JPH03218067A - Manufacture of microlens for solid-state image sensing element - Google Patents

Abstract

PURPOSE:To make it possible to form microlenses having a large curvature, to enhance converging property and to increase the gain of a solid-state image sensing element by a method wherein an etchback is performed under the condition of a prescribed etching rate. CONSTITUTION:A transparent resin is applied on a transparent resin 8 for optical interval formation use provided on a solid-state image sensing element 1, is hardened to form a transparent resin layer 2, a photosensitive resin is applied thereon, desired parts are exposed to light, are developed and islands 3 are formed on photodetecting parts 6. Then, the islands 3 are heated, fused and are fluidized to form lens forms 4. At this time, an etching rate in the layer 2 is larger than that in the lens forms 4 and the transparent resin and the photosensitive resin, which satisfy this condition, are combined with each other and are selected. Then, if an etching of peripheral edge sides 41 of the forms 4 ends, an etchback is performed from parts 51, which are positioned at lower positions to correspond to the parts 41, of the layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a microlens for a solid-state image sensor.

[Conventional technology]

Various types of interbody image sensors have been proposed in the past, but in recent years, there has been a demand for smaller sizes and higher pixel counts, as well as the need to meet the demands for higher sensitivity and lower noise. Since then, various proposals have been made from the viewpoint of circuits and device structures.

In particular, in terms of the de-heis structure, most attempts are made to increase the aperture ratio of the lens. This is because there is a limit to the reduction of inherent noise by the solid-state image sensor itself, so there is no other choice but to rely on an increase in signal strength due to an increase in the amount of incident light.

Among these, the proposal to form a microlens on a solid-state image sensor is one of the effective methods despite its simple structure.

To explain this, in principle, as shown in FIG.
・Micro lenses 22, 22, etc. are provided on the top, and the light receiving section 2
The incident light 29 is focused on the light receiving portions 26, 26, . In other words, this is a method of effectively increasing the aperture ratio of the lens by effectively utilizing incident light on non-light-receiving parts such as the transfer part and the wiring part of the solid-state image sensor.

The manufacturing method of this microlens for solid state 1 most imaging element is as follows:
Broadly divided, heat melting method (for example, JP-A-59-14758
(see Publication No. 6) and the plate-making coating method (for example, Tokuko Sho 6 2-
There are two methods (see Publication No. 51504). That is, the heat melting method will be explained with reference to FIGS. 3(A) to 3(D). After forming a transparent film 28 for forming an optical distance on the solid-state image sensor 2 (see FIG. 3(A)), heat melting is performed. A transparent positive-type photolactic resin 23 having meltability is applied ((B) in the same figure).
This is plate-made to form islands 24, 24, etc. on the light-receiving parts 26, 26, etc. (same figure (C)), and this is heated and melted to form convex lens shapes 25, 25, etc. (same figure CD).
), which forms a lens with good light-gathering properties.

The plate-making coating method forms a similar transparent film 28 on the solid-state image sensor 21, as shown in FIGS. 4(A) to 4(D).
)) After applying the transparent photosensitive resin 23 (as shown in the same figure (B)
)) This is made into a plate to form eyelants 24, 24, etc. on the light-receiving parts 26, 26, etc. ((C) in the same figure), and a transparent resin 25 is further applied on the islands 24, 24, and so on. and forms a convex lens shape 25 ((D) in the same figure).
According to this method, the light-gathering property is less favorable than that obtained by the heating melting method.

[Problem to be solved by the invention]

Although microlenses formed by the heating melting method have a large curvature and are advantageous in terms of light gathering ability, they have the following problems.

First, there is a problem with the physical properties of the microlens itself, which is manufactured by the heating melting method. That is, according to this method, the positive photosensitive resin forming the microlens has 3
Since it is a thermoplastic resin that is not dimensionally crosslinked, it is disadvantageous in that the microlenses are deformed by reheating (heat resistance) and is also inferior in terms of chemical resistance.

Second, the types of photosensitive resins that can be used for microlenses are limited, and they also have good optical properties (
For example, it has been difficult to obtain high refractive index materials. In other words, microlens materials made by heating and melting not only do not absorb light at specific wavelengths in the visible range, but also have positive-working photosensitive resins (negative-working photosensitive resins are crosslinked by light exposure and lose their thermoplasticity). ), and the scope of selective use of such photosensitive resins has been extremely narrow, with only a few bright-type photosensitive resins for deep-UV use.

Thirdly, even with the heat melting method, there is a limit to the curvature that can be obtained for the lens. In other words, the curvature of the lens increases as the area occupied by the lens becomes smaller and the thickness of the lens increases.In principle, the lens should be designed in such a way, but in reality, If the thickness of the lens is large relative to its area, the exclusive area of the lens will expand due to sagging due to heat during heating and melting, and adjacent lenses will fuse together, resulting in a decrease in curvature.

On the other hand, microlenses produced using the plate coating method can be said to be advantageous in terms of the first and second problems of the heat-melting method described above, but the curvature of the lens is smaller than that produced by the heat-melting method. Furthermore, it was small and disadvantageous in realizing the original purpose of the lens, such as light-gathering properties.

The present invention has been made in view of the above-mentioned problems, and its purpose is to further form and replace the microlens shape obtained by the heat melting method or the plate coating method using the Esochibasoku method, thereby creating a better shape. This not only makes it possible to greatly expand the range of applications for selecting materials that have excellent physical properties related to lens properties, but also makes it possible to further increase the curvature of the lens by utilizing the difference in etching speed of the materials. An object of the present invention is to provide a method for manufacturing a microlens for a solid-state image sensor.

[Means to solve the problem]

The present invention is characterized in that at least a hardened transparent resin or transparent inorganic film is coated on the light-receiving surface of the solid-state image sensor, and furthermore, the light-receiving surface of the solid-state image sensor is coated with a transparent inorganic film, and the light-receiving surface of the solid-state image sensor is coated with at least a transparent inorganic film. Form an island using a photosensitive resin and heat and melt it to form a lens shape, or apply and harden a light resin to form a lens shape, and then apply a transparent resin using the Enochino\Noku method. Alternatively, in a method for manufacturing a microlens for a solid-state imaging device, which includes a step of forming a transparent inorganic film into a lens shape, the etching rate of the transparent resin or transparent inorganic film is higher than the etching rate of the photosensitive resin. The present invention is constructed using a satisfactory transparent resin or transparent inorganic film and photosensitive resin.

[Effect]

Apply at least a hardened light-receiving resin or a light-receiving inorganic film to the light-receiving surface of the solid-state image sensor, and further form islands using photoreceptive resin so as to correspond to each light-receiving portion provided on the solid-state image sensor. After the island is formed into a lens shape by heating and melting, or by coating and curing a transparent resin, the processing speed of the transparent resin or transparent inorganic film is determined by the photosensitivity. These are etched using a transparent resin or a transparent inorganic film that satisfies conditions greater than the etching rate of the resin, and a photosensitive resin. As a result, as the photosensitive resin is etched, the transparent resin or the transparent inorganic film is etched at a higher etching rate, so that a lens having a larger curvature than the lens shape formed from the photosensitive resin is formed.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

1(A) to (E) show the process order of one embodiment of the present invention, in which a transparent resin serving as a lens forming material is placed on a transparent resin 8 for forming an optical distance provided on a solid-state image sensor 1. The first step is to apply a resin and harden it to form a transparent resin layer 2.
(Fig. (A)), a photosensitive resin is applied thereon, and desired areas are exposed to light and developed to form islands 3, 3, etc. on the light-receiving areas 6, 6,... of the solid-state image sensor 1 ( Same figure (B)). Next, the islands 3, 3 . are heated and melted and fluidized to form lens shapes 4, 4 . . . of the photoreceptive resin (
Same figure (C)). At this time, the etching rate of the transparent resin layer 2 needs to be higher than the etching rate of the lens shapes 4, 4, etc. formed by the photosensitive resin. It is necessary to select a combination of a transparent resin and a photosensitive resin that satisfy this requirement. Further, it is desirable that the relationship between the film thicknesses of the two is as shown below (1).

That is, (etching rate of transparent resin layer 2) / (etching rate of lens shape 4 made of photosensitive resin) ≦ (model thickness of transparent resin layer 2) / (film thickness of lens shape 4 made of photosensitive resin)... 1) For example, the etching rate of the transparent resin layer 2 is 0.5 (μm/IIin), and the etching rate of the lens shape 4 made of the photoresist is 0.25 (pm/IIin).
In), if the film thickness is 1 μm, it is desirable that the film thickness of the Yumei resin layer 2 is 2 μm or more.

Next, using oxygen plasma or the like, the lens shape 4, 4.
・Start etching. As a result, lens shape 4
, 4... is machined from the surface of the lens shape 4, 4.
- When the etching of the peripheral edges 41, 41, . . . is completed, etching is started from the portions 51, 51, .

As mentioned above, since the etching speed of the transparent resin layer 2 is higher than the etching speed of the lens shape 4, the portions 51, 51, etc. of the transparent resin layer 2 are etched in the middle of etching as shown in FIG. 1(D). It is formed to have a larger curvature than the curvature of the lens shapes 4', 4', . This figure 1 (
As shown in D), the lens shape 4' during etching,
It is also possible to use as a microlens a microlens having 51, 51, . . . whose shape is replaced with the lens shape 4, 4, . However, in general, the lens shape 4', 4',
Continue the chiba-soku process until . is completely removed, and as shown in FIG. A lens is formed.

Note that it is possible to use a transparent inorganic coating in place of the transparent resin described in the above embodiments, and it is also possible to form islands by applying and curing the transparent resin using a plate coating method.

The present invention will be explained in more detail below using examples, but it goes without saying that the invention is not limited to the materials shown in these examples and can be widely applied by appropriately combining desired materials.

Example An interline CCD (horizontal pixel width 3.0 μm, horizontal transfer width 9.0 μm) manufactured by a conventional method was used as a substrate, and 5 μm of acrylic thermosetting resin was applied to the surface of the interline CCD (horizontal pixel width 3.0 μm, horizontal transfer width 9.0 μm).
The coating was applied to a film thickness of m and was thermally cured at 140°C. On top of this, Nopola Noku type positive photosensitive resin is applied to a film thickness of 1.5 μm, dried, exposed through a photomask with a predetermined pattern, developed, and placed on the light receiving part of the solid-state image sensor. formed an island. Furthermore, at 160℃
The island was heated to melt and form a convex lens shape.

Next, using oxygen gas added with 5% Freon-13 as an esochant, plasma was generated using the power of IKW and dry ethoching was performed for 5 minutes. As a result, the upper layer of lens-shaped Nopolanok-based photolactic resin was completely removed. After removal by etching, a convex lens made of thermosetting acrylic resin with a thickness of 3 μm was formed.

When the above etching rates were measured, the acrylic thermosetting resin was 0.6 (μm/min);
Novolanok type positive photosensitive resin has 0. 3 (μm/m
in).

The thickness of the convex lens thus obtained was 3 μm, and the area occupied by each lens remained unchanged.
It was possible to increase the curvature of the acrylic thermosetting resin.

In addition, when the solid-state imaging device obtained in this example and a convex lens having a thickness of 1.5 μm formed by a heating melting method were mounted on a solid-state imaging device under the same other conditions and evaluated, 1. A four-fold increase in gain was observed, confirming that sensitivity improved as the curvature of the microlens increased.

Note that the values of the etching speed of transparent resins other than the transparent resin shown in the above examples are shown below, but these values vary depending on the etching conditions, and are merely an example under the equipment and etching conditions shown below. It is. Of course, there are types of transparent resins that are photosensitive, but the key is to select and combine the photosensitive resin and transparent resin so that the etching conditions for the photosensitive resin and transparent resin satisfy the above conditions. By doing so, the present invention can be implemented.

(1) Equipment: Parallel plate type (cathode cassopple type) dry etching equipment.

(2) Etching conditions: IKW RF 5Pa oxygen gas used.

(3) Technique, Ching Reaction: The number in parentheses indicates the type of photosensitive resin.

(a) Acrylic 0.28, cam/min (UV exposure - negative type) (b) Urethane 0.16, cam/min (no photolactic material) (c) Polyimide 0.14, cam/min (UV (d) Chloromethylated polystyrene 0.1 0 μm/min (Deep-UV exposure, negative type) (e) Polyglycidyl methacrylate 0.40 μm/min (Deep- UV exposure, positive type, X-ray and (Electron beam exposure - negative type) (f) Noporank resin 0.14 μm/min (UV exposure - positive type) [Effects of the Invention] As described above, according to the present invention, on the light receiving surface of the solid-state image element, At least a hardened transparent resin or transparent inorganic film is applied, and islands are formed using a photosensitive resin so as to correspond to the respective light-receiving areas provided on the solid-state imaging element, and this is heated and melted to form a lens. Form into a shape or
Or after coating and curing a transparent resin to form a lens shape,
In a method for manufacturing microlenses for solid-state imaging devices, which includes a step of forming a transparent resin or transparent inorganic film or transparent resin into a lens shape using the Esochibasoku method, the etching rate of the transparent resin or transparent inorganic film is higher than that of the photosensitive resin. Since the structure is configured to perform etching using a transparent resin or transparent inorganic film that satisfies conditions greater than the etching speed, and a photosensitive resin, microlenses formed by heat melting or plate coating methods cannot be used. It is possible to form a microlens with a large curvature, which has an excellent effect of improving light convergence and increasing the gain of the solid-state image sensor.

Furthermore, since the Esochibafuku method is used, it is possible to select materials with excellent physical properties for microlenses for solid-state imaging devices, which can further improve the reliability of microlenses for solid-state imaging devices. In addition, since there is no step that requires high temperature when forming microlenses, it is also suitable for forming microlenses in color solid-state imaging devices in which solid-state imaging devices are equipped with organic color filters.

[Brief explanation of drawings]

1(A) to (E) are diagrams showing an example of the manufacturing method of the present invention in the order of steps, FIG. 2 is a diagram showing an example of a conventional solid-state image sensor with a microlens, and FIG. 3(A) to (D) is a diagram showing the conventional manufacturing method of a microlens for a solid-state image sensor using a heating-melting method in the order of steps, and Figures 4 (A) to (D
) is a diagram illustrating a conventional method of manufacturing a microlens for a solid-state image sensor using a plate-making coating method in order of steps. 1. Solid-state image sensor, 2. Transparent resin layer, 3. Island formed of photosensitive resin, 4. Lens shape formed by heating and melting, 4'. Lens of photosensitive resin in the middle of etching. Shape, 4 ■... Lens shape 40 peripheral part,
5. Lens shape of transparent resin layer during etching, 5l
...Transparent resin layer 2, 6 located at a position corresponding to the lens peripheral portion 4l...Light-receiving section, 8...Transparent film for forming an optical distance to the light-receiving section 6, Dai Nippon Printing Co., Ltd.

Claims (1)

[Claims] At least a cured transparent resin or a transparent inorganic film is applied to the light-receiving surface of the solid-state image sensor, and islands are further formed using a photosensitive resin so as to correspond to the respective light-receiving parts provided on the solid-state image sensor. A solid that includes the step of heating and melting to form a lens shape, or coating and curing a transparent resin to form a lens shape, and then forming the transparent resin or transparent inorganic film into a lens shape using an etchback method. In the method for manufacturing a microlens for an image sensor, a transparent resin or a transparent inorganic film and a photosensitive resin are used such that the etching rate of the transparent resin or transparent inorganic film is greater than the etching rate of the photosensitive resin. 1. A method of manufacturing a microlens for a solid-state image sensor, the method comprising performing etch-back using a microlens.