JPS6042666B2 - solid state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device, in which a photoelectric conversion layer includes a hole blocking layer and a heterojunction having high sensitivity in the entire visible light range, which is composed of (Znl-XCdJe)1-y(In2Te3)y. A self-scanning solid-state imaging device and an XY matrix type solid-state imaging device that uses a photoelectric conversion function and has a function of arranging a plurality of solid-state elements having a photoelectric conversion function as a unit of one pixel and further transferring a photoelectric conversion signal between the units. The present invention provides a solid-state imaging device.

Conventionally, photodiodes have been used as photodetectors, arranged in a matrix, and combined with field effect transistor circuits for XY scanning (hereinafter referred to as XY matrix type). Solid-state imaging devices have been proposed in which a photoconductor film is used in place of a photodiode in order to enlarge the image.

By the way, it is sometimes desirable for a solid-state imaging device to have a self-scanning function in which photoelectric conversion signals from photodetecting sections arranged in a matrix are sent to an external scanning circuit.

Self-scanning imaging devices include those based on BBD, CCD, etc., but all of them share a photodetection section and a signal charge transfer section, so the S/N ratio of the photoelectric conversion output signal is poor, and the incident light is It is absorbed by electrode parts such as polysilicon, resulting in a significant drop in blue sensitivity, which is a major drawback for color solid-state imaging devices. Recently, solid-state imaging devices that combine a photoconductor film and an element with a self-scanning function have been proposed in order to eliminate these drawbacks, but in this case, various characteristics such as photosensitivity are determined by the photoconductor film. Therefore, it is important to develop superior photoconductor films.

The present inventors previously developed a photoconductor with high sensitivity and excellent properties over the entire visible light range using a heterojunction of ZnSe and Znl-0CdJe, and have particularly attempted to apply it to image pickup tube targets (trademark). Newbicon).

In this case, the incident light enters from the high energy gap side on the ZnSe side, but if a p-type semiconductor substrate is used, due to its structure, the light needs to enter from the Znl-XCdOTe side, and the light enters from the Znl-XCdJd side. When it is incident, the blue sensitivity is particularly markedly reduced, making it unsuitable for color solid-state imaging devices. The present invention provides a solid-state imaging device with high sensitivity in the entire visible light range and an excellent S/N ratio by improving blue sensitivity and combining the rays with an element having a self-scanning function and an XY matrix type element. It is. DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an example showing the cross-sectional structure of one unit of a photoelectric conversion device in which the circuit elements formed on the Si substrate are of a charge transfer type.

A diode is provided by forming a dog-shaped region 11 in a p-type semiconductor substrate 10. Reference numeral 12 denotes a p+ type region, which is a potential barrier for blocking injection of electrons from the region 11 in the case of CCD operation.

13 is a potential well in the case of BBD operation in the chu region;
It is only necessary to install them for CCD and BBD respectively.

Although the CCD operation and the BBD operation basically involve the same charge transfer, the BBD operation with the n+ type region 13 will be explained below. 14 is a first gate, and n+ type region 11
It has an overlapping part.

Reference numeral 15 denotes an insulating film provided between the semiconductor substrate 10 and the first gate electrode 14.

16 and 17 are insulating films for separating the first electrode 18 from the semiconductor substrate 10 and the first electrode 18 from the first gate electrode 14, respectively.

The fourth electrode 18 is electrically connected to the n+ type region 11 and also serves as an electrode of the hole blocking layer 19. 20 is (Znl-XCdOTe)1-y(Ir)2Te3)y
A second electrode 21 is formed on the light incident side of the photoconductor, and is maintained at the same potential as the semiconductor substrate 10.

Note that a voltage ■φl may be applied to this electrode as shown by the dotted line. Here, the coupling capacitance CB formed by the semiconductor substrate 10 and the first gate electrode 14 via the insulating film 15 is different from the coupling capacitance CD formed by the n+ region 11 and the semiconductor substrate 10 and the hole blocking layer 19. , and the coupling capacitance C formed by the first electrode 18 and the second electrode 21 via a heterojunction made of the photoconductor 20. 22 is incident light.

Next, the optical information reading operation of the structure shown in FIG. 1 will be explained.

FIG. 2 shows the pulse pattern for driving this element and the potential change at the first electrode 18. When a read pulse CH is applied to the first gate electrode 14 at a certain time, the potential at the first electrode 18 becomes (
■. H-■T) is charged. Here, ■T is the threshold voltage of the FET composed of the thin regions 11 and 13 and the first gate electrode 14. Now, when light is incident from the electrode 21, (Znl-0CdJe)1-, (In2Te3
), electron-hole pairs are generated in the photoconductor 19, each reaching the electrodes 18 and 21, and the potential of the electrode 18 decreases. This potential drop is proportional to the amount of incident light and is accumulated for one field period, so the potential decreases to ■. Further, at time Illt2, when VCH is applied to the first gate electrode 14, the surface potential of the semiconductor therebelow increases, and as a result, electrons are injected from the n+ type region 11 to the n+ type region 13 and transferred to CI3. As a result, the voltage in the dog-shaped region 11 rises again and the implantation stops. At this time, the voltage of the square region 11 becomes (VCH-VT). Therefore, the injection stops when electrons equivalent to the charges lost due to discharge have moved to the storage capacitor, and therefore the total amount of charges moved to the storage capacitor CB corresponds to the illuminance of the incident light. Here, if the potential of the electrode 21 is biased to Vφ as shown by the dotted line in FIG. 1, even if there is strong incident light, the potential of the diode will not drop below ■φ, so blooming can be avoided. The above is an explanation of one unit of the solid-state device including the photodetector and the first gate electrode 14.
The means for sending out the photoelectric conversion signal read in the photoelectric conversion signal 3 to the output section by self-scanning will be explained below. Figure 3 is the first
This is a plan view when one unit of the solid-state element shown in the figure is arranged one-dimensionally, and a portion 23 surrounded by a dotted line indicates the one unit. Items in the same drawing that correspond to other drawing numbers have the same function. Second gate electrodes 24 and 26 are provided between first gate electrodes 14 and 25 included in adjacent units. Through the series of operations described above, the first gate electrode 14
By applying the positive transfer pulse shown in FIG. 2 to the second gate electrode 24, the charges read in are moved under the second gate electrode 24 in the form of charge transfer. Further, the charge that has moved below the second gate electrode 24 is transferred to 25 and 26 one after another based on the same principle, and is transferred to the output stage. In other words, the signal photoelectrically converted by the photodetector is converted into 2
The phase block signal can be sent to the output stage. A further feature of the present invention lies in the structure of the photodetector.

That is, as shown in FIG. 1, the structure includes a first electrode 18 electrically connected to an n+ type region 11, a heterojunction between a hole blocking layer 19 and a photoconductor 20 above the first electrode 18, and a heterojunction between the first electrode 18 and the photoconductor 20 above the first electrode 18, as shown in FIG. It consists of a second electrode 21. Next, an example of a method for manufacturing this photodetecting section will be described. A semiconductor substrate 10 having a transfer function as described above has a hole partially formed in the n+ type region 11, and other parts are covered with insulating layers 16 and 17. A first electrode 15 made of, for example, MO or Ta is formed thereon by electron beam evaporation or sputtering. This first electrode 18 is formed so as not to contact at least an adjacent unit element. Furthermore, a hole blocking layer 19 such as ZnO, ZnS, ZnSe, CdS, CdSe, etc. is formed on the substrate at a substrate temperature of 150 to 350 by vacuum evaporation or sputtering.
It is formed to a thickness of 0.1 to 1.0 pm at ℃. On top of that (Zn
O. 7CdO. 3Te). ．． 95(Ir]2Te3).
．． 05 is formed to a thickness of 0.5 to 4 μm at a substrate temperature of 100 to 350° C. by vacuum evaporation. This photoconductor also had CdTe formed to a thickness of 0.3 to 3.0 μm in the same manner as the above conditions in the first half, and (ZnTe) in the second half. ．． 99(In2Te3
). ．． 01 may be formed to have a thickness of 0.2 to 2.0 μm. The photoconductive film thus obtained was heated at 550°C in a vacuum.
A desired photoconductor film 20 can be formed by adding one layer of heat treatment.
is obtained. By forming the transparent electrode 21 thereon, the unit element of the present invention is obtained. Next, the operation of this photodetector will be explained.

The n+ type region 11 receives a positive voltage (■) due to the reading pulse.
o−■T) and the second electrode 21 is at zero potential, so the heterojunction is reverse biased. Now, Zn
O, ZnS, ZnSe, CdSe, etc. are the hole blocking layer 19, and the difference in dark current depending on the presence or absence of this hole blocking layer 19 is shown in FIG. A is the case with the hole blocking layer 19, and B is the case without the hole blocking layer 19, and a clear reduction in dark current can be seen. FIG. 8 shows the relationship between the blue sensitivity and the composition distribution in the film thickness direction when light is incident from the electrode 21 side. Figure 8a
The composition distribution in the film thickness direction was determined by the Augier analysis method, and shows the composition distribution from the light incident side.
As one goes from C to G, the average composition of CdTe increases and the gradient of the composition in the film thickness direction also increases. Figure 8b shows the measured blue sensitivity of the sample corresponding to a(7)C-G.For example, when looking at the applied voltage of 5V, the blue sensitivity is C
It can be seen that it increases as you go from G to G. C
Although the blue sensitivity also increases with voltage, the dark current increases accordingly, which is unfavorable in terms of S/N. Blue light has a large absorption coefficient, and samples E and F in Figure 8 (
7) The composition distribution below 0.3 μm is approximate, and 0.3
Although the composition distribution over μm differs greatly, in terms of blue sensitivity, E and F are almost the same, so 0.3 μm
It can be seen that the composition distribution below m is important. If the blue sensitivity is higher than Sample D, it is sufficiently superior to the case of only Si photodiode, so if the blue sensitivity of Sample D is set as the lower limit, the composition distribution condition for obtaining high blue sensitivity is that the average composition up to 0.3 μm is x≧0. .05 and X gradually decreases in the direction of light incidence. Further, in the case of x=1, the blue sensitivity is lower than that under the above conditions and the dark current also increases, so it was removed. However, even with compositions other than the above, unless the purpose is for color use, it is necessary to have sufficient sensitivity to white light and to have a proportion of the area of the photodetector in the conventional charge transfer type that forms a transfer stage. Therefore, the entire image area becomes 114 to 115, and defects such as a decrease in light utilization efficiency can be eliminated, which is particularly advantageous for low-illuminance imaging. Next, the characteristics of the photoconductor film according to the present invention and the characteristics of other photoconductor films are summarized in Table 1.

The present invention has better blue sensitivity than other photoconductor films and white light sensitivity and dark current similar to Nubicon. Furthermore, since this photoconductor film can also be formed on a conventional charge transfer electrode section, a solid-state imaging device with high areal light utilization efficiency and extremely high sensitivity can be obtained. FIG. 4 shows another embodiment of the present invention, and is an example showing the cross-sectional structure of one unit of a photoelectric conversion solid-state device when the circuit elements formed on a Si substrate are of an XY matrix type.

N+ regions 28 and 29 are provided on a p-type semiconductor substrate 27, and a gate electrode 34 is provided via an insulating layer 30 to form an FET. Here, 28 is a drain and an electrode 33 connects the adjacent element FE.
It is commonly connected to the drain of T and serves as a row selection line. Further, the gate electrode 34 is commonly connected to the gate electrode of the adjacent element FET, and serves as a column selection line. 29 is the source.

31 and 32 are insulating layers.

35 is an electrode electrically connected to the source 29 and an insulating layer 31
, 32.

36 is a hole blocking layer and 37 is (Znl-0Cd0Te)1
-9(Irl2Te3)y, on which a transparent electrode 38 is formed and kept at the same potential as the semiconductor substrate 27.

39 is incident light.

Next, the optical information reading operation shown in FIG. 4 will be explained using FIGS. 5 and 6. FIG. 5 shows a circuit configuration in which two unit elements of FIG. 4 are formed in each of the X and Y directions.
40 to 45 are FETs, and 46 is an output terminal.

FIG. 6 shows temporal changes in pulses applied from the XY scanning circuit. Lines Yl and Y2 shown in Figure 5
, Xl, and X2. Now line Y1
When the pulse shown in Figure 6 is applied to
42 and 43 are turned on. Furthermore, since a pulse is also applied to X1, FET4O becomes 0n, and Qll and Q''11 are reverse biased from the power supply ■1 through the load resistor RL. Here, Qll is a diode formed by the source 29 and the semiconductor substrate 27. Q″11 is the hole blocking layer 36 and (Zn
1-0Cd0Te)1-y(Irl2Te3)Y37.

Next, at time T1, FET4O is turned off and FET4O is turned off.
l becomes 0n. Therefore, the period from T1 to T2 is Q
l2, Q″1. is reverse biased. Similarly, from T2 to T
Q2l, Q″4 between T3 and Q2 between T3 and T4
2, Q″22 is reverse biased. On the other hand, e.g.
As shown in the figure, when light is incident on the diode Q''11, the anode potential of the diodes Q''11 and Qll becomes T depending on the amount of light. The potential is lower than the potential biased at T1. This amount of decrease is proportional to the amount of light and is accumulated for one field period. T in the period from T4 to T5. Since the FETs 4O and 42 are turned on in the same way as in the period T1, the electric charge that decreases in proportion to the amount of light is supplied from the power source 1 through the load resistor RL. Therefore, a potential change proportional to the amount of light is output to the output terminal 46. Similarly, by sequentially applying pulses, Q″1., Q12, Q″21, Q21
, Q''22, and Q22 can be taken out in time series.As described above, the present invention is capable of producing extremely high-density charge transfer type solid-state devices and XY matrix-type solid-state devices on semiconductor substrates. A device in which a heterojunction with high sensitivity and low dark current is formed makes it possible to provide a solid-state imaging device with a high SN ratio, high sensitivity, and little blooming.

Furthermore, the solid-state imaging device of the present invention can be formed into one-dimensional and two-dimensional structures, and in the case of one-dimensional structure, it can be applied as a sensor for facsimiles, etc. Due to its high sensitivity, the life of the light source can be extended; In the case of a two-dimensional device, it has many advantages, such as being able to capture images even at low illuminance as a solid-state imaging device, and having particularly high blue sensitivity, it is possible to reduce illumination when used as a solid-state color camera.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of one unit of a charge transfer type photoelectric conversion solid-state device according to an embodiment of the present invention, and FIGS. 2A and 2B are diagrams for explaining the operation of the embodiment of FIG. 1. Figure 3 showing the time relationship of clock pulses and potential changes of the photoconductor film.
The figure is a plan view of a structure in which one unit of the photoelectric conversion solid-state element shown in Figure 1 is arranged one-dimensionally to provide charge transfer, Figure 4 is a cross-sectional view of one unit of the XY matrix type photoelectric conversion solid-state element, and Figure 5 is the same circuit diagram, FIG. 6 is a diagram showing the time relationship of pulses to explain the operation of FIG. 5, and FIG. Characteristic diagrams showing the differences, FIGS. 8A and 8B, are composition distribution diagrams obtained by Auger analysis of the photoconductor film according to the present invention, and characteristic diagrams showing the voltage dependence of blue sensitivity. 10... p-type semiconductor substrate, 11, 13...
... Type-resistant region, 14... First gate electrode, 18
...First electrode, 19... Hole blocking layer, 2
0...Photoconductor, 21...Second electrode.

Claims (1)

[Scope of Claims] 1. An impurity region is formed in a semiconductor substrate, a scanning circuit for outputting a video signal accumulated in the impurity region is formed, an insulating layer is provided in a part of the impurity region, and the impurity region other part of the hole blocking layer and (Zn_1_-_x
Cd_xTe)_1_-_y(In_2Te_3)_y
What is claimed is: 1. A solid-state imaging device characterized by electrically joining a heterojunction consisting of: 2 Forming an n-type diode region on the p-type semiconductor substrate,
A first gate electrode is provided on the semiconductor substrate so as to have a portion overlapping the diode region via a first insulator layer, and a second gate electrode is provided so as to cover the first gate electrode.
a first electrode covering the second insulating layer and other surface portions and electrically coupled to the diode region; and a hole blocking layer on the first electrode. and (Zn_1_-_xCd_xTe)_1_-_y(I
A photoconductor layer made of a heterojunction with n_2Te_3)_y is provided, and a second electrode is further formed on this photoconductor layer to electrically connect the second electrode to the p-type semiconductor substrate. , a solid-state device including the diode region, the first gate electrode, and the photoconductor layer is set as one unit, a plurality of units are arranged, and a second gate electrode is arranged between the first gate electrodes of each adjacent unit. A solid-state imaging device comprising a gate electrode. 3. Forming an n-type source/drain region on a p-type semiconductor substrate, and arranging a gate electrode on the semiconductor substrate so as to have a portion overlapping the source/drain region via an insulating layer to form a field effect transistor. , an insulating layer is provided in a portion other than the source region, a first electrode electrically coupled to the source region is formed so as to cover this insulating layer, and a hole blocking layer and (Zn_1_ −_xCd_
xTe)_1_-_y(In_2Te_3)_y, a photoconductor layer consisting of a heterojunction is provided, and a second electrode is further formed on the photoconductor layer, and this second electrode and the p-type semiconductor substrate are connected. are electrically connected, a plurality of solid-state devices consisting of the field-effect transistor and the photoconductor layer are arranged as one unit, and the gate electrodes of the solid-state devices are commonly connected for each column to select a column. A line is obtained, the drain regions of the solid-state elements are commonly connected for each row to obtain a row selection line, and a video signal in each picture element is extracted by applying a predetermined scanning pulse to the column selection line and the row selection line. A solid-state imaging device characterized by: 4. In claim 1, the hole blocking layer comprises at least ZnO, ZnS, ZnSe, CdS, C
Solid-state imaging device using dSe. 5 In claim 1, (Zn_1_
-_xCd_xTe)_1_-_y(In_2Te_3
) A solid-state imaging device having a structure in which the average composition of _y with a film thickness of 0.3 μm or less from the second electrode side is 1.0>x≧0.05, and x gradually decreases toward the second electrode side.