JPS6180976A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain a solid-state image pickup device which is suitable for a high integration, and can reduce remarkably a smear quantity by constituting a P well of a photoelectric converting part so that its density is lower, and its diffusion length is longer than a P well of a signal transfer part. CONSTITUTION:A P well 22a of a photoelectric converting part is depleted completely, and also has an impurity density profile for satisfying spectral sensitivity characteristics as an image pickup device. On the other hand, a P well 22b of an embedded channel CCD part (BCCD part) has a shorter diffusion length than that of a P well 22a of the photoelectric converting part, but has an impurity quantity which is not depleted completely. According to such a structure, first, the P well 22a of the photoelectric converting part is scarcely influenced by diffusion in the horizontal direction by the P well 22b of the BCCD part, and patterning can have an allowance. Secondly, an optical signal charge generated at a position of B becomes an effective signal charge or goes toward a substrate 21, and it is prevented from being mixed into the BCCD. In this way, a smear quantity is reduced remarkably.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a solid-state imaging device.

(Structure of conventional example and its problems) In recent years, the number of pixels per unit area of solid-state imaging devices has tended to increase due to demands for smaller size and higher resolution. A P-well type solid-state imaging device can be cited as a promising structure for realizing this.

The conventional P-well type solid-state imaging device as described above will be described with reference to the drawings.

FIG. 2 shows a partial sectional view of a conventional P-well type interline solid-state imaging device.

In Figure 82, 1 is an n-type substrate, and 2a is P of the photoelectric conversion section.
Well, 2b is a buried channel C which becomes a charge transfer part.
This is the P well of the CD section (hereinafter referred to as BCCD section).

The operation of the P-well type interline solid-state imaging device configured as described above will be described below. First, by applying a positive voltage to the n-type substrate 1, the P well 2a of the photoelectric conversion section is depleted. The result is blooming suppression ability. For this purpose, the P well 2a of the photoelectric conversion section is completely depleted by the back bias voltage,
The P well 2b in the BCCD section requires a well distribution that prevents complete depletion. If this structure is formed by the process of B ion implantation and drive-in,
It usually looks like Figure 2.

However, in the structure shown in Figure 2, as the miniaturization progresses, the BCCD
The lateral inward expansion of the P well 2b in the part cannot be ignored,
It becomes difficult to miniaturize. In addition, the proportion of the optical signal charge generated at the position A mixed into the P well 2b of the BCCD section is also
It increases as the area of the P well 2a of the photoelectric conversion section decreases. As a result, the amount of smear increases as the electric charge mixes into the signal line BCCD.

(Object of the Invention) In view of the above drawbacks, the present invention provides a solid-state imaging device that can reduce the amount of smear.

(Structure of the Invention) In order to achieve this object, the solid-state imaging device of the present invention provides a solid-state imaging device in which a region of the surface of a semiconductor substrate of one conductivity type, which is of a conductivity type opposite to the one conductivity type in which a photoelectric conversion portion is formed, The impurity concentration is lower than that of the region where the signal transfer section is formed, and the region is formed deeper.

(Description of Embodiment) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a partial sectional view of a P-well type interline solid-state imaging device according to an embodiment of the present invention.

In FIG. 1, 21 is an n-type substrate, 22a is a P-well of the photoelectric conversion section, and 22b is a P-well of the BCCD section.

The operation of the device is similar to the conventional example.

The P well 22a of the photoelectric conversion section is completely depleted and has an impurity concentration profile that satisfies the spectral sensitivity characteristics of an imaging device. - P well 22 of 10,000 BCCD section
b has a diffusion length shorter than that of the P well 22a of the photoelectric conversion section, but has an impurity amount that does not completely deplete. According to the above structure, firstly, the P well 22a of the photoelectric conversion section is
Compared to the conventional patterning, this patterning can be effected by the lateral diffusion caused by the P-well 22b in the CBCCD portion.

Second, the optical signal charges generated at the position B in FIG. 1 either become effective signal charges or go toward the n-type substrate 1 and are eliminated to the outside. Also, some try to enter the BCOD, but the P well 22b of the BCCD section is
Since the impurity concentration is higher than that of the P well 22a of the photoelectric conversion section, a potential barrier exists, and the BCC
Contamination with D can be avoided. From the above, 1. The amount of smear is significantly reduced compared to the conventional method.

(Effects of the Invention) As described above, the solid-state imaging device of the present invention is suitable for high integration because the concentration of the P-well of the photoelectric conversion section is lower than that of the P-well of the signal transfer section, and the diffusion length is longer. Its practical effects are significant, such as being able to significantly reduce the amount of smear.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a partial sectional view of a conventional P-well type interline solid-state imaging device. 1.21... N-type substrate, 2a, 22a... P well of photoelectric conversion section, 2b, 22b... P well of BCCD section. Patent applicant: Matsushita Electronics Co., Ltd. Figure 1

Claims (1)

[Claims] A region of a conductivity type opposite to the one conductivity type in which the photoelectric conversion section is formed on the surface of the semiconductor substrate of one conductivity type has a lower impurity concentration and is deeper than a region in which the signal transfer section is formed. A solid-state imaging device.