JPS61265865A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the leakage of light due to the effect such as the multiple reflection and the like of the light which is made incident obliquely as well as to reduce the quantity of smear by a method wherein no electrode material such as polysilicon and the like is used on the part located under the edge of a light-shielding film, the insulating material such as an oxide film is used on the above-mentioned part, and the thickness of said insulating film is brought into the specific measurement or less. CONSTITUTION:The film thickness of an N-type region 15 and the thermally oxided film 100 located on the first polysilicon is set at 1,000Angstrom , and an aluminum light- shielding film 9 is formed on the thermally oxided film 100. An oxide protective film 19 of 5,000Angstrom thickness is formed as the top layer. The distance between a storage region and the N-type region 15 on the edge part of the light-shielding film 9 is 1,000Angstrom , no polysilicon electrode is present between the above-mentioned two regions, and an oxide film is present there. The light-shielding film 9 is formed in such a manner that is envelopes the polysilicon electrode and the thickly formed thermally oxided film 13 located on a channel stopper 6. When the distance between the edge part of the light-shielding film 9 and a silicon substrate 11 is set at (lambda/2n)Angstrom or above, the creeping of light can be prevented completely.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a solid-state image sensor.

(Prior art and its problems) Solid-state imaging devices have a drawback in that a smear phenomenon occurs when a high-brightness object is imaged, and efforts have been made to reduce the amount of smear.

Yasuo Ishihara et al., Journal of the Television Society, Volume 37, 1983, 78
Interline COD image sensor (IL-C0D) described on pages 2 to 787 under the title "Vertical overflow structure CCD image sensor"
was one of the conventional solid-state image sensors with the lowest amount of smear. FIG. 2 is a schematic plan view of the IL-COD.

Storage regions 1 are regularly arranged in the horizontal and vertical directions. The reverse bias capacitance of the PN junction is used to accumulate photoelectrically converted signal charges. A vertical CCD register 2 is provided adjacent to one side of the column of storage regions 1, and a transformer 7 agate section 3 is provided between the vertical COD register 2 and the storage region 1.

At the end of the vertical COD register 2 in the charge transfer direction, there is a horizontal C
An OD register 4 is provided, and an output section 5 is provided at the end of the horizontal COD register 4 in the charge transfer direction. In this IL-CCD, photoelectrically converted signal charges are accumulated in an accumulation region l.

The transfer gate section 3 is turned on every field period or every 7 frame periods, and the vertical CO is removed from the storage region 1.
The signal charge is transferred to the D register 2 and further output to the output section 5 by the functions of the vertical COD register 2 and the horizontal COD register 4.
and output to the outside of the solid-state image sensor.

FIG. 3 is a plan view of a two-dimensionally arranged repeating cell portion of the IL-COD of FIG. 2. FIG. A fishhook pattern with a dotted pattern is a channel stopper 6, which separates the vertical CCD register 2 from the p storage region 1, which is separated from the storage region 1.

The part surrounded by the dashed line and the top right of the dashed line is the 1st part.
This is a polysilicon electrode 7. The first polysilicon electrode 7 is used as an electrode of the vertical COD register 2 and as an electrode of the transfer gate section 3.

This is the portion Fii2 polysilicon electrode 8 surrounded by a dashed dotted line and marked with a notch extending upward to the left of the dashed dotted line.

The second polysilicon electrode 8 is used as an electrode of the vertical COD register 2.

The portion that is not covered by the channel stopper 6 and is not covered by the first polysilicon electrode 7 and the second polysilicon electrode 8 is the S type region 1. The part surrounded by the two-dot chain line and marked with , , and on the upper right of the two points Ml is the aluminum 2ium 'it optical film 9.
It is. It is a strip-shaped turn and shields the vertical COD register 2 and the agate portion 3 of the transformer 7 from light. The edge 10 of the light-shielding film 9 is a key 9 that can be connected to the edge of the channel stopper 6, the M1 polysilicon electrode 7, the second polysilicon electrode, and the contact electrode 8.
It is designed to protrude by 0.5 μm to 1 μm and be located above the accumulation region l, thereby enhancing the light shielding effect.

FIG. 4 is a partial cross-sectional view along I-1' of the third factor.

N8! ! on one main surface of the silicon substrate 11.

In the storage region l, the junction depth is small, and in the transfer gate section 3 and the vertical CCD register 2, a P well 12 with a large junction depth is formed.

The channel stopper 6 has a thick thermal oxide film 13 formed by a selective oxidation method, and the P''' region 1 is formed directly below the thermal oxide film 13.
4 is formed. In the storage region 1, an N-type region 15 is formed above a P well having a small junction depth. Signal charges are accumulated in the reverse bias capacitance of the PN junction between this N-type region 15 and the P-well or middle P'' region 14.
6 is formed.

As described above, there are P wells 12 and P0 in the silicon substrate.
A region 14, a trapezoidal region 15, and a buried layer 16 are formed. A first polysilicon electrode 7 is formed on the transfer gate portion 3 and the buried layer 16 via a thermal oxide film 101 having a thickness of 1000 Å. A thermal oxide film 100 with a thickness of 2000 Å is formed on the first polysilicon electrode. A film with a thickness of 2000 mm is formed on the N-type region 15 of the storage region 1.
Thermal oxidation M100 of A is formed. Thermal oxide film 100
A high-concentration phosphorus glass layer 17 is formed thereon and is useful for flattening the device surface. High concentration phosphorus glass layer 1
The film thickness of No. 7 is approximately 1 μm on average. A silicon oxide film 18 having a thickness of 5000 Å is formed on the high concentration phosphorus glass layer F by vapor phase chemical reaction growth. A light shielding layer M9 made of aluminum and having a thickness of 1 μm is formed on the oxide film 18. Furthermore, a protective film 19 of an oxide film having a thickness of 5000 Å is formed on the uppermost layer by vapor phase chemical reaction growth.

In this IL-COD, the storage region 1 is formed with a small junction depth l.
Forming in the nP well 12 prevents the blooming phenomenon and suppresses smear caused by charge diffusion in silicon.

However, the angle of incidence of light entering the IL-COD from the optical lens ranges from about 0 degrees to about 40 degrees with respect to the normal to the device surface. As shown in FIG. 4, there is an insulating film of about 1.7 μm between the aluminum light shielding layer 9 and the N-type region 5. As shown in FIG. Therefore, obliquely incident light may reach the channel stopper 6, transfer gate section 3, or vertical COD register 2 without being incident on the N-type region 15. This is particularly noticeable when multiple reflections occur. Charges generated by such sources become smear components.

The above is the cause of smear, and when a high-brightness object is imaged, this smear appears on the playback screen as a white band-shaped false signal in the vertical direction above and below the high-brightness object, making it unsightly.

A different type of IL-CCD from the IL-COD shown in FIG. 4 will be explained. Hiroshi Matsumoto et al. published ``High Resistance M
The IL-COD explained under the title "MO8 type sensor CCD image sensor using CZ substrate" is the storage area KMO.
An 8-type diode is used.

FIG. 5 is a partial cross-sectional view of the repeating cell portion, and corresponds to FIG. 4.

A P-type silicon substrate is used. A P-type region 21 as a channel stopper on one main surface, a buried vertical C
A buried layer 16 of the OD register, a barrier region 22 surrounding the buried layer 16i, a barrier region 22 for preventing smearing by utilizing the effect of contact potential difference, and an N layer for preventing pluming.
A 9-type overflow train n and a P-type overflow control section 24 are formed. The above is formed in the semiconductor substrate 20. A first polysilicon electrode 7 is formed on the transfer gate portion and buried layer 16 with a thermal oxide film 101 having a thickness of about 1000 Å interposed therebetween. A third polysilicon electrode 25 with a thickness of 500 Å is formed on the first polysilicon electrode 7 and the storage region with a thermal oxide film 00 having a thickness of 1700 Å interposed therebetween. An aluminum light-shielding film 19 having a thickness of about 1 μm is formed on the third polysilicon electrode stone.

In addition to blocking light, the light shielding film 9 also serves as a wiring for the third polysilicon electrode 251C. In this IL-COD, the blooming phenomenon is prevented by the function of the overflow drain control section. The barrier region n suppresses smear caused by charge diffusion in the silicon.

However, the incident angle of light entering the ft, II, -CCD from the school lens is 0 degrees to 4 degrees with respect to the normal MK of the device surface.
It is up to about 0 degrees. As shown in FIG. 5, there is no light shielding film 9, that is, at the opening, the third polysilicon electrode 2 is placed from above.
5. The structure includes a thermal oxide film 00 and a silicon substrate 20. For this reason, a portion of the obliquely incident light is transmitted through the thermal oxide films 100 and 101 while being reflected multiple times by the third polysilicon electrode 5 and the silicon substrate. Thermal oxidation jllHoo.

A part of the light traveling through the IQI was incident on the vertical COD register 2, causing smear.

This smear made the reproduced image unsightly, especially when a high-brightness subject was imaged.

(Object of the Invention) An object of the present invention is to provide a solid-state imaging device that can eliminate such conventional drawbacks, suppress smear phenomena, and realize good reproduced images.

(Structure of the Invention) According to the present invention, a solid-state image sensor has a plurality of storage regions arranged on a semiconductor substrate, and a region at least partially covered with a light-shielding film to read signal charges stored in the storage regions. In this case, an insulator is formed between at least a part of the edge of the light shielding film and the semiconductor substrate, and the thickness of the insulator is A solid-state imaging device characterized in that the length is (λ/2n)A or less can be obtained.

(Summary of the present invention) The present invention solves the problems of the prior art by adopting the above-mentioned configuration. In a solid-state image sensor formed on a semiconductor substrate such as silicon, it is desirable that there is no polysilicon electrode directly under the edge of a light-shielding film such as aluminum, and that the oxide film has a small thickness. λÅ
, where n is the refractive index of the oxide film, it is preferably (λ/2n)A or less.

In a solid-state imaging device having such a structure, the light-shielding property is greatly improved even against obliquely incident sources, and the amount of smear is reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

A schematic plan view of an IL-CCD according to an embodiment of the present invention is shown in FIG.
Same as the figure, a plan view #i of a two-dimensionally arranged repeating cell part! It is the same as Figure 3.

FIG. 1 and FIG. 3 are partial cross-sectional views along I-I'. In FIG. 1, components having the same functions as those in FIG. 2.3.4 are indicated by the same symbols.

In FIG. 1, the structure inside silicon substrate 11 is the same as that in FIG. The structures of the first polysilicon electrode 7 and the second polysilicon electrode 8 are also the same as those in FIG. N
The thickness of the thermally oxidized gi 00 on the mold region 15 and the first polysilicon is 100 OA.

A light shielding layer M9 made of aluminum is formed on the thermal oxide film 100. Furthermore, the top layer is an oxide film with a thickness of 5000 A! The I film 19 is formed by vapor phase chemical reaction growth.

As can be seen from FIG. 1, at the edge of the light-shielding film J, the distance from the storage region Nfi region 15 is 100 OA.
There is no polysilicon electrode between them, but an oxide film. The light shielding film 9 has a thickness on the polysilicon electrode and the channel stopper 6, and has a shape that wraps around the thermal oxide film 13.

FIG. 6 shows the amount of smear when the distance to the silicon substrate at the edge of the light shielding M9, that is, the film thickness of the thermally oxidized J [100] on the N-type region 15 is changed. The wavelength of the incident light is 550
It is 0A. As is clear from the figure, the smaller the oxide film thickness, the smaller the amount of smear, and when the oxide film thickness is 0.5 μm or more, the change in the amount of smear is small.

However, it can be seen that when the oxide film thickness becomes 0.5 μm or less, the amount of smear decreases rapidly, and particularly when the oxide film thickness decreases to 0.3 μm or less, it decreases significantly. If the oxide film thickness is small, there are disadvantages in that the capacity of the IJ silicon electrode and the light shielding jet amount becomes large, and the number of sheets between the polysilicon electrode and the light shielding film increases.

Consider the case where light travels between parallel mirror surfaces while being reflected. The silicon surface and the aluminum light shielding film form a mirror surface Kfi. In this case, there is a cutoff wavelength λcA, and elements with wavelengths longer than λ(A are attenuated.If the distance between parallel mirror surfaces is 1 person and the refractive index is n, then there is a relationship of λ(=2nt. In the case of Figure 6, the refractive index of thermal oxidation gioo is n = 1.46
Since the wavelength of the incident light is 550 OA, if the thermal oxide film thickness is 1900 Å or less, it should be possible to completely prevent the light from going around.

However, in FIG. 6, the full pressure smear amount is not zero. This is probably because, as can be seen from FIG. 3, the round edge of the light shielding film 9 does not have a structure that prevents light from going around. That is, this is probably because there is a portion where the polysilicon electrode exists directly under the edge of the light shielding film 9.

To reduce smear, it is desirable that the light-shielding film wraps the thick oxide film of the silicon electrode and channel stopper as much as possible. In other words, it is desirable that the distance between the edge of the light-shielding film and the silicon substrate be less than (λ/2n)A, and that only an insulating material be provided between them.

(Effects of the Invention) As is clear from the above detailed explanation of one embodiment of the present invention, according to the present invention, under the green part of the light-shielding film, an electrode made of polysilicon or the like is formed as much as possible. If the structure is such that an insulator such as an oxide film is used, and the thickness of this insulator is less than (λ/2n)A, light leakage will occur due to effects such as multiple reflections of obliquely incident light. This improves the amount of smear and reduces the amount of smear.

This invention is Mado Akiya's frame transformer 77 method COD.
It can be applied to image sensors, MO8 type image sensors, CPDW image sensors, etc., regardless of whether they are -dimensional sensors or two-dimensional sensors.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a solid-state image sensor according to an embodiment of the present invention;
Fig. 2 is a schematic plan view of a solid-state image sensor, Fig. 3 is a plan view of the A cell part of the solid-state image sensor, and Figs. 2 is a diagram showing a change in the amount of smear with respect to a change in the thickness of an oxide film between a light shielding film and a semiconductor substrate. FIG. l...Accumulation area, 2...Vertical CC
D register. 3...Transformer 7 Agut section, 4.Old...Horizontal COD register% 5...Output section, 6.
...Channel stopper, 7...1st
Polysilicon electrode, 9... Light shielding film, 1... Silicon substrate, 13. Old... Thermal oxide film,
100...Thermal oxide film. Agent Patent Attorney Susumu Uchihara Pa. / Figure 2 Figure % 5', t'', 7; ] LA-) --- θ 2nd edition ° Rishirikoshi Denfuyu et al.
7 Expedition Figure 4 Figure 6

Claims (1)

[Claims] In a solid-state image sensor having a plurality of accumulation regions arranged on a semiconductor substrate and a region at least partially covered with a light-shielding film and reading out signal charges accumulated in the accumulation regions, at least a portion of an edge of the light-shielding film is provided. and the semiconductor substrate, and when the wavelength of the incident light is λÅ and the refractive index of the insulator is n, the thickness of the insulator is (
A solid-state imaging device characterized in that it is λ/2n) Å or less.