JP2000124435A - Solid image pickup element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light receiving efficiency of a highly integrated CCD solid image pickup element. SOLUTION: A protective film 10 is formed on the N-type silicon substrate 1 where an isolated region 3 and an N-type diffusion layer 4, which becomes a channel region, are formed. The protective film 10 is extended along the isolated region 3, it contains the first region 11 having the cross section of the width widened on the side of the silicon substrate 1, the second region 12 which flatly forms the surface by covering the first region 11, and the second region having the refractive index larger than the first region, is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device having improved light receiving efficiency and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 4 is a schematic diagram showing a configuration of a frame transfer type solid-state imaging device.

The frame transfer type CCD solid-state image pickup device has an image pickup section i, a storage section s, a horizontal transfer section h, and an output section d. The imaging unit i includes a plurality of shift registers extending in the vertical direction and arranged in parallel with each other, and each bit of each shift register forms a light receiving pixel. The accumulation unit s
It consists of a plurality of light-shielded shift registers that are continuous with the shift register of the imaging unit i, and each bit of each shift register constitutes a storage pixel. The horizontal transfer unit h is composed of a single shift register extending in the horizontal direction, and the output of the shift register of the storage unit s is connected to each bit. Output section d
Includes a capacitor that temporarily stores the charge transferred and output from the horizontal transfer unit h and a reset transistor that discharges the charge stored in the capacitor. As a result, the information charges accumulated in each light receiving pixel of the imaging unit i are independently transferred to the accumulation pixels of the accumulation unit s for each pixel, and thereafter, stored in the accumulation unit s row by row.
From the horizontal transfer unit h to the output unit d in pixel units. The output unit d converts the amount of charge for each pixel into a voltage value, and the change in the voltage value is supplied to an external circuit as a CCD output.

FIG. 5 is a plan view showing the structure of the image pickup section i, and FIG. 6 is a sectional view taken along line XX of FIG. These figures show the case where the transfer electrode is a single layer and is driven in three phases.

On one main surface of an N-type silicon substrate 1, a P-type diffusion layer 2 serving as an element region is formed. In the surface region of this P-type diffusion layer 2, isolation regions 3 into which P-type impurities are implanted at a high concentration extend in the vertical direction and are arranged in parallel with each other. An N-type diffusion layer 4 is formed between these isolation regions 3 to form a channel region serving as a transfer path for information charges. A plurality of transfer electrodes 6 made of polycrystalline silicon are arranged in parallel on the N-type diffusion layer 4 with a certain distance therebetween via a gate insulating film 5 made of a thin silicon oxide film. For example, three-phase transfer clocks φ1 to φ3 are applied to these transfer electrodes 6, and the potential state of the channel region is controlled. Then, on the transfer electrode 6, the same interlayer insulating film 7 as the gate insulating film 5 is laminated.

On the interlayer insulating film 7, a semi-cylindrical microlens 8 having a dome-shaped cross section is arranged along the channel region. The micro lens 8 is, for example, a BP
It is formed of SG (Boro-Phospho Silicate Glass) or the like, and condenses light incident on the separation region 3 or the end of the channel region toward the center of the channel region.

In the solid-state image pickup device having the microlenses 8, the light irradiated on the light receiving surface is collected in a region having high light receiving sensitivity and photoelectric conversion is performed, so that the light receiving sensitivity can be improved.

[0008]

In the case of the solid-state imaging device described above, if the arrangement pitch of the light receiving pixels is narrowed due to the high resolution, it is difficult to form a plurality of micro lenses 8 independently. That is, when the width of the separation region 3 becomes narrow, the microlenses 8 formed in a semi-cylindrical shape along the channel region may fuse together next to each other, making it impossible to obtain a desired shape. If the microlenses 8 cannot be separated on the separation region 3, the light irradiated on the separation region 3 cannot be correctly guided to the channel region. If the microlenses 8 are formed at a sufficient interval, the fusion of the microlenses 8 itself can be prevented. However, since the microlenses 8 cannot be arranged on the separation region 3, irradiation is performed on the separation region 3. The light enters the separation region 3 without being guided to the channel region. Such a problem can occur in an interline system or a frame interline system in which a vertical transfer register is arranged between light receiving pixels as the resolution increases.

Accordingly, it is an object of the present invention to make it possible to effectively use the light irradiated on the separation region even when the arrangement pitch of the light receiving pixels becomes narrow.

[0010]

According to the present invention, there is provided a solid-state imaging device comprising: a semiconductor substrate; a plurality of light receiving pixels arranged on a principal surface of the semiconductor substrate with a predetermined gap therebetween; A light-transmitting protective film that is stacked on one main surface of the semiconductor substrate so as to cover the semiconductor substrate, wherein the protective film covers at least a gap between the plurality of light-receiving pixels and the arrangement of the plurality of light-receiving pixels. A first region extending along the first region and having a cross-sectional shape that is wider on the semiconductor substrate side;
And a second region having a higher refractive index than that of the first region.

The manufacturing method according to the present invention includes a step of forming a plurality of light receiving pixels on one main surface of the semiconductor substrate with a predetermined gap therebetween, and a step of forming a first light-transmitting material on the semiconductor substrate. Laminating a plurality of light-receiving pixels on the first light-transmitting material laminated on the predetermined film thickness along the arrangement of the plurality of light-receiving pixels. A step of forming an extending mask pattern, a step of isotropically etching the first translucent material in accordance with the mask pattern, and forming a cross-sectional shape having a wider width on the semiconductor substrate side; The above-mentioned first type remaining on the substrate
And laminating a second light-transmitting resin having a higher refractive index than the first light-transmitting material.

According to the present invention, the first region formed in the gap between the plurality of light receiving pixels has the same function as the prism, and the light incident on the gap is dispersed to the channel regions on both sides. As a result, the amount of light incident on the channel region increases. At this time, since the width of the light receiving pixel is formed to be wider than the width of the gap between the light receiving pixels, a lens formed to cover the gap is less likely to be adjacent to each other even when the arrangement pitch of the light receiving pixels is narrow. .

[0013]

FIG. 1 is a sectional view showing a first embodiment of a solid-state imaging device according to the present invention, and shows the same portions as FIG.

N-type silicon substrate 1, P-type diffusion layer 2, isolation region 3, N-type diffusion layer 4, gate insulating film 5, transfer electrode 6
The interlayer insulating film 7 is the same as the solid-state imaging device shown in FIG. The feature of the present invention resides in that the first region 11 functioning equivalently to the micro lens is formed on the interlayer insulating film 7.
And a translucent protective film 10 including the second region 12.

The first region 11 in the protective film 10 has a cross-sectional shape that becomes wider on the silicon substrate 1 side, and
It is arranged so as to straddle between the channel regions adjacent to each other, and extends along the isolation region 3. The first region 11 is formed by, for example, SOG (Spin On Glass). Then, the second region 12 of the protective film 10 covers the entire first region 11 and is formed with a flat surface. The second region 12 is formed of, for example, an acrylic resin transparent to visible light. Usually, the refractive index of SOG is about 1.4 to 1.5, while the refractive index of acrylic resin is 1.6 or more. Functions as a prism.

In the first region 11, the interface with the second region 12 forms a curved surface that is concave toward the silicon substrate 11, so that light incident on the central portion of the separation region 3 can be reduced. It is configured to greatly refract. That is, as shown in FIG. 2, the angle formed between the surface of the first region 11 (the interface with the second region 12) and the surface of the silicon substrate 11 becomes larger as approaching the center of the separation region 3. The light vertically incident on the silicon substrate 11 is refracted more toward the center of the separation region 3. Therefore, the light incident on the separation region 3 is efficiently refracted toward the channel region at the interface between the first region 11 and the second region 12 as shown in FIG. It is guided into the diffusion layer 4.

In such a solid-state imaging device, the surface of the protective film 10 is formed flat, so that the package and the protective film 10 can be formed using any kind of translucent resin. Light is no longer refracted at the interface in unwanted directions. Further, since the first region 11 covered by the second region 12 in the protective film 10 functions as a prism, the function of the lens is not affected by the material of the package.

FIGS. 3A to 3D are cross-sectional views for explaining steps of a method for manufacturing a solid-state imaging device according to the present invention. In this figure, the same parts as those in FIG. 1 are shown. (A): First Step A P-type impurity such as boron is diffused in a surface region of an N-type silicon substrate 1 to form a P-type diffusion layer 2 serving as an element region. A plurality of isolation regions 3 are formed by selectively implanting a P-type impurity into the P-type diffusion layer 2. An N-type impurity such as phosphorus is implanted between the isolation regions 3 to form a channel. A P-type diffusion layer 4 serving as a region is formed. Subsequently, the surface of the silicon substrate 11 on which the P-type diffusion layer 4 is formed is thermally oxidized,
A gate insulating film 5 made of silicon oxide is formed. Then, a plurality of transfer electrodes 6 made of polycrystalline silicon are formed on the gate insulating film 5, and an interlayer insulating film 7 is formed to cover the transfer electrodes 6.

This first process is the same as the well-known manufacturing process for manufacturing the conventional solid-state imaging device shown in FIG.

(B): Second Step On the interlayer insulating film 7, SOG is applied, and the SOG is heat-treated to form a first light-transmitting material layer 15. This translucent material layer 15 is to be the first region 11 later, and is formed to be thicker than the maximum thickness of the first region 11 to be formed.

(C): Third Step A resist layer 16 is formed on the translucent material layer 15, and the resist layer 16 is patterned along the separation region 3 to extend along the separation region 3. Mask pattern 1
7 is formed. Then, using the mask pattern 17 as a mask, the translucent material layer 15 is subjected to isotropic etching to expose the surface of the interlayer insulating film 7 in the gap between the mask patterns 17. Due to this isotropic etching, the isolation region 3 has a cross-sectional shape that extends on the interlayer insulating film 7 along the isolation region 3 and becomes wider on the silicon substrate 11 side, and the surface is First curved surface concave toward the substrate 11 side
Region 11 can be formed.

(D): Fourth step An acrylic resin is applied on the silicon substrate 1 on which the first region 11 has been formed, and a second region 12 is formed to completely cover the first region 11. Thus, a protective film 10 that protects the surface of the silicon substrate 11 and flattens the surface is formed.

According to the above-described manufacturing method, a solid-state imaging device having the protective film 10 shown in FIG. 1 can be obtained.

In this embodiment, the application of the frame transfer method to the solid-state imaging device has been exemplified. However, the solid-state image pickup device of the interline transfer method or the frame interline transfer method in which a vertical transfer register is arranged between light receiving pixels. Application to an imaging device, and further application to a MOS type solid-state imaging device are also possible. In the case of these solid-state imaging devices, the separation region extends in both the vertical and horizontal directions,
The first regions 11 of 0 are formed in a mesh along the separation region, and are each configured to function similarly to a prism. When a vertical transfer register or the like is formed along the isolation region, the first region 11 of the protection film 10
It is formed so as to cover the vertical transfer register together with the isolation region.

[0025]

According to the present invention, the light irradiated to the separation region (the region where photoelectric conversion is not performed) is refracted in the protective film so as to go to the adjacent photoelectric conversion region side. Most of the light incident on the light receiving surface is used for photoelectric conversion. In particular, since the light is largely refracted at the center of the separation region, the light applied to the separation region is efficiently guided to the photoelectric conversion region side.

Further, since the surface of the protective film is formed flat, even if a package made of a translucent resin is formed so as to be in contact with the protective film, unnecessary portions are formed at the interface between the protective film and the translucent resin. Refraction does not occur. At the same time, the first region of the protective film functioning as a lens is always covered by the second region, so that no matter what material is laminated on the protective film, the function is not lost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a solid-state imaging device of the present invention.

FIG. 2 is a cross-sectional view showing a state of refraction of light in the solid-state imaging device of the present invention.

FIG. 3 is a cross-sectional view for explaining a method of manufacturing a solid-state imaging device according to the present invention in each step.

FIG. 4 is a schematic diagram illustrating a configuration of a frame transfer type solid-state imaging device.

FIG. 5 is a plan view illustrating a structure of an imaging unit of a conventional solid-state imaging device.

FIG. 6 is a sectional view showing a sectional structure taken along line XX of FIG. 5;

[Explanation of symbols]

 i Imaging unit s Storage unit h Horizontal transfer unit d Output unit 1 Silicon substrate 2 P-type diffusion layer 3 Isolation region 4 N-type diffusion layer 5 Gate insulating film 6 Transfer electrode 7 Interlayer insulating film 10 Protective film 11 First region 12 First 2 region 15 translucent material layer 16 resist layer 17 mask pattern

Claims (3)

[Claims] A semiconductor substrate; a plurality of light receiving pixels arranged on the one main surface of the semiconductor substrate with a constant gap therebetween; and a plurality of light receiving pixels on the one main surface of the semiconductor substrate covering the plurality of light receiving pixels. A light-transmitting protective film to be laminated, wherein the protective film extends along the arrangement of the plurality of light-receiving pixels, covering at least a gap between the plurality of light-receiving pixels, and is provided on the semiconductor substrate side. A first region having a cross-sectional shape having a larger width; and a second region having a larger refractive index than the first region, the second region having a flat surface covering the first region. A solid-state imaging device characterized by the above-mentioned. 2. The solid-state imaging device according to claim 1, wherein an interface between the first region and the second region of the protective film forms a curved surface that is concave toward the semiconductor substrate. 3. A step of arranging and forming a plurality of light receiving pixels on one main surface of a semiconductor substrate with a predetermined gap therebetween, and laminating a first light-transmitting material to a predetermined thickness on the semiconductor substrate. Forming a mask pattern that extends along the arrangement of the plurality of light-receiving pixels over the first light-transmitting material laminated to a predetermined film thickness so as to cover a gap between the plurality of light-receiving pixels. And a step of isotropically etching the first light-transmissive material in accordance with the mask pattern to form a cross-sectional shape that is wider on the semiconductor substrate side; and Covering the first light-transmitting material, and laminating a second light-transmitting resin having a higher refractive index than the first light-transmitting material. .