JP2676814B2 - Multi-type light receiving element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multi-type light receiving element such as a line sensor or a split sensor that can detect even extremely weak light.

[Prior Art] FIGS. 3 and 4 are schematic partial plan views and partial cross-sectional views (FIG. 3B-B) for explaining a structure of a light receiving portion of a line sensor for weak light which has been used in the past. Section).

In the figure, a semiconductor substrate such as p-type or n-type silicon
The semiconductor region 101a, 1 of the opposite conductivity type (p-type if the substrate is n-type) to the semiconductor substrate 104 is formed by diffusing impurities.
01b, 101c are formed at a predetermined interval, the semiconductor substrate 10
A photodiode is constituted by 4 and the semiconductor regions 101a, 101b, 101c, respectively. (Hereinafter, the length and width of the photodiode in this specification refer to the length and width of the above semiconductor region.) Although only three semiconductor regions 101a, 101b, and 101c are shown in the figure, In a normal line sensor, hundreds to thousands of photodiodes are formed. The length of the photodiode is considerably long to improve the sensitivity to light (increasing the amount of received light), and the aspect ratio obtained by dividing the length by the pixel pitch (photodiode width + photodiode spacing) is 10 It is about 100.

In addition, the semiconductor substrate 104 on which the photodiode is formed
A transparent insulating film 103 is laminated on the surface of the, and a portion other than the light receiving portion is covered with a light shielding film 105 made of aluminum or the like.

In the line sensor configured as described above, the reverse voltage is applied to the semiconductor substrate and the semiconductor region, and the photocurrent generated by the light reception is externally output by using a CCD or a MOS switch (not shown). It is outputting.

[Problems to be Solved by the Invention] In the conventional line sensor for weak light as described above, if the pixel pitch is increased, the resolution is lowered.
As described above, by increasing the length of the photodiode, the area of the photodiode is increased and the sensitivity is increased.

However, only increasing the length of the photodiode increases the photocurrent generated by light irradiation, but also increases the dark current generated regardless of light irradiation. .

That is, since the output signal from the line sensor is proportional to the sum of the photocurrent and the dark current, in the conventional line sensor, when the light becomes weak, the ratio of the dark current component of the output signal becomes high, and the accuracy of the weak light becomes high. Was difficult to detect.

The present invention has been made in view of such a point,
It is an object of the present invention to provide a multi-type light receiving element having a high capability of detecting weak light by reducing dark current.

[Means for Solving the Problems] In the present invention, a plurality of photodiodes are formed on a p-type or n-type silicon substrate by forming a plurality of semiconductor regions of a conductivity type opposite to that of the substrate at predetermined intervals, In the multi-type light receiving element formed by stacking transparent insulating films on them, the photodiode is formed to have an aspect ratio of 10 or more, the insulating film has a uniform film thickness,
The above problem is achieved by forming a conductive film in a region corresponding to the interval on the insulating film and applying a voltage to the conductive film.

[Operation] There are dark currents that occur inside the semiconductor substrate and those that occur at the interface between the semiconductor substrate and the transparent insulating film. The dark current component generated inside the substrate is proportional to the area of the photodiode. The component generated at the interface between the substrate and the insulating film is proportional to the peripheral length of the photodiode. When forming a long and narrow photodiode like a line sensor, the peripheral length becomes long, so that the dark current component generated at the interface increases. For example, in a photodiode with a width of 10 μm and a length of 2500 μm, the component generated at the interface is dark. 90% or more of the current.

In the present invention, the plurality of photodiodes formed on the silicon substrate, the aspect ratio is formed to 10 or more,
The insulating film has a uniform film thickness, a conductive film is formed in a region corresponding to the interval between photodiodes on the insulating film, and a voltage is applied to the conductive film. Therefore, the depletion layer and the inversion layer are not generated on the sea surface between the silicon substrate and the transparent insulating film, and thus the dark current generated at the interface can be reduced.

That is, even if electrons and holes are generated at the interface between the semiconductor substrate and the transparent insulating film without relying on light, there is no depletion layer or inversion layer at the interface, so that the charge passes through the interface and has the opposite conductivity type to the substrate. Unable to reach the semiconductor area,
Not detected as an output signal.

The specific voltage applied to the conductive film differs depending on the manufacturing conditions of the light receiving element, and is set by the film thickness of the transparent insulating film, the film quality, the impurity concentration of the semiconductor substrate, and the like.

Since the conductive film in the present invention only needs to have conductivity, it is possible to use a material that does not have a light-shielding property such as polysilicon, but an aluminum film that has been conventionally used as a light-shielding film in the peripheral portion of the light-receiving portion. If it is formed simultaneously with the peripheral portion by using, the manufacturing process can be simplified.

Further, as the transparent insulating film laminated between the conductive film and the semiconductor substrate, SiO ₂ or nitride can be used.

[Embodiment] FIG. 1 is a schematic partial plan view showing an embodiment of the present invention, and FIG. 2 is a sectional view of an AA portion in FIG.

In the silicon substrate 4 (n-type in this embodiment) as a semiconductor substrate, semiconductor regions 1a, 1b, 1c (p-type, width in this embodiment) of opposite conductivity type to the substrate 4 are formed by diffusing impurities.
35 μm, length 2500 μm) were formed at 15 μm intervals. The silicon substrate 4 and the semiconductor regions 1a, 1b, 1c form photodiodes, respectively. Although only three semiconductor regions are shown in the figure, 512 photodiodes are actually formed.

Next, on the silicon substrate 4 and the semiconductor regions 1a, 1b, 1c,
Transparent insulating film as to form a SiO ₂ film 3, zone further corresponding to the spacing of the photo diode on the SiO ₂ film 3 (semiconductor region
An aluminum film 2 as a conductive film was formed on the portions (1a, 1b, 1c are not formed).

In the line sensor obtained as described above, the n-type silicon substrate 4 was biased to the positive voltage V _DD , and the p-type semiconductor regions 1a, 1b and 1c were precharged to the ground level.
In addition, the aluminum film 2 has the same positive voltage as the silicon substrate 4.
Biased to V _DD . (When the substrate is p-type and the semiconductor region is n-type, the substrate and the aluminum film may be at the ground level and the semiconductor region may be applied with a positive voltage.) Then, light is irradiated from above in FIG. The photocurrent generated in the photodiode was detected by using a CCD, a MOS switch or the like (not shown).

At this time, the dark current is also detected together with the photocurrent, but in this embodiment, the aluminum film 2 is set to the same potential as the silicon substrate 4 to eliminate the depletion layer near the interface between the silicon substrate 4 and the SiO ₂ film 3. Therefore, the dark current is significantly reduced.

When the dark current was compared between the line sensor of this embodiment and the conventional line sensor (the same as the structure of the embodiment except that the conductive film is not arranged between the photodiodes) in the state where the light receiving portion is shielded from light, the present embodiment shows that The line sensor's dark current was about 1/10 of that of the conventional one. That is, by using the line sensor of the present embodiment, it is possible to detect even weak light having an intensity that is about 1/10 of that of the conventional one.

[Effects of the Invention] As described above, according to the present invention, by forming the conductive film in the area corresponding to the interval between the plurality of photodiodes of the multi-type light receiving element, the dark current is significantly reduced, and the dark current is much longer than the conventional one. It has the secondary effect that even weak light can be detected.

INDUSTRIAL APPLICABILITY The present invention is particularly effective for improving the detection capability of a line sensor having a large number of elongated photodiodes, and can be applied to various line sensors regardless of the output method.

Further, the technical idea of the present invention is not limited to the line sensor,
The same can be applied to a photodiode array or a single photodiode, and the dark current can be reduced as compared with the conventional one.

[Brief description of the drawings]

FIG. 1 is a partial plan view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA in FIG. 1, FIG. 3 is a partial plan view showing a conventional example, and FIG. It is a B section sectional view. [Explanation of symbols for main parts] 1a, 1b, 1c ... semiconductor region 2 ... aluminum film (conductive film) 3 ... SiO ₂ film (transparent insulating film) 4 ... silicon substrate (semiconductor substrate)

Claims (1)

(57) [Claims] 1. A plurality of photodiodes are formed on a p-type or n-type silicon substrate by forming a plurality of semiconductor regions of a conductivity type opposite to that of the substrate at predetermined intervals, and a transparent insulating film is formed on them. In the multi-type light receiving element formed by stacking, the photodiode is formed with an aspect ratio of 10 or more, the insulating film has a uniform film thickness, and a region corresponding to the interval on the insulating film. A multi-type light receiving element, wherein a conductive film is formed on the conductive film, and a voltage is applied to the conductive film.