JPH07106551A - Electric charge detecting element - Google Patents

Abstract

PURPOSE: To detect the quantity of charge of electrons using the transistor having a carrier of electron by forming a region of the conductive type opposite to a sensing channel on the surface of the sensing channel. CONSTITUTION: In the case of a CCD image sensor, the signal charge generated from the photodiode of each picture element by an incident light is transferred to an embedded channel 3 by a CCD and flows into a sensing channel 5. At this time, a reset drain 7, a reset gate 13, a bias gate 14, an output gate 11 and CCD transer charges 8 to 10 are biased to appropriate voltage respectively. As a p-type surface channel 6 region, which has the conductive type reverse to the sensing channel, is on the surface of the sensing channel 5, the surface becomes an electronic surface channel, and when signal charge flows into the sensing channel 5, the potential in the sensing channel changes, and a signal charge can be detected by the change of surface potential distribution of the sensing channel 6 region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a high-sensitivity charge detection device, and more particularly to the manufacture of a device such as a CCD image sensor which needs to detect a minute signal charge with high sensitivity.

[0002]

2. Description of the Related Art For example, a charge detector of a solid-state image pickup device will be described. Figure 5 shows Toshiba S.I. 1988 International Conf by Ozawa et al.
erence on Solid State Dev
ice and Materials (Fxende
d Abstractsspp. 355-358), which shows a cross-sectional view of a floating surface detector, in which a p ^- well layer 2 is formed on the surface of an n-type substrate 1 and a sensing channel 5 which is an n-type region having a higher concentration than the substrate. And p
Source and drain regions 20 and 21 of the ⁺ region, the gate oxide film 4 formed on the sensing channel 5,
Floating gate 1 formed on gate oxide film 4
2, a thick insulating layer 15 formed on the floating gate 12, and a bias gate 14 formed on the thick insulating film 15.

The sensing channel 5 is connected to a CCD that transfers electric charges in a direction perpendicular to the plane of the sectional view, and signal charges are transferred in an embedded channel (not shown).
When the transferred signal charges are accumulated in the sensing channel 5, the potential distribution in the sensing channel 5 is changed and the interface potential between the gate oxide film 4 and the sensing channel 5 and the floating gate 12 potential are changed.
Due to this potential change, the transistor using holes as carriers and the interface between the gate oxide film 4 and the sensing channel 5 as a p-type surface channel operates.

[0004]

This transistor is
Since the sensing capacitance can be made extremely small and there is almost no parasitic capacitance, highly sensitive operation is possible. Also,
Since the sensing channel transfers signals under the condition of being completely depleted, it becomes possible to transfer signal charges completely.
f noise and the like can be suppressed to a very low level.

Toshiba uses 76 μV / e ^- high sensitivity of 64 μV.
Although it has been reported that the low noise of rms (noise equivalent signal to 1.2 electron rms) or less is achieved at the same time, as shown in FIG. 5, the source and drain of this transistor are p ^{− −.}
There is a problem that the carrier is conductive like a well, and the carrier has the opposite sign to the signal charge. Since the p ^- well is normally grounded, holes are diffused into the source or the drain from all regions in the well. Therefore, it is considered that the influence of the dark current short noise due to the holes becomes a problem.

When incident light is present, holes are generated by the same number as the number of electrons. However, while electrons have overflow drains, holes do not have a functioning drain structure. Although there is a p ^- well contact in the peripheral part, the distance from the pixel part is very long. Therefore, when strong incident light enters, there is a phenomenon that the signal current rises due to the temporarily increased leakage current of holes. Can occur.

In order to solve such a problem, there are methods such as using a substrate of p ⁺ type to stop the horizontal overflow drain structure of electrons, or making the well of the charge detection section independent of the pixel section. Almost impossible. An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a charge detection device capable of detecting the charge amount of electrons by using a transistor whose carrier is an electron. Thereby, short noise due to dark current is reduced and sensitivity is improved.

[0008]

The present invention uses an n-type channel transistor using electrons as carriers in the surface region using a p-type channel transistor, and a p-type channel transistor is formed on the surface of an n-type sensing channel. The surface portion of the n ⁺ region between the sensing channel and each source / drain forms an invertible channel isolation region formed by the p well layer. By forming a region of the opposite conductivity type to the sensing channel on the surface of the sensing channel, a surface channel of electrons is formed below the floating gate, and the surface channel is deformed according to the amount of charges transferred to the sensing channel. It Further, by providing the surface-reversible channel separation region between the sensing channel and the source and between the sensing channel and the drain, a current flows from the source and the drain to the surface channel region, but does not flow to the buried channel region.

By using a transistor in which carriers of the same conductivity type as the detected charges flow, the problem of dark current from the well layer is solved, short noise due to dark current is reduced, and the noise is further increased. A sensitive charge detection element is provided. In addition, there is no need to worry about a phenomenon such as an increase in signal output when strong light is incident. It is also possible to omit the step of forming an additional p ⁺ region for forming the source and drain regions.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings, in which the charge detecting portion of a CCD image sensor is used. FIG. 1 is a sectional structural view in the direction in which signal charges are transferred by the CCD. the n-type Si surface of the substrate 1 p ^- well layer 2 is formed, the p ^- well layer 2
The n-type buried channel 3, the n-type sensing channel 5, the p-type surface channel 6 and the reset drain 7 on the surface part of the
Are formed on predetermined regions, and a gate oxide film 4 is formed on the predetermined regions, and the reset gate 13 and the CCD are formed.
Transfer electrodes 8, 9, 10, an output gate 11, and a floating gate 12 are formed on the gate oxide film 4, and a thick insulating layer 15 and a bias gate 14 are formed on the floating gate 12, respectively. .

Of these, the portions directly related to the present invention are the regions constituted by the portions indicated by reference numerals 5, 6, 12, 14, and 15, and the vertical sectional views of these portions. Is shown in FIG. These regions correspond to n-type surface channel transistors which operate by detecting transfer charges by the CCD. In the case of a CCD image sensor, the signal charges generated from the photodiode of each pixel by the incident light are transferred into the embedded channel 3 by the CCD and flow into the sensing channel 5 from the right side in FIG.

At this time, the reset drain 7, the reset gate 13, the bias gate 14, the output gate 11 and the CCD transfer charges 8, 9 and 10 are respectively biased to appropriate voltages, and the potential shape of the channel for transferring the signal charges is changed. The result is as shown in FIG. Sensing channel 5
When the signal charge flows in, the potential inside the sensing channel 5 changes and the surface potential of the sensing channel region 6 also changes.

The cross-sectional structure in the direction of the substrate depth including the sensing channel and the corresponding potential distribution are shown in FIG.
It shows in (b). The potential distribution in the case where there is no charge in the sensing channel 5 is shown by a solid line, and the potential distribution in the case where a charge flows into the sensing channel 5 is shown by a broken line.

The cross-sectional structure of the channel separation region between the buried channel and the sensing channel and the corresponding potential distribution are shown in FIGS. 4 (c) and 4 (d). The signal charge is detected by such a change in the potential distribution of the surface channel 6 corresponding to the signal charge. The feature of this structure is that the surface of the sensing channel 5 has a p-type surface channel 6 region having a conductivity type opposite to that of the sensing channel, so that the surface becomes a surface channel for electrons. Further, since the p ⁻ well region 2 exists between the sensing channel 5 and the source 16 and the drain 17, the p ⁻ well region 2 serves as a channel separation band for the buried channel 3.
In this region, the substrate surface is inverted and operates as a surface channel, so if the surface potential of the channel separation band is designed to be deeper than the surface channel surface potential on the sensing channel, the current from the source to the drain can be reduced. There is no stopping the flow.

[0015]

As described above, according to the present invention,
It is possible to realize an element in which the amount of charge of electrons is detected by a transistor having electrons as carriers. Although the case where the signal charge is an electron has been described in the above-described embodiments, the present invention can be similarly implemented when the signal charge is a hole. Further, if the element that transfers the signal to the sensing channel is not only the CCD but also the element that transfers the charge with a low transfer loss, the effect of the present invention can be obtained.

[Brief description of drawings]

FIG. 1 is an element cross-sectional structural view of a charge detection element of the present invention in a direction in which charges are transferred.

FIG. 2 is a potential distribution diagram in a silicon substrate corresponding to the device structure of FIG.

FIG. 3 is an element cross-sectional structural view of a charge detection element of the present invention in a direction perpendicular to a direction in which charges are transferred.

FIG. 4 is a partial cross-sectional structure of a charge detection element of the present invention and a potential distribution diagram corresponding thereto.

FIG. 5 is a sectional structural view of a conventional charge detection element.

[Explanation of symbols]

1 n-type substrate 2 p ^- well layer 3 n-type buried channel layer 4 gate oxide film 5 sensing channel region (n type) 6 surface channel region (p type) 7 reset drain (n ⁺ ) 8, 9, 10 CCD transfer Electrode 11 Output gate 12 Floating gate 13 Reset gate 14 Bias gate 15 Thick insulating layer 16 Source (n ⁺ ) 17 Drain (n ⁺ )

Claims (1)

[Claims] 1. A structure in which a buried type charge sensing channel and a surface type floating surface channel are three-dimensionally intersected, and the surface potential of the floating surface channel fluctuates according to the amount of charge in the charge sensing channel. In the charge detection element, a buried type charge sensing channel surface has a region having a conductivity opposite to that of the charge sensing channel, and each of the source and drain formed in the floating surface channel and the charge sensing channel. A charge detection element having a buried channel separation region whose surface is invertible therebetween, and carriers of the floating surface channel and the charge sensing channel are charges of the same sign.