JPS6244696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device using a photoconductor layer.

Although solid-state imaging devices have characteristics such as being small, lightweight, and do not require high voltage, they have not yet achieved characteristics that can be put to practical use.

First, the principle of a conventional solid-state imaging device will be explained using FIG. A solid-state imaging device has a plurality of solid-state elements having a photoelectric conversion function and a signal storage function,
Each solid-state element corresponds to one pixel to form an imaging surface, and external video information is converted into electrical signals by sequentially scanning this imaging surface. In the example shown in FIG. 1, the pixels 14 are arranged in a matrix and read out one by one using the XY addressing method. Selection of each pixel is performed by a horizontal scanning signal generator 11 and a vertical scanning signal generator 12. 13 is a switch section connected to each pixel, and 5 is an output end.

Among solid-state imaging devices, a conventional example in which a photoconductor layer constituting an imaging surface is formed so as to cover a semiconductor substrate on which switches, scanning circuits, etc. are formed is, for example, disclosed in Japanese Patent Laid-Open No. 51-10715. Some have been reported in the official gazette.

The present invention provides a solid-state imaging device with extremely good characteristics by using the following photoconductor layer.

First, the structure of the photoconductor layer of the solid-state imaging device according to the present invention will be explained using FIGS. 7 and 8. FIG. 7 shows a cross-sectional view of the pixel portion of the solid-state imaging device of the present invention. on the semiconductor substrate 20
MOS type field effect transistors 21 to 31 are formed, and a photoconductor 37 is laminated thereon. The transistors are arranged in an array as shown in FIG. 8, and are sequentially switched on to extract optical signals accumulated in the photoconductor to the outside.

FIG. 9 is a component distribution diagram showing an example of the structure of the photoelectric conversion material layer of the solid-state imaging device according to the present invention. Part a in Figure 9 consists of a Se layer doped with at least one element selected from the group of elements that create a deep level in Te or Se. The amount of at least one of the elements added shall be less than 10 atomic percent on average for each added element.

However, if the lifespan is not that much of an issue, just
Se layer may also be used.

In addition, the elements that are thought to create deep levels in Se are at least one of Vb group elements such as As, Sb, and Bi, and IV group elements such as Si and Ge, or at least one of these elements. It may be one of the compounds included. Elements that create such deep levels act to minimize changes in signal current and to significantly reduce burn-in phenomena, especially when the device is operated continuously for a long time.

This part a usually has a film thickness of 0.5 to 10 μm, and has the effect of mainly allowing the holes generated in part c to travel, reducing the capacity of the photoconductor, and eliminating pinholes. . The film thickness of this a is
More preferably, it is 1 to 4 μm.

In part b of the figure, an additive (in this case As) that forms a deep level in Se is introduced to enhance the red sensitivity enhancement effect of Te contained in part c of the figure. This is a part for suppressing changes in signal current when operating for a long time. In order to effectively perform this action, the concentration of the additive that creates deep levels must be 15 atomic % at the peak position of the continuous concentration distribution (in Figure 9, the interface in contact with part c)
It is necessary that there be more than one. In addition, in practice, 40 atomic % or less is often used. In addition, the shape of the concentration distribution of the additive that creates the deep level in the part b of the same figure is c
It is desirable that the concentration is highest at the interface in contact with the part and decreases smoothly over 200 to 3000 Å as the distance from the interface increases. This layer is generally used in thicknesses between 100 Å and 5000 Å.

In the part shown in Figure 9c, in order to obtain sufficient sensitivity in the visible light region, the peak concentration of the continuous distribution of Te concentration must be 15 at.% or more, and particularly preferably 15 to 30 at.%. range. Further, it is desirable that the film thickness of this portion is 200 to 5000 Å.
Although the distribution of Te concentration in portion c in FIG. 9 is uniform and rectangular, the shape is not limited to this shape. The distribution may have a triangular, trapezoidal, semicircular, or even complex shape. In addition, in part c, the element that creates a deep level in Se coexists with Te in Se.

The portion d in FIG. 9 is a portion necessary for this film to contact the n-type transparent conductive film provided on top of the photoconductor layer to form a rectifying contact. In order to obtain a stable rectifying contact, the Te concentration in this part should not exceed 15 at% on average, and elements such as As and Ge added to increase thermal stability should also be added. Must not exceed 15 atomic percent on average. Further, the film thickness in this part needs to be 100 Å or more. Furthermore, if the lifespan is not so important, a simple Se layer may be used.

However, if it is made thicker than necessary, the amount of light incident on the portion c will decrease and the sensitivity will drop, so it is practically desirable that the thickness be 1000 Å or less.

As a result of the above, the film thickness of the entire portions a to d shown in FIG. 9 is about 0.5 to 10 μm, more preferably 1 to 4 μm.
It is about μm.

In the case of the present invention, the concentration distribution of Te, As, Ga, etc. may be grasped as a continuous distribution considered macroscopically, and the concentration may be controlled.

In the case of the photoconductive film described above, Se,
Using As ₂ Se ₃ , Te, Ge, etc., these evaporated materials are cyclically deposited in several thousand thin layers of several to tens of angstroms each on a deposition substrate using a rotary evaporation device. As a result, it is possible to obtain a film that has a macroscopically continuous distribution and exhibits a desired component ratio or component distribution.

In this case, the component ratio of the continuous distribution is defined as a composite layer consisting of the sum of each layer of one or more evaporates deposited cyclically, that is, one layer of rotary evaporation.
It is defined as the continuous distribution of average component ratios within a composite layer formed by a cycle.

The present invention will be explained in detail below with reference to Examples.

Embodiment 1 FIGS. 2 to 7 are cross-sectional views of a pixel portion showing a method of manufacturing a solid-state imaging device of the present invention. Switch circuits, scanning circuits, and the like formed on a semiconductor substrate are manufactured using normal semiconductor device processes. A thin layer of about 800 Å is placed on a p-type silicon substrate 20.
A SiO ₂ film is formed, and a layer of about 1400 Å is deposited on this SiO ₂ film.
Form a Si ₃ N ₄ film.

SiO ₂ film is made by normal CVD method, Si ₃ N ₄ film is made by Si ₃ N ₄ ,
A CVD method using NH ₄ and N ₂ was used. Next, the Si ₃ N ₄ film in the region where the oxide film 22 is to be formed is removed, and ion implantation is performed from above the silicon substrate using the remaining Si ₃ N ₄ film as a mask to form the p-diffusion region 21. . This diffusion area 2
1 was provided to better isolate each element.
Next, silicon is locally oxidized in an atmosphere of H ₂ :O ₂ =1:8 to form a SiO ₂ film 22 . This oxidation step is performed with the remaining Si ₃ N ₄ film still attached. Since oxidation does not proceed in the remaining region of the Si ₃ N ₄ film, the Si ₃ N ₄ film and SiO ₂
When the film is removed, the state shown in FIG. 2 is obtained. This method is a local oxidation method of silicon for element isolation, generally called LOCOS. After this, the gate insulating film of the MOS transistor is coated with SiO ₂
A gate portion 25 made of polysilicon is formed on this gate insulating film. Next, diffusion regions 26 and 27 are formed, and a SiO ₂ film 2 is further formed on top of the diffusion regions 26 and 27.
form 8. Then, holes for the electrodes of the source 26 and drain 27 are opened in this film by etching. FIG. 3 shows this state. As the drain electrode 29, Al is deposited to a thickness of 8000 Å. Furthermore, a SiO ₂ film 30 is formed to a thickness of 7500 Å, and then Al is deposited to a thickness of 1 μm as a source electrode 31. FIG. 4 is a sectional view showing this state. Note that the electrode 31 is connected to the area 26,
27, and was formed wide so as to cover the gate portion.
This is because if light enters the signal processing region between the element isolation diffusion layers 21, it will cause blooming, which is undesirable.

Further, a circuit such as a shift register is arranged around the light receiving area. In this way, the scanning circuit section is completed. A light receiving section is formed above this scanning circuit section. FIG. 8 shows a plan view of the Si substrate. 3
7 is a contact hole for an electrode. In the figures, parts with the same numbers as in the cross-sectional views indicate the same parts.

A Se--As layer 32 containing 5 atomic percent arsenic is formed to a thickness of 3 μm on the semiconductor substrate thus prepared. This is part a of the component distribution diagram in Figure 9.

As shown in FIG. 4, after the scanning circuit and the like are formed on the semiconductor substrate 20, the back surface of the semiconductor substrate has irregularities. Therefore, in this state, the surface of the Se--As layer is not flat, reflecting the unevenness of the IC substrate, as shown in FIG. Next, this substrate was heat-treated at 110° C. for 5 minutes in a nitrogen gas atmosphere. The Se
-The softening point of the As layer is about 70°C, so this heat treatment softens the layer and flattens it as shown in Figure 6. Note that the heat treatment temperature is preferably 50°C or higher. More preferably, the temperature is 80°C or higher and lower than the temperature at which the thin film material does not deteriorate. For amorphous materials containing Se as an essential constituent element, the temperature is actually preferably 120°C or lower. The atmosphere during heating may be nitrogen, rare gas, air, or the like.

Note that a preferred heating method is, for example, irradiation with a lamp (eg, a halogen lamp).

Flattening in this manner has the effect of preventing white scratches and the like from occurring on the TV monitor.

A second layer (portion b) made of Se and As is deposited on this first layer. When depositing the second layer,
Put Se, As ₂ Se ₃ into separate evaporation boards,
Evaporate at the same time. At this time, by controlling the current flowing through the As ₂ Se ₃ evaporation board, the As concentration is initially 5 atomic % and increases smoothly as the evaporation progresses, resulting in a third layer with a thickness of 500 to 1500 Å. The final part should have a concentration of 15 to 25 atom%. Next, Se and Te are simultaneously deposited from separate deposition boards to form the third layer (portion c).
Te is uniformly contained in the third layer, the thickness of the third layer is 500 to 2000 Å, and the Te concentration is 15 atomic % to 25 atomic %. On top of that, as the fourth layer (part d)
100Å to 500Å of Se containing 10 at% As
Deposit to a thickness of .

The above vapor deposition is performed in a vacuum of 3×10 ⁻⁶ Torr. It is preferable to insert a blocking layer such as a CeO ₂ film on top of this fourth layer. This produces the effect of blocking the flow of holes and can control dark current. Materials for this layer include Ce, Zn, Cd, B, Al,
Sc, Y, Si, Ge, Ti, Zr, Hf, Th, La, Sb,
A substance whose main component is an oxide of at least one element selected from the group consisting of Bi, V, Nb, Ta, Fe, U, W, and Mo is preferable. A typical example of this is
_CeO2 , CdO, _B2O2 , _{Sc2O3 , ZrO2} , _{ThO2 ,}
Fe ₂ O ₃ , Cr ₂ O ₃ , CoO, Co ₂ O ₃ , Pr ₂ O ₃ , Tc ₂ O ₃ ,
_ReO3 , MgO, _WO3 , _PbCrO4 , _{Nb2O3 , Ta2O3 ,}
Bi ₂ O ₃ , V ₂ O ₅ , Y ₂ O ₃ , HfO ₂ , La ₂ O ₃ , GeO ₂ ,
NiO, _Cu2O , _MnO , _U3O8 , BeO, _WO3 ,
Examples include Mo ₂ O ₅ , Al ₂ CoO ₄ , etc. The blocking layer is usually provided with a thickness of about 100 Å to 400 Å.

The blocking layer is not limited to this example, and can be widely used in the photoconductive layer of the present invention.

Next, a transparent electrode is formed to produce an amorphous film element. As the transparent electrode, an extremely thin film of gold or the like, or a transparent conductive film containing indium oxide or tin oxide, which can be formed at low temperatures, may be used. Further, a thin metal film or the like may be used as the light-transmitting electrode.

Finally, an ohmic contact conductor film 36 is provided on the other surface of the semiconductor substrate 20. Generally, the conductive film 36 is grounded through a terminal.

In addition, Cr--Au was deposited on a part of the transparent electrode using a mask, and this was used as a wire bonding bias electrode.

Although this embodiment shows an example in which the scanning circuit is composed of MOS field effect transistors, the present invention is not limited to this. For example, as a scanning circuit, CCD (Charge Coupled
Needless to say, a device using a transfer area (Device) may also be used. Of course, even if MOS transistors are used, other circuit systems may be used.

Embodiment 2 As in Embodiment 1, a switch circuit, a scanning circuit, etc. are formed on a predetermined semiconductor substrate. then
A Se-Ge layer (germanium content: 5 at%) is vacuum deposited while maintaining the substrate temperature at 60°C. Inside the vapor deposition equipment
Add heat treatment at 100℃ for 3 minutes. In this step, the surface of the photoconductive film is flattened.

Following this layer, Se and Ge are simultaneously deposited from separate deposition boards at a vacuum level of 3×10 ^-6 Torr. At this time, the Ge concentration is 5 at. % at the initial stage of deposition, increases smoothly as the deposition progresses, and when the thickness of this layer reaches 500 to 1500 Å, the Ge concentration is set to 20 to 25 at. %.

Next, Se and Te are deposited to form the c region of the photoconductive film. At this time, the Te concentration is 20 at the initial stage of deposition.
~25 atomic%, then decreases smoothly and the film thickness
At 1000 Å, the composition is controlled to be 0 to 5 atomic %.

Furthermore, a Se film containing 10 at% Ge is formed to a thickness of 300 Å as the d region of the photoconductive film.

As in Example 1, a transparent electrode is formed on a photoconductive film to produce an amorphous thin film element.

Note that Ge is an element that creates deep levels in Se.
Even if Sb, Bi, or Si is used instead of, the desired effect can be achieved. Further, these elements including As may coexist. Furthermore, Te may be used instead of an element that creates a deep level in Se, or Te and these elements may coexist.

As described using the above embodiments, according to the present invention, a solid-state imaging device with a high SN ratio and high image quality without blooming can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of a solid-state imaging device, FIGS. 2 to 7 are sectional views of main parts showing the manufacturing process of the solid-state imaging device of the present invention, and FIG. 8 is a solid-state imaging device in an embodiment of the present invention. FIG. 9, which is a plan view of the device, is a component distribution diagram showing an example of the structure of the photoelectric conversion material layer of the solid-state imaging device according to the present invention. 10...Horizontal scanning signal generator, 12...Vertical scanning signal generator, 13...Switch section, 14...Pixel, 15...Output end, 20...Semiconductor substrate, 2
6, 27...Diffusion region, 25...Gate electrode, 2
2, 28, 30... Insulating layer, 31... First conductive layer, 37... Photoconductive material layer, 35... Transparent electrode.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate having at least a scanning means for sequentially selecting a plurality of photoelectric conversion parts, a photoelectric conversion material layer on the top of this semiconductor substrate, and a transparent electrode on the top of this photoelectric conversion material layer. A solid-state imaging device including at least a photoelectric conversion section having
The photoelectric conversion material layer is (a) a Se layer doped with at least one of Te or an element that creates a deep level in Se, and the amount of the added Te element or the amount of the element in Se is (b) a first part in which the amount of at least one element that creates a deep level in Se is 10 atomic % or less on average per added element; an Se layer doped with at least one of the elements, in which the peak concentration of the continuous distribution of the at least one element that creates a deep level in the added Se is 15 atomic % or more (c) a Se layer doped with at least Te;
(d) at least one of the elements that creates a deep level in Te or Se; An added Se layer in which the amount of the added Te element or the amount of at least one element that creates a deep level in Se is 15 atomic % or less on average for each added element. A solid-state imaging device, characterized in that it is formed of at least a fourth portion as follows, and each of the above-mentioned portions are successively adjacent to each other.