JPH0449787B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to a photoelectric conversion element.

Background technology and its problems Conventionally, for example, interline transfer method and CCD
The structure shown in FIG. 1 is known as a structure near the light receiving section of an image sensor. That is, in FIG. 1, a channel stopper 2 made of a p ⁺ layer, a vertical register 3 made of an n layer, an overflow control gate 4 made of a p layer, and an overflow drain 5 made of an n layer are arranged in a p-type silicon substrate 1.
are formed respectively. Please note that the above channels
Although a plurality of stoppers 2 and vertical registers 3 are actually formed extending parallel to each other in a direction perpendicular to the plane of the paper, only one of each is shown in FIG. Further, a large number of overflow control gates 4 and overflow drains 5 are formed along the vertical register 3 at equal intervals. On the other hand, on the p-type silicon substrate 1 are a SiO ₂ film 6, a Si ₃ N ₄ film 7, a readout gate 8 made of DOPOS (polycrystalline silicon doped with impurities), a thin DOPOS film 9 as a transparent electrode, and a photoshield. An Al film 10 is formed in each case.

In the above-mentioned CCD image sensor, the portion corresponding to the opening 10a of the Al film 10, the DOPOS film 9, and the SiO ₂
A MOS structure consisting of a film 6 and a p-type silicon substrate 1 constitutes a light receiving section 11 . And the above opening 1
The light 12 incident on 0a causes the p-type cylindrical substrate 1 to
The signal charges generated in the DOPOS film 9 are accumulated on the surface 1a of the p-type silicon substrate 1 by applying a predetermined voltage to the DOPOS film 9, and then transferred to the vertical register 3 by the readout gate 8. ing.

The above-mentioned CCD image sensor has the following drawbacks. In other words, it is used as a transparent electrode.
Since the DOPOS film 9 has a large absorption coefficient for short wavelength light, it has poor sensitivity to blue light in particular. In addition, in order to prevent so-called blooming that occurs when the amount of incident light is too large and excessive photocharge is generated, an overflow drain 5 and an overflow control gate 4 must be formed, so the area occupied by each pixel is large. It is not possible to increase the degree of integration of elements.

OBJECTS OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a photoelectric conversion element of a CCD image sensor with a high degree of element integration.

Summary of the Invention A photoelectric conversion element according to the present invention includes a light-transmitting conductive thin film provided on the semiconductor substrate so that a Schottky barrier is formed between at least a portion of the photoelectric conversion element and the semiconductor substrate. When an excessive amount of photocharge is generated in the semiconductor substrate due to light passing through the thin film and entering the conductive substrate, the excess photocharge is guided to the conductive thin film through the Schottky barrier. It consists of By configuring in this way, the degree of integration of the elements can be increased.

Embodiment Hereinafter, an interline transfer type CCD image pickup device as an embodiment of the photoelectric conversion device according to the present invention will be described with reference to the drawings.

In Figure 2, for example, the p-type impurity concentration is 3.5
In a p-type silicon substrate 1 of ×10 ¹⁴ cm ^-3 , a channel stopper 2 consisting of a p ⁺ layer and a p layer (hereinafter referred to as a p-well) having a p-type impurity concentration of 2 × 10 ¹⁶ cm ^-3 , for example. 13 are formed. Furthermore, within this p-well 13, the surface concentration is, for example, 1×
A vertical resistor 3 consisting of n layers of 10 ¹⁷ cm ^-3 is formed. Note that the channel stopper 2, the p-well 13, and the vertical register 3 are formed in plural numbers, extending in parallel to each other in the direction perpendicular to the plane of the paper, as described in FIG. Also, the above p.
For example, a portion of the type silicon substrate 1 different from the vertical register 3 has an n-type impurity concentration of 5×10 ¹⁶
An n-layer 14 of cm ^-3 is formed. Note that a plurality of the n-layers 14 are formed along the vertical register 3.

Also, the vertical register 3 of the p-type silicon substrate 1
And on a part of the n layer 14, the SiO ₂ film 6 and
A readout gate 8 consisting of DOPOS is formed. Further, on the SiO ₂ film 6 and the n-layer 14, a SnO ₂ film 15 is formed as a transparent electrode having a thickness of, for example, 1000 Å and having light transmittance and conductivity. On this SnO ₂ film 15, an Al film 10 is formed as a photo shield.
Note that the SnO ₂ film 15 in the opening 10a portion of the Al film 10,
The SiO ₂ film 6 and the n-layer 14 constitute the light receiving section 11 .

The SnO ₂ film 15 can be formed, for example, by depositing an Sn film on the SiO ₂ film 6 and the n-layer 14, and then oxidizing the Sn film in a high-temperature furnace or by oxidizing it in an O ₂ +Ar gas atmosphere. While heating the mold silicon substrate 1, a SnO ₂ film is deposited on this p
It can be formed by depositing on the mold silicon substrate 1.

Next, the operation of the CCD image sensor configured as described above will be explained.

In FIG. 2, first, a signal charge consisting of a large number of electrons generated in the n-layer 14 and the p-type silicon substrate 1b below the n-layer 14 by the light 12 incident on the light receiving part 11 is transferred to the SnO ₂ film 15, is accumulated in the n-layer 14 by applying a predetermined voltage to the n-layer 14. Next, by applying a predetermined voltage to the readout gate 8, the p-type silicon substrate 1c directly under the SiO ₂ film 6 is removed.
n-channels are formed within. By transferring the signal charges to the vertical register 3 through this n channel, the signal charges are read into the vertical register 3. Thereafter, the signal charges are transferred from the vertical register 3 to a horizontal register (not shown), and further transferred within this horizontal register to read out the signal charges from this horizontal register as an output signal. Note that the signal charges transferred within the vertical register 3 are prevented from flowing out of the vertical register 3 during the transfer by the channel stripper 2.

In the above embodiment, n constituting the light receiving section
Since the SnO ₂ film 15 is formed on the layer 14,
The sensitivity to blue light is good for the following reasons. That is, the light transmission characteristics of this SnO ₂ film 15 are as shown in FIG.
The transmittance for light of 350-1000 nm shows a high value of 90% or more. As is clear from this transmission characteristic, this SnO ₂ film 15 can absorb blue light (wavelength of about 500nm).
It is also almost transparent to m). In this way, the CCD image sensor described above has extremely good sensitivity to blue light.

Furthermore, in the above embodiment, since no overflow drain and overflow control gate are formed in the p-type silicon substrate 1,
Compared to conventional CCD image sensors, the area occupied by each pixel is smaller, and therefore the element and the degree of integration can be increased.In this case, no overflow drain is formed, but this will be explained below. This makes it possible to prevent the above-mentioned blooming from occurring.

That is, as shown in FIG. 4A, a Schottky barrier is formed between the SnO ₂ film 15 and the n-layer 14, and the potential of the n-layer 14 at the interface between the SnO ₂ film 15 and the n-layer 14 is , is higher than the potential of the SnO ₂ film 15 by φ=1.01ev. Therefore, when the amount of light 12 incident on the light receiving section 11 is large and the amount of signal charges generated is large, the excess signal charges are transferred from the n-layer 14 as shown by arrow A.
As a result of flowing into the SnO ₂ film 15, blooming is prevented from occurring. In this way, in the above embodiment, the SnO ₂ film 15 also serves as an overflow drain in the conventional CCD image sensor.

Furthermore, in the above-described embodiment, the impurity concentration of the n-layer 14 was selected to be 5×10 ¹⁶ cm ^-3 to provide a low impurity concentration, so when a predetermined voltage is applied to the SnO ₂ film 15, the n-layer 14 is completely depleted and signal charges are accumulated in this depletion layer. Furthermore, the above n layer 1
As shown in FIG. 4B, the potential around the contact portion between the SnO ₂ film 15 of No. 4 and the n-layer 14 is deeper than the potential at the center of the n-layer 14. Therefore, if the read gate 8 is turned on with the potential of the vertical register 3 lower than the potential of the n-layer 14 shown in FIG. 4B, the signal charge accumulated in the depletion layer of the n-layer 14 is transferred to the vertical register 3 can be completely transferred. Therefore, when the above-described CCD image sensor is used in a camera, for example, it is possible to prevent afterimages from occurring.

Furthermore, in the above embodiment, since the SiO ₂ film 6 is formed on both ends of the light receiving section 11, there is an advantage that dark current can be reduced. Note that if a thin SiO ₂ film or Si ₃ N ₄ film with a thickness of about 30 Å is formed between the SnO ₂ film 15 and the n-layer 14, the dark current can be further reduced.

In the above-mentioned example, SnO ₂ was used as the conductive thin film and material having optical transparency, but other materials such as ITO (In ₂ O ₃ −SnO ₂ ), Pt, SnO ₂ , etc. Good too.

Effects of the Invention According to the photoelectric conversion element according to the present invention, the degree of integration of the element can be increased.

[Brief explanation of drawings]

Figure 1 shows the conventional interline transfer method.
FIG. 2 is a cross-sectional view showing the structure of a vertical register and a light receiving section of a CCD image sensor, and FIG.
A cross-sectional view similar to FIG. 1 showing the structure of the vertical register and light receiving part of a CCD image sensor, FIG. 3 a graph showing the transmission characteristics of the SnO ₂ film, and FIGS. 4A and 4B respectively It is a potential diagram shown along the cross section of the B line and the CC line. In addition, in the symbols used in the drawings, 1... p-type silicon substrate, 3... vertical register, 8... read gate, 9... DOPOS film, 11... light receiving section,
13...p well, 14...n layer, 15...
_SnO2 film.

Claims (1)

[Claims] 1. A conductive thin film having light transmittance is provided on the semiconductor substrate so that a Schottky barrier is formed between at least a portion of the semiconductor substrate and the semiconductor substrate, and the light is transmitted through the conductive thin film and is incident on the semiconductor substrate. A photoelectric conversion element characterized in that, when an excessive amount of photocharges are generated in the semiconductor substrate by light, the excess photocharges are guided to the conductive thin film through the Schottky barrier.