JPS601980A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To obtain a solid-state image pickup element where signal sensitivity is improved to a blue color light by providing a p<++> layer on an n<+> layer of a photodiode. CONSTITUTION:The p<++> layer 11 having high density and thin film thickness is formed on the n<+> diffusion layer 2 at the source side constituting a part of the photodiode 3 and an MOS transistor (TR) 7 and further a poly silicon electrode 12 applying a requried voltage to the p<++> layer 11 is formed while being bridged over an oxide film 8 for separation at a part of the p<++> layer 11. Thus, electrons among electron/positive hole pairs generated at the boundary between the Si substrate 1 and an SiO2 film on its surface are drawn by the electric field and reach a p<->-n<+> junction part, where they are stored as signal charges. As a result, the sensititvity to the blue light where the light absorption is conducted almost the surface of the Si substrate 1 is improved remarkably and a signal charge with high S/N is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a solid-state imaging device, particularly to a solid-state imaging device with improved sensitivity in a short wavelength region.

[Background of the invention]

FIG. 1 is a cross-sectional diagram of the main parts of an example of a conventional solid-state image sensor, in particular, a pn junction that becomes a photoelectric conversion section, a MOS transistor that reads signals to a vertical signal line, and a vertical signal V
This figure shows the cross-sectional structure of one pixel consisting of .

In the figure, for example, an n+ diffusion layer 2 is formed on the surface of a p-type S1 substrate 1 to constitute a photodiode 3, and an h+ diffusion layer (source) 2. n+ diffusion layer (drain)
4 and a gate electrode 6 is formed through the gate oxide film 5 to constitute a MOS transistor.

Each photoelectric conversion element group consisting of the photodiode 3 and the MOS transistor 7 is separated by an element isolation oxide film 8 and an interlayer insulating film 9, and the n+ diffusion layer 4 is separated by a vertical signal line 10 made of an A7 layer. It is connected to the. (MOS) Langistav transfers the signal charge caused by external light accumulated in the photodiode 3 to the vertical signal line 10.
It is used as a switch to read data to the outside via the

However, the solid-state imaging device with the above configuration has an extremely thin 81(h film (not shown) formed on the surface of the 81 substrate 1 and the Si substrate 1 in the p''-n junction region forming the photodiode 3). There was a problem in that stress was generated due to the difference in thermal expansion between the 5102 film and the 5102 film, and crystal defects were generated on the surface of the St substrate 10 due to the accumulation of this stress.

The occurrence of such crystal defects is caused by the fact that when light enters the photodiode 3 from the outside, blue light with a short wavelength that is easily absorbed on the surface of the substrate 10 causes electron-hole pairs in the diffusion layer 2. Even if it is formed, it will be trapped at the interface between the thin s i,o film formed on the surface of the n0 diffusion layer 2 and the 81 substrate 1, and will not be able to generate sufficient signal charges, corresponding to blue light. There was a problem that signal sensitivity decreased.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a solid-state imaging device with improved signal sensitivity to blue light.

[Summary of the invention]

In order to achieve such objectives, the present invention provides a p'' layer on the n+ layer of the photodiode.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 2 is a cross-sectional configuration diagram similar to FIG. 1 showing an example of a solid-state image pickup device according to the present invention. Since the same symbols as in FIG. 1 represent the same elements, their explanation will be omitted. In the same figure,
A thin p+ layer 11 with high concentration is formed on the photodiode 3 and the n+ diffusion layer 2.
A polysilicon electrode 12 is formed in a part of the p+ layer 11 so as to extend over the isolation oxide film 8 and apply a required voltage to the p+ layer 11.

According to such a depiction, the p +
By applying a voltage of several V to several tens of V to the + layer 11 within a range that does not cause breakdown, an electric field is generated between the n10 diffusion layer 2 and the p++f'f11, and in this case, the p+10 layer Since the p+ layer 11 is extremely thin, the p+ layer 11 is completely depleted. Therefore, among the electron-hole pairs generated at the interface between the SS substrate 1 and the 5iO1 film on its surface, the electrons are attracted by this electric field, reach the pn+ junction, and are stored as signal charges. As a result, the light absorption is mostly SS
The sensitivity to blue light emitted on the surface of the substrate 1 is greatly improved, and signal charges with a high S/N ratio can be obtained. Furthermore, by varying the voltage applied to the p++ layer 11, it is possible to vary the sensitivity corresponding only to the achromatic light and also to match the sensitivity of the eye.

〔Effect of the invention〕

As explained above, according to the present invention, the signal sensitivity to blue light can be greatly improved, so when a color signal is output, a high S-to-blue ratio, which is one of the three primary colors of light, is used. Therefore, it has an extremely excellent effect in that a solid-state camera with extremely good color reproducibility can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram of a main part showing an example of a conventional solid-state image sensor, and FIG. 2 is a cross-sectional view of a main part (7, ? factor) showing an example of a solid-state image sensor according to the present invention. 1...St Substrate, 2...n10 diffusion layer (source)
, 3... Photodiode, 4... N+ diffusion layer (drain), 5... Gate oxide film, 6...
Gate electrode, 7...MOS) transistor, 8...
・Separation oxidation) sample, 9...ffi open abdominal membrane 0・
...Vertical signal line, 11..., p+10 layer, 12...
...Polysilicon electrode.

Claims (1)

[Claims] What is claimed is: 1. A solid-state imaging device comprising a photoelectric conversion section made of a p-n+ diode on an St substrate, characterized in that a p+10 layer is provided on the n10 layer.