JPH03190167A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To obtain a solid-state image sensing device, in which a lens can be finely processed, by a method wherein a microlens is formed of novolak resin. CONSTITUTION:An ultraviolet or a far ultraviolet resist layer (novolak resin) as a positive type resist layer 52 is applied onto a fixed layer 50 through a spin coating method. As novolak resin can be finely processed, photodetective parts 14 can be densely formed. After the positive type resist layer 52 is applied, the layer 52 is exposed to ultraviolet rays excluding the photodetective parts 14 and developed into a prescribed pattern. Then, a semiconductor substrate 12 is thermally treated at a temperature of 160 deg.C or below to thermally deform the positive type resist layer 52 into hemispheres, and thus micro-lenses 28 whose peripheral parts 28a are interlinked together can be obtained. After the micro-lenses 28 are formed, the opaque positive type resist layer 52 becomes transparent by the irradiation with ultraviolet rays.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solid-state imaging device such as a CCD in which a light-condensing microlens is formed on the upper surface of a light-receiving section.

(Prior Art) In solid-state imaging devices such as CCDs, as the chip size becomes smaller and the number of pixels increases, the area of the light-receiving portions that can be formed as pixels has also become smaller. A problem arises in that the amount of light received by each light receiving section decreases, resulting in a decrease in sensitivity (output/amount of incident light).

To solve this problem, a solid-state image sensor has been proposed in which a microlens is formed using a positive resist on the top surface of each light-receiving portion that becomes a pixel. Since the amount of incident light can be focused by the microlens, the effective light-receiving area of the light-receiving section increases, making it possible to compensate for the decrease in sensitivity.

This microlens is formed by etching a positive resist layer, which is the base of the microlens, and then utilizing the thermal sagging of the positive resist layer caused by heat treatment.

A microlens can be formed for each individual light receiving section, or a microlens can be formed for each column or row of light receiving sections.

Transparent photosensitive resins such as polystyrene and acrylic resin are usually used as microlenses.

[Problems to be Solved by the Invention] As mentioned above, transparent photosensitive resins such as polystyrene and acrylic resin are used as microlenses, but as is well known, such photosensitive resins cannot be easily photoetched. Microfabrication is difficult when processing.

Therefore, this microlens could not be formed in a high-density solid-state image sensor.

Therefore, the present invention proposes a solid-state imaging device that solves these conventional problems with a simple structure and enables fine processing of microlenses.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, a microlens is formed for each light receiving section or for each group of light receiving sections, and external light is focused on the light receiving section. The solid-state imaging device is characterized in that a novolac resin is used as the microlens.

[Function] Novolac resin is used as the resist layer 52 for the microlens 28. Novolak resin can be microfabricated. However, this novolac resin is opaque.

However, when irradiated with ultraviolet rays or far ultraviolet rays, it transforms into a transparent body.

Therefore, the resist layer 52 is heat-treated to be thermally deformed to deform the resist layer 52 into a spherical or semicylindrical shape, and then irradiated with ultraviolet rays or deep ultraviolet rays to transform it into a transparent body. When irradiated with ultraviolet rays or far ultraviolet rays, the resin hardens and becomes thermally stable.

[Embodiment] Next, an example of the solid-state image sensor according to the present invention, when applied to the above-mentioned color solid-state image sensor, will be described in detail with reference to FIG. 1 and subsequent figures.

A CCD is exemplified as a solid-state image sensor. The image sensor can be applied either in one-dimensional configuration or in two-dimensional configuration.

FIG. 1 shows an example of a color solid-state image sensor.

In this color solid-state image sensor 60, the semiconductor substrate 12
is a P type, and the light receiving section 14 is an N type. On the semiconductor substrate 12 of the charge transfer section 16 sandwiched between the light receiving sections 14 and 14, two layers of transfer electrodes 18 and 20 are formed with an insulating layer 22 such as 5i02 interposed therebetween as shown.

A light-shielding metal 24 is formed on the upper surface of the transfer electrode 20 to prevent external light from entering the charge transfer section 16.

A flattening layer 26 made of acrylic resin or the like is applied to the upper surface of the light-shielding metal 24 and the upper surface of the light-receiving section 14, respectively, to flatten the surfaces. And to colorize it,
A color filter 40 (40R, 40G) as shown in the figure is placed on the upper surface of this flattening layer 26.

40B) is formed. Color filter 40R, 4
0G and 40B are formed to face the light receiving section 14, respectively, so that monochromatic light of R, G, and B (red, green, and blue) enters the respective light receiving sections 14.

The color filters 40R, 40G, and 40B can be formed by dyeing gelatin, casein, or the like.

Generally speaking, a protective layer 3 is provided to protect the color filters 40R, 40G, and 40B and to fix the microlens layer.
o is formed. On the upper surface of this protective layer 30, the light receiving section 14
The microlens 28 is completely formed at a position facing the .

The protective layer 30 is subjected to a curing treatment before the microlens 28 is formed. That is, when using an ultraviolet ray or far ultraviolet resist as the protective layer 30, it is irradiated with ultraviolet rays or far ultraviolet rays, and when using a thermosetting resin, it is heated and hardened.

Due to this hardening treatment, the protective layer 30 is not thermally deformed even if heat treatment is applied in the process of forming the microlens 28, so that the microlens 28 having a good shape can be formed.

The microlenses 28 can be formed for each individual light receiving section 114, or the microlenses 28 can be formed for each light receiving section in units of columns or rows.

Each of the microlenses 28 is formed so that the respective peripheral edges 28a are continuous with each other.

By making the peripheral edges 28a continuous with each other, external light incident on the peripheral edges 28a can also be guided to the light receiving section 14, as shown in FIG.

By doing so, most of the external light incident on the microlens 28 can be taken into the light receiving section 14, thereby increasing the amount of incident light and improving the sensitivity accordingly.

The microlens 28 is made of a photosensitive resin for ultraviolet rays or far ultraviolet rays, particularly novolac resin. This novolak resin is used as the resist layer 52 (described later).

As is well known, novolak resin can be microfabricated and has the following properties.

That is, novolak resin is normally opaque.

However, when it is irradiated with ultraviolet or far ultraviolet rays, it transforms into a transparent material.

Furthermore, before irradiation with ultraviolet rays or far ultraviolet rays, the material undergoes thermal deformation due to heat treatment, so even if the initial shape is layered, it deforms into a spherical or semicylindrical shape. and,
If the novolac resin is irradiated with ultraviolet rays or far ultraviolet rays after being thermally deformed, the novolac resin that has undergone thermal deformation will be cured and become thermally stable.

Next, FIG. 2 shows an example of a method for manufacturing a color solid-state insurance element according to the present invention. A case is illustrated in which the microlens 28 is formed for each light receiving section 14.

First, a P-type semiconductor substrate 12 made of silicon or the like is doped with an N-type impurity from a predetermined position to form the light receiving portion 14 . Then, on the upper surface of the semiconductor substrate 12, the transfer layer ti18, 20 shown in FIG. 1, the light-shielding metal 24, the planarization layer 26, etc. are sequentially formed by a well-known method.

For the flattening layer 26, other than acrylic resin, polyimide resin, isocyanate resin, urethane resin, etc. can be used. In this example, acrylic resin 'FVR-10J
(manufactured by Fuji Yakuhin Co., Ltd.) is used. This planarization layer 26 is applied by a spin-coating method or the like so that the thickness thereof is, for example, 5.0 am. After forming the color filters 40R, 40G, and 40B on the upper surface, the protective layer 30 is applied and hardened. These layers are collectively shown as fixed layer 50 (FIG. 2A).

On the upper surface of this fixed layer 50, a resist layer for ultraviolet rays or far ultraviolet rays (novolac resin), in this example a positive resist layer 52, is formed by a spin code method or the like so that the thickness thereof is approximately 3.0 μm, for example. (A in the same figure).

Examples of novolak resins that can be used as the positive resist layer 52 include rAZ, 0FPR, and Microposit.
Commercially available products such as (trade name) can be used.

Since novolak resin can be microfabricated, the light receiving part 1
4 can also be formed with high density.

After coating the positive resist layer 52 and drying it, the area other than the light receiving area 14 is exposed to ultraviolet rays and developed to form a predetermined pattern (FIG. B).

Thereafter, the temperature is below 160°C, preferably between 130 and 15°C.
A heat treatment is performed at a temperature of 0° C., and the positive resist layer 52 is thermally deformed into a hemispherical shape (C in the same figure).

Due to thermal deformation of the positive resist layer 52, it has a hemispherical shape in the figure.
In addition, microlenses 28 whose respective peripheral portions 28a are connected to each other are obtained.

The color filters 40R and 40G inserted into the fixed layer 50 made the heating temperature 160° C. or lower.

This is done in consideration of the heat resistance of the color filters 40B and to prevent the color filters 40R, 40G, and 40B from being deteriorated by heat.

The microlens 2 is formed by thermally deforming the positive resist layer 52.
After forming 8, an exposure treatment is performed by irradiating deep ultraviolet rays of 200 to 300 nm. Then, the positive resist layer 52, which has been opaque until now, changes into a transparent material. Even when irradiated with ultraviolet rays, it transforms into a transparent material.

Furthermore, the resist layer is hardened by this irradiation with deep ultraviolet rays. By curing the positive resist layer 52 after thermal deformation, the microlens 28 becomes thermally stable.

The positive resist layer 5z was hardened after being thermally deformed.
It is said that the positive resist 1152 easily softens at 120 to 160°C before being exposed to deep ultraviolet rays, but once it is exposed to deep ultraviolet rays, it becomes thermally very stable after that. This method takes advantage of two properties.

However, this heat treatment and deep ultraviolet or ultraviolet treatment may be performed simultaneously.

Note that the solid-state image sensor according to the present invention is applicable not only to color images but also to monochrome images, and is not limited to CCD, but can also be used for solid-state image sensors of other types.

[Effects of the Invention] As explained above, the present invention uses a novolac resin that transforms into a transparent body by irradiation with ultraviolet rays or far ultraviolet rays as a microlens formed on the upper surface of the light receiving section.

This makes it possible to form transparent microlenses, and also enables fine processing of the microlenses, which has features such as increasing the density of light-receiving parts and making it possible to form microlenses in units of light-receiving parts.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to the present invention, and FIG. 2 is a process diagram showing an example of its manufacturing method. 12 ・ ・ ・ 14 ・ ・ ・ 16 ・ ・ ・ 26 ・ ・ ・ 28 ・ ・ ・ 40R~40B 50 ・ ・ ・ 52 ・ ・ ・ 60 ・ 1

Claims (1)

[Claims] (1) In a solid-state image sensor in which a microlens is formed for each light-receiving section or for each group of light-receiving sections to focus external light on the light-receiving section, novolac resin is used as the microlens. Characteristic solid-state image sensor.