阅读说明：本技术 在成像系统中形成微透镜的方法、图像传感器和微透镜 (Method of forming microlens in imaging system, image sensor, and microlens ) 是由 约瑟夫·R·苏马 C·帕克斯 斯科特·瓦纳伦 于 2020-04-10 设计创作，主要内容包括：本发明题为“在成像系统中形成微透镜的方法、图像传感器和微透镜”。本发明公开了一种成像设备,该成像设备可包括形成为图像像素阵列的一部分的像素中的一个或多个光敏区。微透镜和滤色器结构可形成在像素之上。每个微透镜可由微透镜晶种以及形成在微透镜晶种之上的一个或多个沉积微透镜层形成。沉积的一个或多个沉积微透镜层可能已经限定微透镜的曲率。因此,针对形成在微透镜晶种之上的一个或多个微透镜层,不需要进一步的蚀刻或平滑处理。如果需要,微透镜晶种可具有平面顶表面和平面侧、平面顶表面和倾斜平面侧、或非平面顶表面和平面侧。微透镜晶种可限定微透镜的微透镜特性,诸如曲率半径、高度和/或微透镜凸角的数量和类型。(The invention provides a method for forming a micro lens in an imaging system, an image sensor and a micro lens. An imaging device may include one or more photosensitive regions in pixels forming part of an image pixel array. Microlens and color filter structures may be formed over the pixels. Each microlens can be formed from a microlens seed and one or more deposited microlens layers formed over the microlens seed. The deposited microlens layer or layers may already define the curvature of the microlenses. Thus, no further etching or smoothing is required for the one or more microlens layers formed over the microlens seed. The microlens seed may have a planar top surface and planar sides, a planar top surface and inclined planar sides, or a non-planar top surface and planar sides, if desired. The microlens seed may define the microlens characteristics of the microlens, such as the radius of curvature, height, and/or number and type of microlens lobes.)

1. A method of forming a microlens in an imaging system, the method comprising:

forming a microlens seed structure; and

depositing a first microlens layer over the microlens seed structure, wherein the deposited first microlens layer defines a top surface topology of the microlenses, the top surface topology having a first curvature that is different from a second curvature of the top surface of the microlens seed structure.

2. The method of claim 1, wherein the deposited first microlens layer has a top surface that is the same as a top surface of the microlenses, and wherein depositing the first microlens layer comprises depositing an inorganic material using a lateral deposition rate that is substantially different from a vertical deposition rate.

3. The method of claim 1, wherein the first microlens layer is formed of a graded index material having a refractive index gradient.

4. The method of claim 1, further comprising:

depositing a second microlens layer over the microlens seed structure; and

depositing a third microlens layer interposed between the first and second microlens layers, wherein the first microlens layer has a first refractive index, the second microlens layer has a second refractive index that is less than the first refractive index, and the third microlens layer has a third refractive index that is greater than the first refractive index and less than the second refractive index.

5. The method of claim 1, wherein forming the microlens seed structure comprises:

forming the top surface of the microlens seed structure into a flat surface; and

the peripheral side of the microlens seed structure is formed as an inclined surface.

6. The method of claim 1, wherein forming the microlens seed structure comprises:

forming the top surface of the microlens seed structure with a recessed portion having a first height from a base of the microlens seed structure and a protruding portion having a second height from the base of the microlens seed structure, the second height being greater than the first height, wherein forming the microlens seed structure comprises: forming the top surface of the microlens seed structure with additional raised portions having the second height from the base of the microlens seed structure, the recessed portions being interposed between the raised portions and the additional raised portions, and wherein the top surface topology of the microlenses has first and second lobes, the first lobes being at least partially defined by the raised portions and the second lobes being at least partially defined by the additional raised portions.

7. An image sensor, comprising:

an image sensor pixel array; and

a microlens overlapping a portion of the image sensor pixel array, the microlens comprising:

a microlens precursor structure having a top surface and a base opposite the top surface, wherein the microlens precursor structure has a protruding portion at the top surface surrounding a recessed portion at the top surface; and

depositing a microlens layer formed over the top surface of the microlens precursor structure, wherein the deposited microlens layer defines a top surface of the microlenses.

8. The microlens of claim 7, wherein the protruding portion includes first and second protruding structures having planar symmetry on a plane passing through the recessed portion, wherein the first protruding structures at least partially define first lobes of the microlens and the second protruding structures at least partially define second lobes of the microlens, and wherein the first lobes of the microlens are configured to focus light onto a first photosensitive region in the image sensor pixel array and the second lobes of the microlens are configured to focus light onto a second photosensitive region in the image sensor pixel array.

9. The microlens of claim 7, wherein the raised portion has radial symmetry about an axis through the recessed portion, wherein the raised portion has a first height from the base that is greater than a second height of the recessed portion from the base, and wherein the deposited microlens layer has a recessed portion and the axis extends through the recessed portion.

10. A microlens, comprising:

a microlens seed pillar having a top lateral width at a top surface, a bottom lateral width at a base greater than the top lateral width, and an inclined side plane connecting the top surface to the base; and

a plurality of microlens layers formed over the microlens seed pillars, a topmost layer of the plurality of microlens layers defining a top surface topology of the microlenses.

11. The microlens of claim 10, wherein the plurality of microlens layers are formed of at least one material selected from the group consisting of an oxide material, a nitride material, and an oxynitride material, wherein the topmost layer is unetched, and wherein at least one of the plurality of microlens layers is formed of a passivation material.

Technical Field

The present disclosure relates generally to imaging systems, and more particularly to methods of forming microlenses in imaging systems, image sensors, and microlenses.

Background

Modern electronic devices, such as cellular phones, cameras, and computers, often use image sensors. An image sensor (sometimes referred to as an imager) may be formed from an array of two-dimensional image sensing pixels. Each pixel typically includes a photosensitive element, such as a photodiode, that receives incident photons and converts the photons to electrical signals. Each pixel may also include a microlens that overlaps and focuses light onto the photosensitive element.

Image sensors typically use organic microlenses to optimize quantum efficiency across the visible spectrum. Although effective for visible light, these organic materials forming the microlenses exhibit low transmission characteristics for shorter wavelengths of light (e.g., wavelengths lower than those in the visible spectrum). Although inorganic materials can be used in microlenses, there are significant challenges for efficiently fabricating microlens structures using inorganic materials.

It is therefore desirable to provide improved microlenses in imaging systems.

Disclosure of Invention

According to a first aspect of the present disclosure, a method of forming a microlens in an imaging system is provided. The method comprises the following steps: forming a microlens seed structure; and depositing a first microlens layer over the microlens seed structure, wherein the deposited first microlens layer defines a top surface topology of the microlenses, the top surface topology having a first curvature that is different from a second curvature of the top surface of the microlens seed structure.

According to a second aspect of the present disclosure, an image sensor is provided. The image sensor includes: an image sensor pixel array; and a microlens overlapping a portion of the image sensor pixel array, the microlens comprising: a microlens precursor structure having a top surface and a base opposite the top surface, wherein the microlens precursor structure has a protruding portion at the top surface surrounding a recessed portion at the top surface; and a deposited microlens layer formed over the top surface of the microlens precursor structure, wherein the deposited microlens layer defines a top surface of the microlenses.

According to a third aspect of the present disclosure, a microlens is provided. The microlens comprises a microlens seed pillar having a top lateral width at a top surface, a bottom lateral width at a base greater than the top lateral width, and an inclined side plane connecting the top surface to the base; and a plurality of microlens layers formed over the microlens seed pillars, a topmost layer of the plurality of microlens layers defining a top surface topology of the microlenses.

Drawings

Fig. 1 is a diagram illustrating an exemplary imaging system, according to some embodiments.

Fig. 2 is a cross-sectional view of a portion of an exemplary image sensor according to some embodiments.

Fig. 3 is a cross-sectional view of an exemplary microlens structure having a seed layer and a microlens layer over the seed layer, according to some embodiments.

Fig. 4 is a cross-sectional view of an exemplary microlens structure having a tapered or trapezoidal seed layer, according to some embodiments.

Fig. 5 is a cross-sectional view of an exemplary microlens structure including a microlens seed having a non-planar top, according to some embodiments.

Fig. 6A and 6B are perspective views of exemplary top surface topologies of microlens structures formed from microlens seeds having non-planar tops according to some embodiments.

Fig. 7 is a flow chart of exemplary steps for forming a microlens structure according to some embodiments.

Detailed Description

Embodiments of the present invention relate to imaging systems having microlens structures with improved transmission characteristics and improved processing characteristics.

Electronic devices, such as digital cameras, computers, cellular telephones, and other electronic devices, include image sensors that collect incident light to capture images. The image sensor may include an array of image pixels. An image pixel in an image sensor may include a photosensitive element, such as a photodiode that converts incident light into electrical charge. The charges may be stored and converted into image signals. The image sensor may have any number (e.g., hundreds or thousands or more) of pixels. A typical image sensor may, for example, have hundreds of thousands or millions of pixels (e.g., mega pixels). The image sensor may include control circuitry, such as circuitry for operating the imaging pixels, and readout circuitry for reading out image signals corresponding to the charge generated by the photosensitive elements.

FIG. 1 is a schematic diagram of an exemplary electronic device that captures an image using an image sensor. The electronic device 10 of fig. 1 may be a portable electronic device such as a camera, cellular telephone, tablet computer, web camera, video surveillance system, automotive imaging system, video game system with imaging capabilities, or any other desired imaging system or device that captures digital image data. The camera module 12 may be used to convert incident light into digital image data. The camera module 12 may include one or more lenses 14 and one or more corresponding image sensors 16. During image capture operations, light from a scene may be focused through lens 14 onto image sensor 16. The image sensor 16 provides corresponding digital image data to the processing circuitry 18. The image sensor 16 may be a front-illuminated image sensor or, if desired, a back-illuminated image sensor. The camera module 12 may be provided with an array of lenses 14 and a corresponding array of image sensors 16, if desired.

The control circuitry, such as storage and processing circuitry 18, may include one or more integrated circuits (e.g., image processing circuitry, microprocessors, storage devices such as random access memory and non-volatile memory, etc.), and may be implemented using components separate from the camera module 12 and/or forming part of the camera module 12 (e.g., circuitry forming part of an integrated circuit including the image sensor 16 or within the module 12 associated with the image sensor 16). The processing circuitry 18 may be used to process and store image data that has been captured by the camera module 12. If desired, the processed image data may be provided to an external device (e.g., a computer or other device) using a wired and/or wireless communication path coupled to the processing circuitry 18. Processing circuitry 18 may be used to control the operation of image sensor 16.

Image sensor 16 may include one or more arrays of image pixels. The image pixels may be formed in the semiconductor substrate using Complementary Metal Oxide Semiconductor (CMOS) technology, Charge Coupled Device (CCD) technology, or any other suitable technology. Arrangements in which the image pixels are front-illuminated image pixels are sometimes described herein as examples. However, this is merely exemplary. The image pixels may be back-illuminated image pixels, if desired. The image sensor pixels may be configured to support rolling or global shutter operations. For example, the image pixels may each include a photodiode, a floating diffusion region, a local storage region, a transfer transistor, or any other suitable component.

To further focus the light onto the image pixels, microlenses may be formed over the image pixels. The microlenses may form a microlens array that overlaps the array of filter elements and the array of image sensor pixels. If desired, each microlens may focus light from the imaging system lens onto a corresponding image pixel 22 (in FIG. 2) or multiple image pixels 22.

Fig. 2 is a cross-sectional side view of a portion of an exemplary image sensor having an array of image pixels 22. As shown in fig. 2, each pixel 22 may include a photosensitive element, such as a photodiode 30. The photodiode 30 may be formed in a semiconductor substrate 40 (e.g., a p-type silicon substrate). Memory diode regions and other pixel structures (e.g., floating diffusion regions, transistors, etc.) may also be formed in the substrate 40 in regions between adjacent or neighboring photodiodes 30.

An interconnect stack, such as interconnect stack 42, may be formed on a surface of substrate 40. The interconnect stack 42 may comprise a dielectric material such as silicon oxide (SiO)₂) And forming a dielectric layer. Interconnect layers (sometimes referred to as interconnect wiring structures) may be formed in the interconnect stack 42 to contact the various pixel structures and terminals, and may be separated by dielectric layers. The interconnect layer may include conductive structures such as metal signal routing paths and metal vias. The dielectric layer may sometimes be referred to as an inter-metal dielectric layer, an inter-metal dielectric stack, an interconnect stack, or an inter-layer dielectric (ILD). Layers 32-1, 32-2, etc. in fig. 2 may refer to one or more layers of an interlayer dielectric or interconnect wiring structure.

An array of filters in a filter layer 44 may be formed over the interconnect stack 42. Color filter layer 44 may include an array of filter (color filter) elements such as filter (color filter) elements 34. Each filter (color filter) element 34 may be configured to pass light in a given portion of the electromagnetic spectrum while blocking light outside that portion of the electromagnetic spectrum. For example, each color filter element may be configured to pass one or more of: green light, red light, blue light, cyan light, magenta light, yellow light, infrared light, ultraviolet light, and/or other types of light. A passivation layer may be interposed between color filter layer 44 and interconnect stack 42, if desired.

A microlens array in microlens layer 46 (sometimes referred to as a microlens structure or microlens layer 46 for clarity, when describing the various layers associated with microlens layer 46) may be formed over color filter layer 44. Microlens layer 46 may include a plurality of microlenses 36, each formed over a respective one of color filter elements 34. Each microlens 36 may be configured to focus light toward an associated one of the photodiodes 30. Each microlens 36 may be formed over multiple color filter elements 34, or share a single color filter element with another microlens 36, if desired. Each microlens 36 may be configured to focus light toward a plurality of photodiodes 30, if desired.

In some applications, it may be desirable for the image sensor to obtain data for light having a wavelength shorter than that of visible light (e.g., ultraviolet light, deep ultraviolet light, etc.). However, if care is not taken, these shorter wavelengths of light may be significantly attenuated when passing through the microlens structure. For example, organic materials may exhibit lower transmission characteristics below 300 nanometers (nm). Accordingly, microlens structures formed from these organic materials may undesirably attenuate light at wavelengths of interest less than 300 nm. Although other materials, such as inorganic materials, may be used to form the microlens structure, difficulties may arise when efficiently fabricating the microlens structure using inorganic materials. Embodiments described herein alleviate these problems while forming microlens structures with improved processing and performance.

Fig. 3 is a cross-sectional view of an exemplary microlens structure having a seed layer and a microlens layer over the seed layer. As shown in fig. 3, microlenses 36 may be formed from a seed layer 50 (sometimes referred to herein as a seed lens, a seed pillar, a microlens seed, a seed structure, a microlens seed structure, a precursor structure) and microlens layers 52-1, 52-2, and 52-3 (sometimes referred to herein as deposited layers or deposited microlens layers) formed over seed layer 50. Microlens layers 52-1, 52-2, and 52-3 and seed layer 50 may be formed of an oxide material (e.g., a metal oxide material, a semiconductor oxide material, any suitable type of oxide material) or any suitable type of inorganic material such as a nitride (silicon nitride), an oxynitride (silicon oxynitride), or the like. However, this is merely exemplary. If desired, one or more of the layers 52-1, 52-2, 52-3, and 50 may be formed from organic materials, inorganic materials, and/or any combination of organic and inorganic materials.

Although fig. 3 shows three microlens layers (e.g., layers 52-1, 52-2, and 52-3) over seed layer 50, this is merely exemplary. If desired, a single microlens layer or more than one microlens layer may be formed over the seed layer 50. Although three deposition layers are sometimes described herein, these principles may be similarly applied to microlenses formed from less than three deposition layers or more than three deposition layers. If desired, layer 50 'may be formed integrally with seed layer 50 (e.g., the seed layer may include planar portions 50' and seed protruding portions 50). The seed protrusion may be referred to as a seed lens, a seed pillar, or a microlens seed. Alternatively, layers 50 and 50' may be formed separately using separate processes.

The seed post 50 may be formed in a non-spherical configuration and have straight (non-curved) edges (e.g., having a non-circular side profile, having a rectangular side profile as shown in fig. 3, having a straight perimeter or side or perimeter edge, having a straight top edge), as opposed to the final shape of the microlens 36 (e.g., the top surface and side surface topology of the seed post 50 is not an exact copy of the top surface and side surface topology of the microlens 36). The shape of the seed post 50 (e.g., the top and side surfaces of the seed post 50) may still affect the final shape of the microlens 36 (e.g., the topology of the microlens 36). In other words, microlens layers 52-1, 52-2, and 52-3 may have a different surface profile (side) than seed pillar 50 to form microlens 36. In forming the microlenses 36, the topmost layer (i.e., layer 52-3) may define the (spherical) shape of the microlenses 36 (e.g., define the top surface topology of the microlenses 36). The height of the microlenses 36 can be defined by the thickness of each of the layers 50, 52-1, 52-2, and 52-3. The shape and height of microlenses 36 can be adjusted based on the lateral and vertical deposition rates of layers 52-1, 52-2, and 52-3.

For example, for a given microlens, layers 52-1, 52-2, and 52-3 may have a vertical dimension V1 (e.g., combined thickness V1) and may have a lateral dimension L1 (e.g., radius L1 of the microlens). By adjusting the ratio of the lateral deposition rate and the vertical deposition rate, the ratio of the thickness L1 to the radius V1 can be adjusted. Accordingly, the curvature (e.g., radius of curvature) of the microlenses 36 can be adjusted based on the ratio. In particular, it may be advantageous to deposit one or more of layers 52-1, 52-2, and 52-3 (or a single bulk deposition layer) where the lateral deposition rate is significantly different from the vertical deposition rate (e.g., having a difference of 10% greater, 25% greater, 50% greater, 75% greater, etc. than the vertical deposition rate). By adjusting the lateral deposition rate and deposition time, the height of the microlenses 36 can be adjusted.

By first forming seed layer 50 and then forming microlens layers 52-1, 52-2, and 52-3 using adjusted (lateral and vertical) deposition rates and times, microlenses 36 can be formed without etching (e.g., smoothing or polishing) layers 52-1, 52-2, and 52-3. In other words, after the seed pillars 50 are formed, an etch smoothing step for depositing a microlens (oxide) layer may be omitted. The microlens layer itself may completely fill all of the spaces between adjacent seed pillars 50, forming microlenses 36 in a desired manner. An etching step may be used to form the seed pillars 50, if desired. However, the final shape, curvature, or (top surface) topology of the microlenses 36 may be defined without an etch smoothing step (e.g., the topmost layer 52-3 is not etched (i.e., is unetched) to form the desired curvature and/or height of the microlenses 36).

If desired, different materials may be used to form microlens layers 52-1, 52-2, and 52-3. For example, layers 52-1, 52-2, and 52-3 may be configured to reduce or minimize reflection losses. In particular, layers 52-1, 52-2, and 52-3 may be formed from a layer gradient having a decreasing index of refraction (i.e., refractive index). In other words, the bottommost layer (e.g., layer 52-1) may be formed of a material having the highest refractive index (e.g., silicon nitride), the topmost layer (e.g., layer 52-3) may be formed of a material having the lowest refractive index (e.g., silicon oxide), and the intermediate layer (e.g., layer 52-2) may be formed of a material having an intermediate refractive index between the highest refractive index and the lower refractive index (e.g., silicon oxynitride). If desired, a layer formed of a graded index material having a continuous index gradient may be formed over seed layer 50 in place of layers 52-1, 52-2, and 52-3 or in addition to layers 52-1, 52-2, and 52-3.

If desired, one or more of microlens layers 52-1, 52-2, and 52-3 may be formed from a passivation material (e.g., silicon oxynitride). The silicon oxynitride layer may be used as a passivation layer to protect the imaging device (e.g., one or more layers and/or the substrate over which the passivation layer is formed). The passivation layer may protect the image forming apparatus from moisture, if desired. Incorporating a passivation layer into the microlens layer can help reduce the overall stack height of the imaging device. The topmost layer (or any suitable layer) of the microlenses 36 can be an anti-reflective coating, if desired. If desired, an anti-reflective coating may be formed over the topmost layer forming the microlenses 36.

Although the seed column 50 is illustrated in fig. 3 as having a rectangular shape, this is merely exemplary. The seed column 50 may have any suitable shape, if desired. In particular, the topology of the seed layer 50 may adversely affect the overlapping shape of the microlenses 36. Thus, to reduce the effect of seed layer topology, seed layer 50 may be formed using a pyramidal, pointed, conical, or trapezoidal shape.

Fig. 4 is a cross-sectional view of an exemplary microlens structure having a tapered or trapezoidal seed layer. Fig. 4 shows seed layer 50-1 having a base width (e.g., width/diameter T1, bottom lateral dimension) and a top width (e.g., width/diameter T2, top lateral dimension parallel to the bottom lateral dimension) at the protruding portions of seed layer 50-1. The base width T1 may be greater than the top width T2 (e.g., may be about 50% greater than the top width T2, may be about 40% greater than the top width T2, may be about 60% greater than the top width T2, may be any suitable amount greater than the top width T2) to provide the desired shape for the microlenses 36 and to reduce the effect of the seed layer topology on the final microlens shape. Seed layer 50-1 may also have a height (e.g., height H, vertical dimension H). The height H50-1 may be adjusted to adjust the characteristics of the microlenses 36 (e.g., the thickness or height of the microlenses 36), if desired. The height H may be adjusted to select the appropriate top width T2, if desired. For example, with a pyramidal or trapezoidal seed structure (e.g., a pyramidal or trapezoidal precursor), microlenses 36 can be formed that are free of any undesirable indentations or lobes in the final profile.

The seed pillars in seed layer 50-1 may be used at least to shape microlenses 36 (in combination with microlens layer 52). In other words, the seed pillars of the seed layer 50-1 may have flat top surfaces (or sharp vertices) and sloped sides, thereby having a profile that is better related to the curvature of the final microlens shape (as compared to seed pillars having a rectangular profile). In this way, fewer deposited microlens layers and/or thinner microlens layers 52 may be formed. This can advantageously reduce the thickness of the microlens.

In addition, fig. 4 shows how microlens structures 46 may be formed on other device layers 60. This may be similar to that in the configuration of fig. 3 (e.g., below layer 50'). Layer 60 may include any combination of the device layers described in connection with fig. 2 (e.g., layers 44, 32-1, 32-2, substrate 40, etc.). Layer 60 may include any additional layers not shown in fig. 2, such as an oxynitride layer, a transistor gate layer, a mask layer, etc., if desired. The topmost of the layers 60 may be a non-planar layer (having recessed areas and raised areas) or may be a planar layer, if desired. In particular, when seed layer 50-1 is formed, seed layer 50-1 may be formed over the topmost device layer in layers 60. Microlens layer 52 (e.g., a combination of layers 52-1, 52-2, and 52-3 formed from the same material, a single microlens layer, a combination of multiple different microlens layers formed using different materials, etc.) can be formed over seed layer 50-1.

In some embodiments, the microlens seeds (pillars) may be formed of irregular shapes. Fig. 5 is a cross-sectional view of an exemplary microlens structure including a microlens seed having a non-planar top portion. In the example of fig. 5, the microlens seed 50-2 has an irregular top surface (e.g., non-planar top surface, curved top surface, concave top surface). In particular, the microlens seed 50-2 may have a raised edge or point, or raised portions 70-1 and 70-2 (having a height H1 from the base 82 of the microlens seed 50-2) and a depression or indentation 72 at the center (having a height H2 from the base 82). The projections 70-1 and 70-2 may be separated by a lateral distance T.

Formed in this manner, the two raised edges 70-1 and 70-2 may produce a microlens having multiple (e.g., two) focal points after deposition of microlens layer 52. For example, one or more oxide, oxynitride, and nitride materials may be deposited as microlens layer 52. In other words, the non-planar shape of the top surface of the microlens seed 50-2 may be transferred to the overall (final) shape of the microlens 36, the microlens 36 having a plurality of lobes to assume a plurality of focal points. In the example of FIG. 5, rising edge 70-1 may be translated (e.g., for at least partial definition) to lobe 80-1, and rising edge 70-2 may be translated (e.g., for at least partial definition) to lobe 80-2. The recess 72 in the microlens seed 50-2 can be translated (e.g., for at least partial definition) to the recess 81 in the microlens 36. The distance T between lobes 70-1 and 70-2 may be adjusted to adjust the spacing of lobes 80-1 and 80-2 from one another (e.g., the spacing between the respective peaks in lobes 80-1 and 80-2 may be adjusted). The shape and curvature of each lobe may be adjusted using the shape and curvature of the microlens seed 50-2, the spacing between the protruding portions of the microlens seed 50-2, and/or the deposition rate of the microlens layer.

The example of microlenses 36 in fig. 5 is merely exemplary. If desired, the underlayer seed topology may be raised at more than two points to form more than two lobes, or may be raised at one point. If desired, points 70-1 and 70-2 may be located at different heights and may be separated by a distance T. If desired, the microlens seed 50-2 may have any suitable non-planar top surface topology defined by a suitable number of points at any set of different heights.

For example, a microlens having a plurality of focal points may be placed over the phase detection autofocus pixel (PDAF pixel). If desired, a microlens having multiple focal points may be used with any pixel to perform phase detection and/or autofocus operations. If desired, a microlens having multiple lobes exhibiting multiple focal points may be used for any suitable operation.

Fig. 6A is a perspective view of a microlens top surface topology of a microlens 36 having two convex corners that can be formed from the microlens seed 50-2 in fig. 5. In the example of fig. 6A, microlenses 36 may have bilateral or planar symmetry in a vertical plane through recessed regions 81. In other words, lobe 80-1 may be formed as a mirror image of lobe 80-2 in the vertical plane (or vice versa). Recessed area 81 may separate lobe 80-1 from lobe 80-2. In this example of fig. 6A, microlens seed 50-2 (in fig. 5) can similarly have bilateral or planar symmetry in a vertical plane through recessed region 72 (e.g., a vertical plane through both recessed region 72 and recessed region 81). In other words, the projection 70-1 may be formed as a mirror image of the projection 70-2 in the vertical plane (or vice versa).

The microlens 36 in fig. 6A may be formed over the (PDAF) pixel, if desired. The lobe 80-1 may overlap (e.g., be formed on) a first photosensitive region in the pixel and the lobe 80-2 may overlap (e.g., be formed on) a second photosensitive region in the pixel.

Fig. 6B is a perspective view of a microlens top surface topology of a microlens 36 having continuous convex corners that may be formed from the microlens 50-2 in fig. 5. In the example of fig. 6B, the microlenses 36 can have radial symmetry about an axis passing through the central recessed portion 81. The recessed portion 81 may have a circular or any suitable curved shape, or may be a point. The convex corners 80 may have a continuous surface having a convex shape extending from the peripheral outer edge of the microlenses 36 to an inner concave portion 81. In this example of fig. 6B, the microlens seed 50-2 may similarly have radial symmetry about a central axis through the central recessed portion 72 (e.g., a central axis through both the recessed region 72 and the recessed region 81). In other portions, the protruding portions 70-1 and 70-2 may be connected to each other (and have a circular shape) and may laterally surround the recessed portion 72 (e.g., may have radial symmetry about a central axis).

If desired, the microlenses 36 in FIG. 6B can be formed over (annular) pixels (e.g., pixels having a first inner photosensitive region and a second outer photosensitive region surrounding the first inner photosensitive region). The central recessed portion 72 may overlap (e.g., may be formed on) at least a first (inner) photosensitive region, and the convex corner 80 may overlap (e.g., may be formed on) at least a second (outer) photosensitive region.

The microlens topology and microlens seed topology described in connection with fig. 5, 6A, and 6B are merely exemplary. The topology of the microlens seed may be adjusted in any suitable manner, if desired, to obtain a suitable topology for the microlenses 36. Although not explicitly shown in fig. 6A and 6B, the deposited microlens layer 52 may be interposed between the recessed portions 81 of the microlenses 36 in fig. 6A and 6B and the recessed portions 72 of the microlens seed 50-2 in fig. 5.

Fig. 7 shows exemplary steps for forming a microlens of the type shown in fig. 2-6. In particular, at step 100, a seed layer may be formed over an existing device topology (e.g., over a previously formed color filter layer, interlayer dielectric, semiconductor substrate, etc.). For example, a seed layer may first be deposited over the existing device topology using any suitable deposition process (e.g., a deposition process for inorganic materials).

At step 102, a microlens seed or seed pillar may be formed in the seed layer (e.g., by patterning and etching the seed layer). The seed pillars may be formed to have a desired shape (e.g., a pyramid shape as depicted in fig. 4, a shape with a non-planar top as depicted in fig. 5, a rectangular shape as depicted in fig. 3, or any other suitable shape or topology). For example, the seed layer may be selectively etched (e.g., using a masking layer) to form a seed pillar having a desired shape with desired (perimeter and top) lateral characteristics (e.g., curved sides, recessed portions, sloped sides, etc.). More than one masking layer and/or more than one etching step may be used to pattern and etch the seed layer, if desired.

At step 104, one or more microlens layers may be formed over the seed pillars to define microlens characteristics (e.g., final microlens shape, final microlens height, microlens radius of curvature, microlens radius, microlens lobe count, microlens reflectivity, etc.). For example, one or more microlens layers may be deposited using any suitable deposition process (e.g., a deposition process for inorganic materials). The microlens characteristics may be defined without an etch smoothing process (e.g., without etching one or more microlens layers). Microlens characteristics can be formed by forming one or more microlens layers based on different lateral and vertical deposition rates, using refractive index gradients, using passivation materials, using interlayer dielectric materials, and the like.

In some configurations, a method of forming microlenses in an imaging system includes forming a microlens seed structure, depositing a first microlens layer over the microlens seed structure, depositing a second microlens layer over the first microlens layer and over the microlens seed structure, and depositing a third microlens layer interposed between the first and second microlens layers. Depositing the first, second, and third microlens layers can include depositing one or more inorganic materials using a lateral deposition rate that is substantially different from a vertical deposition rate. The deposited second microlens layer can define a top surface topology of the microlenses (e.g., the deposited second microlens layer can have the same top surface as the top surfaces of the microlenses). The top surface topology may have a first curvature different from a second curvature of the top surface of the microlens seed structure.

As a first example, forming the microlens seed structure may include forming a top surface of the microlens seed structure as a flat surface, and forming a peripheral side of the microlens seed structure as an inclined surface. As a second example, forming the microlens seed structure may include forming a top surface of the microlens seed structure having a recessed portion having a first height from a base of the microlens seed structure and a protruding portion having a second height from the base of the microlens seed structure, the second height being greater than the first height, and forming a top surface of the microlens seed structure having an additional protruding portion having a second height from the base of the microlens seed structure, the recessed portion being interposed between the protruding portion and the additional protruding portion. The top surface topology of the microlens may have first and second lobes, the first lobe being at least partially defined by the raised portion and the second lobe being at least partially defined by the additional raised portion.

In some configurations, an image sensor may include an image sensor pixel array and a microlens overlapping a portion of the image sensor pixel array. The microlens may include: a microlens precursor structure having a top surface and a base opposite the top surface, the microlens precursor structure having a protruding portion at the top surface surrounding a recessed portion at the top surface; and depositing a microlens layer formed over a top surface of the microlens precursor structure, the deposited microlens layer defining a top surface of the microlenses.

As a first example, the protruding portion may include a first protruding structure and a second protruding structure having planar symmetry on a plane passing through the recessed portion, the first protruding structure at least partially defining a first lobe of the microlens, and the second protruding structure at least partially defining a second lobe of the microlens. The first lobes of the microlenses may be configured to focus light onto a first photosensitive region in the image sensor pixel array, and the second lobes of the microlenses may be configured to focus light onto a second photosensitive region in the image sensor pixel array. As a second example, the protruding portion may have radial symmetry about an axis passing through the recessed portion. The deposited microlens layer may have a recessed portion, and the axis may extend through the recessed portion. The protruding portion may have a first height from the base that is greater than a second height of the recessed portion from the base.

In some configurations, a microlens can include a microlens seed pillar having a top lateral width at a top surface, a bottom lateral width at a base greater than the top lateral width, and an inclined side plane connecting the top surface to the base, and can include a plurality of microlens layers formed over the microlens seed pillar, a topmost layer of the plurality of microlens layers defining a top surface topology of the microlens. The topmost layer may be unetched. The plurality of microlens layers are formed of at least one material of an oxide material, a nitride material, and an oxynitride material.

According to one embodiment, a method of forming a microlens in an imaging system may comprise: forming a microlens seed structure; and depositing a first microlens layer over the microlens seed structure. The deposited first microlens layer may define a top surface topology of the microlenses. The top surface topology may have a first curvature different from a second curvature of the top surface of the microlens seed structure.

According to another embodiment, the deposited first microlens layer may have a top surface that is the same as the top surface of the microlenses.

According to another embodiment, depositing the first microlens layer can include depositing an inorganic material.

According to another embodiment, depositing the first microlens layer can include depositing the inorganic material using a lateral deposition rate that is substantially different from a vertical deposition rate.

According to another embodiment, the first microlens layer may be formed of a gradient index material having a refractive index gradient.

According to another embodiment, the method of forming a microlens in an imaging system may further include: depositing a second microlens layer over the microlens seed structure; and depositing a third microlens layer interposed between the first and second microlens layers. The first microlens layer may have a first refractive index, the second microlens layer may have a second refractive index smaller than the first refractive index, and the third microlens layer may have a third refractive index larger than the first refractive index and smaller than the second refractive index.

According to another embodiment, forming the microlens seed structure may include: forming a top surface of the microlens seed structure into a flat surface; and forming a peripheral side of the microlens seed structure as an inclined surface.

According to another embodiment, forming the microlens seed structure may include forming a top surface of the microlens seed structure having a recessed portion having a first height from a base of the microlens seed structure and a protruding portion having a second height from the base of the microlens seed structure greater than the first height.

According to another embodiment, forming the microlens seed structure may include forming a top surface of the microlens seed structure with an additional protruding portion having a second height from a base of the microlens seed structure. The recessed portion may be interposed between the protruding portion and the additional protruding portion.

According to another embodiment, the top surface topology of the microlens may have a first lobe and a second lobe. The first lobes may be at least partially defined by the raised portions and the second lobes may be at least partially defined by the additional raised portions.

According to one embodiment, an image sensor may include an array of image sensor pixels; and a microlens overlapping a portion of the image sensor pixel array. The microlens can include a microlens precursor structure having a top surface and a base opposite the top surface. The microlens precursor structure can have a protruding portion at the top surface surrounding a recessed portion at the top surface. The microlens may also include a deposited microlens layer formed over a top surface of the microlens precursor structure. Depositing a microlens layer may define a top surface of the microlens.

According to another embodiment, the protruding portion may include a first protruding structure and a second protruding structure having planar symmetry on a plane passing through the recessed portion.

According to another embodiment, the first protrusion structure may at least partially define a first lobe of the microlens, and the second protrusion structure may at least partially define a second lobe of the microlens.

According to another embodiment, the first lobes of the microlenses may be configured to focus light onto a first photosensitive region in the image sensor pixel array, and the second lobes of the microlenses may be configured to focus light onto a second photosensitive region in the image sensor pixel array.

According to another embodiment, the protruding portion may have radial symmetry about an axis passing through the recessed portion.

According to another embodiment, the protruding portion may have a first height from the base that is greater than a second height of the recessed portion from the base.

According to another embodiment, the deposited microlens layer may have a recessed portion, and the axis may extend through the recessed portion.

According to one embodiment, the microlens may include: a microlens seed pillar having a top lateral width at a top surface, a bottom lateral width at a base greater than the top lateral width, and an inclined side plane connecting the top surface to the base; and a plurality of microlens layers formed over the microlens seed pillars. The topmost layer of the plurality of microlens layers may define a top surface topology of the microlenses.

According to another embodiment, the plurality of microlens layers may be formed of at least one material selected from the group consisting of an oxide material, a nitride material, and an oxynitride material.

According to another embodiment, the topmost layer may be unetched.

According to another embodiment, at least one microlens layer of the plurality of microlens layers may be formed of a passivation material.

The foregoing is considered as illustrative only of the principles of the invention, and numerous modifications are possible by those skilled in the art. The above-described embodiments may be implemented individually or in any combination.