CN110021618B - An image sensor and its manufacturing method - Google Patents

Abstract

The present invention relates to an image sensor and a manufacturing method thereof. The image sensor includes a photosensitive element formed in a substrate to convert an optical signal into an electrical signal; a color filter layer formed on the photosensitive element; a first microlens formed on the color filter layer, the the first microlens is convex toward the direction of incident light to condense the incident light; and the second microlens is formed between the photosensitive element and the color filter layer and includes a plurality of sub-microlenses separated by a plurality of grooves lens such that the second microlens has an average refractive index that decreases from the center to the edge.

Description

An image sensor and its manufacturing method

technical field

The present disclosure relates to the field of semiconductor technology, and in particular, to an image sensor and a preparation method thereof.

Background technique

An image sensor that includes a photosensitive element is a device that converts an optical image into an electronic signal. Image sensors receive optical signals from objects and convert the optical signals into electrical signals, which can then be transmitted for further processing, such as digitization, and then stored in a storage device such as a memory, optical or magnetic disk, or used in a display. display, print, etc. According to different digital data transmission methods, image sensors can be divided into two categories: Charge Coupled Device (CCD, ChargeCoupled Device) and Metal Oxide Semiconductor (CMOS, Complementary Metal-Oxide Semiconductor). Among them, CMOS sensors have developed rapidly in recent years due to their advantages of high integration, low power consumption, high speed and low cost.

Various performance indicators of the image sensor directly affect the imaging effect, such as the conversion efficiency of incident light. If the light irradiated on the image sensor cannot be received by the photosensitive element due to reflection or scattering and is effectively converted into an electrical signal, the imaging quality of the image sensor will be adversely affected. An external microlens array is usually arranged in an image sensor to focus the incident light from the outside on a photosensitive element with a small light-receiving area. However, as the size of the image sensor array and the photosensitive element gradually decreases, the size of the microlens also needs to be reduced. It is therefore increasingly difficult to manufacture microlenses that match their focal length characteristics for smaller photosensitive elements. As a result, image sensors with smaller sized microlenses have difficulty meeting the requirements for color fidelity and signal-to-noise ratio.

SUMMARY OF THE INVENTION

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide an image sensor and a preparation method thereof, which are used to solve the problems of low photoelectric conversion efficiency and poor sensitivity of the image sensor in the prior art.

In one embodiment of the present invention, an image sensor is provided, the image sensor includes a photosensitive element formed in a substrate to convert an optical signal into an electrical signal; a color filter layer formed on the photosensitive element; a first microlens formed on the color filter layer, the first microlens protruding toward the direction of incident light to condense the incident light; and a second microlens formed on the photosensitive element and the color filter layer and including a plurality of sub-microlenses separated by a plurality of grooves such that the second microlens has an average refractive index that decreases from the center to the edge.

Preferably, the color filter layer fills the plurality of grooves of the second microlens.

Preferably, the plurality of sub-microlenses have substantially flat upper surfaces.

Preferably, the plurality of grooves have an increasing cross-sectional width from the center to the edge of the second microlens.

Preferably, the plurality of sub-microlenses have cross-sectional widths that decrease from the center to the edge of the second microlens.

Preferably, the image sensor further includes an anti-reflection layer formed on the photosensitive element, and the anti-reflection layer has the plurality of grooves etched therein to form the second microlenses.

Preferably, the anti-reflection layer is formed of one or more layers of materials, and the second microlenses are formed in one or more layers of materials of the anti-reflection layer.

Preferably, the material of the anti-reflection layer is selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide and silicon oxide.

Preferably, the thickness of the anti-reflection layer is 20-700 nm.

Preferably, the plurality of trenches are etched just completely through the anti-reflection layer, incompletely etched through the anti-reflection layer, or completely etched through the anti-reflection layer and further into the substrate.

Preferably, the plurality of trenches are etched in the substrate to form the second microlenses.

In another embodiment of the present invention, there is also provided a method of fabricating an image sensor, the method comprising providing a substrate in which a photosensitive element is formed, the photosensitive element converting an optical signal into an electrical signal; forming an inner microlens over the photosensitive element, the inner microlens comprising a plurality of sub-microlenses separated by a plurality of grooves such that the inner microlens has an average refractive index that decreases from the center to the edge; in A color filter layer is formed on the inner microlenses; and an outer microlens is formed on the color filter layer, and the outer microlenses are convex toward the direction of incident light to condense the incident light.

Preferably, the color filter layer fills the plurality of grooves of the inner microlenses.

Preferably, the plurality of sub-microlenses have substantially flat upper surfaces.

Preferably, the plurality of grooves are formed with increasing cross-sectional widths from the center to the edge of the inner microlenses.

Preferably, the plurality of sub-microlenses are formed with cross-sectional widths that decrease from the center to the edge of the inner microlens.

Preferably, the method further comprises forming grooves in the substrate over the photosensitive elements, depositing an anti-reflection layer in the grooves, and forming the plurality of grooves in the anti-reflection layer by etching the plurality of grooves The internal microlens is described.

Preferably, the anti-reflection layer is formed of one or more layers of material, and the inner microlenses are formed in one or more layers of the anti-reflection layer.

Preferably, the material of the anti-reflection layer is selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide and silicon oxide.

Preferably, the thickness of the anti-reflection layer is 20-700 nm.

Preferably, the plurality of trenches are etched just completely through the anti-reflection layer, incompletely etched through the anti-reflection layer, or completely etched through the anti-reflection layer and further into the substrate.

Preferably, the inner microlenses are formed by etching a plurality of trenches in the substrate over the photosensitive element.

In another embodiment of the present invention, there is also provided an image sensor array comprising an array composed of the image sensors according to the above.

In another embodiment of the present invention, there is also provided an imaging device comprising the image sensor array according to the above.

As described above, the present invention provides an improved image sensor that solves the problems of low photoelectric conversion efficiency and poor sensitivity of the prior art image sensor.

Description of drawings

The accompanying drawings, which form a part of the specification, illustrate embodiments of the present disclosure and together with the description serve to explain the principles of the present disclosure.

The present disclosure may be more clearly understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 shows a schematic diagram of an image sensor according to an embodiment of the present invention;

FIG. 2 shows an optical path diagram of incident light of an image sensor according to an embodiment of the present invention;

FIG. 3 shows a schematic diagram of an image sensor according to another embodiment of the present invention;

FIG. 4 shows a schematic diagram of an image sensor according to yet another embodiment of the present invention;

FIG. 5 shows a flow chart of fabricating an image sensor according to one embodiment of the present invention.

6 shows cross-sectional views of an image sensor at various stages in the manufacturing process according to one embodiment of the present invention.

Note that, in the embodiments described below, the same reference numerals are used in common between different drawings to denote the same parts or parts having the same function, and repeated descriptions thereof may be omitted. In this specification, like numerals and letters are used to refer to like items, so once an item is defined in one figure, it need not be discussed further in subsequent figures.

For ease of understanding, the position, size, range, and the like of each structure shown in the drawings and the like may not represent actual positions, sizes, ranges, and the like. Therefore, the disclosed invention is not limited to the positions, dimensions, ranges, and the like disclosed in the drawings and the like.

Detailed ways

Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present disclosure unless specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the disclosure, its application or uses in any way.

Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered a part of this specification.

In all examples shown and discussed herein, any specific value should be construed as illustrative only and not as limiting. Accordingly, other examples of exemplary embodiments may have different values.

FIG. 1 shows a schematic diagram of an image sensor 100 according to one embodiment of the present invention. The image sensor 100 includes a photosensitive element 101 formed in a substrate 102 to convert optical signals into electrical signals; a color filter layer 103 formed on the photosensitive element 101; a first color filter layer 103 formed on the color filter layer 103 Micro-lens 104, the first micro-lens 104 is convex toward the direction of incident light to condense the incident light, preferably, the first micro-lens 104 can be made of transparent organic material, inorganic compound material; A second microlens 105 between the element 101 and the color filter layer 103, the second microlens 105 comprising a plurality of sub-microlenses 105a-105g separated by a plurality of grooves 106a-106f such that the second microlens 105 The microlenses 105 have an average refractive index that decreases from the center to the edge. Since the second microlens 105 has an average refractive index that decreases from the center to the edge, the second microlens 105 actually has a light-converging effect. The second microlens 105 further condenses the incident light from the first microlens 104 into the photosensitive element 101 in the substrate 102, thereby increasing the transmittance of the incident light from the color filter layer 103 to the substrate 102, while enhancing the Convergence effect of incident light. The material of the second microlens 105 is a substantially transparent material, including but not limited to silicon, silicon dioxide, or tin-doped indium oxide, and any other transparent material.

Preferably, the color filter layers 103 of adjacent image sensors are isolated by an isolation structure 107 to reduce crosstalk between adjacent image sensors. Isolation structures 107 may be formed of any suitable opaque material, such as metals, including but not limited to tungsten, copper, or aluminum copper, or, for example, dielectrics, such as oxides (such as silicon oxide), nitrides (such as silicon nitride) ) and oxynitrides (such as silicon oxynitride), etc., or, for example, a combination of metals and dielectrics. Preferably, a grid film may be formed by a sputtering technique, and then a photoresist having a grid pattern is formed on the grid film, followed by etching to form the grid (ie, the isolation structure 107 ). Preferably, a metal interconnection layer (not shown) is further included under the photosensitive elements for realizing electrical connection of each photosensitive element. The metal interconnection layer is located on the backlight surface of the photosensitive element. When light is irradiated from top to bottom, the photosensitive element can be irradiated without passing through the metal interconnection layer, thereby preventing the metal interconnection layer from blocking the incident light.

In one embodiment of the present invention, the plurality of sub-microlenses 105a-105g have substantially flat upper surfaces. The substantially flat upper surfaces of the plurality of sub-micro-lenses make the second micro-lens a flat micro-lens, thereby avoiding the complicated process of manufacturing the curved lens inside and making the device structure more compact.

The substrate 102 may be a silicon substrate or other semiconductor material. Gallium arsenide, germanium, silicon carbide, indium arsenide or indium phosphide or alloy semiconductors such as silicon germanium carbide, indium gallium phosphide, indium gallium arsenide and the like may be used. The substrate may typically be a wafer of semiconductor material. In other embodiments, the substrate may be provided as an epitaxial layer on an insulator, such as an "SOI" layer. Wafers of semiconductor material may be bonded or stacked, and the substrate may be one of these layers. Substrates are typically thinned by wafer grinding methods, such as chemical mechanical polishing ("CMP"), mechanical wafer grinding, or semiconductor etching. The photosensitive element 101 is, for example, a photodiode. For example, a photodiode may include a corresponding first region (not shown) within the substrate 102 having a first doping type (eg, n-type doping), and a region above the first region within the substrate 102 having the same A corresponding second region (not shown) of a second doping type (eg, p-type doping) that is different from the first doping type. The formation method is completed by conventional processes such as impurity ion implantation and annealing process, including impurity ion implantation in the photodiode region to form a doped region, and a PN junction is formed between the doped region and the semiconductor substrate to form a photodiode and a photodiode. diode depletion region. The formation methods of photodiodes and photodiode depletion regions are well known to those skilled in the art and will not be described in detail here.

The substrate 102 may also include other devices, including active transistors, diodes, capacitors, resistors, memory cells, analog devices, filters, transceivers, etc. electronic connections formed in another portion of the substrate for connecting the The signal from the photosensitive element is transmitted to the readout electronics. Furthermore, after forming the image sensor of the present invention, encapsulation material may be disposed over the substrate to form a complete microelectronic assembly, such as an integrated circuit, a solar cell, a processor, and the like. The color filter layer 103 may include a colored or dyed material, such as acrylic. For example, polymethyl methacrylate ("PMMA") or propylene glycol monostearate ("PGMS") are suitable materials with which to add pigments or dyes to form color filters. However, other materials can also be used.

FIG. 2 shows a light path diagram of incident light of an image sensor according to an embodiment of the present invention. As shown in FIG. 2, the second microlens has a plurality of sub-microlenses 105a-105f separated by a plurality of trenches 106a-106f. Preferably, the plurality of trenches 106a-106f have a cross-sectional width that increases from the center to the edge of the second microlens. Preferably, the plurality of sub-microlenses 105a-105f have cross-sectional widths that decrease from the center to the edge of the second microlens. The average refractive index of the second microlenses is based on the area of the material filling the trenches compared to the area of the material of the submicrolenses, and the refractive indices of the material filling the trenches and the material of the submicrolenses. More specifically, when the area where the incident light is incident has more sub-microlens areas and less groove areas (eg, the central area of the second microlens), the average refractive index of the area will be greater. On the contrary, when the area where the incident light is incident has less sub-microlens area and more groove area (eg, the edge area of the second microlens), the average refractive index of the area will be smaller. Therefore, as shown in FIG. 2, when the incident light is incident on the center of the second microlens, it will pass substantially straight; when the incident light is deviated from the center of the second microlens and is incident from the edge near the second microlens , it will be bent toward the center so as to be more efficiently collected to the photosensitive element 101 . Thus, as described with respect to FIG. 1 , the second microlenses 105 actually have a light-converging effect. The second microlens 105 further condenses the incident light from the first microlens 104 into the photosensitive element 101 in the substrate 102, thereby increasing the transmittance of the incident light from the color filter layer 103 to the substrate 102, while enhancing the Convergence effect of incident light.

In one embodiment of the present invention, the color filter layer 103 fills the plurality of grooves of the second microlens. However, those skilled in the art can understand that the grooves can be filled with other materials, as long as the second microlenses formed have an average refractive index that decreases from the center to the edge.

FIG. 3 shows a schematic diagram of an image sensor according to another embodiment of the present invention. The image sensor 100 further includes an anti-reflection layer 108 on the photosensitive element 101, and the anti-reflection layer 108 has the plurality of trenches 106a-106f etched therein to form the second microlenses.

In the embodiment shown in FIG. 3 , the anti-reflection layer 108 is formed of a layer of material, and a plurality of trenches are etched in the anti-reflection layer 108 of the layer to form the second microlenses. In the embodiment shown in FIG. 4 , the anti-reflection layer 108 is formed of two layers of materials, and a plurality of etched trenches are formed in the anti-reflection layers 108 of the two layers to form the second microlenses. However, the present invention is not limited thereto, the anti-reflection layer may be formed of one or more layers of materials, and the second microlenses are formed in only one layer of the anti-reflection layer or in multiple layers. In the embodiments shown in FIG. 3 and FIG. 4 , the plurality of trenches just completely cut through the anti-reflection layer, but the present invention is not limited thereto, and the plurality of grooves may not completely cut through the anti-reflection layer. The reflective layer is either completely etched through the anti-reflective layer and further into the substrate. In one embodiment of the present invention, the material of the anti-reflection layer is selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide and silicon oxide. In an embodiment of the present invention, the thickness of the anti-reflection layer is 20-700 nm. In one embodiment of the present invention, the depth of the plurality of trenches is 40-800 nm. In an embodiment of the present invention, the transmittance of the second microlens to light incident thereto is greater than 80%. Although in the embodiments shown in FIGS. 3 and 4 , the second microlenses are formed in the anti-reflection layer, but the present invention is not limited thereto, and the present invention may also be at any position between the photosensitive element and the color filter layer The second microlenses are formed by any light-transmitting material. In one embodiment of the present invention, the second microlenses are formed in the substrate by etching a plurality of trenches and filling the trenches.

FIG. 5 shows a flow chart of fabricating an image sensor according to one embodiment of the present invention. In step 501, a substrate is provided. In step 502, photosensitive elements are formed in the substrate, the photosensitive elements convert optical signals into electrical signals. In step 503, an inner microlens is formed on the photosensitive element, the inner microlens includes a plurality of sub-microlenses separated by a plurality of grooves so that the inner microlens has a center-to-edge reduction average refraction. Preferably, in step S503, a groove is formed in the substrate above the photosensitive element, an anti-reflection layer is deposited in the groove, and the plurality of grooves are formed in the anti-reflection layer by etching the plurality of grooves. The internal microlens is described. The substrate may be dry-etched or wet-etched to form the antireflection layer. Preferably, in step S503, one or more anti-reflection layers are deposited in the grooves, and trenches are etched in only one or more layers of the anti-reflection layers to form the inner microlenses. Preferably, the plurality of sub-microlenses of the inner microlens have substantially flat upper surfaces. Preferably, the plurality of grooves are formed with increasing cross-sectional widths from the center to the edge of the inner microlenses. Preferably, the plurality of sub-microlenses are formed with cross-sectional widths that decrease from the center to the edge of the inner microlens. In step S504, a color filter layer is formed on the inner microlenses. In step S505, an external microlens is formed on the color filter layer, and the external microlens is convex toward the direction of the incident light to condense the incident light.

6 shows cross-sectional views of an image sensor at various stages in the manufacturing process according to one embodiment of the present invention. Stage ①: A photosensitive element that converts optical signals into electrical signals is formed in the substrate. Stage ②: A groove is formed in the substrate over the photosensitive element. Stage ③: depositing an anti-reflection layer in the groove. Stage ④: forming the inner microlenses by etching the plurality of trenches in the anti-reflection layer. Stage ⑤: A color filter layer is formed on the inner microlenses. Stage ⑥: forming external micro-lenses on the color filter layer, the external micro-lenses protruding toward the direction of the incident light to condense the incident light. The image sensor shown in FIG. 6 is only one embodiment of the present invention. The present invention is not limited to forming internal microlenses in the antireflection layer, the present invention also includes forming internal microlenses between the photosensitive element and the color filter layer (eg, formed in the antireflection layer, formed in the substrate, or formed in the antireflection layer) other embodiments of the reflective layer and the substrate, etc.).

The invention provides an image sensor, the image sensor includes a photosensitive element formed in a substrate to convert an optical signal into an electrical signal; a color filter layer formed on the photosensitive element; a first microlens formed on the On the color filter layer, the first microlens is convex toward the direction of incident light to condense the incident light; and the second microlens is formed between the photosensitive element and the color filter layer and includes a plurality of The plurality of sub-microlenses are separated by trenches such that the second microlens has an average refractive index that decreases from the center to the edge.

Preferably, the color filter layer fills the plurality of grooves of the second microlens.

Preferably, the plurality of sub-microlenses have substantially flat upper surfaces.

Preferably, the plurality of grooves have an increasing cross-sectional width from the center to the edge of the second microlens.

Preferably, the plurality of sub-microlenses have cross-sectional widths that decrease from the center to the edge of the second microlens.

Preferably, the image sensor further includes an anti-reflection layer formed on the photosensitive element, and the anti-reflection layer has the plurality of grooves etched therein to form the second microlenses.

Preferably, the anti-reflection layer is formed of one or more layers of materials, and the second microlenses are formed in one or more layers of materials of the anti-reflection layer.

Preferably, the material of the anti-reflection layer is selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide and silicon oxide.

Preferably, the thickness of the anti-reflection layer is 20-700 nm.

Preferably, the plurality of trenches are etched just completely through the anti-reflection layer, incompletely etched through the anti-reflection layer, or completely etched through the anti-reflection layer and further into the substrate.

Preferably, the plurality of trenches are etched in the substrate to form the second microlenses.

The present invention also provides a method of manufacturing an image sensor, comprising providing a substrate, in which a photosensitive element is formed, the photosensitive element converts an optical signal into an electrical signal; and an internal microlens is formed on the photosensitive element , the inner microlens includes a plurality of sub-microlenses separated by a plurality of grooves so that the inner microlens has an average refractive index decreasing from the center to the edge; a color filter layer is formed on the inner microlens ; and forming external microlenses on the color filter layer, the external microlenses protruding toward the direction of the incident light to condense the incident light.

Preferably, the color filter layer fills the plurality of grooves of the second microlens.

Preferably, the plurality of sub-microlenses have substantially flat upper surfaces.

Preferably, the plurality of grooves are formed with increasing cross-sectional widths from the center to the edge of the second microlens.

Preferably, the plurality of sub-microlenses are formed with cross-sectional widths that decrease from the center to the edge of the second microlens.

Preferably, the method further comprises forming grooves in the substrate over the photosensitive elements, depositing an anti-reflection layer in the grooves, and forming the plurality of grooves in the anti-reflection layer by etching the plurality of grooves the second microlens.

Preferably, the anti-reflection layer is formed of one or more layers of materials, and the second microlenses are formed in one or more layers of materials of the anti-reflection layer.

Preferably, the material of the anti-reflection layer is selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide and silicon oxide.

Preferably, the thickness of the anti-reflection layer is 20-700 nm.

Preferably, the plurality of trenches are etched just completely through the anti-reflection layer, incompletely etched through the anti-reflection layer, or completely etched through the anti-reflection layer and further into the substrate.

Preferably, the second microlenses are formed by etching a plurality of trenches in the substrate above the photosensitive element.

The present invention also provides an image sensor array comprising an array composed of the image sensors according to the above.

The present invention also provides an imaging device comprising the image sensor array according to the above.

The words "front," "rear," "top," "bottom," "over," "under," etc. in the specification and claims, if present, are used for descriptive purposes and not necessarily to describe an invariant relative position. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the disclosure described herein are, for example, capable of other orientations than those illustrated or otherwise described herein. Orientation to operate.

As used herein, the word "exemplary" means "serving as an example, instance, or illustration" rather than as a "model" to be exactly reproduced. Any implementation illustratively described herein is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, the present disclosure is not to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or detailed description.

As used herein, the word "substantially" is meant to encompass any minor variation due to design or manufacturing imperfections, tolerances of devices or elements, environmental influences, and/or other factors. The word "substantially" also allows for differences from a perfect or ideal situation due to parasitics, noise, and other practical considerations that may exist in an actual implementation.

The above description may indicate elements or nodes or features that are "connected" or "coupled" together. As used herein, unless expressly stated otherwise, "connected" means that one element/node/feature is electrically, mechanically, logically or otherwise directly connected to another element/node/feature (or direct communication). Similarly, unless expressly stated otherwise, "coupled" means that one element/node/feature can be mechanically, electrically, logically or otherwise linked, directly or indirectly, with another element/node/feature to Interactions are allowed, even though the two features may not be directly connected. That is, "coupled" is intended to encompass both direct and indirect coupling of elements or other features, including connections that utilize one or more intervening elements.

Additionally, certain terms may also be used in the following description for reference purposes only, and are thus not intended to be limiting. For example, the terms "first," "second," and other such numerical terms referring to structures or elements do not imply a sequence or order unless the context clearly dictates otherwise.

It should also be understood that the term "comprising/comprising" when used herein indicates the presence of the indicated feature, integer, step, operation, unit and/or component, but does not preclude the presence or addition of one or more other features, Entities, steps, operations, units and/or components and/or combinations thereof.

In this disclosure, the term "providing" is used broadly to encompass all ways of obtaining an object, thus "providing something" includes, but is not limited to, "purchasing," "preparing/manufacturing," "arranging/arranging," "installing/ Assembly", and/or "Order" objects, etc.

Those skilled in the art will appreciate that the boundaries between the operations described above are merely illustrative. Multiple operations may be combined into a single operation, a single operation may be distributed among additional operations, and operations may be performed at least partially overlapping in time. Furthermore, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be changed in other various embodiments. However, other modifications, changes and substitutions are equally possible. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

While some specific embodiments of the present disclosure have been described in detail by way of examples, those skilled in the art will appreciate that the above examples are provided for illustration only, and are not intended to limit the scope of the present disclosure. The various embodiments disclosed herein may be combined arbitrarily without departing from the spirit and scope of the present disclosure. It will also be understood by those skilled in the art that various modifications may be made to the embodiments without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims (23)

1. An image sensor, the image sensor comprising:

a light sensing element formed in the substrate to convert an optical signal into an electrical signal;

a color filter layer formed over the photosensitive element;

a trench formed in the substrate over the photosensitive element, the trench having an anti-reflective layer deposited therein;

a first microlens formed on the color filter layer, the first microlens being protruded toward a direction of incident light to condense the incident light; and

a second microlens formed between the photosensitive element and the color filter layer by etching a plurality of grooves in the anti-reflection layer, the second microlens including a plurality of sub-microlenses separated by the plurality of grooves such that the second microlens has an average refractive index decreasing from a center to an edge.

2. The image sensor of claim 1, wherein the color filter layer fills the plurality of trenches of the second microlens.

3. The image sensor of claim 1, wherein the plurality of sub-microlenses have substantially flat upper surfaces.

4. The image sensor of claim 1, wherein the plurality of trenches have a cross-sectional width that increases from a center to an edge of the second microlens.

5. The image sensor of claim 1, wherein the plurality of sub-microlenses have cross-sectional widths that decrease from a center to an edge of the second microlens.

6. The image sensor of claim 1, wherein the image sensor further comprises an anti-reflective layer formed over the photosensitive elements, the anti-reflective layer having the plurality of trenches etched therein to form the second microlenses.

7. The image sensor of claim 6, wherein the anti-reflective layer is formed of one or more layers of material, and the second microlenses are formed in the one or more layers of material of the anti-reflective layer.

8. The image sensor of claim 6, wherein the anti-reflective layer is a material selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide.

9. The image sensor of claim 6, wherein the anti-reflective layer is 20-700nm thick.

10. The image sensor of claim 6, wherein the plurality of trenches are etched through just completely through the anti-reflective layer, not completely through the anti-reflective layer, or completely through the anti-reflective layer and further into a substrate.

11. The image sensor of claim 1, wherein the plurality of trenches etched in the substrate to form the second microlenses.

12. A method of fabricating an image sensor, comprising:

providing a substrate, forming a photosensitive element in the substrate, wherein the photosensitive element converts an optical signal into an electric signal;

forming a groove in a substrate over the photosensitive element, depositing an anti-reflection layer in the groove, forming an inner microlens in the anti-reflection layer by etching a plurality of grooves, the inner microlens including a plurality of sub-microlenses separated by a plurality of grooves such that the inner microlens has an average refractive index that decreases from a center to an edge;

forming a color filter layer over the inner microlenses; and

and forming an external micro lens on the color filter layer, wherein the external micro lens protrudes towards the direction of the incident light to gather the incident light.

13. The method of claim 12, wherein the color filter layer fills the plurality of trenches of the inner microlens.

14. The method of claim 12, wherein the plurality of sub-microlenses have substantially flat upper surfaces.

15. The method of claim 12, wherein the plurality of trenches are formed with increasing cross-sectional widths from a center to an edge of the inner microlens.

16. The method of claim 12, wherein the plurality of sub-microlenses are formed with decreasing cross-sectional widths from a center to an edge of the inner microlens.

17. The method of claim 12, wherein the anti-reflective layer is formed of one or more layers of material and the inner microlenses are formed in the one or more layers of material of the anti-reflective layer.

18. The method of claim 12, wherein the anti-reflective layer is a material selected from the group consisting of silicon oxide, aluminum oxide, hafnium oxide, chromium oxide.

19. The method of claim 16, wherein the antireflective layer has a thickness of 20-700 nm.

20. The method of claim 12, wherein the plurality of trenches are etched through just completely through the antireflective layer, not completely through the antireflective layer, or completely through the antireflective layer and further into a substrate.

21. The method of claim 12 wherein the inner microlenses are formed in the substrate over the photosensitive elements by etching a plurality of trenches.

22. An image sensor array comprising an array of image sensors according to claims 1-11.

23. An imaging device comprising the image sensor array of claim 22.

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