JP2003315506A - Manufacturing method of micro lens - Google Patents

Abstract

(57) [Summary] [Problem] The present invention relates to a lens having a gap between lenses of 0.1 μm.
Provided is a method for manufacturing microlenses in which low-cost microlenses of m or less can be mass-produced inexpensively by a thermal reflow method without the microlenses being fused at each side. An undercoat layer is formed using a thermosetting resin having a thermosetting temperature higher than a thermal reflow temperature of a positive photosensitive resin, and is partially cured by a heat treatment to have a thermal reflow property. Forming a layer, forming a rectangular pattern, and performing heat reflow by heat treatment to produce a microlens. Forming a flow suppression layer on the undercoat layer, which suppresses the flow of the positive photosensitive resin during thermal reflow.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a C-MOS or CC.
The present invention relates to a microlens formed on a solid-state image sensor represented by a light receiving element of D, and in particular, a method of manufacturing a microlens which improves sensitivity by increasing an effective aperture ratio of the microlens and reduces smear. Regarding

[0002]

2. Description of the Related Art CCD (charge coupled)
The area of the plane of each pixel on the solid-state image sensor, such as a device, is composed of two areas: a rectangular photoelectric conversion section and a signal readout circuit section around the photoelectric conversion section. Of these, the signal readout circuit section is an area insensitive to the incident light component. On the solid-state image sensor, conventionally, one of the effective means for condensing the light component incident on the insensitive region on the photoelectric conversion unit to achieve high sensitivity of the image sensor and not deteriorating the other parts. Place a transparent microlens array on
There is a known technique in which an incident light component that reaches the signal reading circuit unit, which is an insensitive region, is focused on the photoelectric conversion unit.

However, in recent years, due to the tendency toward higher pixel size and smaller size, there is a strong demand for a high-definition CCD image pickup device having a chip size of 1/2 inch or less and more than 3 million pixels. In the above, there is a big problem that the aperture ratio of the formed microlens is lowered, that is, the element sensitivity is lowered, and the noise such as smear is increased.

As a known technique for forming a microlens, for example, Japanese Patent Laid-Open No. 60-53073 discloses a method of forming a hemispherical microlens by causing a resin to drip by heat reflow, so-called heat reflow. And a technique of transferring a microlens formed by a thermal reflow method onto an undercoat layer as a base by using an etching technique such as dry etching. In addition, JP-A-5-
Japanese Patent No. 48057 discloses a method of performing vacuum film formation on a lens formed by thermal reflow using plasma CVD or the like.

In a high-definition CCD image pickup device, the pixel pitch is required to be 3 μm or less. The microlenses formed with a pixel pitch of 3 μm are, as described above,
In order to prevent a decrease in element sensitivity, it is essential to form a microlens with a high aperture ratio, and the gap dimension between the lenses is 0.
It is required to be 1 μm or less (hereinafter referred to as a narrow gap). The formation of microlenses by the above-mentioned thermal reflow method is a method in which a photosensitive resin is formed into a rectangular pattern by photolithography, and then it is formed by thermal reflow. It is difficult to form the inter-lens gap dimension of 0.3 μm or less in mass production due to variations in the amount of heat dripping during heat reflow.

Further, the technique of transferring the microlenses formed by the above-mentioned thermal reflow method onto the undercoat layer of the underlying layer by using an etching technique such as dry etching is performed by using a resin which is a microlens layer formed by thermal reflow. It is also possible in mass production to narrow the inter-lens gap dimension to 0.1 μm or less by adjusting the etching rate of the undercoat layer and selecting the gas type during dry etching.

However, in this method, a vacuum device such as dry etching is used, so that there is a concern that the yield may be reduced due to an increase in appearance defects such as foreign matter. Further, since an expensive vacuum device is used, the throughput is reduced. However, the problem of high cost arises. Further, a method of forming an inorganic film such as SiO ₂ by plasma CVD or the like on a microlens of an organic resin formed by the above-mentioned thermal reflow method to narrow the inter-lens gap dimension is an inorganic film on an organic resin. To form a crack, wrinkles, etc. reliability problem, and because a vacuum device is used,
There have been problems that the yield is lowered and the cost is increased due to the increase of defects such as foreign matter.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a microlens having a high aperture ratio, which is indispensable for a high-definition image pickup device, that is, a microlens having a gap dimension between lenses of 0.1 μm or less (narrow gap) is thermally reflowed. It is an object of the present invention to provide a method of manufacturing a microlens that can be mass-produced at low cost without fusion of the microlenses at each side portion.

[0009]

The present invention provides a microlens manufacturing method for manufacturing a microlens using a positive photosensitive resin having a heat reflow property on an undercoat layer provided on a semiconductor substrate, 1) As an undercoat layer material, an undercoat layer is formed using a thermosetting resin having a thermosetting temperature higher than the heat reflow temperature of a positive photosensitive resin, and 2) the undercoat layer. Half-cure by heat treatment, 3) forming a positive-type photosensitive resin layer having a heat reflow property on the half-cured undercoat layer, and 4) exposing and developing the positive-type photosensitive resin layer to form a rectangle. A microlens manufacturing method is characterized in that a microlens is manufactured by forming a pattern and thermally reflowing the rectangular pattern by heat treatment.

The present invention also provides, in the method for producing a microlens according to the above invention, as the material of the undercoat layer, the thermosetting temperature of which is higher than the heat reflow temperature of the positive photosensitive resin. A method of manufacturing a microlens, which is characterized by using a thermosetting resin which is a thermosetting resin and has a heat reflow property.

Further, the present invention is characterized in that, in the method of manufacturing a microlens according to the above invention, the temperature at which the undercoat layer is partially cured by heat treatment is lower than the thermal reflow temperature of the positive photosensitive resin. It is a manufacturing method of a microlens.

Further, the present invention is characterized in that, in the method for producing a microlens according to the above-mentioned invention, a flow suppressing layer is formed on the undercoat layer to suppress the flow of the positive photosensitive resin during thermal reflow. And a method of manufacturing a microlens.

The present invention also provides the method of manufacturing a microlens according to the above invention, wherein the undercoat layer comprises:
A method of manufacturing a microlens, which is a partially cured undercoat layer.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a microlens according to the present invention will be described below based on its embodiment. 1 (1) to 1 (5) are cross-sectional views showing manufacturing steps of a method for manufacturing a microlens according to the present invention. In FIG. 1A, the semiconductor substrate 31 is formed on the Si substrate 11 by the light receiving portion 1.
2, the transfer electrode 13, the interlayer insulating film 14, and the light shielding film 15 are formed. A flattening film 16, a color filter 17, and an undercoat layer 18 are sequentially formed on the semiconductor substrate 31. Then, the flow suppressing layer 19 is formed (FIG. 1).
(2)). Then, a positive photosensitive resin is used to form a predetermined rectangular pattern 20 by a photolithography method. Next, the rectangular pattern 20 is thermally reflowed to form a hemispherical microlens 21, and a microlens having a narrow gap 24 between lenses is formed on the semiconductor substrate 31 (FIG. 1 (4)). .

The present inventors formed an undercoat layer on a semiconductor substrate, and using a positive type photosensitive resin thereon, when forming a microlens by a thermal reflow method, a half-cured undercoat layer 18 was formed. As described above, it was found that by exposing, developing, and thermally reflowing the positive photosensitive resin, it is possible to suppress the flow of the microlens edge portion during the thermal reflow of the formed microlens.

That is, after forming the undercoat layer 18 in a semi-cured state, at the time of thermal reflow for forming the microlenses 21, a heat treatment temperature higher than the temperature at which the undercoat layer 18 is semi-cured is applied to perform heat reflow. Therefore, the region 23 where the rectangular pattern 20 does not exist in the undercoat layer 18 shown in FIG. 1C is pushed upward due to the tension balance. As a result, at the time of thermal reflow when forming the microlenses 21, the pushed up regions prevent fusion of the microlenses 21 with each other, and the inter-lens gap 24 is formed to be 0 to 0.1 μm or less. Will be possible.

As a material for the undercoat layer, a thermosetting resin having a thermosetting temperature higher than that of the positive photosensitive resin is used. The semi-cured undercoat layer is a material in which a crosslinking reaction is performed by radical polymerization such as a thermosetting resin, and the crosslinking reaction is not completely completed. However, when a positive photosensitive resin is applied on the half-cured undercoat layer,
It is necessary that the semi-cured undercoat layer and the positive photosensitive resin be a semi-cured undercoat layer in a state where intermixing does not occur.

The thermosetting resin used in the undercoat layer 18 has an acrylic resin, an epoxy resin, a phenol resin, a novolac resin, a styrene resin, or a copolymer of these resins as a skeleton. A resin having a composition to which a curing agent such as methacrylic acid, acrylic acid, or itaconic acid, a solvent, and if necessary, an adhesive agent, a surfactant, or a photosensitizer is added can be used. Further, it is preferable to add a monomer having a heat reflow property to the above resin composition. The undercoat layer 18 formed of the above resin can be formed as a permanent film by applying a heat treatment after coating, but the heat treatment temperature at this time is as follows.
It is desirable that the temperature is such that the curing agent does not completely complete the curing reaction and there exists a partially cured state.

The inventors of the present invention use, as the material for the undercoat layer, a material such as a thermosetting resin that undergoes a crosslinking reaction by radical polymerization. Among the thermosetting resins, the material is formed by the thermal reflow method. It has been found that a thermosetting resin having a heat reflow property is suitable for suppressing the flow of the micro lens edge portion at the time of heat reflow of the micro lens.

Furthermore, the present inventors have found that when a positive type photosensitive resin is used on a semi-cured undercoat layer to form a microlens by a thermal reflow method, a flow suppressing layer is formed on the semi-cured undercoat layer. It has been found that the formation of the layer can suppress the flow of the microlens edge portion during the thermal reflow of the microlens formed by the thermal reflow method. That is, by forming the flow suppression layer 19, it is possible to reduce the speed at which the edge portion of the rectangular pattern 20 flows at the interface with the flow suppression layer 19 during the thermal reflow process when forming the microlens 21.

To form the flow suppressing layer 19, an epoxy group,
Amino group, carboxyl group, sulfonic acid group, vinyl group,
A water-soluble resin containing a methacryloxy group or a mercapto group, or an alkaline aqueous solution containing an alkali such as triethanolamine, tetramethylammonium hydroxide, dimethylethanolamine, triethanolamine or methyldiethylamine can be used.

The flow suppressing layer 19 is formed on the undercoat layer 18 after the undercoat layer has been subjected to a heat treatment in a state in which the crosslinking reaction is not completely completed, that is, in a semi-cured state. Preferably.

The inventors of the present invention have found that the above-mentioned undercoat layer is formed in a semi-cured state.
When the positive type photosensitive resin is exposed, developed, and thermally reflowed to form microlenses, the undercoat layer is reflowed by performing a thermal reflow process at a temperature higher than the temperature at which the half-cured undercoat layer is formed. It was found that the amount of heat reflow of the microlens can be controlled by changing the ratio of heat generation. That is, the heat reflow amount of the microlens can be controlled by lowering the temperature at which the undercoat layer is partially cured by heat treatment to be lower than the heat reflow temperature of the positive photosensitive resin.

[0024]

EXAMPLES Examples of the present invention will be described below. <Example 1> After a flattening film having a thickness of 1.0 μm was formed on a Si substrate, a photosensitive resin MFR380M (product number) manufactured by JSR Corporation was used as an undercoat layer, and the rotation speed was 3
After coating by spin coating at 000 rpm, in order to dry the solvent, heat treatment was carried out for 90 seconds at 100 ° C. using a hot plate as temporary drying. Next, a 1.2% tetramethylammonium hydroxide aqueous solution manufactured by Tokyo Ohka Co., Ltd. was used as an alkaline aqueous solution for forming the flow suppressing layer, and dipping was performed for 40 seconds, followed by drying. Furthermore, using a hot plate,
A heat treatment was carried out at 150 ° C. for 3 minutes to form a half-cured undercoat layer as the undercoat layer, and at the same time, a tetramethylammonium hydroxide flow suppressing layer was formed on the half-cured undercoat layer.

Next, using TMR-P3 manufactured by Tokyo Ohka Co., Ltd., which is an alkali-soluble type positive photosensitive resin,
After applying by spin coating at a rotation speed of 1500 rpm, to dry the solvent, use a hot plate.
Heat treatment was performed at 90 ° C. for 90 seconds. Next, an i-line stepper manufactured by Nikon Corporation was used to perform exposure through a high-definition photomask. The exposure amount at this time is 220
It was millisecond (110 mJ / cm ² ). Then, using a 2.38% aqueous solution of tetramethylammonium hydroxide, which is an alkaline developer manufactured by Tokyo Ohka Co., Ltd.,
Development was carried out for 0 seconds to form a rectangular pattern.

Finally, using a hot plate, 90 ° C.
The heat treatment was sequentially performed at a temperature of → 160 ° C → 200 ° C for 3 minutes each to form a microlens. As a result, as shown in FIG.
m, and a lens height of 1.5 μm could be formed. At this time, in the Si substrate, there was no appearance unevenness such as lens fusion caused by lenses contacting each other, and it was in a good state.

[0027]

According to the present invention, the undercoat layer is formed by using, as a material for the undercoat layer, a thermosetting resin having a thermosetting temperature higher than the heat reflow temperature of the positive photosensitive resin. , The undercoat layer is half-cured by heat treatment, a positive type photosensitive resin layer having a heat reflow property is formed on the half-cured undercoat layer, and the positive type photosensitive resin layer is exposed and developed to form a rectangular pattern. Since the microlenses are manufactured by forming a microstructure and thermally reflowing the rectangular pattern by heat treatment, the flow of the microlenses is suppressed during the thermal reflow, and the interlens gap dimension is 0.1 μm or less (narrow gap) by the thermal reflow method. The microlenses can be mass-produced at a low cost without fusing the microlenses at each side.

Further, the present invention is characterized in that on the undercoat layer,
Since the positive type photosensitive resin forms the flow suppressing layer that suppresses the flow at the time of heat reflow, the flow of the microlenses is further suppressed at the time of heat reflow, and the inter-lens gap dimension is 0.1 μm or less by the heat reflow method ( Micro-lenses with a narrow gap) are not fused on each side,
This is a method for manufacturing a microlens that can be mass-produced at a lower cost.

[Brief description of drawings]

FIG. 1 (1) to (5) are cross-sectional views showing manufacturing steps of a method for manufacturing a microlens according to the present invention.

FIG. 2 is a cross-sectional photograph showing an enlarged cross section of a microlens in Example 1.

FIG. 3 is a cross-sectional photograph showing an enlarged cross section of a microlens in a conventional method.

[Explanation of symbols]

11 ... Si substrate 12 ... Light receiving part 13 ... Transfer electrode 14 ... Interlayer insulating film 15 ... Shading film 16 ... Flattening film 17 ... Color filter 18 ... Undercoat Layer 19 ... Flow suppression layer 20 ... Rectangular pattern 21 ... Microlens 22 ... Thermal reflow amount 23 ... Region where the rectangular pattern 20 does not exist on the undercoat layer 24 ... Gap between lenses

Continued front page    (72) Inventor Fumihiko Ichiyanagi             1-5-1 Taito, Taito-ku, Tokyo Toppan stamp             Imprint Co., Ltd. (72) Inventor Tadashi Ishimatsu             1-5-1 Taito, Taito-ku, Tokyo Toppan stamp             Imprint Co., Ltd. F-term (reference) 2H025 AA03 AB14 AD03 DA35 DA40                       FA29 FA33                 4M118 AA01 AA05 AB01 BA10 BA14                       EA20 GB03 GC07 GD04 GD07                 5C024 CX41 CY47 EX43 EX52

Claims (5)

[Claims] 1. A microlens manufacturing method for manufacturing a microlens using a positive photosensitive resin having a heat reflow property on an undercoat layer provided on a semiconductor substrate. 1) As a material for the undercoat layer Forming an undercoat layer using a thermosetting resin having a thermosetting temperature higher than the heat reflow temperature of the positive photosensitive resin, 2) half-curing the undercoat layer by heat treatment, 3) A positive photosensitive resin layer having a heat reflow property is formed on the semi-cured undercoat layer, and 4) a rectangular pattern is formed by exposing and developing the positive photosensitive resin layer, followed by heat treatment. A method of manufacturing a microlens, characterized in that the rectangular pattern is thermally reflowed to manufacture a microlens. 2. A thermosetting resin having a thermosetting temperature higher than that of a positive-type photosensitive resin as a material of the undercoat layer, and a thermosetting resin having thermal reflow property. The method for producing a microlens according to claim 1, wherein a resin is used. 3. The microlens manufacturing according to claim 1, wherein the temperature at which the undercoat layer is half cured by heat treatment is lower than the thermal reflow temperature of the positive photosensitive resin. Method. 4. A flow suppressing layer which suppresses the flow of the positive photosensitive resin during thermal reflow, is formed on the undercoat layer. A method for manufacturing the described microlens. 5. The method for producing a microlens according to claim 4, wherein the undercoat layer is a semi-cured undercoat layer.