JPS61290403A - Microlens - Google Patents

Abstract

PURPOSE:To obtain a microlens having large NA and short focal length by forming recessed dents of an underlying layer and intermediate layer and forming a convex lens layer consisting of a material having the refractive index larger than the refractive indexes of the underlying layer and intermediate layer thereon. CONSTITUTION:The underlying layer 11 is formed to an optional thickness at which rugged shaped remain. The intermediate layer 12 to control the bottom surface shape of the lens layers 1d-4d is provided between the layer 11 and the lens layers 1d-4d. The microlens which is a convex lens is obtd. in the above-mentioned manner. The bottom surface shape of the lens is determined by the shapes of the underlying layer and the intermediate layer 12. The layer 11 is thus formed to such a shape at which the ruggedness remains to some extent on the surface of a solid-state image sensing device and the shape of the bottom surface of the lens can be controlled by adding the intermediate layer 12 thereto. The underlying layer is formed of the org. or inorg. material which is optically transparent and has the refractive index smaller than the refractive index of the material for the lens layers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to an optical element that is placed in front of a photoelectric conversion surface (light receiving surface) of a solid-state imaging device, for example, to improve sensitivity, or an optical element such as an optical coupler or optical branch circuit. This relates to the microlens used.

[Conventional technology]

FIG. 2 is a diagram showing an outline of a conventional microlens for a solid-state imaging device. In the figure, 1a to 4a are photoelectric conversion units (light receiving areas) such as photodiodes,
4b is a switching element, e.g. CO
The charge readout sections 1d to 4d, which are composed of signal transfer elements such as D, wiring, etc., are attached to the photoelectric conversion sections 1a to 4a, respectively, in order to improve the aperture ratio (the ratio of the area occupied by the light receiving surface) of the photoelectric conversion section. correspondingly arranged lens layers, 10
is a solid-state imaging device substrate, 11 is a base layer between the lens layers 1d to 4d and the photoelectric conversion surface, and 20 is light incident on the solid-state imaging device. In addition, 21 is the above 11. This is a microlens consisting of ld to 4d.

Next, the function of a conventional microlens will be explained using, as an example, light incident on the photodiode 1a.

The light incident on the photoelectric conversion section la of the solid-state imaging device generates charges in the photoelectric conversion section la according to its intensity, and this is used as a signal charge to send the charge readout section 1b consisting of a switching element, a transfer element, etc. It is read out to the outside via In addition, the lens layer 1d disposed in front of the photoelectric conversion section 1a also collects light incident on the area above the charge readout section lb other than the photoelectric conversion section 1a.
Focus the light upward. Therefore, the effect is substantially the same as that of increasing the area of the photoelectric conversion section 1a, that is, the aperture ratio is improved, and the sensitivity of the solid-state imaging device is improved.

The amount of light focused onto the photoelectric conversion part la is the refractive index of the lens N1a,
It is determined by the radius of curvature, the aperture, and the thickness of the base layer 11, and the larger the difference between the refractive index of the lens N1a and the refractive index in the atmosphere, the smaller the radius of curvature within a certain range, and the thicker the base layer 11. The light-gathering ability is generally thick. However, when an organic polymer material is used for the lens layer 1d, the refractive index is only around 1.5, and the curvature of the lens is also limited due to positional relationships. Ru.

[Problem that the invention seeks to solve]

Since the conventional microlens is configured as described above, in order to obtain a high light collection rate, it is necessary to increase the distance between the lens layer 1d and the photoelectric conversion part 1a.For this reason, if the base layer 11 is made thicker, The stress between the films generated by the base layer 11 also increases, causing problems such as warping of the wafer and deformation of the film due to the release of the stress between the films when thermal cycles are applied. In addition, since the base layer 11 is thick, the top surface is almost flat, and only the top surface of the microlens is responsible for the light-concentrating effect, so the base layer must be made even thicker to compensate for the fact that the bottom surface cannot be expected to have a light-concentrating effect. There was a problem.

This invention was made to solve the above-mentioned problems, and has a short focal length and a large aperture ratio (NA) that has sufficient light gathering ability even if the thickness of the underlying layer is small.

The objective is to obtain a microlens with a large numerical aperture.

[Means for solving problems]

In the microlens according to the present invention, an intermediate layer is formed on a base layer having a refractive index of n2 to form a concave depression, and a refractive lens having a convex upper surface is formed at a position separated by the intermediate layer. A lens layer having a ratio nl (nl>n2) is formed.

[Effect]

In this invention, since the lens layer is formed on the concave depression formed by the intermediate layer and the base layer, the lower surface of the lens layer is convex downward, and the base layer (refractive index n2) and the lens layer (refractive index nl) and the refractive index difference (n 1-n
2 > 0), a light condensing effect occurs at this interface, and light incident on areas other than the photoelectric conversion section is also condensed to the photoelectric conversion section, thereby achieving a substantial improvement in the aperture ratio.

Further, by making the upper surface of the lens convex upward, a large light-gathering ability can be obtained at this interface due to the difference in refractive index with the atmosphere (refractive index #1), for example. Therefore, by giving the lens layer a concave shape on the bottom surface and a convex shape on the top surface,
It is possible to obtain a microlens with an even greater light-gathering ability, that is, a short focal length and a large NA.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a microlens according to an embodiment of the present invention, 1a to 4a and lb to 4b.

10.20 is the same as in FIG.

Reference numeral 11 is a base layer similar to the conventional microlens, but unlike the conventional technology, in this example, since the unevenness of the surface of the underlying solid-state imaging device is actively utilized, the film thickness in this part is such that even the uneven shape does not remain. The film thickness can be selected arbitrarily. Further, 12 is an intermediate layer provided between the base layer 11 and the lens layer in order to control the shape of the lower surface of the lens layers 1d to 4d.

A microlens configured in this manner can be considered as a convex lens, and the shape of one side of the lens, for example, the bottom surface in FIG. 1, is determined by the shapes of the base layer 11 and the intermediate layer 12. This base layer 11 has a shape that leaves some of the irregularities on the surface of the solid-state imaging device substrate, and by further adding an intermediate layer 12 to this, the shape of the lower surface of the lens can be controlled.

The material of the base N11 may be either an organic material or an inorganic material, as long as it is optically transparent and has a refractive index smaller than the refractive index of the materials of the lens layers 1d to 4d.

The material of the intermediate layer 12 is an optically transparent material with a refractive index smaller than that of the material of the lens layer, since the light incident on this part is also collected and used by the photoelectric conversion parts 1a to 4a. Any material may be used, and it may be made of the same material as the base layer 11.

The lens layers 1d to 4d are formed of an optically transparent material and a material with a large refractive index n1 (preferably nl>1.8). Further, the upper surface has an upwardly convex shape, and the light gathering ability can be obtained by the difference in refractive index between the atmosphere and the upper surface of the lens layer.

The base layer, intermediate layer, and lens layer described above can be formed by making full use of Brainer technology, which is often used in the semiconductor field. Even if it is used, the structure described above can be formed.

Next, in the microlens of this example, whose functions and effects will be explained, the incident light 20 has a first condensing effect on the upper surface of the lens layer 1d due to the difference in refractive index between the atmosphere and the lens layer 1d and the effect of the upwardly convex shape. Then, on the lower surface of the lens layer 1d, due to the difference in refractive index between the lens layer 1d and the base layer 11 or the intermediate layer 12 and the effect of the downwardly convex shape, the light is focused a second time □ and focused on the photoelectric conversion part 1a. be done. Therefore, compared to the conventional microlens that has a convex shape only on the upper side, it has the same aperture, the same wall thickness, and a short focal length, that is, N
A large microlens with A is obtained.

In addition, in the above embodiment, the lens layers 1d to 4d have a uniform refractive index n1, but the refractive index of the lens layer may be non-uniform, and the refractive index is directed downward to have a uniform refractive index nl' to n1.
The same effect as in the above embodiment can be obtained even when the value is changed to l (nl'> nl). In particular, when the refractive index is changed with a certain regularity, the direction of light rays can be changed not only at the interface between the lens layer and external layers, but also within the lens layer, which further improves the light-gathering ability of the lens. can be done.

Further, in the above embodiment, only the refractive index of the lens layers 1d to 4d was changed, but the refractive index of the base layer 11, the intermediate layer 12, or both was directed downward to n2 to n2' (n
2>n2') and n3 to n3'(n3>n3'), the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the microlens according to the present invention, a concave (indentation) is formed by the base layer and the intermediate layer, and a convex lens is formed using a material having a higher refractive index than the base layer and the intermediate layer. By forming a layer, it is possible to obtain a microlens with a short focal length and a larger NA than conventional microlenses with the same aperture and thickness, and for example, for solid-state imaging devices, it is possible to reduce the thickness of the base layer. This has the effect of reducing the stress acting between the films, and making it possible to obtain microlenses that are stable against stress such as thermal cycles because the shape of the lens layer approaches a spherical shape.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a microlens according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a conventional microlens. In the figure, 1a to 4a are photoelectric conversion units, 1b to 4b are charge readout units, 1d to 4d are lens layers, 10 is a solid-state imaging device substrate, 11 is a base layer, 12 is an intermediate layer, 20 is incident light,
21 is a microlens. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (4)

[Claims] (1) Refractive index n_ with depressions at regular intervals on its surface
refractive index n_1 (n_1 ＞
A microlens characterized by comprising a lens layer of n_2). (2) The microlens according to claim 1, wherein the refractive index of the lens layer monotonically decreases downward. (3) Claim 1 or 2, characterized in that the refractive index of the underlayer monotonically decreases downward.
Microlens as described in section. (4) Claims 1 to 3, characterized in that the refractive index of the intermediate layer monotonically decreases downward.
The microlens described in any of paragraphs.