JPH0322479A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To reduce the area on a plane occupied by regions of a charge transfer element, a readout element and a channel stopper element and to attain high resolution by forming these elements three-dimensionally in a lateral side part and a bottom part of a groove. CONSTITUTION:A plurality of grooves 3 are formed on a semiconductor substrate 1 and a sensor element 2 is formed between the grooves 3. A readout element 5 constructed of a region of p-type impurities is formed in a lateral side part 3b of the groove 3 adjacent to the sensor element 2. The readout element 5 controls readout of a charge from the sensor element 2. Adjacently to the readout element 5, a charge transfer element 6 constructed of a region of n<+> type impurities is formed in a bottom part 3a of the groove 3. The charge transfer element 6 transfers the charge transferred through the readout element 5. A channel stopper element 7 constructed of a region of p<+> type impurities is formed in a lateral side part 3c of the groove 3 being opposite to the lateral side part 3b. The channel stopper element 7 prevents formation of a channel between the adjacent sensor element 2 in another line and the charge transfer element 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device in which signal charges from a plurality of light receiving sections are transferred and read out by a charge transfer section.

[Summary of the Invention] The present invention provides a solid-state imaging device having a charge transfer section that transfers signal charges from a plurality of light receiving sections, in which the planar area occupied by the charge transfer section, readout control region, and channel stopper region is reduced. In order to reduce the size, a charge transfer section is formed at least at the bottom of the groove formed along the light receiving section, and a readout control region or a channel stopper region is formed at the side surface.

Such three-dimensionalization makes it possible to miniaturize, increase the density, or increase the sensitivity of the imaging device.

Furthermore, the present invention embeds the transfer electrode of the charge transfer section in the groove formed surrounding the light receiving section, thereby making the surface of the semiconductor substrate a substantially flat surface with no step between the light receiving section and the transfer electrode. This improves processing accuracy and prevents smearing.

[Conventional technology]

Currently, interline type CCDs are most commonly used in solid-state imaging devices for color images. usually,
The light receiving section is a photodiode, and the incident light is converted into an electric charge proportional to the intensity of the light by the photodiode. This charge is read out and transferred to the vertical register.

In a CCD imager having such an interline structure, conventional technology has a readout section on the surface of a semiconductor substrate. Impurity regions functioning as a charge transfer section and a channel stopper section are respectively formed.

Then, a transfer electrode for charge transfer using a polysilicon layer is formed on the semiconductor substrate over the impurity region with an oxide film interposed therebetween. Furthermore, the opening surrounded by the polysilicon layer is used as a photodiode.

At this time, (2) the maximum amount of signal charge that can be read out per cell is determined by the maximum amount of charge that can be stored by the photodiode and the maximum amount of charge that can be transferred by the charge transfer section. These maximum charges depend on the area of the photodiode section and the charge transfer section.

Incidentally, current CCD solid-state imaging devices for video cameras are being developed in the direction of increasing the number of pixels in the imaging device in order to obtain high resolution.

However, in order to increase the number of pixels in the above-described structure, it is necessary to reduce the area occupied by the photodiode section or the charge transfer section. Therefore, for the above-mentioned reason, the maximum signal charge amount that can be read out per cell decreases, and as the dynamic range decreases, the characteristics deteriorate.

Therefore, as a technology prior to the present invention, Japanese Unexamined Patent Publication No. 61-17
A technique described in Japanese Patent No. 4765 is known. By forming a V-shaped groove on the semiconductor substrate and forming a charge transfer section on the slope of the groove, the area occupied by the charge transfer section is secured three-dimensionally and the maximum signal charge amount is reduced. That's what I was trying to suppress.

[Problem to be solved by the invention]

However, in the solid-state imaging device described in the above-mentioned Japanese Patent Laid-Open No. 61-174765, only the planar area occupied by the charge transfer section is reduced, but the readout section and channel stopper section are not reduced. Therefore, it cannot be said that this is sufficient in suppressing the decrease in the power range.

In addition, in conventional solid-state imaging devices, there is a difference in level between a part of the sensor and the transfer electrode, which is about 1 micron, and a difference between the first polysilicon layer and the second polysilicon layer. There is a portion where these two layers overlap at the boundary. For this reason, there are problems such as deterioration of processing accuracy due to unevenness in film thickness in the process of forming the resist, and increase in smear due to deterioration of step coverage of the light-shielding aluminum layer, but these problems are described in the above publication. Even in the solid-state imaging device that has been developed, the problem of the step difference caused by the overlapping portion of the first polysilicon layer and the second polysilicon layer remains unsolved.

Therefore, the present invention has been proposed in view of the above-mentioned conventional situation. The purpose is to reduce the planar area occupied by the readout section and the channel stopper section and increase the dynamic range. A further object of the present invention is to provide a solid-state imaging device that improves resist processing accuracy and prevents smearing.

[Means to solve the problem]

In order to achieve the above object, the solid-state imaging device of the present invention includes a plurality of light receiving sections for converting incident light into signal charges and grooves formed along the light receiving sections on a semiconductor substrate. The groove has a bottom part and a side part. The side surface portion may be a sloped plane, a curved surface, or the like, and is shaped to increase the surface area on the semiconductor substrate. In the solid-state imaging device of the present invention, a charge transfer section for transferring signal charges from the light receiving section is formed at least at the bottom of the groove, and a channel stopper region or a readout control region is formed at the side surface of the groove. It is characterized by

Furthermore, the present invention is characterized in that a transfer electrode for charge transfer is buried inside a groove formed so as to surround the light-receiving section in a plane, so that the surface of the semiconductor substrate is made substantially flat.

[Function] In the solid-state imaging device of the present invention, the charge transfer section, readout section, or channel stopper section is three-dimensionally formed using the bottom and both side surfaces of the groove formed along the light receiving section. Therefore, although the planar area occupied by the charge transfer section etc. is reduced, the surface area is secured, so the effective transfer channel width is increased and the guinamine range is increased.

Further, since the transfer electrode for charge transfer is buried inside the groove and the surface of the semiconductor substrate is made substantially flat, the resist is formed evenly and the processing accuracy is improved. Furthermore, since the light-shielding aluminum layer can sufficiently cover the charge transfer portion, etc., it is possible to prevent smearing.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

This embodiment is an example of a CCD area sensor.

FIG. 1 is a sectional view showing the structure of an area sensor.

As shown in FIG. 1, a plurality of grooves 3 are formed on a semiconductor substrate 1, and a sensor portion 2 is formed between the grooves 3.

The groove 3 has a bottom part 3a and a beveled side part 3b. 3c
have. A side surface 3 of the groove 3 adjacent to the sensor part 2
A readout section 5 made of a p-type impurity region is formed at b. The readout section 5 is formed along the inclined surface of the side surface 3b of the groove 3 from the main surface 1a of the semiconductor substrate 1 to the vicinity of the bottom 3a of the groove 3. This reading section 5 is part of the sensor 2.
Controls readout of charge from. Adjacent to this readout section 5, a charge transfer section 6 made of an n1 type impurity region is formed at the bottom 3a of the groove 3. The charge transfer section 6 is a region sandwiched between the readout section 5 and the channels 1/flange section 7. The charge transfer section 6 transfers the charges transferred via the readout section 5. Further, a channel portion 1/substrate portion 7 made of a p-type impurity region is formed on a side surface portion 3c of the trench 3 facing the side surface portion 3b on which the readout portion 5 is formed.

Similarly to the readout section 5, the channel stopper section 7 is also provided in a region from the principal surface 1a of the semiconductor substrate 1 to the vicinity of the bottom 3a of the groove 3 along the polysilicon side surface section 3C. The channel stopper portion 7 is connected to a sensor portion 2 of another adjacent row.
This prevents the formation of a channel between the charge transfer section 6 and the charge transfer section 6.

As described above, the charge transfer section 6, readout section 5, channels 1 and buckle section 7 are connected to the side surface 3b3C and the bottom 3 of the groove 3.
a, and the planar area occupied by these regions on the semiconductor substrate 1 is reduced while maintaining the surface area. Therefore, it is possible to increase the number of pixels while improving the dynamic range, thereby achieving higher resolution.

An oxide film 4 is formed on the semiconductor substrate 1 in which such a groove 3 is formed.
is formed. In particular, an oxide film 4 is formed inside the side surfaces 3b, 3c and bottom 3a of the groove 3, and the oxide film 4
A transfer electrode 8 for charge transfer is formed by two polysilicon layers via the polysilicon layer.

This transfer electrode 8 will be explained in detail using FIG. 2.

FIG. 2 is a schematic plan view of the area sensor shown in FIG. 1, viewed from above. As shown in FIG. 2, the transfer electrode 8 has a two-layer structure consisting of a first polysilicon layer 13 and a second polysilicon layer 14. A horizontally aligned row of the sensor part 2 is a symmetrical set of a first polysilicon layer 13 and a second polysilicon layer 14
The first polysilicon layer 13 and the first polysilicon layer 14 are alternately formed in the vertical direction. The first polysilicon layer 13 and the second polysilicon layer 14 have a shape in which vertically wide portions and narrow portions are alternately arranged in the horizontal direction. In the narrow part, the sensor part 2 is sandwiched between the first polysilicon layer 13 and the second polysilicon layer 14, and in the wide part, the sensor part 2 is sandwiched between the first polysilicon layer 13 and the second polysilicon layer 14. The second polysilicon layer 14 is symmetrically butted against each other. In particular, there is no overlap between these two layers at this boundary.

This transfer electrode 8 is formed to be buried inside the groove 3. As a result, there is no step difference between the sensor part 2 and the transfer electrode 8, and the surface of the semiconductor substrate l becomes a flat surface. In this way, the sensor part 2 surrounded by the transfer electrode 8 whose surface is substantially flat has an n-type structure on the surface of the semiconductor substrate l of the sensor part 2, which has the function of converting incident light into signal charges. An impurity region lO is formed. This n-type impurity region 10
are arranged in a matrix on a plane.

The transfer electrode 8 is buried in the groove 3, and a reflow film 1l is formed on the entire surface of the flattened semiconductor substrate 1 with the oxide film 4 interposed therebetween. Then, on this reflow film 11, a light-shielding aluminum layer 12 is formed in a pattern that opens above the sensor part 2.
is formed. Since this aluminum layer l2 is processed on a substantially flat surface, the processing accuracy is improved.

Furthermore, since there are no unnecessary steps, smear can be reduced.

Next, the manufacturing process of the area sensor shown in FIG. 1 and FIG. 2 will be explained with reference to the drawings.

First, as shown in FIG. 3(a), in order to form the grooves 53, a photoresist 52 is formed on the entire surface of the semiconductor substrate 51, and windows are opened according to the pattern in which the grooves 53 are to be formed. A tapered portion 5 is formed at the windowed end by heat treatment.
2a is formed. Then, using the RrE method, while controlling the shape by tapered etching, the semiconductor substrate 51 is
A groove 53 is formed in the groove 53 . The groove 53 has a pattern that surrounds the sensor portion 65 on a plane, and has a bottom portion 53a and side portions 53b and 53c inclined with respect to the main surface of the semiconductor substrate.

Subsequently, as shown in FIG. 3(b), a photoresist 5 is applied.
After removing the semiconductor substrate 51 , the surface of the semiconductor substrate 51 is oxidized to form a thermal oxide film 54 on the main surface of the semiconductor substrate 51 and inside the groove 53 . Then, ion implantation is performed into the surface of the semiconductor substrate 5I. As a result, a charge transfer portion 56 made of an n-type impurity region is formed at the bottom 53a of the groove 53, and a readout portion 55 and p1 made of a p-type impurity region are formed on the side portions 53b and 53c of the groove 53. Channel stopper portions 57 each made of a type impurity region are selectively formed. When forming the readout section 55, charge transfer section 56, and channel stopper section 57, a step of selectively forming a photoresist may be provided if necessary. Ion implantation from an oblique direction is also effective for formation.

Next, after depositing a polysilicon layer on the entire surface, as shown in FIG.
As shown in c), etch back is performed so that the polysilicon layer is left only inside the area 53. Thereafter, a photoresist is formed on the entire surface, and in order to form a second polysilicon layer, a window is opened in the photoresist at a location where the second polysilicon layer is to be formed. Then, using the photoresist as a mask, the first polysilicon layer is patterned by etching.

Next, thermal oxidation DI! is performed inside the groove 53 in the region where the second polysilicon layer is to be formed. 54 is once removed by HF treatment or the like, a thermal oxide film 59 is again formed on the half l2 conductive substrate 51 in this sprouting area. Thermal oxide film 5
At this time, 9 is also formed on the first polysilicon layer which has already been patterned.

Next, an n-type impurity region is formed at the bottom of the groove in the region where the second polysilicon layer is to be formed by ion implantation in the self-line. Therefore, since the n+ type impurity region is formed in the charge transfer section 56 in the region where the first polysilicon layer is formed, the charge transfer section 56 has the first polysilicon layer and the second polysilicon layer. The storage section and transfer section are shaped differently depending on the polysilicon layer.

Next, after depositing a polysilicon layer over the entire surface in the same manner as described above, a second polysilicon layer is formed only inside the trench by etchback, and then a heat treatment is applied on the second polysilicon layer. An oxide film 59 is formed.

In this manner, after the first polysilicon layer and the second polysilicon layer are formed, the n-type impurity region for forming the sensor portion 65 on the surface of the semiconductor substrate 5l is ionized. Formed by injection.

Then, a reflow film 6l is formed on the entire surface of the semiconductor substrate 51 with a thermal oxide film 59 interposed therebetween. After forming an argonium layer on the reflow film 61, patterning is performed using a mask that opens above the sensor portion 65 to form a light-shielding aluminum layer 62. Since the aluminum layer 62 is uniformly formed on a substantially flat surface, its processing accuracy is improved, and parts other than the sensor part 65 can be sufficiently covered, so that smear is reduced.

As described above, in the CCD area sensor of this embodiment, a groove is formed on a semiconductor substrate surrounding a part of the sensor, a charge transfer section 56 is provided at the bottom of the groove, and the side surfaces of the groove are used as a readout section and a channel. By forming the stopper portion, the area occupied by these regions can be ensured dimensionally, and the area on the plane can be reduced. Therefore, it is possible to increase the dynamic range and increase the sensitivity at the same time.

Further, in the CCD area sensor of this embodiment, a transfer electrode is formed by being buried inside the groove, and the surface of the semiconductor substrate is made substantially flat. This makes it possible to prevent smearing due to deterioration in processing accuracy due to unevenness in resist film thickness and deterioration in step force burage of the light-shielding aluminum layer.

In addition, even if the third polysilicon layer is formed after the first polysilicon layer and the second polysilicon layer are formed in the manufacturing process, and the shape of the peripheral transistors is determined, good.

〔Effect of the invention〕

In the solid-state imaging device of the present invention, a groove having a bottom and side parts is formed, the surface area of the semiconductor substrate is increased, and a charge transfer part, a readout part, or a channel stopper part is formed in the bottom and side parts of the groove. , it is possible to reduce the planar area occupied by the charge transfer section and the like, and to increase the width of the transfer channel. Therefore, it is possible to increase the resolution and the sensitivity of the solid-state imaging device. Furthermore, it is possible to reduce the size and increase the density of the imaging device.

15 In addition, by embedding the transfer electrode inside the groove, problems caused by the difference in level between part of the sensor and the transfer electrode and the part where the polysilicon layers overlap are solved, and the problems caused by the difference in level between the part of the sensor and the transfer electrode and the part where the polysilicon layers overlap are eliminated, and the problem with Since the aluminum layer is processed onto a substantially flat surface, processing accuracy is improved and smear is prevented.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an example of a solid-state imaging device to which the present invention is applied, FIG. 2 is a schematic plan view of the example, and FIGS. ) are process cross-sectional views for explaining the manufacturing method of the above example. 16 ・Channel storage part ・Transfer electrode ・Reflow film ・Aluminum layer

Claims (2)

[Claims] (1) A plurality of light receiving parts for converting incident light into signal charges on a semiconductor substrate, a groove formed along the light receiving parts, and a signal charge formed at least at the bottom of the groove from the light receiving part. What is claimed is: 1. A solid-state imaging device, comprising a charge transfer section for transferring a charge, and a channel stopper region or a readout control region is formed in a side surface of the groove. (2) A groove is formed to surround the plurality of light receiving sections on a plane, and a transfer electrode of a charge transfer section is embedded in the groove to make the surface of the semiconductor substrate substantially flat. solid-state imaging device.