JP2521789B2 - Photosensitive unit structure of solid-state imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photosensitive section structure of a solid-state image pickup device in which a plurality of image pickup elements are arranged in one chip.

(Prior Art) Various types of solid-state imaging devices have been put into practical use. Among these solid-state image pickup devices (also referred to as image sensors), contact-type image sensors have been developed and put into practical use due to reasons such as downsizing, ease of use, and high performance. A CCD image sensor using a charge-coupled device (referred to as CCD) is often used as a contact-type image sensor in order to increase the sensitivity, and a schematic block configuration diagram thereof is shown in FIG. This image sensor (hereinafter sometimes simply referred to as CCD sensor) is
As is conventionally known, a silicon 1 chip 10 is provided with an image pickup device array 12, a photogate 14, a transfer gate 16, a CCD shift register 18, a preamplifier 20 which constitutes a photosensitive section.
It has a structure mainly formed with. A PN junction photodiode is usually used as the image pickup element, and an N channel MOS structure is mainly used as the CCD image sensor. The light receiving windows of these image pickup devices correspond to pixels.

By the way, recently, a CCD in-line contact type image sensor has been developed and put into practical use in which a plurality of CCD sensors are arranged and fixed in a straight line on a substrate such as a thick film ceramic to form a multi-chip.

In this in-line contact type image sensor, each image-forming device array (corresponding to a pixel array) is usually arranged linearly in sequence to form an image-capturing device, which is shown in FIG. As described above, since the gap 24 is formed in the joint between the adjacent chips 22a and 22b, the pixel pitch P between the pixels 26 in the chips 22a and 22b and the chip end side of the respective chips 22a and 22b. The pixel pitch P'between the two pixels 28 is different. The standard of the pixel pitch P'of the chip joint is set by the International Telegraph and Telephone Consultative Committee (CCITT) to be within 125% of the pixel pitch P.

In order to satisfy this standard, as shown in FIG. 4, the processing accuracy is increased and the cutting accuracy of the chip is ± α.
₁ and ± α ₂ , and the scanning direction accuracy ± β ₁ and ± β ₂ due to the inclination of the cut surface during chip scribing is made as small as possible.

However, even if the cutting accuracy is increased, there is a risk that the chip 28 of each of the chips 22a, 22b, etc. is blocked from being imaged, that is, the photodiode 28 is damaged by this cutting. Therefore, the image pickup device on the chip end side of the image pickup device array forming the photosensitive portion is separated from the chip end by distances m ₁ and m ₂ so that the depletion layer 30 expanded during operation is not damaged by this cutting. , And at that time, the distances l ₁ and l ₂ from the chip edge to the center of the pixel 28 on the chip edge side
Need to be smaller respectively. In FIG. 4, numeral 32 is a semiconductor layer of one conductivity type, and numeral 34 is a diffusion layer of the other conductivity type.
Reference numeral 36 is a light-shielding film that defines the pixel and thus the light-receiving window.

Therefore, conventionally, in the literature ("Television Technical Report" ED84-161,
An image pickup device arranging device for a CCD in-line contact type image sensor as disclosed in "CCD in-line contact type image sensor" on pages 41 to 46 has been proposed.

FIG. 5 is a cross-sectional view schematically showing a chip cross section in the direction along the arrangement direction of the image pickup elements, which is used for explaining the structure of the photosensitive section of the conventional solid-state imaging device which constitutes the photosensitive section. In this figure, 40 is one conductivity type (P ⁺ ) substrate, 42 is a P-epitaxial layer, 44a and 44b are other conductivity type (N ⁺ ) diffusion layers, and one conductivity type first layer ( Substrate 40 and epitaxial layer
The second conductive type second layer (diffusion layer 44a,
A plurality of 44b) are formed to form an array of the image pickup device (photodiode) 46a on the chip center side and the image pickup device (photodiode) 46b adjacent to the chip end. Not only these photodiodes 46a but also the photodiodes 46a
And 46b are separated from each other by a P ⁺ channel stop layer 48a. 50a and 52 are SiO ₂ oxide films, and 64 is a light-shielding film that defines a light-receiving window 66 for providing pixels.

In this conventional structure, the width of the diffusion layer 44b of the image pickup element (photodiode) 46b adjacent to the chip end is narrower than the width of the light receiving window 56, and the P ⁺ channel stop layer 48b and SiO on the chip end side are formed. ₂ Place the oxide film 50b on the photodiode 46
Extend it to the inside of b and cut N ^{+ of the} photodiode 46b from the chip cut surface.
The distance to the diffusion layer 44b is increased so as not to be damaged by chip cutting, and the structure is such that the increase in dark output is suppressed, and the width of the light receiving window 56 and the width of the diffusion layer 44a are almost the same. This is different from the structure of the other photodiode 46a on the chip center side in which the P ⁺ channel stop layer 48a and the SiO ₂ oxide film 50a are covered with the light shielding film 54.

FIG. 6 is a schematic plan view showing a pixel 46 near the chip edge.
The arrangement relationship between the N ⁺ diffusion layer 44a of a, the N ⁺ diffusion layer 44b and the P ⁺ channel stop layer 48b of the pixel 46b is shown.

(Problems to be Solved by the Invention) However, the photodiode on the chip end side of this conventional structure has the following problems.

First of all, as a result of making the N ⁺ diffusion layer 44b of the photodiode 46b on the chip end side narrower than the width of the N ⁺ diffusion layer 44a of the other photodiode 46a, the depletion layer 58b of the photodiode 46b becomes the depletion layer 58a of the photodiode 46a. It is smaller than the spread area. Therefore, the light L incident on the photodiodes 46a and 46b is
Photocarriers 60 generated in the P-epitaxial layer 42 are trapped in the N ⁺ diffusion layers 44a and 44b, respectively.
A part of the photo carrier 62 due to the light L incident from above the P ⁺ channel stop layer 48b of the photodiode 46b is trapped in the depletion layer 58b.

Therefore, a difference occurs in the photosensitivity between the pixel on the chip end side and another pixel. Therefore, there is a problem in that the light receiving window 56 of the photodiode 46b needs to be lengthened in the direction orthogonal to the pixel array direction so that the pixels have the same sensitivity.

Further, in the photodiode 46b on the chip end side, light also enters from the upper side of the P ⁺ channel stop layer 48b, so N
^{+ In} addition to light from above the diffusion layer 44b, SiO _{2 having a} film thickness t ₁
Photocarriers generated by light transmitted through the oxide film 52 and the SiO ₂ oxide film 50b having a film thickness t ₂ are also captured by the N ⁺ diffusion layer 44b. The latter light has a difference in sensitivity between the photodiode 46b on the chip end side and the other photodiodes 46a because the transmittance changes depending on the wavelength due to the interference of light by the two-layer oxide films 52 and 50b. was there. This state is shown in FIG.

FIG. 7 is a diagram showing sensitivity characteristics with respect to each image pickup element of the conventional photosensitive section, that is, pixels and light wavelength. FIG. 7A is a schematic sectional view similar to FIG. 5, and FIG. It is a sensitivity output characteristic figure (it represents with au). In FIG. 7B, the horizontal axis plots the position in the element array direction, and the vertical axis plots the sensitivity output. In the figure, λ ₁ , λ ₂ ,
λ ₃ indicates the wavelength of incident light. As can be understood from this figure, the sensitivity output from above the P ⁺ channel stop layer 48b of the photodiode 46b on the chip end side is disturbed.

An object of the present invention is to provide a solid-state image pickup device that has the same element structure and eliminates the difference in sensitivity regardless of whether the image pickup device is on the chip end side or the image pickup device on the chip center side, and thus has uniform photosensitivity and low dark output. It is to provide a light-sensitive part structure.

(Means for Solving the Problem) In order to achieve this object, according to the present invention, photodiodes in which a first layer of one conductivity type and a second layer of the other conductivity type are formed and arranged are mutually arranged. A photosensitive portion of a solid-state image pickup device comprising a plurality of image pickup devices separated by a first channel stop layer, each light receiving window of each image pickup device being defined by a light shielding film, and a transparent insulating film being provided in the region of these light receiving windows. In the structure, the width of the above-mentioned second layer along at least the array direction of the image pickup device is made narrower than the width of the light receiving window along this array direction, and the shallow first layer on both sides of the above-mentioned second layer along this array direction. Two channel stop layers are provided, and the depth of the second layer is formed deeper than the second channel stop layer.

In carrying out the present invention, the planar shape and the sectional shape of all the image pickup devices are made substantially the same. As a result, the photosensitive surface structure of each image pickup device becomes the same.

Further, according to a preferred embodiment of the present invention, the first layer is P
It is preferable that the second layer is of conductivity type and the second layer is of N ⁻ conductivity type.

Further, in implementing the present invention, it is preferable that the first channel stop layer and the second channel stop layer are of P ⁺ conductivity type.

Further, according to the preferred embodiment of the present invention, it is preferable that the film thickness and shape of the transparent insulating layer of each image pickup device are substantially uniform.

(Operation) As described above, according to the present invention, since the width of the light receiving window or the width of the second layer, for example, the N ⁻ diffusion layer is narrower than the width of the light receiving window, the dark current can be reduced. I can.

Further, since a shallow second channel stop layer is formed on at least both sides of this second layer to fill the area of the light receiving window, and the depth of this second layer is formed deeper than this second channel stop layer, depletion The layer spreads over the entire width of the light receiving window below the second channel stop layer, and therefore photocarriers can be efficiently collected in the second layer, and the sensitivity is uniform and high in each image sensor. Becomes

In addition, since the photosensitive surface structure of all image elements is the same, it is possible to eliminate variations in sensitivity output due to the difference in light transmittance due to the thickness of the SiO ₂ oxide film, and to make the dark output of all photodiodes uniform. .

(Embodiment) An embodiment of the photosensitive section structure of the solid-state imaging device of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a portion near a chip end taken along the element arrangement direction of the solid-state imaging device of the present invention, that is, along the pixel arrangement direction.

It should be noted that, in the drawings, the shapes, dimensions, arrangement relationships and the like of the respective constituents are only schematically shown to the extent that the present invention can be understood, and therefore these are not limited to the embodiments shown in the drawings. Absent. Furthermore, the materials, conductivity types, numerical examples, etc. used for the respective constituents are not limited in any way, and may be suitably selected as required.

Structure Description In FIG. 1, a P type substrate 50 of one conductivity type is provided with a P type epitaxial layer 52 as a first layer with a film thickness of, for example, 10 μm. 54 is N ⁻ as the second layer of opposite conductivity type
Reference numeral 56 denotes a type diffusion layer, and reference numeral 56 denotes a P ⁺ type shallow channel stop layer, that is, a second channel stop layer provided at least on both sides of the diffusion layer 54 in the element arrangement direction. Reference numeral 58 is a P ⁺ type channel stop layer for element isolation, that is, a first channel stop layer, 60 is a diffusion layer 54, a shallow channel stop layer 56, and a field oxide such as SiO ₂ formed on the upper side of the channel stop layer 58. Transparent insulating film consisting of a film, 62
Is a transparent intermediate insulating film such as SiO ₂ provided on the upper side of the field oxide film 60, 64 is an individual image pickup device 72, 74 (where 72 is the image pickup device on the chip center side, and 74 is the chip end side). It is a metal light-shielding film such as Al for defining light-receiving windows (henceforth pixels) 66 of the image pickup element. The size of the light receiving window 66 of each of the image pickup devices 72 and 74, and hence the light receiving surface, is formed to be the same.

In the embodiment shown in FIG. 1, the width of the second diffusion layer 54 along at least the arrangement direction of the image pickup devices 72, 74 is narrower than the width of the light receiving window 66 along the direction, for example, 20 μm, for example, 10 μm.
Although not a necessary requirement, the center of the light receiving window 66 is configured to coincide with the center of the diffusion layer 54.
The doping concentration of this diffusion layer 54 is preferably about 8 × 10 ¹⁵ dose / cm ³ .

Then, a shallow channel stop layer 56 is formed around the diffusion layer 54, in this case, on both sides of the diffusion layer 54 along the element arrangement direction and mainly below the light receiving window 66 from the surface of the P-type epitaxial layer 52 to a depth. It is set up to about 3500Å. The doping concentration of this shallow channel stop layer 56 is 3 × 10 ¹⁶
A dose / cm ³ is suitable.

The diffusion layer 54 is formed below the shallow channel stop layer 56 to a depth of about 8500Å.

Further, the P ⁺ channel stop layer 58 has a film thickness of about 2 μm and its doping concentration is about 4 × 10 ¹⁶ dose / cm ^3, and the light receiving window of the field oxide film 60 which is a transparent insulating film.
It is preferable that the lower side of 66 has a uniform film thickness of about 1100 Å, and the lower side of the light shielding film 64 has a uniform film thickness of about 8000 Å.

Further, the thickness of the intermediate insulating film 62 is set to about 8000Å, and at least the light receiving window 66 has a uniform film thickness within the region. The thickness of the light shielding film 46 is also set to about 8000Å.

As described above, the numerical examples described above are merely suitable examples, and can be set to arbitrary suitable values according to the design.

Further, in the embodiment of the present invention, it is preferable that the planar shape and the cross-sectional shape of each image pickup element are formed in the same manner in order to make the photosensitivity and / or other characteristics of each image pickup element match. In particular, it is preferable that the film thickness and shape of the transparent insulating film of each image sensor be substantially uniform. By doing so, the photosensitive surfaces of all the elements have the same size, and the photosensitive characteristics are the same.

FIG. 8 shows a pixel array in the vicinity of the chip edge of two adjacent chips 80 and 82 when a plurality of chips of a solid-state image pickup device having the image sensor array thus constructed are arranged linearly and sequentially. , Diffusion layer 54 and shallow channel stop layer
It is a figure for demonstrating the positional relationship of 56. In this figure, the area of the light receiving window defined by the light shielding film 64, that is, the light receiving surface corresponds to the pixels 84 and 86 of each image pickup element.
Is a pixel on the center side of the chips 80 and 82, and a pixel 86 is a pixel on the edge of the chips 80 and 82.

As can be understood from the configurations of FIGS. 1 and 8 described above, in the photosensitive surface structure, the N ⁻ type diffusion layer 54, which is the second layer of the other conductivity type, is formed narrower than the light receiving surface, and the diffusion is performed. The structure is such that the layer 54 is sandwiched from both sides in the device arrangement direction by a P ⁺ type shallow channel stop layer 56 of one conductivity type. Therefore, when cutting the chip, it is possible to avoid damage to the diffusion layer 54 due to damage from the cut surface of the chip end, and it is possible to reduce the dark output. In addition, regardless of the arrangement position on the chip, since the photosensitive surface structure of each image sensor is the same, the output of all pixels is uniform, and the wavelength sensitivity characteristic of incident light is substantially equal for each pixel. Will be the same.

Further, a diffusion layer 54 which is the second layer of the other conductivity type is provided with a shallow channel stop layer of one conductivity type which is adjacent to the diffusion layer 54.
Since it is formed deeper than 56, a depletion layer (the position of its spread is schematically indicated by a broken line 90 in FIG. 1 is shown around the bottom of the shallow channel stop layer 56 during operation of the image pickup device. Since it spreads to a sufficient extent and spreads to a position in contact with the channel stop layer 58 below the light shielding film 64 in some cases, it is possible to efficiently collect photocarriers by the light incident on the entire light receiving window in all pixels. Can be done,
Therefore, it is possible to suppress a decrease in the sensitivity of the pixels at the chip edge.

Operation Example An operation example of the photosensitive section structure of the solid-state imaging device of the present invention will be briefly described.

When a proper bias voltage is applied to the N ^- diffusion layer 54 of the photodiode constituting the photosensitive portion shown in FIG. 1 in the forward direction with respect to the P-type substrate 50, the depletion layer 90 expands as shown by the broken line. Since the diffusion layer 54 is formed deeper than the adjacent shallow channel stop layer 56, the diffusion layer 54 spreads broadly below the shallow channel stop layer 56 in the lateral direction (element array direction).

Incident light with a light intensity I _o is incident on the intermediate insulating film 62 and the field oxide film.
When the light passes through both oxide films of 60 and enters each of the image pickup devices 72, 74, and thus the pixel, photoelectric conversion is performed in the P-type epitaxial layer 52 and photocarriers (charges) 92 (in the figure, inside and outside the depletion layer 90).
It is indicated by a white circle. ) Occurs.

At this time, if the coefficient considering the reflectance and absorptance of the oxide films 60 and 62 is R, the amount of light transmitted through both oxide films 60 and 62 is (1-R) I _o. Becomes

The charges generated outside the region of the depletion layer 90 by the incident light are diffused, and only the photocarriers 92 taken into the region of the depletion layer 90 within the lifetime τ are accompanied by the photocarriers generated in the depletion layer 90, It is stored in the photogate 14 shown in FIG.

The dark current generated in the N ⁻ type diffusion layer 54 is also accumulated in the photogate 14.

In this way, the photo carriers accumulated in all the photo gates 14 are transferred to the transfer gates 16 as in the conventional case.
To the CCD register 18, transferred by the CCD register 18, passed through the preamplifier 20, and sequentially output from the photocarrier of the photodiode near the preamplifier 20.

Obviously, the invention is not limited to the embodiments described above. For example, the shallow channel stop layer 56 may be included in the N ⁻ diffusion layer 54.
For example, in the above-described embodiment, one and the other conductivity types are set to P.
However, one conductivity type may be N type and the other conductivity type may be P type. In that case, some structural changes are necessary, but these changes are within the range that can be easily considered by those skilled in the art.

Furthermore, a semiconductor material that has been conventionally used can be used as a material for the element structure.

In addition, conditions such as the size, arrangement, and shape of each component can be arbitrarily determined according to the design.

(Effects of the Invention) As is apparent from the above description, according to the photosensitive portion structure of the solid-state imaging device of the present invention, the width of the second layer is narrower than the width of the light receiving window. The dark current can be reduced.

Further, since a shallow second channel stop layer is formed on at least both sides of this second layer to fill the area of the light receiving window, and the depth of this second layer is formed deeper than this second channel stop layer, depletion The layer spreads to the full width of the light receiving window below the second channel stop layer, and therefore, the decrease in the sensitivity output caused by narrowing the width of the second layer can be compensated for by the expansion of the depletion layer. It is possible to suppress the reduction in sensitivity, resulting in high sensitivity.

Further, because of the second channel stop layer, it is possible to avoid damage to the second layer due to the chip end cut surface without impairing the uniformity of sensitivity output.

In addition, since the photosensitive surface structure of all image elements is the same, variations in sensitivity output due to differences in light transmittance due to the thickness of the transparent insulating film are eliminated, and not only the sensitivity output of all photodiodes but also the dark output is uniform. Can be

Due to such advantages, the image pickup element array device of the present invention is particularly suitable for use in a multi-chip CCD image sensor.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a portion near a chip end taken along the element arrangement direction, that is, the pixel arrangement direction of an embodiment of a photosensitive portion structure of a solid-state image pickup device of the present invention, and FIG. FIG. 3 is a schematic block configuration diagram of the image pickup device, FIG. 3 is a diagram for explaining a pixel pitch in a chip joint of an in-line contact CCD image sensor, FIG. 4 is an explanatory diagram of chip processing accuracy, and FIG. FIG. 6 is a cross-sectional view schematically showing a cross section of a chip in a direction along the arrangement direction of image pickup devices, which is used to explain a structure of a conventional solid-state imaging device constituting a photosensing section. FIG. FIG. 7 is a schematic plan structure diagram showing the positional relationship between the diffusion layer and the channel stop layer, and FIG. 7 is an explanatory diagram of sensitivity characteristics with respect to each image pickup element of the photosensitive section structure of the conventional solid-state image pickup device, that is, pixel and light wavelength. , (A) is the same as Fig. 5. A schematic cross-sectional view, (B)
FIG. 8 is a sensitivity output characteristic diagram, and FIG. 8 is a chip end of two adjacent chips when a plurality of chips of the solid-state imaging device having the photosensitive portion structure of the solid-state imaging device of the present invention are arranged linearly and sequentially. FIG. 6 is an explanatory diagram of a positional relationship between a pixel array, a diffusion layer, and a shallow channel stop layer in the vicinity. 50 ... One conductivity type substrate 52 ... One conductivity type epitaxial layer (first layer), 54 ... Other conductivity type diffusion layer (second layer) 56 ... Shallow channel stop layer (second channel) Stop layer) 58 …… Channel stop layer (first channel stop layer) 60 …… Transparent insulation film (field oxide film) 62 …… Intermediate (transparent) insulation film 64 …… Light-shielding film 66 …… Reception window 72,74 …… Image sensor 80, 82 …… Chip, 84, 86 …… Pixel 90 …… Depletion layer, 92 …… Photo carrier.

Claims (5)

(57) [Claims] 1. A plurality of image pickup devices comprising photodiodes in which a second layer of the other conductivity type is formed and arranged in a first layer of the one conductivity type and are separated from each other by a first channel stop layer. In the photosensitive portion structure of the solid-state image pickup device in which the light receiving window of the image pickup device is defined by a light shielding film, and the transparent insulating film is provided in the region of the light receiving window, the width of the second layer along at least the array direction of the image pickup device is The width of the light receiving window along the direction is narrower, and shallow second channel stop layers are provided on both sides of the second layer along the arrangement direction, and the depth of the second layer is set to the second channel stop layer. The photosensitive section structure of the solid-state imaging device is characterized in that it is formed deeper than the above. 2. The photosensitive section structure of a solid-state image pickup device according to claim 1, wherein the planar shape and the sectional shape of all the image pickup elements are substantially the same. 3. The photosensitive portion structure of a solid-state imaging device according to claim 1, wherein the first layer is of P conductivity type and the second layer is of N ⁻ conductivity type. 4. The photosensitive section structure of a solid-state image pickup device according to claim 1, wherein the first channel stop layer and the second channel stop layer are of P ⁺ conductivity type. 5. The photosensitive section structure of a solid-state image pickup device according to claim 1, wherein the transparent insulating layer of each image pickup element has a substantially uniform thickness and shape.