JP2000216370A - Solid state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate signal charges remaining without being read out by providing a photoelectric converting section in a semiconductor substrate, a transfer gate and a second conductivity type diffusion layer immediately under a charge transfer section. SOLUTION: A second conductivity type N type diffusion layer 40 is formed on the surface of a first conductivity type P type silicon substrate 30. After an insulation film 70 and a CCD register electrode 90 are formed on the N type diffusion layer 40, boron ions are implanted in order to form a P- type diffusion layer 50. After an insulation film 70 and a transfer gate electrode 80 are formed respectively, a P+ type diffusion layer 60 is formed on the upper surface of the N type diffusion layer 40 thus transferring photoelectric conversion charges stored in a photoelectric converting section 10 to a charge transfer section 20 through a buried channel. According to the arrangement, signal charges remaining without being read out can be eliminated without causing any damage on the electrical connection between the photoelectric converting section 10 and the charge transfer section 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device, and more particularly, to a solid-state imaging device using a charge-coupled device (CCD).

[0002]

2. Description of the Related Art At present, solid-state imaging devices are widely used in cameras, facsimile machines, image scanners and the like.

FIG. 3 is a diagram showing an example of a configuration of a conventional solid-state imaging device, and is a cross-sectional view of a photoelectric conversion unit of a CCD linear image sensor.

In this conventional example, as shown in FIG. 3, a P-type silicon substrate 30, an N-type diffusion layer 40 formed on a part of the upper surface of the P-type silicon substrate 30, and an N-type An N ⁻ type diffusion layer 41 formed in a part of the region where the type diffusion layer 40 is not formed, a P ⁺ type diffusion layer 60 formed on a part of the upper surface of the N type diffusion layer 40, The insulating film 70 formed on the substrate 30, the N-type diffusion layer 40, the N ⁻ -type diffusion layer 41, and the P ⁺ -type diffusion layer 60, the transfer gate electrode 80 formed on a part of the insulating film 70, And a CCD register electrode 90 formed on a part of the film 70. The N-type diffusion layer 40, the P ⁺ -type diffusion layer 60 and the surrounding P-type silicon substrate 30 form a photoelectric conversion unit 110. The N ^-- type diffusion layer 41, the transfer gate electrode 80, and the CCD register electrode 90 form a charge transfer section (charge coupling section) 120.

[0005] Hereinafter, the manufacturing process of the solid-state imaging device configured as described above will be described.

FIG. 4 is a cross-sectional view for explaining a manufacturing process of the solid-state imaging device shown in FIG.

First, phosphorus ions having a dose of 2.3 × 10 ¹² cm ⁻² are implanted into the surface of a P-type silicon substrate 30, thereby forming an N-type diffusion layer 40 having a depth of 1.0 μm and Dose of 1.6 on the surface of the silicon substrate 30
4 × 10 ¹² cm ⁻² phosphorus ions are implanted, thereby forming a 0.8 μm deep N ⁻ -type diffusion layer 41 (FIG. 4).
(A)).

Next, the N type diffusion layer 40 and the N ⁻ type diffusion layer 4
1 is formed on the P-type silicon substrate 30 on which the insulating film 7 is formed.
0, a CCD register electrode 90 and a transfer gate electrode 80 are respectively formed (FIG. 4B).

Thereafter, P ^{+ is} added to a part of the upper surface of the N-type diffusion layer 40.
A mold diffusion layer 60 is formed.

Hereinafter, the operation of the solid-state imaging device configured as described above will be described.

FIGS. 5A and 5B are diagrams for explaining the operation of the solid-state imaging device shown in FIG. 3, wherein FIG. 5A is a sectional view of the solid-state imaging device, FIG. 5B is a diagram showing potential, and FIG. It is a figure showing a timing.

When t = t ₁ , φ ₁ = φ ₂ = 0 and N
The light that has entered the type diffusion layer 40 and the surrounding depletion layer is:
Here, it is photoelectrically converted into a signal charge, and the photoelectric conversion unit 10
Is accumulated in At this time, the potential immediately below the transfer gate electrode 80 is smaller than the potential of the photoelectric conversion unit 110.

When t = t ₂ , φ ₁ = V ₀ , φ ₂ = 0, and the potential immediately below the transfer gate electrode 80 is larger than the potential of the photoelectric conversion unit 110, and has been accumulated in the photoelectric conversion unit 110. The signal charge passes right under the transfer gate electrode 80 and passes through the CCD register electrode 90.
It is sent immediately below.

[0014]

In the conventional solid-state imaging device as described above, the transfer gate electrode and the N-type diffusion layer are used to obtain an electrical connection between the photoelectric conversion portion and the semiconductor surface immediately below the transfer gate electrode. The area where
That is, since there is a region where charges are always accumulated, there is a problem that signal charges are left unread (afterimages).

Conventionally, in the region where the transfer gate electrode and the N-type diffusion layer overlap, the unread signal charge is minimized without impairing the electrical connection between the photoelectric conversion portion and the semiconductor surface immediately below the transfer gate electrode. Although optimization has been performed as described above, there is a growing demand for further improvement in resolution.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is intended to reduce the unread signal charges without impairing the electrical connection between the photoelectric conversion unit and the charge transfer unit. An object is to provide a solid-state imaging device that can be eliminated.

[0017]

In order to achieve the above object, the present invention provides a photoelectric conversion unit formed on a semiconductor substrate of a first conductivity type, which is connected to the photoelectric conversion unit via a transfer gate electrode. A solid-state imaging device having at least a charge transfer unit, and a second conductivity type formed in the same step immediately below the photoelectric conversion unit, the transfer gate electrode, and the charge transfer unit in the semiconductor substrate. Characterized by having a diffusion layer of

Further, the photoelectric conversion unit has a first conductivity type diffusion layer on the surface of the second conductivity type diffusion layer, and the transfer gate electrode is provided on the surface of the second conductivity type diffusion layer.
It has a first conductivity type diffusion layer different from the first conductivity type diffusion layer.

Further, the first conductivity type is P-type, and the second conductivity type is N-type.

Further, the diffusion layer of the second conductivity type is formed by implanting phosphorus ions into the semiconductor substrate.

Further, the first conductivity type diffusion layer formed below the transfer gate electrode is formed by implanting boron ions.

(Operation) In the present invention configured as described above, since the photoelectric conversion unit and the charge transfer unit are formed in the diffusion layer formed in the same step, the signal charges are transferred by the buried channel. As a result, the signal charges are not left unread, and the afterimage characteristics and the resolution are improved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a solid-state imaging device according to the present invention.

In this embodiment, as shown in FIG. 1, a P-type silicon substrate 30 of the first conductivity type, an N-type diffusion layer 40 of the second conductivity type formed on the P-type silicon substrate 30, P ⁺ -type diffusion layer 60 formed on a part of the upper surface of
And a P ⁻ -type diffusion layer 50 formed in a part of a region of the upper surface of the N-type diffusion layer 40 where the P ⁺ -type diffusion layer 60 is not formed;
N type diffusion layer 40, P ⁺ type diffusion layer 60 and P ⁻ type diffusion layer 50
It is composed of an insulating film 70 formed thereon, a transfer gate electrode 80 formed on a part of the insulating film 70, and a CCD register electrode 90 formed on a part of the insulating film 70. The P ⁺ -type diffusion layer 60, the surrounding P-type silicon substrate 30 and the N-type diffusion layer 40 form the photoelectric conversion unit 10, and the P ^-- type diffusion layer 50, the transfer gate electrode 80, and the CCD register electrode. A charge transfer section (charge coupling section) 20 is formed from the 90 and the surrounding P-type silicon substrate 30 and N-type diffusion layer 40.

Hereinafter, the manufacturing process of the solid-state imaging device configured as described above will be described.

FIG. 2 is a sectional view for explaining a manufacturing process of the solid-state imaging device shown in FIG.

First, phosphorus ions having a dose of 1.5 × 10 ¹² cm ⁻² are implanted into the surface of the P-type silicon substrate 30, thereby forming an N-type diffusion layer 40 having a depth of 1.2 μm. (A)).

Next, an insulating film 70 and a CCD register electrode 90 are formed on the N-type diffusion layer 40, and thereafter, boron ions of a dose of 1.7 × 10 ¹² cm ⁻² are implanted, thereby forming A 0.1 μm P ⁻ -type diffusion layer 50 is formed (FIG. 2B). The P ⁻ type diffusion layer 50 is formed so that the potential below the transfer gate electrode 80 is smaller than the potential below the CCD register electrode 90.

Next, an insulating film 70 and a transfer gate electrode 80 are formed (FIG. 2C).

Thereafter, a P ⁺ -type diffusion layer 60 is formed on the upper surface of the N-type diffusion layer 40.

In the solid-state imaging device configured as described above, the photoelectric conversion operation and the charge transfer operation are the same as those in the conventional example shown in FIG. 5, but in this embodiment, the photoelectric conversion unit 10 and the charge transfer unit 20 is formed in the N-type diffusion layer 40 formed in the same step, the photoelectric conversion charge accumulated in the photoelectric conversion unit 10 is transferred to the charge transfer unit 20 through the buried channel.

This eliminates the need for a conventionally required area where the charge is always accumulated in the portion where the photoelectric conversion unit 10 and the transfer gate electrode 80 are in contact with each other, so that the signal charge can be transferred without being left unread.

[0034]

As described above, in the present invention,
Since the photoelectric conversion unit and the charge transfer unit are formed in the diffusion layer formed in the same process, the signal charges are transferred by the buried channel, so that the signal charges do not remain unread, thereby improving the afterimage characteristics and improving the resolution. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a cross-sectional view for explaining a manufacturing process of the solid-state imaging device shown in FIG.

FIG. 3 is a diagram illustrating a configuration example of a conventional solid-state imaging device.

FIG. 4 is a cross-sectional view for explaining a manufacturing process of the solid-state imaging device shown in FIG.

5A and 5B are diagrams for explaining the operation of the solid-state imaging device shown in FIG. 3, wherein FIG. 5A is a cross-sectional view of the solid-state imaging device, and FIG.
Is a diagram showing a potential, and (c) is a diagram showing a timing.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Photoelectric conversion part 20 Charge transfer part 30 P-type silicon substrate 40 N-type diffusion layer 41 N ^- type diffusion layer 50 P ^- type diffusion layer 60 P ⁺ type diffusion layer 70 Insulating film 80 Transfer gate electrode 90 CCD register electrode

Claims (7)

[Claims] 1. A solid-state imaging device having at least a photoelectric conversion unit formed on a semiconductor substrate of a first conductivity type and a charge transfer unit coupled to the photoelectric conversion unit via a transfer gate electrode. A solid-state imaging device having a second conductivity type diffusion layer formed in the same step in the semiconductor substrate immediately below the photoelectric conversion unit, the transfer gate electrode, and the charge transfer unit. 2. The solid-state imaging device according to claim 1, wherein the photoelectric conversion unit includes a first conductive type diffusion layer on a surface of the second conductive type diffusion layer.
A diffusion layer of a conductivity type, wherein the transfer gate electrode has a diffusion layer of a first conductivity type different from the diffusion layer of the first conductivity type on a surface of the diffusion layer of the second conductivity type. Solid-state imaging device. 3. The solid-state imaging device according to claim 1, wherein said first conductivity type is P-type, and said second conductivity type is N-type. 4. The solid-state imaging device according to claim 3, wherein the diffusion layer of the second conductivity type is formed by implanting phosphorus ions into the semiconductor substrate. 5. The solid-state imaging device according to claim 2, wherein the first conductivity type is P-type, and the second conductivity type is N-type. 6. The solid-state imaging device according to claim 5, wherein the second conductivity type diffusion layer is formed by implanting phosphorus ions into the semiconductor substrate. 7. The solid-state imaging device according to claim 5, wherein the first conductivity type diffusion layer formed below the transfer gate electrode is formed by implanting boron ions. Characteristic solid-state imaging device.