JPH081809A - Microlens formation method - Google Patents

Abstract

PURPOSE:To form a microlens on a CCD type imaging device by a simple process. CONSTITUTION:A positive type lens material resist layer 20 is formed by coating on the surface flattening layer 19 of a CCD type imaging device 11. Subsequently, a part, corresponding to the lens forming area, is exposed employing a photomask 21 having mask patterns 21a at parts corresponding to lens forming areas. The exposure in this case is effected while deviating focus properly. Then, the surface side of the lens material resist layer 20 in the parts corresponding to the lens forming areas is exposed so as to have the shape of reverse concave lens in accordance with the strength distribution of circulating of light as shown by dots in a diagram (B). According to this method, microlenses 20a, consisting of convex lenses whose surface is a curved surface, are formed after development. Accordingly, the microlenses 20a can be formed by a simple process wherein only exposing and developing are effected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a microlens.

[0002]

2. Description of the Related Art For example, a CCD type image pickup device is shown in FIG.
There is one as shown in (D). In this CCD type imaging device, an insulating film 2 is provided on a p-type silicon substrate 1, a photodiode 3 and a CCD 4 are provided on the insulating film 2, and a metal electrode 6 is provided on the CCD 4 via an insulating film 5. , A color filter 7 is provided thereon, a surface flattening layer 8 having a flat surface is provided thereon, and a microlens 9 composed of a convex lens is provided on the portion corresponding to the photodiode 3 thereon. It has a structure. That is, in this CCD type image pickup device, the microlens 9 is integrated.

Next, FIG. 2 shows a case where the microlens 9 is formed in such a CCD type image pickup device.
Description will be made with reference to (A) to (D) in order. First, as shown in FIG. 2A, a color filter 7 having a surface flattening layer 8 formed by coating an acrylic resist is prepared. Next, as shown in FIG. 2B, a positive type lens material resist layer 9 a is applied and formed on the surface flattening layer 8. Next, exposure is performed using the photomask 10 having the mask pattern 10a in a portion corresponding to the lens formation region, and then development is performed, as shown in FIG.
The lens material resist pattern 9b is formed. Then 1
When heat treatment is performed at a temperature of about 50 ° C. for about 5 minutes, when the lens material is melted and then cooled and solidified, the surface of the lens material becomes a curved surface due to surface tension. Thus, Figure 2
As shown in (D), a microlens 9 composed of a convex lens is formed on the surface flattening layer 8.

[0004]

However, in the conventional method for forming such a microlens, the lens material resist pattern 9b is heat-treated to form the microlens 9 composed of a convex lens having a curved surface. Therefore, there is a problem in that a heat treatment step is required and the number of steps is increased accordingly. Further, since the curved surface shape of the surface of the microlens 9 depends on the temperature and time of the heat treatment, it is extremely difficult to select the condition and the controllability is poor. An object of the present invention is to provide a method for forming a microlens that can easily and controllably form the microlens with a small number of steps.

[0005]

According to the present invention, a lens material resist layer is exposed and developed by defocusing it using a photomask having a predetermined mask pattern.
The micro lens is formed by a convex lens having a curved surface.

[0006]

According to the present invention, a microlens consisting of a convex lens having a curved surface is formed by simply exposing the lens material resist layer by defocusing it using a photomask having a predetermined mask pattern and developing it. Therefore, the conventional heat treatment step is unnecessary, and therefore the microlens can be formed easily and with good controllability in a small number of steps.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A to 1D show respective forming steps for forming a microlens in a CCD image pickup device to which an embodiment of the present invention is applied. Therefore, the method of forming the microlens of this embodiment will be described with reference to these drawings in order.

First, a CCD type image pickup device 11 as shown in FIG. 1 (A) is prepared. This CCD type image pickup device 11 is the same as the conventional type shown in FIG.
To explain again, the insulating film 13 is formed on the p-type silicon substrate 12.
Is provided, and the photodiode 14 and C are provided on the insulating film 13.
The CD 15 is provided, the metal electrode 17 is provided on the CCD 15 via the insulating film 16, and the color filter 1 is provided thereon.
8 is provided, on which a surface planarizing layer 19 having a flat surface is provided.
Has a structure.

Next, as shown in FIG. 1B, a positive type lens material resist layer 20 is applied and formed on the surface flattening layer 19. The thickness of the lens material resist layer 20 is the same as or slightly thicker than the maximum thickness of the microlens to be formed. Next, exposure is performed using the photomask 21 having the mask pattern 21a in the portion corresponding to the lens formation region. In this case, the exposure is performed by appropriately shifting the focus, for example, by shifting the focus upward by about 0.6 to 0.9 μm, that is, by defocusing by about 0.6 to 0.9 μm. Then, as shown by the dotted points in the figure, the surface side of the lens material resist layer 20 in the portion corresponding to the lens forming region is exposed in the shape of an inverted concave lens in accordance with the intensity distribution of the light wraparound.

The reason for this is that the light intensity distribution within the lens material resist layer 20 becomes closer to uniform than that during just focus due to defocusing, in other words, from the portion corresponding to the gap of the mask pattern 21a to the mask pattern. This is because the amount of light sneaking into the portion corresponding to 21a increases. Therefore, by developing after this, as shown in FIG. 1C, a microlens 20a made of a convex lens having a curved surface is formed.

As described above, in this microlens forming method, when the photomask 21 having the mask pattern 21a in the portion corresponding to the lens forming area is used to perform exposure by defocusing the light, the intensity distribution of the light wraparound is performed. Since the surface side of the lens material resist layer 20 in the portion corresponding to the lens formation region is exposed in the shape of an inverted concave lens, the microlens 20a made of a convex lens having a curved surface can be formed only by exposing and developing. Therefore, the conventional heat treatment step is not required, and the microlens 20a can be formed in a small number of steps.
Further, the curved surface shape of the microlens 20a can be selected only by controlling the amount of defocus (degree of defocus) at the time of exposure using the photomask 21.
The microlens 20a can be easily formed with good controllability.

[0012]

As described above, according to the present invention, the surface of the lens material resist layer is formed into a curved surface only by defocusing it using a photomask having a predetermined mask pattern, exposing it, and developing it. Since the microlens composed of the convex lens can be formed, the conventional heat treatment step is unnecessary, and therefore the microlens can be easily formed with a small number of steps and with good controllability.

[Brief description of drawings]

1A to 1C are cross-sectional views showing respective forming steps when forming a microlens in a CCD image pickup device to which an embodiment of the present invention is applied.

2A to 2D are cross-sectional views showing respective forming steps when forming microlenses in a conventional CCD image pickup device.

[Explanation of symbols]

 11 CCD image pickup device 20 Lens material resist layer 20a Microlens 21 Photomask

Claims (2)

[Claims] 1. A microlens composed of a convex lens having a curved surface is formed by exposing a lens material resist layer with a photomask having a predetermined mask pattern while defocusing it and exposing it to development. And a method for forming a microlens. 2. The method of forming a microlens according to claim 1, wherein the microlens is formed on an imaging device.