Pad for image sensor and related method

Abstract

The invention relates to a pad for an image sensor and a related method. Particular implementations of a pad for an image sensor may include: a pad base coupled in a pad opening formed in an image sensor die; and a metal layer directly coupled to the pad base extending to a top surface of the pad opening. The pad base may be directly coupled with the first metallization layer of the image sensor die.

Description

Background Art 1. Technical Field

[0001] Aspects of this document generally relate to semiconductor packages, such as packages for image sensor semiconductor devices. 2. Background technology

[0003] Semiconductor packages have been designed to allow electrical interconnections to be formed between the semiconductor die and a circuit board or motherboard to which the semiconductor package is attached. Various semiconductor packages are also used to protect the semiconductor die from environmental factors such as moisture or electrostatic discharge. Summary of the invention

[0004] A specific implementation of a pad for an image sensor may include: a pad base coupled in a pad opening formed in an image sensor die; and a metal layer directly coupled to the pad base extending to a top surface of the pad opening. The pad base may be directly coupled to a first metallization layer of the image sensor die.

[0005] Specific implementations of the pads of the image sensor may include one, all, or any of the following:

[0006] The metal layer may be a single layer of metal.

[0007] The metal layer may be electroless plated.

[0008] The pad base may include aluminum.

[0009] The metal layer may be nickel.

[0010] The pad may include a gold layer directly coupled to the metal layer.

[0011] The perimeter of the metal layer may be within the perimeter of the pad pedestal.

[0012] Implementations of a method of forming a pad for an image sensor may include providing a pad pedestal coupled to a pad opening formed in an image sensor die; and electrolessly plating a metal layer directly onto the pad pedestal to a top surface of the pad opening.

[0013] Specific implementations of the method of forming a pad for an image sensor may include one, all, or any of the following:

[0014] The electroless metal layer may include electroless nickel.

[0015] The method may include forming a gold layer directly on the metal layer.

[0016] The method may include applying an adhesive directly over the metal layer while simultaneously bonding the light-transmissive cover over the image sensor die.

[0017] The cavity wall may be included between the adhesive and the light-transmissive cover.

[0018] The metal layer may be flush with a plane formed by a top surface of the pad opening.

[0019] The metal layer may be substantially flush with a plane formed by a top surface of the pad opening.

[0020] A specific implementation of a method of forming a pad for an image sensor may include: forming a pad opening in an image sensor die; forming a pad pedestal in the pad opening; and electrolessly plating a metal layer onto the pad pedestal, the metal layer being substantially flush with a top surface of the pad opening.

[0021] Specific implementations of the method of forming a pad for an image sensor may include one, all, or any of the following:

[0022] The electroless metal layer may include electroless nickel.

[0023] The method may include forming a gold layer directly on the metal layer.

[0024] The method may include applying an adhesive directly over the metal layer while simultaneously bonding the light-transmissive cover over the image sensor die.

[0025] The cavity wall may be included between the adhesive and the light-transmissive cover.

[0026] The perimeter of the metal layer may be within the perimeter of the pad pedestal.

[0027] 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

[0028] Specific implementations will be described below in conjunction with the accompanying drawings, in which like reference numerals represent like elements, and:

[0029] Figure 1 are cross-sectional and detailed views of a specific implementation of an image sensor die having pad openings;

[0030] Figure 2 are cross-sectional and detailed views of a specific implementation of an image sensor die having a metal layer coupled directly to a pad base;

[0031] Figure 3 is a cross-sectional view of a specific implementation of an image sensor die having filled pad openings coupled to a light-transmissive cover;

[0032] Figure 4is a cross-sectional view of an image sensor die having a pad opening;

[0033] Figure 5 is a cross-sectional view of an image sensor die having populated pad openings;

[0034] Figure 6 is a cross-sectional view of a light-transmitting cover;

[0035] Figure 7 is a cross-sectional view of a light-transmissive cover having a cavity wall and an adhesive coupled thereto;

[0036] Figure 8 Before bonding Figure 7 Light-transmitting cover Figure 5 a cross-sectional view of an image sensor die;

[0037] Fig. 9 After bonding Figure 5 Image sensor die and Figure 7 A cross-sectional view of a light-transmitting cover;

[0038] Fig.10 is a cross-sectional view of the bonded image sensor die and light-transmissive cover after additional packaging operations including interconnect formation; and

[0039] Fig.11 After the cutting operation Fig.10 Cross-sectional view of a bonded image sensor die. DETAILED DESCRIPTION

[0040] 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 conform to the intended pads of an image sensor will be readily apparent for use with specific specific implementations of the present disclosure. Thus, for example, although the present invention discloses specific implementations, such specific implementations and implementation components may include any shape, size, style, type, model, version, measurement, concentration, material, quantity, method element, step, etc. of such pads for image sensors and implementation components and methods known in the art that conform to the intended operation and method.

[0041] In various image sensor devices, the absorption of light by silicon depends on the thickness of the silicon. In order to achieve the desired level of quantum efficiency, a thicker silicon layer is used. In some image sensor devices, the silicon is formed as an epitaxial layer. For specific wavelengths of light, such as near infrared, thicker silicon is required to help achieve an image sensor device with a desired level of quantum efficiency. Because the epitaxial silicon is grown after the back-end layers of the image sensor device are formed, forming an electrical connection on the side of the device where the epitaxial silicon has been formed means removing the entire thickness of the epitaxial layer to form a pad opening for reaching the bonding pad. With the thickness of the epitaxial layer measured in microns, it becomes challenging to try to bond to pads that are 3 microns, 6 microns, 8 microns or deeper into the material of the image sensor.

[0042] Furthermore, even in cases where the pads are used only for probe or other electrical testing prior to additional semiconductor packaging steps, the space formed by the pad openings may create voids where the adhesive used to couple the image sensor device to the cavity wall of the light-transmissive cover fails to completely fill the pad openings. In various image sensor devices, photoresists or other organic materials have been used to fill the pad openings. However, the ability of photoresists or other organic materials to completely fill the pad openings depends on the process capabilities of the coating / application technology used to apply the photoresist, and thus the risk of voids is not completely eliminated.

[0043] refer to Figure 1 , a cross-sectional view of a specific implementation of an image sensor device 2 is illustrated in a die-level view and a detail view showing the structure of a pad opening 4. The die-level view shows the structure of the image sensor device 2 at a detail level that intentionally exaggerates the size of the pad opening 4 for better illustration. The detail view shows the pad opening 4 at a more realistic scale relative to other structures of the image sensor device 2. As shown, the pad opening 4 includes a pad base 6 that has been formed in the bottom of the pad opening and is electrically coupled to the metallization layer 8 of the image sensor device 2. In this specific implementation, because the image sensor device 2 is a backside integrated (BSI) image sensor device, the pad base 6 is electrically coupled to the first metallization layer 10 of the device. In this particular implementation of the image sensor device 2, the pad base 6 is used for electrical testing purposes before bonding a light-transmitting cover. Other image sensor devices such as pixel array 12 and other electrical interconnects and associated pads 14 are included along with other electrical routing structures that allow hybrid bonding of this image sensor device to another semiconductor device 16 such as a digital signal processor.

[0044] The height 18 of the pad opening 4 creates a significant space between the surface of the pad base 6 and the top 20 of the pad opening 4. The top 20 of the pad opening 4 forms a plane parallel to the largest flat surface 22 of the image sensor device. If the pad opening 4 can be filled without gaps up to the plane formed by the top 20 of the pad opening 4, there will be no gaps for adhesive later in the process. In various specific implementations, the pad base 6 can be made of aluminum, but in other specific implementations, other metals can be used.

[0045] refer to Figure 2 , again illustrating the image sensor device 2 in a die-level view and a detailed view, showing that the entire pad opening 4 has been filled with a metal layer 24 up to the top 20 of the pad opening, thereby creating a planarized surface. Because direct electrical connection to the pad base 6 may be difficult to make with a pad base buried in the depth of the pad opening, and because of the bonding of the image sensor die, electroless plating is used to form / deposit the metal layer 24. As shown Figure 2 As shown, the metal layer 24 may also include one or more additional layers of other metals 26 directly coupled to the metal layer 24, such as, but not limited to, gold, palladium, copper, any combination thereof, or any other electrolessly plateable or depositable metal material. The one or additional metal layers 26 may form a desired surface finish on the metal layer 24. However, in other implementations, the metal layer 24 may be only a single layer of metal material formed using electroless plating. In a specific implementation, the metal layer 24 is made of nickel.

[0046] pass Figure 2 In the inspection, the pad base 6 has a perimeter 28, because it is a pad having a perimeter extending to Figure 2 The cross-sectional drawing of the three-dimensional object with dimensions inside and outside the drawing. Similarly, the metal layer 24 also has a Figure 2 6. In various implementations, the perimeter 30 of the metal layer 24 is within the perimeter 28 of the pad base 6. In a particular implementation, the perimeter 30 may be at least partially within the perimeter 28, wherein portions of the perimeter 30 extend over or beyond the perimeter 28 of the pad base 6. In other implementations, the perimeter 30 of the metal layer 24 is completely within the perimeter 30 of the pad base 6, wherein all portions of the perimeter 30 are physically located within the perimeter 28. In some implementations, the perimeter 30 of the metal layer 24 may be coextensive or the same size as the perimeter 28 of the pad base 6.

[0047] refer to Figure 3, illustrates the image sensor device 2 after light-transmitting cover 32 is bonded thereto using cavity wall 34 and adhesive 36. Note that since metal layer 24 fills pad opening up to top surface 20, adhesive 36 can be evenly spread over the entire width of metal layer 24 of pad opening 4. Figure 3 The package embodiment 38 of FIG. 3 illustrates the use of cavity wall 34 to form air gap 40, but in other embodiments, air gap 40 may not exist. In these gapless image sensor embodiments, a material that extends completely across image sensor array 12 can be used to bond the light-transmissive cover. In some embodiments, this material can have a specifically selected refractive index. Because the adhesive can be evenly spread over pad opening 4, the formation of voids in the adhesive can be prevented.

[0048] Various implementations of the method of forming a pad for an image sensor may be used to form implementations of the pad for the image sensor. Figures 4 to 9 A single image sensor device and a light-transmitting cover are illustrated in cross-sectional views, but the same principles and method elements may also be applied across an entire wafer, substrate, or panel in various implementations. Figures 4 to 9 The image in is similar in detail to Figure 1 and Figure 2 The die-level views in the drawings are for the purpose of easier illustration and do not necessarily show the various components to scale.

[0049] refer to Figure 4 , illustrates a specific implementation of an image sensor device 42, which shows a pad opening 44 and an image sensor array (indicated by a microlens array 46). It should be understood that in various specific implementations, more than two pad openings may be present in each image sensor device and may be distributed in various locations around the outer edge of the image sensor device. Within each pad opening 44 is a pad base (for illustration purposes, the pad base is shown in FIG. Figure 4 ), similar to any pad base disclosed in this document.

[0050] refer to Figure 5 , illustrates an image sensor device 42 after pad opening 44 is filled with a metal layer 48. The process of forming metal layer 48 is electroless plating using any metal material disclosed in this document, which can be electrolessly plated on the material of the pad base. As shown, metal layer 48 is flush with the plane formed by the top surface of the pad opening. However, in some specific implementations, metal layer 48 can be substantially flush with the plane formed by the top surface of pad opening 44, because metal layer 48 can extend slightly above or below the plane.

[0051] Figure 6A specific implementation of a light-transmissive cover 50 sized to fit over the image sensor device 42 is illustrated. In the case of processing at the wafer or substrate level, the light-transmissive cover 50 may take on a shape corresponding to the wafer or substrate to allow wafer-level or substrate-level processing. The material of the light-transmissive cover may be translucent or transparent to the desired wavelengths of electromagnetic radiation that the image sensor device 2 is designed to detect. Figure 7 The light-transmissive cover 50 is illustrated after a cavity wall 52 is formed / coupled around the perimeter of the light-transmissive cover 50 and then an adhesive glue 54 is applied to the surface of the cavity wall 52. The cavity wall 52 can be formed of a variety of materials, including, by way of non-limiting example, epoxy, resin, light-transmissive organic compound, optically opaque organic compound, molding compound, or any other structure capable of bonding / coupling with the material of the light-transmissive cover 50. In some implementations, the material of the cavity wall 52 can be selected for its ability to chemically bond with the material of the light-transmissive cover 50. In other implementations, the material of the cavity wall 52 can be separately bonded to the light-transmissive cover using another glue or other adhesive material.

[0052] In various method implementations, the placement of the adhesive can be achieved by using a wide variety of techniques, including, by way of non-limiting example, template printing, jet printing, contact printing, or any other liquid dispensing technique. As non-limiting examples, the material of the adhesive can be a heat-curing adhesive, an ultraviolet (UV) curing adhesive, an evaporation curing adhesive, any combination thereof, or any other adhesive type. In some implementations, the adhesive can be light-transmissive (translucent or transparent) or optically opaque.

[0053] refer to Figure 8 , image sensor device 42 is illustrated adjacent light transmissive cover 50 immediately prior to the bonding process, showing the alignment of metal layer 48 with bonding glue 54 . Fig. 9 The image sensor package 56 is illustrated after using adhesive 54 over the metal layer 48 to bond the light-transmissive cover 60 to the image sensor device 42. An air gap 58 is illustrated as being formed in the image sensor package 56 through the spacing of the cavity 52. Fig. 9 As shown in , because metal layer 48 is flush or substantially flush with the largest planar surface of image sensor device 42 , no voids are observed to form in the material of adhesive glue 54 .

[0054] After forming image sensor package 56, some method implementations may employ additional package formation steps to create additional wiring layers to permit electrical connections to be made between the image sensor device (and any other semiconductor devices bonded thereto) and the final circuit board or motherboard to which the image sensor package will be attached. Fig.10, illustrates two image sensor devices 62 after a light-transmissive cover 64 is bonded over the two devices using an adhesive glue using any material or method disclosed herein. As shown, the image sensor device 62 includes a metal layer 66 formed using any material and method disclosed herein within corresponding pad openings. A side 72 of the image sensor device 62 opposite the pixel array 68 has been thinned and etched to expose the pad base of the metal layer 66 (not shown for easier illustration). Conductive traces 71 have then been formed to connect the metal layer 66 and form a redistribution / routing layer along one side 72 of the image sensor device 62. A solder mask 70 is illustrated as having been deposited over the conductive traces 71 to help passivate the rear surface of the image sensor device 62. By way of non-limiting example, these conductive traces 71 may be formed using electroplating, electroless plating, sputtering, or any other method of depositing conductive material. In this way, electrical connections can be routed from the pixel array 68 side of the image sensor device 62 to the opposite side 72 of the image sensor device 62.

[0055] Fig.11 The image sensor package 74 is illustrated after an opening has been etched in the solder mask 70 into which balls 76 have been dropped and coupled to the conductive traces 71. These balls 76 may be formed of a variety of materials including, as non-limiting examples, solder, copper, any combination thereof, or any other conductive material. In this manner, the resulting package forms a ball grid array (BGA) that can be used to couple to a circuit board or motherboard. Traces then route electrical signals from the metal layer 66 to the balls 76 or from the pixel side of the image sensor device 62 to the balls 76. After the balls 76 are applied, the image sensor device 62 and the light-transmissive cover 64 are then singulated to form the image sensor package 74.

[0056] exist Figure 10 to Figure 11 In the illustrated image sensor device implementation 62, the pad base is not directly located on the metallization layer of the image sensor die 62 because the pad base material is eventually exposed and coupled to the trace 71, as shown in FIG. Figure 1 to Figure 2 In the embodiments of the present invention, the pad base can be located adjacent to the metallization layers and can be attached to the pads of one of those metallization layers. However, in two image sensor device embodiments, the ability to fill the pad openings with chemically deposited metal facilitates the desired electrical connection without creating the possibility of void formation. This ability to be used in a variety of image sensor device configurations and embodiments while permitting adhesion of a light-transmissive cover by substantially avoiding the creation of voids can be an advantage of embodiments of the methods disclosed herein.

[0057] Specific implementations of pads for image sensors may include situations where the pad base includes aluminum. Specific implementations may include situations where the metal layer is nickel. Specific implementations of pads for image sensors may include a gold layer directly coupled to the metal layer. Specific implementations of methods for forming pads for image sensors may include a cavity wall between an adhesive and a light-transmitting cover. Specific implementations of methods for forming pads for image sensors may also include situations where the metal layer is flush with a plane formed by the top surface of the pad opening or substantially flush with a plane formed by the top surface of the pad opening. In various specific implementations, the perimeter of the metal layer may be within the perimeter of the pad base.

[0058] Where reference is made in the above description to specific implementations of pads of an image sensor and to implementation components, sub-components, methods and sub-methods, it should be apparent that various modifications may be made without departing from the essence thereof, and that these implementations, implementation components, sub-components, methods and sub-methods may be applied to other pads of an image sensor.

Claims

1. A pad for an image sensor, comprising: a pad base coupled to a pad opening formed in the image sensor die; and a metal layer directly coupled to the pad base, the metal layer extending to a top surface of the pad opening; The pad base is directly coupled to the first metallization layer of the image sensor die. The pad according to claim 1 , wherein the metal layer is a single layer of metal. The pad according to claim 1 , wherein the metal layer is electroless plated. The pad of claim 1 , wherein a perimeter of the metal layer is located within a perimeter of the pad base.

5. A method for forming a pad of an image sensor, comprising: providing a pad pedestal coupled to a pad opening formed in the image sensor die; as well as A metal layer is electrolessly plated directly onto the pad pedestal to a top surface of the pad opening. The method of claim 5 , wherein electrolessly plating the metal layer further comprises electrolessly plating nickel. 7 . The method of claim 5 , further comprising applying an adhesive glue directly over the metal layer while bonding a light transmissive cover over the image sensor die.

8. A method for forming a pad of an image sensor, comprising: forming a pad opening in the image sensor die; forming a pad pedestal in the pad opening; as well as A metal layer is electrolessly plated onto the pad pedestal, the metal layer being substantially flush with a top surface of the pad opening.

9. The method of claim 8, wherein electrolessly plating the metal layer further comprises electrolessly plating nickel.

10. The method of claim 8, further comprising applying an adhesive paste directly over the metal layer while bonding a light transmissive cover over the image sensor die.

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