JP3677977B2 - Method for forming a microlens - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a microlens independently for each pixel on a pixel surface composed of a large number of pixels.
[0002]
[Prior art]
Conventionally, a solid-state imaging device, an area sensor, an image sensor such as a linear sensor, a liquid crystal display device, and the like are known as devices including this type of microlens.
Among them, in recent years, it has become common to provide a microlens for a solid-state imaging device in order to improve the light collection efficiency and improve the sensitivity.
[0003]
By the way, in such a solid-state imaging device, incident light to this is perpendicular to the screen at the center of the chip, that is, the center of the pixel surface composed of a large number of pixels, and from the vertical as it goes to the peripheral side. It changes into oblique light with an angle.
FIGS. 5A, 5B, and 5C are diagrams showing an imaging model on a solid-state imaging device in each optical system. Except for the telecentric optical system shown in FIG. In the case of an optical system having a negative exit pupil as shown in FIG. 5B or in the case of an optical system having a positive exit pupil as shown in FIG. 5C, the incident angle of light on the pixel surface of the solid-state imaging device is Depending on the position of the pixel surface.
[0004]
Therefore, in recent solid-state imaging devices, when a microlens is formed on the light receiving sensor portion of each unit pixel, the microlens is moved toward the peripheral side of the pixel surface in order to equalize the sensitivity over the entire pixel surface. By shifting the center of the light receiving sensor unit from the center of the light receiving sensor unit, it is devised so that oblique incident light also reliably enters the light receiving sensor unit.
It should be noted that shifting the center of the microlens and the center of the light receiving sensor portion in this way to ensure that obliquely incident light is incident on the light receiving sensor portion is referred to as exit pupil correction in this specification.
[0005]
[Problems to be solved by the invention]
By the way, in the exit pupil minus optical system as shown in FIG. 5B, the condensing by the microlens of the conventional solid-state imaging device subjected to the exit pupil correction is performed as shown in FIGS. As shown in c). Here, FIG. 6A shows a microlens condensing state in the central portion A of the pixel surface 1 of FIG. 7 which is a side view showing the pixel surface of the solid-state imaging device, and similarly FIG. 7 shows a microlens condensing state at B on the peripheral side from the central portion A in FIG. 7, and FIG. 6C shows a microlens condensing state at the peripheral portion C in FIG. 6A, 6B, and 6C, reference numeral 2 denotes a light receiving sensor unit, 3 denotes a microlens, 4 denotes a light-shielding film, and light incident on the pixel surface of the solid-state imaging device is As shown in the figure, the light is condensed by the microlens 3 and is incident on the light receiving sensor portion 2 positioned below the microlens 3.
[0006]
As shown in FIGS. 6A, 6B, and 6C, the microlenses 3 formed on the pixel surface 1 all have the same curvature, and thus have the same curvature radius R. In order to improve the light collection efficiency with respect to the oblique light, the exit pupil is corrected so that the center of the microlens 3 is shifted from the center of the light receiving sensor unit 2 to the center of the pixel surface as it goes from the center of the pixel surface to the periphery. (L _A = 0 <L _B <L _C ; where L _A , L _B , and L _C are the distances between the center of the microlens 3 and the center of the light receiving sensor unit 2).
[0007]
Accordingly, the amount of incident light beam received by the microlens 3 follows the "COSIN fourth power law" in the image plane illuminance as shown in FIG. It becomes smaller in order of W _A , W _B , W _C.
The “COSIN fourth power law” is shown as follows from FIG.
E = E ₀ × COS ⁴ ω
E: Irradiance off the optical axis [1 m / m ² ]
E ₀ : Irradiance on the optical axis [1 m / m ² ]
ω: angle formed by the principal ray of the subject and the optical axis
Thus, with only exit pupil correction, the amount of light flux of incident light decreases from the central part A to the peripheral part C of the pixel surface 1, so that a planar object having a uniform radiation intensity in the pixel surface 1 can be obtained. As shown in FIG. 9, when the image is taken, the obtained display screen becomes brighter at the center and gradually becomes darker as it goes to the peripheral side, resulting in sensitivity shading (defects) and different from the actual one.
[0009]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for forming a microlens that can improve sensitivity non-uniformity due to a condensing position of the microlens.
[0010]
[Means for Solving the Problems]
In the method for forming a microlens according to the present invention, a microlens is provided independently for each pixel on a pixel surface composed of a large number of pixels, and the microlens is arranged at the center of the pixel surface with the center of the microlens. In order to match the center of a single pixel corresponding to this and go to the peripheral part of the pixel surface, the exit lens correction is performed by gradually shifting the center of the microlens from the center of the pixel. A resist layer is applied on the pixel surface to form a resist layer, and then the resist layer is patterned to form an independent resist pattern for each pixel in the exit pupil corrected state, and the resist layer In the center part of the pixel surface, the interval between the resist patterns adjacent to each other is widened, and the pattern is adjacent to each other as it goes to the peripheral part of the pixel surface. Gradually reduce the distance between the resist pattern, the volume is formed as gradually increases As the resist pattern itself toward the periphery side from the central portion of the pixel plane, then, the resist pattern Reflow processing forms convex convex microlenses and gradually increases the radius of curvature of the convex microlenses from the center to the periphery of the pixel surface, and enters each microlens. The solution to the above problem is to adjust the amount of the luminous flux of the oblique light to be the same between the central portion and the peripheral portion of the pixel surface .
[0011]
According to this forming method, not only the exit pupil correction is performed, but also the microlens is formed by gradually increasing the curvature radius from the central part of the pixel surface to the periphery, so that the obtained microlens is Sensitivity non-uniformity due to the light collection position is improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a method of forming a microlens independently for each pixel on a pixel surface composed of a large number of pixels. Specifically, the present invention performs exit pupil correction and goes from the center of the pixel surface to the peripheral side. Accordingly, the radius of curvature is gradually increased to form a microlens.
[0013]
The microlenses formed in this manner can be applied to various types, specifically, image sensors such as solid-state imaging devices, area sensors, linear sensors, and liquid crystal display devices. Note that the liquid crystal display element can be applied not only to a type in which each pixel collects light emitted from a point light source with a microlens and displays it but also to a type with a backlight.
[0014]
Hereinafter, the microlens forming method of the present invention will be described in detail based on an example in which the microlens forming method of the present invention is applied to the formation of a microlens of a solid-state imaging device. explain.
4A, 4 </ b> B, and 4 </ b> C are diagrams illustrating an example of a solid-state imaging device to which the present invention is applied, in which FIG. 4A is a plan view of the solid-state imaging device, and FIG. FIG. 4A is a side sectional view in the horizontal direction (H direction) of the unit pixel portion at a position indicated by b in FIG. 4A, and FIG. 4C is a vertical direction (V direction) of the unit pixel portion in the position indicated by c in FIG. FIG.
[0015]
4B and 4C, reference numeral 10 denotes a solid-state imaging device, and 11 denotes a silicon substrate. The silicon substrate 11 is formed with a light receiving sensor portion 12 that performs photoelectric conversion on the surface layer portion, and a vertical transfer portion 13 (see FIG. 4B) is provided on one side of the silicon substrate 11 via a read gate (not shown). On the other side, another vertical transfer unit 13 is formed via a channel stop (not shown).
Note that by forming one light receiving sensor unit 12, an independent single pixel is basically configured at this point.
An insulating film 14 made of SiO ₂ is formed on the surface portion of the silicon substrate 11. A first transfer electrode 15 made of first polysilicon and a second transfer made of second polysilicon are formed on the insulating film 14. The electrode 16 (see FIG. 4C) is partially overlapped.
[0016]
An insulating film (not shown) is formed on the first transfer electrode 15 and the second transfer electrode 16 so as to cover them, and a part of the light receiving sensor section 12 is opened on the insulating film. A light shielding film 17 is formed in this state.
A protective film 18 is formed on the light shielding film 17 so as to cover it, and a microlens 20 is formed on the light shielding film 17 via a color filter layer 19. Here, the microlens 20 is formed by the method of the present invention.
[0017]
In order to form the microlens 20, first, as shown in FIGS. 1A, 1B, and 1C, the color filter formed by forming the color filter layer 19 in FIGS. 4B and 4C is used. A resist layer is formed by applying a resist as a microlens material on the layer 19, that is, on a pixel surface on which a single pixel is formed for each light receiving sensor portion 12, and further, this resist layer is patterned. Independent rectangular resist patterns 21a, 21b, and 21c are formed for each pixel. Here, FIG. 1A shows the resist pattern 21a formed in the central portion A of the pixel surface 1 shown in FIG. 7, and FIG. 1B shows B on the peripheral side from the central portion A in FIG. FIG. 6C shows the resist pattern 21c formed on the peripheral portion C in FIG.
[0018]
When such resist patterns 21a, 21b, and 21c are formed, the resist patterns 21a, 21b, and 21c are subjected to exit pupil correction in the same manner as in the past, and the resist patterns 21a, 21b, and 21c are applied to the pixels shown in FIG. resist pattern 21a which, as shown in the middle portion a of the surface 1 FIGS. 1 (a) adjacent to each other, to widen the gap G _a between 21a, below, as the go to the periphery of the pixel surface, adjacent to each other resist The distance between patterns is gradually narrowed.
[0019]
That is, in the B pixel surface 1 shown in FIG. 7, FIG. 1 the resist pattern 21b (b), the spacing G _B between 21b narrower than the G _A, pixel surface 1 shown further in FIG. 7 in the peripheral portion C of, narrower than the G _B resist pattern 21c, the gap G _C between 21c as shown in Figure 1 (c). In this way, when the interval between the resist patterns is gradually narrowed from the central part of the pixel surface 1 to the peripheral side, the volume of the resist pattern itself gradually increases from the central part to the peripheral side. Will increase.
[0020]
Note that the resist patterns 21a, 21b, and 21c are positioned at the center of each resist pattern and directly below the center from the center to the periphery of the pixel surface 1 in order to perform exit pupil correction in the same manner as in the past. It is formed by gradually shifting the center of the light receiving sensor part 12 to be shifted. Therefore, the exposure mask used for forming the resist pattern is designed and manufactured in advance so that the exit pupil correction is performed and at the same time the distance between the resist patterns is gradually reduced.
[0021]
As for the degree to which the distance between the resist patterns is gradually narrowed, as will be described later, a difference occurs in the volume of the resist pattern formed by the difference in the distance between the resist patterns, and the curvature radius of the microlens obtained thereby Therefore, the amount of the light beam of the oblique light incident on each microlens is adjusted so as to be the same between the central portion and the peripheral portion of the pixel surface 1.
[0022]
When the resist patterns 21a, 21b, and 21c are formed in this way, the resist patterns 21a, 21b, and 21c are reflow-baked to project upward as shown in FIGS. 2 (a), (b), and (c). Convex microlenses 20a, 20b, and 20c are formed.
The formed microlenses 20a, 20b, and 20c are formed by correcting the exit pupil, and the volume of the resist pattern itself increases from the center to the peripheral side. The radius of curvature gradually increases from the central part of the pixel surface 1 to the peripheral part.
[0023]
That is, the microlenses 20a, 20b, and 20c thus obtained according to the present invention are provided with a pixel in order to improve the light collection efficiency with respect to oblique light, as shown in FIGS. 3 (a), (b), and (c). As the center of the surface moves from the center of the surface to the periphery, the center of the microlens shifts from the center of the light receiving sensor 12 to the center of the pixel surface, and exit pupil correction is performed (L _A = 0 <L _B <L _C ; L _A , L _B and L _C are not only the distance between the center of the microlens and the center of the light receiving sensor unit 12), but also the radius of curvature gradually increases in the order of r _A , r _B and r _C (r _A <R _B <r _C ).
Therefore, the amount of incident light received by the microlenses 20a, 20b, and 20c is unified to the same W as shown in FIGS. 3A, 3B, and 3C. The light captured by the sensor unit 12 is the same, so that the light having a uniform radiation intensity can be displayed (pictured) uniformly.
[0024]
Therefore, in the microlens formation method of the present invention, not only the exit pupil correction is performed, but the curvature radii r _A , r _B , r _C are gradually increased from the central part of the pixel surface to the periphery. Since the microlenses 20a, 20b, and 20c are formed so as to be large, sensitivity nonuniformity due to the condensing position is improved, and therefore, display with no difference in image quality between the central portion and the peripheral portion of the pixel surface becomes possible. Thus, a microlens can be formed.
Further, in the solid-state imaging device obtained in this way, the solid-state imaging device using a microlens having a conventional configuration has a periphery from the center of the imaging area (pixel surface) when the exit pupil distance is plus or minus. There is a phenomenon in which the condensing point moves from the light receiving surface to the upper side as it goes to the side, but this can also be suppressed.
[0025]
The present invention is not limited to the formation of such a microlens of a solid-state imaging device, but can be applied to an image sensor such as an area sensor and a linear sensor, and a liquid crystal display device as described above. For example, when applied to a liquid crystal display element, the screen is made to have the same brightness by enlarging the microlens as it is farther from the light source of the liquid crystal display element that displays an image, and collecting the light emitted from the light source by the microlens for each pixel. Can do.
[0026]
【The invention's effect】
As described above, the microlens formation method of the present invention not only performs exit pupil correction, but also forms a microlens by gradually increasing the radius of curvature from the center to the periphery of the pixel surface. Since this method is used, it is possible to improve the sensitivity non-uniformity due to the condensing position of the obtained microlens.
Therefore, when the present invention is applied to, for example, the manufacture of a solid-state imaging device, it is possible to improve the image surface illuminance non-uniformity associated with the COSINE fourth power rule, and further, when the exit pupil distance is a plus or minus optical system In addition, it is possible to improve the sensitivity non-uniformity due to the change of the condensing point of the microlens from the center to the periphery of the imaging area of the solid-state imaging device.
[Brief description of the drawings]
FIGS. 1A, 1B, and 1C are views for explaining an example in which the present invention is applied to the formation of a microlens of a solid-state imaging device, and shows a state in which a resist pattern is formed. It is a principal part side view to represent.
FIGS. 2A, 2B, and 2C are diagrams for explaining an example in which the present invention is applied to formation of a microlens of a solid-state imaging device; FIG. It is a principal part side view showing the state which formed.
FIGS. 3A, 3B, and 3C are diagrams for explaining an example in which the present invention is applied to formation of a microlens of a solid-state imaging device, and the state of the formed microlens. It is a principal part side view for demonstrating.
4A is a diagram illustrating an example of a solid-state imaging device to which the present invention is applied, FIG. 4A is a plan view of the solid-state imaging device, and FIG. a) A cross-sectional side view in the horizontal direction (H direction) of the unit pixel portion at the position indicated by b in the middle, and (c) in the vertical direction (V direction) of the unit pixel portion at the position indicated by c in (a). FIG.
FIGS. 5A, 5B, and 5C are diagrams showing an imaging model on a solid-state imaging device in each optical system, and FIG. 5A is a diagram showing a case of a telecentric optical system; ) Is a diagram showing a case of an optical system having a negative exit pupil, and (c) is a diagram showing a case of an optical system having a positive exit pupil.
6A, 6B, and 6C are diagrams for explaining a microlens forming method in a conventional solid-state imaging device, and are important points for explaining a state of the formed microlens. FIG.
FIG. 7 is a side view showing a pixel surface of a solid-state image sensor.
FIG. 8 is an explanatory diagram of a COSIN fourth power law.
FIG. 9 is a diagram schematically showing a state of a display screen on which sensitivity puddle occurs.
[Explanation of symbols]
20a, 20b, 20c ... micro lens, 21a, 21b, 21c ... resist pattern

Claims (4)

A microlens is independently provided for each pixel on a pixel surface composed of a large number of pixels, and the microlens is arranged at the center of the pixel surface with the center of the microlens and the center of a single pixel corresponding thereto. A microlens forming method that performs exit pupil correction that gradually shifts the center of the microlens and the pixel center as it goes to the periphery of the pixel surface,
Applying a resist which is a microlens material on the pixel surface to form a resist layer;
The resist layer is patterned to form an independent resist pattern for each pixel in an exit pupil corrected state, and the resist pattern is widened between adjacent resist patterns in the center of the pixel surface. The distance between adjacent resist patterns is gradually narrowed toward the periphery of the pixel surface, and the volume of the resist pattern itself gradually increases from the center of the pixel surface to the periphery. A process of forming to increase ,
Wherein the resist pattern to form a projecting convex microlenses above with reflow process, gradually increasing take the radius of curvature of the convex microlenses toward the peripheral from the center portion of the pixel plane, each Adjusting the amount of light flux of oblique light incident on the microlens to be the same at the central portion and the peripheral portion of the pixel surface . A method of forming a microlens, comprising:   The method of forming a microlens according to claim 1, wherein the microlens is provided on a pixel surface of a solid-state imaging device.   The method of forming a microlens according to claim 1, wherein the microlens is provided on a pixel surface of an image sensor.   The method for forming a microlens according to claim 1, wherein the microlens is provided on a pixel surface of a liquid crystal display element.

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