JPH08250698A - Solid-stat image sensor - Google Patents

Abstract

PURPOSE: To maintain excellent after-image characteristics even if pixel electrodes are microminiaturized by setting the ratio of the peripheral length to the flat surface area of the electrode to a specific value or more and specifying the edge of the electrode opposed to the photoelectric conversion film by the continuously changing surface. CONSTITUTION: A plurality of titanium pixel electrodes 20 are disposed on a second insulating layer 19 covering a signal charge storage region SD. The solid-stage image sensor comprises a photoelectric converting film 22 formed to cover the electrodes 20, and a counter electrode 23 formed on the film 22. The ratio WL,/SA of the peripheral length WL of the electrode 20 to the area SA is 0.67μm<-1> or more, and the edges ED1, ED2 of the electrodes 20 opposed to the film 22 are specified by the continuously changing surface. Thus, the edges ED1, ED2 of the electrode 20 are formed in a specific shape to eliminate the electric field concentration at the edges ED1, ED2, thereby improving the after-image characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly to a solid-state image pickup device in which a photoelectric conversion film is laminated on a signal charge storage region or the like.
The present invention relates to a solid-state imaging device having a floor structure.

[0002]

2. Description of the Related Art In recent years, a photoelectric conversion film has been replaced with a signal charge instead of a general solid-state image pickup device in which a light receiving and accumulating section, a signal charge reading section, and a signal charge transfer section are formed on a plane surface of a semiconductor substrate. A solid-state imaging device having a two-story structure stacked on a storage area or the like has been developed. The solid-state imaging device having this structure has the excellent characteristics of high sensitivity and low smear because the opening area of the photosensitive portion can be increased. Therefore, an HDTV (High
It is expected to be applied to definition televisions, personal computer image input cameras, consumer video cameras, and the like.

[0003]

However, in the solid-state image pickup device having the above structure, when the pixel electrode is miniaturized, the afterimage characteristic is deteriorated. Therefore, it is an object of the present invention to analyze the mechanism of deterioration of the afterimage characteristic and to provide a solid-state imaging device capable of maintaining a good afterimage characteristic even if the pixel electrode is miniaturized.

[0004]

A solid-state image pickup device according to a first aspect of the present invention is formed so as to cover a base layer, a plurality of pixel electrodes formed on the base layer, and the pixel electrodes. A photoelectric conversion film, and a counter electrode formed on the photoelectric conversion film. The peripheral length WL of the pixel electrode and the plane area S are provided.
The ratio WL / SA to A is 0.6 μm ⁻¹ or more, and the edge of the pixel electrode facing the photoelectric conversion film is defined by a continuously changing surface.

According to a second aspect of the present invention, there is provided a solid-state image pickup device, a base layer, a plurality of pixel electrodes formed on the base layer, and a photoelectric conversion film formed so as to cover the pixel electrodes. A counter electrode formed on the photoelectric conversion film, and a ratio WL of a peripheral length WL of the pixel electrode to a plane area SA.
/ SA is 0.6 μm ⁻¹ or more, and the edge of the pixel electrode facing the photoelectric conversion film is formed to have a radius of curvature, and the radius of curvature Rs and the film thickness T of the pixel electrode.
The ratio Rs / Ts with s is 0.25 or more.

According to a third aspect of the present invention, there is provided a solid-state image pickup device, a base layer, a plurality of pixel electrodes formed on the base layer, and a photoelectric conversion film formed so as to cover the pixel electrodes. A counter electrode formed on the photoelectric conversion film, and a ratio WL of a peripheral length WL of the pixel electrode to a plane area SA.
/ SA is 0.6 μm ⁻¹ or more, and the angle of the edge of the pixel electrode facing the photoelectric conversion film is 95 ° or more.

According to a fourth aspect of the present invention, there is provided a solid-state image pickup device, a base layer, a plurality of pixel electrodes formed on the base layer, and a photoelectric conversion film formed so as to cover the pixel electrodes. A counter electrode formed on the photoelectric conversion film, and a ratio WL of a peripheral length WL of the pixel electrode to a plane area SA.
/ SA is 0.6 μm ⁻¹ or more, the pixel electrode is substantially rectangular, and at least one of the four corners is formed to have a radius of curvature.
The ratio Rp / Lp of p to the length Lp of one side of the pixel electrode is 0.125 or more.

According to a fifth aspect of the present invention, there is provided a solid-state image pickup device, a base layer, a plurality of pixel electrodes formed on the base layer, and a photoelectric conversion film formed so as to cover the pixel electrodes. A counter electrode formed on the photoelectric conversion film, and a ratio WL of a peripheral length WL of the pixel electrode to a plane area SA.
/ SA is 0.6 μm ⁻¹ or more, the distance between the pixel electrodes is 1.0 μm or less, and the thickness of the photoelectric conversion film is 1.6 μm or less.

According to a sixth aspect of the present invention, there is provided a solid-state image pickup device, a base layer, a plurality of pixel electrodes formed on the base layer, and a photoelectric conversion film formed so as to cover the pixel electrodes. A counter electrode formed on the photoelectric conversion film, and a ratio WL of a peripheral length WL of the pixel electrode to a plane area SA.
/ SA is 0.6 μm ⁻¹ or more, a groove is formed in the base film between the pixel electrodes, and a ratio Ds / Ts of the depth Ds of the groove and the pixel electrode thickness Ts is 0.2. 1.0 or more
It is characterized by the following.

[0010]

According to the solid-state image pickup device according to the first to third aspects of the present invention, the electric field concentration at the upper edge appearing in the vertical sectional side view of the pixel electrode is eliminated, whereby the afterimage characteristic can be improved. Become. Here, the upper edge appearing in the vertical side view is an edge formed facing the photoelectric conversion film at the end portion of the pixel electrode or an edge formed facing the photoelectric conversion film at the stepped portion and the concave portion of the pixel electrode. Means

According to the solid-state imaging device of the fourth aspect of the present invention, electric field concentration at at least one of the four corners appearing in the plan view of the pixel electrode is eliminated, thereby improving afterimage characteristics. Is possible.

According to the solid-state image pickup device of the fifth aspect of the present invention, it is possible to improve the afterimage characteristic by lowering the electric field intensity in the photoelectric conversion film, particularly in the position corresponding to the end portion of the pixel electrode. Becomes

According to the solid-state imaging device of the sixth aspect of the present invention, the electric field concentration at the lower edge of the end of the pixel electrode, the lower edge of the end of the pixel electrode, and the defect line in the photoelectric conversion film are caused. It is possible to optimally adjust the trade-off relationship with the relative position of, and it is possible to improve the afterimage characteristic.

[0014]

The present invention will be described in detail below with reference to the illustrated embodiments.

FIG. 1 is a schematic sectional view showing a solid-state image pickup device according to the first embodiment of the present invention. In the figure, 11 indicates a p-type silicon substrate which is a semiconductor substrate. Above the p-type silicon substrate 11, a p + type element isolation layer 12, an n- type diffusion layer 13 for forming a storage diode SD which is a signal charge storage region, and a vertical CCD channel which is a signal charge transfer region. An n-type diffusion layer 14 for forming TC is formed. The area between the storage diode and the vertical CCD channel, that is, the area between the diffusion layers 13 and 14 corresponds to the signal charge reading region RO. Transfer electrodes 16 and 17 are formed on the p-type silicon substrate 11 via the first insulating layer 15 in the vertical CCD channel TC and the signal charge reading region RO. The transfer electrodes 16 and 17 transfer the charges from the signal charge storage region SD in which the charges generated in the photoelectric conversion film are stored to the signal charge transfer region TC.

The first insulating layer 15 is a vertical CCD channel T.
C, signal charge reading region RO, and storage diode S
It is formed so as to cover a part of D. First insulating layer 15
The extraction electrode 18 is formed along the line. A second insulating layer 19 is formed on the lead electrode 18. Further, the lead electrode 18 and the second insulating layer 19 have a thickness of 1 nm to
The pixel electrode 20 of 1000 nm is formed, and the extraction electrode 18 and the pixel electrode 20 are electrically connected.

In FIG. 1, the transfer electrode 16 of the adjacent pixel is
b, the extraction electrode 18b, and the pixel electrode 20b are also shown.

A photoelectric conversion film 22 is formed on the pixel electrode 20. Furthermore, for example, ITO is formed on the photoelectric conversion film 22.
A transparent counter electrode 23 is formed. The photoelectric conversion film 22 has a thickness of 1 nm to 1 nm in order from the pixel electrode 20 side.
100 nm i-type hydrogenated a-SiC layer 24, thickness 50
0 nm to 5000 nm i-type hydrogenated a-Si layer 25,
P-type hydrogenated a-SiC layer 2 having a thickness of 1 nm to 100 nm
It is configured by laminating 6 layers. i-type hydrogenation a
The -SiC layer 25 can be formed by a high frequency glow discharge decomposition method, a mercury-sensitized photo-assisted CVD method, or the like.

The solid-state image pickup device according to the first embodiment is characterized in that the electric field concentration at the edge of the pixel electrode 20 is eliminated and the afterimage characteristic is improved. Here, the edge of the pixel electrode 20 means not only the upper edge that appears in the vertical side view of the electrode 20 but also the edge that appears in the plan view of the electrode 20. The upper edge appearing in the vertical side view is the edge ED1 formed at the end of the pixel electrode 20 on the side facing the photoelectric conversion film 22, that is, the edge ED2 formed at the stepped portion and the concave portion of the electrode 20 on the upper side. Can be mentioned. In the edge ED2 in FIG. 1, the pixel electrode 20 is the extraction electrode 1
It is formed so as to surround the concave portion generated for contacting with 8. As the edges appearing in the plan view, mainly when the pixel electrode 20 is rectangular, the four corners, that is, the edges formed on the outer contour can be mentioned.

Next, the influence of the edge of the pixel electrode 20 on the amount of afterimage will be described.

The graph of FIG. 3 shows the results of examining the afterimage characteristics of two samples A and B having different pixel electrode shapes. Here, in the sample A, as shown in FIG. 2A, the pixel electrode is composed of a single electrode 20. Sample B has a plurality of pixel electrodes 20m, as shown in FIG.
The upper edge ED is approximately 90 degrees.
It can be seen from FIG. 3 that Sample B has a larger afterimage amount, which is an important characteristic in the solid-state imaging device, than Sample A.

The graphs of FIGS. 4 (a) and 4 (b) show the calculation results obtained by simulating the electric field intensity distributions in the photoelectric conversion films of Sample A and Sample B, respectively. FIG.
As can be seen by comparing (a) and (b), sample B
The electric field strength at the upper edge of the end portion of the pixel electrode is estimated to be about twice the electric field strength at the pixel electrode of sample A. This result is in excellent agreement with the increase in the afterimage amount that occurs at -14V in sample A and at -7V in sample B.

The graph of FIG. 5 shows the results of examining changes in afterimage currents of Sample A and Sample B with time. It can be seen from FIG. 5 that Sample B is much slower in reducing the afterimage current than Sample A. The graph in Figure 6 is
The results of investigating the change with time of the afterimage current by changing the strength of the electric field using only the sample A are shown. In FIG. 6, a characteristic line F1 shows the case where 1V is applied between the pixel electrode and the transparent counter electrode, and a characteristic line F2 shows the case where 20V is applied between the pixel electrode and the transparent counter electrode. When the electric field is strong, as observed in the sample B (see FIG. 5), the afterimage current decreases very slowly. From this, it is considered that the cause of the increase in the afterimage amount in the sample B is the electric field concentration at the edge ED at the end of the pixel electrode.

The concentration of the electric field at the edge of the pixel electrode is an important problem in the stacked type solid-state image pickup device. The ratio of the area affected by the electric field concentration at the end of the pixel electrode to the entire pixel electrode increases as the area of one pixel decreases. Therefore, the effect of increasing the amount of afterimage due to the electric field concentration at the end of the pixel electrode becomes more remarkable as the area of one pixel becomes smaller.

The graph of FIG. 7 shows the results of examining the relationship between the peripheral length / planar area of the pixel electrode and the amount of afterimage. Here, as the pixel electrode, as shown in the figure as an inset image, an electrode having a square shape with one side length L was used. In FIG. 7, the characteristic line F4 shows the characteristic when the angles of the upper edge of the end of the pixel electrode appearing in the vertical side view and the edges of the four corners of the pixel electrode appearing in the plan view are both approximately 90 degrees. The amount of afterimage after three fields is set to 0.4 as a criterion for the limit that people do not feel afterimage.
% Or less, in order to realize this, in the characteristic line F4, the pixel electrode peripheral length WL = 4L and the pixel electrode flat area SA =
The ratio WL / SA with L ² needs to be 0.6 μm ⁻¹ or less. That is, in the solid-state imaging device having such characteristics, it is difficult to miniaturize the pixels in consideration of the deterioration of the afterimage characteristics,
This is a major impediment to increasing the pixel density.

Further, in the solid-state image pickup device having a two-story structure in which the photoelectric conversion film 22 as shown in FIG. 1 is laminated on the signal charge storage region SD and the like, the pixel electrode 20 and the signal charge storage region S are formed.
Since it is connected to the D lead-out electrode 18, there is a pixel contact portion. Therefore, the step portion or the concave portion is generated in the pixel electrode 20 as described above, and the upper edge (edge ED2 in FIG. 1) is also formed here. Even at such an edge, the electric field is concentrated as in the case of the upper edge of the electrode end portion, and the amount of afterimage is increased.

Similarly, in a pixel electrode having a rectangular plane shape as shown in the inset image of FIG. 7, four corners of the electrode appearing in the plan view are edges. Even with such an edge, the electric field is concentrated and the amount of afterimage is increased similarly to the edge appearing in the vertical side view. Further, in this case, the ratio of the area affected by the electric field concentration at the four corners of the pixel electrode to the entire pixel electrode increases as the area of one pixel decreases. Therefore, the effect of increasing the amount of afterimage due to the electric field concentration at the four corners of the pixel electrode becomes more remarkable as the area of one pixel becomes smaller.

Next, the shape of the edge of the pixel electrode 20 according to the first embodiment and its condition will be described.

FIG. 8A shows the vertical cross-sectional shape of the upper edge EDs at the end of the pixel electrode 20. Edge EDs here
Is formed to have a radius of curvature Rs in order to suppress an afterimage. The graph of FIG. 8B shows the results of examining the relationship between the ratio Rs / Ts of the radius of curvature Rs and the film thickness Ts of the pixel electrode 20 and the amount of afterimage. From FIG. 8 (b), the ratio Rs / T
It can be seen that if s is set to 0.25 or more, the afterimage amount after three fields can be 0.4% or less (a standard of the limit at which a person does not feel an afterimage).

FIG. 9A shows a modification of the vertical cross-sectional shape of the upper edge EDs at the end of the pixel electrode 20. Here, since the edge EDs suppresses the afterimage, the two edges EDs are
1, EDs2, and the angles θ1, θ2 of each edge,
That is, the inside angle formed by the two sides sandwiching the edge is formed to be an obtuse angle. The graph of FIG. 9B shows the result of examining the relationship between the edge angle θ and the amount of afterimage. From FIG. 9B, it can be seen that if the edge angle θ is 95 degrees or more, the afterimage amount after three fields can be 0.4% or less.

FIG. 10A shows a pixel electrode 2 having a substantially rectangular shape.
The planar shape of the edge EDp at the four corners of 0 is shown. Here, the edge EDp is formed to have a radius of curvature Rp in order to suppress an afterimage. The graph of FIG. 10B shows the ratio Rp of the radius of curvature Rp and the length Lp of one side of the pixel electrode 20.
The result of having investigated the relationship between / Lp and the amount of afterimage is shown. Figure 10
From (b), if the ratio Rp / Lp is 0.125 or more,
It can be seen that the afterimage amount after three fields can be reduced to 0.4% or less.

FIGS. 11A to 11D sequentially show an etching process for forming the upper edge EDs at the end of the pixel electrode 20 as shown in FIG. 8A or 9A. Here, the pixel electrode 20 is formed of a titanium film 30, and the second insulating layer 19 is formed of a silicon oxide film 31.

First, as shown in FIG. 11A, a titanium film 30 is formed on the silicon oxide film 31 by a sputtering method or a vapor deposition method. The thickness of the titanium film 30 is 1 nm to 1
000 nm. At this time, in the upper portion 33 of the titanium film 30 for which the radius of curvature Rs is desired, the film forming conditions are changed so that the density of titanium is lower than that of the lower portion 32.

Next, a resist film 34 is formed by coating on the titanium film 30, and an exposure process is performed to form a predetermined pattern on the resist film 34 as shown in FIG. 11B. Next, in the RIE apparatus, the titanium film 30 is etched using a mixed gas of BC1 ₃ and Cl ₂ as shown in FIG. 11C.

Since the titanium film 30 has different titanium densities between the upper portion 33 and the lower portion 32, the upper portion 33 is etched earlier. Therefore, the upper edge of the titanium film 30 has a curved shape or a tapered shape, and the upper edge of FIG.
An upper edge as shown in (a) can be formed. After the etching, as shown in FIG. 11D, the resist film 34 is removed using a stripping solution.

The characteristic line F3 in the graph of FIG. 7 shows the result of examining the relationship between the peripheral length / planar area of the pixel electrode of the pixel electrode 20 thus formed and the amount of afterimage. Here, the upper edge of the end portion of the pixel electrode 20 that appears in the vertical side view has a radius of curvature, and the ratio Rs / Ts between the radius of curvature Rs and the film thickness Ts of the pixel electrode 20 was approximately 0.5. The plane shape of the pixel electrode 20 is a substantially square shape with one side length L as shown in the inset image in FIG. 7, and the curvature radii of the four corner edges of the pixel electrode appearing in the plan view are The angle was approximately zero and the angle was approximately 90 degrees.

As shown by the characteristic line F3 in FIG. 7, in the pixel electrode 20 according to the present invention, the pixel electrode peripheral length WL = 4.
The ratio WL / SA between L and the pixel electrode plane area SA = L ² is 0.
Even after 6 μm ⁻¹ or more, the amount of afterimage after 3 fields could be 0.4% or less (the standard of the limit that humans do not feel afterimage). By the way, L = 1 (μm), 4L / L ² = 4.0
At (μm ⁻¹ ), the sample according to the present invention achieved an afterimage amount of 0.3%.

Although the formation method using the titanium film 30 having a substantially two-layer structure has been described with reference to FIGS. 11A to 11D, the same formation is performed even when the titanium film 30 has a three-layer structure or more. The method is applicable. For example, when the titanium film 30 has a three-layer structure, a pixel electrode having an upper edge inclined in a polygonal shape as shown in FIG. 12 can also be formed. As a result, the characteristics shown in FIG. 7 are further improved,
Low afterimage is realized.

In order to form the edge EDs of the pixel electrode 20 as shown in FIG. 8A or FIG. 9A, a method using a positive type resist is adopted as shown in FIG. You can also

Since the positive type resist has weak adhesion to titanium, a slight gap can be provided between the resist film 34 and the titanium film 30 in the vicinity of the opening where the resist is removed. Therefore, when the titanium film is etched in the RIE apparatus B using a mixed gas of Cl ₃ and Cl ₂ , the upper portion of the titanium film 20 is etched through the gap between the resist film 34 and the titanium film 30. Therefore, a pixel electrode having a curved or tapered upper edge at its end is obtained.

Further, as shown in FIGS. 14A to 14D, a silicon oxide film (Si
Even if the O ₂ ) film 35 is used as a base layer, the edge EDs of the pixel electrode 20 as shown in FIG. 8A or 9A is obtained.
Can be formed.

First, as shown in FIG. 14A, SiO
_{2 The} titanium film 3 is formed on the film 35 by using a sputtering method or a vapor deposition method.
Form 0. The thickness of the titanium film 30 is 1 nm to 100
It is set to 0 nm. Next, a resist film 34 is formed on the titanium film 30.
Is formed by coating, and an exposure process is performed to form a predetermined pattern on the resist film 34 as shown in FIG. Next, in the RIE apparatus, the titanium film 30 is etched using a mixed gas of BC1 ₃ and Cl ₂ as shown in FIG.

The undoped SiO ₂ film 35 has a high resistance to a mixed gas of BC1 ₃ and Cl ₂ which is an etching gas for the titanium film 30. Therefore, when the etching of the titanium film 30 progresses and the surface of the SiO ₂ film 35 is exposed, an undercut occurs in the titanium film 30 under the resist film 34. Therefore, a pixel electrode having a curved or tapered edge at its end can be obtained. After etching,
As shown in FIG. 14D, the resist film 34 is removed using a stripping solution.

By over-etching the resist film, a tapered edge can be formed on the upper end of the titanium electrode. Also, as a simple method, CD
An apparatus capable of performing isotropic etching such as E or Asher may be used. In this case, the isotropic etching causes an undercut in the titanium film under the resist film, and a tapered edge can be formed at the upper end of the titanium electrode.

The pixel electrode 20 as shown in FIG.
In order to form the rounded edges EDp at the four corners, a positive electrode resist is used to form the pixel electrode pattern. At this time, by setting the exposure time to the over-exposure condition, it is possible to give the four corners of the resist film pattern itself that defines the pixel electrode shape a radius of curvature. Therefore, if the titanium film is etched using such a resist film pattern as a mask, pixel electrodes having sufficient radii of curvature at the four corners can be obtained.

As described above, according to the solid-state image pickup device of the first embodiment, the edge of the pixel electrode 20 is processed into a specific shape to eliminate the electric field concentration at the edge.
It is possible to improve the afterimage characteristic.

Next, a solid-state image pickup device according to the second embodiment of the present invention will be described. The outline of the side view of the solid-state imaging device according to the second embodiment is substantially the same as that of the solid-state imaging device according to the second embodiment shown in FIG. 1, and therefore the illustration is omitted by incorporating FIG. The second embodiment is characterized in that the afterimage characteristic is improved by specifying the relationship between the thickness of the photoelectric conversion film 22 and the distance between the pixel electrodes 20.

As described above, the photoelectric conversion film 22 is made of a-Si.
It is composed of an amorphous material such as C or a-Si. There are many defects in which the bonds of silicon are broken in the amorphous material, and these bond defects act as traps for electrons and holes. Therefore, there occurs a phenomenon in which electrons and holes generated by photoelectric conversion are temporarily captured by this defect before reaching the pixel electrode 20 and slowly come out later with a delay, which causes a residual image. .

The thickness of the photoelectric conversion film in the current solid-state image pickup device is about 2 μm, but there is a demand to reduce the film thickness of the photoelectric conversion film in order to reduce the total defect amount and the afterimage amount. However, when the film thickness is reduced, the electric field applied to the film becomes stronger, which causes a problem that the amount of afterimage increases. This is an afterimage characteristic to the electric field peculiar to the photoelectric conversion film, and is development accompanied by the injection of holes from the pixel electrode side.

As shown in the graph of FIG. 4B, the electric field strength in the photoelectric conversion film 22 is the strongest in the portion corresponding to the edge of the end portion of the pixel electrode. The graph of FIG. 15 shows the results of examining the relationship between the thickness of the photoelectric conversion film 22 and the electric field strength when the distance between two adjacent pixel electrodes 20 is used as a parameter. In FIG. 15, characteristic lines F5 and F
6, F7 and F8 have a distance between the pixel electrodes of 1.2 μm, respectively.
The characteristics when m, 1.0 μm, 0.6 μm, and 0.3 μm are shown.

From FIG. 15, to reduce the electric field strength,
It can be seen that it is sufficient to reduce the distance between the pixel electrodes. It is also understood that in order to reduce the electric field strength, the interval between the pixel electrodes may be set shorter in accordance with the decrease in the film thickness of the photoelectric conversion film 22. In order for the solid-state imaging device to exhibit good afterimage characteristics, the electric field strength in the photoelectric conversion film 22 is 7 × 10 ⁴ V.
/ Cm or less is desirable. That is, the photoelectric conversion film 2
When the film thickness of 2 is 1.6 μm, the distance between the pixel electrodes may be 1.0 μm or less. When the film thickness of the photoelectric conversion film 22 is 0.6 μm, the distance between the pixel electrodes is 0. 0.3 μm
You can do the following:

As described above, according to the solid-state image pickup device of the second embodiment, the electric field strength in the photoelectric conversion film 22 is lowered by specifying the relationship between the thickness of the photoelectric conversion film 22 and the interval between the pixel electrodes 20. By doing so, it is possible to improve the afterimage characteristics. In addition, the radius of curvature of the upper edge of the end portion of the pixel electrode is set to
By setting the range as described in the embodiment, it is possible to further improve the afterimage characteristic.

Next, a solid-state image pickup device according to the third embodiment of the present invention will be described. FIG. 16 is a schematic sectional view showing a solid-state imaging device according to the third embodiment of the present invention. In FIG.
Portions corresponding to those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the third embodiment, the pixel electrode 2
The afterimage characteristic is improved by specifying the relationship between the thickness of 0 and the depth of the groove formed in the second insulating layer 19 between the pixel electrodes 20.

As described above, in order to form the pixel electrode, R
The titanium film is etched by the mixed gas of BCl ₃ and Cl ₂ in the IE apparatus. At this time, the second underlayer
The insulating layer 19 is etched to form a groove. FIG. 17
In (a), the groove 27 formed in the second insulating layer 19 between the electrodes 20 is enlarged and shown. It has been clarified that such a groove 27 enhances the electric field strength at the lower edge of the electrode end portion.

In the graph of FIG. 18, the ratio Ds / Ts between the depth Ds of the groove 27 and the thickness Ts of the pixel electrode 20 and the pixel electrode 2 are shown.
The result of having investigated the relationship with the electric field intensity in the lower edge of the end part of 0 is shown. It can be seen from FIG. 18 that the electric field strength increases as the ratio Ds / Ts increases. It is considered that this increase in the electric field intensity is caused by the difference in the positional relationship between the photoelectric conversion film 22 and the insulating layer 19 having different dielectric constants depending on the presence or absence of the groove 27. The increase in the electric field intensity at the lower edge of the end portion of the pixel electrode 20 due to the formation of the groove 27 is very problematic because the hole current from the pixel electrode 20 side increases and the afterimage amount of the solid-state imaging device increases. Become.

The ratio of the area affected by the electric field concentration at the end of the pixel electrode to the entire pixel electrode increases as the area of one pixel decreases. Therefore, the effect of increasing the amount of afterimage due to the electric field concentration at the lower edge of the end portion of the pixel electrode becomes more remarkable as the area of one pixel becomes smaller. This makes it difficult to miniaturize pixels and is a major obstacle to increasing pixel density.

As the depth of the groove 27 increases, the pixel electrode 2
Since the electric field at the lower edge of the end portion of 0 becomes strong, the depth of the groove 27 should not be too large. But,
For the reason as shown in FIG. 17B, it is not desirable that the groove 27 is not provided at all. If there is no groove 27, a defect line 28 is generated in the photoelectric conversion film 22 from the lower edge lower end of the end portion of the electrode 20. If the defect line 28 occurs just at the place where the electric field concentration is the strongest, the current injected from the pixel electrode 20 increases and the amount of afterimage increases.

On the other hand, as shown in FIG. 17A, when the groove 27 is formed, the starting point of the defect line 28 comes off the lower edge of the end portion of the pixel electrode 20. Groove 27
As the depth of the groove 27 increases, the distance between the lower edge of the end of the pixel electrode 20 and the defect line 28 increases, but on the other hand, as the depth of the groove 27 increases, the electric field increases. In other words, the two are in a trade-off relationship.

The graph of FIG. 19 shows the result of examining the relationship between the ratio Ds / Ts of the depth Ds of the groove 27 and the thickness Ts of the pixel electrode 20 and the amount of afterimage. It can be seen from FIG. 19 that the optimum range exists when the ratio Ds / Ts is 0.2 or more and 1.0 or less.

20A to 20D sequentially show an etching process for forming the groove 27 as shown in FIG. 17A together with the pixel electrode 20. Here, the pixel electrode 20 is formed of a titanium film 30, and the second insulating layer 19 is formed of a silicon oxide film 36 doped with impurities such as BPSG, PPSG, and BSG in order to improve flatness.

First, as shown in FIG. 20A, a titanium film 30 is formed on the doped silicon oxide film 36 by a sputtering method, a vapor deposition method or the like. The thickness of the titanium film 30 is 1n
m to 1000 nm. Next, a resist film 34 is formed on the titanium film 30 by coating, and an exposure process is performed.
As shown in (b), a predetermined pattern is formed on the resist film 34. Next, in the RIE device, BC1 ₃ and C
As shown in FIG. 20C, the titanium film 30 is etched using a mixed gas of l ₂ .

Unlike the SiO ₂ film not doped with impurities, the silicon oxide film 36 doped with impurities such as BPSG, PPSG and BSG is formed by a mixed gas of BC 1 ₃ and Cl ₂ which is an etching gas for the titanium film 30. Is etched. Therefore, when the etching of the titanium film 30 progresses and the surface of the silicon oxide film 36 is exposed, the silicon oxide film 36 is also etched to some extent to form the groove 27. At this time, the etching time is adjusted so that the above-mentioned ratio Ds / Ts is 0.2 or more and 1.0 or less. After the etching, as shown in FIG. 20D, the resist film 34 is removed using a stripping solution.

As described above, according to the solid-state imaging device of the third embodiment, by specifying the relationship between the thickness of the pixel electrode 20 and the depth of the groove 27, the lower edge of the end portion of the pixel electrode 20 can be detected. The trade-off relationship between the electric field concentration and the relative position between the lower edge of the end of the pixel electrode 20 and the defect line 28 in the photoelectric conversion film 22 can be optimally adjusted, and the afterimage characteristic can be improved. It will be possible.

In the above description, an example in which RIE is used as the method for forming the pixel electrode has been described, but instead of this, a fine pixel electrode is formed by using a method such as excimer laser, CDE or X-ray. You can also do it. Also,
For ease of understanding, the first to third embodiments have been described individually, but the respective features can be combined with each other to be used in a composite manner, whereby more preferable afterimage characteristics can be obtained. Become.

[0065]

As described above, according to the present invention,
By processing the edge of the pixel electrode into a specific shape and eliminating the electric field concentration at the edge, the afterimage characteristic can be improved.

Further, according to the present invention, the afterimage characteristic can be improved by specifying the relationship between the thickness of the photoelectric conversion film and the distance between the pixel electrodes to reduce the electric field strength in the photoelectric conversion film. Becomes

Further, according to the present invention, by specifying the relationship between the thickness of the pixel electrode and the depth of the groove between the pixel electrodes,
It is possible to optimally adjust the trade-off relationship between the electric field concentration at the lower edge of the end of the pixel electrode and the relative position between the lower edge of the end of the pixel electrode and the defect line in the photoelectric conversion film, It is possible to improve the afterimage characteristic.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a solid-state imaging device according to a first embodiment of the present invention.

2A and 2B are diagrams respectively showing an outline of two types of samples used for examining an afterimage characteristic.

FIG. 3 is a graph showing afterimage characteristics in the two types of samples shown in FIG.

4A and 4B are graphs showing electric field intensity distributions of the two types of samples shown in FIG. 2, respectively.

5 is a graph showing changes in afterimage current with time of the two types of samples shown in FIG.

FIG. 6 is a graph showing changes in afterimage current with time for different voltages in the sample shown in FIG.

FIG. 7 shows a ratio of the peripheral length of the pixel electrode 4L to the plane area L ² of 4L /
Graph showing the relationship between L ² and afterimage amount.

8A and 8B are respectively a vertical sectional view showing the shape of an upper edge of an end portion of a pixel electrode, and its radius of curvature Rs.
3 is a graph showing the relationship between the ratio Rs / Ts of the film thickness of the pixel electrode Ts and the amount of residual image.

9A and 9B are respectively a vertical cross-sectional view showing a modified example of the shape of the upper edge of the end portion of the pixel electrode, and a graph showing the relationship between the edge angle θ and the amount of afterimage.

10A and 10B are plan views showing shapes of edges at four corners of a substantially rectangular pixel electrode, respectively, and a radius of curvature Rp and a length Lp of one side of the pixel electrode. Ratio Rp
The graph which shows the relationship between / Lp and the amount of afterimage.

11 (a) to (d) are the same as FIG. 8 (a) or FIG.
7A to 7C are cross-sectional views sequentially showing an etching process for forming the upper edge of the end portion of the pixel electrode as shown in FIG.

FIG. 12 is a cross-sectional view showing another method of forming the upper edge of the end portion of the pixel electrode.

FIG. 13 is a sectional view showing still another method of forming the upper edge of the end portion of the pixel electrode.

14A to 14D are cross-sectional views sequentially showing an etching process for forming the upper edge of the end portion of the pixel electrode by still another method.

FIG. 15 is a graph showing the relationship between the thickness of the photoelectric conversion film and the electric field strength when the distance between pixel electrodes is used as a parameter.

FIG. 16 is a schematic sectional view showing a solid-state imaging device according to the third embodiment of the present invention.

17 (a) and 17 (b) respectively show a second pixel electrode between pixel electrodes.
FIG. 6 is an enlarged cross-sectional view showing a groove formed in an insulating layer, and an enlarged cross-sectional view showing a state in which no groove is formed in the second insulating layer between pixel electrodes.

FIG. 18 is a graph showing the relationship between the ratio Ds / Ts of the depth Ds of the groove between the pixel electrodes and the thickness Ts of the pixel electrode, and the electric field strength at the lower edge of the end portion of the pixel electrode.

FIG. 19 is a graph showing the relationship between the ratio Ds / Ts of the depth Ds of the groove between the pixel electrodes and the thickness Ts of the pixel electrode, and the amount of afterimage.

20A to 20D are cross-sectional views sequentially showing an etching process for forming a groove between pixel electrodes as shown in FIG. 17A together with the pixel electrodes.

[Explanation of symbols]

11 ... Silicon substrate, 12 ... Element isolation layer, 13 ... Diffusion layer, 14 ... Diffusion layer, 15 ... First insulating layer, 16 ... Transfer electrode, 17 ... Transfer electrode, 18 ... Extraction electrode, 19 ... Second
Insulating layer, 20 ... Pixel electrode, 22 ... Photoelectric conversion film, 23 ... Counter electrode, 24 ... i-type hydrogenated a-SiC layer, 25 ... i-type hydrogenated a-Si layer, 26 ... p-type hydrogenated a-SiC
Layer, 27 ... Groove, 28 ... Defect line, 30 ... Titanium film, 31 ...
Silicon oxide film, 32 ... Titanium film lower part, 33 ... Titanium film upper part, 34 ... Resist film, 35 ... Impurity-undoped SiO ₂ film, 36 ... Impurity-doped silicon oxide film, ED ... Edge, RO ... Signal charge reading area, SD ... Signal charge storage area, TC ... Signal charge transfer area.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Yamaguchi No. 1 Komukai Toshiba Town, Saiwai-ku, Kawasaki City, Kanagawa Prefecture, Corporate Research & Development Center, Toshiba Corporation (72) Yoshinori Iida, Komukai Toshiba, Kawasaki City, Kanagawa Prefecture Town No. 1 Incorporated company Toshiba Research & Development Center (72) Inventor Akihiko Furukawa No. 1 Komukai Toshiba Town, Kouki-ku, Kawasaki City, Kanagawa Prefecture Incorporated company Toshiba Research & Development Center (72) Inventor Naoshi Sakuma Kanzaki Prefecture Kawasaki City Komukai-Toshiba-cho No. 1 Inside the Toshiba Research and Development Center, Ltd. (72) Inventor Hidefumi Oba Komukai-Toshibacho No. 1 inside the Toshiba Research and Development Center, Kawasaki City, Kanagawa Prefecture

Claims (6)

[Claims] 1. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, and the edge of the pixel electrode facing the photoelectric conversion film continuously changes. A solid-state imaging device characterized by being defined by a surface. 2. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, and the edge of the pixel electrode facing the photoelectric conversion film has a radius of curvature. And a ratio Rs / Ts between the radius of curvature Rs and the film thickness Ts of the pixel electrode is 0.25 or more. 3. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, and the edge angle of the pixel electrode facing the photoelectric conversion film is 95 ° or more. The solid-state imaging device according to claim 1. 4. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, and the pixel electrode is substantially rectangular, and at least one of the four corners is One edge is formed to have a radius of curvature, and the ratio Rp / of the radius of curvature Rp and the length Lp of one side of the pixel electrode is Rp /
A solid-state imaging device having Lp of 0.125 or more. 5. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, the distance between the pixel electrodes is 1.0 μm or less, and the photoelectric conversion is performed. A solid-state imaging device having a film thickness of 1.6 μm or less. 6. A base layer, a plurality of pixel electrodes formed on the base layer, a photoelectric conversion film formed so as to cover the pixel electrodes, and a counter electrode formed on the photoelectric conversion film. The ratio WL / SA of the peripheral length WL of the pixel electrode to the plane area SA is 0.6 μm ⁻¹ or more, and the groove is formed in the base film between the pixel electrodes, and the depth of the groove is increased. Ds
A solid-state imaging device, wherein a ratio Ds / Ts between the pixel electrode thickness Ts and the pixel electrode thickness Ts is 0.2 or more and 1.0 or less.