JPH06244394A - Structure and design of solid-state image pick-up device - Google Patents

Abstract

PURPOSE:To provide a structure of a solid-state image pick-up device wherein no smear is allowed to appear and a method for designing the device of such a structure and to enhance the reliability of the solid-state image pick-up device. CONSTITUTION:In a solid-state image pick-up device 1 having an elliptical or nearly elliptical condensor lens 18, the focuses Ox, Oy of which are located on a photodetecting face 12a or below the face and a shielding film 14 which covers electrodes 13a, 13b located on the upper face of a substrate 11 is located outside a flux of light collected by the condensor lens 18. When designing the solid-state image pick-up device 1, the thickness of the condensing lens 18 and the thickness of a flattened film 17 are determined by the designed values of electric characteristics of the solid-state image pick-up device 1 and an area dominated by each unit cell of the solid-state image pick-up device 1. These thicknesses are so set at to satisfy the conditions required for designing the solid-state image pick-up device 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a solid-state image pickup device and a method of designing the solid-state image pickup device. And its design method.

[0002]

2. Description of the Related Art A solid-state image pickup device is a device for efficiently converting a received optical signal into an electric signal, and is widely used in VTR cameras, image sensors for facsimiles, industrial cameras and the like.

6 and 7 show the sectional structure of each unit cell of the solid-state image pickup device. FIG. 6 shows the solid-state image sensor 2 described above.
FIG. 7 is a sectional view in the horizontal shift direction, and FIG. 7 is a sectional view in the vertical shift direction. As shown in FIGS. 6 and 7, the solid-state imaging device 2 is configured as described below. That is, the photodiode 22 is formed on the substrate 21, and the exposed surface of the photodiode 22 serves as the light receiving surface 22a. Further, an electrode 23 is formed on the upper surface of the substrate 21 via an insulating film (not shown). The electrode 23 is covered with an insulating film (not shown). The electrode 23 is formed so as to surround the light receiving surface 22 a, and the light shielding film 24 covers the electrode 23. Then, as shown in the cross-sectional view in the horizontal shift direction of FIG. 6, a channel stop 25 running in the vertical shift direction and a vertical charge transfer unit 26 sandwich the photodiode 22 on the substrate 21 below the electrode 23. It is located on both sides.

The improvement of the sensitivity of the solid-state image pickup device 2 is achieved by increasing the amount of light received by the light receiving surface 22a. Therefore, the height of the electrode 23, the width of the electrode 23 in the horizontal shift direction, and the width of the electrode 23 in the vertical shift direction are designed so that the area of the light receiving surface 22a is as large as possible.

In recent years, in order to further increase the amount of received optical signals, a condenser lens 28 is formed above the substrate 21 for each unit cell via a flattening film 27. The condenser lens 28 is formed so as to fill the area occupied by each unit cell in order to increase the light utilization rate. In general, each unit cell is elongated in the vertical shift direction in order to obtain horizontal resolution. Therefore, the condenser lens 28 is formed in a substantially oval shape or a substantially rectangular shape that matches the shape of each unit cell.

[0006]

However, the solid-state image pickup device 2 has the following problems. That is, since the condensing lens 28 has a substantially oval shape or a substantially rectangular shape, the focal length in the minor axis direction differs from the focal length in the major axis direction, and the focal point Ox in the minor axis direction and the focal point Oy in the major axis direction are different. Misalignment occurs at the depth position of. The larger the difference between the minor axis dimension rx and the major axis dimension ry of the condenser lens 28, the greater the deviation in the depth position between the focal point Ox in the minor axis direction and the focal point Oy in the major axis direction. Moreover, the shape of each unit cell tends to be elongated in the vertical shift direction as the number of pixels of the product increases, and the deviation of the depth positions of the above-mentioned focusing points Ox and Oy tends to further expand. is there.

However, in the solid-state image pickup device 2 having the condenser lens 28, the condenser lens 28 is designed in accordance with the solid-state image pickup device which has already been designed without the condenser lens 28. The condenser lens 28 is
When the dimension rx in the minor axis direction and the dimension ry in the major axis direction are determined due to manufacturing restrictions, the thickness t is also restricted to a certain range. Then, as the solid-state image sensor 2 is miniaturized, the lens diameter of the condenser lens 28 is also reduced,
The regulation range of the thickness t of the condenser lens 28 is narrowed and the lens characteristics are also determined.

Further, the solid-state image pickup device not provided with the condenser lens 28 is already designed. Therefore, the substrate 21 in which unevenness is generated by the formation of the electrode 23
The film thickness d of the flattening film 27 for flattening the surface of is also regulated to a predetermined thickness or more. Due to the progress of miniaturization and the increase in the number of pixels, the difference between the pitch in the horizontal shift direction and the pitch in the vertical shift direction of each unit cell is large to some extent, and the unit lens in the minor axis direction with respect to the major axis direction dimension ry of the condensing lens 28. Solid-state image sensor 2 having dimension rx smaller than 1: 0.86
Then, the focus point Ox in the horizontal shift direction is the light receiving surface 22a.
The structure is located higher.

When the converging point Ox in the minor axis direction of the condensing lens 28 is located above the light receiving surface 22a as described above, the light receiving surface 22a is in the process of expanding from the light converging point Ox. A luminous flux enters. Therefore, the optical signal incident on the light receiving surface 22a is incident on the vertical charge transfer portion from the photodiode 22 to generate smear, and the reliability of the solid-state imaging device 2 is reduced.

The present invention has been made to solve the above-mentioned problems, and provides a structure of a solid-state image pickup device which prevents the occurrence of smear and a method for designing the solid-state image pickup device, and a solid-state image pickup device which has a higher number of pixels and is miniaturized. The purpose is to improve the reliability of.

[0011]

In order to solve the above-mentioned problems, the structure of the solid-state image pickup device of the present invention is configured as follows. First, the structure of the solid-state imaging device of the present invention includes a light-receiving surface arranged on the surface of a substrate for each unit cell,
An electrode formed on the substrate in a state where the light receiving surface is exposed, a light-shielding film that covers the electrode, and a condenser lens formed above the substrate through a flattening film so as to correspond to each light receiving surface. And at least the minor axis direction of the condenser lens is arranged in the horizontal shift direction of the light receiving surface. The condensing lens is substantially oval or rectangular,
The condensing point of the condensing lens is located on the light receiving surface or below the light receiving surface, and the light shielding film is located outside the light beam condensed by the condensing lens. Is characterized by.

Further, the method of designing the solid-state image pickup device having the above structure is performed according to the following procedure. In the first step, the width of the light receiving surface in the horizontal shift direction and the width of the electrode in the horizontal shift direction are calculated from the design values of the electrical characteristics of the solid-state image sensor. In the second step, the dimension of the condenser lens in the minor axis direction and the dimension in the major axis direction orthogonal to the minor axis direction are calculated from the area occupied by each unit cell occupied by the light receiving surface and the electrode. In the third step, the converging point of the condenser lens in the minor axis direction is located on the light receiving surface or below the light receiving surface, and the light flux in the minor axis direction of the condenser lens is the first light beam.
The thickness of the condenser lens and the film thickness of the flattening film are set so as to be within the width of the light receiving surface in the horizontal shift direction calculated in the step. In the fourth step, from the film thickness of the flattening film and the film thickness of the light shielding film calculated in the third step,
The height of the electrode for achieving the flattening of the flattening film is calculated, and the width of the electrode in the vertical shift direction is calculated from the calculated height of the electrode and the electric resistance value of the electrode. In the fifth step, based on the height of the electrode calculated in the fourth step, the width of the electrode in the vertical shift direction, and the width of the electrode in the horizontal shift direction, the light shielding film covering the electrode is collected. It is determined whether or not it is located outside the light beam condensed by the optical lens. When it is determined that the light-shielding film is not located outside the light beam condensed by the condenser lens, the process returns to the third step, and the steps after the third step are sequentially repeated to determine that the light-shielding film is positioned. In some cases, the process ends.

[0013]

Since the condensing lens is substantially oval or rectangular, the focal length in the minor axis direction is shorter than the focal length in the major axis direction, and the focal point in the minor axis direction is shorter than the focal point in the major axis direction. Located shallow. However, in the solid-state imaging device, the condensing point of the condensing lens is located on the light receiving surface or below the light receiving surface. Therefore, all the light beams condensed by the condenser lens are incident on the light receiving surface in the process of being converged toward the condensing point. Moreover, since the light-shielding film that covers the electrodes is arranged outside the light flux condensed by the condenser lens, all the light flux condensed by the condenser lens is incident on the light receiving surface.

Furthermore, in the above solid-state image pickup device designing method, the light-shielding film covering the electrode designed in the fourth step is the third
If it is not located outside the light beam condensed by the condenser lens designed in the step (3), the process returns to the third step and the thickness of the condenser lens and the film thickness of the flattening film are reset. In the third step, the focal point in the minor axis direction of the condenser lens is located on the light receiving surface or below the light receiving surface, and the luminous flux in the minor axis direction of the condenser lens is in the first step. The thickness of the condenser lens and the film thickness of the flattening film are set in a state where the thickness is within the width of the light receiving surface in the horizontal shift direction calculated in step a. Therefore, by repeating this step in sequence, the light condensing point of the condenser lens is located below the light receiving surface and the light receiving surface, and the light shielding film covering the electrode is condensed by the condenser lens. A solid-state image sensor located outside of is designed.

[0015]

Embodiments of the structure and design method of a solid-state image sensor according to the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a unit cell portion of a solid-state image sensor 1 of the present invention. First, the structure of the solid-state image sensor 1 will be described with reference to this figure. In FIG. 1, the substrate 11 is formed of, for example, silicon or the like, and an insulating film such as a silicon oxide film (not shown) is formed on the surface thereof. On the upper surface of the substrate 11, a first electrode 13a and a second electrode 13b forming a transfer electrode are formed of, for example, polysilicon. This first
The electrode 13a and the second electrode 13b each have a specific electric resistance value and are covered with an insulating film (not shown). Then, the first electrode 13a is first formed on the upper surface of the substrate 11, and the second electrode 13b is formed on a part of the upper surface on which the first electrode 13a is formed.

The above-mentioned first electrode 13a and second electrode 13b
Is covered with a light shielding film 14 made of, for example, aluminum. The light shielding film 14 has a predetermined film thickness.

The first electrode 13a and the second electrode 13b
Is formed on the upper surface of the substrate 11 with an opening portion, and the substrate surface exposed in the opening portion is the light receiving surface 12a. The light-shielding film 14 has the light-receiving surface 1
It projects over the periphery of 2a with a predetermined width. Then, the light receiving surface 12a and the first electrode 1 adjacent to the light receiving surface 12a.
The unit cell of the solid-state imaging device 1 is configured by 3a and the second electrode 13b. Each unit cell is the solid-state image sensor 1 described above.
As the number of pixels increases, the shape becomes elongated in the vertical shift direction.

Further, a condenser lens 18 is formed above the substrate 11 via a flattening film 17.
The condenser lens 18 has a resin lens array formed for each light receiving surface 12a.

A photodiode 12 is formed on the substrate 11, and the upper surface of the photodiode 12 is exposed at the openings of the first and second electrodes 13a and 13b to become a light receiving surface 12a. ing. On both sides of the photodiode 12 in the horizontal shift direction, a channel stop 15 running in the vertical shift direction and a vertical charge transfer section 16 are arranged on one side. Therefore, the photodiode 12 has an elongated shape in the vertical shift direction.

The first electrode 13a, the second electrode 13b, and the light-shielding film 14 are formed so that the light-shielding film 14 is located outside the light beam condensed by the condenser lens 18. . Further, the light collecting point Ox in the minor axis direction and the light collecting point Oy in the major axis direction of the condenser lens 18 are the light receiving surface 12a.
Alternatively, it is located below the light receiving surface 12a.

FIG. 2 shows a schematic plan view of the solid-state image pickup device 1. In FIG. 2, the portion surrounded by the first electrode 13a and the second electrode 13b is the light receiving surface 12a. As shown in this figure, the solid-state imaging device 1 has a plurality of the unit cells arranged on a substrate 11. The condensing lens 18 is formed to have a size that occupies the exclusive area of each unit cell occupied by the light receiving surface 12a, the first electrode 13a, and the second electrode 13b. Therefore, the condenser lens 1
8 is formed as a convex lens having a substantially oval or rectangular shape in plan view. The minor axis direction of the condenser lens 18 is arranged in parallel with the horizontal shift direction of the solid-state image sensor 1, and the condenser lens 1 is arranged in parallel with the vertical shift direction.
The major axis direction of 8 is arranged.

Next, the sectional structure of the solid-state image pickup device 1 will be described with reference to FIGS. 3 shows a cross section of the horizontal shift direction XX 'in FIG. 2, and FIG. 4 shows a cross section of the vertical shift direction YY' in FIG. As shown in FIGS. 3 and 4, the first electrode 13a and the second electrode 13b are formed at the same height h.
Further, the condenser lens 18 is formed such that the dimension rx in the minor axis direction is smaller than 1: 0.86 with respect to the dimension ry in the major axis direction.

In the solid-state image pickup device 1 having the above-described structure, the dimension rx in the minor axis direction with respect to the dimension ry in the major axis direction of the condenser lens 18 is a substantially oval shape or a substantially rectangular shape smaller than 1: 0.86. Therefore, in the condenser lens 18, the focal length in the minor axis direction and the focal length in the major axis direction are displaced by a predetermined range, and the focal point Ox in the minor axis direction is located shallower than the focal point Oy in the major axis direction. To do.

However, the solid-state image pickup device 1 has a structure in which both the light collecting point Ox in the short diameter direction and the light collecting point Oy in the long diameter direction are located below the light receiving surface 12a. Therefore, all the light beams condensed by the condenser lens 18 are incident on the light receiving surface 12a in the process of being converged toward the condensing points Ox and Oy.

Further, since the light shielding film 14 covering the first electrode 13a and the second electrode 13b is arranged outside the light beam condensed by the condenser lens 18, it is collected by the condenser lens 18. All the luminous fluxes that have been made incident are incident on the light receiving surface 12a.

Next, a method of designing the solid-state image pickup device 1 having the above structure will be described with reference to the flowcharts of FIGS. 3, 4 and 5. First, in the first step, the width Wx of the light receiving surface 12a in the horizontal shift direction and the widths Wp ₁ and Wp ₂ of the first electrode 13a and the second electrode 13b in the horizontal shift direction are calculated (S1). In the solid-state imaging device 1 to be designed, the width of the vertical charge transfer unit 16 is defined by the design value of its electric characteristics. Therefore, the width Wx where the light receiving surface 12a can be arranged in the horizontal shift direction of each unit cell, and the first
The widths Wp ₁ and Wp ₂ of the electrode 13a and the second electrode 13b in the horizontal shift direction are calculated.

Next, in the second step, the dimension rx in the minor axis direction and the dimension ry in the major axis direction of the condenser lens 18 are calculated (S2). The condenser lens 18 is formed as large as possible to fill the area occupied by each unit cell in order to increase the light utilization rate. Therefore, the dimension rx in the minor axis direction and the dimension ry in the major axis direction of the condenser lens 18 are calculated from the area occupied by each unit cell of the solid-state imaging device 1 to be designed.

Then, in the third step, the thickness t of the condenser lens 18 and the film thickness d of the flattening film 17 are set (S).
3). When the dimension rx in the minor axis direction and the dimension ry in the major axis direction of the condenser lens 18 calculated in the second step are determined, the thickness t thereof is defined within a predetermined range due to manufacturing restrictions. . Further, by defining the range of the thickness t of the condenser lens 18, the range of the focal length in the minor axis direction and the range of the focal length in the major axis direction of the condenser lens 18 are defined.

On the other hand, the film thickness d of the flattening film 17 defines the distance between the condenser lens 18 and the light receiving surface 12a. Therefore, depending on the combination of the film thickness d of the flattening film 17 and the thickness t of the condensing lens 18, the condensing point Ox in the minor axis direction and the condensing point Oy in the major axis direction of the condensing lens 18 described above.
The depth position of is defined. Here, the condenser lens 18
Is a substantially elliptical or substantially rectangular shape in which the dimension rx in the minor axis direction with respect to the dimension ry in the major axis direction is smaller than 1: 0.86, and the depth position of the focal point Ox in the minor axis direction is the focal point in the major axis direction. It is shallower within a predetermined range than the depth position of Oy.

Therefore, the combination of the thickness t of the condenser lens 18 and the film thickness d of the flattening film 17 is set so as to satisfy the following conditions and conditions. Condition: Focusing point Ox of the focusing lens 18 in the minor axis direction
Is located on the light receiving surface 12a or below the light receiving surface 12a. Condition: The condenser lens 18 on the light receiving surface 12a
The light flux in the direction of the shortest diameter is within the width Wx in the horizontal shift direction of the light receiving surface 12a calculated in the first step.

Further, in the fourth step, first, the height h of the first electrode 13a and the second electrode 13b is calculated, and then the vertical shift direction of the first electrode 13a and the second electrode 13b is calculated. The widths Wq ₁ and Wq _{2 of} are calculated (S4). The above-mentioned first electrode 13a, second electrode 13b, and light-shielding film 14
Are formed on the upper surface of the substrate 11 to form irregularities on the substrate 11. The flattening film 17 is for flattening the upper surface of the substrate 11, and the film thickness d of the flattening film 17 required for achieving flattening is determined by the degree of unevenness on the substrate 11. . Therefore, the film thickness d of the flattening film 17 set in the above third step
And the film thickness of the light shielding film 14 having a predetermined thickness, the height h of the first electrode 13a and the second electrode 13b for achieving the flattening of the flattening film 17 is calculated. .

The first electrode 13a and the second electrode 13b have their own electric resistance values.
Therefore, this electrical resistance value and the first and second electrodes 13
The necessary cross-sectional areas of the first and second electrodes 13a and 13b are calculated from the materials forming a and 13b. Then, the calculated first and second electrodes 13a, 13b
From the required cross-sectional area of the first electrode 13a and the height h of the first electrode 13a and the second electrode 13b calculated above.
a and the widths Wq ₁ and W of the second electrode 13b in the vertical shift direction.
q ₂ is calculated.

Next, in the fifth step, the first to fourth steps are performed.
It is determined whether or not the condenser lens 18, the first electrode 13a, and the second electrode 13b designed in the above process satisfy the following conditions (S5). Conditions: the first electrode 13a and the second electrode designed in the above process
The light-shielding film 14 that covers the electrode 13b is located outside the light flux condensed by the condenser lens 18 designed in the above process.

Then, in the fifth step, when it is judged that the condition is satisfied, the step is ended. In the fifth step, if it is determined that the condition is not satisfied, the procedure returns to the third step, and the condenser lens 18
The thickness t and the film thickness d of the flattening film 17 are set again, and the fourth and fifth steps are sequentially repeated.

By repeating the above third to fifth steps, the light-converging point Ox in the short diameter direction and the light-converging point Oy in the long diameter direction of the condensing lens 18 become the light receiving surface 12a and the light receiving surface 12a. The light-shielding film 1 located below
A solid-state image sensor 4 is designed in which 4 is located outside the light flux condensed by the condenser lens 18.

[0036]

As described above, according to the structure of the solid-state image sensor of the present invention, all the light fluxes condensed by the condenser lens are converged on the light receiving surface in the process of being converged toward the condensing point. Since it is incident, the optical signal incident on the light receiving surface does not enter the vertical charge transfer unit from the photodiode. Therefore, the occurrence of smear can be prevented. Further, since all the light fluxes condensed by the condenser lens are incident on the light receiving surface, it is possible to expect improvement in reliability of the solid-state image pickup device with higher pixel count and smaller size while maintaining the sensitivity of the solid-state image pickup device. it can. Further, according to the method for designing a solid-state image sensor of the present invention, it is possible to design a solid-state image sensor that prevents the occurrence of smear in the solid-state image sensor with the increased number of pixels and the miniaturization.

[Brief description of drawings]

FIG. 1 is a perspective view of a solid-state image sensor according to the present invention.

FIG. 2 is a schematic plan view of a solid-state image sensor according to the present invention.

FIG. 3 is a cross-sectional view of a solid-state image sensor of the present invention in the horizontal shift direction.

FIG. 4 is a cross-sectional view of a solid-state image sensor of the present invention in a vertical shift direction.

FIG. 5 is a flowchart showing a design procedure of the solid-state imaging device of the present invention.

FIG. 6 is a cross-sectional view of a conventional solid-state image sensor in the horizontal shift direction.

FIG. 7 is a cross-sectional view of a conventional solid-state image sensor in the vertical shift direction.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solid-state image sensor 11 Substrate 12a Light-receiving surface 13a First electrode (electrode) 13b Second electrode (electrode) 14 Light-shielding film 17 Flattening film 18 Condenser lens Wx Width of light-receiving surface in horizontal shift direction h First and first Height of second electrode Wp ₁ Width of first electrode in horizontal shift direction Wq ₁ Width of first electrode in vertical shift direction Wp ₂ Width of second electrode in horizontal shift direction Wq ₂ Vertical of second electrode Width in shift direction d Film thickness of flattening film rx Short-axis dimension of condensing lens ry Long-axis dimension of condensing lens t Thickness of condensing lens Ox Condensing point Oy condensing lens in short-axis direction Convergence point in the major axis direction

Claims (2)

[Claims] 1. A light-receiving surface arranged on the surface of a substrate for each unit cell, an electrode formed on the substrate in a state where the light-receiving surface is exposed, a light-shielding film covering the electrode, and a substrate of the substrate. A structure of a solid-state image pickup device including a condenser lens formed corresponding to each light receiving surface through a flattening film above, and arranging at least a minor axis direction of the condenser lens in a horizontal shift direction of the light receiving surface. In the above, the condensing lens is substantially oval or substantially rectangular, and the condensing point of the condensing lens is located on the light receiving surface or below the light receiving surface, and the light shielding film is A structure of a solid-state image pickup device, which is located outside a light beam condensed by a condenser lens. 2. The method for designing a solid-state image pickup device according to claim 1, wherein a width of the light-receiving surface in a horizontal shift direction and a horizontal shift direction of the electrode are calculated from design values of electrical characteristics of the solid-state image pickup device. From the first step of calculating the width and the area occupied by each unit cell occupied by the light-receiving surface and the electrode, the dimension of the condenser lens in the minor axis direction and the dimension in the major axis direction orthogonal to the minor axis direction. And a light-converging point in the minor axis direction of the condenser lens is located on the light-receiving surface or below the light-receiving surface, and the light flux in the minor-axis direction of the condenser lens is A third step of setting the thickness of the condenser lens and the film thickness of the flattening film in a state of being within the width of the light receiving surface in the horizontal shift direction calculated in the first step; and the third step. From the film thickness of the flattening film calculated in A fourth aspect of calculating a height of the electrode for achieving the flattening of the flattening film, and calculating a width of the electrode in the vertical shift direction from the calculated height of the electrode and an electric resistance value of the electrode. From the step, the height of the electrode calculated in the fourth step, the width of the electrode in the vertical shift direction, and the width of the electrode in the horizontal shift direction, the light shielding film covering the electrode is the condensing lens. It is judged whether or not it is located outside the condensed light beam, and when it is judged that it is not positioned, the procedure returns to the third step, and the steps after the third step are sequentially repeated. And a fifth step of terminating the steps, the method for designing a solid-state image sensor.