JPS58190167A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the sensitivity of the receiving region of light of a short wavelength, by decreasing the thickness of a region to which the light in short wavelength range is made incident and increasing the thickness of a region to which light of a long wavelength is made incident for a photoconductive film that is laminated on a scanning IC substrate. CONSTITUTION:An MOSFET2 is formed with a source 3, a drain 4 and a gate 5 on a semiconductor substrate 1 to constitute a scanning circuit or a switch which is opened and closed by the output of the scanning circuit. Picture element electrodes 6 are arrayed in a matrix form on the top surface of a scanning IC substrate. A photoelectric converting film 7' and a transparent electrode 8 which applies the target voltage are formed on the electrode 6. For the film 7', the thinnest film 12-1, the intermediate thickness film 12-2 and the thickest film 12-3 form light of a short wavelength receiving region, light of an intermediate wavelength receiving region and light of a long wavelength receiving region respectively.

Description

Detailed Description of the Invention (1) Field of Application of the Invention The present invention provides a scanning circuit and a photoelectric conversion film t on a semiconductor substrate.
-This is a book about integrated solid-state image sensors.

Q) CCD = (
Charge Coupled Devices
) and 2fk types of MOS type (devices used as source junction gold optical diodes of MO8 switches) have been considered.

All of these devices have the advantage that they can be manufactured using MO8 process technology with a high degree of integration. Strength・
However, since the photosensitive part is located under the electrode (in the case of CCD) or on the same plane as the scanning switch and signal output line (in the case of MOS type), the incidence of artificial light on the electrode f switch part is blocked. The disadvantage is that the area is large, which means that the optical loss is large. Furthermore, since the photosensitive section and the scanning section are on the same plane as mentioned above, the area occupied by the picture element becomes large.
In other words, it is not possible to increase the density of picture elements, and the resolution is F.
The problem is that the iLi cannot be raised.

In order to solve these problems (photosensitivity, resolution), the inventors applied for a solid-state image sensor with a two-story structure in which a photoelectric conversion film for exposure to light is provided above the scanning section.
6372. (filed on July 5, 1972). Taking as an example the case where this double-decker solid-state image sensor 'tM08 type element is used,
An outline of the device structure is shown in FIG. It may be composed of a CCD type, in which case an MO8 field effect transistor'
It can be replaced with frCCD. 1 is a semiconductor substrate of a first conductivity type; 2 is an MO8 field effect transistor constituting a scanning circuit (not shown) or a switch that is opened and closed by the output of the scanning circuit; Reference numeral 6 denotes an electrode that determines the dimensions of the 1m element, which is connected to the source here. 7 is a photoelectric conversion film serving as a photosensitive material, and 8 is a transparent electrode for applying a voltage to drive the photoelectric conversion 111. Reference numeral 9 denotes an insulating oxide film, and the nine optical signal charges accumulated on the electrode 6 are taken out via the switch 2 to the signal output line 10 connected to the drain 4. As can be seen from this figure, a semiconductor substrate 1, a scanning circuit and a switch 2
The scanning IC substrate integrated with the photoelectric converter 7 and 8 has a two-story structure.

Therefore, the area utilization rate is high and the dimension 11 per picture element is small, that is, the degree of decomposition is high. Extremely superior performance can be expected compared to conventional solid-state image sensors, such as the ability to obtain the desired spectral sensitivity by selecting the photoelectric conversion section located above the light incidence surface and reducing optical loss. It's a book.

However, in order to expand the range of applications such as low-light imaging and high-sensitivity photodetection devices, it is necessary to further increase the sensitivity of the device. When the current element uses Toshiki gold as a color filter, it is composed of three regions that receive blue, green, and red light.

In addition, if a complementary color filter is used, 11
For example, it is composed of four areas that receive cyan, yellow, green, and white light. The sensitivity of this element is limited by the sensitivity to blue light, as in the case of the MOS type or CCD type element described above. This is because short wavelength light having a larger absorption coefficient than red or green light is absorbed near the surface of the photoelectric conversion film, and the incident light cannot reach deep into the film. Therefore, light as a countermeasure! It is conceivable to reduce the thickness of the conversion film, but this cannot be said to be a preferable measure since it may have the disadvantage of decreasing the sensitivity to red light or the like.

(3) Purpose of the Invention The purpose of the present invention is to improve the sensitivity of the region that receives short wavelength light without reducing the sensitivity of the region that receives long wavelength light.

(4) Detailed description of the invention The film thickness of the photoconductive film laminated on the substrate is set to a different value for each color determined by a color filter, that is, the film thickness is thinner in the region where short wavelength light is incident, and the film thickness is thinner in the region where short wavelength light is incident, and long wavelength light is incident. The film thickness in the region where light is incident is made thicker.

(5) Example Hereinafter, the present invention 1r will be described in detail with reference to Examples.

FIG. 2 shows the pixel structure that is the gist of the solid-state imaging device of the present invention. Here, for convenience of explanation, three adjacent picture elements are shown. 19. The figure shows a MOS as the substrate of the scanning IC.
Although a substrate made up of transistors has been described, it is of course possible to use nine substrates made up of CCDs. In this case as well, the structure of the photoelectric conversion film formed on the picture element electrode is exactly the same as that shown in the same figure. 6 is a picture element electrode arranged in a matrix on the top surface of the scanning IC substrate, 7' is a photoelectric conversion film having a different film thickness corresponding to a predetermined picture element electrode, and 8 is a target voltage v.
This is a transparent electrode that applies tar. Here, the thinnest photoelectric conversion film 12-1 is a region that receives short wavelength light (e.g., blue, cyan, etc.), and the region of intermediate film thickness 12-21d is a region that receives intermediate wavelength light (e.g., green). , thick film 1
2-3 corresponds to a region that receives long wavelength light (for example, red). By changing the thickness of the photoelectric conversion film for each picture element according to the sensitivity required by each picture element in this way, it is possible to obtain the following characteristics necessary for imaging.

(1) In the thin film region 12-1, (1) the distance from the place where photocharge is generated by incident light to the pixel electrode is short, and (11) the electric field (target voltage) applied to the photoelectric conversion film is effective. As a result, the photocharges generated in the film reach the picture element electrodes without being destroyed by recombination or the like during their travel. That is, the sensitivity to short wavelength light increases.

(2) The film thickness of the region 12-3 is not limited to the film thickness of the region 12-1, and can be independently set to a predetermined thickness. Therefore, by increasing the 12-30 film thickness, the sensitivity to long wavelength light, which has a small absorption coefficient and generates photocharge everywhere from near the surface to the deep part (pixel electrode side) 1, can be reduced to the current value (1).
! In other words, this corresponds to not reducing the sensitivity to long wavelength light), or it can be increased even more.

(3) In addition to the sensitivity improvement mentioned in the previous section α) and (2),
By setting the thickness of the photoelectric conversion film to a predetermined value, balanced spectral sensitivity for each color can be obtained. The film thickness for this purpose varies depending on the material of the photoelectric conversion film used. To determine the film thickness ratio of 12-1.12-2゜12-3, the film thickness should be selected as the inverse ratio of the saturated light flow generated by the photoelectric conversion film to the light passing through the filter of each part. . For example, in the case of hydrogen-doped amorphous silicon, the film thickness ratio of 12-1.12-2.12-3 is 1:2:3.
Nipei can obtain approximately equal sensitivity for blue, green, and red, and has advantages such as easier signal processing for producing color signals and good color reproducibility. In the embodiment shown in FIG. 2, we considered a case where the color filter consists of three colors, but if there are four colors, the area 12-1°12-
2. In addition to 12-3, the film thickness is the most jll, 'h
12-4 areas may be provided.

FIG. 3 shows a picture element structure whose main point is to improve sensitivity to only one color of short wavelength light. Here, the region 13-1 corresponds to a region that has a thin film thickness and receives short wavelength light, and the region 13-2, 13-3
have the same film thickness and are thicker than region 13-1, which corresponds to a region that receives light from intermediate wavelengths to long wavelengths. The device of this structure has the advantage that it is easier to manufacture, as will be explained later in the manufacturing process.

In FIGS. 2 and 3, thin regions (concave regions) and thick regions (convex regions) may be made smaller or larger than the dimensions of the picture element electrode. FIG. 4 shows an example of the structure shown in FIG. 2 in a plan view. FIG. L(b) corresponds to the case where the VX region 12-1 is made larger than the picture element electrode (therefore, the regions 12-2 and 12-3 become smaller than the picture element electrode).

FIG. 5 shows the manufacturing process of a solid-state imaging device having the structure of the present invention. Scanning IC substrate t constructed with MOS transistors or COD elements using normal MO8 process technology
(!I). Here, At or Mo is generally used for the picture element electrode 6 regardless of whether it is an MO8 type substrate or a CCD type substrate. Next, a photoconductive film is formed on the top of the main scanning IC. 7
' is deposited by glow discharge method or sputtering method to the thickness necessary for receiving direct wavelength light (the thickest film thickness) (b)
. Here, as the photoconductive material, 8e-Aa-Te, 8b, 8s, which are used in electron tubes for photography, are used.
, PbO.

Zn-Cd-Te, Cd8eTe-As, 8e, I, or amorphous silicon (S i :H), which has been developed as a material for solar cells, can be used.

Next, the thickest region of the photoconductive material gold (12
Etching is performed by a predetermined film thickness except for -3>'e, and the entire intermediate film thickness region (12-2 in FIG. 2) is formed (C). Furthermore, only the region corresponding to the thinnest film thickness is etched by a predetermined film thickness using a photoetching technique, thereby forming the thinnest film thickness region (12-1 in FIG. 2). Finally, the transparent electrode (
8nIt.

Ink, etc.) is deposited by sputtering or the like to complete the device fabrication (d). Here, if the photoconductive material film is made up of two regions, a thick region and a thin region, as in the example shown in FIG. The part excluding the area? Etching is performed by a predetermined thickness to form a thin region (13-1).

In addition to the above-mentioned methods, many other methods can be considered for the manufacturing process of this device, and the process shown in FIG. 6 is also practical. (Here, to simplify the explanation, the case of the embodiment shown in FIG. 3 will be described.) After depositing the photoconductive material 7'-1 with a predetermined thickness on the scanning IC substrate, the photoconductive material 7'-1 is first etched by photo-etching. Etch only the part corresponding to the thin area 13-1 (
a).

Further, a photoconductive material 7'-2 is deposited to a predetermined thickness over the entire surface, and finally a transparent electrode is deposited to complete the device fabrication (b). As a result, a thin region (13-1) determined by the second evaporation film thickness and a thick region (13-2, 13-3) determined by the sum of the first and second evaporation film thicknesses are formed. . Here, when amorphous silicon is used as the photoconductive material, the amount of hydrogen doped into the silicon is set to a different value during the first and second evaporation, and the doping during the second evaporation is If the amount is increased, thin areas (13
-1) The doping th increases. As a result, the band gap of the amorphous silicon in the thin region becomes larger, making it possible to further increase the sensitivity to short wavelength light.

As explained in detail using the embodiments above, the solid-state image sensor of the present invention can improve photosensitivity, especially the short wavelength sensitivity, which has been criticized as a problem with conventional elements, and can also achieve well-balanced spectral sensitivity. The practical value of the present invention is extremely high because it can be easily carried out by adding one or two photoetching steps to the existing process.

In addition, in the above embodiment, an MO8 field effect transistor was used as an element constituting the scanning IC substrate, but COD, BBD, or CI D (Char
The same structure as the present invention can also be applied when using GE Injection Dericea). Since the MOS process is used as the manufacturing technology for these elements as well, the method of forming the picture element electrode connected to the corresponding junction and its structure are exactly the same as in the above-described embodiments. Furthermore, a junction field effect transistor or a bipolar transistor can be used as a component of the scanning IC substrate without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a conventional solid-state image sensor, FIG. 2 is a diagram showing the main structure of the solid-state image sensor of the present invention, and FIG.
The figure shows an embodiment of the solid-state image sensing device of the present invention other than that shown in FIG. 2, FIG. 4 shows the planar configuration of the solid-state image sensing device of the present invention, and FIG. FIG. 6 is a diagram showing an example of the manufacturing process. FIG. 6 is a diagram showing another example of the manufacturing process of the solid-state image sensor of the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... MO8 field effect transistor, 3... Source, 4... Drain, 5... Kate, 6... Pixel electrode, 7.7'... Photoelectric conversion membrane,
..Transparent electrode, 9..Oxide film, 1o..Signal output line, 12-i. 12-2.12-3.12-4... area, 12...
Boundary, 13-1...Thin region, 13-2.13-3.
...Thick region. =354

Claims (1)

[Claims] 1. A switch equipped with two-dimensionally arranged picture element electrodes, and generation of the photocharges on the upper part of a scanning semiconductor substrate integrated with a scanning element that transfers photocharges corresponding to an optical image taken out through the switch. In a two-story solid-state GI device in which a photoconductive film for photoelectric conversion and a transparent electrode are laminated, the thickness of the photoconductive film is varied depending on the pixel area constituting the two-dimensional surface. 1. A solid-state gI element characterized in that each picture element region has a light sensitivity required for each picture element.