JPS6042989A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain high sensitivity over an entire visual region and a characteristic of high dark resistance by surrounding a region made of a material having narrow forbidden band width and sensitivity over a wide wavelength region with a material having high dark resistance and the wide forbidden band width in the photoconductive film of a solid-state image pickup device. CONSTITUTION:The 2nd photoconductive film 15 is >=0.5mum in thickness and transduces >90% of visual light into an electron-positive hole pair. The generated electron-positive hole pairs are attracted respetively to an electrode, recombined with the electron-positive hole pair stored in the junction capacitance between a p channel semiconductor substrate 1 and an n channel semiconductor region and the stored charge is decreased. Then the gate 7 of an MOS transistor is turned on at signal read, a current flows between an n channel semiconductor region 2 and an n channel semiconductor region 3 being a drain and its current value represents a photo signal amount. In this case, since the 2nd photoconductive film 15 having the narrow forbidden band width is used, the sufficient sensitivity to incident light is attained, and the dark current and crosstalk between picture elements are decreased remarkably by the photoconductive film 9 of high dark resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solid-state imaging device, and particularly to the structure of a solid-state imaging device that utilizes the optical 11FI electric effect.

[Prior Art] FIG. 1 is a sectional view showing an example of a conventional solid-state imaging device using the photoconductive effect.

First, the configuration of a conventional solid-state imaging device will be described with reference to FIG. In FIG. 1, on a p-type semiconductor substrate 1, an 11-type semiconductor region 2 which becomes a source of a MOS)-transistor and an n-type semi-S-type semiconductor region II which becomes a drain of a MOS transistor! I83 is formed.

Further, a gate 7 is provided in a region F between n-type semiconductor regions 11jl+2 and 3, and together with n-type semiconductor regions 2 and 3 constitutes a MOS I-transistor. Also, n
A pixel isolation layer 13 and an insulating film 8 are provided in contact with the gate type semiconductor region 3, and serve to isolate adjacent pixels. An insulating film 5 is formed on the wiring 4 and the insulating film 8. Next, a double-layer wiring 6 is formed on the single-layer wiring 4 formed on the r11 type semiconductor region 2 and the above-mentioned insulating film 5. , this two-layer wiring 6 further serves as a positive electrode that applies an electric field to the photoconductive film 9 formed on it.The transparent electrode 10 formed on the photoconductive film 9 It is a negative electrode that applies an electric field to the optical S-electrode 11!9 together with the layer wiring 6.A transparent flattening film 11 is formed on the transparent electrode 10, and an optical filter 1 that separates the incident light is further disposed on the transparent flattening film 11.
2 is provided.

Next, the operation of the conventional solid-state imaging device using the photoconductive effect shown in FIG. 1 will be explained. The incident light is separated by the optical filter 12, further transmitted through the transparent flattening film 11 and the transparent electrode 10, and then absorbed by the photoconductor m9. By absorbing this light, electron-hole pairs are generated in the photoconductive film 9. An electric field is applied to the photoconductive film 9 by the two-layer wiring 6 and the transparent electrode 10, so that the generated electron-hole pairs are accelerated and the electrons are transferred to the two-layer wiring WA6, which is the positive electrode. , holes are attracted to the transparent N-pole 10, which is a negative N-pole. The potential of the two-layer interconnect ta6 is connected to the n-type semiconductor region 2, which is the source of the MOS t-transistor, via the first-layer interconnect I1I4. Here, if the potential of the transparent electrode t, which is the above-mentioned negative electrode, is fixed, when light is irradiated and electron-hole pairs are generated in the photoconductive film 9, the potential of the n-type semiconductor region 2 will be becomes floating. Then, when the signal continues, the gate 7 of the MOS transistor is turned on, and the n-type semiconductor region 2, which is the source, and the n-type semiconductor region, which is the drain, are turned on.
The potential is the same as that of the type semiconductor region 3. Since the source potential of the n-type semiconductor region 2 changes in response to the irradiated optical signal m, the value of the current flowing through the 11-type semiconductor region 2 when the signal is continuously applied represents the optical evaluation 1.

However, the conventional solid-state imaging device constructed as described above has problems in that dark current occurs in the photoconductive film and crosstalk occurs between pixels. In order to overcome this problem, the dark resistance of the photoconductive film 9 must be sufficiently large.
Generally, a resistivity of 1Q 10Ω·am or more is required. In order to increase the light resistance,
It is effective to reduce the carrier density by mixing an i substance or by widening the width of the forbidden band. Therefore, hydrogenated amorphous silicon mixed with nitrogen or the like is used as the photoconductive film 9. It is being

However, the presence of scattering centers (impurities) that reduce the mobility described above is undesirable because it causes a deep trap order in the semiconductor and induces residual charges. Furthermore, when the forbidden band width is increased, the wavelength at which the light-guiding N film becomes sensitive to light shifts to the shorter wavelength side.

FIG. 2 is a graph showing the photoelectric conversion characteristics of the photoconductive film material, where the horizontal axis represents the wavelength of incident light and the vertical axis represents the absorption coefficient.

The solid line in Figure 2 shows the photoelectric conversion characteristics of intrinsic amorphous silicon, which is promising as a high dark resistance material, and its absorption coefficient sharply increases on the energy side lower than the forbidden band width of 1.95 eV (corresponding to a wavelength of 630 nm). descend. Regarding the solid line in FIG. 2, the photoelectric conversion characteristics deteriorate for incident light with a wavelength longer than 630 nm. Color solid-state imaging devices are required to have sensitivity in the entire visible range, and therefore the above-mentioned intrinsic amorphous silicon does not fully satisfy this requirement. On the other hand, 'J! has sensitivity to light! If a photoconductive film material with a narrow forbidden band is used in order to expand the L-length region, the dark resistance will decrease as described above, and noise will increase.

[Summary of the Invention] Therefore, the main object of the present invention is to eliminate the above-mentioned drawbacks and provide a solid-state lff1 imaging device with high sensitivity and high ua and low resistance.

To summarize, this invention secures a wide wavelength range with sufficient sensitivity by making a part of the light incident side of the photoconductive film a material with a narrow M band width as described above, and at the same time,
By using a material with a wide forbidden band width in the concave portion of this part of the region, a high resistance can be obtained.

The above-mentioned objects and other objects and other features of the present invention will become more apparent from the detailed description given below with reference to the drawings. - [Embodiment of the Invention] FIG. 3 is a TJ sectional view showing an embodiment of the invention. The example shown in FIG. 3 is the same as the cross-sectional view shown in FIG. 1 above, except for the following points. That is, in a part of the light incident side of the photoconductive film 9, an amorphous S′ y, Ge +−x (0≦x≦1〉, etc.) whose forbidden band width is narrower than that of the photoconductive film 9 is formed. A second photoconductive film 15 made of a material is provided.

Next, the operation of the embodiment shown in FIG. 3 will be explained. The second photoconductive film 15 has photoelectric conversion characteristics shown by the dotted line in FIG. 2, has a thickness of 0.5 μm or less, and converts more than 90% of visible light into electron-hole pairs. Photoconductive film 9
Similarly to the example shown in FIG. 1, the second photoconductive film 15 includes a two-layer wiring 6 as a positive electrode and a transparent electrode 10 as a negative electrode
An electric field is applied by As a result, the generated electron-hole pairs are attracted to the electrodes, recombine with the electron-hole pairs stored in the junction capacitance between the p-type semiconductor substrate 1 and the n-type semiconductor region, and release the accumulated charge. reduce next,
When reading a signal, the gate 7 of the MOS t-transistor is turned on, and a current flows between the n-type semiconductor region 2, which is the source, and the n-type semiconductor region 3, which is the drain, of the MOS t-transistor. Represents the amount of signal. In this case, since the second photoconductive rice cake 15 with a narrow forbidden band width is used, sufficient sensitivity to incident light is ensured, and a photoconductive rice cake with high dark resistance is also used. ! 9 can significantly reduce dark current and crosstalk between pixels.

In this example, the conductivity of the substrate is p-type, and the scanning circuit M
Although the O8I-transistor is an 11-type MO8l-transistor, the same effect can be obtained even if the substrate is a p-type and the scanning circuit MOS transistor is a p-type.

[Effects of the Invention] As described above, in the present invention, in the photo-S dielectric film of a solid-state image transfer device, a region made of a material with a narrow bandgap that is sensitive over a wide wavelength range is used as a material with a high dark resistance.
Since it is made of a material with a wide band width and has a concave 4 fl, it is possible to use it all times compared to a conventional solid-state imaging device. It has a high @ degree with respect to 31 castles, and can have characteristics of high dark resistance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional solid-state L-image device utilizing the photoconductive effect. FIG. 2 is a graph showing the photoelectric conversion characteristics of photoconductive film materials. FIG. 3 is a sectional view showing an embodiment of the present invention. In the figure, 1 is a p-type semiconductor W board, 2.3 is a 0-type semiconductor region, 4 and 14 are single-layer wiring, 5.8 is an insulating film, 6 is a double-layer wiring, 7 is a gate, and 9 is an optical WJ electric film. , 10 is a transparent electrode,
Reference numeral 11 indicates a transparent flattening film, 12 indicates an optical filter, 13 indicates a pixel portion wm conversion film, and 15 indicates a second photoconductive film. Agent Masuo Oiwa

Claims (2)

[Claims] (1) A solid-state imaging device using a photoconductive effect, comprising a photoelectric conversion means for converting an incident optical signal into an electric signal, the photoelectric conversion means comprising a first layer made of a material having a high dark resistance value. a second photoconductive film, which is provided surrounded by the first photoconductive film and is made of a material having a wide wavelength range of sensitivity to light and whose forbidden band width is narrower than that of the first photoconductive film. A solid-state imaging device consisting of a conductive film. (2) The first photoconductive film is amorphous silicon, and the second photoconductive film is amorphous SIX Ge j-
): A solid-state imaging device where (0≦×≦1).