CHIP PACKAGE AND FABRICATION METHOD THEREOF

[0001] This application claims the benefit of U.S. Provisional Application No. 61/249,399, filed on Oct. 7, 2009, the entirety of which is incorporated by reference herein.

[0002] 1. Field of the Invention

[0003] The present invention relates to a chip package, and in particular relates to a chip package with a through hole and a redistribution layer and a fabrication method thereof.

[0004] 2. Description of the Related Art

[0005] For conventional chip package technologies, chips are adhered to a print circuit board and then electrically connected to the print circuit board by a wire bonding method. Finally, the areas for wire bonding are covered with an encapsulant to form the conventional chip packages.

[0006] However, in the conventional chip packages, the encapsulant protrudes inward or outward at the wire bonding areas, such that the conventional chip packages have a concave and convex surface. When the conventional chip packages are applied to fingerprint readers, the concave and convex surface of the conventional chip packages reduces identification efficiency of fingerprints.

[0007] Therefore, a chip package design with a flat surface and a fabrication method thereof are thus desired.

[0008] According to an illustrative embodiment, a chip package is provided. The chip package comprises a semiconductor substrate, having a first surface and an opposite second surface, wherein the semiconductor substrate contains a semiconductor component and a conductive pad disposed on the first surface. A through hole extends from the second surface of the semiconductor substrate to the conductive pad. A redistribution layer is disposed under the second surface of the semiconductor substrate and electrically connected to the conductive pad in the through hole, wherein an edge of the redistribution layer is exposed at a sidewall of the semiconductor substrate. Then, a conductive trace layer is disposed below the redistribution layer, extending to the sidewall of the semiconductor substrate to electrically contact with the redistribution layer.

[0009] According to another illustrative embodiment, a method for fabricating a chip package is provided. The method comprises providing a semiconductor wafer, having a first surface and an opposite second surface, wherein the semiconductor wafer contains a plurality of semiconductor components and a plurality of conductive pads disposed on the first surface. A plurality of through holes is formed, extending from the second surface of the semiconductor wafer to the conductive pads. A redistribution layer is formed under the second surface of the semiconductor wafer, electrically connecting to the conductive pads in the through holes, and an edge of the redistribution layer is exposed at a sidewall of the semiconductor wafer. Then, a conductive trace layer is formed below the redistribution layer, extending to the sidewall of the semiconductor wafer to electrically contact with the redistribution layer.

[0010] A detailed description is given in the following embodiments with reference to the accompanying drawings.

[0013] The following description is of a mode for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Wherever possible, the same reference numbers are used in the drawings and the descriptions to refer the same or like parts. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual dimensions to practice of the invention. Further, parts of the elements in the drawings may be illustrated by the following description. Some elements not shown in the drawings are known by one skilled the art.

[0014] The embodiments of chip packages of the invention and fabrication methods thereof are illustrated by embodiments of fabricating image sensor chip packages, such as those used for fingerprint readers, in the following description. However, it should be appreciated that the invention may also be applied to forming other semiconductor chips. Therefore, the packages of the embodiments of the invention may be applied to active or passive devices, or electronic components with digital or analog circuits, such as optoelectronic devices, micro electro mechanical systems (MEMS), micro fluidic systems, and physical sensors for detecting heat, light, or pressure. Particularly, a wafer scale package (WSP) process may be applied to package semiconductor chips, such as image sensor devices, solar cells, RF circuits, accelerators, gyroscopes, micro actuators, surface acoustic wave devices, pressure sensors, and ink printer heads.

[0015] The wafer level packaging process herein mainly means that after the packaging process is accomplished during a wafer stage, a wafer with chips is cut to obtain separate independent packages. However, in an embodiment of the invention, separate independent chips may be redistributed overlying a supporting wafer and then be packaged, which may also be referred to as a wafer level packaging process. In addition, the wafer level packaging process may also be adapted to form chip packages of multi-layered integrated circuit devices by stacking a plurality of wafers having integrated circuits together.

[0016] An embodiment of the invention provides a chip package and a fabrication method thereof, using process technologies of forming a through hole and a T-shaped contact to make the chip packages with a flat sensor surface.

[0017] Referring to FIGS. 1A-1J, cross sections illustrating the steps for fabricating a chip package according to an embodiment of the invention are shown. As shown in FIG. 1A, first, a semiconductor substrate 100, generally a semiconductor wafer such as a silicon wafer or a silicon substrate is provided. Moreover, there is a plurality of device areas 100A defined on the semiconductor substrate and each device area 100A is surrounded by a peripheral bonding pad area 100B. The device area 100A and the peripheral bonding pad area 100B are combined to form a portion of a die area.

[0018] Next, a semiconductor device 102 is formed on the device area 100A, for example a fingerprint reader, an image sensor device or other micro electro mechanical structures. An intermetal dielectric (BID) layer 103 is formed to cover the semiconductor substrate 100 and the semiconductor device 102. The intermetal dielectric layer 103 can be selected from low dielectric constant (low k) insulating materials, such as porous oxides. Then, a plurality of conductive pad structures 104 is formed in the intermetal dielectric layer 103 at the peripheral bonding pad area 100B. In this embodiment, the conductive pad structure 104 includes a plurality of metal layers, which are preferably formed from copper (Cu), aluminum (Al) or other suitable metal materials.

[0019] Moreover, the semiconductor substrate 100 may be covered with a chip passivation layer 106. The chip passivation layer 106 is defined to form a plurality of openings 106h in advance to expose the conductive pad structures.

[0020] Then, referring to FIG. 1B, a carrier layer 110, for example a semiconductor substrate or a glass substrate is provided. The semiconductor substrate for the carrier layer may be another blank silicon wafer. The carrier layer 110 is bonded to a first surface 100a of the semiconductor wafer 100 by an adhesive layer 108. The adhesive layer 108 may be an adhesive agent containing epoxy resin. In order to simply illustrate the embodiments, the semiconductor substrate 100 in the drawings only shows the semiconductor device 102 and the conductive pad structures 104. Next, the semiconductor wafer 100 is thinned by a chemical mechanical polishing (CMP) process, an etching process, a milling process, a grinding process or a polishing process. In one embodiment, a thinned semiconductor wafer 100′ has a thickness of about 30 μm to about 50 μm.

[0021] Referring to FIG. 1C, a plurality of through holes 112 is formed on a second surface 100b of the thinned semiconductor wafer 100′ by a photolithography and etching process to expose the conductive pad structures 104. Next, an insulating layer 114 is formed on the second surface 100b of the thinned semiconductor wafer 100′ by a coating method and the insulating layer 114 extends onto the sidewalls of the through holes 112. The material of the insulating layer 114 may be oxides or photosensitive insulating materials, such as photoresist materials containing epoxy resin. The insulating layer 114 formed on the bottom of the through holes 112 can be removed by a development process.

[0022] In an embodiment, the thickness of the insulating layer 114 may be between about 5 μm and about 15 μm, wherein 10 μm is preferred.

[0023] Next, a step of forming a redistribution layer is performed. Referring to FIG. 1D, a conductive layer 116 is conformally formed on the insulating layer 114 and extends to the sidewalls and the bottom of the through holes 112 to be in contact with the conductive pad structures 104 for forming electrical connection between the conductive layer 116 and the conductive pad structures 104. Because the conductive layer 116 can redistribute the conductive trace for signal transmitting of the chip package, the conductive layer 116 is also referred to a redistribution layer. First, a conductive material layer (not shown), made of material such as copper (Cu), aluminum (Al), or nickel (Ni), is deposited on the insulating layer 114 and in the through holes 112 by a sputtering method, an evaporation method or an electroplating method. Then, the conductive material layer is patterned by a photolithography and etching process to form the conductive layer 116.

[0024] Referring to FIG. 1E, an insulating layer 118 is formed on the second surface 100b of the thinned semiconductor wafer 100′ to cover the conductive layer 116 and the insulating layer 114. The material of the insulating layer 118 may be oxides or photosensitive insulating materials, such as photoresist materials containing epoxy resin. In an embodiment, the thickness of the insulating layer 118 may be between about 20 μm and about 30 μm, wherein 25 μm is preferred. Moreover, in an embodiment, the material of the insulating layer 118 may be the same as that of the insulating layer 114.

[0025] Next, a plurality of openings 120 is formed in the insulating layer 118 by an exposure and development process to expose parts of the conductive layer 116. Then, a redistribution layer 122 is conformally formed on the insulating layer 118 and extended to the sidewalls and the bottoms of the openings 120 to be in contact with the conductive layer 116 for forming electrical connection between the conductive layer 116 and the redistribution layer 122. First, a conductive material layer (not shown), made of material such as copper (Cu), aluminum (Al), or nickel (Ni), is deposited on the insulating layer 118 and in the openings 120 by a sputtering method, an evaporation method or an electroplating method. Then, the conductive material layer is patterned by a photolithography and etching process to form the redistribution layer 122. It is noted that, in a subsequent step, a notch channel 130 is formed on the edge of the die area. Thus, the redistribution layer 116 contracts toward the inner of the chip package for disposition apart from the notch channel 130 with a distance. Then, the redistribution layer 122 is extended to, at least, a premeditated area of the notch channel 130 or to the outer edge of the die area for forming a contact area with a subsequently formed conductive trace layer 132.

[0026] Referring to FIG. 1F, a packaging layer 126 is provided. The packaging layer 126 may be a semiconductor substrate or a glass substrate, which is bonded on the redistribution layer 122 and the insulating layer 118 through an adhesive layer 124. The adhesive layer 124 may be an adhesive agent containing epoxy resin. The packaging layer 126 can support the thinned semiconductor wafer 100′ to enhance the mechanical strength of the chip packages. Then, an insulating layer 128 is formed on the packaging layer 126. The insulating layer 128 may be formed from epoxy resin or solder mask materials, which can be used for a stress release layer.

[0027] Referring to FIG. 1G, a notching process is performed to the insulating layer 128 on the second surface 100b of the thinned semiconductor wafer 100′, the packaging layer 126, the adhesive layer 124, the redistribution layer 122 and the insulating layer 118 to form the notch channel 130. The notch channel 130 extends from the insulating layer 128 to the insulating layer 118, but does not pass through the insulating layer 118. The edge of the redistribution layer 122 is exposed by the notch channel 130, wherein the insulating layer 118 is used as a buffer so that a scriber does not cut to the silicon substrate 100′.

[0028] Next, referring to FIG. 1H, the conductive trace layer 132 is formed on the insulating layer 128 and extends to the sidewall and the bottom of the notch channel 130 to electrically contact with the redistribution layer 122. For example, the conductive trace layer 132 and the redistribution layer 122 form a T-shaped contact T. First, a conductive material layer (not shown), made of material such as copper (Cu), aluminum (Al), or nickel (Ni), is deposited on the insulating layer 128 and in the notch channel 130 by a sputtering method, an evaporation method or an electroplating method. Then, the conductive material layer is patterned by a photolithography and etching process to form the conductive trace layer 132. Next, a passivation layer 134, for example a solder mask is coated on the insulating layer 128 and the conductive trace layer 132 to cover the conductive trace layer 132. Then, the passivation layer 134 is patterned to form openings 136, exposing parts of the conductive trace layer 132. A solder material is dispersed in the openings 136 of the passivation layer 134 and then a reflow process is performed to form conductive bumps 138. The conductive bumps 138 can be a ball grid array (BGA) or a land grid array (LGA).

[0029] Referring to FIG. 1I, in an embodiment, the temporary carrier layer 110 can be removed by a chemical mechanical polishing (CMP) process, an etching process, a milling process, a grinding process or a polishing process. In an embodiment, the temporary carrier layer 110 can be removed by a stripping method. Then, in an optional step, a passivation layer 140 is formed on the adhesive layer 108. The passivation layer 140 can be formed from harder solder mask materials with hardness greater than about 7, such that the passivation layer 140 has scratch-proof and wear-resisting effects.

[0030] Then, the semiconductor wafer 100′ is diced along a scribe line SL to form a plurality of chip packages 200 as shown in FIG. 1J.

[0031] Referring to FIG. 1J, a cross section of a chip package according to an embodiment of the invention is shown. The wafer is divided along the scribe line SL to form the chip packages 200. The semiconductor substrate 100′ of the chip packages 200, for example, is formed from dicing the thinned semiconductor wafer containing the die area. In the die area, the device area 100A of the semiconductor substrate 100′ has the semiconductor device 102 thereon and the plurality of conductive pad structures 104 at the peripheral bonding pad area 100B is disposed surrounding the device area 100A. The conductive pad structures 104 may be bonding pads, which can be electrically connected to the semiconductor device 102 through metal interconnections (not shown).

[0032] In an embodiment, the chip packages 200 can be applied in, but is not limited to, the manufacturing of fingerprint readers or sensor devices, such as complementary metal oxide semiconductor (CMOS) devices or charge-couple devices (CCD). Moreover, the chip packages 200 can also be applied in the manufacturing of micro electro mechanical system (MEMS) devices.

[0033] In an embodiment, the redistribution layers 116 and 122 and the conductive trace layer 132 can be formed by firstly depositing a conductive material layer (not shown), made of materials such as copper (Cu), aluminum (Al), or nickel (Ni), by a sputtering method, an evaporation method or an electroplating method, and then the conductive material layer is patterned by a photolithography and etching process to make the redistribution layers of 116 and 122 and the conductive trace layer 132 electrically connected to the conductive pad structures 104.

[0034] According to an embodiment of the invention, in the chip package, by using the through holes 112, the redistribution layers 116 and 122, and the conductive trace layer 132, which are in electrical contact with the edge of the redistribution layer 122, electrical connection to the conductive pad structures 104 of the chip is achieved and a chip package with a flat packaging surface is formed. When the embodiments of the chip packages of the invention are applied in the manufacturing of fingerprint readers, efficiency of fingerprint identification is enhanced.

[0035] Note that the insulating layer thickness required for forming the T-shaped contact can be increased through the redistribution layers and the insulating layers so that the conductive trace layer 132 of the T-shaped contact is not close to the semiconductor substrate 100′.

[0036] Moreover, in the embodiments of the chip packages of the invention, the through holes are formed in the thinned semiconductor wafer. Because the depth of the through hole is reduced by the thinned semiconductor wafer, the diameter of the through hole is also reduced. Accordingly, the embodiments of the chip packages of the invention can be applied to chips with a smaller pitch between the conductive pads. In an embodiment, the pitch between the conductive pads of a chip may be smaller than 100 μm.

[0037] In addition, in the embodiments of the chip packages of the invention, the packaging layer 126 can support the thinned semiconductor wafer 100′ and enhance the mechanical strength of the chip package 200. Also, the insulating layer 128 disposed on the packaging layer 126 can be used for a stress release layer. When external force is placed upon the chip package, the insulating layer 128 can prevent the chip package from damage. Moreover, the passivation layer 140 disposed on the outside of the chip package can provide scratch-proof and wear-resisting effects to prevent the chip package from damage.

[0038] While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.