JPH0540216A - Microlens and production thereof - Google Patents

Abstract

PURPOSE:To obtain the lens having a large aperture ratio by forming the lens of an aspherical shape. CONSTITUTION:A microlens pattern 2 for transfer is formed by thermal melting on a transparent resin layer 3 for microlenses in the method for forming the microlenses consisting of a synthetic resin on a base material. The etching rate of the resin layer for forming the microlenses is set higher than the etching rate of the microlens pattern for transfer at the time of transferring the microlens pattern for transfer by an etching method, by which the lenses molded by the transfer are made into elliptic lenses 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microlens provided on a solid-state image pickup device such as a CCD and a manufacturing method thereof.

[0002]

2. Description of the Related Art Various proposals have been made so far for a solid-state image pickup device used as a solid-state image pickup camera or an image sensor, such as a light receiving portion, an electrode portion, and a transfer system. Among them, a charge-coupled solid-state image sensor (hereinafter CC
(Referred to as “D”) (1) Since the self-scanning is possible, the peripheral circuit becomes simple.

(2) The structure is simple.

(3) The ability to detect light in the visible region is large.

It is widely used because of its properties such as Recently, there is a demand for higher sensitivity and lower noise at the same time as further miniaturization and higher pixel count. Therefore, various proposals have been made regarding the circuit aspect or the imaging device structure aspect relating to this. In particular, the interline CCD has been found to be advantageous because it has less smear than other methods in terms of device structure and can improve the resolution by using a mosaic type color filter. However, in the interline CCD, the charge transfer section must be provided next to the light receiving section, so that the aperture ratio of the light receiving section on the surface must be reduced. As the number of pixels increases, the aperture ratio will decrease.
Further, since there is a limit to the reduction of the intrinsic noise of the solid-state image pickup device itself, the reduction of the aperture ratio, that is, the reduction of the S / N ratio, deteriorates the quality of the image pickup screen.

As a countermeasure, there has been proposed a method of directly forming a microlens on a solid-state image pickup device in order to increase the incident light and increase the input signal intensity. This method is one of the effective methods for increasing the aperture ratio despite its simple structure. A sectional view of a CCD having microlenses is shown in FIG. The CCD substrate 41 has a light receiving portion 42, and a light shielding portion 43 is formed between each light receiving portion. After forming an appropriate color filter 44 on the light-receiving layer, a transparent resin layer 45 is provided to form an appropriate interval for adjusting the focal length of the lens. A microlens 46 is provided on the upper surface of the light receiving portion 42 at a position where the incident light is focused. The external incident light is the micro lens 46.
The light is refracted by the optical refraction function of the light-receiving section 42, and the incident light to the transfer section and the wiring section 47 around it is also incident on the light-receiving section 42. As a result, the aperture ratio increases and light does not enter the transfer section or the wiring section, so that smear can be reduced.

[0007]

The manufacture of the microlenses to be used as described above has the property that the transparent synthetic resin material is heated and melted so that the molten transparent synthetic resin becomes spherical due to the surface tension. It is formed by the heat melting method used and the etch back method of transferring the microlens to the transparent resin layer by etching the microlens formed by heating and melting the photoresist formed on the transparent resin layer for the lens as a pattern. However, the lenses obtained by these methods were only lenses having a spherical surface.

Since a microlens has a relatively short distance between solid-state image pickup elements, it is necessary to make a lens having a large curvature. In a lens whose curved surface is approximate to a spherical surface, the light incident on the end of the lens is Since the light cannot be condensed on the light receiving portion, the substantial amount of light received entering the light receiving portion will be reduced.

[0009]

The present invention has been completed as a result of studies for solving the above problems, and the present invention has been completed. In the etchback method, a lens pattern formed by heat melting a photoresist or the like is formed. When transferring to the transparent resin underneath by etching, the difference in the etching rate between the photoresist and the transparent resin on which the microlens pattern is formed is used. By making it faster than the etching rate, the curved surface of the formed microlens becomes an aspherical surface, particularly a part of an ellipsoid. As a result, the light at the end of the lens is also focused on the central part of the lens, so that if the light receiving part of the CCD is placed at this position, the substantial aperture ratio can be improved.

The present invention will be described with reference to the drawings. In FIG. 2, incident light is collected by a microlens (hereinafter referred to as an elliptical lens) which is a part of an aspherical ellipsoid according to the present invention. FIG. 3 is a diagram showing a state, and FIG. 3 is a diagram showing a state of being condensed by a conventional microlens having a spherical curved surface (hereinafter referred to as a spherical lens).

As shown in FIG. 3, a spherical lens 33 is provided corresponding to the light receiving portion 32 provided on the CCD substrate 31,
The incident light 34 on the spherical lens is refracted by the spherical lens, but the light incident on the end portion of the lens cannot be condensed on the light receiving portion. On the other hand, when the elliptical lens is formed, as shown in FIG.
The incident light 24 incident on the elliptical lens 23 provided corresponding to the above can also collect all the light incident on the end portion of the lens to the light receiving portion, so that even if the area of the light receiving portion 22 is small, The aperture ratio can be increased.

By using an elliptical lens, the focal length can be made shorter than that of a spherical lens even when the resin having the same refractive index is used, so that the distance between the lens and the light receiving portion can be made small. Yes, lens and CCD
Since it is possible to reduce the amount of transparent resin provided in the undercoat layer 25 between the substrate and the substrate, it is possible to reduce the size of the device.

The optimum ellipsoidal shape for the ellipsoidal lens is an ellipsoid long in the direction perpendicular to the substrate. The optimum ellipsoidal ratio of the major axis to the minor axis (hereinafter referred to as flatness) is The value is as shown in Table 1 depending on the refractive index of the resin used. Further, the ratio of the major axis to the uniaxial axis can be arbitrarily adjusted by the ratio of the etching rate of the pattern of the transferred microlens and the transparent resin layer on which the microlens is finally formed.

[0014]

[Table 1]

In the present invention, it is preferable that the focal length of the microlens coincides with the light receiving surface of the CCD substrate. However, since the microlens of the present invention has an improved light-collecting property due to the shape that matches a part of the ellipse, if the light collected in the range of the light-receiving surface is made incident, the focus position will be slightly received. It may be offset vertically or horizontally from the surface. A method of manufacturing the microlens of the present invention will be described with reference to FIG. A photosensitive resin such as an acrylic resin was applied onto an interline CCD 1 having a light receiving portion, a transfer portion, and its peripheral circuits mounted on a silicon substrate shown in FIG. 1A, and prebaked in a clean oven. Next, the film was exposed to ultraviolet light through a desired pattern and then developed to remove the bonding pad and the acrylic resin on the scribe line. Further, it was post-baked in a clean oven at 150 ° C. to form an undercoat layer 2 for keeping the distance between the lens and the light receiving part. Next, a coating layer of polystyrene-based photosensitive resin is formed on the undercoat layer, prebaked in a clean oven, and then exposed to ultraviolet light through a desired pattern, and then developed and bonded on a bonding pad or scribe line. The resin was removed. Further, post-baking was performed in a clean oven to form a resin layer 3 for forming a microlens. As the polystyrene type photosensitive resin, for example, TPS (manufactured by Tosoh Corporation) can be used. Further, a novolac-based photosensitive resin was applied on the microlens-forming resin layer 3 and prebaked in a clean oven. Next, the pattern was exposed to ultraviolet light using a pattern in which only the novolac-based photosensitive resin in the portion corresponding to the light-receiving portion of the CCD remained, and then developed to form the novolac-based photosensitive resin pattern 4 only in the light-receiving portion. AZ1350 (made by Shipley) etc. can be used as a novolac type photosensitive resin.

FIG. 1 (b) The novolac type photosensitive resin pattern was heat-melted in a clean oven, and the molten resin which became spherical due to the surface tension was solidified to form the transfer spherical lens 5. 1C, the transparent resin layer for microlenses is etched by a dry etching means such as microlens oxygen plasma, and the pattern of the spherical lens for transfer is transferred to the resin layer for forming microlens to form an aspherical elliptic lens 6 Got

Using the pattern of the spherical lens for transfer,
In order to form the elliptical lens, it is necessary to etch the microlens-forming transparent resin at a higher etching rate than the pattern of the transfer spherical lens.

For this purpose, the resin used for the pattern of the spherical lens for transfer and the resin for forming the microlenses are selected according to the etching characteristics, but etching may be performed depending on the etching method applied even if the same resin is used in combination. Since the characteristics change, it is necessary to comprehensively judge these and select the resin and etching conditions.

When the etching is performed by dry etching, oxygen plasma can be applied. However, by changing the high-frequency output, the oxygen flow rate, the oxygen pressure and the like in the oxygen plasma generation conditions, there is a difference in the etching rate for both resins. The resulting conditions can be adjusted. The etching conditions are
High frequency power 300-600W, oxygen flow rate 50-200
The sccm and pressure are preferably 4 to 20 Pa.

[0020]

[Function] A transfer spherical lens pattern formed by melting a transfer resin having a pattern formed on a resin layer for a microlens applied on a substrate of a solid-state image pickup device such as a CCD is transferred by an etch-back method, Since an aspherical ellipsoidal lens is formed, the light incident on the peripheral portion of the lens can be surely concentrated on the light receiving portion of the CCD.

[0021]

EXAMPLES Examples of the present invention will be shown below for further detailed description. Example 1 An FVR (Fuji Chemical Industry Co., Ltd.) as an acrylic photosensitive resin was formed on an interline CCD (aperture ratio 20%) having a light receiving part, a transfer part, and its peripheral circuits mounted on a 5-inch silicon substrate. Manufactured) was applied in a film thickness of 5 μm and prebaked in an oven. Next, the film was exposed to ultraviolet light through a desired pattern and then developed to remove the bonding pad and the acrylic resin on the scribe line. Further 150 ℃
Post-baking was performed for 30 minutes in a clean oven to form an undercoat layer for keeping the distance between the lens and the light receiving portion.

On the undercoat layer, a polystyrene type photosensitive resin TPS (manufactured by Tosoh Corporation) was applied as a microlens forming resin in a thickness of 3.5 μm, and put in a clean oven at 120 ° C. for prebaking. Then, the resin on the bonding pad and the scribe line was removed by exposing to ultraviolet light through a desired pattern and then developing. 1 more
Post-baked for 30 minutes in a 50 ° C. clean oven.

Further, AZ1350 (manufactured by Shipley Co.) as a novolac type photosensitive resin was applied on the resin layer for forming microlenses to a thickness of 2.6 μm, and prebaked in a clean oven at 90 ° C. Then, the pattern was exposed to ultraviolet light using a pattern in which only the novolac-based photosensitive resin in the portion corresponding to the light-receiving portion of the CCD was left, and then developed to form a novolac-based photosensitive resin pattern only in the light-receiving portion. Then, it was heat-melted in a clean oven at 120 ° C. and then solidified to form a spherical lens pattern for transfer.

Then, etching was carried out by the oxygen plasma method.
The high-frequency power of was supplied, and the etching was performed under the conditions of an oxygen flow rate of 100 sccm and a pressure of 20 Pa. By the above operation,
An elliptical lens could be formed on each of the light receiving parts of the CCD. The elliptic lens produced by this method has a flatness value of 1.33, and it was possible to raise the aperture ratio from 40% in a spherical lens using the same resin to 50%.

Example 2 An acrylic photosensitive resin FVR (Fuji Yakuhin Kogyo Co., Ltd.) having an etching rate higher than that of a novolak photosensitive resin on the undercoat layer was carried out in the same manner as in Example 1 until formation of the undercoat layer.
Manufactured by K.K.) was applied in a thickness of 3.5 μm, put in a clean oven at 120 ° C., and prebaked. Next, the resin on the bonding pad and the scribe line was removed by exposing to ultraviolet light through a desired pattern and then developing. Further 150 ℃
The resin layer for forming a microlens was formed by post-baking for 30 minutes in the clean oven. Further, AZ-1350 (manufactured by Shipley Co., Ltd.), which is a novolac-based photosensitive resin, was applied thereon with a thickness of 2.6 μm, and prebaked in a clean oven at 90 ° C. Next, the pattern is exposed to ultraviolet light using a pattern in which only the novolac-based photosensitive resin in the portion corresponding to the light-receiving portion of the CCD remains, and is then developed to form a novolac-based photosensitive resin pattern only in the light-receiving portion.
After heat-melting in a 0 ° C clean oven, solidify,
A spherical lens for a transfer pattern was obtained.

CC on which a spherical lens for a transfer pattern is formed
D was dry-etched by the oxygen plasma method. In the dry etching, high-frequency power of 500 W is supplied to the parallel plate electrodes, oxygen plasma is generated at an oxygen supply amount of 100 sccm and a pressure of 20 Pa to perform processing, and each CCD is processed.
I was able to make an elliptical lens for each of the light receiving parts of the. The elliptical lens produced by this method has a flatness value of 1.33, and the aperture ratio, which was 40% for the spherical lens, can be increased to 50%.

[0027]

According to the present invention, when the pattern of the transfer microlens formed on the transparent microlens forming resin layer is transferred by the etching method to form the microlens in the microlens forming resin layer. , The microlens obtained by the difference in the etching rate between the transfer microlens pattern and the microlens forming resin is part of an ellipsoid, and the light at the center of the lens and the light at the end of the lens are simultaneously CCD. Since the light can be condensed on the light receiving portion of the lens, the apparent aperture ratio is improved as compared with a lens whose cross section is a part of a circle, and an effect of increasing the intensity of a signal to be extracted is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of manufacturing the microlens of the present invention.

FIG. 2 is a diagram illustrating a light path when an elliptical lens of the present invention is formed.

FIG. 3 is a diagram illustrating a path of light when a spherical lens is formed.

FIG. 4 is a schematic view of a microlens formed on a CCD substrate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Interline CCD, 2 ... Undercoat layer, 3 ... Microlens transparent resin layer, 4 ... Novolac-type photosensitive resin pattern, 5 ... Transfer spherical lens, 6 ... Elliptical lens, 21
... CCD substrate, 22 ... Light receiving part, 23 ... Elliptical lens, 24
... incident light, 25 ... undercoat layer, 31 ... CCD substrate, 32 ...
Light receiving part, 33 ... Spherical lens, 34 ... Incident light, 41 ... CC
D substrate, 42 ... Light receiving part, 43 ... Shading part, 44 ... Color filter, 45 ... Transparent resin layer, 46 ... Microlens,
47 ... Wiring section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G02B 13/18 8106-2K H01L 27/14 H04N 5/335 V 8838-5C

Claims (2)

[Claims] 1. A microlens made of synthetic resin formed on a solid-state image pickup device substrate, wherein the shape of the microlens substantially matches a part of an ellipse, and the focal length of the microlens is the light receiving of the solid-state image pickup device. A microlens characterized by being arranged near the surface. 2. A method for forming a microlens made of a synthetic resin on a solid-state image pickup device substrate, wherein a transfer microlens pattern is formed on a resin layer for forming a microlens by heat melting, and the microlens pattern for transfer is etched. When transferring, the etching rate of the resin layer for forming the microlens is set to be higher than the etching rate of the microlens pattern for transferring, and the lens obtained by the transfer has a shape that substantially matches a part of the ellipse. And a method for manufacturing a microlens.