JP2001223348A - Solid-state imaging device and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a solid-state imaging device in which a microlens is formed in order to increase sensitivity when increasing the number of pixels and increasing the resolution, in which generation of smear noise is suppressed. In a solid-state imaging device including at least a semiconductor substrate having a plurality of light receiving units for performing photoelectric conversion arranged in an array and a micro lens formed on each of the light receiving units, an end of the micro lens is provided. A solid-state imaging device wherein the thickness of the lens at a portion 0.3 μm from the side toward the center of the microlens is 35% or more of the maximum thickness of the microlens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device having at least a plurality of light receiving units for performing photoelectric conversion and micro lenses formed on each of the light receiving units. The present invention relates to a solid-state imaging device in which image characteristics are improved by improving image quality.

[0002]

2. Description of the Related Art A solid-state imaging device represented by a CCD or the like generally has a photodiode section 51 (light receiving section 72) for converting light into electric charges, a channel stopper, as shown in FIG.
A semiconductor substrate 70 including a vertical register unit 71 and the like;
A flattening film 56 and a color filter 57 formed on a semiconductor substrate 70, a microlens 60 formed for the purpose of condensing incident light on a semiconductor element (particularly, the photodiode section 51) and improving sensitivity, and the like. It is composed of Note that the vertical register section 71 includes the transfer electrode 54 and the transfer section 5.
3, the vertical well 52 and the like. Here, when light enters the vertical register section 71, noise charges are generated and an erroneous signal is generated, and so-called smear, in which a striped white line is displayed on a screen, occurs. In order to avoid this smear, it is common to form a metal thin film made of Al (aluminum) or the like as the light-shielding film 55 so that the photodiode 51 is an opening and the vertical register 71 is light-shielded.

As a technique for increasing the sensitivity of a solid-state imaging device represented by a CCD or the like, there is a method of reducing the area ratio of the vertical register section 71 and increasing the area ratio of the photodiode section 51 as a light receiving section. However, as the definition of the solid-state imaging device increases and the number of photodiodes 51 as light receiving units increases, the proportion of the openings formed in the light-shielding film 55 increases,
That is, the aperture ratio of the photodiode portion decreases, and the area ratio of the photodiode portion decreases. That is, the size of the solid-state imaging device in a plan view is roughly determined, and the size of the device is required. Therefore, even if the device is required to have high definition, the device cannot be unnecessarily enlarged. On the other hand, the vertical register section 71 to be shielded from light by the light shielding film 55 is a part requiring a certain area. For this reason,
This is because if the number of light receiving sections is increased for higher definition, the aperture ratio of each photodiode section must be reduced.

When the aperture ratio of the photodiode unit 51 is reduced to, for example, about 15 to 30% or less, a micro lens 60 is arranged on the photodiode unit 51 (light receiving unit 72) as shown in FIG. It can be said that collecting light incident on the device to the photodiode unit is an effective means for improving the sensitivity of the solid-state imaging device.

In forming a microlens, a photosensitive resin (for example, a positive photosensitive resin) that can be reflowed (melted) by heat is used as a material, and the microlens is formed by a photolithographic process method and a thermal reflow method. Is commonly done. That is, after the photosensitive resin is applied to a thickness of, for example, about 1 to 6 μm, pattern exposure and development are performed on the photosensitive resin, and the photosensitive resin having a predetermined planar shape is left at a predetermined portion. Thereafter, heating is performed to reflow (melt) the remaining photosensitive resin,
This is a technique in which the surface of the reflowed (melted) resin is given a curvature on the resin surface to form a lens shape. After a planarization film, a color filter, and a planarization film or an undercoat film made of an organic resin or the like are sequentially laminated on a semiconductor substrate (silicon wafer) on which a photoelectric conversion element such as a photodiode is formed, the above-described method is applied. To form a microlens to obtain a solid-state imaging device.

A color filter is formed to separate incident light into, for example, three primary colors of R (red), G (green), and B (blue). A color filter of a corresponding color is formed by lamination.

[0007]

As described above, a metal thin film made of Al (aluminum) or the like has conventionally been used as a light-shielding film in order to prevent unnecessary light from being incident on the vertical register portion and generating smear. Often formed. However, light incident on the solid-state imaging device causes multiple reflections in the device, and the reflected light is incident on the vertical register section as oblique light, so that it cannot be said that generation of smear is completely prevented.

In recent years, solid-state imaging devices such as CCDs have
There is a demand for higher resolution of 300,000 pixels, 2,000,000 pixels or more, and a demand for miniaturization of the apparatus is also increasing. Under such demands, it has become a major issue to eliminate noise charges and suppress smear. In other words, although the size of the pixel (light receiving portion) is smaller than in the past as the resolution increases, for example, as the size of the pixel becomes smaller than 5 μm or less than 10 μm, light due to multiple reflection or oblique light becomes smaller. This is because the influence of the wraparound increases, and the rate of generation of smear noise increases.

The fact that the ratio of smear noise increases when the resolution is increased will be further described. 800,000 ~
CC built into digital cameras with 1.3 million pixels
The pitch between the microlenses formed in D is usually about 6 to 7 μm. However, in the case of a digital camera having about 2 million pixels or more in order to meet the demand for higher resolution, the pitch between the microlenses formed on the CCD must be about 3 to 5 μm. For this reason, the aperture ratio of the microlens decreases and the ratio of the non-opening increases, and the ratio of occurrence of smear noise increases.

The present invention has been made in view of the above circumstances, and provides a solid-state imaging device in which a microlens is formed in order to increase the number of pixels and increase the sensitivity when the resolution is increased.
An object of the present invention is to provide a solid-state imaging device in which generation of smear noise is suppressed.

[0011]

Means for Solving the Problems The present inventors have intensively studied to achieve the above object. As a result, attention is paid to the cross-sectional shape of a microlens formed on a semiconductor element such as a photodiode for performing photoelectric conversion and having a pitch between lenses of about 3 to 5 μm. As a result of further study of the cross-sectional shape of the microlens, if the film thickness of the lens at a position 0.3 μm from the edge of the microlens toward the center is 35% or more of the maximum film thickness of the microlens, the amount of smear is obtained. The present inventors have found that the effect of suppressing the occurrence of the noise increases, and propose this. That is, according to claim 1 of the present invention, in the solid-state imaging device having at least a semiconductor substrate in which a plurality of light receiving units for performing photoelectric conversion are arranged in an array, and a microlens formed on each of the light receiving units, The solid-state imaging device is characterized in that the thickness of the lens at a portion 0.3 μm from the edge of the lens toward the center of the microlens is 35% or more of the maximum thickness of the microlens. .

Here, in forming the microlens according to the present invention, as described in the above section (prior art), a photosensitive resin (for example, a positive photosensitive resin) capable of being reflowed (melted) by heat is used. Resin) as a material, and a photolitho process method and a thermal reflow method are used. The present inventors have found that when the photosensitive resin is reflowed (melted), the generation of smear noise can be suppressed by reducing the amount of reflow (melting) of the resin. In other words, if the reflow (melting) amount is large, the resin in the edge region of the lens flows in the outer peripheral direction, and the film thickness in the edge region becomes thin, so that the light condensing property of the lens is reduced and the generation of smear noise increases. It is.
Next, the present inventors also studied a suitable reflow (melting) amount. As a result, in order to suppress the generation of smear noise, the reflow (melting) amount must be set to 0.2 μm.
It is found that it is preferable to set m or less, and this is proposed. That is, in claim 2 of the present invention, a semiconductor substrate in which a plurality of light receiving portions for performing photoelectric conversion are arranged in an array and a photosensitive resin formed on each of the light receiving portions by a photolithographic process method and a thermal reflow method. A method for manufacturing a solid-state imaging device having at least a microlens, wherein the amount of reflow of the photosensitive resin in the side direction during thermal reflow is suppressed to 0.2 μm or less, and It was done.

In general, when a microlens is formed by a photolithography process and a thermal reflow process, a photosensitive resin formed by the photolithography process and subjected to thermal reflow is generally substantially rectangular in plan view. That is, in the photolithography process, pattern exposure is performed using a pattern exposure mask formed with a plurality of rectangular patterns. In the substantially rectangular photosensitive resin, the amount of thermal reflow on each side is larger than the amount of thermal reflow of the photosensitive resin in the corner portion during thermal reflow. For this reason, the present inventors, in order to suppress the amount of thermal reflow of the entire photosensitive resin that has become substantially rectangular in plan view, the amount of thermal reflow of each side of the substantially rectangular pattern (particularly, the side center region). Has been found to be preferable. In other words, it can be said that a desired microlens shape can be obtained by controlling the amount of heat reflow in the side direction at the time of thermal reflow to the photosensitive resin which has become substantially rectangular in plan view. The present inventors have also found that a microlens having a substantially rectangular shape in plan view is more preferable than a substantially circular microlens in plan view in suppressing smear. That is, in claim 3 of the present invention, a semiconductor substrate in which a plurality of light receiving units for performing photoelectric conversion are arranged in an array, and a photosensitive resin formed on each of the light receiving units by a photolithographic process method and a thermal reflow method. A method for manufacturing a solid-state imaging device having at least a microlens, wherein a photosensitive resin for performing thermal reflow is rectangular in a plan view, and a reflow amount in a side direction during thermal reflow is suppressed to 0.2 μm or less. A method for manufacturing a solid-state imaging device according to claim 2.

Next, when forming the microlens using the conventional photolithography process and the thermal reflow method, the heating temperature is set to 16 at the time of the thermal reflow performed to make the photosensitive resin remaining after the development into a microlens shape.
At a high temperature of about 0 ° C. to 180 ° C., heat reflow and curing were performed at once. However, the present inventors have found that dividing the thermal reflow temperature into two stages, a low temperature and a high temperature, can achieve a microlens shape capable of suppressing the generation of smear noise. That is, 100 ° C.
The first heat treatment is performed at a relatively low temperature of ~ 150 ° C. This relatively low temperature heat treatment cures the photosensitive resin to some extent. Thereafter, heating is performed at a high temperature exceeding 150 ° C. to perform thermal reflow and curing of the resin. By performing such a heat treatment, the amount of reflow of the photosensitive resin is suppressed, and a substantially rectangular microlens in plan view having a steeply inclined skirt shape without sagging can be obtained. That is, in claim 4, the heat reflow is divided into two stages, and after the first heat treatment at 100 ° C. to 150 ° C., the second heat treatment is performed at a temperature exceeding 150 ° C. According to a second aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device.

The resin that can be used as the material of the microlens according to the present invention is not particularly limited, and may be a phenol-based photosensitive resin, a polystyrene-based photosensitive resin, an epoxy-based photosensitive resin, or a resin for improving reflow properties. A resin obtained by adding a melamine resin to these resins, an acrylic photosensitive resin, a novolak photosensitive resin, or the like can be used, and may be appropriately selected.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on the following examples.

<First Embodiment> FIG. 1 is an explanatory sectional view showing a solid-state imaging device 10 according to a first embodiment. On a semiconductor substrate 30 made of a silicon substrate, a photodiode section 11 constituting a light receiving section 32 and a vertical well section 12,
Semiconductor elements such as a vertical register unit 31 including a charge transfer unit 13 and a transfer electrode 14 are formed. Next, on the semiconductor substrate, the light-shielding film 15, the flattening film 16, the color filter 17, and the flattening film 1 having the light receiving portion 32 as an opening are formed.
On the flattening film 18, a microlens 20 that covers the light receiving portion 32 in plan view is formed.

The microlens 20 according to the first embodiment was formed by the following manufacturing process. That is, the planarizing film 18 is formed on the semiconductor substrate 30 on which the color filter 17 is formed.
After forming (acrylic transparent resin), a phenolic photosensitive resin (for example, trade name “MFR380” manufactured by JSR Co., Ltd.) is applied on the flattening film 18, and dried. A 2 μm photosensitive resin film was formed. Next, pattern exposure, development, and the like were performed on the photosensitive resin film to leave the photosensitive resin at a predetermined portion (a portion on the light receiving portion 32).

Next, the remaining photosensitive resin was subjected to thermal reflow using a hot plate, and the photosensitive resin was formed into the shape of the microlens 20 as shown in FIG. The thermal reflow was performed at two heating temperatures, a low temperature and a high temperature. That is, the semiconductor substrate was moved on a plurality of hot plates at 150 ° C. to slightly cure the photosensitive resin on the flattening film 18. Next, the semiconductor substrate was moved on a plurality of hot plates at 180 ° C. to perform thermal reflow and final curing of the photosensitive resin on the flattening film 18.

By the above processing, a plurality of microlenses 2 having a distance between lens centers (inter-lens pitch) of 5 μm and an inter-lens distance (inter-lens gap 22) of 0.3 μm.
0 was obtained. FIG. 2 is an explanatory cross-sectional view illustrating an end shape of one of the plurality of microlenses 20 formed in the first embodiment.
As shown in FIG. 2, the microlens 20 formed in the first embodiment has a lens thickness (height of the lens shoulder 23) of 0.3 μm from the lens end toward the center of the lens.
Was set to 0.65 μm. The maximum thickness of the micro lens (the lens thickness 21 at the center) is 1.5 μm,
The film thickness of the lens (the height of the lens shoulder 23) at a position 0.3 μm from the lens end toward the center of the lens is 43% of the maximum thickness of the microlens 20.

FIG. 6 is an explanatory plan view showing one plane of the plurality of microlenses formed in the first embodiment. The solid line in FIG.
0, and the broken line in FIG. 6 indicates the photosensitive resin before thermal reflow. As shown in FIG. 6, in the first embodiment, the planar shape of the photosensitive resin formed by the photolithography process is rectangular, and the reflow amount in the side direction when a microlens is formed.
4 (especially, the reflow amount 24 at the center of the side) is 0.1
μm. That is, as shown in FIG. 1, the microlens 20 formed in the first embodiment is not a sagged skirt but a skirt having a steep slope.

Image evaluation of the solid-state imaging device of the first embodiment was performed, and an extremely favorable image display with less occurrence of smear was obtained.

<Embodiment 2> The solid-state imaging device according to Embodiment 2 has the same configuration as the solid-state imaging device of FIG. 1 described above. That is, the semiconductor substrate 30 made of a silicon substrate includes the photodiode portion 11 constituting the light receiving portion 32 and the vertical register portion 31 composed of the vertical well portion 12, the charge transfer portion 13, the transfer electrode 14, and the like. A semiconductor element is formed. Next, a light-shielding film 15, a flattening film 16, a color filter 17, and a flattening film 18 are formed on the semiconductor substrate with the light-receiving portion 32 as an opening. The microlens 20 that covers the portion 32 is formed.

The microlens 20 according to the second embodiment was formed by the following manufacturing process. That is, after the flattening film 18 (acrylic transparent resin) is formed on the semiconductor substrate 30, a phenolic photosensitive resin (for example, “MFR345” manufactured by JSR Co., Ltd., trade name) is formed on the flattening film 18. ) Is applied and dried to a thickness of 1.4 μm.
m of the photosensitive resin film was formed. Next, pattern exposure, development, and the like are performed on the photosensitive resin film, and a predetermined portion (light receiving portion 3
2), the photosensitive resin was left.

Next, the remaining photosensitive resin was subjected to thermal reflow using a hot plate to make the photosensitive resin into a microlens shape. The thermal reflow was performed at two heating temperatures, a low temperature and a high temperature. That is, the semiconductor substrate is set at 130 ° C.
Is moved on the plurality of hot plates, and the flattening film 1 is formed.
The photosensitive resin on 8 was slightly cured. Next, the semiconductor substrate was moved on a plurality of hot plates at 180 ° C. to perform thermal reflow and final curing of the photosensitive resin on the flattening film 18.

By the above processing, a plurality of micro lenses 2 having a distance between lens centers (inter-lens pitch) of 5 μm and an inter-lens distance (inter-lens gap 22) of 0.3 μm are set.
0 was obtained. FIG. 3 is an explanatory cross-sectional view showing an end shape of one of the microlenses 20 formed in the second embodiment.
As shown in FIG. 3, the microlens 20 formed in the second embodiment is 0.3 μm from the lens end toward the lens center.
The thickness of the lens at the site where the lens enters (the height of the lens shoulder 32
3) was set to 0.53 μm. The maximum thickness of the micro lens (lens thickness 321 at the center of the lens) is 1.5.
μm, and 0.3 μm from the lens edge toward the lens center.
The thickness of the lens at the part where the lens enters
23) is 35% of the maximum thickness of the microlens.
Also in Example 2, as shown in FIG. 6, the planar shape of the photosensitive resin formed by the photolithography process was rectangular (dotted line in FIG. 6). Also, the amount of reflow in the side direction of the photosensitive resin during thermal reflow (particularly the amount of reflow in the center of the side)
Was set to 0.15 μm (solid line in FIG. 6). That is, as shown in FIG. 1, the microlens formed in the second embodiment also has a skirt shape having a steep slope instead of a sagged skirt shape.

Image evaluation of the solid-state imaging device of Example 2 was performed, and a good image display with less occurrence of smear was obtained. The level of occurrence of smear noise of the solid-state imaging device according to the second embodiment is three to three times that of the solid-state imaging device according to the first embodiment.
Although it was eight times, slight deterioration of the screen display quality was recognized,
There was no problem in practical use.

<Comparative Example> FIG. 5 shows a conventional solid-state imaging device 5.
It is sectional explanatory drawing which shows 0. As shown in FIG. 5, a semiconductor substrate 70 made of a silicon substrate includes a photodiode unit 51 constituting a light receiving unit 72 and a charge transfer unit 5.
3. A semiconductor element such as a vertical register section 71 including a transfer electrode 54, a vertical well section 52, and the like is formed.
Next, a light-shielding film 55, a planarizing film 56, a color filter 57, and a planarizing film 58 having a light-receiving portion 72 as an opening are laminated on the semiconductor substrate. Is formed.

The microlens 60 according to this comparative example was formed by the following manufacturing process. That is, after performing the process up to the formation of the planarization film 58 (acrylic transparent resin) on the semiconductor substrate 70, the phenolic photosensitive resin (for example, “TMR-P” manufactured by Tokyo Ohka Co., Ltd.) is formed on the planarization film 58.
3)), and dried to form a photosensitive resin film having a thickness of 1.5 μm. Next, pattern exposure on the photosensitive resin film,
Development and the like were performed to leave the photosensitive resin in a predetermined portion (a portion on the light receiving portion 72).

Next, the remaining photosensitive resin was subjected to thermal reflow using a hot plate to make the photosensitive resin into a microlens shape. Thermal reflow was performed at two heating temperatures. That is, the semiconductor substrate was moved on a plurality of hot plates at 160 ° C. to slightly cure the photosensitive resin on the flattening film 58. Next, the semiconductor substrate is
The photosensitive resin on the flattening film 58 was thermally reflowed and finally cured by moving on a plurality of hot plates at 0 ° C.

By the above processing, a plurality of microlenses 6 having a distance between lens centers (inter-lens pitch) of 5 μm and an inter-lens distance (inter-lens gap 62) of 0.3 μm.
Thus, the solid-state imaging device 50 according to this comparative example in which 0 was formed was obtained. FIG. 4 is a cross-sectional explanatory view showing an end shape of one of the microlenses 60 formed in the comparative example. As shown in FIG. 4, the microlens 60 formed in the present comparative example has a lens thickness (lens shoulder height 63) of 0.39 μm at a portion 0.3 μm from the lens end toward the center of the lens. did. Also, the maximum thickness of the microlens (lens thickness 6 at the center of the lens)
1) is 1.5 μm, and the thickness of the lens (the height of the lens shoulder 63) at a portion 0.3 μm from the end of the lens toward the center of the lens is 26, which is the maximum thickness of the microlens.
%Met. In this comparative example, as shown in FIG. 6, the planar shape of the photosensitive resin formed by the photolithography process is rectangular, and the reflow amount in the side direction (particularly, the reflow amount in the center of the side) when forming a microlens is 0. .25 μm. That is, the microlens formed in this comparative example is
As shown in FIG. 5, the skirt shape was a sagged shape and a flat shape in cross-sectional view.

Image evaluation of the solid-state imaging device obtained in the comparative example was performed. Also,
The smear noise generation level of the solid-state imaging device of this comparative example is
Compared with the solid-state imaging device of the first embodiment, the size was 20 to 90 times larger, and the screen display quality was clearly deteriorated.

In the above Examples 1, 2 and Comparative Examples, the exposure amount when exposing the photosensitive resin to the pattern was set so that the inter-pattern dimension (inter-pattern gap) of the microlenses was substantially the same. Development conditions are adjusted.

Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above description and drawings, and various modifications may be made based on the spirit of the present invention. It goes without saying.

For example, the thickness of the lens (height of the shoulder of the lens) at a portion 0.3 μm from the edge of the microlens toward the center of the microlens is 35% or more of the maximum thickness of the microlens. It may be appropriately determined according to various specifications.

[0036]

As described above, in the solid-state imaging device according to the present invention, the shape of the microlens is optimized. That is, the skirt shape of the microlens is not a sagged shape, but a steeply sloped skirt shape. This makes it possible to eliminate the effects of light incident from an oblique direction and the effects of multiple reflections, and to achieve a high-resolution solid-state imaging device with a large number of pixels and a high-quality solid-state imaging device with reduced screen display quality. Obtainable. In the present invention, the manufacturing conditions of the microlens are also optimized, and a desired microlens shape can be easily obtained. In addition, the present invention uses a photolithography method and a thermal reflow method to manufacture a microlens, which is simpler than a conventional method of forming a microlens by a dry etching (back etching) method or a groove etching method. A solid-state imaging device can be obtained by a simple manufacturing process.

[0037]

[Brief description of the drawings]

FIG. 1 is a sectional explanatory view schematically showing one embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a partially enlarged explanatory view showing an example of a main part of a microlens according to the present invention.

FIG. 3 is a partially enlarged explanatory view showing another example of a main part of the microlens according to the present invention.

FIG. 4 is a partially enlarged explanatory view schematically showing an example of a microlens formed in a conventional solid-state imaging device.

FIG. 5 is an explanatory sectional view schematically showing an example of a conventional solid-state imaging device.

FIG. 6 is an explanatory plan view showing an example of a microlens according to the present invention.

[Explanation of symbols]

 10, 50 solid-state imaging device 11, 51 photodiode section 12, 52 vertical well section 13, 53 transfer section 14, 54 transfer electrode 15, 55 light-shielding film 16, 56 flattening film 17, 57 color filter 18, 58 flattening film 20, 60 micro lens 21, 61, 321 lens thickness 22, 62 gap between lenses 23, 63, 323 height of lens shoulder 24 reflow amount 30, 70 semiconductor substrate 31, 71 vertical register part 32, 72 light receiving part

Claims (4)

[Claims] 1. A solid-state imaging device having at least a semiconductor substrate in which a plurality of light receiving units for performing photoelectric conversion are arranged in an array, and a micro lens formed on each of the light receiving units. A solid-state imaging device, wherein the thickness of the lens at a portion 0.3 μm into the center of the lens is 35% or more of the maximum thickness of the microlens. 2. A semiconductor substrate having a plurality of light receiving portions for performing photoelectric conversion arranged in an array, and a microlens made of a photosensitive resin formed on each of the light receiving portions by a photolithography process and a thermal reflow process. A method for manufacturing a solid-state imaging device, comprising: suppressing a reflow amount of a photosensitive resin in a side direction during thermal reflow to 0.2 μm or less. 3. A semiconductor substrate in which a plurality of light receiving units for performing photoelectric conversion are arranged in an array, and a microlens made of a photosensitive resin formed on each of the light receiving units by a photolithography process and a thermal reflow process. 3. A method for manufacturing a solid-state imaging device according to claim 2, wherein the photosensitive resin to be thermally reflowed has a rectangular shape in a plan view, and a reflow amount in a side direction at the time of thermal reflow is suppressed to 0.2 μm or less.
5. The method for manufacturing a solid-state imaging device according to item 1. 4. The thermal reflow is divided into two stages and is carried out at a temperature of 100.degree.
4. The method according to claim 2, wherein after the first heat treatment at 50 ° C., a second heat treatment is performed at a temperature exceeding 150 ° C. 5.