JPS60214172A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To improve the quality of an output picture by forming a transparent electrode in opposition to a photosensitive picture element in an insulation film of a photosensitive region and applying a polar voltage in a direction rejecting a signal carrier so as to prevent depletion of a boundary between a semiconductor substrate and the insulation film. CONSTITUTION:A carrier of a negative electric charge is generated in a semiconductor by a light incident through an insulation film 2 and a transparent electrode 21 from an opening of an optical shield film 7 in a solid-state area sensor. Since a negative voltage is applied to the transparent electrode 21, the negative electric charge around the surface of the substrate 1 and an inverting layer 6' having a positive hole is formed instead on the surface of the substrate 1 in the photosensitive region. Thus, the signal carrier (negative electric charge -) generated by photoelectric conversion is stored in a picture element 6 surrounded by a p-n junction and the inverting layer 6' between the substrate and the picture element. Thus, no signal carrier exists around the boundary between the substrate 1 and the insulating film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solid-state imaging device used as a linear sensor, two-dimensional area sensor, etc., and particularly relates to a photosensitive region thereof.

[Technical background of the invention]

FIG. 1 shows a portion of a conventional solid-state area sensor incorporating, for example, a charge-coupled device (CCD) (the unit cell area is denoted by A). That is, for example, a two-layer charge transfer electrode 3 is formed on a p-type semiconductor substrate 1 with an insulating film 2 interposed therebetween, and an n-type charge transfer electrode having a conductivity type opposite to that of the substrate is formed in the substrate surface area under this electrode 3. Channel 4 is provided.

A p1°C barrier is provided in a part of the substrate surface region that is in instant contact with the charge transfer channel 4 to prevent the charges in the charge transfer channel 4 from mixing with the charges in other adjacent unit cells. A region 5 is provided. Further, a photosensitive pixel 6 made of an n-type impurity layer having a conductivity type opposite to that of the substrate is provided in the substrate surface region near the charge transfer channel 4, and a p-n junction is formed between the pixel 6 and the substrate 1. A photodiode is formed, and the charge generated by photoelectric conversion of incident light from the direction of the substrate surface is transmitted as a signal to the pixel 6 by the energy gradient of the depletion layer formed at the p-n junction. Accumulated as a career. In addition, the insulation j sample 2
A light shielding film 7 is provided thereon to prevent light from entering areas other than the photosensitive area B including the photosensitive pixel 6 and its two sides. When the charge accumulated in the pixel 6 is applied to the charge transfer electrode 3, the charge accumulated in the pixel 6 is read out to the charge transfer channel 4, and the charge accumulated in the pixel 6 is read out to the charge transfer channel 4. is transferred in a predetermined direction. In this case, the charge transfer electrode 3 has both the function of reading out the aqueous charge of the pixel 60 to the charge transfer channel 4 and the function of transferring the charge in the channel 4.

[Problems with f-view technology: 1 By the way, the p-n junction surface of the photosensitive pixel 6 mentioned above extends to the interface between the substrate 1 and the insulating film 3, so this p-n junction surface extends to the interface between the substrate 1 and the insulating film 3.
A depletion layer is formed along the n-junction surface up to the interface. When the interface is depleted in this way, it becomes susceptible to the effects of surface states at the interface, fixed surface charges in the insulating film 2 near the interface, and the like. This effect causes variations in the dark current between the photosensitive areas, which causes the C1 dark current, so depletion at the interface causes deterioration of the output image from the solid-state imaging device. It is a major factor causing this.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and can prevent depletion at the interface between a semiconductor substrate and an insulating film, eliminate various defects associated with this depletion, and improve the quality of output images. The object of the present invention is to provide a solid-state imaging device that can achieve the following.

[Summary of the invention]

That is, the present invention provides a photosensitive pixel consisting of an impurity layer having a cage shape opposite to that of the semiconductor layer, which accumulates signal carriers generated by photoelectric conversion of incident light on the surface of a predetermined semiconductor layer, and this photosensitive pixel. A solid-state imaging device is provided with a carrier transfer channel that receives a storage gear and transfers carriers, and is provided on the photosensitive pixel with an insulating film interposed therebetween, and has a polarity in a direction to exclude the signal carrier. It is characterized by comprising a transparent electrode to which a voltage is applied.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Fig. 2 shows a part of the solid area 7. A transparent electrode 21 is formed opposite to the element 6, and a constant voltage (in this example, a negative charge) having the same polarity as the signal gear (negative charge in this example) accumulated in the photosensitive pixel 6 is applied to this electrode 21. This example differs in that a negative voltage (-V) is applied via a wiring (not shown).
Since the other parts are the same as those of the conventional example, they will be given the same symbols as in FIG. 1 and their explanation will be omitted. .

J to the solid area center above? The light shield gland 7
When the light enters the opening through the insulating film 2 and the transparent electrode 21, negative charge carriers are generated in the semiconductor. 2', c, since a negative voltage is applied to the transparent electrode 2, negative charges near the substrate surface are avoided, and instead an inversion layer having holes (indicated by 09 in the figure) is formed. A (depletion prevention layer) 6' is formed on the surface of the substrate 10 in the photosensitive region. By kneading, the signal carriers (negative charges, indicated by circles in the figure) generated by the optical η1 conversion are surrounded by the p-n junction between the substrate and the pixel and the inversion layer 6'. It is accumulated within 6.

Therefore, according to the solid-state area sensor described in Section 2, signal carriers exist near the interface between the substrate 1 and the insulating film 2.
No more 9, on the above interface! Since it is no longer affected by surface levels, etc., there is no dark current caused by this effect or variations in dark current between pixels of each unit cell, and a high-quality output image can be obtained. You will be able to do it.

By the way, it is desirable in actual use to make the mark 1jJII voltage 4LL of the transparent electrode 2 small (to a value close to the ground potential), and for this purpose, for example, as shown in FIG. 6, the diffusion depth is shallow, and the conductivity type is opposite to that of the signal carrier (in this example, p
It is sufficient to form a depletion prevention layer 31 made of an impurity layer of type ).

In addition, in FIG. 3, the same parts as in FIG. 2 are given the same reference numerals.

In the solid-state area sensor having the structure shown in FIG. 3 as described above, when the photosensitive region B is viewed in a direction perpendicular to the substrate 1, the regions are in contact with each other in the order of p-type, n-type and p-type. Considering the junction of these regions in terms of energy levels based on negative charges, the energy level of the n region is lower than that of the p region, so the signal carriers (negative charges) generated by photoelectric conversion are transferred to n-type photosensitive It is accumulated in pixel 6. The depletion prevention layer 31 made of a p-type impurity layer on the surface of the substrate in the photosensitive region B serves not only to keep signal carriers away from the interface, but also to make the energy level higher than that in the n region. Therefore, the negative voltage applied to the transparent electrode 21 can be reduced to the extent that the energy level of the substrate surface in the photosensitive area B is higher than the energy level of the photosensitive pixel area.

Note that the depletion prevention layer 31 does not have to be p-type but has the same conductivity type as the photosensitive pixel 6 and has a lower impurity concentration than n-type.
It may also be formed as a mold impurity layer. In this case, as a manufacturing process, after forming the two-layer transfer electrode 3 of polysilicon, for example, impurity ions of the opposite conductivity type to the signal carrier are implanted into the surface of the pixel 6 to form a depletion prevention layer. The transparent electrode 21 may be formed above the protective layer so as to cover the protective layer.

Furthermore, although each of the above embodiments describes a solid-state area sensor using a p-type substrate, when an n-type substrate is used, the other semiconductor regions are made of the opposite conductivity type from the above embodiments, and the transparent electrode is Just apply a voltage. Further, the semiconductor substrate in each of the above embodiments may be a well layer formed in the semiconductor substrate with impurities having a conductivity type opposite to that of the substrate.
In short, any semiconductor layer of a predetermined conductivity type may be used.

〔Effect of the invention〕

As described above, according to the solid-state imaging device of the present invention, a transparent electrode is provided above the photosensitive pixel formed on the surface of a predetermined semiconductor layer with an insulating film interposed therebetween, and the transparent electrode is used to prevent the accumulation in the photosensitive pixel from occurring. By applying a voltage of the same polarity as the signal carriers to expel them from the interface between the semiconductor layer and the insulating film, carriers of the opposite conductivity type to the signal carriers are present in the interface region of the photosensitive pixel surface. A depletion prevention layer is formed. Therefore, a nitrogen-depleted layer is not formed near the interface, and signal carriers are less susceptible to the effects of interface states and fixed surface charges. It is possible to suppress the variation in dark current between the two, and it is possible to improve the quality of the output image. Further, by forming a depletion prevention layer made of an impurity layer containing a predetermined impurity on the surface of the pixel, the voltage applied to the transparent electrode can be reduced, and restrictions on practical use can be reduced.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a part of a conventional solid-state area sensor.
FIG. 2 is a sectional view showing a part of a solid-state area sensor according to one embodiment of the present invention, and FIG. 3 is a sectional view showing another embodiment. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Insulating film, 4... Transfer channel, 6... Photosensitive pixel, 6'... Inversion layer, 21...
...Transparent electrode, 31...Depletion prevention layer. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 3

Claims (2)

[Claims] (1) A photosensitive pixel consisting of an impurity layer of a conductivity type opposite to that of the semiconductor layer that accumulates signal carriers generated by photoelectric conversion of incident light on the surface of a predetermined semiconductor layer, and the accumulated carriers of this photosensitive pixel. A solid-state imaging device is provided with a transfer channel for receiving signal carriers and transferring carriers, the solid-state imaging device including a transparent electrode provided on the photosensitive pixel via an insulating film and to which a voltage having a polarity that excludes the signal carriers is applied. A solid-state imaging device characterized by: (2) The solid-state imaging device according to item 1 of the patent, further comprising an impurity layer containing an impurity of a conductivity type opposite to that of the signal carrier on the surface of the photosensitive pixel.