JPS6032486A - Charge transfer type solid state image pickup element - Google Patents

Abstract

PURPOSE:To enable to remove smear component contained in a signal component by providing a vertical CCD register that carries false signal charge near a vertical CCD shift register for signal transfer and taking the difference between the two registers. CONSTITUTION:When light enters to a solid state image pickup element, the light entered under the photodiode generates photocharge 18 in a semiconductor substrate, and the charge is accumulated in junction capacity formed by the photodiode. On the other hand, a shading film etc. is provided on electrodes 8'-1, 8'-2. However, even when light is sheltered, leaking light exists in the area, and photocharge 19 (19-A, 19-B) is generated by leaking light. Charge 19 enters a vertical register 10 for signal transfer and generates smear, and the charge also enters a vertical register 16 adjoining to the register 10. Consequently, the register 10 carries signal charge Q including smear charge S' (total Q+S'), and the register 16 carries smear charge S. By taking the difference between the two signals, a true light signal Q from which only smear component is removed can be obtained.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a photoelectric conversion element on a semiconductor substrate and a charge transfer element (ChargeCoup) for extracting optical information of each element.
LED Device, hereinafter abbreviated as CCD. ) This relates to solid-state imaging devices.

[Background of the invention]

Solid-state imaging devices require an imaging plate with a resolution comparable to that of the imaging electron tube used in current television broadcasting, and for this reason, 500 pieces in the vertical direction and 800 to 1 piece in the horizontal direction are required.
A matrix of 000 picture elements (photoelectric conversion elements) and a corresponding scanning element are required. therefore,
The above-mentioned solid-state image sensor is manufactured using MO8 large-scale circuit technology that requires high integration, and generally uses COD (MOS) transistors or the like as a component.

FIG. 1(a) shows the basic configuration of a CCD type solid-state image sensor, which is characterized by low noise. Reference numeral 1 denotes a photoelectric conversion element composed of, for example, a photodiode, and 2 and 3 denote a vertical COD shift register and a horizontal shift register for outputting optical signals accumulated in the photoelectric conversion element group to an output terminal 4 of a signal detection circuit. 5 and 6 are clock pulse generators for producing clock pulses for driving the vertical shift register and the horizontal shift register, respectively. Although a two-phase clock pulse generator is illustrated here, either a four-phase or three-phase clock format may be adopted. It's sweet, 7 il, but it shows the transfer date to send the charge accumulated in the diode to the vertical shift register 2. In its current form, this element becomes a monochrome image sensor, but if a color filter is laminated on the two parts, each photodiode, 4-D, is provided with color information and becomes a color image sensor-P.

FIG. 1(b) shows the structure of a pixel which is the heart of the CCD image sensor. 8' is an electrode (usually made of first and second layers of polycrystalline silicon) constituting a vertical register, and 9 is an oxide film (which insulates the I source electrode and the substrate 12).
(generally called the gate oxide film), and 11 is an oxide film (usually selected to have a thickness of 10 to 201t''Il) of the gate oxide film that is always applied to each pixel. .Also, 10t tr t: +3 ?, ・Impurity layer (surface) for making it a buried type ζl! (:(', J)
(In case D, wood chips are not required). 1 is an impurity layer for a photodiode, and both layers are made of impurity atoms having a conductivity type opposite to that of the substrate.

As is well known, solid-state imaging devices have many advantages over electron tubes, such as being small, lightweight, maintenance-free, and have low power consumption, and are expected to have a promising future as the next imaging device. It is. However, when an image is captured using the current device and a reproduced image is displayed on a monitor, vertical striped patterns appear above and below the optical information pattern with high brightness (that is, a bright pattern), significantly degrading the image quality.

This phenomenon is unique to solid-state devices and is called smear. On the other hand, smear with and does not occur in the case of an electron tube.

Therefore, in order to realize a solid-state image pickup device with image quality comparable to that of an electron tube, and furthermore to expand the range of applications, reducing smear is currently a major issue in the development of solid-state devices.

[Purpose of the invention]

The purpose of the present invention is to solve the above problem, namely C.
The object of the present invention is to improve the image quality by removing smear from a CD-type solid-state image sensor.

[Summary of the invention]

In order to achieve the above object, the present invention provides a vertical COD shift register for transferring smear charges in addition to a vertical COD shift register for transferring signal charges near the vertical COD shift register for signal transfer, and outputs (
By taking the difference between signal charge and smear charge, the smear component contained in the signal component is removed to obtain the true signal charge.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using examples.

FIG. 3 shows the construction and construction of a CCDm image sensor, which is the gist of the present invention. In the same figure (a), 2 is Koyu.

Vertical COD shift register 13 for signal transfer that transfers the optical signal charge accumulated in the diode 1 is a vertical COD shift register 13 provided next to the vertical CCD shift register 2 by narrowing the insulation separation band 14.
OD shift register, and 15 is a CCD shift V register that transfers charges sent from these two vertical registers. On the other hand, figure (b) shows the structure of the photodiode section (including the vertical resistor) shown in figure (a), where 10 is an impurity layer for a buried channel forming the vertical resistor 2, and 16 is a vertical resistor. This is an impurity layer for a buried channel forming a resistor 13, and a common electrode 8-1.8 is formed on the top of these buried layers via a gate oxide film 9.
-2 is provided. Further, 14' corresponds to the insulating isolation band 14 shown in FIG. (Produced in the same process as membrane 11)
. In addition, in order to improve insulation, an oxide film 11 may be added as necessary.
．． Under the impurity layer 14', an impurity layer 17 of the same type as the substrate (for example, if the substrate is P type, poron atoms may be formed).

Next, the smear removal operation of the device of the present invention will be explained with reference to FIG. When light enters the device, the light that enters under the photodiode generates a photocharge 18 in the semiconductor substrate 1-4. This charge is accumulated in the junction capacitance formed by the photodiode. On the other hand, since it is a problem if light enters the vertical register and transfer gate regions, a shield, a light film, etc. are usually provided above the electrodes 8.

However, even if the light is dimmed, there is still light leaking into this region, and this leakage light also generates photocharges 19. Charge 19 diffuses into the vertical register and generates smear (this is the smear generation mechanism in the conventional device. In the device of the present invention, this smear load is (i
' is also included in the bow transfer vertical register 10F2), but (
This Tb; load is shown as 19-A), vertical register 10 (
21 (this charge is shown as 19-B). As a result, the signal transfer register carries the load Q (I'Q+s') to the signal 1 containing the smear charge S', and the smear transfer vertical register J
6 will carry the smear load S. Ryo 11 (repair/
The charge sent through the register ((1), +S') J,
, L: (11: is sent into the adjacent bit of the horizontal register 15 (indicated by arrows 20'-x, 20-2), and then output 4 by driving the horizontal register with double transfer.
The smear charge S1 signal Q+S is time-sequentially (9, mutually)
Obtainable.

The signal waveform obtained at output 4 is shown in FIG. 3(a).

The signals of each photodiode are distinguished and expressed with symbols 1 to 11 as y, (Sl, Qi+St'), (82, Q2+Q'')
.

......, (8II, Qn+Sn is l1li
The Nth order has been obtained. As a means for removing the smear component from this signal, a signal processing circuit as shown in FIG. 3(C) can be considered, for example. Here, 21 is a sampling circuit that distributes the signal and the smear signal, and the smear signal selected by the sampling circuit is inputted to the differential circuit 23 through the delay circuit 22. On the other hand, the signals selected by the sampling circuit are directly input to the differential circuit. Here, if the delay time of the delay circuit 22 is set to td (shown in (a) of the same figure), the phase of the smear signal S will be shifted by the time td and match the phase of the signal Q-1-8', so the circuit By taking the difference between the two signals at 23, the output 24 is the true optical signal Q from which only the smear component has been removed (shown in Figure 3(b)).
can be obtained. In the above smear component removal operation, it is implicitly assumed that the amount of smear charge diffused into both vertical registers is equal (S=8'). On the other hand, if the areas, etc. of the two vertical registers are extremely different, or if there is a difference in device structure between the two register areas, the amount of smear charge diffused into both vertical registers will not be equal (SO
8'). In this case, between 22 and 23 (or 21 and 2)
Insert an amplifier circuit or attenuation circuit between s=s'
You can adjust it so that

FIG. 4 shows the device structure shown in FIG. 2(b) which realizes the element configuration of FIG.
) is a diagram showing an example different from the above. Here, in order to electrically insulate the vertical resistors 2 (10) and 13α6), the thick oxide film 14' provided in FIG. 2(b) is not used, but the same thin oxide film as the gate region is used. .

If such a thin oxide film is used, the threshold voltage will generally be lower and the insulation between both resistors will be reduced, so in order to prevent this (in other words, to increase the threshold voltage), an impurity layer is added. It is sufficient to form an impurity layer 25 having a higher concentration than 17-1 (17-21) shown in FIG. 2(b) in the region between 10 and 16.
(Same as 17-21, if the substrate is P type, boron atoms may be ion-implanted.

FIG. 5 is a diagram showing a different embodiment from FIG. 2 of the CCD type image pickup device of the present invention. Here, two rows of horizontal registers are provided, 3-1 is a horizontal register that transfers the signal (Q, +8M) carried by signal transfer register 2 toward output 4-1, and 3-2 is a smear transfer register. This is a horizontal register that transfers the smear S carried by the register 13 to the output 4-2.The horizontal register may be driven by a 2-phase, 3-phase, or 4-phase clock pulse. In the device with this configuration, two types of signals Q-+-8' and S can be obtained at the same time at the outputs 4-1 and 4-2.
The delay circuit shown in FIG. 3, which was provided to remove smear from the component shown in FIG. Smear on output 24.

A true optical signal with components removed can be obtained.

The two components have been described below, but in both the embodiments of FIGS. 2 and 5, if the width (DS) of the smear vertical register is smaller than the width (DQ) of the signal vertical register (ns<Dq )showed that.

This is based on the reality that the amount of smear charge is usually small, about 1/100 of the amount of signal charge or less. Of course, if the required pixel integration degree f is satisfied, 1) s=DQ may be designed. However, in order to improve the degree of integration in the future, it is desirable to design the width 1) s of the smear vertical register with a small amount of transferred current θI to be as small as possible. Also, regarding the width of the water register shown in Figure 5, it is possible to design the width of the smear water register to be smaller than the width of the signal horizontal register. It is.

〔Effect of the invention〕

As explained in detail 1 below using an embodiment, in addition to the signal transfer CCD and CCD shift registers, it is possible to install a vertical CCD shift register for transmitting false signals. By taking the difference between the signals sent out by the registers, the smear component contained in the optical signal can be removed and the image quality can be significantly improved. The present invention can be manufactured using conventional process techniques. Also extra vertical COD
At first glance, the increase in the number of shift registers seems to reduce the pixel integration, but since the smear component is sufficiently smaller than the optical signal, the area given to this register is sufficiently small, so the reduction in the integration is kept to a level that is hardly a problem. be able to,
The practical value of the present invention is extremely high.

The above embodiments have been explained using an interline CCD image sensor, which is the most commonly used COD device, but the present invention applies to a frame transfer type CCD image sensor, which is another type. It is obvious that it can be applied in exactly the same way.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration and structure of a conventional CCD type image pickup device, FIG. 2 is a diagram showing the basic configuration and structure of a CCI) type image pickup device of the present invention, and FIG. 2 is a diagram showing the smear removal operation of the CCD type image sensor shown in FIG. 2, FIG. 4 is a diagram showing another structure of the CCDCC type image sensor shown in FIG. 2, and FIG. 5 is a diagram different from the configuration shown in FIG. 2. Embodiment of the CCD type image pickup device of the present invention having ■ 1 Figure (0-) (b) Figure Z (Figure 3 <C> ■ 4 Figure 1 Figure 5

Claims (1)

[Claims] 1. Photoelectric conversion elements arranged two-dimensionally on the same semiconductor substrate, and a vertical COD that transfers optical signal charges accumulated in the elements.
In a CCD type solid-state imaging device that integrates a shift register and a horizontal COD shift register, a vertical COD shift register that carries false signal charges other than optical signals is provided near the vertical COD shift register that transfers signal charges,
1. A transmissive solid-state image pickup device that carries a mold and is characterized in that only a true optical signal component is obtained by taking the difference between the signal charges output from the two vertical COD shift registers. 2. The charge storage capacity of the vertical COD shift register that transfers false signal charges is replaced by the vertical C that transfers optical signal charges.
The charge transfer type solid-state image pickup device according to claim 1, characterized in that the charge storage capacity is smaller than that of an OD shift register.