JP2006229004A - Solid-state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform sensitivity in the entire pixel array part by suppressing a shading effect that becomes prominent at the peripheral part of the pixel array part.
In a structure in which a light shielding film also serving as a wiring film is provided on the uppermost layer of a multilayer wiring arranged on a pixel array portion of a solid-state image sensor, an opening pattern of the light shielding film is changed from a central region to a peripheral region of the pixel array portion. Then, the opening diameter is gradually increased (that is, the wiring width is reduced). This effectively corrects the shading effect by guiding incident light to the pixel with a small opening in the pixel in the central region of the pixel array unit, while guiding incident light to the pixel with a large opening in the peripheral region of the pixel array unit. Is possible.
[Selection] Figure 3

Description

  The present invention relates to a solid-state imaging device configured by providing an upper laminated film in which a plurality of wiring films, insulating films, and the like are provided on a semiconductor substrate on which a photoelectric conversion unit is formed.

Generally, in a solid-state imaging device such as a CMOS image sensor, various films such as a wiring film (light-shielding film) and an insulating film are arranged in a multilayer on a semiconductor substrate provided with a photoelectric conversion unit (photodiode). It has a structure.
When such a solid-state imaging device is downsized to be mounted on, for example, a mobile phone, the pupil distance of the lens is inevitably shortened, and the imaging surface of the pixel array unit with a plurality of pixels arranged two-dimensionally, particularly An oblique component of light incident on the peripheral edge of the pixel array portion increases.
For this reason, when considered in units of pixels, the larger the light entry angle, the more light is blocked by the wiring and the like, and the amount of light directly incident on the light receiving surface decreases. This increases the shading effect and makes it difficult to maintain the image quality at a high level.
Therefore, conventionally, a method such as so-called wiring pupil correction, which corresponds to oblique light by forming the wiring pattern of the upper laminated film of the solid-state imaging device from the lower layer to the upper layer with a constant reduction rate, has been adopted.
(See Patent Document 1).
Japanese Patent Laid-Open No. 10-229180

However, since the conventional wiring pupil correction is a method of applying a certain reduction ratio to the wiring pattern, one wiring film is formed with a uniform wiring width, and the pattern of the light shielding film also corresponds to each pixel. Therefore, it is difficult to obtain a sufficient correction effect corresponding to each pixel.
On the other hand, in recent years, since the element is increasingly miniaturized and the aspect ratio (ratio of the opening area of the photodiode to the depth) of each pixel increases, the above-described wiring pupil correction method has a correction effect. Insufficient and more effective methods are needed.

  Therefore, the present invention can effectively control obliquely incident light in each pixel of the pixel array unit, and suppresses a shading effect that is particularly noticeable at the peripheral portion of the pixel array unit, thereby obtaining uniform sensitivity throughout the pixel array unit. An object of the present invention is to provide a solid-state imaging device capable of performing

  In order to achieve the above-described object, a solid-state imaging device of the present invention includes a semiconductor substrate on which a pixel array unit composed of a plurality of pixels is formed, and a plurality of wiring films and insulating films provided on the semiconductor substrate. An upper laminated film; and a microlens provided on the upper laminated film, wherein the upper laminated film includes a light shielding film having an opening pattern corresponding to each pixel of the pixel array unit, and the opening pattern of the light shielding film Has a different opening diameter depending on the position of the pixel in the pixel array portion.

According to the solid-state imaging device of the present invention, the opening pattern of the light-shielding film disposed on the pixel array unit has different opening diameters depending on the position of the pixel in the pixel array unit. It is possible to effectively control the obliquely incident light in the pixel, and it is possible to suppress the shading effect that is particularly noticeable in the peripheral portion of the pixel array portion, and to obtain uniform sensitivity throughout the pixel array portion.
Further, as the opening pattern of the light shielding film, for example, a pixel in the central region of the pixel array unit has a small opening diameter, and a pixel in the peripheral region of the pixel array unit has a large opening diameter. It is possible to obtain a uniform sensitivity in the entire pixel array part by making oblique light incident more effectively on the pixels on the peripheral area side of the pixel array, and suppressing the shading effect that becomes prominent particularly in the peripheral part of the pixel array part. it can.

Moreover, since the light shielding film also serves as the wiring film, the shading effect can be suppressed without increasing the wiring layer. Furthermore, in this case, by using the light shielding film as the uppermost wiring film of the upper laminated film, it is possible to suppress the shading effect by modifying the pattern of the uppermost wiring / light shielding film with a loose design rule. There is an effect that an opening pattern can be easily and freely created.
Note that the light shielding film does not necessarily have to be used as the wiring film. For example, the shading effect can be suppressed by the opening pattern by using the light shielding film provided on the upper layer of the multilayer film. Is possible.

In the embodiment of the present invention, in a structure in which a light shielding film serving as a wiring film is provided on the uppermost layer of a multilayer wiring arranged on the pixel array portion of the solid-state imaging device, the opening pattern of this light shielding film is used as the center of the pixel array portion. The opening diameter is gradually increased from the region to the peripheral region (that is, the wiring width is narrowed).
This effectively corrects the shading effect by guiding incident light to the pixel with a small opening in the pixel in the central region of the pixel array unit, while guiding incident light to the pixel with a large opening in the peripheral region of the pixel array unit. Is possible.
In particular, the uppermost wiring / light-shielding film has a looser design rule than the lower wiring film and has a large correction margin for the wiring width, so the wiring width and plug shape can be modified relatively freely. Therefore, it is possible to easily create an opening pattern shape necessary for suppressing the shading effect, and a remarkable effect can be obtained.
Note that the wiring film (light-shielding film) pattern in the region (peripheral circuit portion) other than the pixel array portion can be formed in the same shape as the conventional one, and no modification is required.

FIG. 1 is a plan view showing an outline of a solid-state imaging device according to an embodiment of the present invention, and shows an example of a CMOS image sensor.
As shown in FIG. 1, the image sensor according to the present embodiment is configured on a semiconductor chip 100, and includes a pixel array unit 110 formed at a substantially central portion of the semiconductor chip 100 and a peripheral circuit formed outside the pixel array unit 110. Part 120. The pixel array unit 110 includes a plurality of pixels each including a photoelectric conversion unit such as a photodiode and a readout circuit thereof arranged in a two-dimensional direction, and sequentially outputs pixel signals detected by the pixels. Various methods have been put to practical use in the readout circuit in each pixel. For example, a transfer transistor that transfers the signal charge of the photoelectric conversion unit to the floating diffusion unit, and the signal charge transferred by the transfer transistor is amplified. Thus, an amplifying transistor for converting to a voltage signal or a current signal, a selection transistor for selecting a readout pixel, a reset transistor for periodically resetting the signal charge of the floating diffusion portion, and the like are provided.
On the other hand, the peripheral circuit section is equipped with a drive circuit that controls the operation of the pixel array section and various processing circuits that perform predetermined noise processing and signal processing on the pixel signals read from the pixel array section and output them. ing.

2 and 3 are cross-sectional views showing the pixel structure of the solid-state imaging device shown in FIG. 1, FIG. 2 shows a pixel in the central area of the pixel array section, and FIG. 3 shows a pixel in the peripheral area of the pixel array section. Is shown. 2 and 3, an arrow L indicates light incident on each pixel (for convenience, a parallel line incident from the periphery of one microlens).
As shown in the figure, a photoelectric conversion unit 210 and the like are provided on the upper layer part of the semiconductor substrate 200, a gate insulating film and a gate electrode (not shown) are provided on the upper surface, and three interlayer insulating films 221 and 222 are provided on the upper layer. Three-layer wiring films 231, 232, and 233 constituting a multilayer wiring are provided via 223. Each element and each wiring film 231, 232, 233 in the semiconductor substrate 200 are connected by a via plug 240, a contact plug (not shown) or the like.
The uppermost wiring film 233 is used as a light-shielding film that also serves as a wiring, and is formed of, for example, Al. A passivation film 250 is provided on the light shielding film 233 via an insulating film 224, and a micro lens 270 is disposed on the light shielding film 233 via a color filter 260.

As shown in the drawing, the wiring and light shielding film 233 has a different pattern depending on the position of the pixel in the pixel array section. For example, in the pixel in the central region shown in FIG. The opening pattern is formed with the same line width, but the opening pattern is formed with a line width smaller than those of the other wiring films 231 and 232 in the pixels in the peripheral region shown in FIG. .
In the description of this embodiment, only two pixels, ie, the central region pixel and the peripheral region pixel of the pixel array portion are shown in FIGS. 2 and 3, but gradually from the central region to the peripheral region of the pixel array portion. The line width may be reduced, or the line width may be reduced stepwise.

When creating the multilayer wiring as described above, first, a wiring pattern is formed on the laminated film of the wiring film material formed by the same method as the conventional one using a photolithography process and a dry etching process. Thereafter, an interlayer insulating film is formed by atmospheric pressure CVD so as to cover the entire surface of the substrate, and a planarization process by CMP is performed, the interlayer insulating film is planarized, and the process proceeds to an upper wiring film forming process. .
In such a wiring pattern forming process, when creating a mask of a wiring film material mainly used as a light shielding film, the wiring width is gradually narrowed in advance from the central portion of the pixel array portion toward the peripheral portion. So that the opening diameter increases toward the periphery.

As described above, in this embodiment, as shown in FIG. 3, the opening of the peripheral pixel is enlarged by forming the wiring width of the light shielding film narrower than the central portion at the peripheral portion of the pixel array portion. As indicated by the middle L, the reflection of the oblique light by the wiring film is reduced, and an improvement in sensitivity and suppression of shading can be expected.
In particular, in this embodiment, since the shading is suppressed by adjusting the pattern of the uppermost wiring / light-shielding film having a relatively loose design rule, a necessary pattern can be easily obtained. However, the present invention is not limited to the above-described embodiments. For example, a configuration for adjusting the pattern of the light shielding film that also serves as the wiring film is possible, and the pattern of the lower wiring film having a substantially light shielding function is also possible. It is also possible to use a configuration that is adjusted and used to suppress shading.

It is a top view which shows the outline | summary of the solid-state image sensor by the Example of this invention. It is sectional drawing which shows the pixel structure of the center area | region of the pixel array part of the solid-state image sensor shown in FIG. It is sectional drawing which shows the pixel structure of the peripheral area | region of the pixel array part of the solid-state image sensor shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Semiconductor chip, 110 ... Pixel array part, 120 ... Peripheral circuit part, 200 ... Semiconductor substrate, 210 ... Photoelectric conversion part, 221, 222, 223, 224 ... Insulating film, 231, 232, 233 ... Wiring film, 240 ... Via plug, 250 ... Passivation film, 260 ... Color filter, 270 ... Micro lens.

Claims (5)

A semiconductor substrate on which a pixel array portion composed of a plurality of pixels is formed;
An upper laminated film including a plurality of wiring films and insulating films provided on the semiconductor substrate;
A microlens provided on the upper laminated film,
The upper laminated film has a light shielding film having an opening pattern corresponding to each pixel of the pixel array portion, and the opening pattern of the light shielding film has an opening diameter different depending on the position of the pixel in the pixel array portion,
The solid-state image sensor characterized by the above-mentioned.   2. The opening pattern of the light shielding film has a small opening diameter in a pixel in a central region of a pixel array portion and a large opening diameter in a pixel in a peripheral region of the pixel array portion. Solid-state image sensor.   The solid-state image pickup device according to claim 1, wherein the light shielding film also serves as a wiring film.   4. The solid-state imaging device according to claim 3, wherein the light shielding film also serves as an uppermost wiring film of the upper laminated film.   The solid-state imaging device according to claim 1, wherein the light shielding film is provided in an upper layer of a plurality of wiring films of the upper laminated film.

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