Image sensor charge directing structures and methods

Abstract

The invention relates to an image sensor charge directing structure and method. An electrostatic charge processing system includes an array of photodiodes, a metal grid coupled to the array of photodiodes, and a set of metal protrusions extending away from the metal grid. The set of metal protrusions may be configured to direct charge from one of an electrostatic discharge or an electrostatic charge into the metal grid.

Description

Technical Field

[0001] Aspects of this document generally relate to image sensor devices, such as devices for observing electromagnetic radiation. Background Art

[0002] Packages for semiconductor devices have been designed that allow electrical signals to be routed from the semiconductor die to a circuit board or motherboard to which the package is coupled. Various semiconductor packages have been developed that can protect the semiconductor die from moisture or mechanical stress. Summary of the invention

[0003] An electrostatic charge handling system includes a photodiode array, a metal grid coupled to the photodiode array, and a set of metal protrusions extending away from the metal grid. The set of metal protrusions can be configured to direct charge from one of electrostatic discharge or electrostatic charge into the metal grid.

[0004] An embodiment of a static charge management system may include one, all, or any of the following:

[0005] The set of metal protrusions may be located on a side of the metal grid opposite the photodiode array.

[0006] The set of metal protrusions may each be located at a set of intersection points of the metal grid.

[0007] The set of metal protrusions may be located in a layer of passivation material coupled to the metal grid.

[0008] A photodiode array may be included in a back-illuminated sensor.

[0009] The set of metal protrusions may include one of a rectangular prism, a circular cylinder, or a triangular prism.

[0010] The set of metal protrusions may include one of a square-based cone, a triangle-based cone, a cone, or a truncated cone.

[0011] Embodiments of an electrostatic charge handling system may include a photodiode array, a metal grid coupled on a first side of the photodiode array, and a set of metal protrusions coupled on a side of the metal grid opposite the first side of the photodiode array and extending away from the metal grid.

[0012] An embodiment of a static charge management system may include one, all, or any of the following:

[0013] The set of metal protrusions may each be located at a set of intersection points of the metal grid.

[0014] The set of metal protrusions may each be positioned along the metal grid.

[0015] The set of metal protrusions may be located in a layer of passivation material coupled to a side of the metal grid opposite the first side of the photodiode array.

[0016] A photodiode array may be included in a back-illuminated sensor.

[0017] The set of metal protrusions may include one of a rectangular prism, a circular cylinder, or a triangular prism.

[0018] The set of metal protrusions may include one of a square-based cone, a triangle-based cone, a cone, or a truncated cone.

[0019] An embodiment of a method of processing charge may include providing a photodiode array and a set of metal protrusions, a metal grid coupled to a first side of the photodiode array, the set of metal protrusions coupled to the metal grid on a side of the metal grid opposite the first side of the photodiode array and extending away from the metal grid. The method may also include directing the charge into the metal grid.

[0020] An embodiment of a method of processing charge may include one, all, or any of the following:

[0021] The method may include the case where the metal grid is grounded, and may further include using the metal grid to direct the charge to the ground.

[0022] Receiving the charge may also include receiving the charge from a passivation layer.

[0023] The set of metal protrusions may be formed in the passivation layer.

[0024] The charge may be from one of an electrostatic discharge event or static electricity.

[0025] A photodiode array may be included in a back-illuminated sensor.

[0026] The foregoing and other aspects, features and advantages will be apparent to those skilled in the art from the detailed description and accompanying drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Specific implementations will be described below in conjunction with the accompanying drawings, in which like reference numerals represent like elements, and:

[0028] Figure 1 is a top view of one embodiment of a metal grid over a photodiode array;

[0029] Figure 2 are cross-sectional views of a first embodiment of a metal grid and a metal tab and a second embodiment of a metal grid and a metal tab; and

[0030] Figure 3 is a table showing various shapes of various embodiments of the metal tabs. DETAILED DESCRIPTION

[0031] The present disclosure, its aspects, and specific implementations are not limited to the specific components, assembly processes, or method elements disclosed herein. Many additional components, assembly processes, and / or method elements known in the art that meet the intended image sensor charge directing structures and methods will be readily apparent for use with the specific embodiments of the present disclosure. Thus, for example, although the present invention discloses specific embodiments, such embodiments and implementation components may include any shape, size, style, type, model, version, measurement, concentration, material, quantity, method element, step, etc. known in the art for such image sensor charge directing structures and implementation components and methods that meet the intended operation and methods.

[0032] Image sensor devices may exhibit image artifacts resulting from charge that generates an electric field that disrupts the electrical isolation between individual pixels in the pixel array (photodiode array), resulting in "charge sharing" in clusters of pixels. In images generated by the image sensor device, these image artifacts may appear as drops or spot-like defects in the image. In some embodiments, the charge is generated by an electrostatic discharge (ESD) event that traps the charge in a layer of passivation material included in the image sensor device, particularly on the back side of the image sensor device. In other embodiments, the charge may be a static charge accumulated on the image sensor device / back side of the image sensor device.

[0033] This image artifact effect due to charge storage has been observed in the case of photodiode arrays included in backside illuminated (BSI) sensors. However, the ability of charge to produce image artifacts using this mechanism may exist in a variety of image sensor types.

[0034] In various image sensor systems, a grid of metallic material (metal grid) is used to help handle charge buildup on a photodiode array that forms a pixel array of an image sensor device. The metal grid may be coupled to one side of the photodiode array. In some image sensor embodiments, the metal grid is coupled to the underside of the photodiode array, or to the side of the photodiode array opposite to where other devices such as microlenses, color filter arrays, or light-transmissive covers are adjacent to or coupled to the photodiode array. However, in other embodiments, the metal grid may be coupled to the side of the photodiode array that faces / faces the image sensor device itself. In some embodiments, the metal grid is attached to an electrical ground (ground); in other embodiments, the metal grid is electrically free-floating relative to ground. It has been observed that a metal grid alone does help reduce image artifacts due to charge, but in some cases and / or for some image sensor device types, image artifacts cannot be eliminated because charge cannot reach the metal grid from the material surrounding the metal grid / photodiode array.

[0035] refer to Figure 1 , shows a portion of one embodiment of an image sensor 2, which includes a photodiode array (pixel array) 4, with a metal grid 6 coupled above the photodiode array. It must be understood that Figure 1 Only a small portion of the photodiode array is shown, so the structure of the metal grid 6 is repeated over the entire, substantially most, most, or a portion of the photodiode array 4. Figure 1 are shown in the same layer, but in some embodiments, the metal grid may include features that physically intersect each other while maintaining electrical contact with each other. Figure 1 , a set of metal protrusions 8 extending upward from the page are shown. During operation of the image sensor device, the metal protrusions 8 collect charge and direct the charge into the metal grid 6. As previously discussed, the charge collected by the metal protrusions 8 may be from the charge of an ESD event, and / or may be static charge accumulated on / in the photodiode array. In this way, the charge collection and directing operation of the metal protrusions 8 may be analogous to the operation of a lightning rod, but on a microscopic scale. However, the operation of the metal protrusions 8 and the lightning rod differs in one important respect, namely that the lightning rod is designed to both receive charge from lightning and act as a point source that releases ionized molecules into the surrounding air during a thunderstorm to help reduce the chance of an actual lightning strike during a thunderstorm. In contrast, the metal protrusions 8 are used to collect charge and direct it downward into the metal grid, and therefore specifically do not release any charge during operation of the image sensor device.

[0036] exist Figure 1In the illustrated embodiment, each metal protrusion in the set of metal protrusions 8 in this embodiment is shown as being located at an intersection 10 of the metal grid 6. In this embodiment, each intersection 10 includes a metal protrusion 8 coupled thereto. In other embodiments, the ratio of metal protrusions to intersections may be less than 1:1, with non-limiting examples such as 1:2, 1:3, 1:5, 1:10, or other desired ratios designed to deliver a certain / desired / required charge handling effect. This ratio may also be achieved in a variety of ways, where for a 1:2 ratio, the metal protrusions 8 may be coupled at every other intersection 10, or the coupling pattern may be such that the metal protrusions are coupled in two adjacent intersections 10 and then skip two adjacent intersections. In various system embodiments, various patterns or even random patterns may be used to position the metal protrusions in the intersections.

[0037] Although Figure 1 The illustrated embodiment shows each of the metal protrusions in a set of metal protrusions 8 located at an intersection 10 of the metal grid 6, but in other embodiments, the metal protrusions may be located at other locations along the metal grid, such as along either or both sets of intersecting metal traces that form the metal grid 6. In this way, the set of metal protrusions are positioned along the metal grid, rather than at the intersections of the metal grid. In these embodiments, the concentration of metal protrusions at certain locations on the pixel array / photodiode array can be used to help disperse charge away from known locations on the device (particularly electrostatic charge sensitive locations). The use of concentrations of metal protrusions can also be used to help route charge away from certain areas in the array more quickly, or to move charge to a metal layer more quickly (similar to the electrical traces that span the surface of the pixel array, but instead are made of closely spaced metal protrusions).

[0038] refer to Figure 2 , shows one embodiment of a metal grid 12 that includes two metal protrusions 14 coupled thereto. In the cross-sectional view in this embodiment, the metal grid 12 is coupled to a portion of a photodiode array 16. In this embodiment, the side 18 of the photodiode array 16 that is coupled to the metal layer 12 is the back side of the photodiode array 16, or the side opposite to the side that receives electromagnetic radiation and may include a microlens, a color filter array, or faces a light-transmissive cover. As shown in this embodiment, the two metal protrusions 14 are freestanding, or in other words, they extend from the metal layer 12 without being surrounded by any other supporting / packaging material. In this embodiment, the use of the metal protrusions 14 increases the total surface area of ​​the metal layer 12 and also creates a focusing point on the metal layer 12, which helps to collect / absorb static charges adjacent to the metal layer 12 to route them into the material of the metal layer 12.

[0039] Reference again Figure 2 , a second embodiment of a metal grid 20 is shown that includes metal protrusions 22 extending therefrom. This metal grid 20 is coupled to the back side 26 of the photodiode array 24, similar to the previously described embodiments. In this embodiment, the metal protrusions 22 are located in the passivation material layer 28. Since the backside passivation material is where charge storage has been observed to occur after an ESD event, the ability of the metal protrusions 22 to directly contact the passivation material layer 28 on the back side 26 of the photodiode array 24 can facilitate the collection / absorption of charge into the metal protrusions 22 and then direct the charge downward into the metal grid 20. Although in this embodiment, the metal protrusions 22 are shown as extending completely through the material of the passivation material 28, in other embodiments, the metal protrusions 22 may only partially extend into the thickness of the passivation material layer 28, such that the ends are covered by the passivation material layer.

[0040] Because the metal bumps 14, 22 are freestanding or located only in the passivation material layer 28, the metal bumps 14, 22 do not participate in the process of collecting photon-generated charge in the silicon substrate / photodiode array 16, 24 itself. Therefore, the function of the metal bumps 14, 22 is to help handle charge in the form of static charge or storage charge from the ESD event, rather than to provide / collect any charge used by the photodiode / image sensor to form an image generated by electromagnetic radiation. In various image sensor embodiments disclosed herein, electromagnetic radiation of a wide range of wavelengths may be employed, non-limiting examples of which include infrared light, ultraviolet light, visible light, microwaves, radio waves, x-rays, or any other type of electromagnetic radiation to which the photodiode array is responsive.

[0041] refer to Figure 2 , the freestanding metal protrusion 14 can be formed in a subtractive process, in which a patterned layer is formed on the metal layer. The patterned layer can be formed using a photolithography process involving a patterned photoresist or by using a hard mask process, in which a photolithography / etching process is used to etch an oxide / nitride pattern, which is then used to etch away the metal layer (except where the pattern exists), leaving a set of metal pillars that form the metal protrusion 14. In embodiments of the present method, metal etching can be performed using a dry or wet etching process. In various embodiments using a patterned photoresist, the photoresist will typically be removed after etching the metal protrusion 14. In various embodiments, the hard mask material can be left on the metal protrusion 14, or can be removed depending on the desired conductivity required for the metal protrusion 14. In various method and structural embodiments, the metal material used for the metal protrusion 14 can be the same as the metal material of the metal layer 12; in other method and structural embodiments, the metal materials used for the metal protrusion 14 and the metal layer 12 can be different.

[0042] In another method embodiment, the metal protrusions may be formed using a damascene or additive process, wherein a layer of oxide, nitride, or passivation material is deposited over the metal layer, openings are then formed therein, and metal is deposited into these openings using a chemical vapor deposition process (such as when tungsten is used) or using an electroplating process (such as when copper is used). A chemical mechanical planarization (CMP) process may then be used to lower the deposited metal to the surface of the oxide, nitride, or passivation material layer and electrically insulate the top surfaces of the metal protrusions from each other. The remaining oxide, nitride, or passivation material is then etched away, leaving freestanding metal protrusions 14.

[0043] The aforementioned inlay process can also be used to form Figure 2 The second embodiment shown differs in that the passivation material 28 is not etched away, thereby leaving the metal protrusion 22 within the passivation material 28, as shown. In some embodiments, a damascene process can be used to form the metal layer 20 and the metal protrusion 22 in two different steps. Various method embodiments for forming the metal protrusion can be constructed using the principles disclosed herein.

[0044] refer to Figure 3 , schematic diagrams showing various possible shapes of metal protrusions. In the left column, the side cross-sectional views show prisms (constant or substantially constant cross-section for the metal protrusions) and cones (tapered cross-section for the metal protrusions). Although not shown in the side cross-sectional views, in various embodiments, truncated cone shapes can also be used for the side cross-sections of the various metal protrusions. Figure 3 Three non-limiting examples of cross-sectional shapes of metal protrusions are shown in the schematic diagram of FIG. 1 , namely, circular, square, and triangular. In the case where the cross section is circular and the side cross-sectional view is a prism, the resulting shape will be a circular cylinder. In the case where the cross section is square / rectangular and the side cross-sectional view is a prism, the resulting shape will be a cube / cuboid. In the case where the cross section is triangular and the side cross-sectional view is a prism, the resulting shape is a triangular prism.

[0045] Similarly, in the case where the cross-sectional shape of the bottom of the cone is circular or elliptical, the resulting shape of the metal protrusion is a cone. In the case where the cross-sectional shape is square or rectangular, a square-based pyramid is obtained. In the case where the cross-sectional shape is triangular, the resulting shape is a triangle-based pyramid.

[0046] Although Figure 3The side cross-sectional views in the drawings are shown as having straight sides, but in various embodiments, these sides may be curved or rounded, thereby forming a prism with curved or rounded side surfaces. In addition, although a circle / ellipse, square / rectangle, and triangle are shown, the cross-sectional shape of the metal protrusion may take any of a variety of shapes, including but not limited to a parallelogram, a pentagon, a hexagon, an octagon, or any other closed shape. In this way, using the principles disclosed in this document, a prism or cone having any of a variety of cross-sectional shapes may be formed.

[0047] The image sensor charge directing structures disclosed herein may be included in a backside illuminated sensor.

[0048] The image sensor charge directing structures disclosed herein may be located on a side of the metal grid opposite the photodiode array.

[0049] The image sensor charge directing structures disclosed herein may include rectangular prisms, cylinders, triangular prisms, square-based cones, triangle-based cones, cones, or truncated cones.

[0050] The image sensor charge directing structures disclosed herein may include the case where the set of metal protrusions are formed in a passivation layer.

[0051] The image sensor charge directing structures disclosed herein may include situations where the charge comes from one of an electrostatic discharge event or static electricity.

[0052] Where the above description mentions specific embodiments of image sensor charge steering structures and methods and implementing components, sub-components, methods and sub-methods, it should be readily apparent that various modifications may be made without departing from the spirit thereof, and that these embodiments, implementing components, sub-components, methods and sub-methods may be applied to other image sensor charge steering structures and methods.

Claims

1. A static charge processing system, comprising: Photodiode array; a metal grid coupled to the photodiode array; and A set of metal protrusions extend away from the metal grid, the set of metal protrusions being configured to direct charge from one of an electrostatic discharge or a static charge into the metal grid. 2 . The system of claim 1 , wherein the set of metal protrusions are each located at a set of intersections of the metal grid. 3 . The system of claim 1 , wherein the set of metal protrusions are located in a layer of passivation material coupled to the metal grid.

4. The system of claim 1, wherein the set of metal protrusions comprises one of a rectangular prism, a cylinder, a triangular prism, a square-based cone, a triangle-based cone, a cone, or a truncated cone.

5. A static charge processing system, comprising: Photodiode array; a metal grid coupled to a first side of the photodiode array; and A set of metal protrusions are coupled to a side of the metal grid opposite the first side of the photodiode array and extend away from the metal grid. 6 . The system of claim 5 , wherein the set of metal protrusions are each located at a set of intersections of the metal grid or are each located along the metal grid.

7. The system of claim 5, wherein the set of metal protrusions are located in a layer of passivation material coupled to the side of the metal grid opposite the first side of the photodiode array.

8. A method for processing electric charge, the method comprising: providing a photodiode array and a set of metal protrusions, a metal grid coupled to a first side of the photodiode array, the set of metal protrusions coupled to the metal grid on a side of the metal grid opposite the first side of the photodiode array and extending away from the metal grid; receiving an electric charge into the set of metal protrusions; as well as The charges are directed into the metal grid.

9. The method of claim 8, further comprising the case where the metal grid is grounded, and the charges are directed to the ground using the metal grid.

10. The method of claim 8, wherein receiving charge further comprises receiving charge from a passivation layer.

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