JPH0640161B2 - Micro lens - Google Patents

Description

The present invention is arranged in front of a photoelectric conversion surface (light receiving surface) of, for example, a solid-state image pickup device for improving sensitivity, or for an optical element such as an optical coupler and an optical branch circuit. The present invention relates to a microlens used.

[Prior Art] FIG. 2 is a diagram showing an outline of a conventional microlens of a solid-state image pickup device. In the figure, reference numerals 1a to 4a denote photoelectric conversion units (light receiving regions) such as photodiodes, and 1b to.
Reference numeral 4b is a switching element, for example, a CC, for reading out the charges accumulated in the photoelectric conversion units 1a to 4a.
The charge read-out portions 1d to 4d composed of signal transfer elements such as D and wirings are provided in the photoelectric conversion portions 1a to 4a, respectively, in order to improve the aperture ratio (ratio of the area occupied by the light receiving surface) of the photoelectric conversion portion. 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. Further, reference numeral 21 is a microlens composed of 11, 1d to 4d.

Next, the function of the conventional microlens will be described by taking light incident on the photodiode 1a as an example.

The light incident on the photoelectric conversion unit 1a of the solid-state imaging device generates electric charges in the photoelectric conversion unit 1a according to the intensity of the electric charges. It is read out to the outside via. In addition, the lens layer 1d arranged in front of the photoelectric conversion section 1a includes charge reading sections 1b and 2b other than the photoelectric conversion section 1a.
The light that has entered the upper region is also condensed on the photoelectric conversion unit 1a by its condensing action. Therefore, substantially the same effect as the area of the photoelectric conversion unit 1a is increased, that is, the aperture ratio is improved, and the sensitivity of the solid-state imaging device is improved.

The amount of light collected on the photoelectric conversion unit 1a is the refractive index of the lens layer 1a,
Depending on the radius of curvature, the aperture and the thickness of the underlayer 11, the larger the difference between the refractive index of the lens layer 1a and the refractive index in the atmosphere, the smaller the radius of curvature within a certain range, and the thicker the underlayer 11, Its light-collecting ability generally increases. However, when an organic polymer material or the like is used for the lens layer 1d, its refractive index is only about 1.5, and the curvature of the lens is also limited due to the positional relationship.

[Problems to be solved by the invention]

Since the conventional microlens is configured as described above, it is necessary to increase the distance between the lens layer 1d and the photoelectric conversion unit 1a in order to obtain a high light collection rate. The inter-film stress generated from the underlayer 11 also becomes large, causing warpage of the wafer, and when the thermal cycle is applied, the film is deformed due to the release of the inter-film stress. Further, since the underlayer 11 is thick, this upper surface is almost flat, and only the upper surface of the microlens is responsible for the light condensing action, and the underlayer must be thicker by the amount that the lower surface cannot expect the light condensing action. There was a problem.

The present invention has been made in order to solve the above problems, and has a short focal length and a large numerical aperture (NA, numerical aperture) with a sufficient light-collecting ability even if the thickness of the underlayer is small.
The purpose is to obtain the microlens of e).

[Means for solving problems]

The microlens according to the present invention has a refractive index n2 ', whose refractive index continuously decreases or is uniformed downward.
In the concave depression on the surface of the underlayer having n2, the upper surface is convex and the refractive index continuously increases from the upper surface of the layer to the center plane, and decreases continuously from the center surface to the lower surface of the layer. Refractive indices n1 'to n1 (n1'>n1> n)
2 '≧ n2) is formed.

Further, an intermediate layer having a refractive index of n3 'to n3 is formed on an underlayer having a refractive index of n2' to n2 whose refractive index continuously decreases or is uniformed downward to form a concave depression. , And the upper surface is convex at a position further separated by the intermediate layer, and the refractive index continuously increases from the upper surface of the layer toward the central surface, and continuously decreases from the central surface toward the lower surface of the layer. Refractive indices n1 'to n1 (n1'> n1)
> N3 ′ ≧ n3 ≧ n2 ′ ≧ n2).

[Action]

In the present invention, the lens layers have refractive indices n2 'to n2 whose refractive index continuously decreases or is uniformed downward.
Since it is formed on the concave recess formed on the surface of the underlayer having 2, the lower surface of the lens layer is convex downward, and the underlayer (refractive index n2 ′ to n2) and the refractive index are Of refractive index n1 ′ formed so as to continuously increase from the upper surface of the layer toward the central surface and decrease continuously from the central surface to the lower surface of the layer.
Refractive index difference (n1′-n2>
0, n1-n2> 0), a light-collecting action occurs at this interface, the underlying layer may be thin, and light incident on a region other than the photoelectric conversion unit is also condensed on the photoelectric conversion unit, so An improvement in aperture ratio is achieved.

Further, by making the upper surface of the lens layer convex upward, a large light-collecting ability at this interface can also be obtained due to the difference in refractive index from the atmosphere (refractive index≈1), for example. Further, since the refractive index of the lens layer is continuously increased from the upper surface of the layer toward the center plane and continuously decreased from the center surface to the lower surface of the layer, the inside of the lens layer is also formed. There is a light-collecting effect, and the light-collecting ability is also improved from this point. Therefore, by providing the lens layer with a convex shape on the lower surface and a convex shape on the upper surface, it is possible to obtain a microlens having a larger light converging ability, that is, a large NA with a short focal length.

In addition, since the lens layer is formed on the concave recess formed by the intermediate layer and the underlayer, the lower surface of the lens layer is convex in a more ordered shape on the lower side than when the intermediate layer is not provided,
An intermediate layer (refractive index n3 ′ to n3) and a refraction index formed so that the refractive index continuously increases from the upper surface of the layer toward the central surface and decreases continuously from the central surface to the lower surface of the layer. Rate n
Refractive index difference between the lens layers 1'to n1 (n1'-n
3 '> 0, n1-n3'> 0), a condensing action occurs at this interface, and the light incident on a region other than the photoelectric conversion unit in the lens peripheral region is also collected in the photoelectric conversion unit, and An improvement in aperture ratio is achieved.

Further, by making the upper surface of the lens layer convex upward, a large light-collecting ability at this interface can also be obtained due to the difference in refractive index from the atmosphere (refractive index≈1), for example. In addition, since the refractive index of the lens layer is formed so as to continuously increase from the upper surface of the layer toward the center surface and continuously decrease from the center surface to the lower surface of the layer, also from this point. The light ability is improved. Therefore, by providing the lens layer with a convex shape on the lower surface and a convex shape on the upper surface, an even greater light-collecting ability, that is,
A microlens having a short focal length and a large NA can be obtained. As a result, the distance between the lens layer and the photoelectric conversion unit can be shortened,
The underlayer can be thinned.

Example of Invention

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

FIG. 1 is a sectional view of a microlens according to an embodiment of the present invention, and 1a to 4a, 1b to 4b, 10, 20 are the same as those in FIG.

Reference numeral 11 is an underlayer like the conventional microlens, but in this embodiment, unlike the prior art, the unevenness of the surface of the solid-state image pickup device of the underlayer is positively utilized, so that the film thickness of this portion may have an uneven shape. The film thickness can be arbitrarily selected. Reference numeral 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.

The microlens thus configured can be considered as a convex lens, and the shape of one surface of the lens, for example, the lower surface in FIG. 1, is determined by the shapes of the underlayer 11 and the intermediate layer 12. The underlying layer 11 has a shape in which the surface of the substrate of the solid-state imaging device has some irregularities, and the intermediate layer 12 is added to this to control the shape of the lower surface of the lens.

The material of the base layer 11 may be either an organic material or an inorganic material, and may be formed of an optically transparent material having a refractive index smaller than that of the material of the lens layers 1d to 4d.

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

The lens layers 1d to 4d are made of an optically transparent material and have a large refractive index n1 (preferably n1> 1.8). In addition, the shape of the upper surface is convex upward, and the light collecting ability can be obtained by the difference in refractive index between the atmosphere and the upper surface of the lens layer.

The underlayer, intermediate layer, and lens layer as described above can be formed by making full use of the planar technology that is often used in the semiconductor field. The lens layer may be an array-shaped one or a stripe-shaped one. However, the above structure can be formed.

In the microlens of the present embodiment, the incident light 20 has a first condensing action due to the difference in refractive index between the atmosphere and the lens layer 1d on the upper surface of the lens layer 1d and the effect of the convex shape on the upper side. The light is then received by the lower surface of the lens layer 1d and the light is condensed for the second time 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 convex shape on the lower side. It
Therefore, compared with the conventional microlens having a convex shape only on the upper side, the same aperture, the same thickness, and a short focal length, that is, NA
A large microlens can be obtained.

Further, in the above embodiment, only the refractive indexes of the lens layers 1d to 4d are changed, but the refractive indexes of the underlayer 11 and / or the intermediate layer 12 or both of them are set to n2 to n2 '(n2>).
The same effect as that of the above-described embodiment can be obtained even when the values are continuously changed from n2 ') and n3 to n3'(n3> n3 ').

〔The invention's effect〕

As described above, according to the microlens of the present invention, the surface of the microlens has indentations at regular intervals, and the refractive index thereof is continuously reduced or uniform toward the lower side.
It is formed on the concave surface formed by the underlayer 2 ′ to n2 and the surface of the depression so that the upper surface thereof becomes a convex surface, and the refractive index thereof is continuously increased from the upper surface of the layer toward the center surface. Refractive indices n1 ′ to n1 (n1 ′>n1>) formed so as to increase and decrease continuously from the central surface to the lower surface of the layer.
n2 ′ ≧ n2) is provided, so that
NA of the same diameter and same thickness as conventional microlenses
, A microlens with a large short focal length can be obtained. For example, for a solid-state imaging device, the thickness of the underlayer can be reduced, the stress acting between the films can be reduced, and the shape of the lens layer is spherical. Therefore, it is possible to obtain a microlens that is stable against stress such as heat cycle.

Further, according to the microlens of the present invention, the refractive index n2 ′ to n2 has dents on its surface at regular intervals and the refractive index thereof continuously decreases or is uniform toward the lower side.
Of the underlayer, an intermediate layer having a refractive index of n3 ′ to n3 formed between a plurality of depressions on the underlayer, and a concave surface formed by the surface of the depression and the outer surface of the intermediate layer, Refractive indices n1 ′ to n1 (n1 ′>n1>) formed such that the refractive index thereof continuously increases from the upper surface of the layer toward the central surface and continuously decreases from the central surface to the lower surface of the layer. n
3 ′ ≧ n3 ≧ n2 ′ ≧ n2), the microlens having a short focal length with a larger NA can be obtained.

[Brief description of drawings]

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 reading 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, and 20 is incident light.
21 is a microlens. The same reference numerals in the drawings indicate the same or corresponding parts.

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Claims (3)

[Claims] 1. An underlayer having refractive indices n2 'to n2, which have dents at regular intervals on its surface, and whose refractive index continuously decreases or is uniform downward, and a surface of the dents. The concave surface is formed so that its upper surface becomes a convex surface, and its refractive index continuously increases from the top surface of the layer to the center surface, and decreases continuously from the center surface to the bottom surface of the layer. Refractive index n formed to
A microlens having a lens layer of 1'-n1 (n1 '>n1>n2' ≧ n2). 2. An underlayer having refractive indices n2 ′ to n2, which have dents at regular intervals on its surface, and whose refractive index continuously decreases or is uniformed downward, and a plurality of underlayers on the underlayer. Refractive index n formed between the depressions
3'-n3 intermediate layer, a concave surface formed by the surface of the depression and the outer surface of the intermediate layer, the refractive index of which increases continuously from the upper surface of the layer toward the central plane, Refractive indices n1 ′ to n1 formed so as to decrease continuously from the surface to the lower surface of the layer
(N1 ′>n1> n3 ′ ≧ n3 ≧ n2 ′ ≧ n2) lens layers. 3. The microlens according to claim 2, wherein the refractive indices n3 'to n3 of the intermediate layer are continuously reduced or uniform downward.