JP3020563B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a stacked solid-state imaging device configured by laminating a photoconductive film on a solid-state imaging device chip, and in particular, relates to an optical The present invention relates to a solid-state imaging device in which a conductive film is improved.

(Prior Art) A solid-state imaging device having a two-story structure in which a photoconductive film is stacked on a solid-state imaging device chip can increase an opening area of a photosensitive portion, and thus has excellent characteristics of high sensitivity and low smear. Have. For this reason, this solid-state imaging device is expected to be applied to cameras such as various monitoring televisions and HDTV (High Definition Television). At present, an amorphous material film is used as a photoconductive film for this type of solid-state imaging device. For example, Se-As-Te film, ZnSe-Z
nCdTe film, a-Si: H film (hydrogenated amorphous silicon film)
And so on. Among these materials, an a-Si: H film is particularly preferred for reasons of good properties, good workability, low-temperature formation, and the like.

FIG. 1 is a cross-sectional view showing the schematic structure of this type of stacked solid-state imaging device. In the figure, 10 is a p-type Si substrate, 11 is a p ⁺ element isolation layer, 12n is a ⁺ vertical CCD channel, 13 is an n ⁺⁺ storage diode, 15a and 15b are transfer gate electrodes, 16 is a first insulating layer, and 17 is a pixel. Electrode wiring, 18 denotes a second insulating layer, 20 denotes a pixel electrode, 21 denotes a photoconductive film, and 22 denotes a transparent electrode. The photoconductive film 21 includes a hole injection blocking layer 21a, a photoelectric conversion layer 21b, and an electron injection blocking layer 21c.
It consists of.

FIG. 2 is an energy band diagram of the photoconductive film 21 at the time of imaging. The incident light from the transparent electrode 22 side is absorbed by the photoelectric conversion layer 21b to generate electron-hole pairs. The generated electrons and holes drift to the pixel side and the transparent electrode side. Of these, electrons are injected and stored as signal charges into the storage diode 13 via the pixel electrode 20 and the pixel electrode wiring 17, and thereafter, the vertical CCD 1
2, read via horizontal CCD.

Here, the hole injection blocking layer 21a and the photoelectric conversion layer 21b need to have high resistance in order to electrically separate the adjacent pixel electrodes 20, and usually use an i-type semiconductor film. In this case, in order to prevent hole injection from the pixel electrode 20, the band gap of the hole injection blocking layer 21a is larger than the band gap of the photoelectric conversion layer 21b. For example, the photoelectric conversion layer 21b
When a hydrogenated amorphous silicon (a-Si: H) film is used as the material, a hydrogenated amorphous silicon carbide (a-SiC: H) film and a hydrogenated amorphous silicon nitride (a- (SiN: H) film has been proposed (Japanese Patent Application No. 58-137594).

However, when the above-described i-type semiconductor film is used as the hole injection blocking layer 21a, the afterimage characteristic which is one of the important characteristics of the solid-state imaging device is deteriorated. The afterimage generated in the photoconductive film of the stacked solid-state imaging device is explained by the capture and thermal emission of signal charges at the localized level of the photoelectric conversion layer 21b. It is known to be proportional to the thickness (JGSimmons et a
l., Phys. Rev. B 7,3076 (1973)). Therefore, in order to improve the afterimage characteristics, it is conceivable to optimize the local level density and the film thickness of the photoelectric conversion layer 21b.

On the other hand, since the hole injection blocking layer 21a is a thin film that is only about 1/100 of the photoelectric conversion layer 21b, it has been considered that the localized level of the hole injection blocking layer 21a affects the afterimage characteristics. Was not considered. However, the localized level density of the wide gap material as the hole injection blocking layer 21a is generally higher than the localized level density of the a-Si: H film of the photoelectric conversion layer 21b. Hundred times. This time, as a result of our experiments, it has been clarified that an afterimage also occurs in the localized level of the hole injection blocking layer 21a by the same mechanism as that of the photoelectric conversion layer 21b.

(Problems to be Solved by the Invention) As described above, in the conventional stacked solid-state imaging device,
When a wide-gap i-type semiconductor film is used as a hole injection blocking layer in order to suppress an increase in dark current and image defects due to hole injection from a pixel electrode, an afterimage, which is one of the important characteristics of a solid-state imaging device, is used. There is a problem that characteristics are deteriorated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an i-type hydrogenated amorphous silicon having a wider gap than an i-type hydrogenated amorphous silicon (a-Si: H) film used as a photoelectric conversion layer. Silicon carbide (a
-SiC: H) film is used as a hole injection blocking layer to reduce the increase in dark current and image defects due to hole injection from the pixel electrode, and to improve the afterimage characteristics. It is to provide a device.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is an i-type hydrogenated amorphous silicon carbide (a) used as a hole injection blocking layer of a photoconductive film.
-SiC: H) film thickness and carbon content are optimized to maintain sufficient hole injection blocking layer capability on the valence band side, and dark current and image defects due to hole injection from pixel electrodes It is an object of the present invention to realize a photoconductive film structure in which the localization level in the hole injection blocking layer, which causes an afterimage, is kept at a sufficiently low density while suppressing a remarkable increase in the afterimage, and the afterimage value is kept at a low value.

That is, the present invention relates to a solid-state imaging device chip in which an array of signal charge storage diodes and a signal charge readout unit are formed on a semiconductor substrate, and a pixel electrode electrically connected to the signal charge storage diode is formed at the top. In a solid-state imaging device including a photoconductive film including an electron injection blocking layer, a photoelectric conversion layer, and a hole injection blocking layer stacked on the solid-state imaging device chip, and a transparent electrode formed on the photoconductive film, A hydrogenated amorphous silicon carbide (a-SiC: H) film is used as a hole injection blocking layer in the photoconductive film,
Further, the thickness d of the hydrogenated amorphous silicon carbide film is set in the range of 100 ° to 590 °, and the carbon content C is set to 9%.
% To 21%.

In the present invention, more preferably, the relationship between the film thickness d (Å) and the carbon content C (%) is set so as to satisfy C ≦ 189.2 × d− ^0.477 .

(Action) According to the present invention, the dark current is reduced by 3 as described later by defining the carbon content C and the film thickness d in the i-type amorphous silicon carbide (a-SiC: H) film serving as the hole injection blocking layer. × 10 ^-10 Acm ^-2 or less.
Field afterimage can be reduced to 1% or less. Therefore, it is possible to suppress an increase in dark current and image defects due to hole injection from the pixel electrode, and to improve afterimage characteristics.

(Examples) Before describing the examples, the thickness d and the carbon content C of the hole injection blocking layer defined in the present invention will be described.

First, in the structure shown in FIG. 1, amorphous silicon carbide (s-SiC:
H) The relationship between the film thickness and the dark current is as shown in FIG. From this figure, it can be seen that the dark current decreases as the film thickness increases, and that the dark current sharply increases as the film thickness decreases below 100 °. In addition, this property has a carbon content of 9%.
%, The dark current was sufficiently small and stable when the film thickness was 100 mm or more. Even when the carbon content was changed, the characteristic that the dark current increased sharply when the film thickness was 100 mm or less, and remained stable when the film thickness was 100 mm or more. The thickness of 100 mm is close to the optimum thickness that can be formed by the CVD method or the like. Therefore, in the present invention, the lower limit of the film thickness d is
Set to 100 mm.

The dark current depends not only on the film thickness d but also on the carbon content C. Therefore, the change in the dark current with respect to the carbon content C was measured. The result is shown in FIG. From this figure, the range of the carbon content C that is generally 3 × 10 ¹⁰ Acm ⁻² or less, which is generally accepted as dark current, is 4% or more and 37% or less. Note that this characteristic is obtained when the film thickness d is set to 200 °. However, when the film thickness d is in the range of 100 ° or more, the basic characteristics do not change even when the film thickness d is changed, and the carbon content C is 4% ≦ If C is in the range of 37%, the dark current can be made sufficiently small (3 × 10 ⁻¹⁰ Acm ⁻² or less).

The three-field afterimage value increases as the film thickness d increases, and increases as the carbon content C increases. Therefore,
3 for carbon content C when film thickness d is minimum (100 °)
Field afterimage values were measured, and three-field afterimage values were measured for the film thickness d when the carbon content C was the minimum (4%). The results are shown in FIGS. 5 and 6. From FIG. 5, it can be seen that in order to suppress the afterimage of three fields to 1% or less, the carbon content C may be reduced to 21% or less. Similarly, from FIG. 6, in order to suppress the afterimage of three fields to 1% or less,
It can be seen that the film thickness d should be 3200 ° or less.

On the other hand, the change in the dark current value with respect to the carbon content C becomes sharp in the region where the carbon content is 10% or less, as shown in FIG. 4, and there is a large variation in the dark current value in this region. When the dark current partially increases due to the variation of the dark current, an image defect called a so-called white defect occurs. The possibility of the occurrence of white flaws increases as the carbon content C decreases, and hardly occurs when the carbon content C increases. According to our experiments, the carbon content C
Was set to 9% or less, the occurrence of white scratches could be almost completely prevented. Considering this point, when the carbon content is 9%, the film thickness d
FIG. 7 shows the results of measuring the after-image values of three fields with respect to. From this figure, it can be seen that the upper limit of the film thickness d is 590 ° in order to surely eliminate white flaws and suppress the afterimage of 3 feet to 1% or less.

The dependence of the afterimage value on the localized state density N _SIC of the hole injection blocking layer is as shown in FIG. 8, where N _SIC ≧ 5 × 10
^In the region of ¹⁶ cm ^-3 , the afterimage value increases in proportion to _NSIC . From this figure, it can be seen that an afterimage is also generated in the hole injection blocking layer by the same mechanism as the photoelectric conversion layer. The relationship between the localized level density and the carbon content is as shown in FIG. 9. It is possible to control the localized level density of the hole injection layer by controlling the carbon content. It is.

From the following experimental results, it was found that the dark current was sufficiently small (3 × 10
^-10 Acm ^-2 or less) and to reduce the afterimage (1% or less), the thickness d of the amorphous silicon carbide (a-SiC: H) film serving as the hole injection blocking layer and the carbon concentration C are set as follows: 4% ≦ C ≦ 21% 100 ° ≦ d ≦ 3200 ° Further, in order to surely prevent white flaws, 9% ≦ C ≦ 21% 100 ° ≦ d ≦ 590 °. These results are shown together in the figure.
FIG. Strictly speaking, the dark current should be small (3 × 10
^-10 Acm ^-2 or less) and to reduce the afterimage (1% or less), it is necessary to make the area shown by hatching in FIG.
In order to prevent white flaws, it is necessary to set the areas shown by cross-hatching in FIG. 10. These ^areas may satisfy the conditions of C% ≦ 189.2 × (dÅ) ^−0.477 in addition to the above conditions.

Hereinafter, one embodiment of the present invention will be specifically described.
FIG. 1 is a cross-sectional view showing a schematic configuration of a stacked solid-state imaging device according to an embodiment of the present invention, in which an interline transfer CCD is used for a reading section.

If this is explained along the manufacturing process, first, a p-type Si substrate
A p ⁺ layer (element isolation region) 11, an n ⁺ layer (vertical CCD channel) 12 and an n ⁺⁺ layer (storage diode) 13 are formed on the surface layer 10. Furthermore, the substrate 10 is vertically placed on the substrate 10 with a gate insulating film interposed therebetween.
The transfer gate electrodes 15a and 15b of the CCD are formed. Next, after depositing the first insulating layer 16 thereon, a contact hole for electrical connection between the pixel electrode wiring 17 and the storage diode 13 is formed in the insulating layer 16. After the pixel electrode wiring 17 is formed, a second insulating layer 18 made of a BPSG film or a PSG film is formed for the purpose of planarizing the surface shape.
Then, a pixel contact hole is formed. Next, a pixel electrode 20 made of a metal such as Ti or Al or a metal silicide such as TiSi _X or MoSi _X is formed, and finally, for example, ITO is formed as a photoconductive film 21 and a transparent electrode 22. Hereinafter, the structure 21 of the photoconductive film will be described for an example in which an i-type a-Si: H film is used as the photoelectric conversion layer.

First, an i-type a-SiC: H film is formed as a hole injection blocking layer 21a.
0 °, and then an i-type a-Si: H film of 2 μm as the photoelectric conversion layer 21b.
m, and finally a p-type a-siC: H film as the electron injection blocking layer 21c.
Each is formed by a photo-CVD method at 200 °.

The conditions for forming the hole injection blocking layer 21a include, for example, silane (SiH ₄ ) and acetylene (C ₂ H ₂ ) as source gases, and helium (He) as carrier gases at 10 sccm and 3.6 scc, respectively.
At a flow rate of m, 100 sccm, it is mixed with mercury vapor and introduced into the CVD reaction chamber, and the pressure is set to 0.1 Torr. Heat the semiconductor substrate to 230 ° C, turn on the low-pressure mercury lamp as excitation light,
By irradiating the semiconductor substrate with vacuum ultraviolet light of m and 254 nm, an i-type a-SiC: H film serving as the hole injection layer 21a is formed.

In forming the i-type a-Si: H film as the photoelectric conversion layer 21b or the p-type a-SiC: H film as the electron injection blocking layer 21c, the conditions of the substrate temperature and the irradiation light are completely the same, The introduced gas and pressure are different. In forming the photoelectric conversion layer 21b, a SiH ₄ gas of 20 sccm is introduced, and the pressure is set to 0.2 Torr. In the formation of the electron injection blocking layer 21c, SiH
₄ Gas 10sccm, C ₂ H ₂ gas 0.5 sccm, diborane (B ₂ H ₆₎ gas 2s
ccm, He gas 100 sccm is introduced, and the pressure is set to 0.1 Torr.

In this embodiment, the i-type aS of the hole injection blocking layer 21a is
The carbon content of the iC: H film is 9 atomic%, and the band gap and activation energy are 1.93 eV and 0.97 eV, respectively. The carbon content can be controlled by the flow ratio of the gas introduced during film formation, and at the same time, the band gap and the activation energy can be controlled.

In this embodiment, the three-field afterimage value caused by the photoconductive film under the condition that the signal current is 2.6 × 10 ⁻⁷ Acm ⁻² and the electric field in the photoconductive film is 0.03 MVcm ⁻¹ is a very low value of 0.66%. Could be obtained. Further, no image defect caused by hole injection from the pixel electrode occurred, and the dark current value was 3 × 10 ⁻¹¹ Acm ⁻²
It showed a very low value.

The present invention is not limited to the embodiments described above. In the embodiment, the CCD image sensor is used.
The present invention can also be applied to a case where a D-type imaging element chip is used and a photoconductive film is stacked thereon. further,
The method of manufacturing the photoconductive film is not limited to the embodiment, but may be, for example, a plasma.
It may be formed by a CVD method or the like. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, the film thickness and carbon content of an i-type hydrogenated amorphous silicon carbide (a-SiC: H) film used as a hole injection element layer of a photoconductive film. By optimizing the amount, the hole injection blocking layer maintains a sufficient hole injection blocking ability on the valence band side, and suppresses a significant increase in hole injection from the pixel electrode. It is possible to greatly reduce the afterimage caused by the layer. Therefore, without increasing the dark current and image defects of the solid-state imaging device,
Afterimages can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of a solid-state imaging device according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing an energy band at the time of imaging a photoconductive film in the device, and FIGS. The figure is for explaining the film thickness d and the carbon content C of the hole injection blocking layer defined in the present invention. FIG. 3 is a characteristic diagram showing the relationship between the film thickness and the dark current, and FIG. FIG. 5 is a characteristic diagram showing the relationship between the carbon content and the dark current, FIG. 5 is a characteristic diagram showing the relationship between the carbon content and the afterimage, and FIG. 6 is a relationship between the film thickness and the afterimage when the carbon content is 4%. FIG. 7 is a characteristic diagram showing the relationship between the film thickness and the afterimage when the carbon content is 9%, and FIG.
FIG. 9 is a characteristic diagram showing the relationship between the localized level density and the afterimage. FIG. 9 is a characteristic diagram showing the relationship between the carbon content and the localized level density.
FIG. 10 is a schematic diagram showing the optimum ranges of the film thickness and the carbon content. 11 …… p-type Si substrate, 12 …… n ⁺ vertical CCD channel, 13 …… n ⁺⁺ storage diode, 15a, 15b …… transfer gate electrode, 16,18 …… insulating layer, 17 …… pixel electrode wiring, 20 pixel electrode, 21 photoconductive film, 21a hole injection blocking layer, 21b photoelectric conversion layer, 21c electron injection blocking layer, 22 transparent electrode.

────────────────────────────────────────────────── (5) References JP-A-63-144565 (JP, A) JP-A-55-127080 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/146

Claims (2)

(57) [Claims] An array of signal charge storage diodes and a signal charge read-out unit formed on a semiconductor substrate, and a solid-state image pickup device chip having a pixel electrode formed at an uppermost portion and electrically connected to the signal charge storage diode. A solid-state imaging device comprising: a photoconductive film including an electron injection blocking layer, a photoelectric conversion layer, and a hole injection blocking layer laminated on the solid-state imaging device chip; and a transparent electrode formed on the photoconductive film. Wherein a hydrogenated amorphous silicon carbide (a-SiC: H) film is used as a hole injection blocking layer in the photoconductive film, and the film thickness d of the hydrogenated amorphous silicon carbide film is
And a carbon content C is set as follows: 100 ° ≦ d ≦ 590 ° 9% ≦ C ≦ 21%. 2. The relationship between the thickness d (Å) of the hydrogenated amorphous silicon carbide film as the hole injection blocking layer and the carbon content C (%) is set to C ≦ 189.2 × d− ^0.477. The solid-state imaging device according to claim 1, wherein: