JPS60120555A - Solid state image pick-up device - Google Patents

Abstract

PURPOSE:To sufficiently remove the noise components of internal cause by absorbing the remaining charge in an active region to a dummy shift registor to externally transfer the charge and absorbing a dark current out of the active region. CONSTITUTION:When a reset pulse phir is applied to a reset electrode 21 of a transfer gate 20 provided between a CCD shift register 3 and a dummy shift register 30, a potential barrier A disposed under the gate 20 is removed, a potential state of solid line is formed, and the remaining charge in the register 3 is transferred to the register 30. The transferred charge is shifted toward an output gate and exhausted externally via clocks phi3, phi4 applied to the electrodes 32, 33. The register 30 can remove not only the dark current fed from outside of the active region but also the remaining charge in the active region, thereby reducing the noise components.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a photodetection technology and a technology that is effective when applied to a solid-state imaging device, such as a CCD (charge-coupled device).
The present invention relates to techniques that are effective for reducing noise in photo sensors.

[Background Art] A one-dimensional CCD sensor is known as one of the applications of COD (Integrated Circuit Application Handbook, published by Shokusen Shoten, 1981, p. 96). In such a solid-state imaging device, a problem arises in that the SN ratio and dynamic range decrease due to noise components. There are two kinds of noise components: endogenous and extrinsic.What is currently a problem is the endogenous noise called dark current, and by reducing this dark current, It is possible to significantly improve the SN ratio and dynamic range.

Therefore, the present inventor developed a device as shown in FIG. 1 in order to absorb the dark current in the one-dimensional CCD sensor and reduce the noise component. That is, this one-dimensional CC
The D photosensor is an active one-dimensional CCD photosensor in which CCD shift registers 3, 3 are arranged on both sides of a photodiode 1-array 1, which is a photoelectric conversion unit consisting of PN junction photodiodes, with transfer gates 2, 2 in between. As shown in FIG. 2, dummy channel portions 4, 4 made of an n-type diffusion layer 14 are provided outside the region. By applying a voltage such as +12V to the dummy channel sections 4, 4, the dark current flowing into the active region from outside the active region is absorbed, thereby improving the S/N ratio, etc. .

In FIG. 1, reference numeral 5 denotes a floating diffusion layer 6 that transfers signal charges transferred from a CCD shift register 3゜3 driven by transfer locks φ1゜φ2 to a floating diffusion layer 6 consisting of an n medium-sized diffusion layer.
The potential change due to the charge transferred to the floating diffusion layer 6 is amplified by the preamplifier 7 to form an output signal V out . Qr is a glue cell 1 to charge the floating diffusion layer 6 before outputting.
MO3FET for Further, reference numeral 8 is provided at the other end of the CCD shift registers 3, 3, and is normally biased to the ground potential to prevent the inflow of charges. The input gate 9 is an input diode for inputting charges into the CCD shift registers 3, 3 when measuring transfer speed, etc.

On the other hand, in FIG. 2, 11 is an n+ diffusion layer constituting a photodiode, and the charge photoelectrically converted by the photodiode is transferred to the photogate 10 to which a DC bias voltage vb is applied.
As a result, it is temporarily accumulated in the n-mineral dispersion layer 11 and the photogate 10. 12b is the electrode 12a of the transfer gate 2
a boron implanted layer that creates a potential staircase underneath to facilitate charge transfer and prevent charge backflow, 13a, 1;
Reference numeral 3b represents an electrode and an n-type diffusion layer that constitute the CCD shift register 3.

In the CCD photosensor having the above structure, the dummy channel section 4 can certainly catch and absorb the dark current coming in from outside the active region. However, dark current occurs not only outside the active region but also within the active region. Furthermore, in the photoelectric conversion section and shift register section within the active region, charges remaining after transfer also reduce the SN ratio and dynamic range.

However, it has been found that the CCD photosensor shown in FIG. 1 cannot absorb the dark current and residual charges generated within the active region, and the S/N ratio and dynamic range cannot be sufficiently improved.

[Object of the Invention] An object of the present invention is to provide a photodetection technique that is more effective than the conventional one.

Another object of the present invention is when it is applied to a solid-state imaging device such as a one-dimensional CCD photosensor.

The purpose is to make it possible to significantly improve the SN ratio and dynamic range.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the Invention] Representative inventions disclosed in this application will be summarized as follows.

That is, in the present invention, for example, in a one-dimensional CCD photo sensor, a dummy shift register is provided outside the CCD shift register, a transfer gate is provided between the two, and the transfer gate is operated with an appropriate set signal and a transfer lock, thereby transferring data from the photodiode. Before transferring the charge to the shift register, the residual charge (including dark current) in the active area is absorbed into a dummy shift register so that it can be transferred to the outside.
The above object of improving the S/N ratio and dynamic range is achieved by absorbing dark current from outside the active region.

[Embodiment] FIGS. 3 and 4 show an embodiment in which the present invention is applied to a one-dimensional CCD photosensor.

In this embodiment, a dummy shift register 30.30 is arranged outside the CCD shift registers 3, 3 via a transfer gate 20.20. As shown in FIG. 4, the electrode 21 of the transfer gate 20 (hereinafter referred to as a reset electrode) is made of the same second layer polyurethane as the transfer gate 2 provided between the photodiode array 1 and the CCD shift register 3. Made of silicon, a relatively thin oxide film (15) is formed on the substrate surface below the reset electrode 21, similar to the CCD shift register 3 portion.

The dummy shift register 30 also includes an n-type diffusion layer 31 formed continuously in the transfer direction, similar to the n-type diffusion layer 14 constituting the dummy channel section 4 in FIG. It consists of an electrode 32 formed through an oxide film (15). Furthermore, the dummy shift register 30 is
As shown in FIG. 5, which shows a cross-sectional view in the transfer direction, the electrodes 33 are formed at appropriate intervals, and potential barrier electrodes 32 are formed between the electrodes 33. A potential barrier layer 34 is formed on the substrate surface below the potential barrier electrode 32. This structure is exactly the same as the COD shift register 3, and can be formed by the same process.

Moreover, the n+ diffusion layer 11 constituting the diode,
The n-type diffusion layer 13 serving as a charge storage portion of the CCD shift register 3 and the n-type diffusion layer 31 serving as a charge storage portion of the dummy shift register 1 are generally connected to each of the electrodes 10.12a,
When the same voltage, such as +12V, is applied to 13a, 21 and 32, the concentration is determined so that the potential deepens stepwise from dummy shift 1 to the resistor, as shown in Figure 4. There is. Alternatively, if the n-type diffusion layers 13 and 31 are formed with the same concentration, an appropriate voltage is applied to each of the electrodes 10, 12a, 13a, 21 and 32 so as to form a votive state as shown in FIG. Just apply it.

FIG. 6 shows the voltage applied to each electrode when the residual charge in the active region is absorbed by the dummy shift register 30 in a CCD photosensor that is capable of forming the above-mentioned potential state in the active region of the semiconductor substrate. An example of the timing of the driving pulse is shown.

In the figure, φtg is the electrode 12a of transfer gate 2.
Transfer lock applied to φ4. φ2 is a transfer tarlock applied to the electrode of the CCD shift register 3, and the clocks φ and φ2 are in opposite phases to each other. Also, φr
is CCD shift register 3 and dummy shift register 30
The reset electrode 21 of the transfer gate 20 provided between
This reset pulse φ is applied to
When r is applied at the timing as shown in the enlarged view of FIG. 7, the potential barrier that was initially present under the transfer gate 20 as shown by the broken line A in FIG. 4 is removed, and the potential barrier shown in FIG. The potential state shown by the solid line is made, and the residual charge in the CCD shift register 3 is transferred to the dummy shift register 30.

The charge transferred to the dummy shift register 30 is transferred to the electrode 3
2 and 33 as shown in FIG. 6(4). By φ4, the signal is shifted toward the output gate and discharged to the outside.

"In the case of 2, the dummy shift register 30 is CCL)
In addition to the residual charge transferred from the shift register 3,
Since the n-type diffusion layer 31 absorbs dark current entering the active region from outside, it also functions to shift the charge and discharge it to the outside.

As a result, not only the dark current entering from outside the active area but also the residual charge (including dark current) within the active area can be removed, which reduces noise components and improves the S/N ratio and dynamic range. Improved.

In the above embodiment, the residual charge in the CCD shift register 3 is removed by the reset pulse φr having the timing as shown in FIG. 6, but the reset pulse φr and the clock φjg+φ1. By appropriately setting the timing of φ2, a potential state exactly the same as shown in FIG. 4 can be created to remove residual charges not only in the CCD shift register 3 but also in the portions from HO1 to diode array 1. You can also do it.

In the embodiment shown in FIG. 4 above, only the polysilicon electrodes formed on the cutting board are shown, and the glabella insulating film, aluminum wiring layer, passivation film, etc. are not shown, but these are the same as those shown in FIG. is formed in the same way.

That is, an insulating film j5 such as a silicon oxide film is formed under the IM-th gate electrode 10 made of polysilicon, the electrode 13a of the CCD shift register 3, and the electrode 32 of the dummy shift register 30. . Also,
On the polysilicon electrode, electrodes 12a and 21 of the 2Mth polysilicon transfer gates 2 and 20, a CCD shift register 3, and a dummy shift register are placed on the polysilicon electrode via an interlayer insulating film 16 also made of a silicon oxide film or the like. 3
0 potential barrier electrode 32 is formed. And this 2
An aluminum layer 18 is formed on the second polysilicon electrode with a PSG film (phosphorus silicate glass film) 17 interposed therebetween. This aluminum layer 18 forms the opening of the photodiode and also serves as a wiring layer.

An insulating film 19 such as a PSG film is formed on the aluminum layer 18, and a second aluminum layer 28 is formed on the insulating film 19 to block light in unnecessary parts such as the register part and outside the active area. Further, a final passivation film 29 is formed thereon.

In the figure, 60 is a field oxide film, and 61 is a P+ diffusion layer serving as a channel stopper.

Next, FIG. 8 shows another embodiment of the present invention.

In this embodiment, the electrode 32 in the dummy shift register 30 is formed of the same polysilicon layer as the electrode 13a of the CCD shift register 3.

FIG. 9 shows still another embodiment of the present invention. In this embodiment, one end of the n-type diffusion layer 31 constituting the dummy shift register 30 is formed in advance so as to extend below the electrode 21 of the transfer gate 20, and boron ions are implanted from above to form the electrode. A P raw mineral dispersion layer 22 and a potential barrier layer 23 are provided under the layer 21.

Accordingly, in this embodiment, the electrode 2 of the transfer gate 20
When no voltage is applied to the electrode 21, a potential barrier exists as shown by the broken line A in the figure, but the electrode 21 has a voltage of +12V, for example.
By applying a voltage like this, a potential staircase is generated below it as shown by the solid line in the same figure. Therefore, charges move easily from the CCD shift register 3 side to the dummy shift register 30 side, and the transfer efficiency is improved compared to that of the first embodiment.

[Effect] As explained above, in a one-dimensional CCD photosensor consisting of a photoelectric conversion section such as a photodiode array, a transfer gate, and a COD shift register, a dummy shift register is provided outside the COD shift register, and a dummy shift register is provided between the two. Since a transfer gate is provided, it is operated with an appropriate set signal and transfer lock, and the residual charge (including dark current) in the active region is absorbed into the dummy shift register before the charge is transferred from the photodiode to the shift register. In addition to being able to absorb dark current from outside the active region, endogenous noise components are sufficiently removed, and the S/N ratio and dynamic range are significantly improved.

Although the invention made by the present inventor has been specifically explained based on Examples above, it should be noted that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Not even. For example, in the above embodiment, the photoelectric conversion section is composed of a photodiode array, but the photoelectric conversion section may be composed of a CCD image sensor array.

[Field of Application] In the above explanation, the invention made by the present inventor was mainly applied to a one-dimensional photo sensor, which is the field of application that formed the background of the invention, but the invention is not limited to this. A two-dimensional image sensor can be generally used as a low-level solid-state imaging device.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the configuration of a one-dimensional CCD photosensor, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 2, and Fig. 3 is an application of the present invention to a one-dimensional CCD photosensor. FIG. 4 is a sectional view taken along the line ■-■ in FIG. 3. 5 is a sectional view taken along the line ■-V in FIG. 4; FIG. 6 is a timing chart showing an example of the timing of the control signal for operating the CCD sensor of the above embodiment; The figure is an enlarged explanatory view of the main part in Fig. 6, and Fig. 8 is an explanatory cross-sectional view showing a second embodiment of the present invention. Fig. 9 is an explanatory cross-sectional view showing a third embodiment of the present invention. It is. 1... Photodiode array, 2... Transfer gate, 6... Floating diffusion layer, 7... Preamplifier, l
O...Photogate, 12a...Transfer gate electrode, 13a...Shift register electrode, 21...Reset electrode, 32.33...Dummy shift 1-register electrode. Fig. 5 Fig. 6 (4 Seeds φ■ Seeds---1---
7 Figure

Claims (1)

[Claims] 1. In a solid-state imaging device comprising a photoelectric conversion section into which an optical signal is incident, and a transfer section for transferring signal charges generated in the photoelectric conversion section to the outside, the photoelectric conversion section A false transfer section is provided outside the active region in which the transfer section and the transfer section are formed, so that at least the residual charge in the transfer section can be transferred to the false transfer section and discharged to the outside by an appropriate control signal. A solid-state imaging device characterized by: 2. The transfer section includes a CCD shift register and this CCD
In a transfer gate that transfers signal charges generated in a photoelectric conversion section to a shift register, the above C
The solid-state imaging device according to claim 1, characterized in that a false transfer section consisting of a transfer gate and a CCD shift register is provided outside the CD shift register.