JP2004055669A - Solid-state imaging element and method manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging element which can reduce deterioration of image quality, particularly deterioration of the image quality at the edge portion of substrate and assure high accuracy read images. <P>SOLUTION: A frame type field oxide film 4 is formed to a concave area R to surround the effective imaging region 1A of the solid-state imaging element. Accordingly, this surface is located so as to be at approximately the same level as the surface level of a photosensor 2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly to a miniaturized structure of a solid-state imaging device and a manufacturing method thereof.
[0002]
[Prior art]
With the high integration and high density of semiconductor devices, the number of imaging pixels is also increasing in solid-state imaging devices, but due to the demand for high-speed signal charge transfer, that is, high-speed driving with the increase in the number of pixels, Device miniaturization is progressing.
[0003]
As shown in an example of the cross section in FIG. 6, the solid-state imaging element is formed by forming a field oxide film 14 made of a thick CVD oxide film of about 300 to 600 nm on the periphery and the like and surrounded by the field oxide film 14. In the element area, photoelectric conversion elements and charge transfer elements are arranged as an effective imaging area 11A. On the other hand, on and outside the field oxide film 14 is a non-imaging region 11B. In this non-imaging region 11B, a signal processing circuit and the like are separated from a horizontal transfer register or a solid-state imaging device that transfers signal charges in the horizontal direction. An element isolation region (field oxide film) is formed, and a wiring layer 17 is formed thereon.
[0004]
That is, as shown in FIG. 6, the photodiode 12 and the charge transfer element 13 are formed in the effective imaging region 11 </ b> A surrounded by the field oxide film 14 in the silicon substrate 11, and the upper layer is covered with the insulating film 15. Has been.
[0005]
A wiring electrode 17 is formed on the field oxide film 14, and the upper layer is covered with a planarizing film 16. Further, a color filter 18 and a microlens 19 are provided.
In the solid-state imaging device having such a structure, as shown in FIG. 6, a large step is formed at the boundary between the effective imaging region 11A and the non-imaging region 11B.
[0006]
Further, when field oxidation is used to reduce the capacitance between the substrate and the wiring, a certain amount of oxide film thickness is required.
[0007]
[Problems to be solved by the invention]
As described above, in the conventional solid-state imaging device, a large step is generated between the effective imaging region 11A at the center of the chip and the non-imaging region 11B surrounding the effective imaging region 11A. Therefore, as shown in FIG. 7, an image quality deterioration portion 21 in which the image quality deteriorates from the vicinity of the effective imaging region 11A to the outside.
[0008]
That is, since there is a large step in the periphery, even if the planarizing film 16 is formed, as shown in FIG. 8, it becomes thinner at the center portion, and the formation of a gentle step cannot be avoided. For this reason, the color filter 18 and the microlens 19 formed in the upper layer of the planarizing film 16 are also formed obliquely at the periphery. Therefore, in the periphery of the effective imaging region 11A, the light condensed by the on-chip lens may not enter the center of the photosensor. As a result, sensitivity and color non-uniformity occur in the peripheral portion of the imaging screen, and this peripheral region becomes a problem as the image quality deterioration portion 21.
[0009]
As described above, due to the step due to the frame-shaped field oxide film pattern at the peripheral edge of the substrate, there is a problem that sensitivity and color non-uniformity occur in the peripheral portion of the imaging screen, and the image quality deteriorates.
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid-state imaging device capable of providing a high-accuracy read image by reducing image quality deterioration, in particular, image quality degradation at the periphery of the substrate. .
[0011]
[Means for Solving the Problems]
The semiconductor device of the present invention is characterized in that the surface of the field oxide film formed in a frame shape so as to surround the effective imaging region of the solid-state imaging device is positioned at the same level as the surface level of the photosensor.
[0012]
According to such a configuration, since the surface of the field oxide film formed in a frame shape so as to surround the effective imaging region of the solid-state imaging device is formed to be approximately the same as the surface level of the photosensor, the effective imaging region The whole is kept flat. Therefore, the lens formed on the chip surface is maintained so that the optical axis is parallel to the substrate surface even at the periphery of the chip, and can be efficiently incident on the center of the photosensor. Therefore, the image quality degradation portion is reduced without causing sensitivity and color non-uniformity in the peripheral portion of the imaging screen, and a captured image can be obtained with high accuracy over the entire effective imaging region.
Further, even when a thick field oxide film is formed so as to obtain a sufficient wiring capacity, the step on the substrate surface can be reduced.
[0013]
Desirably, the field oxide film is formed by selective oxidation, whereby an oxide film with good film quality can be formed, and more reliable insulation separation can be achieved.
[0014]
More preferably, the field oxide film is formed in a recess formed in a frame shape. According to this configuration, it is possible to form an oxide film that is flat and has good film quality.
[0015]
The present invention is also a method for forming a solid-state imaging device on the surface of a semiconductor substrate, wherein the step of forming a field oxide film so as to surround the solid-state imaging device formation region is a frame so as to surround the effective imaging region of the solid-state imaging device. And a step of forming the field oxide film so that the surface of the field oxide film formed in the shape is positioned at the same level as the surface level of the photosensor.
[0016]
According to such a configuration, it is possible to form a thick field oxide film and reduce the step on the substrate surface while sufficiently reducing the wiring capacitance.
[0017]
Preferably, the step of forming the field oxide film includes a step of forming a recess in a region surrounding at least a solid-state imaging device formation region on the surface of the semiconductor substrate, and a step of forming a silicon oxide film in the recess. .
[0018]
According to this configuration, since the silicon oxide film is formed in the recess after the recess is formed in advance, the surface can be efficiently planarized.
[0019]
Desirably, if this silicon oxide film is formed by selective oxidation, it becomes an insulating film with good film quality, and therefore, it is possible to perform reliable element isolation without fear of leakage.
[0020]
Preferably, the step of forming the field oxide film includes a step of forming silicon oxide by selective oxidation, and a step of removing and planarizing the protruding portion of the silicon oxide film by CMP.
[0021]
According to such a configuration, it is possible to form an element isolation region with less distortion without requiring a further lithography process.
[0022]
Here, the field oxide film is not limited to selective oxidation, but may be formed by chemical vapor deposition (CVD). Further, a frame-shaped recess may be formed in advance, and an insulating film may be formed in the recess by a coating method. Furthermore, the present invention is not limited to a silicon oxide film formed by CVD or thermal oxidation, and a silicon oxide film doped with impurities, such as a BPSG film or a PSG film, or a film formed by a coating method is also applicable.
[0023]
In addition, a silicon oxide film formed by CVD and a silicon oxide film formed by selective oxidation are used in combination, and a silicon oxide film formed by CVD is used in the vicinity of an amplifier that places importance on element isolation. Then, you may make it use properly in one board | substrate like using selective oxidation.
[0024]
In addition, since the flatness of the substrate surface is improved, the processing margin of the photolithography process and the etching process is widened, which is effective for miniaturization.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
[0026]
In the semiconductor device of this embodiment, as shown in FIG. 1, the surface of the field oxide film 4 formed in a frame shape so as to surround the effective imaging region 1 </ b> A of the solid-state imaging device is approximately the same as the surface level of the photosensor 2. It is characterized by being configured to be located at.
Other portions are formed in the same manner as the conventional solid-state imaging device shown in FIG.
[0027]
That is, as shown in FIG. 1, the field oxide film 4 is formed in the recess R formed on the surface of the substrate 1, and the protruding height from the surface level of the substrate 1 is reduced. And
[0028]
A field oxide film 4 by selective oxidation is formed in the recess R formed on the surface of the silicon substrate 1, and there is almost no step at the interface between the non-imaging region 1B and the effective imaging region 1A. A photodiode 2 is formed in the silicon substrate 1, and a photoelectric current generated by the photodiode 2 is read out through the charge transfer electrode of the charge transfer element 3.
[0029]
Here, a silicon oxide film 4 having a thickness of 800 nm by selective oxidation is formed in a recess R having a depth of about 600 nm formed in a peripheral shape of the silicon substrate 1. In the element region surrounded by the silicon oxide film 4, the photodiode 2 and the charge transfer element 3 are arranged as an effective imaging region 1A. On the other hand, the field oxide film 4 and the outside thereof become a non-imaging region 1B. In the non-imaging region 1B, a field for separating a signal processing circuit and the like from a horizontal transfer register or a solid-state imaging device for transferring signal charges in the horizontal direction. A silicon oxide film 4 as an oxide film is formed, and a wiring layer 17 is formed thereon.
[0030]
That is, as shown in FIG. 1, a photodiode 2 and a charge transfer device 3 are formed in an effective imaging region 1A surrounded by a field oxide film 4 in a silicon substrate 1, and an upper layer thereof is covered with an insulating film 5. Has been.
[0031]
A wiring electrode 7 is formed on the field oxide film 4, and the upper layer is covered with a planarizing film 6. Further, a color filter 8 and a microlens 9 are provided.
[0032]
According to such a configuration, as shown in FIG. 1, in the effective imaging area 1A, good imaging characteristics can be obtained up to the boundary with the surrounding non-imaging area 1B. Will almost match.
[0033]
Next, the manufacturing process of the solid-state imaging device of the present embodiment will be described with reference to FIGS.
[0034]
First, as shown in FIG. 3A, an n-type silicon substrate 1 is prepared.
Then, a buffer silicon oxide film 10 and a silicon nitride film 11 are formed and patterned by photolithography to form a two-layer mask pattern.
Next, as shown in FIG. 3B, the substrate surface is removed by etching using this mask pattern as a mask to form a recess R on the surface.
[0035]
In this state, heating is performed in an oxidizing atmosphere at 900 ° C. to form a field oxide film 4 made of a silicon oxide film having a thickness of about 400 to 600 nm, as shown in FIG. Then, the silicon nitride film 11 is removed, a gate oxide film is formed by a normal method, and the photodiode 2, the charge transfer element 3, the wiring layer 7, and the like are formed.
In this way, the solid-state imaging device shown in FIG. 1 is formed.
[0036]
In this structure, a thick field oxide film of 400 to 600 nm is formed, but since it is formed in the recess R, the level difference is small, so the surface is flat even around the field oxide film, and is formed in the upper layer. Condensation by the microlens 9 is also performed with high accuracy, and image quality is not deteriorated.
[0037]
Further, according to this solid-state imaging device, since a step due to the field oxide film is small, a focus margin in photolithography is widened, and a fine pattern can be processed.
[0038]
Also, in manufacturing, a recess is formed, and the silicon oxide film is filled in the recess, so that the manufacturing is easy.
[0039]
In the above embodiment, the concave portion formed by selectively removing the silicon oxide film by selective oxidation is used. However, the concave portion may be formed by etching the substrate.
[0040]
In the above embodiment, the silicon oxide film is formed by performing selective oxidation in the recess. However, a silicon oxide film may be formed by a CVD method and used as a field oxide film.
[0041]
Needless to say, an impurity doped film such as a BPSG film or a PSG film may be filled in the recess by a coating method.
[0042]
(Second Embodiment)
In the first embodiment, the step of the substrate surface is reduced by forming the silicon oxide film in the recess, but in this example, after the silicon oxide film is formed by selective oxidation, the silicon oxide film is formed. The surface may be planarized by selectively removing the film by CMP.
[0043]
That is, in the semiconductor device of this embodiment, as shown in FIG. 4, the surface of the field oxide film 4 formed in a frame shape so as to surround the effective imaging region 1A of the solid-state imaging device is planarized by CMP, The sensor 2 is configured to be located at the same level as the surface level.
[0044]
Other portions are formed in the same manner as the solid-state imaging device of the first embodiment of the present invention shown in FIGS.
[0045]
That is, as shown in FIG. 4, the field oxide film 4 is planarized and formed so that the protruding height from the surface level of the substrate 1 is lowered.
[0046]
In this example, the field oxide film 4 by selective oxidation is formed on the surface of the silicon substrate 1, and the surface of the field oxide film 4 is removed by etching and polishing. Therefore, the non-imaging area 1B and the effective imaging area 1A are removed. There are almost no steps at the interface. A photodiode 2 is formed in the silicon substrate 1, and a photoelectric current generated by the photodiode 2 is read out through the charge transfer electrode of the charge transfer element 3. The upper insulating film 5, the planarizing film 6, and the wiring layer 7 are also formed in the same manner as in the first embodiment.
[0047]
Here, a silicon oxide film 4 having a thickness of 800 nm formed in a frame shape on the periphery of the silicon substrate 1 is left only by a thickness of about 400 nm by surface polishing, thereby forming a substantially flat surface. It is like that.
[0048]
According to such a configuration, as in the first embodiment, in the effective imaging region 1A, good imaging characteristics can be obtained up to the boundary with the surrounding non-imaging region 1B, and the image quality degradation unit 21 Substantially coincides with the non-imaging area.
[0049]
Next, the manufacturing process of the solid-state imaging device of the present embodiment will be described with reference to FIGS.
First, as shown in FIG. 5A, an n-type silicon substrate 1 is prepared.
Then, as shown in FIG. 5B, a mask pattern made of a non-oxidizing film such as silicon nitride (not shown) is formed and heated in an oxidizing atmosphere at 900 ° C. to oxidize with a thickness of about 800 nm. A field oxide film 4 made of a silicon film is formed.
[0050]
Thereafter, as shown in FIG. 5C, the field oxide film 4 protruding from the substrate surface is removed, and the surface is flattened by CMP.
[0051]
Then, a gate oxide film is formed by a normal method, and the photodiode 2, the charge transfer element 3, the wiring layer 7, and the like are formed.
In this way, the solid-state imaging device shown in FIG. 4 is formed.
[0052]
Even in such a configuration, as in the first embodiment, since the substrate surface is flat, the area where the imaging characteristics are good and the image quality is deteriorated almost coincides with the non-imaging area, which is maximally effective. An imaging region can be obtained.
[0053]
The present invention is particularly effective for a CCD area sensor, but can also be applied to other imaging devices such as other line sensors and CMOS sensors.
[0054]
【The invention's effect】
As described above, according to the solid-state imaging device of the present invention, the step due to the element isolation film (field oxide film) can be reduced at the boundary portion between the effective imaging region and the non-imaging region. The color separation filter and the on-chip lens to be used can be arranged in a flat state. As a result, it is possible to improve sensitivity, color non-uniformity, and the like in the periphery of the effective imaging region, and to prevent deterioration in image quality.
[0055]
Further, since the flatness of the substrate surface is improved, the processing margin of the photolithography process and the etching process is widened, and the element can be miniaturized.
[0056]
Furthermore, the thickness of the field oxide film can be made sufficiently large without increasing the level difference, and the capacitance between the substrate and the wiring can be made sufficiently small.
[0057]
In addition, the substrate can be planarized without any significant process changes, and manufacturing is also easy.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a solid-state imaging device according to a first embodiment of the present invention.
FIG. 2 is a plan view of the solid-state imaging device according to the first embodiment of the present invention.
FIG. 3 is a diagram showing a manufacturing process of the solid-state imaging device according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating a solid-state imaging element according to a second embodiment of the present invention.
FIG. 5 is a diagram showing a manufacturing process of the solid-state imaging device according to the second embodiment of the present invention.
FIG. 6 is a diagram illustrating a conventional solid-state imaging device.
FIG. 7 is an explanatory diagram showing a plan view of a conventional solid-state imaging device.
FIG. 8 is a cross-sectional explanatory diagram of a conventional solid-state image sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Photodiode 3 Charge transfer element 4 Field oxide film 5 Insulating film 6 Flattening film 7 Wiring 8 Color filter 9 Microrod lens

Claims (7)

A solid-state imaging device, characterized in that a surface of a field oxide film formed in a frame shape so as to surround an effective imaging region of the solid-state imaging device is located at the same level as the surface level of a photosensor. The solid-state imaging device according to claim 1, wherein the field oxide film is a film formed by selective oxidation (LOCOS). The solid-state imaging device according to claim 1, wherein the field oxide film is formed in a recess formed in a frame shape. A method of forming a solid-state imaging device on a semiconductor substrate surface,
The step of forming a field oxide film so as to surround the solid-state imaging element formation region,
Including a step of forming a field oxide film so that the surface of the field oxide film formed in a frame shape so as to surround the effective imaging region of the solid-state imaging device is positioned at the same level as the surface level of the photosensor. A method for manufacturing a solid-state imaging device. The step of forming the field oxide film includes:
Forming a recess in a region surrounding at least a solid-state image sensor forming region on the surface of the semiconductor substrate;
The method for forming a solid-state imaging element according to claim 4, further comprising: forming a silicon oxide film in the recess. 6. The method for manufacturing a semiconductor device according to claim 5, wherein the step of forming the silicon oxide film is a step of forming by selective oxidation. The step of forming the field oxide film includes the step of forming silicon oxide by selective oxidation,
5. The method of manufacturing a semiconductor device according to claim 4, further comprising a step of removing and planarizing the protruding portion of the silicon oxide film by CMP.

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