JPS59148363A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To decrease the operating voltage and thus prevent the deterioration of the resolution by doping an amorphous hydrogenated Si photoconductive film with a chalcogen element. CONSTITUTION:An n<+> type region 11 is formed in a p type Si substrate 10 and decided as a diode region, and a gate electrode 15 is formed via an insulation layer 14 and then decided as a charge transfer stage which reads out signal charges in a vertical direction. A low melting point glass 16 is provided thereon, and the first electrode 17 made of Mo is formed. Then, the arrangement of Si single crystal with Se ion-implanted on Si polycrystal is decided as a target, the first layer amorphous hydrogenated Si 18 is formed at the discharge power of approx. 100W and the second layer one 19 at the discharge power of approx. 200W, further a clear electrode In2O3 20 is formed. Thereby, the operating voltage of the photoconductive film of amorphous hydrogenated Si can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device in which photoconductive films are laminated.

Conventional configuration and problems With the spread of home video recorders, the demand for video cameras is rapidly increasing, but solid-state imaging devices are
Because it has many characteristics such as small size, light weight, and low power consumption,
It is considered to be a favorite camera for home video recorders.

A solid-state imaging device (hereinafter referred to as a stacked solid-state imaging device), which has a structure in which a photoconductive film is layered on a semiconductor substrate with a signal scanning function, is more efficient in utilizing light than a solid-state imaging device made only of ordinary 81 semiconductors. Since the ratio is large, the sensitivity is high, and since the incident light is mostly absorbed by the photoconductive film, a smearing phenomenon that causes image deterioration occurs, which is characterized by a V-shape. . However, while the photoconductive film for a normal image pickup tube target is formed on a flat face plate, in the case of a stacked solid-state imaging device, it is formed on a semiconductor circuit board with a step metal. Many restrictions arise in the photoconductive film that needs to be formed.

The basic configuration of the stacked solid-state imaging device will be described below with reference to the drawings, and the drawbacks of the conventional technology will be described.

Figure 1 is a cross-sectional view of one pixel of a stacked solid-state imaging device when a CAN (charge-coupled device) is used in the signal scanning circuit, and Figure 2 is a cross-sectional view of one pixel of the solid-state imaging device shown in Figure 1. FIG. 7 is a plan view of a case where a plurality of one picture element are arranged. Further, FIG. 3 is an equivalent circuit diagram of one pixel of the solid-state imaging device having the configuration shown in FIG. 1.

In these figures, 012, in which a y1+ type region 11 is formed on a p-type S1 substrate 10 to serve as a diode region, is a charge transfer stage 2 for vertically reading out signal charges transferred from the diode region 11, and an insulating layer It is driven by a gate electrode 15 via a gate electrode 14. This gate electrode 15 is made of polycrystalline Si with a thickness of about 6,000 yen. The gate electrode 15 functions as a transfer electrode for vertically transferring signal charges, and also serves as a gate electrode for reading signal charges accumulated in the diode region 11 into the charge transfer stage 12. Reference numeral 17 denotes a first electrode for collecting signal charges generated in the photoconductive film 19 by the incident light 21, and is electrically connected to the diode region 11. The first electrode 17 and the gate electrode 15 are insulated by a low melting point glass layer 16 such as PS (20 mm), photoconductor 1
The transparent electrode is formed on the surface of the transparent electrode 9, and the incident light 21 enters from the transparent electrode 20 side.

In the solid-state imaging device having the above configuration, it is driven by CCDI'i two-phase drive. In this case, the maximum level difference for the photoconductive film 19 is a cross-sectional view taken along the line AB in FIG. 2, and there is a level difference of 1.0 to 1.2 μm. Further, the material of the first electrode 17 is Mo.

A metal containing Ta and W% is used, but in order to prevent incident light from reaching the Si substrate and causing a smearing phenomenon, it is necessary to have sufficient light-shielding properties, and the thickness is at least 1000 Å. In order to make each picture element independent, it is necessary to separate the first electrode 17 into a mosaic pattern, and a step also occurs in the separation section 22 of FIG. 1. These two types of steps increase the dark current of the photoconductive film 19 due to normal vapor deposition, and significantly lower the withstand voltage.

It has been proposed to use amorphous hydrogenated silicon as a photoconductive film that has low dark current and high photosensitivity even on a substrate with such steps. Since amorphous aqueous silicon is formed using a plasma CVD method, a reactive sputtering method, an ion blating method, etc., a film is formed in the same direction even on a substrate with steps, and has excellent step coverage. It is speculated that this is because the film is formed in the plasma and the constituent molecules fly in from various directions.

A disadvantage of using amorphous silicon hydride is the problem of balance between the maximum amount of signal charge generated in the photoconductive film 19 and the maximum amount of charge handled by the charge transfer stage 12.

This problem will be explained using the equivalent circuit diagram of one picture element in FIG. In FIG. 3, 31 denotes the first electrode 17 and the transparent electrode 20 (indicated by 20 & in FIG. 3).

Further, it is the capacitance of the photoconductive film 19 and the buffer layer 18 which are sandwiched between the gate electrode (indicated by 16&), and its size is expressed as ON. 32 is the capacitance of a diode formed between the p-type S1 substrate 1o and the n+ type region 11, and its size is expressed as Cs. 33 is a capacitance that is parasitically generated between the first electrode 17 and the gate electrode 16, and its size is expressed as Op. Further, 34 is referred to as a node, and its potential is hereinafter referred to as a node potential. Here, the node potential is the first electrode 17
□Equal to electric potential. At this time, the charge Qmax that can be accumulated per -picture element is Qmax:=(C
N+CP+O3), Δv=CT ΔV. where 07 =: CM-1-CP-1-C8
, which represents the total capacity. On the other hand, the maximum amount of charge handled per bucket 7) of the charge transfer stage 12 is Qma
Assuming x, there is no problem as long as Qmax l Qmax, but if Qmax ) Qmax, an afterimage phenomenon or an overflow phenomenon at the transfer stage will occur. The latter overflow phenomenon is a so-called blooming phenomenon.

In order to prevent this phenomenon, it is necessary to reduce the total capacity (=ON 10s -1-Op) or to lower the operating voltage of the photoconductive film 19. In particular, reducing the latter operating voltage is important in order to reduce the burden on the scanning circuit.

This low-voltage-operated amorphous hydrogenated silicon photoconductive film can be easily realized with a nip structure by plasma CVD, but there is a problem in terms of resolution. Although the reactive sputtering method has no problem with resolution, it has been difficult to realize amorphous hydrogenated silicon that can operate at low voltages.

Purpose of the Invention The purpose of the present invention is to fabricate a multilayer film with excellent characteristics by forming amorphous hydrogenated silicon having the above-mentioned excellent characteristics by a reactive sputtering method and using a photoconductive film that eliminates the drawbacks of high voltage operation. An object of the present invention is to provide a shape oscillating device.

When this photoconductive film is laminated, it can greatly improve the voltage resistance defects, afterimages, and blooming phenomena of the photoconductive film, which have hindered the practical use of laminated solid-state imaging devices, as described above, and also prevent burn-out. A solid-state imaging device with very little resolution degradation can be realized.

Structure of the present invention The present inventor uses a reactive sputtering method. It has been found that chalcogen elements such as S, Ss, and Te are effective as doping elements for lowering the operating voltage of amorphous hydrogenated silicon with excellent resolution. This photoconductive film can provide a photoconductive film with no reduction in resolution, a reduction in operating voltage, and excellent step coverage, and is suitable for use in stacked solid-state imaging devices.

In the present invention, in order to reduce dark current and operating voltage, the effect is even greater when amorphous silicon doped with a chalcogen element is used. This blocking layer can be realized by using a large amount of hydrogen, and has the advantage that it can be produced by reactive sputtering without introducing other elements.

An experimental example is shown in which a film was formed using a reactive sputtering method using an S1 crystal and a Se target in an Ar and H2 atmosphere.

Total pressure 6 x 10'T on MO substrate on S1 single crystal
orr.

10oW, 60 minutes, and 200W at hydrogen partial pressure 0.2,
Film formation was carried out in 90 minutes, and a transparent electrode of 111M square was formed.

Figure 4 shows the dark current value 4 when -10V is applied to the transparent electrode.
The dependence of the photocurrent saturation voltage 42 on the area ratio of 81 and Se 2 target when irradiated with light of 0.5 μW/c4 at wavelengths of 1 and 436 nm is shown. Since the photocurrent saturation voltage corresponds to the operating voltage, a low voltage is preferable.

Description of examples Examples of the present invention will be specifically described below.

Example 1 A low melting point glass 16 with a thickness of 1.0 μm or more is formed on a CCD using the n+ layer 11 as an opening.

The first electrode is made of MO with a thickness of 200 OA.

On top of this, an S1 single crystal in which Se was ion-implanted onto the S1 polycrystal was placed and used as a target, Ar, = 4.6
10'Torr H2=5X10'Torr is introduced, and amorphous hydrogenated silicon is formed by reactive sputtering. Substrate temperature 260℃, discharge power 300W
When formed for 70 minutes, the result is amorphous hydrogenated silicon with a thickness of 2 μm. A 100 OA transparent electrode layer N2O3 is formed on this by reactive sputtering to obtain the solid-state imaging device of the present invention having the cross-sectional structure shown in FIG.

An example in which only Si polycrystal is used as a target and is not doped with Se is also shown. If the applied voltage is not set above the voltage at which the signal current is saturated, burn-in will occur.

Therefore, whereas a voltage of 10 W or more was required, in this embodiment, 3 V is sufficient. However, the dark current that occurs when there is no light increases slightly.

The following example is the first electrode 17 on the CCD of Example 1.
The forming methods up to this point and the forming method of the transparent electrode 20 are the same, and a detailed explanation thereof will be omitted.

Actual example 2 As shown in Figure 6, two layers of amorphous hydrogenated silicon are used.
The first layer 18 is 0.2 μm with a discharge bar '7-100W, and the second layer 18 is
Layer 19 is formed with a thickness of 1.6 μm using a discharge puff of 200 W. The target used was one in which a polycrystalline S1 and an S1 single crystal doped with Ss were arranged as in Example 1. Figure 6 shows 435 nm, 0.5, cz at this time.
The dependence of photocurrent 61 and dark current 52 on applied voltage when W is irradiated with light is shown. For comparison, 1.5μm at 200W from the beginning
Photocurrent 63 and dark current 64 when amorphous hydrogenated silicon is formed are also shown. If there is a layer formed at 100W, the withstand voltage (
It can be seen that the white spot generation voltage) has improved. When only the discharge power is changed under the same conditions, lower power changes the hydrogen bonding state and increases the band gap. It is presumed that the amorphous hydrogenated silicon that was previously formed at 1oOW also functions to block hole injection.

Amorphous hydrogenated silicon a-8i formed with this 100W
:H instead of a S 1xC1x :H.

It was also effective for a-Si:H:O and a-3i:H:N.

It was still effective for ZnS and Zn5e.

Example 3 As shown in FIG. 7, [S
Targeting only polycrystals, Ar and N2 mixed gas pressure 6 x' 1O-3 Torr, N2 partial pressure 0.2 K
Then, the third layer of Si Hz 23 was formed at 30OA with a discharge power of 3KVV and a substrate temperature of 200'C, and later a transparent electrode 20
form. Figure 6 shows the photocurrent 55. Dark current 5
6 is shown. It can be seen from this that a low dark current can be achieved and the photoconductive film has a low operating voltage. A solid-state imaging device in which such a photoconductive film is formed on a CCD is
It has sufficient resolution, good blooming characteristics, and high sensitivity.

The hole injection blocking layer of Example 2.3 shows an example in which the discharge power is small, therefore the amount of hydrogen is large, and Ss is fully introduced as donor doping. However, other elements such as P may be used as the injection blocking layer. But it is possible.

In addition, the photoconductive layer is doped with Se, but S,
A similar effect was obtained with Te, although the amount was different.

Effects of the Invention The photoconductive film stacked solid-state imaging device of the present invention is formed by doping a photoconductive film with a chalcogen element using a reactive Nubatta method using amorphous hydrogenated silicon that operates at low voltage and has high resolution. . In addition, by providing a blocking layer,
Furthermore, efforts are being made to reduce dark current. By solving the problems in applying such amorphous hydrogenated silicon to solid-state imaging devices, we have obtained a photoconductive film that retains the features of high breakdown voltage and high sensitivity, and we hope to develop solid-state imaging devices with excellent blooming characteristics. realizable.

[Brief explanation of drawings]

Figures 1 and 2 are a cross-sectional view and a plan view of a stacked solid-state imaging plate, respectively. Figure 3 is an equivalent circuit diagram of one pixel, and Figure 4 is dark current and charging current saturation voltage Ss. Figures 5 and 7 are cross-sectional views of the respective embodiments of the present invention, and Figure 6 shows the light intensity of the photoconductive film used in the embodiments shown in Figures 6 and 7, respectively. Current, dark current characteristics
″--A cross-section diagram. 18...CC:D, 19...Photoconductive film, 28...Amorphous hydrogenated silicon with a large amount of hydrogen ,
23...5iNz. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Fig. 4 se/si (complementary to area ratio) Fig. 5 Fig. 6 Applied voltage LV Fig. 7

Claims (2)

[Claims] (1) Diode region and accumulation σ in the above diode region
a conductive substrate ``1'' covering the entire surface of a circuit element for scanning signal charges; an insulating film formed on the semiconductor substrate so as to have an opening in a part of the diode region; a first electrode formed on the insulating film for each unit pixel so that a part thereof is in contact with the diode region through the insulating film; and a chalcogen formed on the first layer and the insulating film. A solid-state imaging device characterized by having a photoconductive film whose main component is amorphous hydrogenated silicon containing elements, and a transparent electrode formed on the photoconductive film. (2) Mainly composed of hydrogenated silicon containing dozy impurities between the photoconductive film, the first electrode and the insulating layer (3) Hydrogenated silicon containing acceptor impurities between the photoconductive film and the transparent electrode (4) Semiconductor sound whose bandgap is larger than that of the photoconductive film, at least one between the photoconductive film and the first electrode and the insulating layer, or between the photoconductive film and the transparent electrode (6) Claim 1, characterized in that the photoconductive film is amorphous hydrogenated silicon formed by reactive sputtering using a target containing silicon as a main component.
The solid-state imaging device described in .