JPH0411774A - Solid state image sensor - Google Patents

Abstract

PURPOSE:To prevent generation of a false signal by forming a groove buried with an insulator for isolating a photodetector from a vertical transfer path, and reading charge by a thin film transistor formed on the groove. CONSTITUTION:A photodetector 3 and a vertical transfer unit 4 are formed by selectively introducing an n-type impurity to a p-type well 2, surrounded by a groove 5 buried with an insulator 6 therein to be formed deeper, and electrically isolated. Here, photo-excited charge stored in the photodetector 3 in response to the incident light amount is read by a transfer gate electrode 10, a pulse is applied to conduct a thin film transistor to be read to a transfer path 4, and transferred therein. Since the photodetector 3 and the path 4 are isolated by the groove 5. The photo-excited charge generated at the outer region of a depleted layer formed at the lower part of the photodetector 3 is not fed to the path 4. Thus, a smearing, i.e., a false signal can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state image sensor, and particularly to a solid-state image sensor that transfers signal charges accumulated in a light receiving section using a charge transfer device (CCD).

``Conventional technology a'' A conventional CCD solid-state image sensor will be explained using an interline transfer method as an example. Fig. 3 is a diagram showing the structure of a conventional solid-state image sensor in a cross section perpendicular to the vertical transfer path. In the same figure, 1 is an n-type silicon substrate, 2 is a p-type well formed in the n-type silicon substrate 1, and 3.4 is a structure in which n-type impurities are selectively introduced into the surface of the p-type well 2. 9 is a gate insulating film, 10 is a transfer gate electrode formed of polycrystalline silicon, 11 is an insulating film between the eyebrows, and 12 is an aluminum film having an opening directly above the light receiving part 3. The light shielding film 14 is a channel stopper region formed by introducing n-type impurities at a high concentration outside the light receiving section 3 and the vertical transfer path 4.

In this conventional solid-state image sensor, photoexcited charges accumulated in the light receiving section 3 according to the amount of incident light are transferred to the transfer gate electrode 1.
By applying a voltage to 0 and forming an inversion layer on the surface of the p-type region between the light receiving section 3 and the vertical transfer path 4, the data is read out to the vertical transfer path 4. The inside is transferred toward a horizontal transfer path (not shown).

[Problems to be Solved by the Invention] In the conventional semiconductor device described above, when the amount of incident light increases, photoexcited charges are generated also in the region outside the depletion layer formed around the light receiving part, and these charges are directly vertically transferred by diffusion. Flows into the transfer path. Therefore, during a vertical transfer operation, this diffused charge is added to signal charges from other pixels using the same vertical transfer path, generating a false signal called smear.

[Means for Solving the Problems] A solid-state imaging device of the present invention includes a semiconductor region of a first conductivity type,
a plurality of light receiving portions of a second conductivity type provided within the surface region of the semiconductor region; and a plurality of light receiving portions provided within the surface region of the semiconductor substrate separated from the light receiving portions by a groove formed in the semiconductor substrate. a charge transfer region for transferring charges accumulated in the light receiving section; an insulating film embedded in the groove; and a charge transfer region extending over the insulating film, at least a portion of which
A semiconductor thin film of a second conductivity type that connects the light receiving section and the charge transfer region, and a gate electrode formed on the semiconductor thin film to control the conductivity of the semiconductor thin film. It is something to do.

[Example 1 Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the structure of a cross section perpendicular to a vertical transfer path of an embodiment related to an interline transfer method. In the figure, 1 is an n-type silicon substrate, 2 is a p-type well formed in the n-type silicon substrate 1, and 3.4 is a p-type well formed by selectively introducing n-type impurities into the surface of the p-type well 2. The formed light receiving section and vertical transfer path, each light receiving section 3
and vertical transfer l? 84 is formed sufficiently deeper than the light receiving section 3 and the vertical transfer path 4, and is surrounded by the groove 5 buried in the insulating film 6, and is electrically isolated from each other. 7 is a p-type polycrystalline silicon film selectively formed on the trench 5 in which the insulating film 6 is buried; 8a, 8;
b is an n-type polycrystalline silicon film formed by selectively introducing impurities into both ends of the p-type polycrystalline silicon film 7; Parts of the silicon films 8b are in contact with the vertical transfer paths 4, respectively. Further, 9 is a gate insulating film, and 10 is a transfer gate electrode made of polycrystalline silicon, including a p-type polycrystalline silicon film 7, n-type polycrystalline silicon films 8a and 8b.
, the gate insulating film 9 and the transfer gate electrode 10 constitute a thin film transistor. 11 is the glabella insulating film,
Reference numeral 12 denotes an aluminum light-shielding film having an opening directly above the light-receiving section 3 .

In the image sensor of this embodiment, the photo-excited charges accumulated in the light receiving section 3 are transferred to the transfer gate electrode 1 according to the amount of incident light.
By applying a high voltage read pulse to 0 and making the thin film transistor conductive, data is read out to the vertical transfer path 4 and transferred within the vertical transfer path 4.

- As shown in the figure, since the light receiving section 3 and the vertical transfer path 4 are separated from each other by the insulating film 6 or the buried layer 5, photo-excited charges generated in the outer region of the depletion layer formed at the bottom of the light receiving section will no longer flow directly into the vertical transfer path due to diffusion, and smear linking will be completely prevented.

FIG. 2 is a sectional view showing another embodiment of the invention. This embodiment has the same structure as the previous embodiment except that a highly concentrated p-type region 13 is provided around the groove 5 in which the insulating film 6 is buried.

In the previous embodiment, since the light receiving section 3 and the vertical transfer path 4 are directly separated by the insulating film 6 or the buried trench 5, the contact surface between the light receiving section 3 and the vertical transfer path 4 and the insulating film 6 is interface states are formed, but if thermally excited charges are generated via these interface states, the dark current will increase. However, in this embodiment, a highly concentrated p-type region 13 is provided around the well 5 in which the insulating film is buried, and the potential of this region is fixed to the same potential as that of the p-type well, so that the interface level is Always filled with holes. Therefore, generation of thermally excited charges via these interface states can be prevented, and an increase in dark current can be prevented.

Although the area-type solid-state imaging device has been described above, the present invention is not limited thereto, and can be similarly applied to a linear-type device. Further, the charge transfer device can be of a surface channel type instead of a buried channel type. Further, in the embodiment, a groove filled with an insulator was used to separate the light receiving part from the cowl, but this part can be made into a high concentration p-type diffusion region as in the conventional example.

[Effects of the Invention] As explained above, the present invention provides a light receiving section of the second conductivity type provided in the semiconductor region of the first conductivity type, and a light receiving section provided in the semiconductor region of the first conductivity type, which is located close to the light receiving section in order to transfer the charges accumulated in the light receiving section. In the semiconductor device having a vertical transfer path of a second conductivity type provided in the semiconductor region of the first conductivity type, a groove buried with an insulating film is provided to separate the light receiving part and the vertical transfer path, Since a thin film transistor is provided on the trench in order to read charges from the light receiving section to the vertical transfer path, according to the present invention, the photo-excited charges generated in the region outside the depletion layer formed at the bottom of the light receiving section will no longer flow directly into the vertical transfer path due to diffusion, making it possible to completely prevent the occurrence of smear.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing embodiments of the present invention, and FIG. 3 is a cross-sectional view of a conventional example. 1...n-type silicon substrate, 2...p-type well, 3
... Light receiving section, 4... Vertical transfer path, 5...
Groove, 6... Insulating film, 7... P-type polycrystalline silicon film, 8a, 8b... N-type polycrystalline silicon film, 9...
Gate insulating film, 10... Transfer gate electrode,
11... Interlayer insulating film, 12... Light shielding film, 13
...high concentration ρ type region, 14...channel stopper region.

Claims (1)

[Claims] a semiconductor region of a first conductivity type; a plurality of light receiving sections of a second conductivity type provided in a surface region of the semiconductor region; and a semiconductor substrate separated from the light receiving section by a groove formed in the semiconductor substrate. a charge transfer region provided in a surface region of the light receiving section for transferring charges accumulated in the light receiving section;
an insulating film buried in the groove; and a semiconductor thin film of a second conductivity type extending over the insulating film, at least a portion of which is of the first conductivity type, connecting the light receiving section and the charge transfer region. and a gate electrode formed on the semiconductor thin film to control conductivity of the semiconductor thin film.