JPH033269A - Ccd image pickup element - Google Patents

Abstract

PURPOSE:To obtain a highly-sensitive CCD image pickup element by enabling an effective utilization of generated carriers by forming a multilayer structure in which plural photodiode parts are arranged in depth direction and making a reading gate a common reading gate. CONSTITUTION:Under a first charge storing region 13 consisting of a photodiode D1, a second N-type layer 22 sandwiched by P-type substrate regions 12 is arranged, so that a second photodiode D2 due to a P-N junction formed in a boundary part between those upper and lower layers exists. Also, one end of this second N-type layer 22 is placed right under a reading gate 18 and the reading gate 18 becomes a common reading gate for reading out the stored charges from the first charge storing region 13 and the second charge storing region 21. In the above described constitution, signal carriers generated and stored in the second charge storing region 21 by near-infrared rays L2 entering from the outside are added to the carriers generated and stored in the first charge storing region 13 by visible lights L1, resulting in the approximately doubled sensitivity of a conventional one.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a CCD image sensor, and particularly to a structure of a CCD image sensor for near-infrared detection, which is optimal for a video camera in the near-infrared region.

(Prior Art) FIG. 4 is a cross-sectional view showing an example of the configuration of a unit pixel area 10 of a conventional CCD image sensor. explain. In the figure, 11 is, for example, an N-type silicon substrate;
A P-type substrate region 12 is formed on this main surface side.

A charge storage region 13 is provided on the surface side of this P-type substrate region 12.
and a transfer area 14 are formed. 15 is unit area 1
This is a separation layer for separating between 0 and 0, and is formed from a P+ layer.

The charge storage region 13 has an N-type layer 16 formed on the P-type substrate region 12, and forms a photodiode DI by a PN junction at the boundary thereof.

The transfer region 14 is formed between the charge storage region 13 and the separation layer 15, and above this region 13, for example, S L 0
A readout gate 18 is formed through an insulating film 17 made of 2 or the like.

In the above configuration, the read gate 18 and the P type substrate region 1
When a reverse bias voltage (10 voltage in this case) is applied between 2 and 2, a depletion layer 19 is formed in the P-type substrate region 12 below the readout gate 18.
occurs. At this time, the electrons generated and accumulated in the charge storage region 13 by the visible light L1 are transferred below the readout gate 18 by the readout pulse. Read gate 18 as above
The carriers of each unit area transferred downward are sequentially sent out to a transfer unit (not shown) connected to the transfer area of each unit area,
It is taken out as a signal voltage.

(Problem to be Solved by the Invention) In the unit area 10 of a conventional CCD image sensor, when used in the visible light wavelength range, the penetration depth of the visible light L1 is approximately 0.5 μm, and therefore, The thickness of the N-type layer 16 was preferably about 0.5 μm.

However, the conventional CCD image sensor is limited to near infrared region (wavelength λ).
-0.8μ to 1μ), the penetration depth of near-infrared light L2 increases to 30 to 40 μI at once, so the signal carriers generated are not used and are discarded. become. In addition, carriers generated by light penetrating below the depletion layer 19 of the transfer region 14 enter adjacent unit regions or the transmission section, becoming noise, causing image disturbances such as blooming and smearing, and causing camera characteristics. There were problems such as worsening of

(Means for Solving the Problems) The present invention has been made to solve the above problems, and includes a photodiode section that forms a charge accumulation region by incident light, and a photodiode section provided adjacent to the charge accumulation region. In a CCD imaging device in which a unit pixel region is formed by a transfer region and a readout gate provided above the transfer region via an insulating film, a multilayer structure is provided in which a plurality of photodiode portions are provided in the depth direction, and , there is provided a CCD image pickup device characterized in that the readout gate is a common readout gate.

(Embodiment) FIG. 1 is a sectional view showing one embodiment of a unit area 20 of a CCD image sensor according to the present invention, and FIG. 2 is a plan view of FIG. 1, but the structure is similar to the conventional example described above. The same reference numerals are used for the elements, and explanations thereof will be omitted.

In the figure, reference numeral 21 indicates a second charge storage region which is the main part of the present invention. By providing the second N-type layer 22 sandwiched between the P-type substrate regions 12 below the first charge storage region 13 consisting of the photodiode D1 described above, the PN layer 22 is formed at the upper and lower boundaries. It has a second photodiode D2 formed by a junction.

Further, one end of this second N-type layer 22 is connected to the read gate 1
The readout gate 18 is located directly below the readout gate 18.
serves as a common readout gate for reading accumulated charges from the first charge accumulation region 13 and the second charge accumulation region 21.

In the above configuration, near-infrared light L2 entering from the outside
If the second N-type layer 22 is provided at a position where the charge accumulation region 13 passes through the first charge accumulation region 13 and reaches the second charge accumulation region 21,
The signal carriers generated and accumulated in the second charge accumulation region 21, together with the signal carriers generated and accumulated in the first charge accumulation region 13 by the visible light L1, are transferred to the depletion layer 19 under the readout gate 18 in response to the readout pulse. Since the signal voltage is transferred to the signal voltage and read out as a signal voltage as described above, the sensitivity is approximately twice that of the conventional one, and a highly sensitive CCD image sensor can be obtained.

Further, carriers generated near the second charge accumulation region 21 are absorbed into the second charge accumulation region 21 and read out at the readout gate 18.
This also prevents wasted carriers from being mixed into a signal carrier transmission section (not shown) as in the conventional case, contributing to improved resolution.

In the above example, the first and second charge storage regions 13.21
Although the example has been described in which two layers of N-type regions are provided to form a
In the case of infrared rays having a wavelength of 0nI11 or more, it reaches deep into the St substrate (for example, about 30μ), so by providing several layers of N-type regions in the depth direction, multiple photodiodes can be formed in the depth direction. A multilayer structure may also be provided.

Next, the main manufacturing steps of the CCD 1 image element according to the present invention will be explained using FIGS. 3(a) to 3(d).

First, as shown in Figure (a), an N-type silicon substrate 1
An N layer 30 is formed on the main surface of the P type substrate 12, which is an epitaxial layer formed on the epitaxial layer 1. Next, as shown in FIG. 3B, a second layer 31 is formed on this N layer 30 so that a portion thereof remains in an L shape. Next, a P layer is formed. A second charge storage region 21 is thus formed.

Next, as shown in FIG. 3C, the first charge storage region 13 is formed by forming eight layers 32 on top of the two layers 31.

Next, as shown in FIG. 1(d), a readout gate 18 is formed via a gate insulating layer 33, and a protective insulating layer 34 is formed thereon, thereby achieving the structure of the present invention shown in FIG. C.C.
A D image sensor is obtained.

(Effects of the Invention) As described above, according to the CCD imaging device of the present invention, a photodiode portion forming a charge accumulation region by incident light, a transfer region provided adjacent to the charge accumulation region, In a CCD image sensor in which a light receiving section of a unit pixel region is formed by a readout gate provided above the transfer region via an insulating film, the photodiode section has a multilayer structure in which a plurality of photodiode sections are provided in the depth direction, and Since the readout gate is configured to be a common readout gate, generated carriers can be used effectively, enabling a highly sensitive CCD image pickup device, and has the effect of preventing excess carriers from entering the transmission section. CCD with excellent resolution due to
This makes it possible to provide imaging devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a unit area of a CCD image sensor according to the present invention, FIG. 2 is a plan view of FIG. 1, and FIG.
a) to (d) are explanatory diagrams for explaining the main manufacturing steps of the CCD image sensor of the present invention, and FIG. 4 is a sectional view showing an example of a unit area configuration of a conventional CCD image sensor. 11... Silicon substrate, 12... P-type substrate region, 1
3.21...Charge accumulation region, 14...Transfer region, 1
5... Separation layer, 16.22... N-type layer, 17...
Insulating film, 18... Readout gate, 19... Depletion layer,
20... Unit area, D, D2... Photodiode.

Claims (1)

[Scope of Claims] A photodiode section forming a charge accumulation region by incident light, a transfer region provided adjacent to the charge accumulation region, and a readout gate provided above the transfer region with an insulating film interposed therebetween. A CCD imaging device formed by forming a unit pixel region, characterized in that the photodiode portion has a multilayer structure in which a plurality of photodiode portions are provided in the depth direction, and the readout gate is a common readout gate.