Image sensor and method of forming the same

Abstract

Embodiments of the present disclosure provide an image sensor and a method of forming the same. The method of forming the image sensor includes providing a substrate including a plurality of sensing portions; forming a color filter layer on the substrate; forming a microlens material layer on the color filter layer; and forming a hard mask pattern on the microlens material layer, wherein the hard mask pattern has a first gap and a second gap larger than the first gap. The method of forming the image sensor includes reflowing the hard mask pattern to form a plurality of round caps; transferring the round caps to the microlens material layer to form a plurality of microlenses; and forming a top membrane conformally on the microlenses.

Description

Technical Field

[0001] Embodiments of the present invention relate to an image sensor and a method for forming the same, and more particularly to the configuration of microlenses of the image sensor. Background Art

[0002] Image sensors, such as complementary metal oxide semiconductor image sensors (CIS), are widely used in image capture devices such as digital still cameras, digital still cameras, and other similar devices. The light sensing portion of an image sensor detects color changes in the environment and generates a signal charge based on the amount of light received by the light sensing portion. Furthermore, the signal charge generated in the light sensing portion is transmitted and amplified to obtain an image signal.

[0003] Due to industry demand, pixel size continues to shrink. To maintain high-level performance, a set of phase difference auto focus (PDAF) pixels can be integrated with traditional pixels. The light received by this set of PDAF pixels can be focused by color filters and collected at the corresponding sensing portion at the bottom, and the image focus of the device can be detected. However, image sensors with reduced pixel size may suffer from slight deviations in accuracy, which can significantly affect the overall performance of the image element. Therefore, the above and related issues need to be addressed through the design and manufacture of image sensors. Summary of the Invention

[0004] An object of the embodiments of the present invention is to provide an image sensor and a method for forming the same to solve at least one of the above problems.

[0005] In one embodiment, a method for forming an image sensor includes: providing a substrate including a plurality of sensing portions; forming a color filter layer on the substrate; forming a microlens material layer on the color filter layer; forming a hard mask pattern on the microlens material layer, wherein the hard mask pattern has a first gap and a second gap larger than the first gap; reflowing the hard mask pattern to form a plurality of domes; transferring the domes to the microlens material layer to form a plurality of microlenses; and forming a top film conformally on the microlenses.

[0006] In another embodiment, an image sensor includes: a plurality of autofocus sensing units; each autofocus sensing unit includes a plurality of sensing portions, a color filter layer disposed on the sensing portions, and a plurality of microlenses disposed on the color filter layer and correspondingly on the sensing portions; a top film conformally disposed on the microlenses; a seam having a first depth between the microlenses within one of the autofocus sensing units; and a gap having a second depth between the microlenses of the plurality of autofocus sensing units, wherein the second depth is greater than the first depth.

[0007] The advantageous effect of an embodiment of the present invention lies in forming a hard mask pattern on the microlens material layer, wherein the hard mask pattern has a first gap and a second gap larger than the first gap. This not only solves the problem of insufficient incident light received by each sensor portion, but also achieves the autofocus function of traditional phase-difference autofocus pixels. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following will be used in conjunction with the accompanying drawings to describe various aspects of the embodiments of the present disclosure in detail. It should be noted that, in accordance with standard industry practice, various features are not drawn to scale. In fact, the sizes of various elements may be arbitrarily enlarged or reduced to clearly illustrate the features of the embodiments of the present disclosure.

[0009] Figure 1 is a cross-sectional schematic diagram of an image sensor according to some embodiments of the present disclosure.

[0010] Figures 2A to 2E According to some embodiments of the present disclosure, Figure 1 Schematic cross-sections of an image sensor at various intermediate manufacturing stages.

[0011] Figure 3A-3B is a schematic cross-sectional view of another image sensor at various intermediate manufacturing stages according to another embodiment of the present disclosure.

[0012] Figure 4A-4B is a schematic cross-sectional view of another image sensor at various intermediate manufacturing stages according to another embodiment of the present disclosure.

[0013] The reference numerals are as follows:

[0014] 10: Image sensor

[0015] 20: Image sensor

[0016] 30: Image sensor

[0017] 100A: Autofocus sensor unit

[0018] 100A-L: Left autofocus sensor unit

[0019] 100A-R: Right autofocus sensor unit

[0020] 100B: Autofocus sensor unit

[0021] 100B-L: Left autofocus sensor unit

[0022] 100B-R: Right autofocus sensor unit

[0023] 102: Base

[0024] 104: Deep trench isolation structure

[0025] 106: Sensing unit

[0026] 110: Color filter layer

[0027] 112: Grid structure

[0028] 114: shading structure

[0029] 120: Microlens material layer

[0030] 122: Microlens

[0031] 124: Top membrane

[0032] 130: Hard mask layer

[0033] 132: Hard mask pattern

[0034] 140: Photomask

[0035] 140a: transparent part

[0036] 140b: non-transparent part

[0037] A: First gap

[0038] B: Second gap

[0039] D1: First depth

[0040] D1': first depth

[0041] D2: Second Depth

[0042] R1: First radius of curvature

[0043] R1': first radius of curvature

[0044] R2: Second radius of curvature DETAILED DESCRIPTION

[0045] The following disclosure provides many different embodiments or examples for implementing different components of the present invention. Specific examples of components and configurations are described below to simplify the embodiments of the present disclosure. Of course, these are merely examples and are not intended to limit the embodiments of the present disclosure. For example, the description of a first component being formed on a second component may include an embodiment in which the first and second components are in direct contact, and may also include an embodiment in which an additional component is formed between the first and second components so that the first and second components are not in direct contact.

[0046] It should be understood that additional operating steps may be implemented before, during, or after the method, and in other embodiments of the method, some operating steps may be replaced or omitted.

[0047] Additionally, spatially relative terms such as "below," "beneath," "lower," "above," "above," "upper," and the like may be used herein to describe the relationship of one element or component to other elements or components as illustrated in the figures. These spatial terms are intended to encompass different orientations of the device in use or operation, as well as the orientations depicted in the figures. When the device is otherwise oriented (rotated 90 degrees or at other orientations), the spatially relative descriptors used herein should be interpreted in that rotated orientation.

[0048] In the embodiments of the present disclosure, the terms "about," "approximately," and "substantially" generally mean within 20%, or within 10%, or within 5%, or within 3%, or within 2%, or within 1%, or even within 0.5% of a given value or range. The quantities given herein are approximate quantities. That is, in the absence of specific descriptions of "about," "approximately," and "substantially," the meanings of "about," "approximately," and "substantially" may still be implied.

[0049] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meanings as commonly understood by those skilled in the art. It should be understood that these terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with the background or context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal manner unless specifically defined in the embodiments of the present disclosure.

[0050] The different embodiments disclosed below may reuse the same reference symbols and / or signs. Such repetition is for the purpose of simplicity and clarity and is not intended to dominate the relationship between the various embodiments and / or structures discussed.

[0051] In response to the continued shrinking pixel size, the amount of light received by each pixel and the uniformity of light received between pixels have become key concerns. One way to improve the amount of light received in smaller pixels of an image sensor is to incorporate a group of autofocus sensing units (also known as phase difference auto focus (PDAF) pixels). According to some embodiments of the present disclosure, when light is received uniformly by each autofocus sensing unit (or pixel) in this group, the image sensor will be able to focus. However, if the light received by each autofocus sensing unit is uneven, the image sensor will be out of focus. Therefore, the autofocus sensing unit group can detect and track the image focus of the entire element. Traditionally, only a single microlens is set on the entire group of autofocus sensing units. In other words, all autofocus sensing units in its group share a single microlens, and the remaining sensing units are each provided with a microlens on top. The single microlens on the autofocus sensing unit group enables light to be converged together for the purpose of tracking and detection. For example, when light strikes at an oblique angle, one AF sensor within a group may receive a greater amount of light than another. Based on the signal reading between the AF sensors, the direction of the incident light can be accurately determined. However, conventional microlenses on an AF sensor group converge the incident light, focusing it at a single center point within the group. Consequently, each AF sensor within the group may not receive sufficient light to provide an accurate signal reading.

[0052] When process overlay occurs, the microlenses arranged on the autofocus sensing unit group may be misaligned. Since the amount of light received by each autofocus sensing unit is already insufficient, the overlap of the microlenses may cause some autofocus sensing units to receive too much light, while other autofocus sensing units may not actually receive any light. When the above situation occurs, the signal reading between the autofocus sensing units may be seriously misaligned, and the determination of the direction of the incident light may also be misaligned. The embodiment of the present disclosure provides an innovative microlens configuration method to solve the above problem. The microlens of the embodiment of the present disclosure can enable each autofocus sensing unit in the group to receive a sufficient amount of light, thereby increasing the process margin (process window). Therefore, even if process overlay occurs, the signal reading between the autofocus sensing units can still be appropriately used to track and detect the incident light. Furthermore, the embodiment of the present disclosure also includes a top film coated on the microlens to enhance the autofocus function of the image sensor.

[0053] Figure 1FIG1 is a cross-sectional view of an image sensor 10 according to some embodiments of the present disclosure. In some embodiments, the image sensor may actually include millions of sensing units. For the purpose of simplicity, Figure 1 Only a portion of the actual image sensor is shown. Figure 1 The image sensor 10 shown in includes two groups of autofocus sensing units 100A and 100B arranged adjacent to each other. From the upper diagram (not shown) of the image sensor 10, the autofocus sensing unit group 100A and the autofocus sensing unit group 100B may each include four sensing units arranged in 2×2, but the embodiments of the present disclosure are not limited to this. For example, from the upper diagram, the autofocus sensing unit group 100A and the autofocus sensing unit group 100B may be arranged in 1×2 or 2×1. In some embodiments, from the upper diagram, the autofocus sensing unit group 100A and the autofocus sensing unit group 100B may be arranged in 3×3, 4×4 or 5×5. For illustrative purposes, the autofocus sensing unit group 100A and the autofocus sensing unit group 100B each include a left autofocus sensing unit and a right autofocus sensing unit. In particular, the auto focus sensing cell group 100A includes a left auto focus sensing cell 100A-L and a right auto focus sensing cell 100A-R, and the auto focus sensing cell group 100B includes a left auto focus sensing cell 100B-L and a right auto focus sensing cell 100B-R.

[0054] It should be noted that if Figure 1 As shown, the autofocus sensing unit group 100A and the autofocus sensing unit group 100B each have multiple microlenses 122 instead of the traditional single microlens. The left autofocus sensing unit 100A-L and the right autofocus sensing unit 100A-R, or the left autofocus sensing unit 100B-L and the right autofocus sensing unit 100B-R, each have a microlens 122 disposed on the top thereof, corresponding to the sensing portion 106 of each autofocus sensing unit. Such a modification can increase the process margin by allowing a sufficient amount of incident light to be transmitted to each sensing portion 106 of the image sensor 10. At the same time, the microlenses 122 can include different gaps therebetween, and the inclusion of the top film 124 together can enhance the autofocus function of the autofocus sensing unit group 100A and the autofocus sensing unit group 100B.

[0055] refer to Figure 1AF sensing unit group 100A and AF sensing unit group 100B each include multiple sensing units 106, a color filter layer 110, and microlenses 122. The sensing units 106 may be embedded within a substrate 102. The substrate 102 also includes multiple deep trench isolation (DTI) structures 104 embedded therein. The DTI structures 104 separate the sensing units 106 and define the dimensions of each AF sensing unit. In some embodiments, the substrate 102 may be a single structure shared by all AF sensing units of the image sensor 10.

[0056] In some embodiments, the substrate 102 may be, for example, a wafer or a die, but the present disclosure is not limited thereto. In some embodiments, the substrate 102 may be a semiconductor substrate, such as a silicon substrate. Furthermore, in some embodiments, the semiconductor substrate may also be: an elemental semiconductor including germanium; a compound semiconductor including gallium nitride (GaN), silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs) and / or indium antimonide (InSb); an alloy semiconductor including silicon germanium (SiGe) alloy, gallium arsenide phosphide (GaAsP) alloy, aluminum indium arsenide (AlInAs) alloy, aluminum gallium arsenide (AlGaAs) alloy, gallium indium arsenide (InSb) alloy, and / or indium arsenide (InSb) alloy. In some embodiments, the substrate 102 may be a photoelectric conversion substrate, such as a silicon substrate or an organic photoelectric conversion layer.

[0057] In other embodiments, the substrate 102 may also be a semiconductor-on-insulator (SOI) substrate. The SOI substrate may include a base plate, a buried oxide (BOX) layer disposed on the base plate, and a semiconductor layer disposed on the BOX layer. Furthermore, the substrate 102 may be of N-type or P-type conductivity.

[0058] As described above, the substrate 102 may include a plurality of deep trench isolation structures 104 to define an active region and electrically isolate active region components within or on the substrate 102, but the embodiments of the present disclosure are not limited thereto. In some embodiments, other isolation structures may be applied as alternatives. Shallow trench isolation (STI) structure and local oxidation of silicon (LOCOS) are examples of other isolation structures. In some embodiments, forming a plurality of deep trench isolation structures 104 may include, for example, forming an insulating layer on the substrate 102, selectively etching the insulating layer and the substrate 102 to form trenches extending from the top surface of the substrate 102 into the substrate 102, wherein the trenches are located between adjacent sensing portions 106. Next, forming the plurality of deep trench isolation structures 104 may include growing a nitrogen-rich liner (e.g., silicon oxynitride (SiON)) along the trenches. Then, an insulating material (e.g., silicon dioxide (SiO2), silicon nitride (SiN), or silicon oxynitride) is deposited into the trenches. Subsequently, the insulating material in the trenches is annealed, and the substrate 102 is planarized to remove excess insulating material, ensuring that the insulating material in the trenches is flush with the top surface of the substrate 102.

[0059] In some embodiments, the substrate 102 may include various P-type doped regions and / or N-type doped regions (not shown) formed by processes such as ion implantation and / or diffusion. In some embodiments, transistors, photodiodes, or other similar devices may be formed in the active region (defined by the plurality of deep trench isolation structures 104).

[0060] As described above, the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B may each include a color filter layer 110 disposed on the substrate 102. In some embodiments, the height of the color filter layer 110 may be between approximately 0.3 μm and 2.0 μm. In some embodiments, the color filter layer 110 may include a plurality of cells, which may be red, green, blue, white, or infrared. Each cell of the color filter layer 110 may correspond to a respective sensing portion 106 of the image sensor 10, and the color of each cell depends on the individual requirements of the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B. The individual sensing portions 106 (e.g., photodiodes) may convert received light signals into electronic signals for each of the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B. In some embodiments, the auto-focus sensing units in the same group may have the same color cells. In some embodiments, the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B are separated from each other by a grid structure 112, which will be described in detail later. According to some embodiments of the present disclosure, a color filter layer 110 is deposited on the substrate 102 within the spaces defined by the grid structure 112. The color filter layer 110 can be formed through a series of coating, exposure, and development processes. Alternatively, the color filter layer 110 can be formed by inkjet printing.

[0061] refer to Figure 1 , a grid structure 112 is provided between one or more cells of the color filter layer 110. For example, a center line (not shown) of the grid structure 112 may define the boundary between the autofocus sensing unit group 100A and the autofocus sensing unit group 100B. According to some embodiments of the present disclosure, the grid structure 112 may have a refractive index (refractive index) lower than that of the color filter layer 110. The refractive index is a property of a substance that changes the speed of light, which is a value obtained by dividing the speed of light in a vacuum by the speed of light in a substance. When light propagates at an angle between two different materials, the refractive index determines the angle of light propagation (refraction). According to some embodiments of the present disclosure, the refractive index of the grid structure 112 is between approximately 1.00 and 1.99. When incident light enters the color filter layer 110, the grid structure 112 may isolate the light within a specific cell to achieve a light-trapping effect.

[0062] The material of the grid structure 112 may include a transparent dielectric material. First, an isolation material layer is coated on the substrate 102. Then, a hard mask layer (not shown) is coated on the isolation material layer. In some embodiments, the material of the hard mask layer is a photoresist. The hard mask layer is subjected to a photolithography process to pattern it. Then, an etching process is performed on the isolation material layer using the patterned hard mask layer. The etching process may be dry etching. After the etching process, a portion of the isolation material layer is removed on the substrate 102, and a plurality of openings are formed therein. As mentioned above, the openings will be filled with the color filter layer 110 later.

[0063] Continue to refer Figure 1 , a light shielding structure 114 is provided on the substrate 102 between the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B. In some embodiments, the light shielding structure 114 is embedded in the grid structure 112. In some embodiments, the height of the grid structure 112 may be greater than or equal to the light shielding structure 114, depending on the design requirements of the image sensor 10. In some embodiments, the light shielding structure 114 spans the boundary between the auto-focus sensing unit group 100A and the auto-focus sensing unit group 100B. In other words, the light shielding structure 114 is configured to be shared by any two adjacent auto-focus sensing units. The configuration of the light shielding structure 114 can prevent one of the sensing portions 106 below the unit of the corresponding color filter layer 110 from receiving light from an adjacent unit of a different color, which may affect the accuracy of signal reception. In some embodiments of the present disclosure, the height of the light shielding structure 114 may be between approximately 0.005 μm and 2.000 μm. In some embodiments, the material of the light shielding structure 114 may include an opaque metal (e.g., tungsten (W), aluminum (Al)), an opaque metal nitride (e.g., titanium nitride (TiN)), an opaque metal oxide (e.g., titanium oxide (TiO)), other suitable materials, or combinations thereof, but the present disclosure is not limited thereto. The light shielding structure 114 may be formed by depositing a metal layer on the substrate 102 and then patterning the metal layer using photolithography and etching processes, but the present disclosure is not limited thereto.

[0064] Continue to refer Figure 1, a microlens material layer 120 is provided on the color filter layer 110 and the grid structure 112. According to some embodiments of the present disclosure, a plurality of microlenses 122 are provided on the lens material layer 120, wherein the plurality of microlenses 122 correspond to the plurality of sensing portions 106. As previously stated, a conventional single microlens provided on the auto-focus sensing unit group 100A or the auto-focus sensing unit group 100B causes most of the light to converge on the center point of the auto-focus sensing unit group 100A or the auto-focus sensing unit group 100B. Unfortunately, when a conventional single microlens is used, the center point of the auto-focus sensing unit group 100A or the auto-focus sensing unit group 100B is the position of the deep trench isolation structure 104, rather than the position of any sensing portion 106. Therefore, the image sensor 10 of the present disclosure is designed to have a plurality of microlenses 122 corresponding to the plurality of sensing portions 106. Figure 1 The resulting structure shown can make most of the incident light converge on each sensing portion 106, thus solving the problem of light convergence.

[0065] Furthermore, the microlens 122 of the present disclosure is designed to have two or more different gaps to improve the autofocus function. It should be noted that forming multiple microlenses 122 (rather than a single microlens) may inadvertently disable the autofocus function. Since each autofocus sensing unit includes its own microlens 122, and the multiple microlenses 122 are the same, the light received by each sensing portion 106 will be substantially the same. The signal reading between the autofocus sensing units within the group does not allow the user to track and detect the incident light, and therefore cannot determine the direction of the incident light. In order to overcome this problem, the gaps between two adjacent microlenses 122 in the same group of the autofocus sensing unit group 100A or the autofocus sensing unit group 100B and the gaps between two adjacent microlenses 122 in the autofocus sensing unit group 100A and the autofocus sensing unit group 100B are designed to be different. For example, the gap between the microlenses 122 on the left auto-focus sensing unit 100A-L and the microlenses 122 on the right auto-focus sensing unit 100A-R of the auto-focus sensing unit group 100A is smaller than the gap between the microlenses 122 on the right auto-focus sensing unit 100A-R of the auto-focus sensing unit group 100A and the microlenses 122 on the left auto-focus sensing unit 100B-L of the auto-focus sensing unit group 100B. Research has found that the different gaps between the microlenses 122 allow the image sensor 10 to restore its original auto-focus function.

[0066] Furthermore, in the embodiment of the present disclosure, the top film 124 is introduced to further enhance the auto-focus function of the image sensor 10. Figure 1As shown, after the top film 124 is conformally deposited on the surfaces of the plurality of microlenses 122 (and on the exposed surface of the microlens material layer 120), the gaps between the microlenses 122 on the left auto-focus sensing cell 100A-L and the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A become seams having a first depth D1, while the gaps between the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A and the microlenses 122 on the left auto-focus sensing cell 100B-L of the auto-focus sensing cell group 100B have a second depth D2, wherein the first depth D1 is less than the second depth D2. Furthermore, the first depth D1 defines the seams between the microlenses 122 within the auto-focus sensing cell group 100A or the auto-focus sensing cell group 100B, and the portions of the microlenses 122 within the seams have a first radius of curvature R1. The second depth D2 defines a gap between the microlenses 122 of the autofocus sensing unit group 100A and the autofocus sensing unit group 100B, and the portion of the microlens 122 within the gap has a second radius of curvature R2. According to some embodiments of the present disclosure, the first radius of curvature R1 is greater than the second radius of curvature R2. The combination of the difference in gap size, gap depth, and curvature radius between the microlenses 122 enables the image sensor 10 to restore the autofocus function, and each sensing portion 106 can receive a sufficient amount of incident light.

[0067] like Figure 1 As shown, according to some embodiments, the image sensor of the present disclosure includes multiple sets of auto-focus sensing units 100A / 100B; each set of auto-focus sensing units 100A / 100B includes multiple sensing portions 106, a color filter layer 110 disposed on the sensing portions 106, and multiple microlenses 122 disposed on the color filter layer 110 and correspondingly on the sensing portions 106. The image sensor includes a top film 124 conformally disposed on the microlenses 122; seams between the microlenses 122 within one set of auto-focus sensing units 100A / 100B having a first depth D1; and gaps between the microlenses 122 in the multiple sets of auto-focus sensing units 100A / 100B having a second depth D2, wherein the second depth D2 is greater than the first depth D1.

[0068] Figures 2A to 2ESchematic cross-sectional views of the image sensor 10 at various intermediate manufacturing stages according to some embodiments of the present disclosure. Since the present embodiments primarily focus on the microlenses 122 and the top film 124, the process features of the substrate 102, the plurality of deep trench isolation structures 104, the plurality of sensing portions 106, the color filter layer 110, the mesh structure 112, and the light shielding structure 114 will not be described in detail here. According to some embodiments of the present disclosure, a microlens material layer 120 is disposed on the top surface of the color filter layer 110 and the mesh structure 112. In some embodiments, the material of the microlens material layer 120 may be a transparent material. For example, the material may include glass, epoxy resin, silicone resin, polyurethane, or any other suitable material or combination thereof, but the present embodiments are not limited thereto. Next, a hard mask layer 130 is formed on the microlens material layer 120. In some embodiments, the hard mask layer 130 includes any resin-containing material or a combination thereof. In some embodiments, the hard mask layer 130 may have a thickness less than that of the microlens material layer 120. In this embodiment, a photomask 140 is introduced in the fabrication of the image sensor 10, and is particularly used for patterning the hard mask layer 130. According to some embodiments of the present disclosure, the photomask 140 may include various transparent portions 140a and non-transparent portions 140b, which are used to pattern the hard mask layer 130 during a photolithography process.

[0069] In some embodiments, the photolithography process may include forming a photoresist (not shown) on the hard mask layer 130 by spin-on coating, followed by exposing the photoresist using a photomask 140. In this embodiment, the non-transparent portion 140b of the photomask 140 defines the portion of the hard mask layer 130 to be retained, while the transparent portion 140a of the photomask 140 defines the remaining portion of the hard mask layer 130 to be removed. The photomask 140 is designed so that the transparent portion 140a has a specific width, which corresponds to the gap size within the subsequently formed hard mask pattern 132. After exposure, the photoresist is developed. The hard mask layer 130 is then etched through the patterned photoresist, thereby completing the patterning of the hard mask layer 130.

[0070] refer to Figure 2BAfter photolithographic patterning and etching, the hard mask layer 130 may form a hard mask pattern 132. Based on the predetermined design of the photomask 140, the hard mask pattern 132 may include a first gap A and a second gap B between the remaining portions of the hard mask layer 130. According to some embodiments of the present disclosure, the size of the first gap A is between approximately 10% and 20% of the size of the auto-focus sensing unit, the size of which is defined by the multiple deep trench isolation structures 104, and the size of the second gap B is between approximately 30% and 40% of the size of the auto-focus sensing unit, the size of which is also defined by the multiple deep trench isolation structures 104.

[0071] refer to Figure 2C , a reflow process is performed on the hard mask pattern 132. The reflow process is performed by heating the hard mask pattern 132 at a temperature higher than the glass transition temperature of the hard mask layer 130. For example, the reflow process can be performed at a temperature between approximately 130°C and 160°C for a suitable duration (depending on the material of the hard mask layer 130). It should be noted that before the reflow process, the hard mask pattern 132 is substantially rectangular, while after the reflow process, the hard mask pattern 132 may become a dome. Furthermore, the reflow process will change the dimensions of the first gap A and the second gap B measured at the bottom of the hard mask pattern 132. Specifically, the reflow process will reduce the dimensions of the first gap A and the second gap B by approximately 10% to 30%.

[0072] refer to Figure 2D According to some embodiments of the present disclosure, the reflowed hard mask pattern 132 and the microlens material layer 120 are simultaneously etched through a dry etching process. In some embodiments, one or more cycles of the dry etching process may be performed until the shape of the hard mask pattern 132 is completely transferred to the microlens material layer 120. It should be noted that during the dry etching process, only the top portion of the microlens material layer 120 is etched, while the remaining bottom portion of the microlens material layer 120 is not etched. In some embodiments, the dry etching process may use an etching gas including carbon tetrafluoride (CF4), trifluoromethane (CHF3), octafluorocyclobutane (C4F8), nitrogen trifluoride (NF3), oxygen (O2), carbon dioxide (CO2), nitrogen (N2), or a combination thereof, and may be diluted in argon (Ar2). In this embodiment, the etching selectivity of the hard mask pattern 132 to the microlens material layer 120 can be controlled to be between approximately 1:1 and 1:3. After the dry etching process, a plurality of microlenses 122 may be generated on the top of the microlens material layer 120 , and the bottom of the microlens material layer 120 may serve as a base for the microlenses 122 .

[0073] refer to Figure 2E, a top film 124 is conformally deposited on the top surfaces of the plurality of microlenses 122 and the exposed surface of the bottom of the microlens material layer 120. In some embodiments, the top film 124 is a continuous structure that covers the entire surface of the image sensor 10. According to some embodiments of the present disclosure, the material of the top film 124 has a lower refractive index than the microlenses 122 (or the microlens material layer 120). In some embodiments, the top film 124 may be a transparent material, including, for example, glass, epoxy resin, silicone resin, polyurethane, other suitable materials, or a combination thereof, but the embodiments of the present disclosure are not limited thereto. The formation of the top film 124 may include a deposition process, which may include, for example, a spin coating process, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), other suitable methods, or a combination thereof.

[0074] According to some embodiments of the present disclosure, Figures 2A to 2E The process flow for manufacturing the image sensor 10 is shown. By having a hard mask pattern 132 with two different predetermined intervals (a first gap A and a second gap B), a microlens 122 with two types of gaps can be obtained: a relatively small gap within the autofocus sensing unit group 100A or the autofocus sensing unit group 100B, and another relatively large gap between the autofocus sensing unit group 100A and the autofocus sensing unit group 100B. According to some embodiments of the present disclosure, the inclusion of a top film 124 can increase the size difference between the two gaps. Furthermore, after depositing the top film 124, the relatively small gap can become a seam having a first depth D1 that is smaller than the second depth D2 of the relatively large gap. The above-mentioned features of the microlens 122 can not only solve the problem of insufficient incident light received by each sensing portion 106, but also achieve the autofocus function possessed by the conventional phase difference autofocus pixel.

[0075] Figure 3A and Figure 3B is a schematic cross-sectional view of another image sensor at various intermediate manufacturing stages according to another embodiment of the present disclosure. Figure 3A and Figure 3B The process flow of the image sensor 20 is shown. Figure 2E In the illustrated image sensor 10 and image sensor 20, the microlenses 122 within the auto-focus sensing unit group 100A or the auto-focus sensing unit group 100B are adjacent to each other. The features of the substrate 102, multiple deep trench isolation structures 104, multiple sensing portions 106, color filter layer 110, mesh structure 112, and light shielding structure 114 of the image sensor 20 are similar to those of the image sensor 10 and will not be repeated here.

[0076] refer to Figure 3A In this embodiment, the photomask 140 (not shown for simplicity) is designed so that the microlenses 122 obtained within the auto-focus sensing cell group 100A or the auto-focus sensing cell group 100B are substantially adjacent to each other. The gap between the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A of the image sensor 20 and the microlenses 122 on the left auto-focus sensing cell 100B-L of the auto-focus sensing cell group 100B is substantially equal to the gap between the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A and the microlenses 122 on the left auto-focus sensing cell 100B-L of the auto-focus sensing cell group 100B of the image sensor 10.

[0077] refer to Figure 3B A top film 124 is conformally deposited on the top surfaces of the plurality of microlenses 122 and the exposed bottom surface of the microlens material layer 120. In some embodiments, the top film 124 is a continuous structure that covers the entire surface of the image sensor 20. According to some embodiments of the present disclosure, the material of the top film 124 has a lower refractive index than the microlenses 122 (or the microlens material layer 120). After depositing the top film 124, the seams between the microlenses 122 on the left auto-focus sensing unit 100A-L and the microlenses 122 on the right auto-focus sensing unit 100A-R of the auto-focus sensing unit group 100A have a first depth D1', while the gaps between the microlenses 122 on the right auto-focus sensing unit 100A-R of the auto-focus sensing unit group 100A and the microlenses 122 on the left auto-focus sensing unit 100B-L of the auto-focus sensing unit group 100B have a second depth D2, wherein the first depth D1' is less than the second depth D2. It should be noted that the first depth D1 ′ of the image sensor 20 is smaller than the first depth D1 of the image sensor 10 , and the second depth D2 of the image sensor 20 is substantially equal to the second depth D2 of the image sensor 10 .

[0078] Continue to refer Figure 3B, the first depth D1' defines the seam between the microlenses 122 within the autofocus sensing unit group 100A or the autofocus sensing unit group 100B, and the portion of the microlens 122 within the seam has a first curvature radius R1'. The second depth D2 defines the gap between the microlenses 122 of the autofocus sensing unit group 100A and the autofocus sensing unit group 100B, and the portion of the microlens 122 within the gap has a second curvature radius R2. According to some embodiments of the present disclosure, the first curvature radius R1' is greater than the second curvature radius R2. It should be noted that the first curvature radius R1' of the image sensor 20 is greater than the first curvature radius R1 of the image sensor 10, and the second curvature radius R2 of the image sensor 20 is substantially equal to the second curvature radius R2 of the image sensor 10. Compared to image sensor 10, the resulting structure of image sensor 20 shows that the difference between first depth D1′ and second depth D2, and the difference between first radius of curvature R1′ and second radius of curvature R2, are both greater than the difference between first depth D1 and second depth D2, and the difference between first radius of curvature R1 and second radius of curvature R2 of image sensor 10. In some embodiments, image sensor 20 may have a more effective autofocus function than image sensor 10 to track and detect incident light.

[0079] Figure 4A and Figure 4B is a schematic cross-sectional view of another image sensor at various intermediate manufacturing stages according to another embodiment of the present disclosure. Figure 4A and Figure 4B The process flow of the image sensor 30 is shown. Figure 2E The image sensor 10 and Figure 3B In the illustrated image sensor 20 or image sensor 30, the microlenses 122 within the auto-focus sensing unit group 100A or auto-focus sensing unit group 100B overlap. The features of the substrate 102, multiple deep trench isolation structures 104, multiple sensing portions 106, color filter layer 110, mesh structure 112, and light shielding structure 114 of the image sensor 30 are similar to those of the image sensor 10 or image sensor 20 and will not be repeated here.

[0080] refer to Figure 4AIn this embodiment, the photomask 140 (not shown for simplicity) is designed so that the microlenses 122 obtained within the auto-focus sensing cell group 100A or the auto-focus sensing cell group 100B substantially overlap each other. The gap between the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A of the image sensor 30 and the microlenses 122 on the left auto-focus sensing cell 100B-L of the auto-focus sensing cell group 100B is substantially equal to the gap between the microlenses 122 on the right auto-focus sensing cell 100A-R of the auto-focus sensing cell group 100A and the microlenses 122 on the left auto-focus sensing cell 100B-L of the auto-focus sensing cell group 100B of the image sensor 10 or the image sensor 20.

[0081] refer to Figure 4B A top film 124 is conformally deposited on the top surfaces of the plurality of microlenses 122 and the exposed surface of the bottom of the microlens material layer 120. In some embodiments, the top film 124 is a continuous structure that covers the entire surface of the image sensor 30. According to some embodiments of the present disclosure, the material of the top film 124 has a lower refractive index than the microlenses 122 (or the microlens material layer 120). After the top film 124 is deposited, a substantially smooth top surface is formed between the microlenses 122 in the auto-focus sensing unit group 100A or the auto-focus sensing unit group 100B, wherein the first depth D1 no longer exists, while the gaps between the microlenses 122 on the right auto-focus sensing unit 100A-R of the auto-focus sensing unit group 100A and the microlenses 122 on the left auto-focus sensing unit 100B-L of the auto-focus sensing unit group 100B still have a second depth D2. It should be noted that the second depth D2 of the image sensor 30 is substantially equal to the second depth D2 of the image sensor 10 or the image sensor 20 .

[0082] Continue to refer Figure 4B It should be noted that, particularly in this embodiment, the portion of the top film 124 covering the autofocus sensing unit group 100A or the autofocus sensing unit group 100B appears to be a single microlens structure, which is very similar to a conventional phase difference autofocus pixel structure. The second depth D2 defines the gap between the microlenses 122 of the autofocus sensing unit group 100A and the autofocus sensing unit group 100B, and the portion of the microlens 122 within the gap has a second curvature radius R2. Compared to the image sensor 10 and the image sensor 20, the resulting structure of the image sensor 30 appears to have only one specific depth (e.g., the second depth D2) and one specific curvature radius (e.g., the second curvature radius R2). In this way, the image sensor 30 can function as a conventional phase difference autofocus pixel to track and detect incident light, but without the problem of insufficient incident light received by the sensing portion 106.

[0083] The above summarizes the components of several embodiments so that those skilled in the art can better understand the viewpoints of the embodiments of the present disclosure. Those skilled in the art should understand that they can design or modify other processes and structures based on the embodiments of the present disclosure to achieve the same purposes and / or advantages as the embodiments introduced herein. Those skilled in the art should also understand that such equivalent structures do not deviate from the spirit and scope of the embodiments of the present disclosure, and they can make various changes, substitutions and replacements without violating the spirit and scope of the embodiments of the present disclosure. Therefore, the scope of protection of the embodiments of the present disclosure shall be as defined by the appended claims. In addition, although the present disclosure has been disclosed as above with several preferred embodiments, they are not intended to limit the scope of the embodiments of the present disclosure.

[0084] References throughout this specification to features, advantages, or similar language do not imply that all features and advantages that may be achieved with embodiments of the present disclosure should or may be achieved in any single embodiment of the present disclosure. Rather, language referring to features and advantages is understood to mean that a particular feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, discussions of features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

[0085] Furthermore, in one or more embodiments, the described features, advantages, and characteristics of the embodiments of the present disclosure may be combined in any suitable manner. Based on the description herein, one skilled in the art will recognize that the embodiments of the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other cases, additional features and advantages may be identified in certain embodiments that may not be present in all embodiments of the present disclosure.

Claims

1. A method for forming an image sensor, comprising: Providing a substrate comprising a plurality of sensing portions; forming a color filter layer on the substrate; forming a microlens material layer on the color filter layer; forming a hard mask pattern on the microlens material layer, wherein the hard mask pattern has a first gap and a second gap larger than the first gap, wherein a portion of the hard mask pattern defined by the first gap corresponds to a single color unit of the color filter layer; reflowing the hard mask pattern to form a plurality of domes; transferring a plurality of the domes to the microlens material layer to form a plurality of microlenses; as well as A top film is formed conformably on the plurality of micro lenses.

2. The method for forming an image sensor as claimed in claim 1, wherein the substrate further comprises a plurality of deep trench isolation structures to separate the plurality of sensing portions, wherein the formation of the plurality of deep trench isolation structures defines the size of an auto-focus sensing unit.

3. The method for forming an image sensor as claimed in claim 2 , wherein two or more of the auto-focus sensing units constitute a group of auto-focus sensing units, and before forming the color filter layer on the substrate, the method further comprises forming a grid structure within the color filter layer, wherein the grid structure surrounds the group of auto-focus sensing units.

4. The method for forming an image sensor as described in claim 3, before forming the grid structure, further comprising forming a light shielding structure embedded in the grid structure, wherein the step of forming the hard mask pattern includes forming the first gap in the grid structure, and wherein the step of forming the hard mask pattern includes forming the second gap directly above the grid structure.

5. The method of forming an image sensor as claimed in claim 2 , wherein the first gap is between 10% and 20% of the size of the auto-focus sensing unit, and the second gap is between 30% and 40% of the size of the auto-focus sensing unit, wherein the second gap is located between two adjacent first gaps. 6 . The method for forming an image sensor as claimed in claim 1 , wherein the plurality of microlenses are formed only on a top portion of the microlens material layer, and wherein a refractive index of the top film is lower than a refractive index of the plurality of microlenses.

7. An image sensor comprising: Multiple autofocus sensor units; Each set of auto-focus sensing units includes a plurality of sensing portions, a color filter layer disposed on the plurality of sensing portions, and a plurality of micro lenses disposed on the color filter layer and correspondingly on the plurality of sensing portions; a top film, conformably disposed on the plurality of microlenses; a seam between the plurality of micro-lenses in one set of auto-focus sensing units and having a first depth, wherein the plurality of micro-lenses in the set of auto-focus sensing units correspond to a single color unit of the color filter layer; as well as A gap is between the plurality of micro lenses of the plurality of auto-focus sensing units and has a second depth, wherein the second depth is greater than the first depth. 8 . The image sensor as claimed in claim 7 , wherein the plurality of sensing portions are buried in a substrate, wherein the substrate further comprises a plurality of deep trench isolation structures separating the plurality of sensing portions.

9. The image sensor as claimed in claim 7, further comprising a grid structure in the color filter layer, and a light shielding structure embedded in the grid structure, wherein the grid structure separates each group of auto-focus sensing units.

10. The image sensor of claim 7 , wherein a portion of the plurality of microlenses within the seam has a first radius of curvature, and a different portion of the plurality of microlenses within the gap has a second radius of curvature, and the first radius of curvature is greater than the second radius of curvature; wherein the microlenses in each group of autofocus sensing units are separated from, adjacent to, or overlap with each other; wherein the refractive index of the top film is lower than the refractive index of the plurality of microlenses; and wherein the gap is located between two adjacent seams.

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