阅读说明：本技术 无腔芯片级图像传感器封装 (Cavity-free chip-level image sensor package ) 是由 叶剑蝉 郭盈志 林蔚峰 范纯圣 于 2019-06-12 设计创作，主要内容包括：无腔芯片级图像传感器封装包括基板、微透镜阵列和低折射率层。基板包括形成像素阵列的多个像素。微透镜阵列包括多个微透镜，微透镜各自(i)具有透镜折射率、(ii)与多个像素中的相应一个对齐、以及(iii)具有背对多个像素中的相应一个的非平面微透镜表面。低折射率层具有小于透镜折射率的第一折射率。低折射率层还包括下表面，下表面的至少部分与每个非平面微透镜表面共形。微透镜阵列在像素阵列和低折射率层之间。(The cavity-free chip-level image sensor package includes a substrate, a microlens array, and a low refractive index layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses each having (i) a lens index of refraction, (ii) being aligned with a respective one of the plurality of pixels, and (iii) a non-planar microlens surface facing away from the respective one of the plurality of pixels. The low refractive index layer has a first refractive index smaller than a refractive index of the lens. The low refractive index layer also includes a lower surface, at least a portion of the lower surface conforming to each of the non-planar microlens surfaces. The microlens array is between the pixel array and the low refractive index layer.)

1. A cavity-less chip-scale image sensor package, comprising:

a substrate including a plurality of pixels forming a pixel array;

a microlens array comprising a plurality of microlenses each (i) having a lens index of refraction, (ii) being aligned with a respective one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels; and

a low index layer having a first index of refraction less than the index of refraction of the lens and a lower surface, at least a portion of the lower surface conformal with each non-planar microlens surface, the microlens array between the pixel array and the low index layer.

2. The cavity-less chip-scale image sensor package of claim 1, wherein the first refractive index is between 1.20 and 1.25.

3. The cavity-less chip-scale image sensor package of claim 1, wherein the thickness of the low refractive index layer over the apex of one of the plurality of microlenses is between 95 nanometers and 115 nanometers.

4. The cavity-less chip-scale image sensor package of claim 1, wherein the low refractive index layer has a quarter-wavelength optical thickness above a vertex of one of the plurality of microlenses at visible electromagnetic wavelengths.

5. The chamberless, chip-scale image sensor package of claim 4, wherein the visible electromagnetic wavelength is between 480 nanometers and 515 nanometers.

6. The cavity-less chip-scale image sensor package of claim 1, wherein the lens refractive index exceeds the first refractive index by at least 0.20 for a range of visible electromagnetic wavelengths.

7. The cavity-less chip-scale image sensor package of claim 1, wherein the low refractive index layer has a planar upper surface opposite the lower surface.

8. The cavity-less chip-scale image sensor package of claim 1, wherein the low refractive index layer has a non-planar upper surface opposite a lower surface, the non-planar upper surface conformal with the lower surface.

9. The cavity-less chip-scale image sensor package of claim 1, wherein the lower surface of the low refractive index layer abuts each non-planar microlens surface.

10. The cavity-less chip-scale image sensor package of claim 1, wherein the pixel array is configured to detect light incident to an upper die surface of the substrate, the upper die surface including bond pads adjacent to the pixel array and below the low index layer.

11. The cavity-less chip-scale image sensor package of claim 1, wherein the low refractive index layer is formed of a nanoporous material.

12. The cavity-less chip-scale image sensor package of claim 1, wherein the low refractive index layer completely covers the microlens array.

13. The cavity-less chip-scale image sensor package of claim 1, further comprising:

an adhesive layer adjacent to the low index layer such that the low index layer is between the microlens array and the adhesive layer; and

a protective glass disposed on the adhesive layer, opposite the adhesive layer,

the adhesive layer and the cover glass have a second refractive index and a third refractive index, respectively, each exceeding the first refractive index.

14. The cavity-less chip-scale image sensor package of claim 13, wherein the pixel array is configured to detect light incident to an upper die surface of the substrate, the upper die surface including bond pads adjacent to the pixel array and underlying each of the low index layer, the bonding layer, and the protective glass.

15. The cavity-less chip-scale image sensor package of claim 13, wherein the lens index of refraction, the second index of refraction, and the third index of refraction are approximately equal for a range of visible electromagnetic wavelengths such that a difference between each other is no greater than 0.08.

16. The cavity-less chip-scale image sensor package of claim 13, wherein the lens index of refraction, the second index of refraction, and the third index of refraction are in a range from 1.46 to 1.54 for a range of visible electromagnetic wavelengths.

17. The cavity-less chip-scale image sensor package of claim 13, wherein the bonding layer has a coefficient of thermal expansion of less than 200ppm/K for a temperature range less than a glass transition temperature of the plurality of microlenses.

18. The cavity-less chip-scale image sensor package of claim 13, wherein the adhesive layer has a thickness of between 5 and 10 microns.

19. A method for packaging an image sensor, comprising:

covering a pixel array of the image sensor with a low index layer having a first index of refraction, the image sensor including a microlens array including a plurality of microlenses that each (i) are aligned with a respective one of a plurality of pixels and (ii) have a non-planar microlens surface facing away from the respective one of the plurality of pixels, a lower surface of the low index layer conformal with each non-planar microlens surface.

20. The method of claim 19, wherein the low refractive index layer further comprises an upper surface opposite the lower surface, the method further comprising bonding a cover glass to the upper surface.

Technical Field

The present invention relates to image sensors, and in particular to packaging of pixel arrays for image sensors.

Background

Camera modules in products such as stand-alone digital cameras, mobile devices, automotive components, and medical devices typically include Complementary Metal Oxide Semiconductor (CMOS) image sensors. CMOS image sensors convert light from a scene imaged by a camera lens into a digital signal that is converted into a displayed image and/or a file containing image data. A CMOS image sensor includes an array of pixels and a corresponding array of microlenses, where each microlens focuses light onto a respective pixel. In many camera modules, the CMOS image sensor is part of a chip scale package that includes a protective layer over the photosensitive area of the CMOS image sensor. Common problems with existing image sensors include delamination and image artifacts caused by light reflected from the protective layer.

Disclosure of Invention

In a first aspect, a cavity-less chip scale image sensor package includes a substrate, a microlens array, and a low refractive index layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses each (i) having a lens reflectivity, (ii) being aligned with a respective one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels. The low refractive index layer has a first refractive index smaller than a refractive index of the lens. The low refractive index layer also includes a lower surface, at least a portion of the lower surface conforming to each of the non-planar microlens surfaces. The microlens array is between the pixel array and the low refractive index layer.

In a second aspect, a method for packaging an image sensor includes covering a pixel array of the image sensor with a low refractive index layer having a first refractive index. The image sensor includes a microlens array including a plurality of microlenses that each (i) are aligned with a respective one of the plurality of pixels, and (ii) have a non-planar microlens surface facing away from the respective one of the plurality of pixels. Covering the pixel array results in the lower surface of the low refractive index layer conforming to each non-planar microlens surface.

Drawings

Fig. 1 shows a camera including a chip-scale image sensor package.

Fig. 2 and 3 are a schematic cross-sectional view and a plan view, respectively, of a chip-scale image sensor package.

Fig. 4 is a schematic cross-sectional view of a first cavity-less chip-scale image sensor package according to an embodiment.

Fig. 5 is a schematic cross-sectional view of a second cavity-less chip-scale image sensor package in an embodiment.

Fig. 6 is a scanning electron microscope image of a third cavity-less chip scale image sensor package of an embodiment.

Fig. 7 is a schematic cross-sectional view of a fourth cavity-less chip-scale image sensor package according to an embodiment.

Fig. 8 is a schematic cross-sectional view of a fifth cavity-less chip-scale image sensor package in an embodiment.

Fig. 9 is a scanning electron microscope image of a sixth cavity-less chip scale image sensor package of an embodiment.

Fig. 10 is a graph illustrating the visible light transmittance of low index layers used in embodiments of the cavity-less chip-scale image sensor packages disclosed herein.

Fig. 11 is a graph showing the visible light transmittance of the low refractive index layer on the first side of the cover glass in the example.

Fig. 12 is a flow chart illustrating a method for packaging an image sensor in an embodiment.

Detailed Description

Fig. 1 shows a camera 190 imaging a scene. Camera 190 includes a chip-scale image sensor package 100, chip-scale image sensor package 100 including a pixel array 114. Hereinafter, "CSP" denotes "chip-scale image sensor package". Fig. 2 is a schematic cross-sectional view of the CSP 200, the CSP 200 being an example of the CSP 100. The cross-sectional view of fig. 2 is parallel to planes formed by orthogonal directions 298X and 298Z (298X and 298Z being orthogonal to direction 298Y, respectively). FIG. 3 is a plan view illustration of the CSP 200. In the following description, fig. 2 and 3 are best viewed together.

The CSP 200 includes a device substrate 210, a spacer 230, and a cover glass 250. For clarity of illustration, the cover glass 250 is not shown in fig. 3. The device substrate 210 includes a pixel array 214, the pixel array 214 configured to detect light transmitted by the cover glass 250. Pixel array 214 includes a plurality of pixels and is an example of pixel array 114. The CSP 200 may also include a microlens array 220. Microlens array 220 includes a plurality of microlenses that are each aligned with a respective one of the plurality of pixels of pixel array 214. The device substrate 210 may be a semiconductor die and may be formed of or may include a semiconductor (e.g., silicon, germanium, or a combination thereof). The device substrate 210 has an upper surface 219 perpendicular to the direction 298Z.

The spacers 230 are on the upper surface 219 of the device substrate 210 and at least partially surround the pixel array 214. The spacer 230 has an inner surface 231, an upper surface 232, and a lower surface 233. A cover glass 250 is attached to the upper surface 232 and covers the pixel array 214. The CSP 100 can include (a) an upper surface 232 and a lower surface 250B, and (B) an adhesive between at least one of the lower surface 233 and the upper surface 219.

The CSP 200 may also include one or more bond pads 205, a redistribution layer 206, and a dielectric layer 204. The redistribution layer 206 electrically connects the pixel array 214 to the conductors 204. The individual bond pads 205 have dimensions 205X and 205Y, each of which is, for example, 100 ± 20 μm. Fig. 2 designates a bare image sensor 229 including a device substrate 210, a pixel array 214, and a microlens array 220. The bare image sensor 229 may also include one or more of a redistribution layer 206, a dielectric layer 208, a conductor 204, and/or an adhesive pad 205. The dielectric layer 208 may be formed from a solder mask material, such as a polymer.

The cover glass 250 may be formed of aluminosilicate glass, alkali-free glass, borosilicate glass, quartz glass, or a combination thereof. Cover glass 250 has a thickness 259, for example, between 0.20 mm and 0.50 mm.

The CSP 200 has a disadvantage in that light transmitted through the cover glass 250 may be reflected by the inner surface 231 toward the microlens array 220, which results in artifacts of the image captured by the camera 190. A second disadvantage of the CSP 200 is that the spacers 230 are easily delaminated from the device substrate 210 and/or the cover glass 250.

FIG. 4 is a cross-sectional schematic view of a chamberless CSP 400, the CSP 400 being an example of the CSP 100 of the camera 190 of FIG. 1. The cavity-less CSP 400 includes a device substrate 410 and a low index layer 430. The device substrate 410 includes a pixel array 214 with a microlens array 220 on the pixel array 214. The microlens array 220 may be between the device substrate 210 and the low refractive index layer 430. Device substrate 410 is an example of device substrate 210.

The low refractive index layer 430 may serve the same protective function as the cover glass 250, with the cover glass 250 being supported by the spacers 230 in the CSP 200. Since the low index layer 430 does not require spacers 230, the low index layer provides the benefits of the cover glass 250 without the image artifacts and delamination problems previously described.

The low refractive index layer 430 has a refractive index n less than each microlens of the microlens array 220₂Refractive index n of₃. The microlens array 220 has a plurality of non-planar microlens surfaces 222 that each correspond to (e.g., are aligned with) a respective one of the plurality of microlenses. Microlens surface 222 can form a single continuous non-planar upper surface of microlens array 220. Microlens array 220 has a maximum height 225 above upper surface 219. The maximum height 225 may correspond to the apex or local maximum height of one or more of the non-planar microlens surfaces 222. Each microlens of microlens array 220 has a width (or diameter) between 0.8 and 10 microns in at least one of directions 298X or 298Y.

The low refractive index layer 430 has a lower surface 431 and an upper surface 439. The lower surface 431 includes a surface area 432 that conforms to the microlens surface 222. As shown in fig. 4, a low refractive index layer 430 covers the microlens array 220. Surface area 432 covers microlens array 220 and conforms to microlens surface 222. Low index layer 430 and/or surface area 432 may completely cover microlens array 220. For example, low index layer 430 and/or surface area 432 cover each microlens surface 222 and the area between adjacent microlens surfaces 222. Portions of lower surface 432 may conform to and may abut upper surface 210 of device substrate 410. Surface area 432 may correspond to the entirety of lower surface 431 without departing from the scope thereof. The upper surface 439 may be planar and may be parallel to the upper surface 219 of the device substrate 210 within manufacturing tolerances. The low index layer 430 may cover one or more bond pads 205 of the device substrate 410.

At the visible electromagnetic wavelength, the refractive index n of the microlens array₂The refractive index n of the low refractive index layer 430 may be exceeded by at least Δ n-0.2₃. Refractive index n of lens₂Can be in visible electromagnetic wavelengthAnd is in the range of 1.50 ± 0.04. Refractive index n₃May be between 1.20 and 1.25 at visible electromagnetic wavelengths. The low index layer 430 has a minimum thickness 437 between the surface region 432 and the upper surface 439. The minimum thickness 437 can be in a range between 100 and 110 nm. Minimum thickness 437 and refractive index n of low refractive index layer 439₃The product of (d) may correspond to a quarter wavelength light thickness at the visible electromagnetic wave length. For example, the visible electromagnetic wavelength may be between 480 nanometers and 515 nanometers, or between 525 nanometers and 575 nanometers. The foregoing ranges of refractive indices and thicknesses are advantageous for optimizing the amount of light incident on microlens array 220 onto pixel array 214.

The low refractive index layer 430 may be a nanoporous film or a nanoporous layer, for example, formed of silica or aluminum hydroxide (alo (oh)). When the low refractive index layer 430 is a nanoporous layer, such as an aerogel, the layer can include pores having a maximum width ("pore size") of less than one hundred nanometers, such that the pores do not scatter visible light. The average pore size (e.g., root mean square) may be between 7 nanometers and 15 nanometers, e.g., 10 nanometers. The low refractive index layer 430 may be formed via oblique angle deposition (a vapor deposition process).

FIG. 5 is a cross-sectional schematic view of a chamberless CSP500, the CSP500 being an example of CSP 100 of camera 190 of FIG. 1. The chamberless CSP500 includes a low index layer 530, an adhesive layer 540, and a protective glass 250 over the bare image sensor 229. The low refractive index layer 530 is an example of the low refractive index layer 430 and covers the adhesive pad 205 of the bare image sensor 229. In the chamberless CSP500, the bond pad 205 is under at least one of the low index layer 530, the bonding layer 540, and the cover glass 250. The low index layer 530 may be in direct contact with the bond pad 205. Judicious selection of the material of the low index layer 530 (e.g., its refractive index) may also result in increased transmission of light reaching the pixel array 214 as compared to the CSP 200.

The low refractive index layer 530 may completely cover the microlens array 220. In an embodiment, the low index layer 530 covers each microlens surface 222 and the area between adjacent microlens surfaces 222. Fig. 5 shows the surface region 254 and the side surface 252 of the lower surface 250B of the cover glass 250. Surface region 254 is above surface region 224 of microlens array 220. Surface region 224 may include: portions of a single or multiple microlens surfaces 222, surfaces between adjacent microlens surfaces 222, surfaces adjacent to microlens surfaces 222, or combinations thereof. Low index layer 530 may completely cover microlens array 220 such that volume elements 534 of low index layer 530 are located directly between surface region 254 and surface region 224.

The bonding layer 540 and the cover glass 250 have corresponding refractive indexes n₄And n₅Refractive index n₄And n₅May exceed the refractive index n of the low refractive index layer 530₃. Refractive index n₄And n₅May be approximately equal, e.g. | n₄-n₅|<0.08, which has the benefit of minimizing reflections from the lower surface 250B. At visible electromagnetic wavelengths, the refractive index n of the adhesive layer₄And refractive index n of protective glass₅May each be in the range of 1.50 ± 0.04.

The adhesive layer 540 may be an epoxy, such as a two-component epoxy, and may be room temperature curable. The bonding layer 540 may have physical properties amenable to applying a minimum pressure to the cover glass 250 and the low refractive index layer 530. For example, the temperature range Δ T at the glass transition temperature of the plurality of microlenses of microlens array 220_LIn some embodiments, the bonding layer 540 may have a coefficient of thermal expansion of less than 200 ppm/K. Temperature range Δ T_LMay have a lower boundary greater than or equal to-15 deg.c and may have an upper boundary less than the glass transition temperature. For example, the glass transition temperature is between 65 ℃ and 70 ℃. In an embodiment, at a temperature range Δ T_LThe bonding layer 540 has a coefficient of thermal expansion between 130ppm/K and 150ppm/K and an elastic modulus of less than 350 mPa. In an embodiment, at a temperature range Δ T_LAlso, the coefficient of thermal expansion of the bonding layer 540 is between 65ppm/K and 75ppm/K, and the coefficient of thermal expansion of the bonding layer 540 is between 200ppm/K and 220ppm/K at a temperature range above the glass transition temperature.

The adhesive layer 540 has a thickness 549 and side surfaces 542. Reducing thickness 549 results in improved optical performance, such as by minimizing reflected glare and absorption losses from side surface 542. In addition, reducing the thickness 549 also reduces process yield. Applicants have determined that a thickness 549 of between 5 microns and 10 microns is satisfactory for a tradeoff between performance and manufacturability.

The low refractive index layer 530 has a side surface 532. In an embodiment, the dielectric layer 208 extends upward (in a direction opposite to the direction 298Z) to cover at least one of the side surfaces 532, 542, and 252 of the low refractive index layer 530, the adhesive layer 540, and the cover glass 250, respectively.

Fig. 6 is a scanning electron microscope image 600 of a low refractive index layer 630 between a microlens array 620 and an adhesive layer 640. Low index layer 630 is an example of low index layers 430 and 530. Adhesive layer 640 is an example of adhesive layer 540. Microlens array 620 is an example of microlens array 220.

Microlens array 620 includes a plurality of microlenses each having a respective microlens center at a maximum height above device substrate 210. For example, plane 621 intersects at least one microlens center of microlens array 620. The following description of microlens array 620 and low index of refraction layer 630 considers scanning electron microscope image 600 as a cross section of microlens array 620 through the center of the microlenses, such that distance 624 is the diameter of the microlenses. The microlens array has a peak-to-valley height 622. Low index layer 630 has a thickness 632 over the center of one or more microlenses. The thickness 632 may be less than the peak-to-valley height 622.

FIG. 7 is a cross-sectional view of a chamberless CSP 700, CSP 700 being an example of CSP 100 of camera 190 of FIG. 1. The cavity-less CSP 700 includes a device substrate 410 and a low index layer 730. Microlens array 220 may be between device substrate 210 and low index layer 730.

The low refractive index layer 730 has a refractive index n₃As described above with respect to the low index layer 430 of fig. 4. The low refractive index layer 730 includes a lower surface 731 and an upper surface 739. Lower surface 731 includes surface regions 732 above microlens surface 222 that conform to microlens surface 222. The upper surface 739 includes a surface region 738 above both the microlens surface 222 and the surface region 732, the surface region 738 conforming to the surface region 732 below it, and thus also conforming to the microlens surface 222. Watch (A)The face regions 732 and 738 may each be directly above the plurality of microlens surfaces 222. The peaks and valleys of the surface region 738 may be aligned with the corresponding peaks and valleys of the surface region 732, and the peaks and valleys of the surface region 732 may be aligned with the corresponding peaks and valleys of the microlens surface 222. Surface region 738 may have a peak-to-valley height that is less than the peak-to-valley height of surface region 732. The conformality of surface regions 732 and 738 to microlens surface 222 may enhance the antireflective properties of low index layer 730 compared to low index layer 430.

The low index layer 730 may extend beyond the microlens array 220 such that the lower surface 731 abuts the upper surface 219 of the device substrate 210. In such embodiments, the low index layer 730 may cover one or more bond pads 205 of the device substrate 210. Alternatively, surface areas 732 and 738 may correspond to the entirety of lower surface 731 and upper surface 739, respectively.

Fig. 8 is a cross-sectional schematic view of a chamberless CSP 800, CSP 800 being an example of CSP 190 of camera 190 of fig. 1, chamberless CSP 800 including a low refractive index layer 830, an adhesive layer 840, and a protective glass 250 over bare image sensor 229. Low refractive index layer 830 is an example of low refractive index layer 730 and covers bond pad 205 of bare image sensor 229. In the cavity-less CSP 800, the adhesive pad 205 is under at least one of the low refractive index layer 830, the adhesive layer 840, and the protective glass 250. Low index layer 830 may be in direct contact with bond pad 205. The adhesive layer 840 may be formed of the same material as the adhesive layer 540, and thus may have a refractive index n₄. The bonding layer 840 has a minimum thickness 849 above the microlens array 220. The minimum thickness 849 suffers from similar constraints and ranges as the thickness 549 of the adhesive layer 540 of fig. 5. In an embodiment, the dielectric layer 208 extends upward (in a direction opposite to the direction 298Z) to cover respective side surfaces of at least one of the low refractive index layer 530, the adhesive layer 540, and the cover glass 250.

Fig. 9 is a scanning electron microscope image of a low refractive index layer 930 between microlens array 920 and bonding layer 940. Low index layer 930 is an example of low index layers 730 and 830. Bonding layer 940 is an example of bonding layer 540. Microlens array 620 is an example of microlens array 220. Low index layer 930 includes surface regions 932 and 928, which are examples of surface regions 732 and 738, respectively. Surface region 938 has a peak-to-valley height 938H that is less than a peak-to-valley height 932H of surface region 932.

The microlenses of the microlens array have a diameter 921, which can range from 1 to 12 microns. For example, when bare image sensor 229 is part of a mobile device, diameter 921 may be between 1.0 and 1.2 microns. When bare image sensor 229 is part of a full frame camera, diameter 921 may be between 8 and 9 microns. The peak-to-valley height 932H is, for example, between twenty-three percent and thirty-three percent of the diameter 921. The peak-to-valley height 938H is, for example, between thirteen percent and twenty-three percent of the diameter 921.

Fig. 10 is a graph 1000 illustrating visible light transmission 1010, 1020, and 1030, each of which represents transmission through a corresponding example of cover glass and low refractive index layer 530 on a first side thereof. The cover glass is an example of cover glass 250 and has a multilayer antireflective coating on a second side opposite the first side. Visible light transmittance 1010 corresponds to having a thickness t₁₀₁₀109nm and a refractive index n across the visible electromagnetic spectrum₁₀₁₀1.10 low refractive index layer. Visible light transmittance 1020 corresponds to having a thickness t₁₀₂₀105nm and a refractive index n between 1.20 and 1.25 across the visible electromagnetic spectrum₁₀₂₀The low refractive index layer of (1). Visible light transmittance 1030 corresponds to having a thickness t₁₀₃₀97nm and refractive index n across the visible electromagnetic spectrum₁₀₃₀1.30 low refractive index layer. Each of the foregoing thicknesses is the minimum thickness 437 of the low refractive index layer 430 of fig. 4.

The transmittances 1010, 1020 and 1030 correspond to quarter-wave thickness optical coatings with a design wavelength between 480nm and 525 nm. The low index layer 530 may have a refractive index and thickness such that its optical thickness is equal to the visible electromagnetic wavelength, e.g., a wavelength between 480nm and 525 nm.

Graph 1000 also includes visible light transmittance 1040, which is the transmittance of cover glass with multilayer coating but no low refractive index layer on the first side. The multilayer antireflective coating is a six layer coating comprising three alternating pairs of tantalum pentoxide and silicon dioxide layers. The layer thickness t (i) is: t (1-6) ═ 18.49, 28.45, 79.36, 6.75, 41.91, and 91.66 nanometers, where the odd layers (i is odd) are formed of tantalum pentoxide, and the even layers (i is even) are formed of silicon dioxide. The first layer (i ═ 1) is directly on the second side of the protective glass.

Fig. 11 is a graph 1100 illustrating visible light transmittance 1120 through a cover glass and a low refractive index layer on a first side thereof. The cover glass is an example of cover glass 250 and has a multilayer antireflective coating on a second side opposite the first side. Visible light transmittance 1120 corresponds to 105nm thick and has a refractive index n₁₀₂₀The low refractive index layer of (1).

Graph 1100 also includes visible light transmittance 1140, which is the transmittance of a cover glass having a multilayer coating but no low index layer on the first side. The multilayer antireflective coating is a10 layer coating comprising 5 alternating pairs of tantalum pentoxide and silicon dioxide layers. Layer thickness t (i) is t (1-10) ═ 8.32, 64.64, 10.45, 230.21, 20.94, 31.17, 83.2, 11.22, 38.28, and 97.16, where odd layers (layer index i is an odd integer) are formed of tantalum pentoxide, and even layers (layer index i is an even integer) are formed of silicon dioxide. The first layer (i ═ 1) is directly on the second side of the protective glass.

Fig. 12 is a flow chart illustrating a method 1200 for packaging an image sensor. Method 1200 includes at least one of steps 1210 and 1220. Step 1210 includes covering a pixel array of an image sensor with a low refractive index layer having a first refractive index. The image sensor includes a microlens array including a plurality of microlenses that each (i) are aligned with a respective one of the plurality of pixels, and (ii) have a respective one of a plurality of non-planar microlens surfaces facing away from the respective one of the plurality of pixels. Step 1210 results in the lower surface of the low refractive index layer conforming to each of the plurality of non-planar microscope surfaces. In step 1210, the low refractive index layer may be formed via a bevel deposition process, a spin coating process, a spray coating process, or a combination thereof. Step 1210 may be a wafer level process such that each pixel array of the plurality of image sensors of the device wafer is coated with a low refractive index layer in the same process step.

In a first example of step 1210, a low refractive index layer 430 (fig. 4) is deposited on bare image sensor 229 over pixel array 214 to cover microlens array 220. In a second example of step 1210, a low refractive index layer 730 (fig. 7) is deposited over bare image sensor 229, over pixel array 214 to cover microlens array 220.

Step 1210 may include covering the bond pads on a substrate in or on which the image sensor is formed. For example, step 1210 may include covering the adhesive pad 205 with a low index layer 430 or a low index layer 730.

Step 1220 includes bonding a cover glass to an upper surface of the low refractive index layer, the upper surface being opposite the lower surface. In a first example of step 1220, protective glass 250 is bonded to low index layer 530 by bonding layer 540, fig. 5. In the example of step 1220, protective glass 250 is bonded to low index layer 830 by bonding layer 840, fig. 8.

Feature combination

The features described above as well as those claimed below may be combined in various ways without departing from the scope thereof. The following examples illustrate some possible, non-limiting combinations:

(A1) a cavity-less chip scale image sensor package is shown comprising a substrate, a microlens array and a low index of refraction layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses each (i) having a lens index of refraction, (ii) being aligned with a respective one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels. The low index layer has a first index of refraction less than the index of refraction of the lens and a lower surface, at least a portion of the lower surface conformal with each non-planar microlens surface, the microlens array being between the pixel array and the low index layer.

(A2) In the cavity-less chip-level image sensor package represented by (a1), the first refractive index may be between 1.20 and 1.25.

(A3) In the cavity-less chip-scale image sensor package represented by one of (a1) and (a2), a thickness of the low refractive index layer over a vertex of one of the plurality of microlens arrays may be between 95 nanometers and 115 nanometers.

(A4) In the cavity-less chip-scale image sensor package represented by one of (a1) to (A3), the low refractive index layer may have a quarter-wavelength optical thickness above a vertex of one of the plurality of microlenses at the visible electromagnetic wave length.

(A5) In the cavity-less chip-scale image sensor package represented by one of (a1) to (a4), the visible electromagnetic wavelength may be between 480 nanometers and 515 nanometers.

(A6) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (a5), the lens refractive index may exceed the first refractive index by at least 0.20 as Δ n for a range of visible electromagnetic wavelengths.

(A7) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (a6), the low refractive index layer may have a planar upper surface opposite to the lower surface.

(A8) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (a6), the low refractive index layer may have a non-planar upper surface opposite to the lower surface that is conformal to the lower surface.

(A9) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (A8), the lower surface of the low refractive index layer may abut the plurality of non-planar microlens surfaces.

(A10) In a cavity-less chip-scale image sensor package as represented by one of (a1) through (a9), when the pixel array is configured to detect light incident on the upper die surface of the substrate, the upper die surface may include bond pads adjacent to the pixel array and below the low refractive index layer.

(A11) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (a10), the low refractive index layer may be formed of a nanoporous material.

(A12) In the cavity-less chip-scale image sensor package as represented by one of (a1) to (a11), the low refractive index layer may completely cover the microlens array.

(A13) The cavity-less chip-scale image sensor package as represented by one of (a1) to (a12) may further include an adhesive layer and a protective glass. The adhesive layer is adjacent to the low index layer such that the low index layer is between the microlens array and the adhesive layer. A cover glass is disposed on the adhesive layer opposite the low refractive index layer. The adhesive layer and the cover glass have a second refractive index and a third refractive index, respectively, each exceeding the first refractive index.

(A14) In a cavity-less chip-scale image sensor package as represented by (a13), when the pixel array is configured to detect light incident on an upper die surface of the substrate, the upper die surface may include bond pads adjacent to the pixel array and beneath each of the low refractive index layer, the bonding layer, and the protective glass.

(A15) In a cavity-less chip-scale image sensor package as represented by one of (a13) and (a14), the lens refractive index, the second refractive index, and the third refractive index may be approximately equal for a range of visible electromagnetic wavelengths, such that a difference therebetween is within Δ n of 0.08.

(A16) In the cavity-less chip-scale image sensor package as represented by one of (a13) to (a15), the lens refractive index, the second refractive index, and the third refractive index may be in a range from 1.46 to 1.54 for a range of visible electromagnetic wavelengths.

(A17) In the cavity-less chip-scale image sensor package as represented by one of (a13) to (a16), the adhesive layer may have a coefficient of thermal expansion of less than 200ppm/K for a temperature range less than a glass transition temperature of the plurality of microlenses.

(A18) In the cavity-less chip-scale image sensor package as represented by one of (a13) to (a17), the adhesive layer may be between 5 and 10 micrometers thick.

(B1) A method for packaging an image sensor is presented that includes covering a pixel array of the image sensor with a low refractive index layer having a first refractive index. The image sensor includes a microlens array including a plurality of microlenses each having (i) a lens index of refraction exceeding a first index of refraction, (ii) being aligned with a respective one of the plurality of pixels, and (iii) a non-planar microlens surface facing away from the respective one of the plurality of pixels.

(B2) In any of the methods represented by (B1), where the low refractive index layer includes an upper surface opposite a lower surface, the method may further include bonding a cover glass to the upper surface.

Changes may be made in the above methods and systems without departing from the scope thereof. It is, therefore, to be understood that the manner in which the above description is contained or illustrated in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. Herein, unless otherwise indicated, the adjective "exemplary" means serving as an example, instance, or illustration. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.