 2 via the P-type region 27.
Flows into 6. In other words, the photoelectric conversion section 19 and P
By applying a reverse bias voltage to the substrate semiconductor and the P-type region 27 so that the junction potential of the type region 27 becomes high, excess charges generated in the photoelectric conversion section 19 can be completely swept out to the substrate semiconductor.

With this structure and operation, it is possible to completely suppress the blooming phenomenon, which has been a drawback of the prior art. On the other hand, FIG. 7 shows the potential distribution in the vertical charge transfer region, that is, on the - line shown in FIG. 3, in a state where blooming is suppressed in the photoelectric conversion section. The vertical shift register 10 is described as being configured with embedded channels.

A curve 35 is a potential distribution when the pulse applied to the vertical charge transfer electrode 17 is at a high level and there is no signal charge in the vertical register. As shown by curve 35, under the operating conditions in which blooming is suppressed in the photoelectric conversion section, it is desirable to form the P-type region 28 directly under the vertical shift register 10 to a thickness that does not completely deplete it. Channel 10, P-type region 28, and P-type region 2
The thickness and impurity concentration of the P-type region 28 must be such that the P-type region 8 and the substrate semiconductor 26 are not in the forward direction.

The reason for this will be explained using the drawings. 1st
FIG. 1 shows the potential distribution in the depth direction assuming that the vertical shift register 10 consisting of a buried channel is formed on the shallow P-type region 27. Also shown in the figure for comparison is a potential curve 32 on which the photoelectric conversion region 19 is set.

A curve 57 is a potential distribution when the pulse of the transfer electrode 17 is at a high level and no signal exists in the vertical shift register. Further, the same reverse bias as the curve 32 in FIG. 6 is applied to the P-type region 27 and the substrate 26. The potential 57 of the buried channel vertical shift register 10 is higher than the high level applied to the vertical transfer electrode 17 (usually a voltage greater than the voltage V _TG applied to the transfer gate electrode). Further, the potential 57 of this vertical shift register 10 is set to the photoelectric conversion area 1 shown in FIG.
9 is set at a potential higher than the potential (V _TG -V _T ).

The potential of the P-type region 27 becomes high due to the reverse bias voltage of the buried channel vertical shift register 10 and the P-type region 27, and the reverse bias voltage of the P-type region 27 and the N-type substrate 26, and the potential of the P-type region 27 increases as shown by a curve 57. 2
6 and the P-type region 27 may be in the forward direction. In this case, electrons flow from the substrate semiconductor 26 to the vertical shift register 10 as indicated by an arrow 58. For this reason, the parts other than the photoelectric conversion part 19 must be formed in the P-type region 28 having an impurity concentration and junction depth that prevent injection of electrons from the substrate.

Figure 8 is a horizontal cross section V-V in Figure 3.
This shows the potential distribution on the line. Directly below the light aperture (photoelectric conversion section) 11, the potential is high as shown by the curve 36, so all the charges generated around the aperture flow into the photoelectric conversion section. The P-type region in FIG. 3 is completely depleted, and there is a barrier as shown by the curve 36 at any position in the depth direction from this P-type region 27 to the corresponding vertical register or adjacent vertical shift register. There is no charge leakage due to diffusion. Therefore, the so-called smear phenomenon described in FIG. 2b hardly occurs.

As described above, the present embodiment shown in FIG. 3 can significantly reduce blooming and smear phenomena.

9 and 10 are for explaining other embodiments of the present invention, 37 is a photoelectric conversion element formed by forming a P-n junction with the substrate, and 38 is a vertical readout switch which is a MOS transistor. It is formed. The gates of the vertical switch MOS transistors 38 are commonly connected to a tap 41 of a vertical shift register that generates vertical delay pulses for each row.
Further, the drains of each vertical switch MOS transistor 38 are commonly connected to the elements arranged in the vertical direction by a vertical signal readout line 39. 42 is a horizontal switching MOS transistor, each gate of which is connected to each tap 44 of the horizontal shift register 43.

The imaging device shown in FIG. 9 is commonly called a MOS type sensor, and its operation is such that when an arbitrary tap 41 of the vertical shift register becomes high level, the optical information signal stored in the photoelectric conversion element group 37 is transferred to this tap. Vertical switch in the row connected to 41
The MOS transistors 38 become conductive at the same time, and the signal charges are transferred to the corresponding vertical readout lines 39.
is read out. This signal charge is sequentially read out to an output line 45 by each tap output 44 from the horizontal shift register 43 via a horizontal switch MOS transistor. When all the signals of the photoelectric conversion element group 37 corresponding to an arbitrary tap 41 of the vertical shift register are read out in this way, the vertical shift register 40 advances by one stage and the next tap becomes high level, and at the same time The signal charges of the photoelectric conversion element group 37 in the corresponding row are read out to the corresponding vertical readout line 39. By repeating the same operation thereafter, the signal charges stored in the photoelectric conversion element 37 shown in FIG. 9 can be sequentially read out row by row. However, since the vertical readout line 39 is connected to all the photoelectric conversion elements arranged in the vertical direction via the vertical switch MOS transistor 38, if a part of the vertical line is irradiated with strong light and the element blooms, Excess charge leaks into the vertical readout line 39, and similarly, charge generated inside the substrate also diffuses into the vertical readout line 39.
It leaks into 9. These phenomena deteriorate the reproduced image as in the charge transfer type imaging device described in FIG. FIG. 10 shows a schematic cross-sectional view of a region 46 constituting one element of the imaging device shown in FIG. The photoelectric conversion element 37 corresponding to FIG. 9 is shown as an N-type region 47. Similarly, 48 is a vertical switch
The gate 50 of the MOS transistor is connected to the metal of the vertical readout line 51 at the drain. A terminal 49 of the gate 48 is connected to a tap 41 of the vertical shift register 40, although not shown. 55 is a channel stop area.

Immediately below the photoelectric conversion region 47 is a shallow junction region 53 having a conductivity type opposite to that of the substrate semiconductor 52, and a drain 50 connected to the vertical readout line 51.
Immediately below is a region 54 with deep junctions. With this structure, the substrate semiconductor and regions 53 and 54
By applying a reverse bias voltage to the photoelectric converter 47, all the excess charge stored in the photoelectric converter 47 can be swept out to the substrate semiconductor 52 by the same effect as explained in the embodiment of FIG. Furthermore, by controlling the impurity concentration of the region 54 and the junction depth, the drain 50 can be connected to the vertical readout line 51.
can be made completely unaffected by the substrate semiconductor 52.

Although the structure and driving method of the embodiments of the present invention have been described above, the present invention may be applied to any solid-state imaging device in which a photosensitive element and a readout device are configured as a pair. Further, the photoelectric conversion section 19 in the embodiment shown in FIG. 3 may be an element formed with a MOS structure.

Furthermore, although the embodiments have been described with reference to an N-channel semiconductor device, it goes without saying that the present invention can be applied to a P-channel semiconductor device by reversing the conductivity type of each region.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an imaging device using a conventional charge transfer device, and FIG. 2 is a schematic cross-sectional view on the - line shown in FIG. 1, and a potential distribution diagram immediately below the cross-sectional view. FIG. 3 is a sectional view of an apparatus showing an embodiment of the present invention, and FIGS. 4 and 5 are diagrams for explaining an example of a manufacturing method for constructing the embodiment of the present invention. FIGS. 6, 7, and 8 show potential distributions on the -, -, and - lines shown in FIG. 3. FIG. 9 and FIG. 10 show a configuration diagram and a schematic cross-sectional view of an imaging device showing another embodiment of the present invention. FIG. 11 is a diagram showing the potential distribution in the depth direction assuming that a vertical shift register consisting of a buried channel is formed on the shallow P-type region 27. 10 is a vertical shift register; 11 and 37 are photoelectric conversion elements; 27 and 53 are regions with a conductivity type opposite to that of the substrate and a shallow junction; and 28 and 54 are regions with a conductivity type opposite to that of the substrate and a deep junction.

Claims (1)

[Scope of Claims] 1. A junction region formed on the main surface of a semiconductor substrate and having a conductivity type opposite to that of the substrate, including a first region with a shallow junction depth and a second region with a deep junction depth. A region is provided, a group of photoelectric conversion elements is formed on the main surface of the first region, and a device for reading signals from the group of photoelectric conversion elements is formed on the main surface of the second region. A solid-state imaging device. 2. A first region having a shallow junction depth and a second region having a deep junction depth are provided on a main surface of a semiconductor substrate, the junction region having a conductivity type opposite to that of the substrate, and the second region having a shallow junction depth. In a solid-state imaging device, a group of photoelectric conversion elements is formed on the main surface of the first region, and a device for reading out signals from the group of photoelectric conversion elements is formed on the main surface of the second region. 1. A method for driving a solid-state imaging device, comprising: applying a reverse bias voltage necessary to completely deplete one region between the first region and the second region and the semiconductor substrate.